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416 Cards in this Set
- Front
- Back
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Who will pass the PE |
Me!
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What is the best Engineering forum on the planet |
Engineerboards.com |
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Energy of a mass |
the capacity of a mass to do work |
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Joule's Constant
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778 ft-lbf/Btu
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work (def) |
the act of changing the energy of a particle, body, system
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potential energy (def and eq)
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a form of mechanical energy possessed by a body due to it's position in a gravitational field
E=m*g*h/gc E is per unit mass in the fluids chapters and not in the thermo chapters |
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kinetic energy (def and eq)
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a form of mechanical energy associated with a moving or rotating body |
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Convert from rpm to rad/sec (eq)
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rpm*2*pi/60 |
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Ideal fluids (def)
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has no viscosity, & is incompressible
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absolute pressure (def) |
measured with respect to a true 0 pressure reference
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gage pressure (def)
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measured with respect to atmospheric pressure
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Standard atmospheric pressure (numerical value)
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1 atm
14.7 psia |
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Density (def)
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a fluid's mass per unit volume
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Specific gravity (def)
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a dimensionless ratio of a fluid's density to some standard reference density
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Specific wieght (def) |
the weight of a fluid per unit volume
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absolute viscosity (def)
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μ |
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kinematic viscosity (def)
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∨
the ratio of absolute viscosity to mass density |
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hydrostatic pressure (def)
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pressure a fluid excerts on an immersed object or container walls |
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The relationship between pressure and depth (eq) |
p=ρ*g*h/gc
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gravitational constant (numerical value) |
32.2 lbm-ft/(lbf-sec^2)
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laminar flow (numerical value)
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re below 2100 |
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Reynolds number (eq)
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Re=D*V*ρ/(gc*μ)
Re=D*v/∨ Re=D*G/gc*μ G=mass flow rate per unit area |
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Turbulent flow (numerical value)
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re greater than 4000
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mass flow rate (eq) |
ρ*A*v
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laminar flow eq for friction factor (eq)
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f=64/Re
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darcy equation (eq)
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hf=(f*L*v^2)/(2*D*g)
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Specific energy (def and units)
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energy per unit mass ft-lbf/lbm
E is per unit mass in the fluids chapters and not in the thermo chapters |
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Ef (specific frictional energy) (eq)
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Ef=(f*L*v^2)/(2*D*gc)
E is per unit mass in fluids chapters and not in the thermo chapters |
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head loss due to pressure drop (eq)
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deltap=hf*ρ*(g/gc)
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Fluid velocity in terms of mass flow rate, density, and area (eq)
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v=mdot/(ρ*A)
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terminal velocity (def)
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the velocity of an object falling through a fluid will continue to increase untill the drag force equals the net downward force
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frictional head (eq)
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hf=(f*L*v^2)/(2*D*g)
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velocity head (eq)
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hv=(v^2/2*g)
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static suction head hz(s) (def)
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the vertical distance above the centerline of the pump inlet to the free level of the fluid surface. If the free level of the fluid is below the pump inlet, hz, will be negative and is known as static suction lift
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static discharge head hz(d) (def)
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The vertical distance above the centerline of the pump inlet to the point of free discharge or surface level
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weight (eq)
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W=m*g/gc
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acceleration of gravity (numerical value)
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32.0 ft/sec^2
9.8 meter/sec^2 |
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Area and circumference of a circle (eq)
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A=π* r^2
C=2*π*r |
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volume and surface area of a shere (eq)
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V=4*π*r^3/3
A=4*π*r^2 |
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Right triangle equations (eq)
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Some Old Hags Can't Hide There Old Age
sin= opposite side/ hyp cos= adj side/ hyp tan= opposite side/ adj side a^2 + b^2 = c^2 |
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Power (eq and def)
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is the amount of work per unit time
P=W/Δt P=F*v (linear systems) P=T*ω (rotational systems) |
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what the eq that relates lbm to slugs (eq)
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Lbm=slugs*g (g in ft per sec2)
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density of water at STD (numerical value)
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62.4 lbm/ft^3
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1 HP equals? (eq to change units)
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hp=550 ft-lbf/s
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How are mass and volume related (eq)
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m=ρ*V
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What is a subcooled liquid (def)
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If a liquid is not saturated (not at it's boiling point) it is said to be subcooled. Water at room temp is subcooled since adding a small amount of heat will not cause vaporization
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what is a saturated liquid (def)
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a liquid that has absorbed as much heat energy as it can without vaporizing. Liquid water at 212F is an example
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liquid vapor mixture (def)
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a liquid and vapor can coexist at the same temp and pressure.
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saturated vapor (def) |
a vapor on the verge of condensing. steam at 212F and STD pressure
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superheated vapor (def)
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is a vapor that has absorbed more heat than is needed merely to vaporize it. A superheated vapor will not condense when a small amount of heat is removed
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ideal gas (4 eq)
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p*V=Rstar*T
p*V=n*R*T ρ=p/(R*T) mdot=p*Vdot/(R*T) note R is gas specific and Rstar is not. |
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What is a gas (def)
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a highly superheated vapor
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specific volume in terms of density, and what are the units for specific volume (eq)
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ν=1/ρ
ft3/lbm |
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enthalpy (def)
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is the total useful energy of a substance (internal energy, u, and flow energy, p*V. Define as useful energy because all of it can be used to preform useful tasks.
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entropy (def)
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a measure of the energy that is no longer available to proform useful work within the current environment
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The specific gas constant, R, for air is
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53.35 ft-lbf/(lbm-degreeR)
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Eq for Mass flow rate
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mdot=ρ*v*A
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What is the Energy Efficiency Ratio? (eq)
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EER=3.41*COP
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What is the Sefan Boltzman Constant (numerical value) |
5.67*10^(-8) Btu/hr*ft^2-R^4
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Sensible Heat (def)
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pure thermal energy that increases the air's dry bulb temp
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Latent heat (def) |
moisture that increases the air's humidity ratio
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What is total cooling load equation? |
q (btu/h) = 4.5 * CFM * delta h |
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What is sensible cooling load equation? |
q (btu/h) = 1.08 * CFM * delta T (dry bulb) |
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What is latent cooling load equation? |
q (btu/h) = 4840 * CFM * delta W (humidty ratio, lbs of H20/lb of dry air) |
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What is the relationship between ACH and CFM? |
ACH = 60 * CFM / room volume |
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Autosuggestion #1 - Persistence |
You're doing well and learning a lot. Persistence by repetition is key |
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Autosuggestion #2 - Love |
Once you understand the definitions, concepts, and principles, it can actually be very interesting |
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What is Energy? |
the ability to do work or produce heat |
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What are the units for Energy and Heat? |
Btu |
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What is Work? |
force acting on an object over a distance |
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What are the units for Work? |
ft-lbf or Btu/ lbm |
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What is Power? |
Work over time |
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What is Mass? |
the amount of material in an object |
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What are the units for Mass? |
lbm (British uses slug) |
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What is Force? |
a property that causes a mass to accelerate |
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What are the units for Force? |
lbf |
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What is Weight? |
Gravitational force acting on a mass |
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What are the units for Weight? |
lbf |
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What is Pressure? |
Force acting upon an area |
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What are the units for Pressure? |
psi or lbf/in^2 |
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How many feet of head in 1 psi? |
2.31 feet |
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How many inches of water column in 1 ft of head? |
12" wc |
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How many inches of water gauge in 1 psi? |
27.73 in wg |
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How many inches of mercury gauge in 1 psi? |
2.036 in Hg |
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What is the difference between Kelvin and Rankine? |
Kelvin goes with C, Rankine goes with F |
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What are the units for Absolute Temperature? |
Rankine, R = F + 461 |
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What is Potential Energy? |
Energy due to position |
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What are the units for Potential Energy |
ft-lbf |
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What is Kinetic Energy? |
Energy due to motion |
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What are the units for Kinetic Energy |
ft-lbf |
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What is Heat? |
Energy due to a temperature difference |
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What is Internal Energy? |
Sum of kinetic and potential energies of all particles in the system [ Btu] |
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What are the units for Internal Energy |
Btu |
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What is Entropy? |
Unavailable energy for work [btu\lb F] or [btu/lb R] |
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What is Enthalpy? |
Total amount of energy in air [btu/lb], both sensible and latent, the warmer the air the higher its enthalpy and ability to hold moisture |
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What is the difference between an intensive and extensive property? |
Intensive properties do not depend on mass or size of system, extensive properties are proportional to size and can be additive |
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What are some examples of Intensive properties? |
temperature, pressure, specific volume |
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What are some examples of Extensive properties? |
energy, mass, volume |
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What are the psychometric properties of 75F and 50% RH air? |
62.7 F WB, 55.1 F dew point, 28.1 btu/lb enthalpy, 64 gr/lb specific humidity |
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What are the psychometric properties of saturated air at 55F? |
55 F WB, 55F dew point, 64 gr/lb specific humidity, 23.2 btu/lb enthalpy |
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Convert 1 watt to Btu/h? |
3.412 Btu/h |
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Convert 1 hp to watts? |
746 watts |
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What is Ohm's Law |
V = I * R |
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What is Ohm's Law for Power? |
P = 1^2 R |
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What is the relationship between kW and kVA? |
kW = kVA * PF |
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How do you get equipment capacity from current draw? |
Can determine tons from measured amps and equipment efficiency |
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What are the 2 voltage designations? |
System Voltage and Equipment Voltage Rating |
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What is the difference between the System and Equipment Voltage ratings? |
Difference is allowance for voltage drop between service delivery or transformer and point of use |
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What is the difference between RLA and FLA? |
RLA - Rated Load Amps (max current of compressor), FLA - Full Load Amps (was replaced by RLA in 1976) |
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What is the difference between MCA and MOP? |
MCA - Minimum Circuit Ampacity (used for selecting wire sizes), MOP - Maximum Overcurrent Project (used to size circuit breakers and fuses) |
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How is MCA calculated? |
MCA = 125% * RLA of largest device + RLA other devices |
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What is a transformer? |
Its an electrical device that takes electricity from a higher voltage to a lower voltage |
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What is the purpose of a electrical Switchboard? |
Its an electrical device that directs electricity from a main source(s) to smaller regions of usage |
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What is the equation for Power Factor? |
PF = cos(theta) = kW/ kVA, (other side of triangle is kVAR) |
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What is load shedding? |
Reducing electrical load in building during peak demand times |
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What is decoupling? |
Disassociation between utility sale of energy with profits |
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What is total cooling load equation? |
q [btu/h] = 4.5 * CFM * delta h |
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What is sensible cooling load equation? |
q [btu/h] = 1.08 * CFM * delta T (dry bulb) |
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What is latent cooling load equation? Using lbs of H20 |
q [btu/h] = 4840 * CFM * delta W (humidity ratio, lbs of H20/lb of dry air) |
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What is latent cooling load equation? Using grains of H20 |
q [btu/h] = 0.68 * CFM * delta W (humidity ratio, grains of H20/lb of dry air) |
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How many grains in a pound of H20? |
7000 grains |
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What is the relationship between ACH and CFM? |
ACH = 60 * CFM / room sq ft. |
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What is the weight of 1 gallon of water? |
8.31 lbs. |
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What is the weight of 1 cubic feet of water? |
62.4 lbs. |
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How many gallons of water can fit in 1 cubic feet? |
7.48 gallons |
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What is Refrigeration? |
Moving heat from one location to another. |
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What are the 4 processes in the vapor compression cycle? (refrigeration, reverse Rankine) |
1. Isentropic Compression 2. Isobaric Heat Rejection 3. Throttling Expansion 4. Isobaric Heat Absorption |
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What is the Net Refrigeration Effect? |
The amount of BTU's a refrigerant can absorb |
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How do you determine the Net Refrigeration Effect? |
Q [btu/h] = H1-H4 [btu/lb] * Refrigerant flowrate [lb/min] * 60, where H1 and H4 is leaving and entering evaporator enthalpy |
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How do you determine work done by the compressor? |
W [btu/h] = H2-H1 [btu/lb] * Refrigerant flowrate [lb/min] * 60, where H2 and H1 is leaving and entering compressor enthalpy |
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How do you determine the Net Condenser Effect? |
Q [btu/h] = H2-H4 [btu/lb] * Refrigerant flowrate [lb/min] * 60, where H2 and H3 is entering and leaving condenser enthalpy |
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How do the Net Condenser Effect, Compressor Work and Refrigeration Effect relate? |
Refrigeration Effect = Net Condenser Effect - Compressor Work |
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What is the function of a Compressor? |
To take a refrigerant at low pressure and temperature and raise it to a high pressure and temperature |
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What are the functions of the Evaporator and Condenser? |
To absorb and reject heat into the refrigeration system as heat exchangers |
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At what condition does air condense on a surface? |
When temperature of surface is less than dew point of the air, moisture in air condenses on surface |
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At what condition does a liquid evaporate? |
When liquid reaches boiling point or saturation temperature |
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What is Saturation Temperature? |
The boiling point of a liquid. |
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What is Saturation Pressure? |
The corresponding pressure to a liquid's saturation temperature |
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What is Subcooling? |
Removal of heat from a liquid below its saturation temperature |
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What is Superheat? |
Additional heat added after all the liquid has turned to vapor |
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What is de-superheating? |
BTU's removed from a superheated vapor back to its saturation state |
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What is the Latent Heat of vaporization vs. the Enthalpy of vaporization? |
It's the same thing |
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What is the Latent Heat of Vaporization? |
The heat required for phase change from a liquid to gas without changing its temperature [btu/lb] |
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What s the Latent heat of vaporization (hfg) for water? |
970.1 btu/lb |
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What is the Latent Heat of Condensation? |
The heat required for phase change from gas to liquid without changing its temperature [btu/lb] |
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What is the Latent Heat of Fusion? |
The required for phase change from liquid to solid [btu/lb]. The temperature at which this occurs is the melting temperature. |
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What is Sublimation? |
The process of water going from a solid phase to gas phase |
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What is Deposition? |
The process of water going from gas phase to solid phase |
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Do not get confused with latent load vs. latent heat. |
load is btu/h vs. heat or enthalpy which is btu/lb |
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What is Specific Heat or Specific Heat Capacity? |
Amount of heat per unit mass required to raise the temperature of a substance 1 degree [btu/lb-R] as in c for Q = cm(T2-T1) |
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What s the specific heat capacity of water? |
1 btu/lb-R |
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What s the specific heat capacity of air? |
0.24 btu/lb-R |
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What s the specific heat capacity of steam? |
0.45 btu/lb-R |
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What has a higher specific heat capacity, water or air? |
Water can hold more heat than air per unit mass. Water in pipes vs. air in pipes or duct |
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What is Coefficient of Performance? |
For a refrigeration cycle, it's the net refrigeration effect divided by the compressor work. |
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What is the saturation temperature and pressure of water at standard conditions? |
212 F, 14.7 PSI |
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What is the relationship between Enthalpy of vaporization, saturated vapor and liquid? |
hg = hf + hfg where hg =enthalpy of saturated vapor or gas [btu/lbm], hf = enthalpy of saturated fluid, and hfg = enthalpy of vaporization |
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What is Quality? |
It's the percentage or ratio of vapor or air in a mixture to total mass |
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What is the quality of the saturated liquid and vapor curves? |
0 or 0% and 1 or 100% |
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What is the enthalpy of wet steam in the mixed region (dome) as a function of quality? |
hmix = hf + x * hfg, where hmix = enthalpy of steam (mixture of liquid and vapor or fluid and gas and x = steam quality or dryness fraction, % vapor |
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What is the entropy of wet steam in the mixed region (dome) as a function of quality? |
smix = sf + x * sfg, where smix = entropy of steam (mixture of liquid and vapor or fluid and gas and x = steam quality or dryness fraction, % vapor |
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What is the heat available from condensing steam? |
Q [btu/h] = m [ lbm/h] * hfg |
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What is the Apparatus Dew Point? |
Temperature at which all air would be cooled to if the cooling coil was 100% effective. Also known as Effective Surface Temperature |
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What is the Bypass Factor? |
Percentage of air that is not cooled to the apparatus dew point |
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What is the equation for Bypass Factor for coils? |
BF = (leaving coil-apparatus dew point) / (entering coil - apparatus dew point), substitute h, dry bulb temperature, or humidity ratio |
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What is the Moisture Transfer Equation? |
H [lb/hr] = 60 * density of air * Q * (entering Humidity - exiting Humidity) |
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What are the 4 main refrigerant lines? |
1. Discharge (compressor to condenser) 2. Liquid (condenser to TX-valve to evaporator) 3. Suction (evaporator to compressor) 4. Hot Gas Bypass (compressor to TX valve) |
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What is an Absorption Refrigeration Cycle? |
A heat activated cycle, there's no mechanical equipment performing work (compressor) |
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Air is able to hold more moisture at what conditions? |
Higher temperature and lower pressures |
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What is Vapor Pressure? |
Term used for the partial pressure of the water vapor in the air |
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Def of Adiabatic? |
A process experiencing constant enthalpy, there's no heat transfer, no heat coming in or out |
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Def of Isentropic? |
A process experiencing constant entropy, also a process which is both reversible and adiabatic |
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Def of Isothermal? |
A process under constant temperature |
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Def of Isobaric? |
A process under constant pressure |
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Def of Isochoric or Isometric? |
A process under constant volume |
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Def of Polytropic? |
A process where the relation of PV (pressure, volume) as in PV^n = C, any real number |
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What is Relative Humidity with respect to water vapor pressure? |
The partial pressure of the water vapor divided by the saturation pressure |
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Def of Relative Humidity? |
The amount of water in the air relative to the max amount it can actually hold |
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Def of Humidity Ratio or Specific Humidity (even absolute humidity)? |
Actual amount of water in air [lb of h20/ lb of dry air] |
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What does the top curve of the psychometric chart called? |
Saturation curve, where the air is fully saturated with water, RH is 100%, DB=WB |
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How do you determine the dew point of air at a specific condition? |
Move left along the humidity ratio horizontal line until you reach the saturation curve |
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Air Mixing Equations using Dry Bulb Temp or Enthalpy? |
T=t1*%1 + t2*%2 and H = h1*%1 + h2* %2 |
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What are the 3 modes of Heat Transfer? |
1. Conduction 2. Convection 3. Radiation |
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What is the most important topic in the Heat Transfer section? |
Determining heat transfer coefficients [ btu/hr*ft^2*F] |
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What are the 2 classifications of Heat Exchangers? |
1. Parallel Flow 2. Counter-Flow |
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What is LMTD and when is it used? |
Log Mean Temperature Difference describes average temperature difference in a heat exchanger (counter or parallel) without phase change (can't be used in condensers or evaporators) |
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What is the significance of the LMTD? |
Used to calculate total heat exchanged: Q = U * A * LMTD |
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What is the def and units for R value? |
Thermal resistance [hr*ft2*F/Btu] |
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What is the def and units for U value? |
Heat transfer coefficient [Btu/hr*ft2*F] |
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What is the def and units for k? |
Thermal conductivity [Btu/hr*ft*F] |
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What are the relationships between R, U, and k? |
R = 1/ U, R = t/k where t is thickness in feet |
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Addition of R-Values vs. U-Factors? |
R = R1+R2+R3, U = 1/U1+1/U2+1/U3 |
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What are the 3 methods to calculate cooling load calculations? |
1. Radiant Time Series (computer) 2. Total Time Equivalent Time Difference (computer) 3. Cooling Load Temperature Difference (CLTD)(by hand) |
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What is SC, SCL, and SHGC? |
SC - shading coefficient, SCL - solar cooling load factor, SHGC - solar heat gain coefficient |
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How are the shading coefficient (SC) and solar heat gain coefficient (SHGC) related? |
SHGC = SC / 1.15 |
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General Heat Transfer Equation? |
Q [btu/hr] = U * A * delta T |
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Conduction Heat Transfer Equation? |
Q [btu/h] = k * A * (Thot-Tcold) / t where k is thermal conductivity of material, and t is thickness in ft |
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Convective Heat Transfer Equation? |
Q [btu/h] = h * A * T where h is the convective heat transfer coefficient |
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Radiative Heat Transfer Equation? |
Q [btu/h] = h * A * T where h is the radiation heat transfer coefficient |
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Mechanical Horsepower of a Fan? |
Mhp = CFM * TSP [in wg] / 6356 |
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Relationship between fan mechanical, brake, and electrical horsepower? |
electrical HP > fan brake hp > mechanical hp |
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Equation that relates fan mechanical, brake, and electrical horsepower? |
BHP = HP * motor efficiency, MHP = BHP * fan efficiency |
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Fan Mechanical Horsepower Equation if total static pressure and CFM are known |
P [mech hp of fan] = Q * TP [in wg]/ 6956 |
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Relationship between pump, motor, and electrical horsepower? |
electrical hp > motor hp > pump or brake hp |
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Pump Horsepower Equation if head and GPM are known |
P [mech hp of pump] = h [ft of head] * Q[gpm] * SG / 3956, using specific gravity of water |
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Pump Horsepower Equation if pressure and GPM are known |
P [mech hp of pump] = psi * Q[gpm] * SG / 1714, using specific gravity of water |
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What is velocity pressure? |
Pressure caused by the moving fluid |
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What is static pressure? |
Pressure caused by compression, the outward force of the fluid on the duct or pipe |
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What is total static pressure? |
Pressure that is the sum of the static and velocity pressures |
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How do you find total static pressure? |
Use the friction charts |
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What are the 2 types of fans? |
1. Axial 2. Centrifugal |
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What are the main components on a fan curve? |
Depicts various points that the fan can operate based on impeller diameter. Total Pressure [in wg] (y-axis) vs.Flowrate [CFM] (x-axis). Graphs fan, system, and efficiency curves. |
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What is the equation that relates air velocity and velocity pressure? |
VP [in wg] = (Velocity [ft/min] /4005)^2 |
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What is total pressure in a duct the sum of? |
Static pressure and velocity pressure |
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What is the relationship between velocity, pressure, and noise? |
As air velocity increases, pressure drop and noise criteria both increase |
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What is the Darcy Weisbach Equation ? |
It determines pressure drop in ducts or pipe due to friction: h [ft of head] = fLv^2/2Dg, where D = inner diameter [ft], g=32.2 ft/s^2, V is in ft/sec |
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What is the Hazen-Williams Equation? |
It determines head loss for turbulent flow in pipes from 40-75F only |
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How do you determine pressure drop due to Pump velocity? |
V^2/2g [ft of head] |
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What is Cooling Tower Range? |
Difference between water temperatures: Tin-Tout [F] |
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What is Cooling Tower Approach? |
Difference between water temp out and air wet bulb temp in: T wet bulb water out - T wet bulb air in [F] |
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What is Cooling Tower Effectiveness? |
Effectiveness = Range/ (Range+Approach) |
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What is the significance of Cooling Tower Approach? |
It's an indicator of cooling tower performance, the smaller the approach, the better the cooling tower is at providing cooling. Typical approach is 10 F. |
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What is EER? |
Energy Efficiency Ratio [btuh/W] applies to unitary AC and heat pumps at full load conditions |
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What is COP? |
Coefficient of Performance [btu/btu] applies to chillers and heat pumps in heating mode |
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How are EER, COP, and kW/ton related? |
EER = 3.412 * COP = 12/ (kW/ton) |
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If a chiller's efficiency is rated at 1 kw/ton, what is its EER and COP? |
EER = 12, COP = 3.5 |
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What is the Carnot cycle? (heat pump cycle) |
Most efficient cycle for converting thermal energy into work or conversely, creating a temperature difference by doing a given amount of work |
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What is the Reverse Carnot cycle? (heat pump cycle) |
Heat is absorbed from a low-temperature reservoir and, heat is rejected to a high-temperature reservoir, and work input is required to accomplish this |
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What is the Rankine cycle? (heat pump cycle) |
Steam engine cycle and steam is used to make power, compression and expansion are adiabatic and heat addition and rejection are isobaric |
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What is the Reverse Rankine cycle? (heat pump cycle) |
Refrigeration cycle or Vapor Compression cycle, can achieve up to 60% efficiency of Reverse Carnot cycle |
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What is the Otto cycle? (internal combustion cycle) |
Gasoline engine cycles, where compression and expansion is adiabatic and heat addition and rejection is isochoric |
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What is the Brayton cycle? (internal combustion cycle) |
Jet engines cycle where compression and expansion are adiabatic and heat addition and rejection are isobaric |
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What are the 6 thermodynamic properties? |
Pressure (P), Temperature (T), Specific Volume (v) Internal Energy (u), Enthalpy (h) , Entropy (s) |
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Draw the T-S and P-v diagrams for the 6 thermodynamic cycles |
draw the dome, isotherms, entropy, density, specific volume, and quality lines, arrow direction for flow, the Q and W in or out |
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What are the differences between the P-v vs. P-h vs. T-s diagrams? |
P-v useful for mechanical cycles, T-s for thermodynamic cycles, P-h for refrigeration cycles, h-s for steam turbine cycle |
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What can be determined from a P-V diagram? |
Net work performed by a thermodynamic cycle such as steam engine (Rankine cycle) |
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What is the 1st Law of Thermodynamics? |
Energy is neither created or destroyed. The net energy crossing the system boundary is equal to the change in energy inside the system. Q-W = delta (U + KE + PE) |
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What is the 1st Law of Thermo also known as? |
The Conservation of Energy |
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What is the 2nd Law of Thermodynamics? |
Entropy change in an isolated system is positive (or greater than 0 or increasing) |
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Simple way to state 3 Laws of Thermodynamics |
1. You can't get something from nothing 2. You can't break even 3. Absolute 0 temperature is unattainable |
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Thermodynamic Process |
A series of state going from an initial to a final state using 3 variables, P, V, and T |
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Sign Convention in Thermodynamics |
Positive Q when heat into system and Positive W when work done by system, Negative Q when heat out of system and Negative W when work done on a system |
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How to classify Thermodynamic problems |
S-S-P, System, Substance, Process. The System can be Open or Closed. The System determines the form of the 1st Law. The Substance can be ideal gas or water. The Substance determines the State equations. The Processes for closed systems with ideal gas are isoprocesses or polytropic processes. The processes for closed systems with water are isoprocesses or other. The Processes for open systems are classified by the kind of device used: nozzle, diffuser, turbine, pump, compressor, throttle, heat exchanger. |
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What information does a Pressure-Enthalpy diagram (P-h) give? |
It provides the vapor compression cycle of a refrigerant or steam, psia (y-axis) vs. btu/lb (x-axis). |
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What are the various parts of a Thermodynamic Cycle Diagram? |
The subcooled liquid region, mixed region in dome, superheated vapor or steam region, saturated liquid line on left curve, saturated vapor line on right curve, lines of constant entropy and enthalpy |
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Locate lines of constant entropy and enthalpy for a compressor and expansion device? |
Locate the lines on the Pressure-Enthalpy (P-H) diagram |
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What are the 3 ways to find properties of Steam? |
1. P-H diagram 2. Mollier Diagram 3. Steam Tables |
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What are the 3 main types of Steam Tables? |
1. Saturation Table as function of pressure 2. Saturation Table as function of temperature 3. Superheated Steam Tables |
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What information does the Mollier Diagram give? |
Shows properties of steam from superheated steam to a mixed region with enthalpy [btu/lb] (y-axis) vs. entropy [btu/lb R] (x-axis). Also known as enthalpy-entropy diagram. |
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What are the 3 components of a Boiler System? |
1. Feed-water system 2. Combustion system 3. Steam system |
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How do you determine a Boiler's capacity? |
W [ kbtu/h] = (hg-hf)*m where hg is enthalpy of steam, hf is enthalpy of condensate, m is steam evaporated |
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How do you determine the efficiency of a Boiler? |
Divide the output energy (enthalpy change between feed water and super heated steam) by input energy(mass flow rate of fuel and higher heating value of fuel) |
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What is the equivalent of 1 boiler horsepower? |
33,475 btu/h |
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How do you size steam piping based on pressure drop? |
Use the Darcy Wesisbach equation or steam pipe tables |
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What is Steam Trap? |
Devices used to separate steam from the rest of the condensate. Located after a steam coil, the condensate goes back to the boiler |
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What is a Furnace? |
Equipment used for space heating using a combustion burner with natural gas being the most common fuel |
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What are the different types of furnaces? |
Condensing (more efficient) and non-condensing furnace |
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What is an Enthalpy Wheel? |
Equipment that transfers energy (enthalpy) from one air stream to another |
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What is the difference between a Rotary Sensible Wheel and an Enthalpy Wheel? |
The rotary sensible only transfers sensible heat, enthalpy transfers both from one air stream to another |
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How do you determine the thermal insulation required for a pipe or duct? |
use 2 separate equations |
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What are the fundamental principles of Fluid Mechanics? |
Continuity Equation (Conservation of Mass), Momentum Equation, and Energy Equation (Conservation of Energy) |
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What is the Continuity Equation (Conservation of Mass) in Fluid Mechanics? |
Continuity Equation: conservation of mass, for gases (compressible flow) summation of mass flow rates is zero, for fluids (incompressible) summation of volume flowarates is zero |
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Simple way to express Continuity Equation? |
Mass flow rate in must equal mass flow rate out |
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What is Momentum Equation in Fluid Mechanics? |
F = ma as applied to fluids, draw 2 diagrams, first is control volume with velocities, areas, and densities at inlets and exists, then free-body diagram showing forces acting on inside of control volume |
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What is the Energy Equation (Conservation of Energy) in Fluid Mechanics? |
Inlet and exit, indicate velocity, elevation, and pressure, then write equation in direction of flow with pump head on left side and head loss on right side |
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For fluids, what is the best way to apply energy, continuity, and manometer equations? |
Apply Energy Equation between unknown and known point, use Continuity Equation to get velocity, and Manometer Equation to get pressure. |
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What is the frictionless Energy Equation for fluids? |
Pressure Head + Velocity Head + Elevation at State 1 = same at State 2 |
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What is Pump Head? |
The mechanical energy imparted to the fluid by the pump in feet. |
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What are the components of the pump curve? |
Describes the operating points of the pump for a specific impeller diameter. Graphs total head [ft] vs. flowrate [GPM]. Composes of pump, system, efficiency, power, and NPSHR curves. |
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What is the System Characteristic Curve comprised of? |
Frictional losses and minor losses in piping system |
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What is the System Operating Point on a pump curve? |
The intersection between the system curve and pump curve |
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What equation relates head and flowrate on a system curve? |
H1/H2 = (Q1/Q2)^2 |
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Pumps in parallel vs. series? |
Parallel pumps add flow, series pumps add head |
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What does Bernoulli's Equation state? |
In steady flow, the sum of all forms of mechanical energy (potential, kinetic, pressure) in a fluid is the same at all points on that streamline. Therefore, pressure of a fluid decreases as its speed increases and vice versa |
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What is the Bernoulli's Equation? |
1/2pv^2 + pgz + P = constant, this is assuming no friction loss in piping |
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What is the Bernoulli's Equation for an open system? |
Q + ( U + PE + KE + PV) in = Q + ( U + KE + PE + PV ) out + stored energy |
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What is the simplified version of the Bernoulli Equation? |
(PE + KE + PV)1 = (PE + KE + PV )2, assumes no work is done on or by fluid, no heat transferred to and from, and no internal energy change or no temperature change of fluid |
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What larger principle does the Bernoulli Equation represent? |
It is the conservation of energy and momentum along a streamline. The total energy of a fluid flowing without friction is constant. |
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What does the Moody Chart show? |
It provides the friction factor (y-axis) based on the Reynolds Number (x-axis) and relative roughness of pipe or duct |
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What is the Reynold's Number? |
A number indicating turbulent or laminar flow, dimensionless |
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What Reynold's Number indicate turbulent or laminar flow? |
>4000 is turbulent, <2000 is laminar, in between is mixed region |
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What does the Darcy-Weisbach Equation state? |
It's used to size duct or pipe and provides the pressure drop in ft given inner diameter, velocity, and friction factor of duct or pipe. Can also find friction factor if given pressure drop. |
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How do you determine duct size? |
Use friction charts to find pressure drop or use Darcy-Wesierbach equation |
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What is Suction Head? |
Pressure at the inlet of the pump |
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How do you calculate Suction Head? |
Sum up all pressures leading to the pump inlet: absolute, elevation, friction, and velocity pressures |
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What is difference between suction head and suction lift? |
It depends if the pump suction above or below the centerline of the pump |
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What is Net Positive Suction Head Available (NPSHa)? |
It's the difference between the Suction Head at inlet of pump and the Saturation Pressure of the fluid. |
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What is Net Positive Suction Head Required (NPSHr)? |
The amount of pressure needed by pump to prevent cavitation |
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What is Cavitation? |
The formation and implosion of small water bubbles that damage pumps. Occurs when the suction pressure (head) is less than the vapor pressure of the water. |
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What are the conditions when Cavitations occurs? |
NPSHa < NPSHr |
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What are the components of Total Dynamic Head (TDH)? |
1. Static Head or Elevation difference between inlet and outlet (only for open systems) 2. Friction loss |
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What is a typical example of a open hydronic system? |
Condenser water loop to the cooling tower. TDH must incorporate the Static Head or Elevation Head to size the condenser water pump |
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What is Specific Volume? |
Volume per unit mass [ft^3/lbm] |
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How does Specific Volume relate to Density? |
It's the inverse of density |
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What is Buoyancy? |
The tendency of a body to float or rise when submerged in a fluid, depends on density of body and fluid |
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What is Pascal's Law? |
Pressure applied to a confined fluid is transmitted undiminished throughout the confining vessel of the system |
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What is Control Volume? |
Fixed region of study where the mass and energy crosses a boundary |
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What is Steady-State Flow? |
Refers to the condition where fluid properties (temperature, pressure, velocity) at any single point in the system do not change over time |
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What is a Venturi? |
A device used to determine mass flow rate based on changes in fluid pressure and velocity (application of Bernoulli Equation) |
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What is Head Loss? |
Sum of elevation head, velocity head, and pressure head |
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What are Minor Losses in Fluid Mechanics? |
Losses that occur in pipelines or ducts due to bends, elbows, joints, and valves |
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What is the misnomer about Minor Losses? |
Minor losses can be larger than losses due to friction in pipes |
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What is Equivalent Piping Length? |
Minor losses that may be expressed in length of pipe that would have same head loss for same flow rate |
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What is Water Hammer? |
A liquid shock wave resulting from the sudden starting and stopping of flow |
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What are standard conditions (temperature and pressure)? |
60F and 520R (I've seen 70F) and 1 atm |
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What is the density of water at standard conditions? |
62.4 lb/ft^3 |
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What is the density of air at standard conditions? |
0.075 lb/ft^3 @ 70F, 1 atm |
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What is the gravitational constant in Imperial Units? |
32.2 ft/s^2 vs. 9.81 m/s^2 |
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What is Specific Weight? |
It's the weight of a fluid per unit mass [lb/ft^3] |
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What is Specific Gravity? |
The density of a fluid with respect to the weight of water [dimensionless]. A value greater than 1.0 requires more pump horsepower |
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What are the units for dynamic or Absolute Viscosity? |
[lb/ft-s] or cP |
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What is the conversion between imperial units and cP for Absolute Viscosity? |
1 cP = 6.72*10^-4 |
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What are the units for Kinematic Viscosity? |
[ft^2]/s] |
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What is the difference between Absolute and Kinematic Viscosity? |
Kinematic viscosity is the ratio of absolute viscosity to fluid's density |
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Do I have quick access to viscosity tables for water at different temperatures? |
Does MERM have it? |
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What is the NC Rating? |
Used to rate sound levels of air conditioning equipment and mechanical rooms |
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How are sound levels reported for HVAC equipment like chillers? |
Decibel levels at various frequencies at various distances |
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What are ASHRAE 15 ASHRAE 34? |
Safety Standard for Refrigeration Systems and Designation and Safety Classification of Refrigerants |
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What are NFPA 90A and 90B? |
Standard for the Installation of Air Conditioning and Ventilation Systems and 90B is for Heating |
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What is NFPA 96? |
Standard for Ventilation Control and Fire Protection for Commercial Cooking Operations |
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What is Present Value (worth)? |
Sum of the present values or worths of all periods (takes into consideration time value of money) |
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What does a negative Present Value indicate? |
Indicates that the investment doesn't recoup the initial investment |
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What is Future Value? |
Sum of the annual values? |
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What is Annualized Value? |
Mortgage Payment, takes present, future costs, and time value of money and translates to annual value |
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What is Simple Payback? |
Ratio of total cost over cost savings |
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What is Savings to Investment Ratio (SIR)? |
Ratio of present value savings (P/A) to initial costs (Government projects) |
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What's the relationship between Simple Payback and SIR? |
They are inversely related |
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What is Internal Rate of Return (IRR)? |
Return on investment over a defined period |
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What is Life Cycle Cost? |
Cumulative cost of implementation, operation, and maintenance costs over lifetime period |
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When would you use an Annualized comparison vs. the Life Cycle Cost? |
When periods are different, use the Annualized |
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What refrigerants did the Montreal Protocol ban? |
CFC's due to their Ozone Depleting Potential (ODP). R-22 and R-123 are HCFC's. R-134A and R-410A are HFC's. |
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What is Global Warming Potential (GWP)? |
Potential for refrigerant to prevent infrared radiation from leaving the atmosphere , CO2 has a GWP of 1 |
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What is Polytropic? |
PV is constant |
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What is adiabatic? |
Constant heat or no transfer
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What is sensible heat ratio? |
It's the ratio of sensible heat to total heat and can be used to find the slope of the sensible/latent process line to establish other points on the psychrometric chart |
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What is humidification rate? |
It is the flowrate of air and is equal to the the product of the air volume of the space number of air changes an hour. Units are lbm/hr. |
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What is Polytropic? |
PV is constant |
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What is the equation that relates static head and velocity in a pipe? |
H = density * velocity^2 / 2g |
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What are the 3 main types of head in fluid dynamics? |
1. Velocity head due to kinetic energy 2. Elevation head due to fluid's weight and position 3. Pressure head due to static pressure or compressive forces on pipe 4. Resistance head, friction head or head loss |
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Pressure gauges are only capable of sensing what type of head? |
Static head only |
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What is static lift? |
It's the height the water will rise before arrivign at the pump, also known as suction head |
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What is suction head? |
It's the height the water will rise before arrivign at the pump, also known as static lift |
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What is static height? |
It's the maximum height reached by the pipe after the pump, also known as discharge head |
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What is head loss? |
loss due to friction, also known as friction loss |
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What is friction loss? |
loss due to friction, also known as head loss |
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What is Total Dynamic Head (TDH)? |
It's the total equivalent height that a fluid is to be pumped, taking into account friction losses in a pipe |
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What is the equation for TDH? |
htotal = P2-P1/(density*g) |
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How do you calculate glazing solar cooling load? |
Q = Area * SCL * SC |
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What are the units for Solar Cooling Load factor (SCL)? |
btuh/ft^2 |
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What is PI, PID control? (proportional-integral-derivative) |
It's modulating control, inifite variation over the controller range |
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What is throw? |
The distance air will travel in feet based on a set air speed |
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What the recommended air speed of the diffuser to test throw? |
50 feet per minute |
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Given mass flow rate of air in lbm/min, how do you find moisture content? |
use humidity ratio that's also in lbm of h20 / lbm of dry air |
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What is total static head? |
It's the sum of the static suction head or lift and static discharge head |
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State the affinity laws for pumps using words |
Increasing RPM speed is increases flwo proportionally, pressure increases by a square factor, horsepower increases by a cube factor |
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What is a Venturi? |
It's a flow measuring device based on a choked point in a pipe. Pressure decreases when area of pipe is choked. This is based on the Bernoulli Equation, where pressure decreases when the velocity increases along a streamline |
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How is the 4.5 in the total heat equation derived? |
60 min/1 hour * 0.075 lbm/ft^3 (density of air) = 4.5 |
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How is the 1.08 in the sensible heat equation derived? |
60 min/1 hour * 0.075 lbm/ft^3 (density of air) * 0.24 Btu/lb-F (specific heat capacity of air) = 1.08 |
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What is the difference between the 4840 and 0.68 in the latent heat equation? |
Since 1 lb of water is 7000 grains, 0.68 * 7000 = 4840 |
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How the 500 in the Btuh output equation derived? |
8.33 lb/gal of water * 60 min/ 1 hour = 500 |
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What are the densities of air and water? |
0.075 lbm/ft^3 and 62.4 lbm/ft^3 |
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What is Annual Fuel Utilization Efficiency (AFUE)? |
It's a thermal efficiency measure of combustion equipment like boilers, furnaces, and water heaters. Used in place of thermal efficiency. |
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How do you convert psf to psi? |
Multiply by (1 ft /12 in)^2 or 1/144 |
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|
What is the definition of thermal conductivity, k? |
It's the measure of a substance's ability to transfer heat through a solid by Conduction. |
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What is the convective heat transfer coefficient, h? |
Heat transfer due to convection, also referred to as the film coefficent. |
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What is the overall heat transfer coefficient, U? |
It combines the heat transfer coefficient of the fluids and conductivity of materials. |
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What is the equation for volumetric flow rate? |
CFM or GPM = velocity * area |
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What is the equation for mass flow rate? |
M dm/dt = density * volumetric flowrate (CFM or GPM) or density * Area * velocity |
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What is steady state flow? |
Fluid properties like temperature, pressure, velocity, and mass at any single point don't change over time. |
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What is an ideal fluid? |
It has no viscosity, therefore no friciton and it's incompressible |
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State the Conservation of Mass or Continuity Equation in words |
The sum of mass flow rates into a control volume equals the sum of the mas flow rates out. |
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Don't get confused: energy components in the Bernoulli can also be expressed as? |
Head. Although head is a reference to pressure, it can also be expressed as energy. If kinetic energy is converted to potential energy, the height the fluid will rise to is the head. |
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When is a combustion process considered complete? |
When all carbon in fuel burns to C02, and all hydrogen burns to H20. |
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What is the most commonly used oxidizer in the combustion process? |
Air |
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|
What is a subcooled liquid? |
A liquid that is not about to vaporize. Its temperature is lower than the saturation temperature. |
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What is saturated vapor? |
A gas that is not about to condense. Its temperature is higher than its saturation temperature. |
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What is saturation pressure? |
The pressure at which a substance changes phases from liquid to vapor. |
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In which form is energy transported across boundaries of a closed system? |
Energy in the form of heat or work |
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What is conduction? |
Transfer of heat by collisions of molecules within a substance due to temperature difference. |
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What is convection? |
Transfer of heat due to movement of fluid |
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What is radiation? |
Transfer of heat due to a radiating body that's sending out electromagnetic waves |
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|
What can cause entropy of a system to change? |
Heat transfer, mass flow, irreversibility |
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|
What is a power cycle? |
A cycle where net amount of work or power is generated |
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|
What is a refrigerator or vapor compression cycle? |
A cycle where heat is removed from a cold temperature resevoir to a high temperature resevoir by using compressor work |
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|
Do not get confused with Moody vs Mollier diagrams |
Moody is used to determine friction factor based on Reynolds number, Mollier is the enthalpy-entropy chart, h-s |
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|
What is the Carnot Cycle? |
It's a reversible cycle consisting of two isothermal and two adiabatic processes. |
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|
What the Brayton Cycle? |
It's a gas turbine engine cycle |
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|
What is the specific heat ratio? (not sensible heat ratio) |
Ratio of the heat capacity at constant pressure Cp to heat capacity at constant volume Cv |
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What is a nozzle? |
A device that increases velocity of a fluid by decreasing pressure |
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What is a turbine? |
A devices that uses energy to produce shaft work |
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|
How are mass and volumetric flow rate related? |
Mass rate = density * Volumetric flow rate |
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|
What is the significance of a boiler in a Rankine cycle? |
It’s the steam generator used to boil water, make steam to drive the turbine to generate electricity |
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|
What is a throttling valve? |
A device that generates pressure drop by restricting flow |
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|
How do you find the specific heat of an air mixture? |
Find the humidity ratio to find the water to air mixture percentage, then use the specific heat of water and air to get the final specific heat of the mixture |
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|
What is the difference between the units for mass flow rate and volumetric flow rate? |
Mass flow rate: lbm/sec, volumetric flow rate: ft^3/min or gpm |
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|
What is the difference between specific volume, weight, and gravity? |
Specific volume is inverse of density, specific weight is weight per unit of volume, specific gravity is ratio of densities of fluid to water and is dimensionless |
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|
Don't get confused about Quality. |
It's the ratio of the mass of the vapor to total mass of mixture. It's not the ratio of moisture or liquid. |
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|
What is the difference between the Critical Point and the Triple Point? |
Critical point is where the saturated and vapor phases exist at a single point. Triple point is where all 3 phases exist at equilibrium |
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|
What are the 5 basic properties shown on property diagrams? |
Pressure, temperature,specific volume (v) enthalpy (h), entropy (s). Quality (x) is also used for a mixture of 2 phases, liquid and gas or water and steam |
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|
What the 6 common types of property diagrams? |
P-T, P-v, P-h, h-T, T-s, h-s (Mollier diagram) |
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|
What 2 property diagrams exhibit the same features? |
P-v and P-h (refrigerant tables) |
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|
What's special about the T-s diagram? |
It's most frequently used to analyze energy transfer because work done by or on the system and heat added or removed can be visualized. |
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|
What is steam quality (x)? |
Mass of steam present per unit of mass of steam-water mixture |
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|
What equation relates electric power with voltage and current? |
P = VI [watts = volts*amps], probably the most useful electrical equation used out in the field |
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|
What are the difference between the 2 Reynold's Number equations? |
One is based on the absolute viscosity and the shorter one is based on kinematic viscosity. |
|
|
How can you find pump horsepower based on GPM and head? |
Convert gpm to (ft^3/min ) volumetric flow rate, then to mass flow rate then multiply mass flow rate by head and use a conversion to get horsepower |
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|
What is the difference between latent heat of vaporization and condensation? |
It's the same thing except for a sign difference, condensation is negative |
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|
What is the Schedule number for a pipe represent? As in Schedule 40. |
Refers to pipe wall thickness, the larger the schedule number, the thicker the pipe wall |
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|
What is the Type K,L.M in a pipe represent? |
Refers to pipe wall thickness, with K being thickest, then Type L, then Type M is the thinnest |
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What is duct sheet metal gauge a representation of? |
It's a measurement of thickness, the lower the gauge, the thicker the sheetmetal. |
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What are the units for mass flow rate (m dot)? |
lbm/s or lbm/min or lbm/h |
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What is equation for enthalpy? |
H = U + pV; units are the same for U, Internal Energy and Work. |
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How many different types of effectiveness equations are there? |
cooling coil, cooling tower, heat exchanger, heat recovery (sensible) enthalpy wheel, evaporative cooler, heat pipe |
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How do you determine the density of air from the psych chart? |
Find the specific volume and take the inverse to find density of the air |
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Summarize what latent heat of vaporization, condensation, sublimation means? |
The required energy, heat, or enthalpy added or removed for phase change |
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Summarize what heat capacity or specific heat means? |
Energy, heat, or enthalpy required to raise a substance (air, steam, water, ice) one degree. |
