Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
56 Cards in this Set
- Front
- Back
|
What is unrestricted air flow in layers or straight lines called |
Laminar flow |
|
|
What limits the amount of air that can be forced through a duct |
Fan and motor size and Noise may also play an important role |
|
|
What is the average pressure at sea level |
14.7 psia |
|
|
What is used to measure the pressure of atmospheric air |
A barometer |
|
|
What is psia |
Absolute pressure in pounds per square inch |
|
|
What is PSIG |
Gauge pressure in pounds per square inch |
|
|
How do you find the absolute pressure in a tank |
By adding the barometric or atmosphere pressure to the Gage reading |
|
|
What is a manometer |
A Gauge that utilizes the elevation of a column of water to measure pressures |
|
|
What unit of pressure is commonly used when measuring the pressure in ducts |
Inches of water because they are measured by means of a water gauge |
|
|
What pressures are often measured in air conditioning and ventilating work |
As small as one tenth of an inch of water |
|
|
What type of a gauge is used for measuring the pressure in air conditioning and ventilating work |
A gauge having an inclined tube |
|
|
What is the slope on an inclined tube |
An angle of about 10 to 1 |
|
|
What are a u-tube and well type manometer used to measure pressures of |
Approximately 1 in or more |
|
|
What is static pressure |
The outward push of air against the walls |
|
|
How is static pressure measured |
Perpendicular to airflow |
|
|
How is total pressure measured |
Tube inserted into the duct pointing towards the direction of air movement |
|
|
How is velocity pressure measured |
By connecting total and static pressure tubes to opposite ends of the manometer |
|
|
How is total pressure calculated |
Is the sum of the static and velocity pressures |
|
|
How is velocity pressure found |
Is the difference between the static and total pressure |
|
|
What size are the openings in the static pressure tube |
8 openings .04 in in diameter have been found to give accurate results |
|
|
What is the instrument that combines the static and total pressure tubed together |
A pitot tube |
|
|
Pitot tubes used with standard manometer with a slope of aboat 10 to 1 cannot be used to accurately measure air velocity of less than what |
700 fpm |
|
|
How can you accurately measure velocities lower than 700 fpm with a pitot tube |
By using ultra-sensitive manometers |
|
|
How can static pressure be measured alone using a pitot tube |
The total pressure tube of the pitot is disconnected and the static pressure tube is connected to the cup of the manometer |
|
|
How is total pressure alone measured using a pitot tube |
The static pressure tube is disconnected from the manometer connected in this way the total pressure will be indicated on the gauge |
|
|
Because air is invisible tasteless odorless and touchless how can it be recognized |
By pressure, temperature, weight, heat energy, the space it occupies, and the speed of its movement |
|
|
How is air considered and treated in HVAC work |
As an individual gas not as a compound |
|
|
What is air made up of |
Hydrogen nitrogen and oxygen |
|
|
How does air move around |
Changes its shape easily and takes the course of least resistance |
|
|
How is the pressure in air balancing measured |
By the number of inches the pressure can lift a column of water in a tube, if the pressure in the duct for 2 in it means that the amount of force can push up or lift the water 2in in a vertical column |
|
|
What is gauge pressure |
The amount of pressure under or over the surrounding atmospheric pressure |
|
|
What is positive static pressure |
A discharge duct, it exerts an outward or bursting pressure against the walls of the duct |
|
|
What is negative static pressure |
A suction duct on the intake side of the fan, exerts an inward or section force on the walls of the duct |
|
|
What is air velocity |
Speed of air flow and is expressed in feet per minute or fpm |
|
|
What is air volume |
Quantity of airflow and is expressed as cubic feet per minute or CFM |
|
|
What creates resistance to airflow |
Friction and dynamic loss |
|
|
What creates are friction |
Molecules rubbing against the sides of a duct |
|
|
What is dynamic loss |
Results from changes in duct size , shape or Direction |
|
|
What is turbulence |
It is a form of dynamic loss which results in Eddy currents |
|
|
What is aspect ratio |
The ratio of one side of a duck to the other the longer Dimension / the shorter dimension |
|
|
What is system resistance |
Another term for static pressure loss in a system |
|
|
When does Total pressure equal velocity pressure |
When static pressure is 0 at the duct Outlet |
|
|
What is the resulting value when the viscosity friction and velocity are combined in laminar flow |
The Reynolds number |
|
|
Laminar flow produces less friction loss velocities are what |
Impractically low |
|
|
What type of flow is most commonly dealt with in HVAC |
Turbulent flow |
|
|
What are dampers used for |
To control air flow by introducing system resistance |
|
|
What are two types of dampers used in HVAC |
Multi blade dampers and opposed blade damper |
|
|
What are opposed blade damper is also known as |
Squeeze blade dampers |
|
|
What type of static pressure is an exhaust system |
Negative static pressure |
|
|
What type of static pressure is a supply system |
Positive static pressure |
|
|
What is sound attenuation |
The process of dissipating sound |
|
|
What are the two ways of achieving sound attenuation in HVAC |
Duct liners, and sound traps |
|
|
What specifications would be included for ductwork |
The type of liner, adhesives and fasteners, and the type of equipment to structure isolators |
|
|
Duck liners are placed inside ducks in order to reduce what |
Sound and heat transfer |
|
|
What material is most frequently used for duct liners |
Fiberglass because it can withstand high temperatures and is an effective sound barrier |
|
|
Vibration can be reduced by using what |
Flexible duct connections, and equipment to structure isolators |
