Heat Transfer

Front 1

Is energy in transit. The transfer of energy as heat, occurs at the molecular level as a result of a temperature difference.

Back 1

Heat

Front 2

A precise temperature change between two fluids across the heat exchanger is best represented by the ______

Back 2

log mean temperature difference (LMTD or Delta Tsublm),

Front 3

The fluid temperature (Tsub b), referred to as the _____ , varies according to the details of the situation

For flow adjacent to a hot or cold surface, Tb is the temperature of the fluid that is "far" from the surface, for instance, the center of the flow channel.

For boiling or condensation, Tb is equal to the saturation temperature.

Back 3

bulk temperature

Front 4

Is a measure of the amount of energy possessed by the molecules of a substance.
It is a relative measure of how hot or cold a substance is and can be used to predict the direction of heat transfer.

Back 4

Temperature

Front 5

Distinction should also be made between the energy terms heat and work. Both represent what?

Back 5

energy in transition

Front 6

_____ is the transfer of energy resulting from a force acting through a distance

Back 6

work

Front 7

_____ is energy transferred as the result of a temperature difference.

Back 7

Heat

Front 8

____can be transferred into or out of a system and work can be done on or by a system.

Back 8

Heat

Front 9

____ can be done on or by a system.

Back 9

work

Front 10

Heat into a system and work out of a system are considered ______

Back 10

positive quantities

Front 11

When a temperature difference exists across a boundary, the Second Law of Thermodynamics indicates the natural flow of energy is from what to what?

Back 11

the hotter body to the colder body.

Front 12

______ denies the possibility of ever completely converting into work all the heat supplied to a system operating in a cycle.

Back 12

The Second Law of Thermodynamics

Front 13

Second Law of Thermodynamics described by Max Planck in 1903

Back 13

It is impossible to construct an engine that will work in a complete cycle and produce no other effect except the raising of a weight and the cooling of a reservoir.

Front 14

The second law says that if you draw heat from a reservoir to raise a weight, lowering the weight will not generate enough heat to return the reservoir to its original temperature, and eventually _______

Back 14

the cycle will stop.

Front 15

Involves the transfer of heat by the interactions of atoms or molecules of a material through which the heat is being transferred.

Back 15

Conduction

Front 16

Involves the transfer of heat by the mixing and motion of macroscopic portions of a fluid

Back 16

convection

Front 17

Involves the transfer of heat by electromagnetic radiation that arises due to the temperature of a body.

Back 17

Radiation or radiant heat transfer

Front 18

Common units for heat transfer rate is ____

Back 18

Btu/hr

Front 19

The rate at which heat is transferred is represented by ____

Back 19

the symbol Q dot

Front 20

heat transfer rate per unit area

Back 20

heat flux

Front 21

The ___ can be determined by dividing the heat transfer rate by the area through which the heat is being transferred

Back 21

heat flux

Front 22

The heat transfer characteristics of a solid material are measured by a property called the

Back 22

thermal conductivity (k) measured in Btu/hr-ft-℉

Front 23

It is a measure of a substance's ability to transfer heat through a solid by conduction.

Back 23

Thermal Conducticity

Front 24

The thermal conductivity of most liquids and solids varies with _____. For vapors, it depends upon pressure

Back 24

temperature

Front 25

At a nuclear power plant, heat transfer by conduction most often occurs in_____, rather than slab, geometry.

Back 25

cylindrical

Front 26

______ is simply a factor by which we multiply the black body heat transfer to take into account that the black body is the ideal case.

Back 26

Emissivity

Front 27

Emissivity is a dimensionless number and has a _____.

Back 27

maximum value of 1.0

Front 28

There are two main types of boiling :

Back 28

Local or Nucleate
Bulk

Front 29

_____ occurring at the heating surface.
Steam bubbles collapse when carried into the bulk coolant stream.
Bulk coolant temperature is below the saturation point for system pressure.

Back 29

Nucleate Boiling

Front 30

Region II of the Pool Boiling Curve represents a rise in heat input until the heat transfer surface temperature is slightly above the saturation temperature of the water

Back 30

Nucleate Boiling

Front 31

At this point, bubbles begin forming at surface scratches and irregularities on the bottom of the container.

Back 31

Nucleate Boiling

Front 32

Providing a greater heat transfer area than a smooth surface.

Back 32

Nucleation Sites

Front 33

Critical Heat Flux:
If the heat applied rises further, more bubbles form on the heat transfer surface.
Eventually the bubbles start to collect on the surface.

Back 33

Film Boiling

Front 34

The _____ is the ratio of the maximum heat flux expected at any area to the average heat flux for the core.

Back 34

nuclear heat flux hot channel factor (HFHCF)