MEC203 Chapter 1 Definitions

Question 1

Define Heat

Answer 1

The form of energy that can be transferred from one system to another as a result of temperature difference

Question 2

Define Specific heat

Answer 2

The energy required to raise the temperature of a unit mass of a substance by one degree

Question 3

Define Incompressible substance

Answer 3

A substance whose specific volume (or density) does not change with temperature or pressure

Question 4

Define Heat transfer rate

Answer 4

The amount of heat transferred per unit time

Question 5

Define Heat flux

Answer 5

The rate of heat transfer per unit area normal to the direction of heat transfer

Question 6

Define Power

Answer 6

The work done per unit time

Question 7

Define The First Law of Thermodynamics

Answer 7

Energy can neither be created nor destroyed during a process; it can only change forms

Question 8

Define Mass flow rate

Answer 8

The amount of mass flowing through a cross section of a flow device per unit time

Question 9

Define Volume flow rate

Answer 9

The volume of a fluid flowing through a pipe or duct per unit time

Question 10

Define Conduction

Answer 10

The transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles

Question 11

Define Thermal conductivity

Answer 11

The rate of heat transfer through a unit thickness of the material per unit area per unit temperature difference

Question 12

Define Temperature gradient

Answer 12

The slope of the temperature curve on a T-x diagram

Question 13

Define Convection

Answer 13

The mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion

Question 14

Define Forced convection

Answer 14

If the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind

Question 15

Define Natural (free) convection

Answer 15

If the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid

Question 16

Define Radiation

Answer 16

The energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules

Question 17

Define Blackbody

Answer 17

The idealized surface that emits radiation at the maximum rate

Question 18

Define Emissivity

Answer 18

A measure of how closely a surface approximates a blackbody for which ε = 1 of the surface. 0 ≤ ε ≤ 1

Question 19

Define Absorptivity

Answer 19

The fraction of the radiation energy incident on a surface that is absorbed by the surface. 0 ≤ α ≤ 1

Question 20

Define Kirchhoff’s law

Answer 20

The emissivity and the absorptivity of a surface at a given temperature and wavelength are equal

Question 21

Define Net radiation heat transfer

Answer 21

The difference between the rates of radiation emitted by the surface and the radiation absorbed