MEC203 Chapter 1 Definitions Flashcards
Define Heat
The form of energy that can be transferred from one system to another as a result of temperature difference
Define Specific heat
The energy required to raise the temperature of a unit mass of a substance by one degree
Define Incompressible substance
A substance whose specific volume (or density) does not change with temperature or pressure
Define Heat transfer rate
The amount of heat transferred per unit time
Define Heat flux
The rate of heat transfer per unit area normal to the direction of heat transfer
Define Power
The work done per unit time
Define The First Law of Thermodynamics
Energy can neither be created nor destroyed during a process; it can only change forms
Define Mass flow rate
The amount of mass flowing through a cross section of a flow device per unit time
Define Volume flow rate
The volume of a fluid flowing through a pipe or duct per unit time
Define Conduction
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
Define Thermal conductivity
The rate of heat transfer through a unit thickness of the material per unit area per unit temperature difference
Define Temperature gradient
The slope of the temperature curve on a T-x diagram
Define Convection
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
Define Forced convection
If the fluid is forced to flow over the surface by external means such as a fan, pump, or the wind
Define Natural (free) convection
If the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid
Define Radiation
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
Define Blackbody
The idealized surface that emits radiation at the maximum rate
Define Emissivity
A measure of how closely a surface approximates a blackbody for which ε = 1 of the surface. 0 ≤ ε ≤ 1
Define Absorptivity
The fraction of the radiation energy incident on a surface that is absorbed by the surface. 0 ≤ α ≤ 1
Define Kirchhoff’s law
The emissivity and the absorptivity of a surface at a given temperature and wavelength are equal
Define Net radiation heat transfer
The difference between the rates of radiation emitted by the surface and the radiation absorbed
