Definitions part 3 Flashcards
define heat
Heat (which can also be described as heat transfer) is energy in transit across a
boundary due to temperature difference or gradient.
heat is defined as the transfer of thermal energy between two systems or a system and its surroundings due to a temperature difference. It flows spontaneously from a region of higher temperature to one of lower temperature until thermal equilibrium is reached
____(which can also be described as ____ transfer) is energy in transit across a
boundary due to temperature difference or gradient.
heat
define adiabatic processes
An adiabatic process is a process during which there is no heat transfer:
- Isolated system
- System and surroundings are in thermal equilibrium (at same temperature)
An ______ ______ is a process during which there is no heat transfer:
- Isolated system
- System and surroundings are in thermal equilibrium (at same temperature)
adiabatic
define conduction
Conduction is the mechanism of heat transfer through a material by molecular diffusion due to
a temperature gradient
_____ is the mechanism of heat transfer through a material by molecular diffusion due to
a temperature gradient. Microscopic collisions
conduction
define convection
Convection is the heat transfer due to the bulk movement of a fluid - usually between a solid and a fluid.
__is the heat transfer due to the bulk movement of a fluid - usually between a solid and a
fluid.
convection
define radiation
Radiation is the transfer of energy by electromagnetic radiation with a defined range of wavelengths.
All surfaces emit radiant heat
____ is the transfer of energy by electromagnetic radiation with a defined range of wavelengths.
All surfaces emit radiant heat
Radiation
define fourier’s law (relevant for conduction)
“The heat transfer rate through a material is proportional to the negative gradient of temperature and
the area through which the heat flows.”
define the thermal conductivity coefficient
The thermal conductivity coefficient 𝑘 [W/m.K] is a measure of a materials ability to transfer
thermal energy by conduction. the higher this value, the better the material is at conducting
define free or natural convection
Free or natural Convection: is the heat transfer due to the bulk movement of a fluid – fluid motion usually caused by natural effects such as the buoyance affect
___/___ _______: is the heat transfer due to the bulk movement
of a fluid – fluid motion usually caused by natural effects such as the
buoyance affect
free or natural convection
define forced convection
Forced Convection: the fluid is forced to flow over a surface or in a tube
by external means such as a pump or fan
______ ________: the fluid is forced to flow over a surface or in a tube
by external means such as a pump or fan
forced convection
define thermal radiation
Thermal radiation involves the transfer of heat from one body to another at a lower
temperature by electromagnetic waves passing through a separating medium (which
can be a void/vacuum).
___ __ involves the transfer of heat from one body to another at a lower
temperature by electromagnetic waves passing through a separating medium (which
can be a void/vacuum).
thermal radiation
define emissivity
The property Emissivity, is a measure of how closely a
surface approximates to a Black body.
Emissivity is a measure of a material’s ability to emit thermal radiation compared to that of a perfect blackbody. A perfect blackbody, which is an idealized object, absorbs all incident radiation and emits the maximum possible radiation at any given temperature. Emissivity is a dimensionless quantity that ranges from 0 to 1
define thermal resistance
Thermal resistance is a heat transfer property and a measurement of how resistant a material is to heat flow. It is described as the relationship between the temperature difference across a substance or object and the rate of heat flow through it.
__ __ is a heat transfer property and a measurement of how resistant a material is to heat flow. It is described
as the relationship between the temperature difference across a substance or object and the rate of heat flow through it.
thermal resistance
absolute thermal resistance
Absolute thermal resistance, R, in SI units of kelvins per watt [k/W] is the temperature difference across a structure when a unit of heat energy flows through it in unit time. It is a property of a particular component
___ ___ ___, R, in SI units of kelvins per watt [k/W] is the temperature difference across a structure when a unit of heat energy flows through it in unit time. It is a property of a particular component
Absolute thermal resistance
define specific thermal resistance
Specific thermal resistance or specific thermal resistivity, 𝑹′, has SI units of [m².K/W] and is the resistance to heat flow per unit area of the material. It represents how well a material of a given thickness resists heat transfer for each square meter of area and is a material constant.
