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Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes.
This mechanism is found very commonly in everyday life, including central heating and air conditioning and in many other machines. Forced convection is often encountered by engineers designing or analyzing heat exchangers, pipe flow, and flow over a plate at a different temperature than the stream (the case of a shuttle wing during re-entry, for example).
A heat exchanger is the part of the system that transfers heat from the hot parts of the machine or a system to the cold parts of the machine or system. heat gain heat load heat loss Terms for the amount of cooling (heat gain) or heating (heat loss) needed to maintain desired temperatures and humidifies in controlled air.
Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants.
Convection (or convective heat transfer) is the transfer of heat from one place to another due to the movement of fluid. Although often discussed as a distinct method of heat transfer, convective heat transfer involves the combined processes of conduction (heat diffusion) and advection (heat transfer by bulk fluid flow ).
The heat transfer coefficient has SI units in watts per square meter per kelvin (W/(m 2 K)). The overall heat transfer rate for combined modes is usually expressed in terms of an overall conductance or heat transfer coefficient, U. In that case, the heat transfer rate is: ˙ = where (in SI units):
The CLF is the cooling load at a given time compared to the heat gain from earlier in the day. [1] [5] The SC, or shading coefficient, is used widely in the evaluation of heat gain through glass and windows. [1] [5] Finally, the SCL, or solar cooling load factor, accounts for the variables associated with solar heat load.
The macroscopic energy equation for infinitesimal volume used in heat transfer analysis is [6] = +, ˙, where q is heat flux vector, −ρc p (∂T/∂t) is temporal change of internal energy (ρ is density, c p is specific heat capacity at constant pressure, T is temperature and t is time), and ˙ is the energy conversion to and from thermal ...