air conditioner - An air conditioner is an air refrigerator whose refrigerated space is a room or a building instead of the food compartment.

Carnot cycle - A Carnot cycle is a reversible cycle first proposed by Sadi Carnot, and is composed of four reversible processes, among which two are isothermal and two are adiabadic, and it can be executed either in a closed or a steady-flow system.

Carnot efficiency - Carnot efficiency is the highest efficiency a heat engine operating between the two thermal energy reservoirs at a lowest temperature and a highest temperature can have, and it is equal to (1 - (lowest temperature) / (highest temperature)).

Carnot heat engine - A Carnot heat engine is the hypothetical heat engine that operates on the reversible Carnot cycle.

Carnot principles - Carnot priciples are two conclusions pertain to the thermal efficiency of reversible and irreversible heat engines: (1) The efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs. (2) The efficiencies of all reversible heat engines operating between the same two reservoirs are the same.

Carnot refregerator or Carnot heat pump - A Carnot refregerator or a Carnot heat pump is a refrigerator or a heat pump that operates on the reversed Carnot cycle.

Clausius statement - Clausius statement states that it is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower temperature body to a higher temperature body.

coefficient of performance of a heat pump - Coefficient of performance of a heat pump is the measure of performance of a heat pump and is defined as the fraction of the desired output over the required input of the heat pump.

coefficient of performance of a refrigerator - Coefficient of performance of a refrigerator is the efficiency of a refrigerator and is defined as the fraction of the desired output over the required input of the refrigerator.

Energy Efficiency Rating - Energy efficiency rating is the performance of refrigerators and air conditioners in the U.S., denoted by EER, which is the ampunt of heat removed from the cooled space in Btu's for 1 Wh (watt-hour) of electricity consumed.

externally reversible - A process is called externally reversible if no irreversibilities occur outside the system boundaries during the process.

heat engine - A heat engine is a device used to convert heat to work directly and completely. Heat engines differ considerably from one another, but all can be characterized by the following: (1)They receive heat from a high-temperature source (solar energy, oil furnace, nuclear reactor, etc.). (2)They convert part of this heat to work (usually in the form of a rotating shaft). (3)They reject the remaining waste heat to a low-temperature sink (the atmosphere, rivers, etc.). (4)They operate on a cycle.

heat pump - A heat pump is a device that transfers heat from a low-temperature medium to a high-temperature one.

heat reservoir - A heat reservoir is a thermal energy reservoir that supplies or absorbs energy in the form of heat. Both source and sink are heat reservoirs.

internally reversible - A process is called internally reversible if no irreversibilities occur within the boundaries of the system during the process.

irreversibility - Irreversibility is a factor that causes a process to be irreversible.

irreversible process - An irreversible process is a process that is not reversible.

Kelvin-Planck statement - Kelvin-Planck statement states that no heat engine can have a thermal efficiency of 100 percent, or as for a power plant to operate, the working fluid must exchange heat with the environment as well as the furnace.

Kelvin scale - The Kelvin scale is a thermodynamic temperature scale first proposed by Lord Kelvin, and the temperatures on this scale are called absolute temperatures. In a reversible process, the ratio of the heat associated with the high temperature to the heat associated with the low temperature is equal to the ratio of the high temperature over the low temperature.

perpetual-motion machine - A perpetual-motion machine is a device that violates either the first or second law of thermodynamics.

perpetual-motion machine of the first kind (PMM1) - A perpetual-motion machine of the first kind is a device that violates the first law of thermodynamics (by creating energy).

perpetual-motion machine of the second kind (PMM2) - A perpetual-motion machine of the second kind is a device that violates the second law of thermodynamics.

refrigerant - Refrigerant is the working fluid used in the regrigeration cycle.

refrigerator - A refrigerator is a cyclic device to transfer heat from a low-temperature medium to a high-temperature one.

reversible process - A reversible process is a process which can be reversed without leaving any trace on the surroundings. That is, both the system and the surroundings are returned to their initial states at the end of the reverse process.

sink - A sink is a reservior that absorbs energy in the form of heat.

source - A source is a reservoir that supplies energy in the form of heat.

thermal efficiency - Thermal efficiency is the fraction of the heat input that is converted to net work output and is a measure of the performance of a heat engine.

thermal energy reservoir - A thermal energy reservoir is a hypothetical body with a relatively large thermal energy capacity (mass times specific heat) that can supply or absorb finite amounts of heat without undergoing any change in temperature.

thermodynamic temperature scale - The thermodynamic temperature scale is a temperature scale that is independent of the properties of the substances that are used to measure temperature.

totally reversible - A process is called totally reversible if it involves no irreversibilities within the system or its surroundings.

working fluid - Heat engines and other cyclic devices usually involve a working fluid to and from it heat is transferred while undergoing a cycle.