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For a heat engine, thermal efficiency is the ratio of the net work output to the heat input; in the case of a heat pump, thermal efficiency (known as the coefficient of performance or COP) is the ratio of net heat output (for heating), or the net heat removed (for cooling) to the energy input (external work). The efficiency of a heat engine is ...
Quantity (common name/s) (Common) symbol/s Defining equation SI unit Dimension Temperature gradient: No standard symbol K⋅m −1: ΘL −1: Thermal conduction rate, thermal current, thermal/heat flux, thermal power transfer
A realistic indication of energy efficiency over an entire year can be achieved by using seasonal COP or seasonal coefficient of performance (SCOP) for heat. Seasonal energy efficiency ratio (SEER) is mostly used for air conditioning. SCOP is a new methodology that gives a better indication of expected real-life performance, using COP can be ...
90–95% (multiply by the energy efficiency of electricity generation to compare with other water-heating systems) Electric heater: Electrical to thermal ~100% (essentially all energy is converted into heat, multiply by the energy efficiency of electricity generation to compare with other heating systems) Others: Firearm: Chemical to kinetic
Just as with the internal energy version of the fundamental equation, the chain rule can be used on the above equations to find k+2 equations of state with respect to the particular potential. If Φ is a thermodynamic potential, then the fundamental equation may be expressed as:
To express the efficiency of a generator or power plant as a percentage, invert the value if dimensionless notation or same unit are used. For example: A heat rate value of 5 gives an efficiency factor of 20%. A heat rate value of 2 kWh/kWh gives an efficiency factor of 50%. A heat rate value of 4 MJ/MJ gives an efficiency factor of 25%.
The method proceeds by calculating the heat capacity rates (i.e. mass flow rate multiplied by specific heat capacity) and for the hot and cold fluids respectively. To determine the maximum possible heat transfer rate in the heat exchanger, the minimum heat capacity rate must be used, denoted as C m i n {\displaystyle \ C_{\mathrm {min} }} :
In thermal physics and thermodynamics, the heat capacity ratio, also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient, is the ratio of the heat capacity at constant pressure (C P) to heat capacity at constant volume (C V).