Enthalpy

Enthalpy is a description for an amount of energy, and can be found in reference material for different elements at different temperatures and pressures. Enthalpy is often given as kJ/Kg.

Enthalpy, typically denoted by H, is a state defined as

H = U + p · v.

Enthalpy H is given in Joule (J)
U = inner energy; given in Joule (J)
p = pressure; given in pascal (Pa)
v = volume; given in cubic metres (m3).
The inner energy in, for example a gas, is an expression of the movement of the gas molecules. If heat is added to a gas, the inner energy will increase.
Enthalpy is thus a description for an amount of energy, and can be found in reference material for different elements at different temperatures and pressures. Enthalpy is often given as kJ/Kg.
In ventilation and cooling systems, air changes state all the time. A Mollier’s diagram can be used to acquire an overview of these different state changes. Different types of Mollier’s diagrams are available for different purposes and situations.
Enthalpy is an expression of the energy/work that is necessary for a process.
For example:
Steam at a pressure of 1 bar is heated from 200 ºC to 400 ºC. At 200 ºC, steam has one particular enthalpy, and another at 400 ºC. This difference in enthalpy measures how much heat (energy) needs to be added for the steam to achieve this temperature increase.




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