Enthalpy – Definition and Pronunciation
What is Enthalpy?
Enthalpy is a thermodynamic measure of the total heat content of a liquid or vapour at a given temperature and is expressed in energy per unit mass (k Joules per 1 kg) from absolute zero. Therefore, for a liquid/vapour mixture, it will be seen that it is the sum of the enthalpy of the liquid plus the latent heat of vaporization.
Examples of Enthalpy
Since a variation of enthalpy represents the total energy change in a fluid as it passes through any thermodynamic process and the transformations of fluid status in the thermal machines may be considered isentropic, enthalpy is a useful unit for the analysis of energy changes, in particular for the cyclic processes involving evaporation, compression, condensation and expansion, such as the reliquefaction cycle of the vapor generated in the cargo tanks (boil-off) of the refrigerated LPG carriers.
From “Liquefied natural gas (LNG) – The Ideal Gas”.
In the international system of units (SI) system, enthalpy is measured in kilojoules per kilogram, but other energy units, such as kilocalories per kilogram, may be used in practice. The SI unit of newtons (N) = kg m/sec2 and joules (J) = kg m2/sec2.
From “Gas laws, thermodynamic principles and reliquefaction”.
A change of state from liquid to vapour at constant temperature also requires the input of energy, called the “latent heat of vaporisation” (or standard enthalpy change of vaporisation).
From “Liquefied Natural Gas Fundamental Knowledge and Understanding”.
Pronunciation of Enthalpy
