The lower heating value (also known as net calorific value) of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C. Fuel is a material with one type of energy which can be transformed into another usable energy. ... In physics, heat is defined as energy in transit. ...
The lower heating value assumes the latent heat of vaporization of water in the reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below 150°C cannot be put to use. The standard enthalpy change of vaporization is a physical property of substances. ... Water (from the Old English waeter; c. ...
Some engine manufacturers rate their engines using Lower Heating Values (LHV) which can be both confusing and potentially misleading to the casual user of their product literature. Lower heating values neglect the energy in the water vapor formed by the combustion of hydrogen in the fuel. This water vapor typically represents about 10% of the energy content. Therefore the lower heating values for natural gas are typically 900 - 950 Btu per cubic foot.
The error can occur when a manufacturer says their engine uses 900,000 Btu/hr but it was expressed on a LHV basis. The engine would actually use about 1,000,000 Btu/hr as purchased from a gas supplier. Therefore, always check the fuel rating method when natural gas is the fuel for the system. This potential confusion almost never exists with liquid fueled systems. Compare to higher heating value. The Higher Heating Value (HHV) of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the reactants have returned to a temperature of 25°C. The Higher Heating Value takes into account the latent heat of...
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