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Calorific value is defined as amount of calories generated when a unit amount of substance is completely oxidized and is determined using the bomb calorimeter. The calorific value is usually expressed as a unit of energy per unit of mass. (J/kg, for example). Two ways to express calorific value are the gross calorific value (GCV) and the net calorific value.
The gross calorific value (GCV) (or higher heating value (HHV)) indicates the upper limit of the available thermal energy produced by a complete combustion of fuel. It is measured as a unit of energy per unit mass or volume of substance. The GCV is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced.
The net calorific value (often referred to as the lower heating value (LHV) or lower calorific value) assumes that the water component of a combustion process is in the vapour state at the end of combustion, as opposed to the gross calorific value, which assumes that all of the water in a combustion process is in a liquid state after a combustion process.
Net calorific value = gross calorific value – condensation heat
A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of combustion of a particular reaction. Basically, the composition of equipment a bomb calorimeter is showed in Fig. 1. Bomb calorimeters have withstand the large pressure within the calorimeter as the reaction is being measured. Electrical energy is used to ignite the fuel; as the fuel is burning, it will heat up the surrounding air, which expands and escapes through a tube that leads the air out of the calorimeter. When the air is escaping through the copper tube it will also heat up the water outside the tube. The change in temperature of the water allows for calculating calorie content of the fuel.
Fig.1 The bomb calorimeter
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The chemists at Alfa Chemistry have extensive experience in the testing of chemical substances. Alfa Chemistry provides calorific value testing for a wide range of chemicals in strict accordance with DIN 51900-1, DIN 51612, DIN 51857, ASTM D240, ASTM D5865, ISO 18125, ISO 1928 and other standards. Please feel free to contact us for more details.