Bombkalorimetern

Bombkalorimetern, or the bomb calorimeter, is a device used to measure the heat released during the complete combustion of a sample, typically at constant volume. It consists of a robust steel vessel (the bomb) in which the sample, placed in a crucible, is ignited in pure oxygen. The bomb is immersed in a water-filled jacket and is equipped with a stirring mechanism and an ignition system. The entire assembly is designed to withstand the high pressure generated by combustion.

Principle and operation: When the sample burns, the released heat is transferred to the surrounding water and the bomb. The temperature rise ΔT of the water is recorded with a thermometer or thermocouple. The total heat Q released by the combustion is the product of the calorimeter’s heat capacity C and the temperature change, Q = C ΔT. The calorimeter constant C accounts for the heat capacity of the water, the vessel, and accessories. Calibration with a substance of known heat of combustion, such as benzoic acid, determines C.

Procedure and calculations: A weighed sample is placed in a crucible, placed in the bomb, and filled with oxygen at high pressure. After ignition, the bomb is sealed and immersed in the water bath. Following complete combustion, the temperature change is recorded. The energy content per mass or per mole is obtained from Q and the sample mass or amount of substance (e.g., Q/m or Q/n), and can be expressed in units such as kJ/g or kcal/mol.

Applications and limits: Bomb calorimetry provides direct measurement of the calorific value of fuels (coal, oil, gas) and, in some cases, foods. It offers high accuracy but requires careful calibration, thermal isolation, and safety handling due to high-pressure oxygen and explosive potential.