Bombkalorimeter

Bomb calorimeter, also known as a constant-volume calorimeter, is a device used to measure the heat of combustion of a sample. In operation, a weighed sample is placed in a small steel vessel called a bomb, which is sealed, filled with oxygen at high pressure, and submerged in a water bath inside a rigid bomb container. The sample is ignited electrically by a fuse wire. The combustion occurs at constant volume, and the heat released raises the temperature of the water and the bomb. The temperature change is recorded by a thermometer or a thermocouple. The calorimeter has a known heat capacity, including the water and the bomb, and the heat of combustion is calculated from q = -C ΔT, where C is the calorimeter constant (the heat capacity of the whole system).

To obtain accurate results, calibration with a substance of known heat of combustion, typically benzoic acid, is performed to determine C. Corrections may be applied for heat losses, formation of water from hydrogen, and the heat capacity of the surroundings. The main applications are determinations of the calorific value of fuels (coal, oil, gas) and food energy content. Advantages include direct measurement of heat at constant volume and good accuracy for combustible samples. Limitations involve safety hazards due to high-pressure oxygen, potential incomplete combustion, and the need for careful calibration. Modern devices may integrate automated data acquisition and safety interlocks.