Bomb calorimeter is used to determine the calorific value of solid and liquid fuels.
Construction
It consists of following parts
1. Stainless steel bomb: here, the combustion of fuel takes place. The bomb has a lid, which can be made gas tight by means of screws. The lid consists of two electrodes and an oxygen inlet valve. To one of the electrodes, a small ring is attached to support a nickel or stainless steel crucible. Fuel is taken in the crucible. Magnesium wire touching the fuel sample is stretched across the electrodes. Bomb is capable to with stand high pressure (25 - 50 atm). It is lined inside with platinum so that it resists corrosion.
2. Copper calorimeter: the stainless steel bomb is placed in a copper calorimeter containing known amount of water.
3. Air jacket/water jacket: copper calorimeter is surrounded but an air jacket and a water jacket to prevent heat losses due to radiation.
4. Beckmann's thermometer: the copper calorimeter is provided with a Beckmann's thermometer, which can read accurately a temperature difference upto 1/100th of a degree.
5. Stirrer: the copper calorimeter is provided with an electrically operated stirrer.
Working
A known amount of fuel whose calorific value is to be determined is placed in crucible. Magnesium wire touching the sample is stretched across the electrodes. Bomb is filled with oxygen through oxygen value and a pressure of 25 - 30 atm. is maintained. Bomb is then kept in a copper calorimeter containing known amount of water. Temperature of water is noted. The fuel is ignited by connecting electrodes to the battery. The fuel burns and the energy liberated increases the temperature of water in the calorimeter. Water is stirred with the stirrer and the maximum temperature attained is noted. The calorific value of the fuel is calculated as follows:
Weight of fuel sample taken = x gm
Weight of water taken in calorimeter = W gm
Higher calorific value = L cal/gm.
Water equivalent of calorimeter = W gm.
Initial temperature of water in calorimeter = t 1 0C