Junker's Gas Calorimeter

1.      History:

The junker’s gas calorimeter was named by Antoine Lavoisier. In 1870, he used guinea pig with this device to measure heat production in his experiments. The heat produced by the pig melted the snow arround the calorimeter. This shows that respiratory is the combustion similar to burning of candle. The junker’s gas calorimeter is almost similar to bomb calorimeter in respect that heat evolved by burning gas is taken away by water. 

2.      Description:

The junker’s gas calorimeter is used to determine the calorific value of the gaseous fuels.

2.1.Construction:

The junker’s gas calorimeter is a device used to measure the calorific value of the gaseous fuels. The device is essentially a Bunsen burner with a cooling jacket. The jacket is cylindrical in shape  with water in it. The burner is inside the cylinder. The calorimeter allows the user to measure the temperature of water flowing in and flowing out. Once steady state is reached, the water flowing through is collected for a specified period of time. Measuring the mass of the water and the temperature rise in the water, the operator can calculate the number of joules which went into the water to heat it. There is a flow meter on the fuel gas, so the operator can also calculate the volume of gas that was burned in the same time period. The amount of energy, in J, available per litre of gas can then be calculated. A Junkers calorimeter is a flow calorimeter, with heat transfer happening continuously, as opposed to a batch calorimeter. 

 The device consist of a cylindrical shell and two paths for water are there which have copper coil arranged in it. One path is the inlet and the other is outlet. Water pass through the copper coils. There is pressure regulator in the path of water flow which is further connected with gas flow meter. Gas flow meter is used to measure the flow rate of gas. Temperature sensors are used in the device to measure the inlet and outlet water temperature and also for the flue gases. 

2.2.Main Parts:

1. SHELL

2. WET TYPE LABORATORY GAS METER

3. PRESSURE REGULATOR

4. AIR HUMIDIFIER

5. FUEL BURNER

6. AIR INLET

7. COOLING WATER

8. COOLING WATER CHAMBER

9. THERMOMETER (INLET WATER TEMPERATURE)

10. THERMOMETER (OUTLET WATER TEMPERATURE)

11. FLUE GAS OUTLET

12. CONDENSATE OUTLET

2.3. Working:

The junker’s gas calorimeter works on the principle of burning of a gas whose volume is known. The temperature of water and gas is measured along with flow rate of gas to measure the calorific value. The formula is:

 Calorific Value of Gas X Volume of Gas = Volume of water X Rise in Temperature, is then used to determine the Calorific Value of the Gas (assuming that heat capacity of water is unity). 

A measured quantity of gas whose calorific value is required supplied to a gas meter which measures the volume of gas and after it the gas pass through the pressure regulator which measures the pressure of gas using the manometer. When the gas inside the chamer is burned, the products produced in the combustion rise into the chamber and then move downward where it is extracted as gas flues. After this gas finally escapse to the atmosphere. There is thermometer at the end of the outlet which measures the temperature of the escaping gas. This temperature should be near room temperature so that whole heat is absorbed by the water. Cold water enters the calorimeter near the bottom of device and leaves from top. Water that was formed by condensation is collected in a pot. The quantity of gas in te process is measured accurately and the temperature of ingoing and outgoing gas is also measured. By using above ccollected data we can measure the calorific value from formula as mentioned earlier. 

3.      Example:

Following results were obtained when a gas was tested in a junker’s gas calorimeter:

Gas burnt in calorimeter = 0.08m3

Pressure of gas supply = 5.2 cm of water

Barometer  = 75.5 cm of Hg

Temperature of gas = 13 degree centigrade

Weight of water heated by gas = 28 kg

Temperature of water at inlet = 10 degree centigrade

Temperature of water at outlet = 23.5 degree centigrade

Steam condensed = 0.06 kg

Determine the higher and lower calorific values per meter cube of gas at temperature of 15 degreecentigrade and barometeric pressure of 76 cm of Hg.

Solution:

The volume of gas is measured at 13 degreecentigrade and pressure of 5.2 cm of water. Let us reduce this volume to S.T.P. by using general gas equation.

P1V1/T1 = P2V2/T2

P1 = 75.5+ (5.2/13.6) = 75.882 cm of Hg

T1 =  273+13 = 286K

V1 = 0.08 m3

P2 = 76 cm of Hg

V2 = ?

T2 =  273+15 = 288K

75.882 x 0.08/286 = 76 x V2/288

V2 = 75.882 x 0.08 x 288/76

V2 = 0.0804 m3

Heat received by water = 28 x 4.18 x (23.5 – 10) = 1580 KJ

Higher calorific value of fuel = 1580/0.08 = 19750 KJ/m3

Amount of water vapours formed(steam condensed) per m3 of gas burnt = 0.06/0.08 = 0.75 Kg

Lower calorific value (L.C.V) = H.C.V -2465 x 0.75

                                                 = 19750 – 1848.7 = 17901.3 KJ/Kg