Determining the heating value of a propellant sample using a bomb calorimeter.

 

Report submitted by Krishnadev C. (AE01B031) on the experiment done on 28^th January 2003 in the Rocket and Missiles Laboratory, Department of Aerospace Engineering, IIT-Madras.

 

Aim:

            The aim of this experiment is to measure the heating value of a sample of propellant using a bomb calorimeter.

 

Apparatus:

            A bomb calorimeter, Beckmann’s thermometer, magnifying eye-piece, a sample of virgin propellant, stirrer, a compressor, nichrome wire and Nitrogen cylinder.

 

Theory and Procedure:

            The aim of the experiment is to find the high calorific value of a sample of virgin propellant. A bomb calorimeter was used for this purpose. The propellant sample is burned inside a bomb and the temperature variation is studied using an extremely sensitive thermometer. The rise in temperature corresponds to the calorific value of the propellant. In this experiment a solid propellant (HTPD + Oxidizer) was used. The sample was virgin propellant, it had only fuel and oxidizer, and there were no catalysts.

The propellant is carefully fixed on to the bomb lid using nichrome wire. A few drops of water is poured into the bomb in order to make it air tight, and to bring about uniformity in temperature when the propellant burns. The bomb is to be freed of any oxidizing gas, hence pressurized Nitrogen is supplied into it repeatedly, finally the bomb is prepared with about 4 bar of Nitrogen gas in it. Thus prepared bomb is carefully placed in the calorimeter. Then measured quantity of water is poured into the calorimeter to absorb the heat generated. Later the Beckmann thermometer and stirrer is fixed and the calorimeter is also sealed.

The sample is ignited by passing electricity through the nichrome wire. The temperature variation is analyzed using Beckmann thermometer. Beckmann’s thermometer is high sensitivity mercury thermometer with a least count of 0.001^oC. The temperature is measured with the help of a magnifying eye-piece at regular intervals of time (1 minute).  The temperature of the water increases gradually as it slowly absorbs the temperature generated in the combustion of the propellant. Then the temperature slowly begins to decreases as the water gets cooled. The readings are taken until the temperature stabilizes with the ambient value. The Calorific value of the propellant is determined from the readings taken.

 

Formulae used:

m_w C_p ΔT = m_f H

 

Where: -         H = heating value of fuel

m_f = mass of propellant sample

m_w = total equivalent of water

ΔT = temperature change

C_p = Specific heat (= 4.8 J/K)

 

Observations:

 

Mass of the propellant used, m_f = 3.2494g

 

(i)      Before the combustion process.

 

 

(ii)      After the combustion process.

 

 

 

Calculations:

 

            Amount of water added = 1860g

            Initial reading of Beckmann’s thermometer = 1.21

            Final reading of Beckmann’s thermometer = 2.642

            Rise in temperature = 1.432^oC

Water Equivalent of the calorimeter = 670g

Water Equivalent of Nichrome = 0.032g

Mass of propellant = 3.2494g

 

Calorific value of the propellant used = 4.66 kJ/kg.

 

Result:

 

The temperature variation was carefully measured using the Beckmann’s Calorimeter. The Calorific value of the propellant sample was determined to be 4.66kJ/kg.

 

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