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Experiment No. 5

TEST OF OXYGEN BOMB CALORIMETER: OBTAINING THE CALORIFIC VALUE OF FUEL

Course Code: MEF420L2Program: BSME

Course Title: ME Laboratory 2Date Performed: February 11, 2015

Section: ME42FA1Date Submitted: March 1, 2015

Members: 1. Zafra, Charles Jourdan M. (Leader)Instructor: Engr. Nelson DelaPea Jr.

2. Arcay, Andrew

3. Caringal, John Martin U. (Safety Officer)

4. Dela cruz, John Kelvin B.

5. Gaela, Vanjochris

6. Macapagal,Roel U. (Quality Control)

1. Objective(s):

The activity aims to demonstrate how to determine the calorific value of different types of fuel.

2. Intended Learning Outcomes (ILOs):

The students shall be able to:2.1 Perform the procedure of operating an oxygen bomb calorimeter.2.2 Determine the calorific value of different types of fuel.2.3 Develop professional work ethics, including precision, neatness, safety and ability to follow instruction.

3. Discussion:

Calorimetry is a fundamental test of great significance to anyone concerned with the production or utilization of solid or liquid fuels.

One of the most important tests in the evaluation of materials, which are burned, as fuels, is the determination of the heat of combustion, or calorific value. These measurements can be made in the Bomb Calorimeter Set for Testing Calorific Value of Fuels, TBCF.

The Bomb Calorimeter is a classic device used to determine the heating or calorific value of solid and liquid fuel samples at constant volume. Basically, this device burns a fuel sample and transfers the heat into a known mass of water. From the weight of the fuel sample and temperature rise of the water, the calorific value can be calculated. The calorific value obtained in a bomb calorimeter test represents the gross heat of combustion per unit mass of fuel sample. This is the heat produced when the sample burns, plus the heat given up when the newly formed water vapor condenses and cools to the temperature of the bomb. Determining calorific values is profoundly important; fuels are one of the biggest commodities in the world, and their calorific value.

The Bomb Calorimeter study is carried out to gain a better understanding of the working principles behind the bomb calorimeter and also to find out the gross calorific values of different types of liquid fuel.

Description:The unit comprises the calorimeter, a calorimeter vessel, an outer double walled water jacket, control unit to switch on/off the stirrer and the ignition device, a Beckman type thermometer, and charging unit with pressure gauges to facilitate the charging of the calorimeter with oxygen. The particular features of the calorimeter bomb are the method of sealing and the method of ensuring ignition. The calorimeter vessel and outer jacket wall are manufactured in stainless steel. The calorimeter bomb is a container made of stainless steel that can support high pressures. It is sealed by a screw top. The bomb is charged with gas (oxygen) through the filling valve. This bomb is introduced inside a calorimeter vessel made of stainless steel that is filled with water, and at the same time it is introduced inside a double walled water jacket.

The rod of the calorimeter supports a metallic crucible. The calorimeter bomb, which contains the fuel sample to be burned, is hermetic to the gas by closing the filling valve and its cover. Combustion is started through a thin wire that is red hot-heated up momentarily due to the passing of an electrical current that flows through an isolated terminal and the rod, which is electrically connected to the cover.

The water in the calorimeter vessel is agitated automatically with a stirrer driven by a small motor. The top of the double walled jacket is closed with a cover that has some orifices. A Beckman thermometer to measure the temperature of the calorimeter vessel passes through one of these orifices. Other orifices are used to fasten the jacket to the cover. Also, one of these holes is used to insert the wire that supplies the electric current to the rod. The unit includes a control unit that switches on/off the stirrer and the ignition device through the heating up of the thin wire, and a load unit with pressure gauges to make the filling with oxygen of the calorimeter easier.

Specifications:

Calorimeter for testing calorific value of fuels, including: 1. Main metallic elements in stainless steel. 2. Diagram with a distribution of the elements similar than the one in the real unit. 3. Calorimeter bomb. 4. Calorimeter vessel. Characteristics: o Stainless steelMaximum volume: 4 litters. 5. Double walled outer jacket in stainless steel, with water inlet and outlet. 6. Electric stirrer with one rod and two blades. Characteristics: 330rpm. 7. Control unit to switch on/off the stirrer and the ignition device 8. Beckman thermometer. Range: 6C. 9. Charging unit with pressure gauges. 10. One nickel crucible. 11. Reel of Nickel-Chrome wire.

Dimensions: 500 mm x 400 mm x 1000 mmVolume: 0.2 m3 Weight: 40 kgElectrical Supply: single-220V/50Hz or 110V/60HzWater: 7.7 LiterOxygen CylinderSeveral Types of Fuel: Benzoic Acid (C7H6O2)

Theoretical Consideration:Almost all chemical reactions adsorb or release energy, generally as heat. Heat is the thermal energy transfer between two bodies whose temperatures are different. Heat flow from a hot body to a cold one is frequently mentioned. Generally, absorbed heat or released heat is used to describe the energy changes that take place during a process.

Reactions that take place during a process can be endothermic, if they absorb heat, or exothermic, if they release heat. Endothermic changes are expressed with a positive sign, and exothermic changes with a negative sign, according to the first law of thermodynamics. The enthalpy change occurred in the direct reaction is exactly opposed in the inverse reaction. This thermal effect is the same regardless whether the reaction takes place in one or several stages. The magnitude of the change depends on the composition, the physical state of the reagents and products and the stoichiometric expression.

Thermal changes can happen at constant pressure or at constant volume and are expressed with the following equations:

H = qp = 0

E = qv = 0

Where: H represents the enthalpy change and E represents the energy change. The H can be experimentally determined by measuring the heat flow that accompanies a constant pressure reaction, and the E a constant volume.

Heat changes of physical or chemical processes are measured with a calorimeter, which is a closed vessel specifically designed for that purpose. The calorimetry study, that is to say, the measurement of heat changes, depends on the understanding of specific heat and heat capacity. The specific heat (cp) of a substance is the amount of heat required to increase one Celsius degree the temperature of one gram of the substance. The heat capacity (Q) of a substance is the amount of heat required to increase one CelsiusDegree the temperature of a certain amount of substance. The relationship between the heat capacity and the specific heat of a substance is:

Q = mcpWhere m is the mass of the substance in grams and cp is the specific heat of a substance

The Heat of Combustion and Its Determination:Fuels are those substances predominantly containing carbon, or carbon and hydrogen, or carbon, hydrogen and oxygen, which are utilized for the energy they produce upon union with oxygen. The products of combustion are carbon dioxide, water and other oxides. The amount of heat given out in a chemical reaction depends on the conditions under which the reaction is carried out. The standard heat of reaction isthe heat released when the reaction is carried out under standard conditions: pure components, pressure (1 atm.) and temperature, usually but not necessarily, at 25C.

The Heat of Combustion (Calorific Value or Heat Value) of a compound is the standard heat of reaction for complete combustion of the compound with oxygen. The terms higher calorific value (HCV) and lower calorific value (LCV) are used, respectively, to distinguish the cases in which any water formed is in the liquid or gaseous phase. The two calorific values are related as follows:

HCV = LCV + (mw x LH)

Where mw is the mass of water produced per unit mass of fuel and LH is the latent heat of evaporation of water.

The Bomb Calorimeter:The heat of combustion is a required value in the design of any type of combustion system. There are two methods for its determination one by calculation based on the chemical composition and other by actual combustion in a bomb calorimeter. For fuels with complex chemical formulae, it is more reliable and simpler to evaluate the heat of combustion by doing a bomb calorimeter test. Further, if there is any doubt in the composition and structure of a fuel or the formula for calculating the heat of combustion, it may prove more reliable to perform the bomb calorimeter test, as it is a direct measure of the heat of combustion.

Bomb calorimeters for rapid combustion are composed of a combustion chamber (bomb) and a calorimeter vessel, usually a cylinder surrounding the bomb and containing a known quantity of water. The elevation in temperature of that water will be measured. The combustion is made in oxygen, pure or diluted. Combustion chambers are either under a constant pressure or with a constant volume. The results obtained with a calorimeter of constant volume are not e