 Myself, Dr. Nitin Gramopadhe, Department of Basic Sciences and Humanities, Walton Institute of Technology, Sallapur. Today, we are going to learn determination of calorific value of a given sample of fuel by using bomb calorimeter method. This is the learning outcome for today's session. At the end of this session, students will be able to describe the terms fuel, calorific value, higher calorific value, hcv, lower calorific value, lcv and determination of hcv and lcv of a given sample of fuel by using bomb calorimeter method. This is the content we are learning in this session. First, we will see some definition such as fuel, hcv that is higher calorific value, lcv that is lower calorific value and determination of calorific value of a given sample of fuel. What do you mean by fuel? Fuel is a material that is used as a source of energy. Energy source is mainly required in domestic, agriculture, industry and transportation sector. Fuel exists in the form of solid, liquid and gas form. Few energy sources such as solar, wind belongs to renewable type of resources whereas some sources such as fossil fuels belongs to non-renewable type of resources. Fuel is a material which essentially consists of carbon as a major ingredient which on burning in open atmosphere combines with atmospheric oxygen and form carbon dioxide as a product along with heat. Such heat is used for different kind of work. Now after learning the fuel, we will learn one more concept that is what do you mean by calorific value of a fuel because calorific value of a fuel decides the quality of the fuel. So, calorific value is the property of fuel which decides usefulness of the fuel. Every work requires certain amount of heat to get it completed therefore calorific value of a fuel must be known before its use. Calorific value is the capacity of the fuel to supply the heat or the total quantity of heat evolved after burning a unit mass of fuel. Calorific value is measured in either calorie per gram or kilo calorie per kg unit. Solids are low in calorific value, liquids are moderate in calorific value and gases are more in calorific value and a good fuel is the fuel which shows more calorific value. Now we will learn what do you mean by hcv and lcv after learning the calorific value. What is hcv? It is the total amount of heat produced when unit mass or volume of the fuel has been burned completely and the products of combustion have been cooled to room temperature. Usually all fuel contain some hydrogen. The hydrogen is converted into steam. If the products of combustion are condensed to room temperature then the latent heat of condensation of steam also get included in the measured heat which is then called as higher or gross calorific value. What is lower calorific value? In actual practice it is difficult to condense the products of combustion. It is the net heat produced when unit mass or volume of the fuel is burned completely and the products are permitted to escape. In actual use of any fuel, the water vapors and moisture are not condensed and escape as such along with hot combustion gases hence lower amount of the heat is available so it is known as the lower calorific value. Now I would like to ask you one question here. A good fuel should possess dash dash calorific value. Think for a moment we will come with the answer and the correct answer is higher. Just now we have learned that the solids are low in calorific value, liquids are moderate in calorific value and gases are more in calorific value. Now after learning the theoretical concept how to determine the hcv and lcv by using bomb calorimeter method. Now what is the principle of this method? This method is used to determine calorific value of solid and non-volatile types of fuel only. In this experiment a unit mass of the fuel is burned and the heat evolved is allowed to absorb in water where it is recorded as function of temperature. Construction of the bomb calorimeter is as shown in the figure. So see the figure this is the outer part this is called as a water jacket followed by the gap is there that is called as the air jacket. This is the copper calorimeter which is filled with the water in that stainless steel bomb is inserted which is divided into two parts one is the lead and second one is the body. The lead is having a provision of two electrodes during its use these two electrodes are connected to battery and at a lower portion these two electrodes are having a provision of either platinum or magnesium wire to which a crucible is there and in that crucible we are using a very small sample of which we are going to determine the calorific value. Then here it is a thermometer which is used to record the temperature of water before combustion and after combustion and this is the mechanical stirrer but this is the overlook of the diagram of bomb calorimeter method. Now how it is constructed? It consists of strong cylindrical stainless steel bomb in which the combustion of fuel is made. The bomb has a lead which can be screwed the body of bomb so as to make perfect gas tight seal. The lead is provided with two stainless steel electrodes and an oxygen inlet one. To one of the electrodes a small ring is attached in the bottom portion just now I shown. In this ring a nickel or stainless steel crucible can be supported. The bomb is placed in a copper calorimeter which is surrounded by air jacket and water jacket to prevent the heat losses due to radiation. The calorimeter is provided with an electrically operated stirrer and thermometer which can be used to actually measure temperature difference of water that is before combustion and after combustion. Now how it work? During working a known mass of 0.5 to 1 gram of the fuel is taken in a clean crucible. The crucible is then supported over the ring. A fine magnesium wire touching the fuel sample is then stretched across the electrode. The bomb lead is tightly screwed and bomb filled with oxygen then the bomb is then lowered into copper calorimeter which is filled with water. The stirrer is working and initial temperature of the water is noted. The electrodes are then connected to 6 volt battery and the circuit is completed. When the current is passing from the battery to electrode it enters into the magnesium wire. The wire gets red heated and because of that rise in temperature the fuel catches the fire that it undergoes the ignition and it produces the heat and that heat is allowed to absorb in a surrounding water. Now what are the observations of this experiment? What is the mass of fuel sample we have taken that is expressed as m gram? Mass of water taken in copper calorimeter that is capital W gram. Water equivalent due to stirrer etcetera that is small W gram. Initial temperature of water T1 degree centigrade. Final temperature of water T2 degree centigrade and hcv of the fuel is Q calorie per gram. Now the two statements are there heat liberated is the product of mass and capacity so it is expressed as mQ and heat absorb is equal to W plus W into bracket T2 minus T1. Therefore heat liberated is always equal to heat absorb so mQ is equal to W plus W into bracket T2 minus T1. So now Q that is hcv is equal to W plus W into another bracket T2 minus T1 divided by m and the unit goes to calorie per gram or kilo calorie per kg. It depends in which unit we are using the water weight, fuel weight etcetera. What is lcv? lcv is equal to Gcv that is gross or higher calorific value minus 0.09 multiplied by percentage of hydrogen multiplied by 587 which is known as standard latent heat of steam. Now certain corrections are there to this experiment one is known as acid correction fuel containing sulfur and nitrogen are oxidized under high pressure and temperature of ignition to sulfuric acid and nitric acid respectively. Therefore such heat should be subtracted from the total heat. What is fuse wire correction? The heat liberated which include the heat given out by ignition of the fuse wire therefore such heat should be subtracted because metal is getting heated wire and therefore it also adds certain heat to the total heat and we know that that is not the heat because of our fuel sample therefore the heat coming due to heating of the metal that we should subtract and then the cooling correction this is the amount of heat that gets lost due to local condensation and hence this is needed to add in the total amount of heat. Now finally the corrected Hcv equation becomes w plus w into bracket T2 minus T1 plus Tc that is cooling correction minus Ta that is acid correction plus Tf that is fuse wire correction divided by m that is mass of fuel. There is no change for Lcv because already we are using here the corrected Gcv. So Lcv remains same.