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ST.ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR, DEPT.OF MECHANICAL ENGINEERING ENGINEERING THERMODYNAMICS (ME-304) ENGINEERING THERMODYNAMICS 1 INDEX S. No. Name of Experiment 1 To find mechanical equivalent of heat using Joules apparatus. 2 To study working of impulse and reaction steam turbine by models. 3 To calculate COP of vapor compression refrigeration system and to plot on T-s, p-H diagrams. 4 To study working of Gas turbines by models and to identify various processes of Brayton Cycle. 5 To plot specific fuel consumption versus rpm diagrams for diesel and petrol engines. Signature Date Remark 2 Experiment No. 1 Object: To find mechanical equivalent of heat using Joules apparatus. Joules equivalent definition: It is the ratio of work done to the heat transferred from a system during a cycle and denoted by J cwhich is known as Joules constant. It is only a unit conservation factor. Jc = work/Heat In SI system of units the value Jc is unit i.e., 1Nm = 1J. Joules apparatus: The main component of joules apparatus is following there, 1. Water bath 2. Thermometer 3. Weight 4. Paddle wheel 5. Pulley 6. Rope Fig: - 3 Theory The ratio of the mechanical (or electrical) unit for energy to the heat unit for energy is called the mechanical equivalent of heat or Joule's equivalent. It is named after the British physicist Sir James Joule (1818-1889) who was the first to measure the ratio in 1850. He used a mechanical device in which mechanical energy of rotating paddle wheels (turned by falling weights) heated water in a calorimeter. In this experiment, we shall determine the ratio of the energy supplied by an electric current to the heat that it produces. When a current flows in a conductor, the amount of work done to cause the current to flow is given by W = VIt (1) where W is the work done in J, I is the current flowing in A, V is the potential difference across the ends of the conductor in V, and t is the time that the current flows in seconds. If the heat energy that this current produces raises the temperature of a certain amount of water (contained in a calorimeter) from temperature T1 to T2o C, the heat energy produced is given by H = (mwcw + mccc + h)(T2 - T1) (2) where H is the heat energy produced in calories, m w is the mass of the water in g, m c is the mass of the calorimeter in g, c w is the specific heat of water (1 cal/goC), c c is the specific heat of the calorimeter in cal/goC) h is the heat capacity of the immersion heater, thermometer, and stirrer in cal/oC. The value of the mechanical equivalent of heat may then be calculated from the ratio W/H = IVt/{(mwcw + mccc + h)(T2 - T1)} J/cal (3) The accepted value for this ratio is 4.186 J/cal. 4 The Circuit Electrical Calorimeter Procedure 1. Connect up the circuit as shown above. Do not switch on the power supply yet. The heating coil will quickly burn out if the current is switched on and it is not immersed in water. 2. Weigh the inner calorimeter and record its mass in grams in the table below. 3. Weigh the stirrer and thermometer separately and record their values. 4. Fill the calorimeter with sufficient water from the cold water tap to just cover the heating coils when immersed. Reweigh the calorimeter with the water and replace it in its insulating container. Place the heating coil in the calorimeter. 5. Set the variable resistor for maximum resistance. Stir the water in the calorimeter and measure its initial temperature, T1 to the nearest 0.1 oC. 6. Switch on the power supply and quickly adjust the variable resistor so that the ammeter reads 2.0 A. Start the stopwatch. Take the voltmeter reading and record it in the table. Adjust the variable resistor periodically as needed to maintain the current at 2.0 A. 7. Read the voltmeter at the beginning and end of the heating period and record the values in the table. Stir the water periodically until its temperature has risen between 6 and 8 oC. 8. Turn off the power supply and stop the stopwatch. Record the heating time in seconds in the table. Continue stirring the water gently for a few minutes until it reaches its maximum temperature. Read this value to the nearest 0.1oC and record the temperature, T2, in the table. 9. Repeat procedures (4) through (8) for a current of 2.5 A. Mass of calorimeter empty, mc...................................................... ______ g Specific heat of calorimeter, cc...................................................... ______ cal/goC Mass of stirrer ............................................................................... ______ g Specific heat of stirrer ................................................................... ______ cal/goC Mass of thermometer .................................................................... ______ g Specific heat of glass .................................................................... ______ cal/goC 5 Specific heat of mercury (or alcohol) ........................................... ______ cal/goC Heat capacity of stirrer, thermometer and heater, h ..................... ______ cal/oC CALCULATIONS Current I = 2.0 A Current I = 2.5 A Mass of calorimeter + water (g) Mass of water (g) Initial Temperature of water, T1 (oC) Final Temperature of water, T2 (oC) Difference in Temperature (T2 - T1) (oC) Initial Voltage (V) Final Voltage (V) Average value of the mechanical equivalent of heat = ________ J/cal. Percent error ________ Calculations: 1.Using Equation (1), calculate the electrical energy used in J. 2.Calculate the heat energy produced in calories using Equation (2). The heat capacity of the stirrer, thermometer, and immersion heater may be determined from the relation: h = mass of stirrer x specific heat of stirrer + mass of the thermometer x specific heat of glass + mass of the thermometer x specific heat of mercury (or alcohol) + the heat capacity of the immersion heater (about 1 cal/oC). 3.Calculate the value of the mechanical equivalent of heat using Equation (3) and determine its average value from the two sets of data. Result: mechanical equivalent of heat (J). It is the ratio of work done to the transferred from a system during a cycle and denoted by Jc which is known as Joule’s Constant. It is only a unit conservation factor. 6 Experiment No. 2 Object:To study working of impulse and reaction steam turbine by models. Apparatus:Model of Impulse and Reaction steam turbines. Theory: Steam turbines: The steam turbine is a prime mover in which the potential energy of steam is transformed into kinetic energy and later in its turn is transformed into the mechanical energy of the rotation of the turbine shaft. Classification of steam turbine: With respect to the action of steam, turbine are classified as: Impulse turbine Reaction turbine 1. Impulse turbine: It is a turbine, which runs by the impulse of steam jet. In this turbine, the steam is first made to flow through a nozzle. Then the steam jet impinges on the turbine blades with are curved like bucket and are mounted on the circumference of the wheel. The steam jet after impinges glide over the concave surface of blades and finally leave the turbine. The top portion of Impulse turbine exhibits a longitudinal section through the upper half, the middle portion shows one set of nozzle which is flowed by a ring of moving blades, while lower part indicate changes in pres and velocity during the flow of steam through the turbine. The principle equation of this turbine is the well known “De level” turbine. 7 Figure of Impulse Turbine 2. Reaction turbine: In a Reaction turbine, the steam enters the wheel under pressure and flow over the blades. The steam while gliding proper the blades and then makes them to move. The turbine runner is rotated by the reactive forces of steam jets. In this, there is a gradual pressure drop takes place continuously over the fixed and moving blades. The fuel of fixed blades is that they after allow it expand to a larger velocity as the steam passes over the moving blades. Its K.E. is absorbed by them a three stage Reaction turbine. Compounding: If the steam is expended from the boiler pressure in one stage the speed of rotor becomes tremendously high which drop up practical complicacies. They are several methods of reducing this speed to lower value, all these methods utilized a multiple system of rotor in series. Keyed on a common shaft and the steam pressure or jet velocity is absorbed in stage as the steam flows over the blades. This is known as compounding:- 1. Velocity compounding: Steam is expanded through a stationary nozzle from the boiler or inlet pressure to condenser pressure. So the pressure in the nozzle drops, the K. E. of steam increase due to 8 increase in velocity. A portion of this available energy is absorbed by a row of moving blades. The steam then flow through the second row of the blades which are fixed. They redirect the steam flow without altering its velocity to the flowing nearest row moving blades. Where again work is done on them and steam with a low velocity from the turbine. 2. Pressure compounding: In this rings of fixed nozzle incorporated between ring of moving blades. The steam of boiler pressure enters the first set of nozzle and expands partially. The K.E. of steam thus obtained in absorbed by the moving blades. The steam then expands partially in the second set of nozzles whose its pressure again falls and the velocity increases. The K.E. thus obtained is observed by the second ring of moving blades. This is repeated in stage 3 and steam finally leaves the turbine at low velocity and pressure. 3. Pressure- Velocity compounding: This method is the combination of velocity and pressure compounding. The total drop in steam pressure is divided into stages and velocity obtained in each stage is also compounded. The ring of nozzle, are fired at beginning of each stage and pressure remains constant during each stage. 9 Figure of Reaction Turbine VIVA-VOCE 1. State principle of working of Reaction steam turbine? 2. Define the term stage efficiency of a turbine? 3. Define the term vacuum efficiency of a turbine? 4. What is prime mover? 10 5. What is compounding? Experiment No. 3 Object:To calculate COP of vapor compression refrigeration system and to plot on T-s, p-H diagrams. Apparatus:REFRIGERATION CYCLE TEST RIG. Theory: Introduction: Now a daysRefrigeration & air conditioning system have become important due to the wide applications. The Refrigeration effect is produced either by vapor absorption cycle or Vapor Compression Cycle. In these system the refrigerants used may be Ammonia, CO2, Freon gases. Equipments: 1. COMPRESSOR: Hermetically sealed type KirloskarMake 1/3 T. Capacity. 2. AIR COOLED CONDENSOR: Copper Coils with fins & cooling fan. 3. EXPANSION DEVICE: i) Thermostatic expansion valve. ii) Capillary Tube 4. EVAPORATOR: Copper Coil immersed in water. The evaporator is installed from outside to prevent heat loss. 5. ROTAMETER: For measuring flow of Refrigerant Eureka Make. Calibrated for Freon : 134a Gas 6. ENERGY METER: One each for power supply to the Measurement of Compressor & Evaporator Heater. 7. DIMMERSTAT: To control power supply to heater. 8. PRESSURE GAUGE: One each for the measurement of high &low pressure. 9. ELECTRIC HEATER : Immersion type 1.5 Kw 10. DIGITAL TEMPERATURE INDICATOR: To Measure the temperatures at various Points i. e. Evaporator Inlet & OutletCondenser Inlet & Outlet temperatures of Refrigerant & Evaporator bath Temperature. 11. SOLINOID VALVE: Castle, Italy, Mate. 11 12. HP &LP CUTOUT: Safety device suitable for the low & high pressure of compressor. 13. SERVICE VALVE: Needle type for changing gas. 14. AMMETER: for compressor 15. VOLTMETER: 230 V, A.C. for compressor 16. FILTER DRYER: 1 No. 17. THERMOSTAT: Safety Device. 18. SWITCHES: For various controls The refrigerant circuit is mounted on a board. The unit is supported on frame. Do not operate the changing valve. See the sufficient water is filled in the evaporator container. Operation Instruction: Connect the two plugs to main. Before ON the supply, confIrm that all the switches on panel are off position. See the dimmerstat is at zero position. Then put ON the heater switch & give power to heater. This will heat the water in evaporator & this can be seen dial thermometer. Adjust the heater voltage such that the Temperature dial thermometer reading reaches 25 - 300 C. Now ON the D.P. switches. Put ON the condenser fan switch & wait for 2 - 3 minutes. Now switch ON the solenoid valve switch & the compressor switch. The refrigeration flow will start. This can be confirmed on the Rotameter. Now the ammeter, voltmeter will show the current & voltage for compressor. Note down the time for 10 revolutions of energy for compression. After some time we will see that the Temperature of water in the evaporator slowly goes down & reaches steady state.( Adjust this temp. at 28 to 300 C. After the steady state note down the readings as follows: 1. HP Condenser pressure in Kg/cm2. = Kg/cm2 2. LP Evaporator Pressure in Kg/Cm2 = Kg/cm2 3. Rotameter in Reading LPH = LPH 4. Condenser Inlet Temperature in 0C = Tci 12 0 C = Tco 5. Condenser Outlet Temperature 6. Evaporator Inlet Temperature in 0C = Tci 7. Evaporator Outlet Temperature 0C = Teo 8. Time for 10 Pulses of heater energymeter = in sec 9. Time for 10 Pulses of comp energymeter = in sec. 10. Evaporator Bath Temp in 0C = 0 C. Conclusion: From the high pressure, & low pressure & the temperature draw the refrigeration cycle on the pressure enthalpy chart. The cycle will be some what as shown : 3 2 1. Compressor Power ( Wact ) = Nc x 3600 tc x Emc x ( Comp ) P Pressure 4 1 in kg/cm2 Where, Nc = 10 H Tc = Time for 10 Pulses in sec Enthalpy in K J / kg Emc( Comp ) = Energy Meter constant. 2. Heater Power ( Nact) : Nh x 3600 Th x Emc x ( Heater ) Where, Nh = 10 Th = Time for 10 Pulses in sec Emc( Heater ) = Energy Meter constant. 3. C.O.P ( Act ) : = Power CosumedBy Heater Power Consumed By Compressor Compressor Power Consumed = Heater Power Consumed 13 Nact = Wact. Heo – Hei 4. Theoretical C.O.P = Hci – Heo Where, Heo= Enthalpy of gas at evaporator outlet Hei = Enthalpy of gas at evaporator inlet Hco = Enthalpy of gas at condenser outlet Above values are obtained for P.H. chart 5. Carnot C.O.P TL TH - TL. Where, TH = Saturated Temperature of Condenser Pressure in ° K. TL = Saturated Temperature of Evaporator Pressure in ° K. 6. COP Relative Actual C.O.P Theoretical C.O.P Observations: 1. Compressor Energymeter Constant ( E M C)com = 3200 Pulses/kwatthr 2. Heater Energymeter Constant ( E M C) h = 3200 Pulses/kwatthr 14 Observation Table: S r. No HP PSI LP PSI Q LPH Tci oc Tco oc Tei oc Teo oc Tbath oc Tc Sec Th Sec 9 26 27 27.6 10.3 25 27 26.0 10.1 Expansion Valve 1. 140 32 22 49 39 Capillary Tube 2 142 40 25 43 39 11 HP : Condenser Pressure in PSI L.P. : Evaporator Pressure in PSI Q : Refrigerant flow Rate in LPH Tci : Refrigerant inlet Temp. To Condenser in 0C Tco : Refrigerant Outlet Temp. from condenser in 0C Tei : Refrigerant Inlet Temp to Evaporator in 0C Teo : Refrigerant Outlet Temp from Evaporator in 0C Tbath : Evaporator Container Temp. in0C tc : Time for 10 Pulses of Compressor energy meter in sec. Th : Time for 10 Pulses of Heater Energy meter in sec. Sample Calculation: 1. Compressor Power ( Wact ) Nc x 3600 = tc x Emc comp 10 x 3600 = 27.6 x 3200 = 0.407Kwatt. 15 2. Heater Power ( Nact ) N h x 3600 = 10.3 x 3200 10 x 3600 = 10.3 x 3200 = 1.092 3. Actual C. O. P. of the System Refrigeration Effect Produced = Actual Work Done Power Consumed by Heater = Power Consumed by Compressor Nact = Wact 1.092 = 0.407 = 2.68 4. Carnot C.O.P TL = TH - T L Where TL = Saturated Temp. of Evaporator Pressure in 0 K TH = Saturated Temp. ofCondensor Pressure In 0 K Where LP = 32 PSI = ( 32 X 0.0731 ) + 1.0133 = 3.263 TL = (3 + 273 ) Kg/cm2 From properties of R-134a 16 = 2760 K HP = 140 PSI = ( 140 x 0.07031 ) + 1.0133 = 10.856 Kg/cm2 TH = ( 43 +273 ) From Properties of R-134a = 316 0 K 276 Cornot C. O. P.= ( 316 – 276) = 6.90 5. Efficiency of the Plant ( ) Actual C.O.P. = Carnot C.O.P 2.68 = X 100 6.90 = 38.84 % 6. Theoretical C. O. P. Heo -Hei = Hci -Heo 413.1 - 212.2 = 423.5 - 413.1 = 19.31 7. Relative C.O.P. Actual C.O.P. = Theoretical c.o.p. 17 2.68 = 19.31 = 0.138 8. Ton of Refrigeration ( T ) Refrigeration Effect Produced in K J/Min = 210 = N act X 60 210 = 1.092 x 60 210 = 0.312 ton of refrigerant Conclusion: The actual C.O.P. is less than the theoretical due to the losses at different points also the temperature are measured at somewhat different positions. Precautions: 1. Do not operate the charging valve 2. Before switching ON supply see that all the switches on the panel board are off & the dimmer stat is at ‘Zero’ position 3. The evaporator contains adequate water. 4. Proper earthing is provided. 5. In case supply fails while the trial is going on. Off the switches & also dimmer stat restore before switching ON confirm that the H.P. & L.P. pressure gauges show equal readings. If there is difference of pressure wait till the gauge pressure are equal. 6. Stabilised supply for the equipment is necessary for better performance & the life of the compressor 18 Experiment No. 4 Object:To study working of Gas turbines by models and to identify various processes of Brayton Cycle. Theory: A simple gas turbine power plant is shown in Fig. 5.1. Air is first compressed adiabatically in process a-b, it then enters the combustion chamber where fuel is injected and burned essentially at constant pressure in process b-c, and then the products of combustion expand in the turbine to the ambient pressure in process c-d and are thrown out to the surroundings. The cycle is open. The state diagram on the p-v coordinates is shown in fig. 5.2. Open cycles are used in aircraft, automotive (buses and trucks) and industrial gas turbine installation. 19 The Brayton cycle is the air standard cycle for the gas turbine power plant. Here air is first compressed reversibly and adiabatically, heat is added to it reversibly at constant pressure, air expands in the turbine reversibly and adiabatically, and heat is then rejected from the air reversibly at constant pressure to bring it to the initial state. The Brayton cycle, therefore, consists of: Two reversibly isobars and two reversible adiabatics. 20 The flow, p-v, and T-s diagrams are shown in fig. 5.3. For m kg of air 𝑄1 = ℎ𝑒𝑎𝑡 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = 𝑚𝑐𝑝 (𝑇3 − 𝑇2 ) 𝑄2 = ℎ𝑒𝑎𝑡 𝑟𝑒𝑗𝑒𝑐𝑡𝑒𝑑 = 𝑚𝑐𝑝 (𝑇4 − 𝑇1 ) ∴ Cycle efficiency, 𝜂 = 1 − 𝜂 =1− 𝑄2 𝑄1 𝑇4 −𝑇1 𝑇3 −𝑇2 Now 𝑇2 𝑝2 (𝜆−1)⁄𝜆 𝑇3 =( ) = (𝑆𝑖𝑛𝑐𝑒 𝑝2 = 𝑝3 , 𝑎𝑛𝑑 𝑝4 = 𝑝1 ) 𝑇1 𝑝1 𝑇4 21 ∴ 𝑇4 −𝑇1 or 𝑇3 −𝑇2 = 𝑇1 𝑇2 𝑝1 (𝜆−1)⁄𝜆 𝑣 = ( 2) =( ) 𝑝2 𝑣 (𝜆−1) 𝑣1 If 𝑟𝑘 = compression ration = 𝜂 = 1 − ( 2) 𝑇4 𝑇3 −1= −1 𝑇1 𝑇2 𝑣1 𝑣2 the efficiency becomes (𝜆−1) 𝑣1 or 𝜂𝐵𝑟𝑎𝑦𝑡𝑜𝑛 = 1 − 1 𝑟𝑘𝜆−1 𝑝 If 𝑟𝑝 = pressure ration = 𝑝2 the efficiency may be expressed in the following form also 1 𝑝1 (𝜆−1)⁄𝜆 𝜂 =1−( ) 𝑝2 or 𝜂𝐵𝑟𝑎𝑦𝑡𝑜𝑛 = 1 − 1 (𝑟𝑝) (𝜆−1)⁄𝜆 The efficiency of the Brayton cycle, therefore, depends upon either the compression ratio or the pressure ration. For the same compression ratio, the Brayton cycle efficiency is equal to the Otto cycle efficiency. A closed cycle gas turbine plant (fig. 5.3) is used in a gas-cooled nuclear reactor plant, where the source is a high temperature gas-cooled reactor (HTGR) supplying heat from nuclear fission directly to the working fluid (a gas). 22 Experiment No.5 AIM- To plot specific fuel consumption versus rpm diagrams for diesel and petrol engines. Apparatus- Four-Stroke Single-Cylinder Diesel Engine & Petrol Engine, Stop Watch, and Digital Tachometer, THEORY:Under some circumstances (i.e Electric Generator) C. I. Engines are required to run at constant speed. For this purpose the test is to be performed at constant speed and the load is varied from zero to maximum. When load on the engine increases its speed decreases. Accordingly the fuel supply is adjusted to keep the engine speed constant. Corresponding to each load setting, dynamometer readings and fuel consumption rate are measured. The BP, BSFC, BMEP, A/F, and Mechanical Efficiency are calculated from measured data and plotted against the load. FORMULE USED:(i) Torque, T = 9.81 x W x R Effective N-m. Where R Effective = (D + d)/ 2 or (D + tBelt)/ 2 m, W (Load) = ( S1 - S2)Kg, (ii) Brake Power, B P = ( 2πN T ) / 60, 000 KW Where N = rpm, T = Torque N-m, (iii) Fuel Consumption, m f = ( 50 ml x 10 -6 x ρ Fuel ) / ( t ) Kg/Sec. 23 Here; 1 ml = 10-3 liters, and 1000 liters = 1 m3 So, 1 ml = 10-6 m3 (iv) Brake Mean Effective Pressure, BMEP = (BP x 60,000)/ ( L Stroke x A x N’) N/ m2 Where L Stroke = Stroke m, A (Cross Section of the Cylinder) = (π D2Bore)/ 4 m2, N’ (Number of Power Strokes/ min.) = N/ 2 per min. ; For Four-Stroke Engine.= N per min; For Two-Stroke Engine., and N = rpm. (v) Brake Specific Fuel Consumption, BSFC = ( m f x 3600 ) / B P Kg/ KW . hr (vi) Mass of the Air, m Air = Cd Ao √2 g Δh ρ Air ρ Water Kg/ Sec Where Cd ( Co-efficient of Discharge ) = 0.6, ρ Air = ( Pa x 102 ) / ( R x Ta ) Kg/ m3 A2 o ( Area of Orifice ) = (π do )/ 4 m2, Pa = 1.01325 Bar, R = 0.287 KJ/Kg . K, Ta = ( ta + 273 ) K, ta = Ambient Temperature C (vii) Air Fuel Ratio, A/F = ( m Air / m f ) Kg/ Kg of Fuel (viii) Mechanical Efficiency, η mechanical = BP / IP PROCEDURE:1. Before starting the engine check the fuel supply, lubrication oil, and availability of cooling water. 2. Set the dynamometer to zero load. 3. Run the engine till it attains the working temperature and steady state condition. 4. Adjust the dynamometer load to obtain the desired engine speed. Note down the fuel consumption rate. 5. Change the dynamometer load so that the engine speed Change, to maintain the engine speed constant fuel consumption increases. 24 6. Note down the fuel consumption rate, speed, air inlet temperature, at this load setting. 7. Repeat steps 5 and 6 for various loads. 8. Disengage the dynamometer and stop the engine. 9. Do the necessary calculation. OBSERVATIONS:Engine Speed, N = 1500 rpm No. of Cylinders, n = Single Bore Diameter, Dbore =m Stroke Length, Lstroke =m Calorific Value of Fuel, C.V. = 38,000 KJ/Kg Gas Constant, R = 0.287 KJ/Kg . K Ambient Temperature, ta = oC Atmospheric Pressure, Pa = 1.01325 Bar Orifice Diameter, do = 25 x 10-3 m Co-efficient of Discharge, Cd= 0.6 Specific Gravity of fuel, ρfuel= 810 to 910 Kg/m3 Density of Water, ρwater = 1,000 Kg/m3 Brake Drum Diameter, D = 181.5 x 10-3 m Rope Diameter, d =m or Belt thickness, t Belt = 5.5 x 10-3 m OBSRVATIONS:S.No. Engine Speed N (rpm) Dynamometer spring balance S1 (kg) Time taken t(sec) Manometer fuel H (m) S2 (kg) 1 2 3 4 25 CALCULATIONS:S.No. N Torque BP Mair Mf BSFC BMEP A/f Mech. (rpm) (N-m) (kW) (kg/hr) (kg/hr) (kg/kW.hr) (N/m2) Ratio Effe. % 1 2 3 4 RESULT :- Performance curves are plotted & they are similar to the standard performance curves. 26