ASSIGNMENT-2ME 215 Fundamentals of Mechanical Engineering4th. Semester, CE ( Gr.-A)/ENE(To be submitted latest by 29th.April, 2015)Q.1 (a) Classify various types of air compressors. Define the volumetric efficiency of a compressor. On what factors do it depends? Derive the maximum values of these factors for zero volumetric efficiency.(b) A single-acting air compressor has a cylinder of bore 15 cm and the piston stroke is 25 cm. The crank speed is 600rpm. Air taken from the atmosphere (1atm, 27 C) is delivered at 11bar. Assuming polytropic compression pv 1.25=const. Find the power required to drive the compressor, when the mechanical efficiency is 80%. The compressor has a clearance volume which is 1/20th. of the stoke volume. How long will it take to deliver 1 m of air at the compressor outlet conditions? Find the volumetric efficiency of the compressor.Q.2 (a) What are rotary compressors? Describe the working of Root blower and Vane type compressors with suitable diagrams.(b) A twostage single-acting reciprocating air compressor takes in air at the rate of 0.2m/sec. Intake pressure and temperature are 0.1MPa and 16 C respectively. The air is compressed to a final pressure of 0.7 MPa .The intermediate pressure is ideal and inter cooling is perfect. The compression index is 1.25 and the compressor runs at 10 rps. Neglecting clearance, determine (a) the intermediate pressure (b) the total volume of each cylinder (c) the power required to drive the compressor and (d) the rate of heat absorption in the intercooler. Q.3(a) Show that the optimum intermediate pressure of a two stage reciprocating compressor for minimum work is the geometric mean of the suction and discharge pressures.(b) The cylinder of an air motor has a bore of 63.5 mm and stroke of 114 mm. The supply pressure is 6.3 bar. The supply temperature is 24 C and the exhaust pressure is 1.013bar. The clearance volume is 5% of the swept volume and the cut off ratio is 0.5. The air is compressed by the returning piston after it has travelled through 0.95 of its stroke. The law of compression and expansion is polytropic with index of 1.2. Calculate (a) the temperature at the end of expansion (b) the indicated power of the motor which runs at 300 rpm and (c) the air supplied per minute. Q.4(a) Discuss briefly the concept of entropy. Derive an expression for increase in entropy of an ideal gas when heated in any general form.(b) An ideal gas of mass 0.25kg has a pressure of 400KN/m, a temperature of 80 C and volume of 0.07 m . The gas undergoes an irreversible adiabatic process to a final pressure of 300 KN/m and a final volume of 0.1 m, during which the work done on the gas is 25 KJ. Find Cp and Cv of the gas and increase in entropy of the gas.

Q.5(a) Establish that the entropy is the property of the system.(b) 2.5 kg of air is expanded at constant pressure to four times its initial volume. The initial temperature is 400 C. Calculate the change in entropy of the system. Q.6(a) Describe the three basic modes of heat transfer and specify their differences. State and explain Fouriers law of heat conduction.(b)A refrigerated container in the form of a cube with 2m sides and 5 mm thick aluminium walls (k=204W/mK) is insulated with a 0.1m layer of cork (k=0.043W/mK) and the surface temperatures are Ti=-5 C and To =20 C. Find out the cooling load of the refrigerator. Q.7(a) Define overall heat transfer coefficient. Comment on relative magnitudes of the thermal resistances. What is the difference between Uo and Ui ?(b) Steam at 350 C flowing in a pipe (k=80W/mK), 5.0 cm inside diameter and 5.6 cm outside diameter is covered with 3 cm thick insulation (k=0.05W/mK). Heat is lost to the surroundings at 5 C by natural convection and radiation with combined h=20W/mK and h i =60 W/mK . Find out(i) the rate of heat loss from the pipe per unit length and (ii) the temperature drop across the pipe and the insulation. Q.8(a) State Stefan-Boltzmann law. On what factors the radiant heat exchange between two gray bodies depend? (b) A wire of 0.5 mm in diameter is stretched along the axis of a cylinder 50mm in diameter and 250 mm long. The temperature of the wire is 750K while the cylinder is at 250K and the gas in it has a K=0.0251W/mK. Find out the rate of heat transfer through the gas by conduction and by radiation, if the wire is black. (S.K.Das) Asst. Professor (Mech ) /Class Teacher Date: 07 th.April,2015 Mobile No. 9953965727 Room No. FW4TF22 (Top Floor, Mechanical Block)