1 (a) A steam power plant shown schematically in Fig. Q1 operates ...

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1 (a) A steam power plant shown schematically in Fig. Q1 operates on an ideal Rankine cycle with boiler and condenser pressure of 80 and 0.5 bar, respectively. Steam the rate of 18 kg/s leaves the oiler/superheater unit, which has an efficiency 53% atemperature At the condenser inlet the steam quality, x, is 0.82. Show the cycle on T-s diagram with respect to saturation lines and marks) determine: (i) the turbine power output if its mechanical efficiency 88%: (4 marks) (ii) the heat rejected in the condenser (4 marks) (iii) the pumping power fthe mechanical efficiency pump is (4 marks) 86%: (iv) the total heat added to the steam in the biler/superheater unit; (4 marks) (v) the net power output fthe plant: (4 marks) (vi) the fuel consumption assuming fuel calorific value of 42,5000 kJke: (4 marks) (vii) the overall thermal fficiency of the plant: (4 marks) (viii) the rate of cooling water needed the condenser fthe increase in the cooling water temperature is 20°C and its heat 4.2 kJ/(kg.K); (4 marks) (ix) the combustion air mass flow rate the air to fuel ratiois 12; (4 marks) (x) the temperature of the combus tion gases leaving boiler/superheater unit. marks) You may assume that both the air and fuel temperatures are 20°C before entering the boiler/superheater unit. Assume, also, that the specific heat capacity of the gases and air, 1.005 kJ/(kg.K) (b) Explain the impact of low plant efficiency on the environment and fossil fuel resources. (4.5 marks) (c) Explain the principle difference between the Kelvin- Plank and Clausius statements of the second law of thermo namics (4.5 marks) Beiler and Steam Sirger- - (Fuel Heate unit Cooling wrier Pump A Condenter mm Fix. Q1 Schematic diagram of power generating plant Page 1of3 2 (a) Consider refrigeration system that removes 4kw of heat from a refrigerated space and operates on the vapour compression refrigeration cycle that uses Isceon 49 the working fluid The refrigerant enters the compressor superheated vapour pressure and temperature of 210 kPa and 10°C respectively. It is then compressed in non isentropic manner to pressure of 1500 kPa and temperature of 50°C. The refrigerant sub -cooled in the condenser toa temperature of 25'C. Subsequently, the refrigerant is throttled in constant enthalpy process, to the evaporator pressure. Show the cycle T-s and p-h diagrams with respect to the saturation line and determine:- (4.5 marks) (i) the mass flow rate of the refrigerant; (4.5 marks) (ii) the quality of frigerant at the end of the throttling process and the isentropic efficiency of the compressor; (4.5 marks) (iii) the compressor power input its mechanical efficiency is 92%: (4. (iv) the coefficient of performance of the refrigerator. marks) Use the Isceon pressure-enthalpy diagram provided to show the details of the refrigeration cycle and attach with your answer. (b) Explain the operation principle of heat pumps and comment on their role in energy saving when used in space heating. Explain why the energy output of any heat pump always higher than its work input (4.5 marks) 3 (a) A turbocharger operates on exhaust gases of an actual pressure and temperature of 270kPa and 1000 C,respectively Exhaust gases at rate of 0.070m³ enter the turbocharger velocity of 70m/s and leave at an actual temperature of 750 K. Assuming turbine isentropic efficiency of 83% sketch the expansion processes on diagram and determine: (3 marks) (i) the energy consumed bv the turbocharger; marks) (ii) the isentropic temperature of the exhaust gases the turbine outlet; marks) (iii) the diameter of the turbocharger inlet. marks) You may assumethat the exhaust gases flowing through the turbine behave an ideal gas with constants identical to those of air room temperature. (b) Sub-cooled water at a steady rate of 13 kg/s enters gas fired boiler/superheater combination Thetemperature and velocity of the water the boiler inlet are 80 and m/s, respectively The pressure and temperature of the generated steam at the superh eater outlet are 40 bar and 500 C. respectively. The oiler/superheater combination consumes 2.5 kg/s of natural gas of calorific value of 43,000 kJ/kg. Determine: (i) the boiler/superhcater efficiency: (4 marks) (ii) the diameter of the pipe feeding the boiler. (3 marks) Page 2of3 : - so 000 uno son 120 cob 460 of 430 I SA & SE 300 2000 200 240 200 20 (ie) req

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