Ref. No. : Ex/IEBE/PE/T/122/1/7/2012 Form A Paper-setting Blank B.E. Instrumentation 1st Year 2Dd Semester Examination, 2012 (11t/2DdSemesterlRepeat/Su13plementaryl }.B RuelfRi hnBU91) Subject: Applied Thermodynamics (Name in full) Paper Time: Twe beHFSI Three hours I FAUF hAUAI I "i.. Full Full Mark 100 hAUAI Answer question number / and any fiye from the rest. For Air R=287 J/ki!K; Cv=O.718 kJ/kgK, Use of Steam Table is allowed. No.of uestions 1. (a) (b) (c) (d) (e) (f) (g) (h) II (i) 1\ G) I Marks What is the difference between closed system and open system? What is a pressure transducer? What is the zeroth law of thermodynamics? Show that heat is a path function and not a property. What is a PMMl? Why is it impossible? Show that the enthalpy of a fluid before throttling is equal to that after throttling. What is a thermal energy reservoir? Explain the term 'source' and 'sink'. Why is the second law called a directional law of nature? What do you mean by the word 'dryness fraction'? What are the four basic components of a steam power plant? . I 2. (a) (b) (c) What do you understandby path function and point function? What are exact and inexactdifferential? 2 2 2 2 2 2 2 2 2 2 2+2 I A mass of gas is l~omrre~s~(!Jti"a qnasi-st<!ticproc~s frem 80 kPa,O.l m3 to GA . l:: ..J MPa, 0.03 m3.Assumingthat the pressure and volume are related by pv"=;::constant, find the work done by the gas system. 7 The heat capacity at constant pressure of a certain system is a function of temperatureonly and may be expressedas C = 2.093+ 41.87 JfC t + 100 Where t is the temperature of the system in °C. The system is heated while it is maintained at a pressure of 1 atmosphere until its volume increases from 2000 cm3 to 2400 cm3 and its temperature increases from OoCto 100°C. Find the magnitude, of heat interaction and also calculate the increase in internal energy. P 3. (a) (b) (c) (e) Define the specific heats atconstant volume and at cor.sta.'lt pressU;re Write the. steady flow energy equation for a single stream entering and a single stream leaving a control volume and explain the various terms in it. What will be the velocity of fluid leaving a nozzle, if the velocity of approach is very small? A turbine operates under steady flow conditions, receiving steam at the following state: pressure 1.2 MPa, temperature 188°C, enthalpy 2785 kJ/kg, velocity 33.3 mls and elevation 3m. The steam leaves the turbine at the following state: pressure 20 kPa, enthalpy 2512 kJ/kg, velocity 100 mls and elevation Om. Heat is lost to the surroundings at the arte of 0.29 kJ/s. If the rate of steam flow through the turbine is 0.42 kg/s, what is the power outputofthe turbine in kW. ---~~. --- 1+1 5 3 6 I 1 I 4. (a) (b) (c) 5. (a) (b) (c) 6. (a) Consider two Camot heat engines operating in series. The first engine receives heat from the reservoir at 1800K and rejects the waste heat to another reservoir at temperature T. The second engine receives this energy rejected by the first one, converts some of it to work, and rejects the rest to a reservoir at 300 K. If the thermal efficienciesof both engines are the same, determinethe temperature T. Air is compressed steadily by a 5-kW compressor from 100 kPa and 17°C to 600 kPa and 167°C at a rate of 1.6 kg/min. During this process, some heat transfer takes place between the compressor and the surrounding medium at 17°C Determinethe rate of entropy change of air during this process. Show that the COP of a heat pump is greater than the COP of a refrigerator by unity. For the same maximum pressure and temperature of the cycle and the same heat rejection with the help of p-v and T-s diagram compare the efficiency of Diesel, Dual and Otto cycle. State the various assumptionsfor the air standardcycle and based on that calculate the efficiencyof Diesel cycle in terms of compressionratio and cut-off ratio. An air-standard Diesel cycle has a compressionratio of 16 and a cutoff ratio of2. At the 'beginning of the compression process, air is at 95 kPa and 27°C. Accounting for the variation of specific heats with temperature, determine (a) the temperature after the heat-addition process, (b) the thermal efficiency, and (c) the mean effective pressure. A simple saturation cycle using Freon 22 is designed for a load of 100 TR. The saturated suction and discharge temperatures are 5°C and 40°C respectively. Calculate: 1. the mass flow rate ofthe refrigerant, 2. the COP, 3. the heat rejected in the condenser. Use the following data; Temp Pressure (C) (bar) 5 5.836 - .0404 205.9 40 15.331 - - Sp. Volume (m3/kg) Vf Vg xl03 Enthalpy (kJ/kg) hf . hg Entropy (kJ/kgK) Sf 407.1 1.0211 5 5 6 5 5 2+4 5 7 _,I Sg 1.744 7 249.53 416.4 1.6659 1.699 53 Specific heat of vapour is 0.65 kJ/kgK (b) (c) 7. (a) (b) (c) A mass of 5 kg of saturated water vapor at 300 kPais heated at constant pr~ssure until the temperature reaches 200°C. Calculate the work done by the steam during this process. What do you mean by refrigerating effect and tonne of refrigeration? Find out the optimum pressure ratio for a simplegas turbine plant. Why reheating is essential in gas turbine power plant? What is the' value of optimum reheat pressure? An open cycle gas turbine power plant works on Brayton cycle. The maximum pressure and temperature of the cycle are limitedto 5 bar and 900K. The pressure and temperature of the gas entering into the compressor are 1 bar and 27°C. Reheating is used at a pressure of 2.5 bar where the temperature of the gas is increased to its original turbine inlet temperature.The air flow rate is given by 10 5 2+2 3"= 2+3 8 kg/sec. Determine the thermal efficiency and plant capacity in MW. The exhaust pressure of turbine is also 1 bar. Assume that both compression and expansion are isentropic. Take Cp=1.005 kJ/kgK, y=1.4 for both compression and expansion process. CV offuel is 40,000 kJ/kg. ,18. (a) (b) (c) An ideal Rankine cycle uses water as a working fluid, which circulates at a rate of 80 kg/so The boiler pressure is 6 MPa, and the condenser pressure is 10 kPa. The steam is superheated and enters the turbine at 600°C and leaves the condenser as a saturated liquid. Determine (A) the power required to operate the pump, (B) the heat transfer added to the water in the boiler, (C) the power developed by the :Iturbine, (D) the heat transfer removed from the condenser, (E) the quality of steam at the exit ofthe turbine, and (F) the thermal efficiency ofthe cycle. 6 A six cylinder gasoline engine operates on the 4 stroke cycle. The bore of each cylinder is 80 mm and the stroke is 100mm. The clearance volume per cylinder is 70 cc. At a speed of 4000 rpm, the fuel consumption is 20 kg/hr and the torque developedis 150Nm. Calculatei. The brake power. ii. The brakemean effectivepressure. Hi. The brakethermalefficiency. 6 Whythe compressionratio of CI engine is more than SI engine? 4