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Eme2231:Introduction To Thermodynamics Question Paper
Eme2231:Introduction To Thermodynamics
Course:Bachelor Of Science In Food Science And Nutrition
Institution: Meru University Of Science And Technology question papers
Exam Year:2013
QUESTION ONE (20 MARKS)
a) Define each of the following thermodynamic terms; ( 5 Marks)
i. Extensive property ii. Universe iii. Heat pump iv. Isolated systems v. Enthalpy b) A system operating in a cyclic process employs a perfect gas with constant specific heats. The molecular weight of the gas is 28.5 kg/kgmol and the specific heat at constant pressure is 1.005 kJ/kg.K. The sequence of processes undergone by unit mass of the working fluid are as follows; i. Constant pressure heating form initial conditions of 2.0 MPa and 300 K to double the volume. ii. Constant volume heat rejection to initial temperature. iii. Constant temperature compression and heat rejection to initial conditions. (12 Marks) Calculate:
1. Work done for each process 2. Net work done by the cycle 3. Net heat transfer by the cycle c) What is the height thermal efficiency possible for a heat engine operating between two reservoirs whose temperatures are 800oC and 15oC respectively? (3 Marks)
2
QUESTION TWO (20 MARKS) a) A mass of 0.9 kg of steam, initially at a pressure of 15 bar and temperature of 250oC, expands reversibly and polytropicaly to 1.5 bar. Find the final temperature, work and heat transfer and change of entropy, if the index of expansion is 1.25. ( 12 Marks)
b) Air in a closed vessel of fixed volume of 0.14m3, exerts a pressure of10 bar at 250oC. If the vessel is cooled so that the pressure falls to 3.5 bar, determine the final temperature, heat transfer and change entropy. ( 8 Marks)
QUESTION THREE (20 MARKS)
a) Air flows steadily at the rate of 0.4 kg/s through an air compressor entering at 6 m/s with a pressure of 1 bar and a specific volume of 0.85 m3/kg and leaving at 4.5 m/s with a pressure of 6.9 bar and a specific volume of 0.16 m3/kg. The specific internal energy of the air leaving is 88 kJ/kg greater than that of the air entering. Cooling water in a jacket surrounding the cylinder absorbs heat from the air at the rate of 59kJ/s. Calculate the power required to drive the compressor and the inlet and outlet pipe cross-section areas. (10 Marks) b) Steam from a superheated at 7 bar, 300oC is mixed in steady adiabatic flow with wet steam at 7 bar, dryness fraction 0.9. Calculate the mass of wet steam required per kg of superheated steam to produce steam at 7 bar, dry saturated. ( 10 Marks)
QUESTION FOUR (20 MARKS)
a) For certain air-conditioning process, steam at 0.2 MPa and specific enthalpy of 2600 kJ/kg is required. 1. What is the required temperature of the steam? 2. Determine the following: i. Dryness fraction ii. Specific volume iii. Specific entropy ( 10 Marks) b) 1kg of gas expands reversibly and adiabatically, its temperature falling from 240oc to 115oc while its volume is doubled. The gas does 90 kJ of work in the process. Find the volume of C?? and C??, and the molecular mass of the gas. ( 10 Marks)
QUESTION FIVE (20 MARKS) a) Air initially at 155.5oC and 1 bar is compressed reversibly and isothermally to a state where the specific volume is 0.28m3/kg. Find the change of internal energy, change of entropy, and heat and work transfers per kg of air. (10 Marks)
b) A mass of 0.2 kg of steam with initial dryness fraction of 0.7 and temperature of 165oC, expands reversibly at a constant pressure of 7 bar until the volume is doubled. Find the final temperature, work and heat transfers. ( 10 Marks)
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