THERMODYNAMICS I - BMM2513

THERMODYNAMICS I - BMM2513 - Universiti Malaysia PAHANG...

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Unformatted text preview: Universiti Malaysia PAHANG Engineering - Technology . Creativity FACULTY OF MECHANICAL ENGINEERING FINAL EXAMINATION COURSE ' : THERMODYNAMICS I COURSE CODE : BM 2513 LECTURER : KUMARAN KADIRGAMA DATE : 25 APRIL 2009 DURATION : 3 HOURS SESSION/SEMESTER : SESSION 2008/2009 SEMESTER II PROGRAMME CODE : BMM/BMA/BMF , INSTRUCTIONS TO CANDIDATE: This examination paper consists of FIVE questions. Answer ALL questions. All answers to a new question must start on new page. All the calculation and assumptions must be clearly stated. PPS”? Candidates are not allowed to bring any material other than those allowed by the invigilator into the examination room. EXAMINATION REQUIREMENTS 1. PROPERTY TABLE DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO This examination paper consists of FOUR (4) printed pages including front page. CONFIDENTIAL BMM/BMA/BMF/0607I/BMMZSI3 QUESTION 1 A piston-cylinder device contains 250 kg of water at 250 kPa and 25°C. The cross sectional area of the piston is 0.1 n12. Heat IS now transferred to the water, causing part of it to evaporate and expand. When the volume reaches 0.2 m3, the piston reaches a linear spring whose spring constant is 100 kN/m. More heat 13 transferred until the piston rises 20 cm more Determine; a) The final pressure and temperature and (13 Marks) b) The work done during the process. Also show the process on a P-V diagram (7 Marks) QUESTION 2 A 50 kg copper block, initially at 80°C, is dropped into an insulated tank that contains 120 L of water at 25°C. Determine the final equilibrium temperature and the total entropy change for this process. (20 Marks) CONFIDENTIAL BMM/BMA/BMF/0607I/BMMZSI3 QUESTION 3 A well insulated air compressor has a low-velocity inlet stream with a pressure and temperature of 100 kPa and 300 K; its outlet stream is at 1 MPa and 600 K and has a velocity of 50 m/s. a) Sketch a block diagram for this system showing the inlet flow(s), the outlet flow(s) and any possible heat or work effects. (5 Marks) b) Construct the first law and the mass balance equation for the inlet(s) and outlet(s) that you have in this problem. (2 Marks) c) Discuss the assumptions you would have to make to reduce the equations you wrote in answering the previous question to the following result: _. W. V3. Wu = m =hin _hout _ 2t (5 Marks) d) Select an appropriate set of property relations and find the work (8 Marks) QUESTION 4 Two kilograms (2 kg) of ammonia in a piston-cylinder apparatus are initially at a temperature and pressure of 700 K and 4 MPa. The ammonia expands in a two-step process. The first step is a reversible isothermal expansion to a volume of 0.68 ms. The second step is a reversible adiabatic expansion to a pressure of 100 kPa. Determine the work done during this expansion (20 Marks) CONFIDENTIAL BMM/BMA/BMF/0607I/BMMZSI3 QUESTION 5 The outlet stream from a Refrigerant 134a compressor is cooled by a heat exchanger as shown in the figure 1 below. The refrigerant mass flow rate is 0.8 kg/s. a) Determine the heat transfer in the heat exchanger. (12 Marks) b) Calculate the minimum power input required for the compressor if the heat transfer is zero? Determine the heat transfer in the heat exchanger in this case? (8 Marks) The compressor inlet temperature and pressure are T1 = -20 C and P1 = 100 kPa. The compressor exit pressure, P2 = 1 MPa. The outlet temperature and pressure of the heat exchanger are T3 = 40 C and P3 = 1 MPa. Heat Exchanger Compressor The power input to the compressor is 400 kW. The heat loss from the compressor is 30 kW. Figure 1: Compressor and Heat Exchanger Diagram END OF QUESTION PAPER ...
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