Final exam ENGI 2800 Engineering Thermodynamics I
Date: December 11th, 2007 Time: 8h35 11h30 Open book, no question allowed Question #1 (5 points) Give a short written answer to this question: a) Explain why the compression ratio in a diesel engine can be much higher than the compression ration of a spark-ignition engine. b) How do internal and external combustion engines differ? Give one example for each. Question #2 (12 points) Air as an ideal gas flows through the compressor and heat exchanger shown in the following figure. A separate liquid water stream also flows through the heat exchanger. The data given on the figure are for operation at steady state. Stray heat transfer to the surroundings can be neglected through the entire system. Determine: a) the compressor power, in kW; b) the mass flow rate of cooling water, in kg/s; c) the rates of entropy production, each in kW/K, for the compressor and heat exchanger. Room: Dalplex Professors: Dr. Dominic Groulx Dr. George Jarjoura
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Question #3 (20 points) The figure to the right shows the schematic diagram of a cogeneration cycle. In the steam cycle, superheated vapor enters the turbine with a mass flow rate of 5 kg/s at 4 MPa, 440C and expands isentropically to 150 kPa. Half of the flow is extracted at 150 kPa and used for industrial process heating. The rest of the steam passes through a heat exchanger, which serves as the boiler of the R-134a cycle and the condenser of the steam cycle. The condensate leaves the heat exchanger (state 3) as saturated liquid at 100 kPa before it is combined with the return flow from the process, at 60C and 100 kPa, before being pump isentropically to the steam generator pressure of 4 MPa. The R-134a cycle is an ideal Rankine cycle with refrigerant entering the turbine at 1.6 MPa, 100C and saturated liquid leaving the condenser at 900 kPa. Draw the two T-s diagrams needed and determine, in kW: a) the rate of heat transfer to working fluid passing through steam generator. b) the net power produced by binary cycle c) the rate of heat transfer to industrial process. the the the the
Hints: 1) start your analysis at state 1, before the steam turbine 2) Steam pressure goes down through the heat exchanger but R-134a pressure stays constant in the same heat exchanger, so don't forget to account for it. Question #4 (13 points) Air, treated as an ideal gas, enters the compressor of a simple gas turbine at 100 kPa, 300 K, with a volumetric flow rate of 5 m3/s. The compressor pressure ration is 10 an...