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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. System ii. Intensive property iii. Heat iv. Wetness fraction v. Degree of super heat
b. State Joule’s law. (1 Mark)
c. Prove that for a reversible process p??= constant for a perfect gas heat flow Q is equivalent to the work done W by the system. (6 Marks)
d. A system undergoes a cyclic process composed of three processes. During the first process Q=10kJ and ?u=20kJ, during the second process Q=30kJ, during the third process ?u=5kJ and Q = -20kJ. (8 Marks) i. How much work is done during the second process?
ii. What is the net work done in the cycle? Is it done by or on the system?
2
QUESTION TWO 20 MARKS
a. Dry saturated steam at 100 bar expands isothermally and reversibly to a pressure of 10 bar. Calculate the heat supplied and the work done per kg of steam during the process. (10 Marks)
b. A rigid cylinder containing 0.006m3 of nitrogen (molar mass 28kg/kmol) at 1.04 bar, 15oC , is heated reversibly until the temperature is 90oC. Calculate the change of entropy and the heat supplied. Sketch the process on a T-s diagram. Take the isentropic indet for nitrogen as 1.4 and assume that nitrogen is a perfect gas. (10 Marks)
QUESTION THREE 20 MARKS
a. Steam from a super heater 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) b. A gas turbine receives gas from the combustion chamber at 7 bar and 650oC with a velocity of 9m/s. The gases leave the turbine at 1 bar with a velocity of 45m/s. Assuming that the expansion is adiabatic and reversible in the ideal case, calculate the work done per kg of gas. For the gases take r = 1.333 and Cp = 1.11 kJ/kg.k (10 Marks)
QUESTION FOUR 20 MARKS
a. 1 kg of steam in a cylinder expands reversibly behind a piston according to a law p??= constant from 7 bar to 0.75 bar. If the steam is initially dry saturated, find the temperature finally, the work done by the steam and the heat flow to or from the cylinder walls. (10 Marks) b. 0.05 kg of carbondioxide (molar mass 44kg/kmol), occupying a volume of 0.03m3 at 1.025 bar is compressed reversibly until the pressure is 6.15bar. Calculate the final temperature, the work done on the CO2 and the heat flow to or from the cylinder walls. The process is according to a law p??1.4= constant (Assume carbon dioxide to be a perfect gas; take r=1.3) (10 Marks)
QUESTION FIVE 20 MARKS
a. With aid of a well labelled T-S diagram for a Carnot cycle describe the processes that constitute the cycle. (6 Marks) b. State two reasons why a steam generating plant operating between temperature limits of a Carnot cycle would have a lower thermal efficiency. (2 Marks) c. The data in the following table apply to two hypothetical heat engine cycles. Complete the table. (12 Marks) Reservoir Temperature Heat Supplied Heat Rejected Work Output Thermal Efficiency Maximum Possible thermal efficiency T1 (oc) T2 (oc) Q1 kJ/s Q2 (kJ/s) w(kW) 283 ? 100 ? 45 0.45 ? 540 38 2857 1000 ? ? ?
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