UNIVERSITY OF WATERLOODepartment of Electrical and Computer EngineeringIntroduction to Thermodynamics and Heat Transfer

E&CE 309

Mid-Term Examination Spring 2002R. Karimi June 8, 02, 11:00-1:00 P.M.

NOTE:

1. Closed book/notes examination. You are permitted to use your calculator, and 1 pageaid-sheet double sided.

2. Clear systematic solutions are required.

3. Very briefly state the assumptions that are made in each problem.

4. Ask for clarification if any problem statement is unclear.

1. (6) A 68-kg man whose average body temperature is 38 °C drinks 1 L of cold water at3 °C in an effort to cool down. Taking the average specific heat of human body and waterto be 3.6 and 4.184 kJ/(kg.°C), respectively, determine the drop in the average bodytemperature of this person under the influence of this cold water.

2. (10) A cylinder fitted with a piston contains propane (Tcr = 370 K, Pcr = 4.26 MPa, R =0.1885 kJ/kg.K) gas at 100 kPa, 300 K, at which point the volume is 200 L. The gas isnow slowly compressed according to the relation

constant1.1 =PV

until the final temperature reaches 340 K.

(a) what is the final pressure?(b) Justify that the ideal gas model is reasonable.(c) How much work is done during the process?

3. (12) A cylinder fitted with a piston has a volume of 0.1 m3 and contains 0.5 kg ofsteam at 0.4 MPa. While the pressure remains constant, heat is transferred to the steamuntil the temperature is 300 °C.

Determine the heat transfer and the work for this process.

4. (12) Water contained in a piston-cylinder assembly undergoes two processes in seriesfrom an initial state where the pressure is 10 bar and the temperature is 400 °C.

Process 1-2: The water is cooled as it is compressed at constant pressure of 10 bars to thesaturated vapor state.

Process 2-3: The water is cooled at constant volume to 150 °C.

(a) Sketch both processes on T-ν and P-ν diagrams.(b) For the overall process determine the work, in kJ/kg.(c) For the overall process determine the heat transfer.