課程名稱︰熱力學
課程性質︰必修
課程教師︰謝正義
開課系所︰生工
考試時間︰06/14/2005
試題 :
Thermodynamics
Second Midterm examination
1.A heat pump is used to meet the heating requirements of a house and maintain
it at 20°C. On a day when the outdoor air temperature drops to -2°C,the
house is estimated to lose heat at a rate of 8000kJ/h. If the heat pump under
these conditions has a COP if 2.5,determine (a)the power consuned by the heat
pump and (b) the rate at which heat is absorbed from the cold outdoor air.
(20%)
2.Steam enters an adiabatic turbine at 5MPa and 450°C and leaves at a pressure
of 1.4MPa. Determine the work output of the turbine per unit mass of steam if
the process is reversible.(20%)
3.A well-insulated heat exchanger is to heat water(Cp = 4.18kJ/kg˙°C)from
25°C to 60°C at a rate of 0.5kg/s. The heating is to be accomplished by
geothermal water (Cp = 4.31kJ/kg˙°C)available at 140°C at a mass flow rate
of 0.75kg/s.Determine (a) the rate of heat transfer and (b) the rate of
entropy generation on the heat exchanger.(20%)
4.An insulated piston-cylinder device contains.5L of saturated liguid water at
a constant pressure of 150kPa. An electric resistance heater inside the
cylinder is now turned on,and 2200kJ of energy is transferred to the steam.
Determine the entropy change of the water during this process,in kJ/K(20%)
5.A reversible device is used as refrigerator for cooling in summer and as heat
pomp for heating in winter. The house is maintained at 24°C year around. The
heat loss or gain is 0.44kW per degree difference between outside and inside
temperatures. The average outside temperature is 32°C in the summer and
-4°C in the winter. Determine the power requirements for both heating and
cooling.(20%)
6.Show the Carnot cycle process and heat supplied QH, heat rejected QL,and the
(下標) (下標)
net work output Wnet,out.(10%)
(下標)
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