Ch-AnsTheSecondLawofThermodynamics.docVIP

PAGE  PAGE 4 I-Ch.18 The Second Law of Thermodynamics; Ex. P.451(e-p405): 6, 15, 30; Ch17- 29, Ch17- 29 II-Ch.18 The Second Law of Thermodynamics; Ex. P.452(e-p405): 18, 20, 67, 68*; Ch17- 53 Ch17- 53 6. Figure 18-15 is a PV diagram for a reversible heat engine in which 1.0mol of argon, a nearly ideal monatomic gas, is initially at STP( point a). Points b and c are on an isotherm at T =423K. Process ab is at constant volume. Process ac at constant pressure. (a) Is the path of the cycle carried out clockwise or counterclockwise? (b) What is the efficiency of engine? Figure 18-15 15. Assume that a hiker needs 4000kcal of energy to supply a days worth of metabolism. Estimate the maximum height the person can climb in one day. using only this amount of energy. As a rough prediction, treat the person as an isolated heat engine, operating between the internal temperature of 37℃ (98.6℉) and the ambient air temperature of 20℃ 18* At a steam power plant, steam engines work in pairs, the heat output of the first one being the approximate heat input of the second. The operating temperatures of the first are 680 0C and 430 0C, and of the second 415 0C and 280 0C. If the heat of combustion of coal is 2.8×107 J/kg, at what rate must coal be burned if the plant is to put out 900MW of power? Assume the efficiency of the engines is 65 percent of the ideal (Carnot) efficiency 20* Show that if two different adiabatic paths intersected(相交) at a single point on a PV diagram, they could be connected by an isotherm to form a cycle, and that an engine run on this cycle would violate(违犯) the 2nd law of thermodynamics. What do you conclude about the crossing of adiabatic line? 30. (a) Given that the coefficient of performance of a refrigerators defined as show that for an ideal (Carnot)refrigerator, (b) write the CP in term of the efficiency e of the reversible heat engine obtained by running the refrigerator backward. (c) What is the coefficient of performance for an ideal re