9.8. Problems 345 324 CHAPTER 8. Production of Power from Heat 9.11. A refrigerator with tetrafluoroethane (Table 9.1, Fig. F.2) as refrigerant operates with an evaporation temperature of –25°C and a...

Extracted text: 9.8. Problems 345 324 CHAPTER 8. Production of Power from Heat 9.11. A refrigerator with tetrafluoroethane (Table 9.1, Fig. F.2) as refrigerant operates with an evaporation temperature of –25°C and a condensation temperature of 26°C. Satu- rated liquid refrigerant from the condenser flows through an expansion valve into the evaporator, from which it emerges as saturated vapor. 8.14. Calculate the efficiency for an air-standard gas-turbine cycle (the Brayton cycle) operating with a pressure ratio of 3. Repeat for pressure ratios of 5, 7, and 9. Take y = 1.35. r - 1 y(r. – 1) n=1- 8.14 where r is the compression ratio and r. is the cutoff ratio, defined as r. = VA/Vp- PB Ratio = PA If y = 1.4, how does the thermal efficiency of an air-standard Otto cycle with a compression ratio of 8 compare with the thermal efficiency of an air-standard Diesel cycle with the same compression ratio and a cutoff ratio of 2? How is the comparison changed if the cutoff ratio is 3? (a) For a cooling rate of 5 kJ-s-1, what is the circulation rate of the refrigerant? (b) By how much would the circulation rate be reduced if the throttle valve were replaced by a turbine in which the refrigerant expands isentropically? Ratio := Y:= 1.35 9 Еg. (8.12) пow becomes: y-1 0.248 1 0.341 n := Ans. Ratio 0.396 0.434 252