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 26C. Satu- rated liquid refrigerant from the condenser flows through an expansion valve into the evaporator, from which it emerges as saturated vapor. 8.14. Calkulate 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. 7(r, = 1) 8.14 where r is the compression ratio and r, is the cutoff ratio, defined as r = V/Vp. Pg 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 kJs-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 Eq. (8.12) now becomes: 0.248 0.341 n := Ans. Ratio 0.396 0.434
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 26C. Satu- rated liquid refrigerant from the condenser flows through an expansion valve into the evaporator, from which it emerges as saturated vapor. 8.14. Calkulate 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. 7(r, = 1) 8.14 where r is the compression ratio and r, is the cutoff ratio, defined as r = V/Vp. Pg 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 kJs-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 Eq. (8.12) now becomes: 0.248 0.341 n := Ans. Ratio 0.396 0.434
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Question
Transcribed Image 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
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