Chapter 7, Problem 7.88P

10. Carnot cycle thermal efficiency is increased by reducing lower(sink) temperature 11. A system with higher exergy has more capacity to do work than a system with lower exergy. 12. A diffuser has low pressure at inlet and high pressure at outlet 13. Carnot efficiency equation can also be used to find efficiency of conversion of electrical and/or magnetic energy to work. 14. Quality factor of 0.75 indicates supersaturated vapor 15. Law of conservation of Mass and energy applied to Nozzles and Diffusers indicates that under ideal conditions, the change in kinetic energy of the fluid results in a complimentary change in enthalpy of the fluid

Exergy flow associated with a fluid stream when the fluid properties are variable can be determined by.

7.29 A gearbox operating at steady state receives 4 hp along the input shaft and delivers 3 hp along the output shaft. The outer surface of the gearbox is at 130°F. For the gearbox, (a) determine, in Btu/s, the rate of heat transfer and (b) perform a full exergy accounting, in Btu/s, of the input power. Let To 70°F.

Figure PZ55 and the accompanying table provide the schematic and steady-state operating data for a flash 7.55 chamber fitted with an inlet valve that produces saturated vapor and saturated liquid streams from a single entering stream of liquid water. Stray heat transfer and the effects of motion and gravity are negligible. Determine (a) the mass flow rate, in Ib/s, for each of the streams exiting the flash chamber and (b) the total rate of exergy destruction, in Btu/s. Let To = 77°F, Po =1 atm State Condition T(°F) p(lbf/in.°) h(Btu/lb) s(Btu/lb R) liquid 300 80 269.7 1 0.4372 1.6996 30 1164.3 2 sat. vapor 3 sat. liquid 218.9 0.3682 30 2 Saturated vapor P2=30 lbf/in.2 Flash chamber Valve =100 lb/s T 300°F P=80 lbf/in.2 Saturated liquid,A+ P3=30 lbf/in.2 3 FIGURE P7.55

Define the Mechanisms of exergy transfer.

Using image below Evaluate the exergy X1 of the initial state 1 and answer the following question: • Is the useful work in the process 1 → 2 → DS smaller, equal, or greater than exergy X1? • Discuss your result

EXERGY TRANSFER BY HEAT, WORK, AND MASS

As shown in the figure below, two reversible cycles arranged in series each produce the same net work, Weycle: The first cycle receives energy QH by heat transfer from a hot reservoir at TH = 1000°R and rejects energy Q by heat transfer to a reservoir at an intermediate temperature, T. The second cycle receives energy Q by heat transfer from the reservoir at temperature Tand rejects energy Qc by heat transfer to a reservoir at Tc = 450°R. All energy transfers are positive in the directions of the arrows. Hot reservoir at TH R1 W cycle Reservoir at T W cycle R2 Cold reservoir at Te Determine: (a) the intermediate temperature T, in °R, and the thermal efficiency for each of the two power cycles. (b) the thermal efficiency of a single reversible power cycle operating between hot and cold reservoirs at 1000°R and 450°R, respectively. Also, determine the ratio of the net work developed by the single cycle to the net work developed by each of the two cycles, Wcycle

7.36 At steady state, hot gaseous products of combustion from a gas turbine cool from 3000°F to 250°F as they flow through a pipe. Owing to negligible fluid friction, the flow occurs at nearly constant pressure. Applying the ideal gas model with ₂ = 0.3 Btu/lb/ºR, determine the exergy transfer accompanying heat transfer from the gas, in Btu per lb of gas flowing. Let T. = 80°F and ignore the effects of motion and gravity. -568.43