Chapter 7, Problem 7.40CU

Define the Mechanisms of exergy transfer.

If a closed system undergoes a process for which S2=S1, the process must be internally reversible. - True or False One of the Carnot principles states that all power cycles operating between the same two thermal reservoirs have the same thermal efficiency. - True or False One statement of the second law of thermodynamics recognizes that the extensive property entropy is produced within systems whenever internal irreversibilities are present. - True or False

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

1. A source of heat at 1000 K transfers 1000 kW of power to a power generation device, while producing 300 kW of useful work. Determine: a. The rate of exergy destruction in this process if the environment is at 300K. b. The second law efficiency of the system.

.......A gas turbine power plant is operated between 1.5 bar and 15 bar with minimum and maximum cycle temperatures of 25 C and 1420 C, respectively. Neglect the mass of the fuel.   Determine the following: Work of the compressor in kJ/kg (2 decimal places) = Work of the gas turbine in kJ/kg (2 decimal places) = Heat added in the combustion chamber in kJ/kg (2 decimal places) = Net Work in kJ/kg (2 decimal places) = Thermal Efficiency in % (1 decimal place only) =

A closed system undergoes a cycle consisting of three process 1-2, 2-3 and 3-1.  Given that Q12 = 30kJ, Q23 = 10 kJ, 1w2 = 5 kJ, 3w2 = 5 kJ and DE31 = 15 kJ, Evaluate Q31, w23, DE12 and DE23.

If the specific exergy of a gas in a cylinder of an internal combustion engine modeled as air behaving like an ideal gas is 368.91 kJ / kg and the cylinder contains 2450 cm2 of gaseous combustion products. Åt what elevation in meters 3-kg mass does it have to be lifted from zero elevation with respect to the reference environment so that its exergy equals the exergy of the cylinder? Assume gravity as g = 9.81 m /s^2 NOTE: The density of dry air at a pressure of 7 bar and a temperature of 867 ° C is 2.1388 kg / m^3.

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

Figure below shows a simple vapor power plant operating at steady state with water as the working fluid. Data at key locations are given on the figure. The mass flow rate of the water circulating through the components is 109 kg/s and isentropic turbine efficiency is 80%. Stray heat transfer and kinetic and potential energy effects can be ignored. Determine (a) the net power developed, in MW. (b) the thermal efficiency. (c) the isentropic pump efficiency. (d) the mass flow rate of the cooling water, in kg/s. (e) the rates of entropy production, each in kW/K, for the turbine, condenser, and pump. P-100 bar Ty-$60°C Power out Turbine Py-0.08 bar -80% Steam Cooling water in at 20°C generator Condenser P-100 bar T-60°C Cooling water out at 40°C 4. Pump 3 P= 0.08 bar Saturaied liquid Power in ww