Chapter 7, Problem 7.7P

A power cycle operating between two reservoirs receives energy Qu by heat transfer from a hot reservoir at TH = 2000 K and rejects energy Qc by heat transfer to a cold reservoir at Tc = 400 K. For the cases below you will be asked to determine the cycle n and whether the cycle operates Reversibly, Irreversibility, or is Impossible. Сycle Сycle Сycle Assume: п — пСarnot n пСarnot 1. The maximum thermal efficiency nCarnot for the cycle is equal to а. 0.2 b. 0.8 с. 1.0 d. none of the above. 2. If QH = 1100 kJ and the Weycle = 900 kJ then the cycle is Reversible b. Irreversible c. Impossible а. d. none of the above. 3. If QH = 1000 kJ and Qc = 200 kJ then the cycle is a. Reversible b. Irreversible c. Impossible d. none of the above. 4. If Wq a. Reversible b. Irreversible c. Impossible d. none of the above. суcle 1400 kJ and Qc= 600 kJ then the cycle is 5. If n = 50% then the cycle is a. Reversible b. Irreversible c. Impossible d. none of the above.

A system executes a power cycle while receiving 1000 Btu by heat transfer at a temperature of 900oR and discharging 600 Btu by heat transfer at a temperature of 540oR. There are no other heat transfers.Determine the cycle thermal efficiency.  Use the Clausius Inequality to determine σcycle, in Btu/oR. Determine if this cycle is internally reversible, irreversible, or impossible.

Two reversible power cycles are arranged in series. The first cycle receives energy by heat transfer from a reservoir at temperature TH and rejects energy to a reservoir at an intermediate temperature T. The second cycle receives the energy rejected by the first cycle from the reservoir at temperature T and rejects energy to a reservoir at temperature TC lower than T. Derive an expression for the intermediate temperature T in terms of TH and TC when,a. The net works of the two power cycles are equalb. The thermal efficiencies of the two power cycles are equal

Which of the following statements best describes the 2nd law of thermodynamics? The total entropy of a a reservoir must stay the same or increase. The change in internal energy for an ideal gas is given as A U=mc _▲T. V Heat energy will always be transferred from a hotter object to a colder object. Around a complete cycle, the net heat and net work additions must sum to zero. O A reversible cyclic engine can convert all the heat input it receives into useful work output.

A system executes a power cycle while receiving 900 Btu by heat transfer at a temperature of 900°R and discharging 800 Btu by heat transfer at a temperature of 540°R. There are no other heat transfers. Determine the cycle thermal efficiency. Use the Clausius Inequality to determine Ocycle, in Btu/°R. Determine if this cycle is internally reversible, irreversible, or impossible. Step 1 Determine the cycle thermal efficiency. n = i %

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

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

An open feedwater heater is a direct-contact heat exchanger used in vapor power plants. Shown in the figure below are feedwater heater with H20 operating data for an open 31 °C as the working fluid operating at steady state, where T1 P2=3 bar = 0.92 +2 P3 3 bar Saturated liquid m380 kg/s T, PT=3 bar Open feedwater 3 heater Ignoring stray heat transfer from the outside of the heat exchanger to its surroundings and kinetic and potential energy effects, determine the rate of entropy production, in kW/K.

A reversible heat pump cycle operates at steady state between hot and cold reservoirs at TH = 30°C and Tc 10°C, respectively. The rate of heat transfer at the high temperature is 10 kW. a. Determine the net power input, in kW. b. Determine the heat transfer rate from the cold reservoir at Tc, in kW. c. Determine the coefficient of performance of the cycle.