Chapter 5, Problem 5.41P

Exercise 5.50 The refrigerator shown in Fig operates at Refrigerator B = 4.5 steady state with a coefficient of performance of 4.5 and a power input of 0.8 kW. Energy is rejected from the refrigerator to the surroundings at 20°C by heat transfer from metal coils whose average surface temperature is 28°C. Surroundings, 20°C - Coils, 28°C Determine (a) the rate energy that is rejected, in kW. (b) the lowest theoretical temperature inside the refrigerator, in K. (c) the maximum theoretical power, in kW, that could be developed by a power cycle operating between the coils and the surroundings. Would you recommend making use of this opportunity for developing power? 0.8 kW 49 Chapler

Example 5.23. When a closed system executes a certain non-flow process, the work and heat interactions per degree rise in temperature at each temperature attained are given by SW = (4 0.08 T) kJ/kg and 8Q = 1.00 kJ/K dT dT Make calculations for the increase or decrease in the internal energy of the system if it is to operate between the temperature limits of 200 °C and 400 °C.

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Shown in Fig. P2.87 is cogeneration power plant operating in a thermodynamic cycle at steady state. The plant provides electricity to a community at a rate of 80 MW. The energy discharged from the power plant by heat transfer is denoted on the figure by Qout. Of this, 70 MW is provided FMKK-YZSS to the community for water heating and the remainder discarded to the environment without use. The electricity is valued at $0.08 per kW h. If the cycle thermal efficiency is 40%, determine the (a) rate energy is added by heat transfer, Q, in MW, (b) rate energy is discarded to the environment, in MW, and (c) value of the electricity generated, in $ per year. Welec =80 MW Power plant n=40

4. What is the second law of thermodynamics, give its Clausius and Kelvin-Planck statements and justify on their basis why a perpetual motion machines that extracts heat from ambient environment to do work is not feasible. What is difference between reversible and an internally reversible process, and why are most actual processes considered irreversible. Numerical:

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Refrigerators to preserve perishable foods have long been one of the essential appliances in a household. The refrigeration system of the household refrigerator is basically based on the vapor-compression refrigeration cycle, as shown in Figure Q2.1. Among the important components of the vapor-compressions refrigeration cycle are a throttling valve (A) and a compressor (B). In this refrigeration system, tetrafluoroethane (R-134a) is used as the refrigerant. Condenser W B A Evaporator Figure Q2.1: Basic components of a refrigeration system. (a) If the refrigerant enters A as a saturated liquid at 1100 kPa and leaves at 120 kPa, (i) Estimate the quality of the refrigerant at the exit of A. (ii) Calculate the temperature drop during the process. (iii)With appropriate assumptions, prove that the conservation of energy for A as follows the equation below, h= h2 (b) If the refrigerant enters B as a saturated vapor at 120 kPa with flow rate of 1.5 m³/min and leaves at 1100 kPa, (i) Calculate…

Chapter 5 no. 3

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