Chapter 5, Problem 5.63P

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

Chapter 5 no. 4

At steady state, a refrigeration cycle operates between hot and cold reservoirs at 300K and 275K respectively. The refrigerator removes 600 kW of heat from the cold reservoir. If the cycle's coefficient of performance is 4, determine the power input required in kW. Compare this with the minimum theoretical power required in kW.

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A heat pump is used to maintain the interior of a building at 21 °C. At steady state, the heat pump receives energy by heat transfer from well water at 9°C and discharges energy by heat transfer to the building at a rate of 120000 kJ/h. Over a period of 14 days, an electric meter records that 1490 kW-h of electricity is provided to the heat pump.      1. Draw a schematic diagram(s)

Three sub steps of a thermodynamic cycle are employed in order to change the state of a gas from 1 bar, 1.5 cubic meter and internal energy of 512 kJ. The processes are: 1st step: Compression at constant PV to a pressure of 2 bar and internal energy of 690 kJ. 2nd step: A process where work transferred is zero and heat transferred is - 150 kJ. 3rd step: A process where work transferred is -50 kJ. without KE and PE changes, determine: a. heat transferred during 1st step (kJ) b. heat transferred during 3rd step (kJ)

An automobile industry using piston cylinder arrangement for their operation it under goes a thermodynamic cycle which includes three processes with an initial state where pressure is 1.5 bar, volume is 2 m3 and internal energy equals to 480 kJ. The processes are as follows: 1)first stage to second stage: Compression with pV equals to constant to p2 is equals to 2 bar, U2 equals to 720 kJ 2)Second stage to third stage: work is equals to zero, and Q2-3 = - 150 kJ 3)Stage third to one: work is equals to 75 kJ. Neglecting kinetic energy and potential energy changes, find the heat transfer Q1-2 and Q3-1.

One kg of fluid expands reversibly according to a linear law from 4.2 bar to 1.4 bar. The initial and final volume are 0.004 and 0.02 m² respectively. The fluid then cooled reversibly at constant pressure, and finally compressed reversibly according to a law PV=C back to initial condition of 4.2 bar and 0.004 m². Calculate the work done for each process, the net work done and sketch the cycle on the P-V diagram. (4480, -1120, -1845 &1515 N-m)

Five kg of steam is contained within a piston- cylinder assembly. It undergoes an expansion from state 1, where the specific internal energy is u_1=2709.9 kJ/kg to state 2, where u_2=2659.6 kJ/kg. During the process, heat is transferred to the steam with a magnitude of 80 kJ. Also, a paddle Ww=-18.5 kJ wheel transfers energy to the steam by work in the amount of 18.5 kJ. There is no significant change in the kinetic or potential energy of the steam. Determine the energy transfer by work from the steam to the piston during the process, in kJ. Indicate whether the work is done on or done by the system. Q=+80 kJ 5 kg of steam W u₁ = 2709.9 kJ/kg U₂ = 2659.6 kJ/kg piston =?