Chapter 5, Problem 5.45P

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)

As shown in the figure, an air conditioner operating at steady state maintains a dwelling at 70°F on a day when the outside temperature is 103.5°F. The rate of heat transfer into the dwelling through the walls and roof is 30,000 Btu/h and the net power input to the air conditioner compressor is 3.45 hp. Step 1 B Inside, 70° F Determine the coefficient of performance for the air conditioner. = Evaporator i 30,000 Btu/h Determine the coefficient of performance of the air conditioner. Determine the power input required, in hp, and the coefficient of performance for a reversible air conditioner providing the same cooling effect while operating between the same cold and hot temperatures. Refrigerant loop Compressor Outside Q + Condenser

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)

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.

During transient state operation, a gearbox receives 60 kW through the input shaft and delivers power through the output shaft. For the gearbox as the system, the rate of energy transfer by convection isQ T = −hA (Tb – Tf)where h = 0.171 kW/m 2 ⋅⋅ K is the heat transfer coefficient, A = 1.0 m 2 is the outer surface area of the gearbox, Tb = 300 K (27°C) is the temperature at the outer surface, and Tf = 293 K (20°C) is the temperature of the surrounding air away from the immediate vicinity of the gearbox. The rateof specific internal energy is 5kJ/Kg. For the gearbox, evaluate the heat transfer rate and the power delivered through the output shaft, each in kW.

The refrigerator shown in the figure below operates at steady state with a coefficient of performance (COP) of 5.0 within a kitchen at 23 °C. The refrigerator rejects 4.8 kW by heat transfer to its surroundings from metal coils located on its exterior. Determine: (a) the power input, in kW.(b) the lowest theoretical temperature inside the refrigerator, in K.

An air conditioner is a device used to cool the inside of a home. It is, in essence, a refrigerator in which mechanical work is done and heat removed from the (cooler) inside and rejected to the (warmer) outside. A home air conditioner operating on a reversible Carnot cycle between the inside, absolute temperature T2, and the outside, absolute tempera- ture T1 > T2, consumes P joules/sec from the power lines when operating continuously. (a) In one second, the air conditioner absorbs Q2 joules from the house and rejects Q1 joules outdoors. Develop a formula for the efficiency ratio Q2/P in terms of T1 and T2. (b) Heat leakage into the house follows Newton's law Q = A(T, – T2). Develop a formula for T, in terms of T1, P, and A for continuous operation of the air conditioner under constant outside temperature T and uniform (in space) inside temperature T2. (c) The air conditioner is controlled by the usual on-off thermostat and it is observed that when the thermostat set at 20°C and an…

In your own words, define efficiency as it applies to a device designed to perform an energy transformation.

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