A two-stage cascade refrigeration system is to provide cooling at -38°C while- operating the high temperature condenser at 1.6 MPa. Each stage operates on the deal vapor-compression cycle. The upper system uses water as its working fluid and operates its evaporator at 5°C. The lower system uses R-134a as its working fluid and perates its condenser at 400 kPa. This system produces a cooling effect of 20kJ/s. Sketch a T-s diagram and evaluate; i) the mass flow rate of R-134a; ii) the mass flow rate of water; and

A two-stage cascade refrigeration system is to provide cooling at -38°C while- operating the high temperature condenser at 1.6 MPa. Each stage operates on the deal vapor-compression cycle. The upper system uses water as its working fluid and operates its evaporator at 5°C. The lower system uses R-134a as its working fluid and perates its condenser at 400 kPa. This system produces a cooling effect of 20kJ/s. Sketch a T-s diagram and evaluate; i) the mass flow rate of R-134a; ii) the mass flow rate of water; and

Refrigeration and Air Conditioning Technology (MindTap Course List)

8th Edition

ISBN:9781305578296

Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Chapter22: Condensers

Section: Chapter Questions

Problem 7RQ: When a standard-efficiency air-cooled condenser is used, the condensing refrigerant will normally be...

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In a conventional refrigeration cycle which uses Freon-12 as the refrigerant, the temperature of the evaporating fluid is -20°C. It leaves the evaporator as saturated vapor at -20°C and enters the compressor. The pressure in the condenser is 1.30 MPa. The liquid leaves the condenser and enters the expansion valve at 40°C. It is proposed to modify this cycle by adding a heat exchanger that would superheat the suction vapor to 25°C. Compare the coefficient of performance of these two cycles. What is the temperature of the refrigerant entering the expansion valve with the heat exchanger? For a load of 50 kW, determine the volume flow rate for both cycles.
In a conventional refrigeration cycle which uses Freon- 12 as the refrigerant, the temperature of the evaporating fluid is -20°C. It leaves the evaporator as saturated vapor at -20°C and enters the compressor. The pressure in the condenser is 1.30 MPa. The liquid leaves the condenser and enters the expansion valve at 40°C. It is proposed to modify this cycle by adding a heat exchanger that would superheat the suction vapor to 25°C. Compare the coefficient of performance of these two cycles. What is the temperature of the refrigerant entering the expansion valve with the heat exchanger? For a load of 50kW, determine the volume flow rate for both cycles. Ans. 2.79, 2.80, 12°C, 0.0522m³/s, 0.0523 m³/s
Consider a two-stage compression refrigeration system operating between the pressure limits of 0.8 and 0.14 MPa. The working fluid is refrigerant-134a. The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.4 MPa. Part of the refrigerant evaporates during this flashing process, and this vapor is mixed with the refrigerant leaving the low-pressure compressor. The mixture is then compressed to the condenser pressure by the high-pressure compressor. The liquid in the flash chamber is throttled to the evaporator pressure, and it cools the refrigerated space as it vaporizes in the evaporator. Assuming the refrigerant leaves the evaporator as saturated vapor and both compressors are isentropic, determine (a)the fraction of the refrigerant that evaporates as it is throttled to the flash chamber, (b)the amount of heat removed from the refrigerated space and the compressor work per unit mass of refrigerant flowing through the condenser,…
Consider a two-stage compression refrigeration system operating between the pressure limits of 1.2 MPa and 0.16 MPa. The working fluid is refrigerant-134a. The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.7 MPa. Part of the refrigerant evaporates and the remainder is mixed with the refrigerant leaving the low-pressure compressor. The mixture is then compressed to the condenser pressure by the high-pressure compressor. The liquid in the flash chamber is throttled to the evaporator pressure, and it cools the refrigerated space as It vaporizes in the evaporator. Assume that the refrigerant leaves the evaporator as saturated vapor and both compressors are isentropic. a) i) Determine the amount of heat removed from the refrigerated space ii) Determine the compressor work per unit mass of refrigerant flowing through the condenser b) Determine the coefficient of performance
Consider a two-stage compression refrigeration system operating between the pressure limits of 1.2 MPa and 0.16 MPa. The working fluid is refrigerant-134a. The refrigerant leaves the condenser as a saturated liquid and is throttled to a flash chamber operating at 0.7 MPa. Part of the refrigerant evaporates and the remainder is mixed with the refrigerant leaving the low-pressure compressor. The mixture is then compressed to the condenser pressure by the high-pressure compressor. The liquid in the flash chamber is throttled to the evaporator pressure, and it cools the refrigerated space as It vaporizes in the evaporator. Assume that the refrigerant leaves the evaporator as saturated vapor and both compressors are isentropic. a) Draw the 'T-S' Diagram and state the assumptions b) Determine the fraction of the refrigerant that evaporates as it is throttled to the flash chamber (x_e).
: In a conventional refrigeration cycle which uses Freon-12 as the refrigerant, the temperatureof the evaporating fluid is -20°C. It leaves the evaporator as saturated vapor at -20°C and enters thecompressor. The pressure in the condenser is 1.30 MPa. The liquid leaves the condenser and enters theexpansion valve at 40°C. It is proposed to modify this cycle by adding a heat exchanger that would superheatthe suction vapor to 25°C Compare the coefficient of performance of these two cycles What is the temperature of the refrigerant entering the expansion valve with the heatexchanger? For a load of 50 kW, determine the volume flow rate for both cycles. inlcude PH diagram and TS diagram, show complete solution
Consider an ice-producing plant that operates on the ideal vapor-compression refrigeration cycle and uses refrigerant-134a as the working fluid. The refrigeration cycle operating conditions require an evaporator pressure of 180 kPa and the condenser pressure of 1400 kPa. Cooling water flows through the water jacket surrounding the condenser and is supplied at the rate of 250 kg/s. The cooling water has a 10°C temperature rise as it flows through the water jacket. To produce ice, potable water is supplied to the chiller section of the refrigeration cycle. For each kg of ice produced, 333 kJ of energy must be removed from the potable water supply. (Take the required values from saturated refrigerant-134a tables.) Determine the mass flow rate of the refrigerant, in kg/s. Take cp of water as 4.18 kJ/kg·K. (You must provide an answer before moving on to the next part.) The mass flow rate of the refrigerant is _________kg/s.