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e of refrigerant are 48°C and -20°C respectively. Saturated liquid leaves the condenser and saturated vapour leaves the e

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

Chapter28: Special Refrigeration Applications

Section: Chapter Questions

Problem 15RQ: Why is two-stage compression popular for extra-low-temperature refrigeration systems?

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Condensers in these refrigerators are all_______cooled.
A vapour compression refrigeration system using refrigerant F-12 is employed to produce 8640 kg of ice per day. The condensing and evaporating temperature of refrigerant are 48°C and -20°C respectively. Saturated liquid leaves the condenser and saturated vapour leaves the evaporator. Compression is isentropic, water at 35°C is used to form the ice. The temperature of ice should be-8°C. Heat flow into the brine tank from surroundings may be taken as 10% of total heat absorbed from water to form ice. Determine the power required to drive the compressor. Take specific heat of ice = 2.26 kJ/kg-K. Latent heat of ice = 335 kJ/kg. Specific heat of water = 4.2 kJ/kg-K.
An ammonia system with a 158-kW evaporator operating at -1°C and a 35-kW evaporator operatingat -40°C uses flash gas removal and intercooling. The condensing temperature is 32°C. Thearrangement is as shown. How many kilograms per minute of ammonia are compressed by the high-pressure compressor?
The evaporator and condenser temperatures are -20°C and 35°C, respectively, in an ammonia simple saturation cycle. The method will be used to produce 12,500kg of ice at -15°C in 32 hours from water at 25°C. Assuming that 25 percent of the heat absorbed from the water is lost. Ice has a specific heat of 2.094Kj/kg-K, while fusion has a heat of 335kj/kg. Determine the: a) Total Heat b) Mass flow rate
A vapour-compression refrigeration system operates with Refrigerant 134 with two evaporators with varying cooling capacity. The low temperature evaporator (#1) operates at -20°C with saturated vapour at its exit and has a refrigeration capacity of 3 tons. The higher temperature evaporator (#2) produces saturated vapour at 3.6 bar at its exit and has a refrigerating capacity of 2 tons. Compression is isentropic to the condenser pressure of 12 bar. There are no pressure drops in the flow through the condenser and the two evaporators and the refrigerant leaves the condenser as saturated liquid at 12 bar. Determine: The mass flow rate of the refrigerant in kg/s through each evaporators;The power input for the compressor, in kW;The coefficient of performance of this refrigeration system;The heat transfer through the condenser in kW;The rates of exergy destruction in each expansion valves in kW for T0 = 300K;Draw the T-s diagram of this system.
An ammonia refrigerating system has a load of 250 kW and operates at a condensing pressure of 1400 kPa and an evaporating temperature of -20°C. The refrigerant exits at the evaporator with a 5- degree superheat. The vapor enters the compressor suction at 10-degree superheat. The compressed vapor is discharged from the compressor at the condensing pressure and 150°C. The refrigerant exits the condenser as saturated liquid. a. State the enthalpies at each point: Point enthalpy kJ/kg h kJ/kg kJ/kg h2 kJ/kg h3 kJ/kg h4 Answer: kg/sec b. Calculate the mass flow of refrigerant Answer: kW C. Determine the size of the motor drive if the mechanical efficiency of the motor- compressor is 77%. Answer: kW Calculate the total heat rejected in the condenser. d. Determine the refrigerating efficiency of the system. Answer: е.
A plant using R134a refrigerant has a cooling capacity of 352 kW of refrigeration. It evaporates at 0 Cand condenses at 35 C, with the 5 of superheat at the evaporator outlet and 5 K of sub-cooling at the condenser outlet. Assuming isentropic compression and ignoring pressure drops in the piping, the evaporator and condenser, determi the following; a) The refrigeration effect b) The mass flow rate of refrigerant ) The compressor power d) The rate of heatrejection at the condenser e) The COP 0 The corresponding Carnot COP g) The percentage Carnot-efficiency
3. A vapour compression refrigeration system of 2400 kJ/min capacity works at an evaporator temperature of 263 K and a condenser temperature of 303 K. The refrigerant used is R-12 and is subcooled by 6°C before entering the expansion valve and vapour is superheated by 7°C before leaving the evaporator coil. The compression of refrigerant is reversible adiabatic. The refrigeration compressor is two-cylinder, single acting with stroke equal to 1.25 times the bore and runs at 1000 r.p.m. Determine: 1. Refrigerating effect per kg ; 2. Mass of refrigerant circulated per minute ; 3. Theoretical piston displacement per minute; 4. Power required to run the com pressor; 5. Heat removed in through condenser; and 6. Bore and stroke of the compressor.
A food storage locker requires a refrigeration system of 2,400 kJ/min capacity at an evaporator temperature of -10OC and a condenser temperature of 30OC. The refrigerant used is freon-12 and sub-cooled by 6OC before entering the expansion valve and vapor is superheated by 7OC before leaving the evaporator coil. The compression of refrigerant is isentropic. The refrigeration compressor is two-cylinder, single-acting with stroke equal to 1.25 times the bore diameter and operates at 1000 rpm. Determine: (a) refrigerating effect, (b) mass of refrigerant to be circulated, (c) theoretical piston displacement per minute, (d) theoretical power to run the compressor in kW, (e) heat removed from the condenser per min. (f) theoretical bore and stroke of compressor.
A refrigeration system using R-22 has a capacity of 320 kW of refrigeration. The evaporating temperature is -10C and the condensing temperature is 40C.Calculate the fraction of vapor in the mixture before the evaporator.
Aa 3. A vapour compression refrigeration system of 2400 kJ/min capacity works at an evaporator temperature of 263 K and a condenser temperature of 303 K. The refrigerant used is R-12 and is subcooled by 6°C before entering the expansion valve and vapour is superheated by 7°C before leaving the evaporator coil. The compression of refrigerant is reversible adiabatic. The refrigeration compressor is two-cylinder, single acting with stroke equal to 1.25 times the bore and runs at 1000 r.p.m. Determine: 1. Refrigerating effect per kg ; 2. Mass of refrigerant circulated per minute; 3. Theoretical piston displacement per minute ; 4. Power required to run the com pressor; 5. Heat removed in through condenser ; and 6. Bore and stroke of the compressor. I want the solution on a piece of paper and using the diagram الأصدقاء المقربون
A vapor compression refrigeration cycle uses refrigerant-134a as its working fluid. The condenser pressure is 800 kPa and the evaporator temperature is -20 C. The compressor has an isentropic efficiency of 80 percent. The mass flow rate is 1.7489 kg/s. In the question that follows, select the answer that is closest to the true value. What is the heat going to the evaporator in units of kW?