THERMODYNAMICS LLF W/ CONNECT ACCESS
9th Edition
ISBN: 9781264446889
Author: CENGEL
Publisher: MCG
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Chapter 11.10, Problem 7P
In a refrigeration system, would you recommend condensing the refrigerant-134a at a pressure of 0.7 or 1.0 MPa if heat is to be rejected to a cooling medium at 15°C? Why?
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Answer d,e,f,and g
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:
enthalpy
Point
kJ/kg
h
kJ/kg
kJ/kg
h2
kJ/kg
h3
kJ/kg
h4
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.
Chapter 11 Solutions
THERMODYNAMICS LLF W/ CONNECT ACCESS
Ch. 11.10 - Why do we study the reversed Carnot cycle even...Ch. 11.10 - Why is the reversed Carnot cycle executed within...Ch. 11.10 - A steady-flow Carnot refrigeration cycle uses...Ch. 11.10 - Refrigerant-134a enters the condenser of a...Ch. 11.10 - Does the ideal vapor-compression refrigeration...Ch. 11.10 - Why is the throttling valve not replaced by an...Ch. 11.10 - In a refrigeration system, would you recommend...Ch. 11.10 - Does the area enclosed by the cycle on a T-s...Ch. 11.10 - Consider two vapor-compression refrigeration...Ch. 11.10 - It is proposed to use water instead of...
Ch. 11.10 - The COP of vapor-compression refrigeration cycles...Ch. 11.10 - A 10-kW cooling load is to be served by operating...Ch. 11.10 - An ice-making machine operates on the ideal...Ch. 11.10 - An air conditioner using refrigerant-134a as the...Ch. 11.10 - An ideal vapor-compression refrigeration cycle...Ch. 11.10 - A refrigerator operates on the ideal...Ch. 11.10 - A refrigerator uses refrigerant-134a as the...Ch. 11.10 - An ideal vapor-compression refrigeration cycle...Ch. 11.10 - A refrigerator uses refrigerant-134a as its...Ch. 11.10 - A refrigerator uses refrigerant-134a as the...Ch. 11.10 - A commercial refrigerator with refrigerant-134a as...Ch. 11.10 - The manufacturer of an air conditioner claims a...Ch. 11.10 - Prob. 24PCh. 11.10 - How is the second-law efficiency of a refrigerator...Ch. 11.10 - Prob. 26PCh. 11.10 - Prob. 27PCh. 11.10 - Prob. 28PCh. 11.10 - Bananas are to be cooled from 28C to 12C at a rate...Ch. 11.10 - A vapor-compression refrigeration system absorbs...Ch. 11.10 - A room is kept at 5C by a vapor-compression...Ch. 11.10 - Prob. 32PCh. 11.10 - A refrigerator operating on the vapor-compression...Ch. 11.10 - When selecting a refrigerant for a certain...Ch. 11.10 - A refrigerant-134a refrigerator is to maintain the...Ch. 11.10 - Consider a refrigeration system using...Ch. 11.10 - A refrigerator that operates on the ideal...Ch. 11.10 - A heat pump that operates on the ideal...Ch. 11.10 - Do you think a heat pump system will be more...Ch. 11.10 - What is a water-source heat pump? How does the COP...Ch. 11.10 - A heat pump operates on the ideal...Ch. 11.10 - Refrigerant-134a enters the condenser of a...Ch. 11.10 - A heat pump that operates on the ideal...Ch. 11.10 - The liquid leaving the condenser of a 100,000...Ch. 11.10 - Reconsider Prob. 1144E. What is the effect on the...Ch. 11.10 - A heat pump using refrigerant-134a heats a house...Ch. 11.10 - A heat pump using refrigerant-134a as a...Ch. 11.10 - Reconsider Prob. 1148. What is the effect on the...Ch. 11.10 - Prob. 50PCh. 11.10 - How does the COP of a cascade refrigeration system...Ch. 11.10 - Consider a two-stage cascade refrigeration cycle...Ch. 11.10 - Can a vapor-compression refrigeration system with...Ch. 11.10 - Prob. 54PCh. 11.10 - A certain application requires maintaining the...Ch. 11.10 - Prob. 56PCh. 11.10 - Repeat Prob. 1156 for a flash chamber pressure of...Ch. 11.10 - Prob. 59PCh. 11.10 - A two-stage compression refrigeration system with...Ch. 11.10 - A two-stage compression refrigeration system with...Ch. 11.10 - A two-evaporator compression refrigeration system...Ch. 11.10 - A two-evaporator compression refrigeration system...Ch. 11.10 - Repeat Prob. 1163E if the 30 psia evaporator is to...Ch. 11.10 - Consider a two-stage cascade refrigeration cycle...Ch. 11.10 - How does the ideal gas refrigeration cycle differ...Ch. 11.10 - Prob. 67PCh. 11.10 - Devise a refrigeration cycle that works on the...Ch. 11.10 - How is the ideal gas refrigeration cycle modified...Ch. 11.10 - Prob. 70PCh. 11.10 - How do we achieve very low temperatures with gas...Ch. 11.10 - An ideal gas refrigeration system operates with...Ch. 11.10 - Air enters the compressor of an ideal gas...Ch. 11.10 - Repeat Prob. 1173 for a compressor isentropic...Ch. 11.10 - An ideal gas refrigeration cycle uses air as the...Ch. 11.10 - Rework Prob. 1176E when the compressor isentropic...Ch. 11.10 - A gas refrigeration cycle with a pressure ratio of...Ch. 11.10 - A gas refrigeration system using air as the...Ch. 11.10 - An ideal gas refrigeration system with two stages...Ch. 11.10 - Prob. 81PCh. 11.10 - Prob. 82PCh. 11.10 - What are the advantages and disadvantages of...Ch. 11.10 - Prob. 84PCh. 11.10 - Prob. 85PCh. 11.10 - Prob. 86PCh. 11.10 - Prob. 87PCh. 11.10 - Heat is supplied to an absorption refrigeration...Ch. 11.10 - An absorption refrigeration system that receives...Ch. 11.10 - An absorption refrigeration system receives heat...Ch. 11.10 - Heat is supplied to an absorption refrigeration...Ch. 11.10 - Prob. 92PCh. 11.10 - Prob. 93PCh. 11.10 - Consider a circular copper wire formed by...Ch. 11.10 - An iron wire and a constantan wire are formed into...Ch. 11.10 - Prob. 96PCh. 11.10 - Prob. 97PCh. 11.10 - Prob. 98PCh. 11.10 - Prob. 99PCh. 11.10 - Prob. 100PCh. 11.10 - Prob. 101PCh. 11.10 - Prob. 102PCh. 11.10 - A thermoelectric cooler has a COP of 0.18, and the...Ch. 11.10 - Prob. 104PCh. 11.10 - Prob. 105PCh. 11.10 - Prob. 106PCh. 11.10 - Rooms with floor areas of up to 15 m2 are cooled...Ch. 11.10 - Consider a steady-flow Carnot refrigeration cycle...Ch. 11.10 - Consider an ice-producing plant that operates on...Ch. 11.10 - A heat pump that operates on the ideal...Ch. 11.10 - A heat pump operates on the ideal...Ch. 11.10 - A large refrigeration plant is to be maintained at...Ch. 11.10 - Repeat Prob. 11112 assuming the compressor has an...Ch. 11.10 - An air conditioner with refrigerant-134a as the...Ch. 11.10 - A refrigerator using refrigerant-134a as the...Ch. 11.10 - Prob. 117RPCh. 11.10 - An air conditioner operates on the...Ch. 11.10 - Consider a two-stage compression refrigeration...Ch. 11.10 - A two-evaporator compression refrigeration system...Ch. 11.10 - The refrigeration system of Fig. P11122 is another...Ch. 11.10 - Repeat Prob. 11122 if the heat exchanger provides...Ch. 11.10 - An aircraft on the ground is to be cooled by a gas...Ch. 11.10 - Consider a regenerative gas refrigeration cycle...Ch. 11.10 - An ideal gas refrigeration system with three...Ch. 11.10 - Prob. 130RPCh. 11.10 - Derive a relation for the COP of the two-stage...Ch. 11.10 - Prob. 133FEPCh. 11.10 - Prob. 134FEPCh. 11.10 - Prob. 135FEPCh. 11.10 - Prob. 136FEPCh. 11.10 - Prob. 137FEPCh. 11.10 - An ideal vapor-compression refrigeration cycle...Ch. 11.10 - Prob. 139FEPCh. 11.10 - An ideal gas refrigeration cycle using air as the...Ch. 11.10 - Prob. 141FEPCh. 11.10 - Prob. 142FEP
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- Condensers in these refrigerators are all_______cooled.arrow_forwardA 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.arrow_forwardAdditional Instructions: Define each enthalpy obtained from tables and chart and draw the p-h diagram labeling the respective evaporating and condensing pressures and temperatures in each problem. (2) A standard vapor compression system produces 20 tons of refrigeration using R-12 as a refrigerant while operating between a condenser temperature of 41.6 C and an evaporator temperature of -25°C. Determine (a) the refrigerating effect in kJ/kg, (b) the circulating rate in kg/s, (c) the power supplied, (d) the COP, (e) the heat rejected in kW, and (f the volume flow rate in L/s. Ans. (a) 100.26 kJ/kg, (b) 0.7022 kg/s, (c) 25.69 kW, (d) 2.74, (e) 96.09 kW, (f) 92.18 L/sarrow_forward
- Avapour 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 orme 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.arrow_forwardRefrigerant-134a enters the compressor of a cooling system as superheated vapor at 0.18 MPa and 0°C with a flow rate of 0.15 kg/s. It exits the compressor at 0.8 MPa and 60°C. Post compression, the refrigerant is cooled in the condenser to 28°C and 0.7 MPa. Subsequently, it's throttled to 0.16 MPa. Neglecting any heat transfer and pressure drops in the pipelines between the components, represent the cycle on a T-s diagram concerning saturation lines. Calculate: (a) The rate of heat extraction from the cooling area and the energy input to the compressor. (b) The isentropic efficiency of the compressor. (c) The Coefficient of Performance (COP) of the cooling system.arrow_forwardIn a cooling machine that uses R-134a as a refrigerant and operates according to the ideal vapor compression refrigeration cycle, the cooled environment is kept at -30 °C and the condensation temperature entering the condenser at 18 °C with a flow rate of 0.25 kg/s and leaving the water at 26 °C. are given. The refrigerant enters the condenser at a pressure of 1.2 MPa and 65 °C and exits at 42 °C. The inlet condition of the compressor is 60 kPa and -34 ° C, and it gains 450 W of heat from the environment during the compression process. Accordingly, calculate (a) dryness fraction of the refrigerant in the evaporator inlet (b) the cooling capacity (c) the COP value of the cooling system.arrow_forward
- A vapor-compression refrigeration machine uses refrigerant-134a as much as 2 kg/min with operating conditions leaving the evaporator at a temperature of -14°C and a condenser pressure of 0.8 Mpa. Determine the COP value and cooling load of the machine.arrow_forwardQuestion 3 In a vapour-compression refrigeration system, refrigerant - 134a enters the compressor superheated at 200 kPa and - 5 °C. The refrigerant enters the condenser at 1.4 MPa and 75 °C, and exits at 1.4 MPa as a saturated liquid. There is no significant heat transfer between the compressor and its surroundings, and the refrigerant passes through the evaporator with a negligible change in pressure. If the refrigerating capacity is 105 kW, represent the cycle on a T-s diagram and determine: a) the mass flow rate of the refrigerant in kg/s, b) the power input to the compressor in kW, c) the coefficient of performance, and (2) d) the isentropic compressor efficiencyarrow_forwardA vapor-compression refrigeration system circulates refrigerant 134a at a rate of 0.15 kg/s. The refrigerant enters the compressor at -10 degrees Celcius and 100 kPa, and exits the compressor at 800 kPa. The isentropic efficiency of the compressor is 76%. Pressure drop through the condenser and evaporator are negligible. The refrigerant exits the condenser at 30 degrees Celcius and 800 kPa. Ignoring the heat transfer between the compressor and its surroundings, determine: The rate at which heat energy is removed from the refrigerated space in kW. The coefficient of perfromance.arrow_forward
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