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    in a vapour compression refrigeration cycle for making ice, the condensing temperature for higher cop

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    [Solved] In case of a vapor compression refrigerator, if the condense

    Vapour Compression Refrigeration Cycle:   A vapour compressor refrigerator consists of the following process  1-2: Isentropic compression 2-3: H

    Home Refrigeration and Air Conditioning Refrigeration Cycles and Devices Vapour Compression (V-C) Cycle

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    In case of a vapor compression refrigerator, if the condenser temperature of the refrigerant is closer to the critical temperature, then there will be

    1. Excessive power consumption

    2. High compression

    3. Large volume flow

    Which of the above statements are correct?

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    1 and 2 only 1 and 3 only 2 and 3 only 1, 2 and 3

    Answer (Detailed Solution Below)

    Option 1 : 1 and 2 only

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    Vapour Compression Refrigeration Cycle:

    A vapour compressor refrigerator consists of the following process

    1-2: Isentropic compression

    2-3: Heat rejection in the condenser

    3-4: Isentropic expansion

    4-1: Evaporation (Heat absorption)

    Now when the condenser pressure is increased to the critical temperature the cycle will become as shown in the figure

    From the figure, it is clear that if the condenser temperature reaches the critical point, the compression work will increase as 1-2” > 1-2’ > 1-2 and will lead to excessive power consumption.

    Now the higher temperature in the condenser will require higher pressure because of the phase change in the condenser from the figure 2”-3”-4” is at higher temperature and pressure than 2’-3’-4’ than 2-3-4.

    The volume flow rate of the refrigerant will decrease because the volumetric efficiency of the compressor will reduce, the volumetric efficiency of the compressor is given

    ηv=1+C−C(PhPl)1n

    Where Ph is the higher pressure and PL is the lower pressure, if the higher pressure will increase the volumetric efficiency will decrease which means that volume of refrigerant flow will be low or at higher temperatures (Higher pressures) the specific volume of the refrigerant will be low.

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    More Vapour Compression (V-C) Cycle Questions

    Q1. In a vapour compression refrigeration cycle, the refrigerant enters the compressor in saturated vapour state at evaporator pressure, with specific enthalpy equal to 250 kJ/kg. The exit of the compressor is superheated at condenser pressure with specific enthalpy equal to 300 kJ/kg. At the condenser exit, the refrigerant is throttled to the evaporator pressure. The coefficient of performance (COP) of the cycle is 3. If the specific enthalpy of the saturated liquid at evaporator pressure is 50 kJ/kg, then the dryness fraction of the refrigerant at entry to evaporator is ________.Q2. Household refrigerators operate onQ3. One ton of refrigeration is equal toQ4. Wet compression in vapour compression cycle meansQ5. The component of vapour compression refrigeration system which raises the temperature and pressure of vapour is known as:Q6. If heat rejected by the refrigerant in condenser is 175 kJ/kg and heat absorbed by the refrigerant in evaporator of vapour compression is 125 kJ/kg, COP (Coefficient of Perfomance) of the refrigeration system is:Q7. In a Vapour Compression Refrigeration System, refrigerant exists in the liquid state between the _________.Q8. In an ideal vapor-compression refrigeration cycle, ______ is the process during which heat is rejected to the environment.

    स्रोत : testbook.com

    [SOLVED] In a vapour compression refrigeration cycle for making ice, the c

    In a vapour compression refrigeration cycle for making ice, the condensing temperature for higher COP

    In a vapour compression refrigeration cycle for making ice, the c

    In a vapour compression refrigeration cycle for making ice, the c

    | In a vapour compression refrigeration cycle for making ice, the condensing temperature for higher COP

    A. Should be near the critical temperature of the refrigerant

    B. Should be above the critical temperature of the refrigerant

    C. Should be much below the critical temperature of the refrigerant

    D. Could be of any value as it does not affect the COP

    Please scroll down to see the correct answer and solution guide.

    Right Answer is: C

    SOLUTION

    When condenser temperature is near or above the critical temperature, then work done by the compressor increases and COP decreases. When condenser temperature is below the critical temperature then compressor work will be less. i.e. COP is higher.

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    Compression Refrigeration Cycle

    Compression Refrigeration Cycle

    the compression refrigeration cycle in which the refrigeration side is driven by a solar powered engine;

    From: Sun Power (Second Edition), 1983

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    Management of Heating and Cooling

    Craig B. Smith, Kelly E. Parmenter, in Energy Management Principles (Second Edition), 2016

    Space Cooling Systems

    In most commercial and industrial applications, cooling systems and associated auxiliary equipment account for the majority of the HVAC energy use. Cooling systems range from small individual air conditioning units, to unitary systems, to large central plants. Individual air conditioning units are self-contained systems that are mounted in windows or on an external wall and provide cooling to a space without the use of ducts. Unitary air conditioning (or heat pump) systems include packaged rooftop units and split systems, often with multiple units cooling separate zones of the building. Central systems generate cooling in a central chiller and then distribute the cooling with chilled water systems to air-handling or fan-coil units.

    Vapor Compression Refrigeration Cycle. The majority of cooling systems are based on the vapor compression refrigeration cycle. Figure 8.3 shows how the vapor compression cycle compresses, condenses, expands, and boils refrigerant to provide cooling. The bullet points below describe each step in the cycle. Note that in the ensuing discussion we assume the reader has a basic familiarity with thermodynamics and fluid mechanics.

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    Figure 8.3. Vapor compression refrigeration cycle.

    States 1 and 2 on the figure represent the compression portion of the cycle, which requires input of electrical energy. In the compressor, refrigerant vapor leaving the evaporator is compressed from its low evaporating pressure to the required condensing pressure. The temperature of the vapor also increases. The energy used during this stroke is determined by subtracting the enthalpy of the State 2 from that of the State 1.

    Condensing and cooling of high-pressure refrigerant occurs between States 2 and 3 at a constant pressure. Heat absorbed in the evaporator and then added by the compressor is removed from the vapor by either an air-cooled or water-cooled condenser. Large central chiller systems are generally water-cooled and use cooling towers to reject the heat. The refrigerant leaving the condenser is now a liquid. The amount of heat rejected in this step is determined by subtracting the enthalpy of the State 2 from that of State 3.

    Between States 3 and 4 there is a constant enthalpy expansion through the expansion valve that reduces the liquid refrigerant pressure before it enters the evaporator.

    In the cooling part of the cycle between States 4 and 1, the liquid refrigerant evaporates (boils) and absorbs heat in the evaporator. Within the two-phase region, this is a constant temperature/constant pressure process, but when all the refrigerant has evaporated, it begins to increase in temperature as it continues to absorb heat. This is called super heating the refrigerant and is required to assure that no liquid refrigerant gets back to the compressor, where it could cause damage. The amount of heat absorbed by the evaporating refrigerant is determined by subtracting the enthalpy of State 1 from that of the State 4.

    In central chiller plants (chilled water systems), water is pumped through the evaporator where it cools and then is piped to cooling coils in the air distribution system. This is the approach sketched in Figure 8.2. In smaller or packaged systems the cooling tower shown in Figure 8.3 is not required.

    An alternative approach, suitable when the cooling coils can be located close to the compressors, is the direct expansion (DX) unitary system. The cooling technology behind DX systems is similar to chillers except that the refrigerant expands in the evaporator coils and cools air directly as it moves across the coils, rather than using chilled water as a heat transfer medium. The most common DX air conditioning (or heat pump) systems for commercial and industrial applications are forced air packaged units (especially rooftop units) or split systems. These forced air systems use air handlers and duct systems to distribute conditioned air to zones. In split systems, the components of the refrigeration cycle are split into an outdoor unit and an indoor unit. The outdoor unit consists of the compressor, condenser coil, and cooling fan. The indoor unit consists of the evaporator and supply fan (blower). In packaged systems, all the equipment is contained within one package that is located outdoors. DX units eliminate the need for chilled water pumps and also eliminate the efficiency losses associated with transfer of heat to and from chilled water since the air is cooled directly with the evaporator. A typical DX system is designed to serve one air handling unit, so large buildings will have multiply DX systems to condition the entire space. In contrast, one chiller can serve multiple air handling units.

    स्रोत : www.sciencedirect.com

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