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    Sample Problems

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    Lul Lol
    The document contains 3 sample problems related to refrigeration. The first problem calculates the fraction of vapor in a refrigerant mixture before the evaporator using properties of R-22. The second problem calculates the temperature of a hot source for a Carnot engine producing 15 kW of power. The third problem calculates the coefficient of performance for an ideal vapor compression cycle given the enthalpy values at each state and the compressor power.

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    Sample Problems

    Uploaded by

    Lul Lol
    107 views2 pages
    The document contains 3 sample problems related to refrigeration. The first problem calculates the fraction of vapor in a refrigerant mixture before the evaporator using properties of R-22. The second problem calculates the temperature of a hot source for a Carnot engine producing 15 kW of power. The third problem calculates the coefficient of performance for an ideal vapor compression cycle given the enthalpy values at each state and the compressor power.

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    Formulas Ref

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    The document contains 3 sample problems related to refrigeration. The first problem calculates the fraction of vapor in a refrigerant mixture before the evaporator using properties of R-22. The second problem calculates the temperature of a hot source for a Carnot engine producing 15 kW of power. The third problem calculates the coefficient of performance for an ideal vapor compression cycle given the enthalpy values at each state and the compressor power.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    107 views2 pages

    Sample Problems

    Uploaded by

    Lul Lol
    The document contains 3 sample problems related to refrigeration. The first problem calculates the fraction of vapor in a refrigerant mixture before the evaporator using properties of R-22. The second problem calculates the temperature of a hot source for a Carnot engine producing 15 kW of power. The third problem calculates the coefficient of performance for an ideal vapor compression cycle given the enthalpy values at each state and the compressor power.

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    © All Rights Reserved
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    Download as docx, pdf, or txt
    of 2

    Sample Problems

    Chapter 5 – Refrigeration

    1. A refrigeration system using R-22 has a capacity of 320 kW of refrigeration. The evaporating
    temperature is -10°C and the condensing temperature is 40°C. Calculate the fraction of vapor in
    the mixture before the evaporator. Properties of R-22:
    At -10°C ; hg = 401.60 kJ/kg, hf = 188.43 kJ/kg
    At 40°C ; hf = 249.69 kJ/kg

    Solution:
    For throttling process:
    h3 = h 4
    h3 = (hf + xhfg)4
    249.69 = 188.43 + x (401.60 – 188.43)
    x = 0.287

    2. A carnot engine requires 35kJ/s from the hot source. The engine produces 15 kW of power and
    the temperature of the sinks is 26°C. What is the temperature of the hot source in °C ?

    Solution:

    e = Wnet/QA = T1 – T2/T1

    15/35 = T1 – (26 + 273) / T1

    T1 = 523.25 K= 250.25 °C

    thus;

    t2 = 250.25 °C

    3. An ideal vapor compression cycle requires 2.5 kW to power the compressor. You have found the
    following data for the cycle: the enthalpy at the condenser entrance = 203 kJ/kg; exit = 55 kJ/kg;
    evaporator entrance = 55 kJ/kg; exit 178 kJ/kg. If the mass of the refrigerant is 0.10 kg/s, then
    the coefficient of performance of this refrigeration cycle is most nearly:

    Solution:

    COP = Refrigerating Capacity / Compressor Power

    COP = QA / Wc

    where;

    QA= m(h1 – h4)

    = 0.10(178-55)

    =12.30 kW

    thus;
    COP = 12.30 / 2.5

    COP = 4.92

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