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Hot and cold fluids enter a parallel flow double tube heat exchanger at 100oC and 15oC, respectively. The heat capacity rates of hot and cold fluids are Ch = 2000 W/K and Cc = 1200 W/K, respectively. If the outlet temperature of the cold fluid is 45oC, the log mean temperature difference (LMTD) of the heat exchanger is ________ K (round off to two decimal places).
    Correct answer is '57.71°'. Can you explain this answer?
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    Hot and cold fluids enter a parallel flow double tube heat exchanger a...

    Using the energy balance equation for the heat exchanger


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    Hot and cold fluids enter a parallel flow double tube heat exchanger a...
    Given data:
    Hot fluid inlet temperature (Th1) = 100°C
    Cold fluid inlet temperature (Tc1) = 15°C
    Outlet temperature of cold fluid (Tc2) = 45°C
    Heat capacity rate of hot fluid (Ch) = 2000 W/K
    Heat capacity rate of cold fluid (Cc) = 1200 W/K

    To find:
    Log mean temperature difference (LMTD)

    Solution:
    Step 1: Calculate the temperature difference between the hot and cold fluids at the outlet:
    ΔT1 = Th1 - Tc2
    ΔT1 = 100°C - 45°C
    ΔT1 = 55°C

    Step 2: Calculate the temperature difference between the hot and cold fluids at the inlet:
    ΔT2 = Th2 - Tc1
    Since Th2 is not given, we need to find it.

    Step 3: Calculate the outlet temperature of the hot fluid (Th2) using the heat capacity rates:
    Q = Ch * ΔT1 = Cc * ΔT2
    2000 * 55 = 1200 * ΔT2
    ΔT2 = (2000 * 55) / 1200
    ΔT2 = 91.67°C

    Step 4: Calculate the temperature difference between the hot and cold fluids at the inlet:
    ΔT2 = Th2 - Tc1
    91.67°C = Th2 - 15°C
    Th2 = 91.67°C + 15°C
    Th2 = 106.67°C

    Step 5: Calculate the log mean temperature difference (LMTD):
    LMTD = (ΔT1 - ΔT2) / ln(ΔT1 / ΔT2)
    LMTD = (55°C - 91.67°C) / ln(55°C / 91.67°C)
    LMTD = -36.67°C / ln(0.6)
    LMTD = -36.67°C / -0.5108
    LMTD = 71.74°C

    Step 6: Round off the LMTD to two decimal places:
    LMTD = 71.74°C ≈ 71.74°C

    The correct answer is 71.74°C, rounded to two decimal places, which is approximately 71.74°C.
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    Hot and cold fluids enter a parallel flow double tube heat exchanger at 100oC and 15oC, respectively. The heat capacity rates of hot and cold fluids are Ch = 2000 W/K and Cc = 1200 W/K, respectively. If the outlet temperature of the cold fluid is 45oC, the log mean temperature difference (LMTD) of the heat exchanger is ________ K (round off to two decimal places).Correct answer is '57.71°'. Can you explain this answer?
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