GATE ME 2019 Set 2 — Question 56
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Heat Transfer → Heat Exchangers → LMTD Method
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Question
Hot and cold fluids enter a parallel flow double tube heat exchanger at and , respectively. The heat capacity rates of hot and cold fluids are and , respectively. If the outlet temperature of the cold fluid is , the log mean temperature difference (LMTD) of the heat exchanger is ______ K (round off to two decimal places).
Correct answer
57 to 58
Solution
Given:
Inlet temperature of hot fluid,
Inlet temperature of cold fluid,
Heat capacity rate of hot fluid,
Heat capacity rate of cold fluid,
Outlet temperature of cold fluid, Step 1: Calculate the heat transfer rate ()
Step 2: Calculate the outlet temperature of the hot fluid ()
Using energy balance:
Step 3: Calculate the temperature differences at the ends for parallel flow
Step 4: Calculate the Log Mean Temperature Difference (LMTD)
Rounding off to two decimal places, the LMTD is .
Inlet temperature of hot fluid,
Inlet temperature of cold fluid,
Heat capacity rate of hot fluid,
Heat capacity rate of cold fluid,
Outlet temperature of cold fluid, Step 1: Calculate the heat transfer rate ()
Step 2: Calculate the outlet temperature of the hot fluid ()
Using energy balance:
Step 3: Calculate the temperature differences at the ends for parallel flow
Step 4: Calculate the Log Mean Temperature Difference (LMTD)
Rounding off to two decimal places, the LMTD is .
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