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In a counterflow heat exchanger, hot fluid enters at 60°C and cold fluid leaves at 30°C. Mass flow rate of the hot fluid is 1 kg/s and that the cold fluid is 2 kg/s. Specific heat of the hot fluid is 10 kJ/kgK and that of the cold fluid is 5 kJ/kgK. The Log Mean Temperature Difference (LMTD) for the heat exchanger in °C is
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- 15
- 30
- 35
- 45
Correct Option: B
Heat capacity of hot fluid
= 1 × 10 = 10 kJ/ k – s
Heat capacity of cold fluid
= 2 × 5 = 10 kJ/ k – s
Since heat capacity is same, so LMTD is difference of temperature at either end
i.e. LMTD = 60° – 30° = 30° C 
