Subtopic: Steady state heat transfer in conduction, convection and radiation
Question Statement:
Milk enters into the heating section of a HTST pasteurization plant at 45ºC and leaves at 72ºC. Hot water at 95ºC enters counter-currently and leaves at 77ºC. The effectiveness of the heat exchanger is
Options:
(A) 0.18
(B) 0.36
(C) 0.54
(D) 0.84
Official Answer Key:
C
Step-by-Step Solution & Explanation
Heat exchanger effectiveness, ε = actual heat transfer / maximum possible heat transfer. The maximum possible temperature rise for the cold fluid (milk, which has the smaller temperature change and is the limiting/C_min side here) is bounded by the hot fluid's INLET temperature: ε = (T_cold,out − T_cold,in)/(T_hot,in − T_cold,in) = (72−45)/(95−45) = 27/50 = 0.54. Answer: (C).
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