Ans: The LMTD of counterflow HX is greater than LMTD of parallel flow HX because the temperature difference between hot and cold fluids remains nearly constant whereas in the parallel flow HX the temperature difference between hot and cold fluids is very high at the beginning but decreases immediately and hence the heat transfer rate does not remain as high as in the beginning. On the other hand, the heat transfer rate remains relatively constant throughout counterflow HX.
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