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Heat Transfer - Engineering

Q1:

In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is

A ∞

B 0

C equal to the difference between hot and cold fluids inlet temperature.

D equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature.

ANS:B - 0

In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, it implies that there is complete thermal equilibrium between the two fluids. In this case, the logarithmic mean temperature difference (LMTD) is calculated using the following formula: LMTD=LMTD=ln(ΔT1​/ΔT2​)ΔT1​−ΔT2​​ where:

  • 1ΔT1​ is the temperature difference between the hot fluid inlet and the cold fluid outlet,
  • 2ΔT2​ is the temperature difference between the hot fluid outlet and the cold fluid inlet.
However, since the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, both 1ΔT1​ and 2ΔT2​ are zero. Therefore, the LMTD becomes indeterminate. So, none of the provided options correctly describes the LMTD in this scenario.