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Heat Transfer

Q1:

Pick out the wrong statement.

A The controlling resistance in case of heating of air by condensing steam is in the air film.

B The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant temperature.

C In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs.

D Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature.

ANS:D - Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature.

The wrong statement is: "In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs." In a 1-2 shell and tube heat exchanger, the LMTD correction factor does not necessarily increase sharply when a temperature cross occurs. The LMTD correction factor may increase or decrease depending on the specific conditions of the temperature cross and the fluid properties. It is not a general rule that the correction factor will always increase sharply in such cases. Therefore, the correct statement is: "In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs."



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