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Heat Transfer - Engineering

Q1:

Pick out the wrong statement.

A In case of heat transfer by purely forced convection, GR/Re2 ≤ 1.

B The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x.

C Distillation process is not the same as evaporation.

D The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface.

ANS:B - The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x.

The wrong statement is: "The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x." For a duct of square cross-section, the equivalent diameter for heat transfer purposes is not equal to 4 times the side length 'x'. Instead, it is calculated based on the hydraulic diameter, which for a square duct is the side length itself. Therefore, the equivalent diameter would be 'x', not '4x'. Therefore, the correct statement is: "The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x."