Heat transfer coefficient problem

The correct answer should be B, right! Because the heat transfer coefficient on the air side is low.

The answer should be B. As long as you understand the principles, it’s fine; the answers given may not be entirely correct. If you look at textbooks on chemical engineering principles, there are even cases where the formulas in them are wrong.

This post was last edited by wiseboy on 2011-9-10 21:40, version 1. The examiner’s intention: The answer is B; 2. “The statement “water vapor exchanges heat with air” is not precise: 1) because the conditions of the air are not specified; if it is high-pressure air, or even liquid air, then there are problems ； 2) If there is heavy dirt, the problem is even more serious. 3. If this question comes from the question bank for registered engineers or universities, I suggest making some changes; otherwise it really poses a problem. No wonder it is said that the quality of college students born in the 1980s is declining; it turns out it’s the fault of the teachers. It is recommended to make the following modifications (the red parts are added by me): In a shell-and-tube heat exchanger, saturated steam exchanges heat with air at normal temperature and pressure; ignoring fouling resistance, the overall heat transfer coefficient is close to the convective heat transfer coefficient of ( ).

Saturated water vapor has a water film layer; it seems that the examiner is focusing on this aspect... Saturated water vapor has a high latent heat of phase change, and it adheres to the pipe walls. Since it is saturated vapor, its temperature is close to that of the vapor side. Saturated vapor cannot continue to condense, which results in a low heat transfer coefficient. Therefore, the answer is “water vapor”. The question itself isn’t clear enough...

It’s just that the explanation of this question needs further refinement.