Question 66 on the first morning of the 2011 Chemistry and Chemical Engineering exam
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66. Regarding the heat transfer during liquid boiling, which of the following statements are correct? A. Large-volume saturated boiling is a type of boiling phenomenon that involves forced convection. B. Heat transfer during liquid boiling is a heat transfer process that involves phase change. C. The industrial application area for heat transfer during liquid boiling is nucleate boiling. D. Under normal conditions, the heat transfer coefficient α increases as the thermal conductivity λ and density ρ of the liquid increase, while it decreases as the viscosity μ and surface tension σ of the liquid increase. Dear candidates preparing for the exam, why is option D incorrect? Could someone please explain this?
D is correct; it’s the exact wording from the textbook on principles of chemical engineering (the version I use is from Dalian University of Technology).
The answer key provided for the real exam does not include option D
The effects of thermal conductivity, density, and viscosity can be found, but surface tension cannot; it is not mentioned in the Tianjin University textbooks nor in the association’s textbooks
I used the textbook on Principles of Chemical Engineering compiled by Dalian University of Technology, published by Higher Education Press. d is the exact wording from there, identical. I’m sorry I don’t have an electronic version to take a screenshot of for you.
Take a look at a previous post on the boiling heat transfer coefficient: http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1606753&page=1#pid16259176
Okay, thank you. Next time I encounter this question, I’ll remember it very well
D is correct; it’s the exact wording from the book. I’m not quite sure about A – isn’t nucleated boiling considered a form of forced convection?
Whether it is forced convection boiling is not determined by whether it is film boiling or nucleate boiling; rather, it is determined by the size and shape of the equipment. Boiling inside tubes is forced convection boiling, while boiling in large volumes, that is, pool boiling, is not.
Is forced convection related to the size and shape of the device? What type of heat transfer occurs in the air when there is wind?
It is recommended to check the explanations in the textbook on chemical engineering principles regarding the ways in which liquids boil.