Heat Transfer Questions & Answers  
Question by Student 201427135
Professor, I have some questions of Assign#1 [Assign#1-1] It's insulated wall but heat is transferred through the insulation wall. Is it not perfectly insulated so they give me conductivity ? I don't know exactly why heat can be transferred. [Assign#1-2] They give me velocity but we don't think about velocity. I think if velocity exists, convective heat transfer is much higher than if velocity doesn't exist. Also they give me convective heat transfer coefficient. Does this coefficient include velocity effect? Thank you.
04.24.19
Hm, 1 question per post only. And keep in mind there are no bonus points for questions that are obviously asked for the sole purpose of getting a bonus. Spend time rather working harder on the assignment problems: this will help you more get a higher grade.
Question by Jaehyuk
Professor, I have a question regarding assignment #3, question #5. There are two sources of heat, which are internal(heat generation) and external(radiation). As the system is in between these sources, how does the direction of the heat flux can be determined when using resistance analogy?
You can set the direction from left to right and if $q$ ends up being negative it means your guess was wrong. What matters is to be consistent. If you draw $q$ from left to right and $q$ is negative in your answer, then keep the answer as negative but make a note that the heat transfer is going from right to left.
Question by Student 201427135
Professor, I have a question A2 Q5-(c).

I should get shape factor for solving insulation thickness.
So I think it's steady state, the insulation is isothermal so I used isothermal cylinder shape factor. It's actually the first thing of shape factor table. But it didn't give me answer so I used hollow shape factor, then it did.

I don't know why shape factor is about hollow cylinder. I think inside of cylinder, it's full of steel cable so it's not hollow cylinder. Thank you
04.25.19
I don't understand. If it has steel cables in it, the cylinder must be hollow. It can not be full.
Question by Student 201428239
Professor, I have a question about radiation H-T. Should I always use unit of temperature K instead of Celcius degree??
Yes of course.
Question by Student 201312147
Professor, i have a one question. We said that most of the problems were not radiation. However, I think that radiation occurs in most situations. why we thought no radiation?? Is there an exact reason to assume that we don't have a radition?
Radiation heat transfer coming out of objects at 300 K is generally quite small compared to convection heat transfer. It becomes more important thus when the temperatures are higher because its intensity scales with the 4th power of the temperature. At low temperatures, you can ignore it. But at higher temperatures, you should take it into consideration unless there's not enough information to calculate it.
Question by Student 201312147
Professor, i solve the assignment#4, problem 7 (a) using iterative method. But I don't know if this is the right way to solve it. So, I want to know when to use the iterative method.
Sure, you must use an iterative method for this problem.
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