Heat Transfer Questions & Answers  
Question by Student 201428239
Professor, I have a question about Assignment 7 of Q5. In this problem, Can I use correlation equation about vertical plane?? Or Should I use irregular solids?? And also, In your lecture note, there is an example about free conv H-T example(Desktop problem with q=30W). In that problem, we determined surface T first and then free convection heat transfer coefficient. But this problem is opposite. Can I determine free convection heat transfer coefficient without surface Temperature??? Thank you.
05.27.19
Use the most accurate correlation generally. Yes, you can find the $h$ without knowing the surface temperature a priori through an iterative process.
Question by Student 201428239
Professor, I have a question about A7 of Q6. In this problem, I think I should use Nu as flow across a sphere. But in table, there is a expression about $u_w$ (viscosity at the wall)what is it exactly?? Do I go right??
Well, as you mention, $\mu_{\rm w}$ is the viscosity of the fluid at the wall determined at the temperature of the wall.
Question by Student 201428239
Professor, I have a question about A7 of Q6. I don't know how to find $\mu_w$ in this problem. Is it fine to assume this is same as $\mu_\infty$??
Find the wall temperature, and then find $\mu_{\rm w}$ from this wall temperature.
Question by Student 201427135
Professor, I have a question about the class. You taught us about hydraulic diameter, example for river. But I can't understand why it doesn't have friction area on the both sides. I thought river has ground on bottom and on both sides (actually extended ground ) also. Thank you.
06.03.19
True, it could be this way, but I was thinking of a river section where the sides are flowing water.
Question by Student 201527136
Professor, I have a question about heat transfer in pipe. You said $\,\Delta T_{lmtd}$ is almost same with $T_{w}-\frac{1}{2}(T_{b,o}-T_{b,i})$ when $\,\frac{T_{w}-T_{b,o}}{T_{w}-T_{b,i}}\geqslant 0.5$. If $\, T_{b,o}$ is not given, I can't judge$\,\frac{T_{w}-T_{b,o}}{T_{w}-T_{b,i}}\geqslant 0.5$. Then, do I have to use only $ \,\Delta T_{lmtd}$ instead of $ T_{w}-\frac{1}{2}(T_{b,o}-T_{b,i})$?
Solve the problem and check if the simplified expression can be used or not. If it can not be used, re-solve the problem with the full expression.
Question by Student 201428239
Professor, I have a question about A8 of Q1. I need $\mu$ to calculate Reynolds Number. In your lecture note of EG H-T in pipe, we used $\mu$ at average bulk T. What happened if I use $\mu$ at wall Temperature??? Does it cause wrong answer?
If you really want to know, you can try this in the quiz or exams and find out how many points you will lose.
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