Heat Transfer Questions & Answers  
Question by Student 201527130
professor, I have a question about Tube banks (staggered). Is minimum area lcated at between 1st line to 2nd line? If that’s right, I think Is my thinking right?
05.26.19
You're on the right track, but this is not correct still. Work on it more — the diameter of the tubes should be somewhere in your areas.. Also, use the PREVIEW command and make sure your math show up clearly: your expressions are too close to each other and hard to read. Separate them on different lines.
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.
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