Heat Transfer Questions & Answers  
Question by Student 201527136
Professor, I have question about fully-developed flow in pipe. You said the equation $\frac{U}{U{_{b}}}=2\left ( 1-\frac{r^{2}}{R^{2}} \right )$. Is this expression valid for both laminar flow and turbulent flow?
06.09.19
This is valid only for laminar flow.
Question by Student 201428239
Professor, I have a question about A7 of Q5. In this question, I need to use correlation of free convection H-T. I should use vertical plane correlation. In the table, a comment written as "x the distance from the bottom". In this comment, the x means height?? Then, when I use correlation ( $Nu_x = C(Gr_xPr)^m$, should I use x = H??
06.14.19
In this correlation, $x$ is the distance from where the boundary layer starts.
Question by Student 201428239
Professor, I have a question about A6 of Q3. In this question, I know the value of q local and q average.Then, I can get the relation between $Nu_x and Nu_L$ average. To solve (a), Do I need to compare these values and find the flow type??? If so, I can easily get Laminar flow, but in your comments, it could be either laminar or lam-Turb mix. How can find Lam-Turb mix relation??? Thank you
06.15.19
Well, by using a Nusselt number correlation that is suited to the turbulent/laminar regimes.
Question by Jaehyuk
Professor, I have a question regarding A7Q5. As far as I believe, it is suitable to use the correlation for a vertical plane with constant heat flux;$Nu_x = C(Gr^*_{x}Pr_{f})^m$. Here starts my problem. In order to find constants(C and m), the range of $Gr_x^*$ has to be set first. However, when $Gr_x^*$ is in between $1E11<Gr_x^*<2E13$, there is no option for constants(C and m). In this case, is it possible to choose any one of two options?
06.18.19
If you can't find a correlation that fit perfectly your situation, then choose the one that is the closest.
Question by Student 201428239
Professor, I have a question about A7 of Q5. In this problem, I should find free convection heat transfer coefficient. But in correlation, I should know $T_s$ first. I can get $T_s$ through iteration process. And then get h. Is this procedure correct?? Because in the problem, the order is to find h first and then find $T_s$.
Yes, exactly. I mentioned this in class.
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