Heat Transfer Questions & Answers
 Question by Student 201327111 Professor I have a question about this assignment 8 question 1. I was able to get right answer(63degree) using correlation for fully developed turbulent flow (smooth and rough tubes) with assumed average bulk temperature of 57degree. But after several iteration process, the bulk temperature of second state converged to 48degree. I wonder if the answer is right. If you don't mind, can you check the answer again?
 06.04.19
Right, both answers for A8Q1 were not for this problem. I fixed them: check again.
 Question by Student 201527143 Professor I have a question about A8Q5-b hint. I got friction factor value from the hint using momentum eqn. The value is same with F-D Laminar friction factor from the table. However, flow of (b) is turbulent. Which one should I use? F-D turb friction factor from the table or Hint?
The friction factor mentioned in the “hint” is valid for both laminar or turbulent flows.
 Question by Student 201527130 I have a question about assumptions. $$m(Cp_2Tb_2-Cp_1Tb_1) = q_{ADDED}$$ For using this equation(m is massflow) and defining bulk temperature, I need to assume that density is constant. But in gass case, density is not constant. So the question is how to use bulk temperature in gass case?
 06.06.19
For a gas, you don't need to assume constant density but you need to assume negligible kinetic energy change. I think I mentioned this in class..
 Question by Student 201428239 Professor, I have a question about Design set 2 of #2. In this problem, I think I need to fine h which is natural convection H-T coefficient. So I need to select correlations. Can I use correlation about Horizontal cylinders??
 06.08.19
Yes, this sounds correct.
 Question by Student 201527130 I have a question about entrance region_length. To find the length, I use equations from handout $$\delta = {4.64x\over{R_E^{1\over2}}} , \delta_t = {4.64x\over1.025R_E^{1\over2}P_R^{1\over3}}$$ and I think “x” is entrance length when 2$\delta$ is D(diameter of duct). on my thinking, I calculate these equations. $$L_u = 0.108R_E^{1/2}D$$ $$L_t = 0.11R_E^{1/2}P_R^{1/3}D$$ But in this case, $$R_E = R_{E_x}$$ so, there is error i think.. Am i going the right way?
I don't understand what you write. What is $L_u$ and $L_t$? How do you calculate this? You need to define these new terms and explain how you got them.
 Question by Student 201527130 I am sorry about omission. I use equations from handout. $$\delta = {4.64x\over{R_E^{1\over2}}} , \delta_t = {4.64x\over1.025R_E^{1\over2}P_R^{1\over3}}$$ and I think x is entrance length when 2$\delta$ is D(diameter of duct). $$2\delta = D , 2\delta_t = D$$ If we summarize this equation about x, $$x = 0.108R_E^{1/2}D = L_u$$ $$x = 0.11R_E^{1/2}P_R^{1/3}D =L_t$$ Here, $L_u$ is entrance length of velocity and $L_t$ is entrance length of temperature that I think. But in this case, $R_E = R_{E_x}$. I remember that values are determined by diameter, not the length in duct. so, there is error i think.. Am i going the right way? I'm sorry I have always had a scanty question.
You're on the right track!
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