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?
 06.07.19
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.
 06.09.19
You're on the right track!
 Question by Student 201527130 I have a question about design projects Q#5. I think the velocity in duct is too high. so, density is too big(10.2kg/m^3). I think it seems to be 20m / s instead of 200m / s when we match the answer.Could you confirm it if it does not work?
There is no problem with the question formulation.
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