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Tue 17 May, 2022 07:03 pm
This critical number always appears as a rather large range. How do I determine a more precise number? For example, this website (https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html) gives the range 50 W/K*m^2 to 10,000 W/K*m^2 for water undergoing forced convection.
Related question: my specific application involves heat transfer between two fluids, one being mixed aggressively and the other completely stagnant. Between them is a very thin (0.25 cm) plate of silver (k = 429 W/m*K) .
For the Biot number to be less than 0.1, the convective heat transfer coefficient would have to be:
h(W/m^2*K)<0.1*(429W/m*K)/(0.0025m)=17,160. Based on the range, which caps at 10,000 for water and other fluids, I'm pretty sure that even for forced convection, I can ignore the transient behavior within the steel plate. But how does it shake out after that? Should I treat it as a forced convection just between two fluids? Should there be two convective heat transfer coefficients, one for each side of the plate?
Any help would be greatly appreciated. You're all amazing.
@Moshe L,
There are a lot of challenges here which is why you get a wide range of values for the transfer coefficients. How wide is the laminar region around the plate on the forced convection side? That is going to depend on how you mix, the shape of the container, etc. Honestly, the best way to do this is to put a thermocouple on the wall and get the wall temperature then model the situation. Then you can treat the stagnant side strictly a conduction situation. I very distantly remember trying to solve heat transfer equations from a turbulent bulk fluid through a laminar region to a tube wall in reactor design, but that was decades ago. I didn't quickly find much online other than modeling solutions.
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