Finding heat transfer coefficient

[matthewrangeley]

Hi, I am trying to find a suitable correlation to relate nusselts number with raleighs number in order to find the heat transfer coefficient on a vertical plate and vertical fins in natural confection. I have found correlations for the average over the length but cannot find ones for varying lengths. (ie Nux). I need this as i am investigating the effect of interupted fins as appose to continuous fins.

Thank you

 

[borgwiser]

For a vertical plate (if properly sized and used with a horizontal plate you should be able to model a fin):
a = 0.387 * (Ra^(1/6))
b = [1 + ((0.492/Pr)^(9/16)) ]^(8/27)

Nu = [0.825 + a/b]^2
(I used this truncated form to make it easier to read).
This is using a characteristic length value for Nu and Ra.

For a horizontal plate:
hot surface facing up/cold surface facing down:
If 10^5 < Ra < 2*10^7
Nu = 0.54*(Ra^(1/4))
If 2*10^7 < Ra < 3*10^10
Nu = 0.14*(Ra^(1/3))

hot surface facing down/cold surface facing up:
3*10^5 < Ra < 10^10
Nu = 0.27*(Ra^(1/4))


***Taken from ISBN: 0-471-38149-7