Heat transfer of impinging jet and cross flow

[dbecker]

Hello,

QUESTION 1:

I have to calculate convection coefficients (h's). I have a textbook here in front of me (Incropera/DeWitt/Bergman/Levine 6th edition fundamentals of heat and mass transfer).

On page 451, equation 7.75 represents a relation between Nusselt number and other parameters (Re, Pr, H, D etc...) to calculate heat transfer on a surface due to an impinging jet.

I want to calculate h's on the flat surface being impinged upon, but the relation gives me everything in terms of Nusselt.

In this case, can I use the equation Nu = hL/k? But what do I use for my L? And, if L is the distance from the center of the impingement to some point outward, then must I make a 2D plot of the h's or can I make this a 1D solution with a lumped "h" to simplify things.


QUESTION 2:

For a flat plate experiencing external flow, the relation is on page 414 in the form of a lumped solution equation 7.49. Do I use the length of the plate L to calculate Reynolds number?
I am assuming so.
And if so, relation 7.49 gives me Nusselt, can I use
Nu = hL/k to compute h?


Thank you,


- Dan

 

[ione]

Question 1:

h = Nu * k / D

Where D is the hole diameter

 

[dbecker]

ione,

so if D = 1 than h = Nu*k ? where k is the thermal conductivity of the fluid.

Thanks for the help

 

[ione]

Be consistent with your unit: D= 1 m???? Do not think so

 

[ione]

dbecker,

Further to your second question, take a look to the link below.

It is a good calculator which also offer some theoretical background.

http://www.thermal-wizard.com/tmwiz/default.htm

 

[dbecker]

ione i am not working in meters