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Heat constant change with temperature

by a.mlw.walker
Tags: constant, heat, temperature
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Aug24-10, 12:07 PM
P: 153
please can someone help me with the equations to use for Cp and h(convection coefficient) because i am doing a finite difference problem over time, of a gas being heated, and i need these two constants to be variable as temperature changes, which at the moment they are just constants.

I think its to do with nusselt, prandtl, reynolds (of which i also dont know how to calculate, and whether they vary with temperature), and whether the convection is forced or natural.

I am looking for dCp/dt and dh/dt

If anyone can help that would be greatly appreciated
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Aug27-10, 05:25 AM
P: 30
I do not actually understand your question, but to find
Cp at different temperature there are an equation with many constants you can find it at the end of this book or i thing you will find that equation in Perry Chemical Engineering handbook

about the value of h you can find it at the end of any heat transfer book like this one

h will be given as a constant for different temperatures so by know these values you do iterpolation for this points and find the equation that describe h with respect to T .
On the same book you can find the equations of nusselt, prandtl, and reynolds numbers.

i think you will need the value of viscosity which is very depending on temperature so you can search on the internet to find empirical equation that describe your gas behavior.

remember in a heat transfer problems, it is acceptable to make a reasonable precision it is impossible to be 100% accurate.
Aug27-10, 05:40 AM
P: 153
ok so just to clear up, none of these have straight forward equations relating them to temperature, i have to interpolate for the values between values at known temperatures?

Aug27-10, 06:19 AM
P: 30
Heat constant change with temperature

just h have to be interpolated , but you might find empirical equation describe behavior of h with respect of T if you search through internet (difficult and time consuming).
Pr,Nu,Re , vescosity and Cp have a specific equation.
Aug27-10, 06:37 AM
P: 153
In terms of Cp, I cant use the equation that relates it to Cv and I cant use the equation that relates it to heat transfer Q =mCpDT

Is there another one that relates it to the current temperature?
Aug27-10, 06:55 AM
P: 30
why not
R=Cv-Cp (not sure but something like that)
i think there are another way to find Cv.
try to have a look to this book.

unfortunately I'm away from my home , so i can not give you the equation directly.

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