Heat constant change with temperature

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Discussion Overview

The discussion revolves around the equations and methods for determining the specific heat capacity (Cp) and convection heat transfer coefficient (h) as they vary with temperature in the context of a finite difference problem involving the heating of a gas. Participants explore the relationships between these properties and other dimensionless numbers such as Nusselt, Prandtl, and Reynolds numbers, as well as the implications of forced versus natural convection.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks equations for Cp and h that account for temperature variations, indicating a need for these constants to be variable rather than fixed.
  • Another participant suggests that Cp can be found using equations from reference texts, such as the Perry Chemical Engineering Handbook, and mentions the importance of interpolation for h based on known temperature values.
  • A later reply clarifies that while h may require interpolation, empirical equations may exist to describe its behavior with respect to temperature.
  • One participant expresses uncertainty about using the equation relating Cp to Cv and seeks alternative equations that connect Cp to the current temperature.
  • Another participant proposes a relationship involving the gas constant R and suggests looking into additional resources for equations related to Cv.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the straightforwardness of equations relating Cp and h to temperature. There is acknowledgment that interpolation may be necessary for h, while specific equations exist for other properties, but the exact methods and equations remain contested.

Contextual Notes

Participants note the dependence of viscosity on temperature and the potential need for empirical equations to describe gas behavior, indicating limitations in the available information and the complexity of the relationships involved.

a.mlw.walker
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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 don't 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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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

http://www.3mints.info/upload/uploads/c5ed22f563.jpg

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

http://www.3mints.info/upload/uploads/c0790d9e11.bmp

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.
 
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?
 
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.
 
In terms of Cp, I can't use the equation that relates it to Cv and I can't use the equation that relates it to heat transfer Q =mCpDT

Is there another one that relates it to the current temperature?
 
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.
http://www.3mints.info/upload/uploads/e1b85696fd.jpg

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

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