Typical Heat Transfer Coefficients of Common Materials

[cltengr]

I am attempting to perform some heat convection calculations on a process with a granular, rubber-type material but don't have the heat transfer coefficient for the material. I figure I could complete my calculations if I was able to find a list of heat transfer coefficients for common materials. Does anyone know where such a list exists online?

 

[ivymike]

could try matweb

 

[cltengr]

I thought you were onto something but no heat transfer coefficients on Matweb.com.

 

[insult2injury]

Heat transfer coefficient is not a material property. Much more information is needed.

 

[tkordyban]

Convection is heat transfer from a solid surface to a fluid in motion (like air or water). The convection coefficient depends on the motion of the fluid and the material properties of the fluid, not on the solid surface material.

 

[cltengr]

I've got this rubbery material in a tank with air blowing over the exposed area. I am attempting to calculate how much quicker it will cool if I use cooler air instead of ambient air. It seems like a convective application to me.

 

[IRstuff]

Matweb has thermal conductivity, which IS the heat transfer coefficient of a solid.

TTFN

 

[25362]

To cltengr, convection involves movement. Thus, it can not be a property of the static exposed solid. You are right in that cooler air may improve the htc over ambient air.

The htc, h, W/(m[sup]2[/sup].[sup]o[/sup]C) can be approximated for turbulent air in free convection (Gr/Re[sup]2[/sup]> 1.0) over a horizontal surface by

h = 1.43([Δ]t)[sup]1/3[/sup]​

where [Δ]t is in [sup]o[/sup]C

Since, apparently, the process would be of unsteady state heat transfer, with changing [Δ]t, the value of h is bound to drop with time.

 

[IRstuff]

You have two thermal transfers, one from the bulk of the material to the surface and then from the surface to the air. Cold and fast moving air only solves the second transfer.

Your "rubbery" material is like a thermal insulator, therefore, you're ultimately limited by your material's thermal conductivity and heat capacity.

TTFN

 

[insult2injury]

Thermal conductivity and heat transfer coefficient are NOT the same thing.

 

[ivymike]

...but they are mathematically similar:
conduction: q = -k*A*(dT/dx)
convection: q = h*A*(deltaT)

based on the way the original question was worded, I had assumed that the OP wanted conductivity, not a convective htc.

 

[IRstuff]

from OP: "granular, rubber-type material but don't have the heat transfer coefficient for the material"

That can only be rationally interpreted as requiring a thermal conductivity, since the convective heat transfer coefficient is a function of fluid, not the immersed material.

TTFN

 

[ivymike]

...depends on how much credit you're willing to give...

 

[IRstuff]

no doubt, as events have shown.

TTFN

 

[mcatan]

Convection coefficients are not hard to calculate, but often you just need a quick and dirty range to get a ballpark figure.

These are film coefficients. All units are W/m^2-K

Free convection
air 5-20
water 100-600

Forced convection
air 10-100
water 500-10,000