# Heat conductivity and Grashofs number

1. Jan 10, 2006

### TSN79

1)
I'm in need of some values (tables) about heat resistance, conductivity, and such for different types of building materials. Any good sites out there?

2)
I have the following equation for calculating Grashofs number:

$$Gr = g \cdot \beta \cdot \Delta t \cdot {{l^3 } \over {v^2 }}$$

All well and good, but the $\beta$ is described as being the "volume expansion coefficient", something I have never heard of before. The unit is 1/C, where C is Celsius. This wouldn't be a problem if I just knew what this number actually is, or where to find it. Any ideas?

2. Jan 11, 2006

### FredGarvin

1) Don't know of any sites. If your school has access to them, engineering handbooks are usually your best bet. If you have specific materials and properties you are looking for post them and someone should be able to pass some along to you.

2.) In free convection, the Grashof number is akin to the Reynolds number for forced convection. The $$\beta$$ term comes from the variation in density required for natural convection flow.

$$\beta = - \frac{1}{\rho} (\frac{\partial \rho}{\partial T})_p$$

it can be approximated by

$$\beta \approxeq - \frac{1}{\rho} (\frac{\rho_\infty - \rho}{T_\infty - T})$$

$$(\rho_\infty - \rho) \approxeq \rho \beta (T_\infty - T)$$

The RHS should look very similar to the first three terms of the Grashof number.

Last edited: Jan 11, 2006
3. Jan 11, 2006

### Gokul43201

Staff Emeritus
#1)
matweb.com lists properties for most metals, polymers and ceramics. This is a valuable resource for all kinds of property searches.

The more relevant resource for you is the NIST database for Heat Transmission Properties of Insulating and Building Materials : http://srdata.nist.gov/insulation/insul_search_menu_12.asp [Broken]

Last edited by a moderator: May 2, 2017