# Grashof: Determines the Grashof number for an object In Thermimage: Thermal Image Analysis

## Description

Determines the Grashof number for an object. The Grashof number is used in calculations of heat exchange.

## Usage

 `1` ```Grashof(L = 1, Ts = 25, Ta = 20) ```

## Arguments

 `L` Characteristic dimension of object in metres. Usually height, depending on object shape. `Ts` Surface Temperature of object, in degrees Celsius. `Ta` Air/Ambient Temperature surrounding object, in degrees Celsius.

## Details

The Grashof number is a dimensionless number describing the ability of a parcel of fluid warmer or colder than the surrounding fluid to rise against or fall with the attractive force of gravity as follows: Gr=agL^3(Ts-Ta)/v^2 where L is the characteristic dimension, usually the vertical dimension. For reference, a cylinder's characteristic L would be its height, assuming it is standing on its end Units of L should be in metres This L should be the same L as is used for the convective coefficient calculation Ts is the surface temperature Ta is the ambient temperature v2 is the kinematic viscosity squared (calculated from airviscosity(Ta))

## Author(s)

Glenn J Tattersall

## References

Blaxter, K. 1989. Energy Metabolism in Animals and Man. Gates, D. M. 2003. Biophysical Ecology. Dover Publications, Mineola, New York. 611 pp.

`airviscosity`
 ```1 2 3 4 5 6 7``` ```# Typical values for Grashof number range from 0.016 to 4.6e+09 if Ts-Ta varies from # 0.1 to 30oC L<-1 Ts<-30 Ta<-20 Grashof(L, Ts, Ta) ```