# Heat Transfer

HI

when dealing with natural convection, we use grashof's number. suppose we have a heated plate of temperature Tp. and heat being transferred to surrounding air by convection, air of temp Ta.

So film temp is Tf = 0.5(Tp + Ta)

If grashofs numbers, $$Gr = \frac { \beta gL^3 \delta T}{\nu^2}$$

im wondering what $$\delta T$$ and what $$\beta$$ we use.

thanks

Mapes