Vertical cavity affected by external free convection is considered as a model of a double pane window and this conjugate heat transfer phenomena is numerically investigated. Boussinesq equation in the cavity is solved by finite difference method and local similarity solution is adopted in the region of external boundary layer.
The result indicates that external free convection has influence on the flow structure in the cavity and specially on the heat transfer rate.
Finally, the optimal gap in this model is suggested in the range, $4\times10^7 $<$ Gr_H$ <$ 2\times10^8$.
