Nu correlations for the air gap and the rear glass

The average convection heat transfer coefficients are derived from the Nusselt numbers (Nu ). In laminar free convection flows the Nu is obtained through different correlations: in the case of symmetric uniform heat fluxes the correlation of Roshenow with c=1.15 [14] is used, in the case of asymmetric uniform heat fluxes the new correlations obtained in this research (equations 1 and 2.) are used for hot and cold walls. In turbulent free convection flows, in the case of wide channels, the correlation of Churchill [5] is used. In forced convection flows, a distinction between developing and fully developed flows is made. In case of laminar developing flows, the correlations of Bejan [2] and Kays [10] are used. In case of laminar fully developed flows, the Nu are constants. In case of turbulent developing flows, a correlation obtained by Saelens [15] is used. Concerning to the turbulent developed flows, the equations of Kays [10] are also valid.

In the case when the rear glass is formed by multiple glass layers, the equations and correlations obtained for air cavities will be used.