TRANSFER CALCULATION IN A FREE-CONVECTION AIR SOLAR COLLECTOR

This paper deals with the free convective air how developing in a vert ical channel with a rectangular cross-section heated on one side. The channel geometric and physical properties are such as to simulate an a ir solar collector suitable for building heating. A calculation method that can be applied to the transient combined heat transfer by conduc tion through the wall and by convection from the wall to the air strea m is presented. The conduction across the wall is computed with a one- dimensional, time-dependent finite difference scheme, with convective boundary conditions at both wall surfaces. For the free convective flo w along the channel, the air flow rate and the mean convective coeffic ient on the heated wall are evaluated by means of suitable correlation s. To test the practical applicability of the method, some cases have been calculated and the results are presented. Input data are the inte rnal and external temperatures and the solar power absorbed per unit a rea as functions of time. The calculation outputs the solar heat gains by convection and conduction and the heat dispersed through the glass . The results show that the method lends itself to a relatively simple application in some realistic cases. (C) 1998 Elsevier Science S.A.