FLOW DISTRIBUTION IN UNGLAZED TRANSPIRED PLATE SOLAR AIR HEATERS OF LARGE-AREA

Unglazed transpired plate solar air heaters have proven to be effectiv e in heating outside air on a once-through basis for ventilation and d rying applications. Outside air is sucked through unglazed plates havi ng uniformly distributed perforations. The air is drawn into a plenum behind the plate and then supplied to the application by fans. Large c ollectors have been built that cover the sides of sizeable buildings, and the problem of designing the system so that the air is sucked unif ormly everywhere (or nearly so) has proven to be a challenging one. Th is article describes an analytical tool that has been developed to pre dict the flow distribution over the collector. It is based on modellin g the flow-held in the plenum by means of a commercial CFD (computatio nal fluid mechanics) code, incorporating a special set of boundary con ditions to model the plate and the ambient air. This article presents the 2D version of the code, and applies it to the problem of predictin g the flow distribution in still air (no wind) conditions, a situation well treated by a 2D code. Results are presented for a wide range of conditions, and design implications are discussed. An interesting find ing of the study is that the heat transfer at the back of the plate ca n play an important role, and because of this heat transfer, the effic iency of a collector in nonuniform flow can can actually be greater th an that of the same collector in uniform flow. Copyright (C) 1996 Else vier Science Ltd.