Performance Evaluation of a Glazed Transpired Solar Collector with Chimney in Natural Convection Mode

Abstract

Transpired solar collectors require adequate pressure difference across them to work and electric fans usually produce the pressure difference in forced convection mode. In natural convection mode no fan is used and little or no pressure is produced across the collector. A chimney can replace the fan in natural convection mode and buoyancy forces in the chimney and collector produce pressure difference across the collector. An experimental rig was set up in the field to study a glazed transpired solar collector (GTC) with chimney in natural convection mode. The chimney height range was 4.04m to 8.04m while absorber hole diameter range was 1.0mm to 3.0mm. The study considered the influence of absorber hole diameter, collector air velocity and chimney height on the performance of the GTC. Results showed that heat exchange effectiveness decreased from 0.97 at absorber hole diameter of 1.0mm to 0.78 at absorber hole diameter of 3.0mm. Thermal efficiency increased from 6% at absorber hole diameter of 1.0mm to 75.4% at absorber hole diameter of 3.0mm. The efficiency also increased from 16.5% at a pressure difference of 6.81N/m2 corresponding to a chimney height of 4.04m to 75.2% at a pressure difference of 14.11N/m2 corresponding to a chimney height of 8.04m for the absorber with hole diameter of 3.0mm. The collector outlet velocity increased from 0.045m/s at a chimney dimensionless height of 11.74 to 0.075m/s at a chimney dimensionless height of 23.44 for an absorber hole diameter of 3.0mm. Finally, the pressure difference across the absorber increased from 6.81N/m2 at a chimney dimensionless height of 11.74 to 14.11N/m2 at a chimney dimensionless height of 24.31. The thermal efficiency and heat exchange effectiveness obtained in this study show that the GTC with chimney has promise for application in the areas of space heating and crop drying in natural convection mode.