Computational Fluid Dynamics Modelling and Performance Analysis of a Flat-Box Solar Thermal Collector with Multi-Channel Absorber

A novel multi-channel flat-box solar thermal collector was designed, constructed and tested. The collector was mounted on a 2-axis solar tracking system. An instantaneous efficiency curve for this collector was developed and... [ view full abstract ]

A novel multi-channel flat-box solar thermal collector was designed, constructed and tested. The collector was mounted on a 2-axis solar tracking system. An instantaneous efficiency curve for this collector was developed and collector parameters determined. Collector parameters were used to characterize the collector. A CFD model of the collector was developed. This model was used to investigate the significant influences of the mass flow rate, inlet water temperature, collector box dimensions and the effect of changing the flat-box materials. The efficiency of the multichannel collector was found to be 80.1%. The heat loss coefficient was found to be 4.0 W/m²K. Comparison of experimental and model predicted data showed a close agreement with a 10.3% error. However, differences between experimental and model predicted data increase with time of day due to the collector restoring more energy and thus causing more radiation and convection losses than assumed in the CFD model. Four materials of the flat-box collector were tested. Test results showed small differences of the outlet temperature when different materials are used for construction. This indicates the relative importance of radiation in solar collectors in comparison to other heat transfer regimes. The lower flow rate exhibited higher output temperatures and the higher flow rate showed lower temperatures. The conductivity of the flat-box is crucial in heating up the water from all direction. From the obtained results, it can be inferred that the CFD model is able to simulate the solar collector with known sources of errors.  Therefore, the CFD model is a useful tool that can be used to improve the design of flat plate solar collectors. The model can also be used to optimize the dimensions of the flat collector box for improved performance of the multichannel solar thermal collector. Collector performance demonstrate potential for solar thermal applications for water heating and desalination in Qatar.

Acknowledgement: This research was made possible by a NPRP award NPRP No. : 5 -161 – 2 - 053 from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the authors.