The use of grid-generated turbulence to improve heat transfer in passive solar systems

• Published in: Renewable energy 1992-06, Vol.2 (3), p.333-336
• Main Authors: Maad, R.Ben, Belghith, A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Energy; Energy. Thermal use of fuels; Exact sciences and technology; Heat transfer; Theoretical studies. Data and constants. Metering
• ISSN: 0960-1481; 1879-0682
• DOI: 10.1016/0960-1481(92)90046-6

In order to design and realize a solar chimney of greatest efficiency for drying agricultural products, we have investigated the natural convective flow between two heated vertical plates. The equations of continuity, momentum and energy are solved by a finite difference method, taking into account the variation of the fluid properties with temperature and the pressure drop due to flow acceleration at the channel entrance. In order to validate the theoretical predictions, an experimental study was carried out. Good agreement between the experimental results and the theoretical predictions was obtained. The average Nusselt number at the exit was calculated. This value is comparable to that obtained on a flat plate, despite the thermosyphon effect. In order to improve the heat transfer in the channel, grid-generated turbulence was used. The experimental results show that flow was no longer laminar; the hydrodynamic and thermal fields become very unstable. The temperature in the middle of the channel is high and can reach 50% of the wall temperature. In spite of the decrease of the volumetric air flow, the average Nusselt number increases according to the quality of grid arrangements.