Numerical model and parametric analyses of an inflatable solar heater

This paper presents a new solar heater model which is shaped as an inflatab le hemisphere. It is called SOLARBALL(C). This solar heater is above all di stinguished by its small weight and volume. The final form is blown up by t he user. The objective of this work was to develop a mathematical and a num erical model to analyse solar radiation and heat transfer in such a heater. The numerical model was verified by a series of experiments. After success ful verification, the numerical model was used for the parametric analyses to establish the time required to heat water for different meteorological d ata, size of reflector and optical properties of the transparent cover, ref lector and absorber surface. It was found out that typical optical efficien cy and overall heat transfer coefficient of the hemispherical solar heater are between 0.45 to 0.5 and 0.6 to 1.6 W/m(2) K respectively. By standardis ed conditions (G(cov) = 700 W/m(2) and temperature difference T-w - T-a equ al 50 degrees C) the required heating time for heating 0.33 I of water vari es between 15 and 25 min according to the construction parameters. (C) 1999 Elsevier Science Ltd. All rights reserved.