An experimental study of heat transfer in curved pipe with periodically varying curvature for application in solar collectors and heat exchangers

Experiments were conducted for a varying curvature curved pipe within a double-pipe heat exchanger with water as the working medium. The heat transfer coefficients were obtained using the Wilson plot method. The effect of the Dean, Prandtl, Reynolds number and curvature ratio on the average heat transfer coefficients and the friction factors are presented. A higher Dean number results in a higher heat transfer rate. It is found that the heat transfer rate may be increased by up to 100%, as compared with a straight pipe, while the friction coefficient increased by less than 40%. Therefore, it is promising to use S-shaped pipes instead of straight pipes for the enhancement of a solar collector performance