Convective mass transfer in a double-condensing chamber and a conventional solar still Shruti Aggarwal, G.N. Tiwari* Centre for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 1I0016, India Tel. +91 (11) 686-1977-86, ext. 5064; Fax +91 (11) 686-2208; email: gntiwari@ces.iitd.ernet.in Received 6 February 1998 ; accepted 30 March 1998 Abstract In this communication an attempt has been made to develop the convective mass transfer relation for a double- condensing chamber solar still (DCS) and a single-sloped conventional solar still (CSS) for different operating temperature ranges. Rigorous experimentations were carried out, on both the DCS and CSS during 1996-97. The experimental data have been used to discover C and n in Nu = C (Gr.Pr)" by applying linear regression analysis. Based on the results, it is inferred that (1) the order of C and n are the same as proposed by Dunkle [1] for low operating temperature ranges and (2) the value of C and n changes for operating temperatures other than Dunkle's. Keywords: Solar distillation; Mass transfer 1. Introduction The heat transfer in solar distillation is basic- ally classified as external and internal heat losses. The internal heat losses are mainly govemed by radiation, convection and evaporation. In fact, evaporation and convection losses are coupled together. It is noted from the literature that various researchers have analyzed the effect of internal heat and mass transfer on the performance of solar stills. It can be predicted by using expression Nu = (hcw *cO/ R = C(Gr.Pr)" *Corresponding author, (1) On the basis of experimental data, Dunkle[1], found the values of coefficients C and n as C= 0.075 and n = 1/3 with following limitations: • it is only valid for a mean operating tempera- ture range of 120°F (-50°C) and an equivalent temperature difference of 30 °F • it is independent of cavity volume, i.e., the average distance between the condensing and evaporating surfaces, and