Heat transfer and fluid flow studies in the collector tubes of a closed-loop natural circulation solar water heater

Studies on heat transfer and the resulting fluid flow through the collector tubes of a closed loop thermosyphonic solar water heater have been conducted at Aligarh (27 degrees 5' latitude) for some experimental data. The collector, facing south, has 45 degrees tilt from the horizontal. The data, in terms of temperatures, were collected for hot water withdrawal rates of 0, 50 and 60 l/h on various days. The local and length averaged heat transfer coefficients were calculated for some tubes on the collector, using the global radiation recorded near the heater. Subsequently, various dimensionless parameters governing the heat transfer and the fluid flow were also estimated. The Nusselt and Reynolds numbers show some remarkable characteristics when studied against a new dimensionless parameter: S-i = S/U-1(T-p - T-a). Also, grouping of the Nu, Re, Gr and Pr numbers in a particular form show that the system obeys the well known behaviour of the natural circulation loop. The collector efficiency and flow factors were made the bases for selecting the data and standardisation of the system under study. (C) 1997 Elsevier Science Ltd.