The paper presents the results of some investigations to establish the validity of various correlations for estimating masstransfer rates in a solar still. For this purpose, the results of steady‐state experiments in a controlled environment are compared with the predictions of different correlations. It has been observed that the correlation leading to the widely used Dunkle's relation is valid only when the Grashof number is less than 2.51 × 105 and needs modification for higher values of the Grashof number.

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SUMMARYHourly thermal performance (both in laboratory and field conditions) of three designs of built-in-storage solar water heating systems of 100 litres capacity each has been reported. A different storage tank design is used in each of the three cases. Design I consists of three tanks connected in series; in Design II, a parallelepipedic tank is divided into five zones with baffles; Design III is a simple parallelepipedic tank. The first two designs help in inducing thermal stratification in the tank. It is seen from the results that the performance of Design II is the best of the three.

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