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Evacuated tube (ET) solar collectors are utilized in all climatic conditions for harnessing solar energy. This work aims to investigate thermal performance of ET with compound parabolic concentrator collector, integrated to a multiple phase change material-based thermal energy storage (TES) system. The phase change material (PCM) have been selected depending on the degree of stratification in sensible heat storage configuration under constant heat load conditions. The charging experiments have been performed under three different TES configurations viz. sensible heat storage, three ("Case 1") and five ("Case 2") PCMs, using water as the heat transfer augmenting the energy storage by 41% than the sensible heat storage. A higher stratification number in "Case 2" reveals the significance of multiple PCMs in improving the charging efficiency of TES system. Cascaded arrangement of PCMs facilitates the supply of HTF at lower temperature to the collector resulting with an increase in useful heat energy gained. The instantaneous thermal efficiency of collector with "Case 2" is as high as 58%, storing 27 MJ d −1. Use of ET-CPC and TES system with cascaded arrangement of PCMs finds potential application in water heating system.

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A B S T R A C T The behaviour of a pile-up of screw dislocations at a circular inclusion, with its tip away from the interface is analyzed using the method of continuously distributed dislocations. This leads for the first time, to a distribution function representing a shear crack at the inclusion. The stress required to extend the crack is derived and some new conclusions drawn on the deformation and fracture behaviour of the two-phase systems.