Abstract
The study is aimed to evaluate the impact of multi-phase nanofluid flow to enhance heat transfer. The effect of liquid medium and pumping medium together with enabling a bubble pump to reverse thermosyphon arranged as an extension of the U-tube of solar thermal collector could affect a passive downward heat transfer numerically. The liquid and pumping medium selection were based on different nanofluid and phase change material accomplishment with respect to their optimal concentrations, optimal geometry of the reverse thermosyphon were compared. The occurrence of dry out limit and expansion boiling phenomena were identified by experimental work. The amount of optimal heat transfer in reverse thermosyphon was adjudged with respect to the thermal resistance, temperature between evaporator and condenser, fill ratio, tilt angle, heat transfer coefficient, thermal efficiency, etc. In this paper, the effects of major control parameters on thermal performance of passive heat transfer of solar energy are discussed.
 HIGHLIGHTS
 
 Continuous operation of reverse thermosyphon with 2 working media, a bubble pump and using solar thermal collector as heat source and finned U-tube for a passive downward heat transfer is feasible
 CFD model with a 2-D geometry considering multi-phase flow has successfully reproduced both the characteristics of fluid flow and heat transfer
 Optimal heat transfer was adjudged with respect to the thermal resistance, temperature between evaporator and condenser, fill ratio, tilt angle, heat transfer coefficient, and thermal efficiency
 Reduced rate of heat loss, increased rate of energy storage by integrating PCM directly inside the U-tube, and enhanced heat transfer by incorporating nanofluid with high heat capacity were realized
 Suitable working media selection was vital and contributed in improved system efficiency and reduced operational cost
 
 GRAPHICAL ABSTRACT
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