Search

Purpose: This study aims to investigate a three-dimensional computational modelling of free convection of Al2O3 water-based nanofluid in a cylindrical cavity under heterogeneous heat fluxes that can be used as a thermal storage tank. Design/methodology/approach: Effects of different heat flux boundary conditions on heat transfer and entropy generation were examined and the optimal configuration was identified. The simulation results for nanoparticle (NP) volume fractions up to 4 per cent, and Rayleigh numbers of 104, 105 and 106 were presented. Findings: The results showed that for low Ra (104) the heat transfer and entropy generation patterns were symmetric, whereas with increasing the Rayleigh number these patterns became asymmetric and more complex. Therefore, despite the symmetric boundary conditions imposed on the periphery of the enclosure (uniform in Ɵ), it was necessary to simulate the problem as three-dimensional instead of two-dimensional. The simulation results showed that by selecting the optimal values of heat flux distribution and NP volume fraction for these systems the energy consumption can be reduced, and consequently, the energy efficiency can be ameliorated. Originality/value: The results of the present study can be used for the design of energy devices such as thermal storage tanks, as both first and second laws of thermodynamics have been considered. Using the optimal design will reduce energy consumption. [ABSTRACT FROM AUTHOR]

The purpose of this study was to optimize the performance of a double-exposure solar cooker based on exergy efficiency. Two similar solar cookers with variable parabolic mirror position were used for this experimental research. The system's exergy depends on many variables, which were kept fixed with the exception of the mirror position and operation time. The mathematical model of exergy efficiency was obtained based on the experimental variables, which could be used to optimize the mirror positions at any time. As a result, a new system with a variable mirror on a parabolic curve was developed, which can yield up to 30% increased mean exergy efficiency. Validation of the results was carried out by both the variance analysis test and comparing with the experimental data. The experiments were carried out in Mashhad, Iran, at 37 latitude, 54 longitude, and a height of 985 m above sea level.