Asker, Mustafa; Alptekin, Ersin; Ezan, Mehmet Akif; Ganjehsarabi, Hadi

In this study, the utilisation of composite phase change materials (PCMs) slabs with fins in a thermal energy storage (TES) system is numerically analysed. The storage system consists of three PCM layers at different melting temperatures. First, the predicted results are verified against the analytical solution that is taken from literature. Afterwards, the influence of the design parameters such as fin length and fin spacing on time for complete melting of the multi-layer TES are examined. Custom field functions are integrated into the ANSYS-FLUENT software to assess the local and volume averaged entropy generation within the system. The results show that at constant fin spacing, that increasing fin length from 20 mm to 80 mm enhances the melting rate up to 50%. In addition, when the fin spacing is doubled, the elapsed time for complete melting decreased about 37%. Moreover, the fin arrangement has a considerable effect on entropy generation.

Ganjehsarabi, Hadi; Dincer, Ibrahim; Gungor, Ali

In this paper, comprehensive thermodynamic analysis and optimisation of a cascade active magnetic regenerative refrigeration system are performed. A parametric study is conducted to investigate the effects of various design parameters on the cycle performance through energy and exergy efficiencies. A multi-objective optimisation method based on a fast and elitist non-dominated sorting genetic algorithm is applied to determine the best design parameters for the system. Two objective functions utilised in the optimisation study are the total cost rate of the system and the system exergy efficiency. The total cost rate of the system is minimised while the cycle exergy efficiency is maximised using an evolutionary algorithm. To provide insight, the Pareto frontier is shown for a multi-objective optimisation. The results show that exergy efficiency could be increased by 14.53% using exergy-based optimisation and the cost could be reduced by 12% using the cost-based optimisation.

Tandiroglu, Ahmet

This paper presents the resülts of an experimental investigation of transient forced convective heat transfer for turbulent flow of nine circular tubes with baffle plate inserts using different pitch to tube inlet diameter ratios and baffle orientation angles in the range of Reynolds number 3000 < Re < 20000 in the case of constant heat flux. The characteristic parameters of the tubes are: pitch to tube inlet diameter ratio H/D — 1, 2 and 3; baffle orientation angle ß — 45, 90 and 180 degree. Air, having a Prandtl number of 0.71 was used as the working fluid, while stainless steel was considered as the pipe material. The data show that unsteady entropy generation numbers for the baffled tubes are higher than those from the steady one. A generalised correlation for the unsteady entropy generation number relative to the steady dimensional entropy generation number for the baffle inserted tubes has been developed.