Abstract
The solidification process in a multi-tube latent heat energy system is affected by the natural convection and the arrangement of heat exchanger tubes, which changes the buoyancy effect as well. In the current work, the effect of the arrangement of the tubes in a multi-tube heat exchanger was examined during the solidification process with the focus on the natural convection effects inside the phase change material (PCM). The behavior of the system was numerically analyzed using liquid fraction and energy released, as well as temperature, velocity and streamline profiles for different studied cases. The arrangement of the tubes, considering seven pipes in the symmetrical condition, are assumed at different positions in the system, including uniform distribution of the tubes as well as non-uniform distribution, i.e., tubes concentrated at the bottom, middle and the top of the PCM shell. The model was first validated compared with previous experimental work from the literature. The results show that the heat rate removal from the PCM after 16 h was 52.89 W (max) and 14.85 W (min) for the cases of uniform tube distribution and tubes concentrated at the bottom, respectively, for the proposed dimensions of the heat exchanger. The heat rate removal of the system with uniform tube distribution increases when the distance between the tubes and top of the shell reduces, and increased equal to 68.75 W due to natural convection effect. The heat release rate also reduces by increasing the temperature the tubes. The heat removal rate increases by 7.5%, and 23.7% when the temperature increases from 10 °C to 15 °C and 20 °C, respectively. This paper reveals that specific consideration to the arrangement of the tubes should be made to enhance the heat recovery process attending natural convection effects in phase change heat storage systems.
Highlights
The governing equation in this case for 2D laminar, incompressible, transient, and Newtonian fluid flow are provided as follows, built on the enthalpy-porosity technique defined by Brent et al [67] considering the assumptions of employing a Boussinesque approximation for natural convection effects due to low-temperature variation in the domain [67], and neglecting viscous dissipation because of the non-appearance of high velocities [67]:
This is due to the fact that hot liquid phase change material (PCM) tends to travel upward, and warm streams always settle at the top of the enclosure; the density of the warm liquid PCM is lower than that of the cold solid PCM
A geometrical model of an LHTES system cooled by heat-transfer fluid (HTF) channels was analytically
Summary
Comprehensive socio-economic changes are coupled with higher requirements of major energy sources, while the global demand for energy supply have increased by 1.5 times creativecommons.org/licenses/by/. The shell and tube thermal exchanger combined with extended surfaces is an ideal case because of the high heat transfer performance, its simple design, and its easier combination in applications This unit is based on the PCM’s position and the number and location of tubes, which are categorized into several types, including pipe, cylinder, and multi-tube [46]. Talebzadehsardari et al [36] analyzed the optimum shape and location of airflow pipes on the discharging process of a combined metal foam-PCM unit They found that the solidification time dropped by 57%, and the temperature difference between both ends of the discharging rate improved by three times compared with the unit with the straight air tube. The current work, with the novel idea, aimed to scientifically optimize and design the efficiency of a shell-and-tube LHTES to increase the solidification rate and improve the thermal rate from the PCM to the HTF. The aim was to move the HTF tubes’ location through the PCM area to reach the best location and take full benefit of free convection flows to reduce the discharging time
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