Abstract
Solar Water Heater (SWH) has low efficiency and the performance of this type of device needs to be improved to provide useful and ecological sources of energy. The passive techniques of augmentation heat transfer are an effective strategy to increase the convective heat transfer coefficient without external equipment. In this way, recent investigations have been done to study the potential applications of different inserts including wire coils, vortex generators, and twisted tapes for several solar thermal applications. However, few researchers have investigated inserts in SWH which is useful in many sectors where the working fluid operates at moderate temperatures. The longitudinal vortex generators (LVG) have been applied to promote heat transfer enhancement with a low/moderate pressure drop penalty. Therefore, the present work investigated optimal geometric parameters of LVG to enhance the heat transfer for a SWH at low Reynolds number and laminar flow, using a 3D periodical numerical simulation based on the Finite Volume Method coupled to the Genetic Algorithm optimization method (NSGA-II). The LVG was stamped over a flat plate inserted inside a smooth tube operating under a typical residential application corresponding to Reynolds numbers of 300, 600, and 900. The geometric parameters of LGV were submitted to the optimization procedure which can find traditional LVG such as rectangular-winglet and delta-winglet or a mix of them. The results showed that the application of LGVs to enhance heat transfer is an effective passive technique. The different optimal shapes of the LVG for all Reynolds numbers evaluated improved more than 50% of heat transfer. The highest augmentation heat transfer of 62% is found for the Reynolds number 900. However, the best thermo-hydraulic efficiency value is found for the Reynolds number of 600 in which the heat transfer intensification represents 55% of the pressure drop penalty.
Highlights
The heat exchangers (HE) are presented in several engineering applications such as automotive, aerospace industry, electronics devices, and chemical engineering
The present research evaluated by optimization procedure the impact of the geometric parameters of the longitudinal vortex generators (LVG) on the heat transfer for a solar water heater inserted in a circular tube
The performance of the heat transfer and pressure drop was numerically evaluated through the software ANSYS Fluent 19.2 coupled to Genetic Algorithm for optimization procedure
Summary
The heat exchangers (HE) are presented in several engineering applications such as automotive, aerospace industry, electronics devices, and chemical engineering. Some examples of HE applications include condensation and evaporation for refrigeration, cooling of fluids in power plants, the radiator of cars, cogeneration, and steam generation Design this type of equipment with a smaller possible size, higher heat transfer, and lower pressure drop penalty remains a great challenge for engineers and researchers, encouraging them to develop studies to find innovation to increase the performance of HE [1, 2]. The management of affordable energy such as solar sources is a global concern, mainly in nations that do not have a secure supply of energy or indiscriminately consume fossil fuel, rising environmental pollution due to pollutant emissions These issues could create instability for several countries which have a single principal resource of energy, increasing the importance to find alternatives to improve the performance of thermal systems such as solar thermal devices to provide useful and ecology alternative [4,5,6,7]
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