Effect of perforated concave delta winglet vortex generators on heat transfer augmentation of fluid flow inside a rectangular channel: An experimental study (original) (raw)
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A compact heat exchanger can be found in air conditioning, automotive industry, chemical processing, etc. Most compact heat exchangers use gas as a heating or cooling fluid. However, gas has high thermal resistance, which affects lower heat transfer. In order to reduce thermal resistance on the gas side, the convection heat transfer coefficient is increased. One effective way to enhance the convection heat transfer coefficient is to use a vortex generator. Vortex generators are surface protrusions that are able to manipulate flow resulting in an increase in convection heat transfer coefficient by enhancing the mixture of air near the wall with the air in the main flow. Therefore, this work aims to evaluate the thermal and hydraulic characteristics of airflow through the perforated concave delta winglet vortex generator. This study was conducted on delta winglet vortex generators (DW VGs) and concave delta winglet vortex generator (CDW VGs) with the 45 angle of attack with a number of hole three-holes that applied on every vortex generator with one-line fitting, two-line fitting, and three-line fitting respectively. Results of simulation revealed that heat transfer coefficient (h) for perforated CDW VGs decrease 16.07% and pressure drop decrease 7% compare to that without hole configuration at Reynolds number of 8600. Convection heat transfer coefficient for perforated DW VGs decrease 13.76% and pressure drop decrease 5.22% compare to delta winglet without hole at Reynolds number of 8600.
International Journal of Heat and Technology, 2019
This study is intended to analyze numerically and experimentally the characteristics of heat transfer augmentation and pressure drop of airflow through vortex generators mounted to a heated plate inside a rectangular channel. Delta winglet pairs (DWPs) and concave delta winglet pairs (CDWPs) vortex generators (VGs) with one, two, and three rows were used in this study. Heat transfer enhancement and pressure drop of flow passing through the VGs with a 5 mm diameter hole for one, two, and three holes in certain positions were investigated. VGs were mounted in-line with an attack angle of 15° to the flow. The airflow was assumed to be incompressible; the steady-state and air velocity were varied in the range of 0.4 m/s to 2 m/s. The analysis showed that the use of holes in the delta winglet vortex generators could reduce the pressure drop of 34.14% from the delta winglet without holes at a velocity of 2 m/s. By using perforated delta (DWP VGs) and concave delta winglet (CDWP VGs), the heat transfer coefficient is reduced by 1.81% and 7.03% of the delta and concave delta winglet vortex generators without holes at a velocity of 2 m/s.
Heat transfer augmentation techniques are used in heat exchanger, air conditioning, chemical reactors and refrigeration systems. Many techniques have been investigated to enhance heat transfer rate and decrease the size and cost of involving equipment. Among different techniques delta winglet vortex generators become popular in recent days. It generates stream wise vortices which creates high turbulence in fluid flow over the heat transfer surface and shows a very good heat transfer performance. This study presents recent works taken by researchers on delta winglet vortex generators to enhance thermal efficiency in heat exchange with different types and arrangements of delta winglet vortex generators.
Fluids
Passive methods using vortex generators (VGs) to enhance heat transfer have been a concern of researchers in recent decades. This study is intended to investigate the strength of the vortex generated by VGs by trying to reduce the pressure drop in the flow. The present work also takes into account the influence of the vortex intensity on the improvement of heat transfer, which can be indicated by the low value of the synergy angle. Experiments were carried out in the current investigation to validate the results of the numerical simulations in the Reynolds number range of 3102 to 16,132. The study results indicate that the observed heat transfer coefficients from the experimental and simulation results have a similar tendency with relatively small errors. A reduction in pressure drop is observed with the use of perforated concave rectangular winglets (PCRWs) against the nonperforated ones although there was a slight decrease in heat transfer improvements.
European Journal of Engineering and Technology Research, 2021
Vortex generators (VGs) are one of the effective passive models used to increase the heat transfer rate in heat exchangers. In this experiment, heat transfer from six cylinders heated to the airflow was improved by attaching rectangular winglet vortex generators (RWVGs) to a plate in a rectangular channel. The installation aimed to increase the value of the thermal-hydraulic performance evaluation criteria in the line. This experimental study was carried out by varying the fluid flow velocity from 0.4 m/s to 2 m/s with an interval of 0.2 m/s in the channel. Three pairs of VGs were arranged in both in-line and staggered configurations. The experimental results show that the thermal-hydraulic performance evaluation criteria for three pairs of vortex generators in the staggered configuration was 15.17% higher than the baseline, while the thermal-hydraulic performance of the in-line arrangement was 1.54% higher than the staggered one.
Numerical simulation of Heat Transfer Enhancement in A channel Flow by Rectangular Winglet Vortex Generator, 2021
A numerical simulation was performed to investigate the effects of longitudinal vortices on the heat transfer enhancement of a laminar flow in a rectangle duct mounted with rectangular winglet pair on the bottom wall. A CFD ANSYS Fluent software was used to compute the 3-D steady viscous flows with heat transfer. The effects of Reynolds number ranging from 250 to 2000, winglet heights and different attack angles of the vortex generators were studied. The comparisons of the fluid flow and heat transfer characteristics for the cases with and without rectangular winglet pair were carried out using parameters such as the Nusselt number, the friction coefficient and performance evaluation criteria PEC to gauge the overall efficiency of the system. Results show that mounting rectangular winglet pair on a channel flow can significantly enhance heat transfer. The distributions of secondary flow on the cross sections are consistent with the distributions of Nu and f for different attack angles. The results show that there is a 11-29% increase in the Nusselt number for channels with LVGs, while the friction factor increased by 19-30%, causing the overall PEC to increase by 4-18%, for the studied range of Reynolds number. Under constant geometrical
International Journal of Heat and Technology
Longitudinal vortex generators (LVG) over the last decades have been investigated to enhance heat transfer in rectangular channels with different design to obtain high thermal performance (TEF). In this investigation, the shear-stress transport (SST) k-ε model is used to model the turbulence. The turbulent flow and heat transfer, using delta wing (DW), delta winglet pair (DWP), DWP inclined (DWPI) and rectangular winglet pair curved (RWPC) was compared in a rectangular channel. The best TEF by 1.26 was obtained using DW for Reynolds number of 2800. The DW is a simple to manufacture LVG, and the TEF is only a little lower compared to other new, complex to manufacture, conic type LVG recently found in the literature.
International Journal of Technology
The numerical simulation of heat transfer and pressure drop characteristics was carried out on the airflow through a rectangular channel-mounted vortex generator (VG). The VG was installed on a plate that was attached to the heater. The inlet velocity of the airflow varied from 0.4 to 2.0 m/s. The VGs used in this study were concave delta winglet pairs (CDWPs) with the attack angle of 30° and with variation in the number of rows: one pair, two pairs, and three pairs. The CDWPs are predicted to produce the longitudinal vortex (LV), which increases the intensity of turbulence resulting in better mixing of flow. This, in turn, can improve the heat transfer between the plate surface and the airflow in the rectangular channel. The results showed that the installation of CDWPs does improve the overall heat transfer performance. However, it has the consequences of a greater pressure drop. Based on the variation in the number of rows, the greater the number of pairs of VGs was the greater the convection heat transfer coefficient (h) in both laminar and turbulent flows. The h value was based on the number of row of CDWPs: one pair, two pairs, and three pairs exhibited increases of 65.9108.4%; 34.471%; and 42.2110.7% compared to the baseline, respectively. A great number of rows of VGs also led to an increasing pressure drop value in laminar and turbulent flows. The percentage increases in pressure drop for CDWPs with one pair, two pairs, and three pairs, as compared to the baseline, were 70.192.1%; 123.6161.3%, and 180266.9%, respectively.