Comparison of Turbulent Flow and Heat Transfer in a Rectangular Channel with Delta Wing and Winglet Type Longitudinal Vortex Generators (original) (raw)
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HEAT TRANSFER ENHANCEMENT IN RECTANGULAR CHANNEL USING RECTANGLE WINGLET VORTEX GENERATOR
There are many applications in engineering industry that require heat addition or removal and a wide variety of heat exchange devices are used for different applications. Performance of improving coefficient of heat transfer becomes essential in all applications. Most of thermal devices like high temperature gas turbines, heat exchangers, electronic equipment, convective heat transfer plays a major role in most of the engineering applications. To attain higher coefficient of heat transfer, it is necessary that the surface of heat transfer flow is to be made turbulent. However, energy for producing such turbulence must come from the blower or fan and the maximum turbulence leads to excessive power requirement to make the air flow through the duct. Therefore, maximum turbulence must be produced in the region which is very near to surface of heat transfer i.e. in the laminar sub-layer only and this is done by using vortex generators. Vortex generator is responsible for creating the turbulence in the flow of fluid. The analysis is carried out to enhance the heat transfer coefficient with installing the rectangular winglet type of vortex generator in rectangular duct. These vortex generators are provided on bottom plate of the rectangular duct. These vortex generators cause stream wise longitudinal vortices in the test section which disrupt the growth of the thermal boundary layer and enhances heat transfer rate. Influence of geometrical parameter of rectangular winglet vortex generator such as winglet height, wings attack angle on heat transfer coefficient is studied. Air is taken as the working fluid; the flow regime is assumed to be laminar. By varying the above parameter, the heat transfer coefficient is calculated and by comparing all the result optimum height of rectangular winglet and attack angle is achieved
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
The vortex generators in the form of semi circular winglets with punched hole of different diameter at centroid position in-line and staggered manner were used in the present study to investigate heat transfer characteristics. In this experiment punched 45 0 inclined semicircular vortex generators were developed which were directly punched on thin aluminium plate. These vortex generators induced stream wise longitudinal vortices. These vortices disrupted the growth of the thermal boundary layer near the test plate and leads to enhancement of heat transfer between the air and surfaces. In this experiment semi circular vortex without hole, with holes of 3, 5 and 7mm diameters at centroid were used in in-line and staggered position and results were compared with each other. The heat transfer and friction factor data obtained was compared with the data obtained from flat smooth plate under similar geometric and fluid flow conditions. Measurements were carried out for a rectangular channel of an aspect ratio of AR = 1.12, for a winglet transverse pitch (S) to a longitudinal winglet height (e) ratio of S/e = 0.59, and a winglet height (e) to a channel height (H) ratio of e/H = 0.24. The Reynolds numbers considered were ranged from 16458 to 41147. The vortex generators with hole of 5 mm diameter at centroid in staggered position show a more significant increase in heat transfer 38.34 to 57.7% followed by vortex generators with hole of 5 mm diameter at centroid in in-line position(24.75-32.80%)as compared to the vortex generators without hole and with 3 and 7 mm hole diameter.
International Journal of Heat and Mass Transfer, 1993
Flow structure. heat transfer. and drag by longitudinal vortices generated by double rows of delta winglcts in transition channel llow arc investigated for the reduction of the gus side heat transfer resistance of compact heat exchangers. The experiments consist of flow visualization by laser light sheets, liquid crystal thermography for local heat transfer and balance measurcrnents for drag. Angle of attack and channel Reynolds number have been varied. Aligned delta winglct double rows show higher heat transfer enhancement than staggered. The critical angle of attack for the formation of longitudinal vortices is smaller behind the second row than behind the first. Heat transfer enhancements of 80% and drag increases of 160% have been found on wall areas 40 times the winglet area. The ratio of heat transfer enhancement and drag increase is larger for higher Reynolds numbers.
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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.
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.
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.
International Journal of Heat and Mass Transfer, 2012
In this study, the heat transfer and friction characteristics of four different rib geometries-45 angled, Vshaped, W-shaped and M-shaped ribs in a two-pass stationary channel have been numerically investigated. The aspect ratio (Height to Width) of the cooling channel was 1:1 (square). The rib pitch-to-rib height ratio (p/e) and the rib-height-to-channel hydraulic diameter ratio (e/D h) were 16 and 0.125 respectively. The Reynolds number was varied from 20,000 to 70,000. For the computations, the Reynolds averaged NaviereStokes (RANS) equations were solved with the commercial software ANSYS Fluent using the realizable version of k-ε (RKE) model. The heat transfer results were benchmarked with experiments on a test rig with similar geometries and flow conditions. Detailed analysis of the flow characteristics in the two-pass channel was carried out so as to understand the interaction of the ribinduced secondary flows and the bend-induced secondary flows and their contribution to heat transfer enhancement. The heat transfer enhancement provided by V-shaped ribs was 7% higher than 45 ribs, 28% higher than W-shaped ribs and 35% higher than M-shaped ribs. However, the pressure penalty for Vshaped ribs was 19% higher than 45 ribs, 24% higher than W-shaped ribs and 28% higher than M-shaped ribs. On comparing the overall thermal hydraulic performance, V-shaped and 45 ribs were observed to perform significantly better than W-shaped and M-shaped ribs.
International Mechanical and Industrial Engineering Conference 2018 (IMIEC 2018), 2018
Compact heat exchanger with gas as a heat exchange medium is widely used in power plants, automotive, air conditioning, and others. However, the gas has a low thermal conductivity resulting in high thermal resistance causing a low rate of heat transfer. Therefore an improvement to the convection heat transfer coefficient is necessary. One way to enhance the convection heat transfer coefficient is to use a longitudinal vortex generator. However, the increase in convection heat transfer coefficient is followed by an increase in pressure drop. Therefore, this work aims to improve the convection heat transfer coefficient with a low pressure drop. To achieve this goal, experiments were carried out by perforating a longitudinal vortex generator with a diameter of 5 mm with variations in holes number one, two and three. Two types of longitudinal vortex generators are compared. The experimental results show that the convection heat transfer coefficient for the case of perforated concave delta winglet vortex generator is only decreased by 1% from that without a hole, while the pressure drop is decreased by 11.6%.
THE 4TH BIOMEDICAL ENGINEERING’S RECENT PROGRESS IN BIOMATERIALS, DRUGS DEVELOPMENT, HEALTH, AND MEDICAL DEVICES: Proceedings of the International Symposium of Biomedical Engineering (ISBE) 2019
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.