Effect of the angle of attack of a rectangular vortex generator on the heat transfer in a parallel plate flow

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Heat Transfer and Pressure Drop in a Developing Channel Flow with Streamwise Vortices

Experiments to assess the heat transfer and pressure-drop effects of delta-wing vortex generators placed at the entrance of developing channel flows are reported in this study. The experimental geometry simulates common heat exchanger configurations and tests are conducted over a velocity range important to heating, air conditioning and refrigeration. An innovative liquid-crystal thermography technique is used to determine the local and average Nusselt numbers for an isoflux channel wall, and conventional methods are used to determine the Fanning friction factor. Vortex generators with aspect ratios of A = 2 and A = 4 are studied at attack angles of a. = 20?? to 45????. The results indicate that the streamwise vortices generated by a delta wing can enhance local Nusselt numbers by more than 200% in a developing channel flow. Under some conditions, the spatially average Nusselt number nearly doubled for a heat transfer area that was 37 to 63 times the wing area. The Fanning friction factor increased by a few percent to nearly 60%, depending on the Reynolds number.Air Conditioning and Refrigeration Project 4

Performance Evaluation of Vortex Generator of Finite Thickness to Augment Heat Transfer in a Compact Heat Exchanger

The effect of non dimensional thickness of a winglet type vortex generator is investigated in terms of heat transfer rate, stream-wise vortices and flow losses in a plate fin heat exchanger with triangular inserts as secondary fins. The winglet type vortex generators are mounted alternatively on the upper and lower plates of the heat exchanger to disrupt the flow in the triangular domain formed by the inserts. The fluid flow within the duct is considered to be confined and laminar. While the hydrodynamic flow is fully developed, the thermal characteristics are assumed to be in developing stage under isothermal boundary conditions. The winglet is located in the duct where the flow is fully developed (Xi = 2.765 w.r.t. leading edge) at an angle of 27o with respect to the bulk flow direction. The aforesaid performance characteristics are computed numerically by solving the mass continuity, momentum and energy equations. Computational results clearly show an enhancement of 12.91% in the heat transfer rate (quantified as Num/ Nuo) for an increase in non dimensional thickness c/2H from 0.00 to 0.05. Besides, the pressure drop penalty is found to be only 3.8% at Re = 150. The results have also been substantiated by carrying out experiments on a scaled model configuration. Three dimensional velocity components are verified behind the winglet to ensure the stable flow field for non dimensional thickness of winglet c/2H=0.05 and Reynolds number of 350

An Experimental Study on the Effect of Shape and Location of Vortex Generators Ahead of a Heat Exchanger

An experimental study is carried out on the effect of vortex generators (Circular and square) on the flow and heat transfer at variable locations at (X = 0.5, 1.5, 2.5 cm) ahead of a heat exchanger with Reynolds number ranging from 62000< Re < 125000 and heat flux from 3000 ? q ? 8000 W/m2 .In the experimental investigation, an apparatus is set up to measure the velocity and temperatures around the heat exchanger. The results show that there is an effect for using vortex generators on heat transfer. Also, heat transfer depends on the shape and location. The circular is found to be the best shape for enhancing heat transfer at location [Xm=0.5 cm] distance before heat exchanger is the best location for enhancing heat transfer. The square is the best shape for enhancing heat transfer at location [Xm=2.5 cm] distance before heat exchanger is the best location for enhancing heat transfer.The results of flow over heat exchanger with vortex generators are compared with the flow over heat exchanger without vortex generators. Heat transfer around heat exchanger is enhanced (56%, 50%, 36%) at location (X=0.5, 1.5, 2.5cm) respectively by using circular vortex generators without turbulator and heat transfer around heat exchanger is enhanced (39%, 42%, 51%) at location (X=0.5, 1.5, 2.5cm) respectively by using square shape vortex generators without turbulator

Effect of the angle of attack of a rectangular wing on the heat transfer enhancement in channel flow at low Reynolds number

Convective heat transfer enhancement can be achieved by generating secondary flow structures that are added to the main flow to intensify the fluid exchange between hot and cold regions. One method involves the use of vortex generators to produce streamwise and transverse vortices superimposed to the main flow. This study presents numerical computation results of laminar convection heat transfer in a rectangular channel whose bottom wall is equipped with one row of rectangular wing vortex generators. The governing equations are solved using finite volume method by considering steady state, laminar regime and incompressible flow. Three-dimensional numerical simulations are performed to study the effect of the angle of attack α of the wing on heat transfer and pressure drop. Different values are taken into consideration within the range 0° &lt; α &lt; 30°. For all of these geometrical configurations the Reynolds number is maintained to Re = 456. To assess the effect of the angle of attack on the heat transfer enhancement, Nusselt number and the friction factor are studied on both local and global perspectives. Also, the location of the generated vortices within the channel is studied, as well as their effect on the heat transfer enhancement throughout the channel for all α values. Based on both local and global analysis, our results show that the angle of attack α has a direct impact on the heat transfer enhancement. By increasing its value, it leads to better enhancement until an optimal value is reached, beyond which the thermal performances decrease

Vortex Induced Convective Heat Transfer Augmentation

Delta winglet is an effective means to passively augment heat convection from a hot surface such as a solar panel. The effects of an inclination angle on the flow downstream of the winglet were studied. A delta winglet with an aspect ratio (c/h) of 2 and an attack angle of 30 degrees was mounted on a flat plate to scrutinize the role of its inclination angle (90° and 120°) on the flow downstream. The inclined winglet was placed in a wind tunnel, and the flow was measured by the hotwire. The experiment shows the 120-degree-inclination-angle delta winglet can generate an inflow velocity larger than 90 degrees. The heat transfer enhancement caused by the delta winglet was then investigated. Three different inclination angles (60°, 90° and 120°) of the delta winglet were studied, and a thermal camera was used to maintain the heat transfer enhancement of the heated panel. The result shows that the delta winglet with the inclination angle of 120 degrees can generate the best thermal performance

Numerical Study of Thermal Performance Improvement By Novel Structures in the Building Energy Storage Systems

In this work, numerical studies were conducted to investigate the effectiveness of two fin-like novel structures used for heat-transfer enhancement in two building energy storage systems including thermal energy storage and battery energy storage. Firstly, thin layer ring structure was numerically investigated for thermal performance improvement in the thermal energy storage. From the results obtained in this study, the area ratio can be increased by 4% when using the thin layer ring during the same time period. The thin layer ring structure can shorten ice formation period and increase its efficiency. Further study was conducted for the factorial analysis of three parameters, including thickness, material and arrangement of thin layer ring. From the results, it shows that ice formation period can be shortened with the increase of conductivity and area of thin layer ring, while it is also dependent on thickness. Using Taguchi method, the statistic results show that material has the greatest impact on ice increased area. After that, arrangement has relatively less influence on ice increased area. However, thickness has the trifling effect on ice-increased area. The optimal combination of each factor (parameter) has been determined, and the optimal condition is A3B2C1. That is to say, for material = copper, thickness = 1mm，and arrangement = staggered, the best result of heat-transfer enhancement was obtained among all the cases studied. The reproducibility of these conditions has been verified by two analytical results. Secondly, in battery energy storage, numerical simulations have been conducted to explore the air flow and heat transfer at different discharging rates in a horizontal rectangular channel with two different configurations of vortex generator (VG), such as rectangular rib and delta winglet. The simulation in air flow domain with characteristics of heat transfer and flow structure show that both types of vortex generators can enhance heat transfer before VGs, but only delta winglet VG can still enhance local heat transfer after it due to more vortices generated that can mix cold and hot air flow between the top and bottom thermal layers completely. The encouraging result shows that the maximum temperature of pouch cell can be decreased more by delta winglet than by rectangular rib. For the discharging rate at 5C, it can be decreased by 10% and the local Nusselt number can be increased by 38% compared to the baseline scenario without any VGs

Engineering Flow Turbulence for Transport Enhancement

The cooling of solar photovoltaic panels is not only critical, due to the dropping of cell efficiency with the increased temperature, but also challenging, since the heat transfer enhancement must be accomplished without blocking the sun radiation. Longitudinal vortices can be generated by small geometries and last a long distance, thus it is suitable to be applied on solar photovoltaic panels. Delta winglet is one of the most effective longitudinal vortex generators. This work presents four papers, one on the importance of cooling solar panels and three on the investigations and optimizations of the delta winglet. In the first paper, the mitigation effect by solar panels on climate change, as well as the possible beneficial outcomes by employing turbulence generators is discussed. The second paper studies the flow structure of the longitudinal vortex generated by a delta winglet with an aspect ratio of 2 and an attack angle of 30 degrees. It is followed by a paper that investigates the influence of aspect ratio on the flow behavior, and its effect on heat transfer is studied in Appendix A. The final paper presents the impact of attack angle on the heat transfer and correlates the heat transfer with the flow parameters

Numerical investigation of heat transfer and pressure loss of flow through a heated plate mounted by perforated concave rectangular winglet vortex generators in a channel

The low thermal conductivity of air in fin-and-tube heat exchangers causes high thermal resistance of the air side and results in a low heat transfer rate. This heat transfer rate on the air side can be improved by increasing the heat transfer coefficient. One way to increase the heat transfer coefficient on the air side is to use a vortex generator (VG), which can generate longitudinal vortex (LV) increasing fluid mixing. Therefore, this study aims to numerically analyze heat transfer characteristics and pressure drop of airflow through a heated plate by installing VG in a rectangular channel. Vortex generators (VGs) used in numerical modeling are rectangular winglet pairs (RWPs) and concave rectangular winglet pairs (CRWPs) with 30 attack angle. The number of pairs of VG is varied by one, two, and three with/without holes. The velocity of airflow varies in the range of 0.4-2.0 m/s at intervals of 0.2 m/s. The simulation results show that in the configuration of the three pairs of VG, the decrease in the convection heat transfer coefficient in the case of the perforated CRWP is 3.98% of the CRWP without holes at a velocity of 2.0 m/s. While in the configuration of three pairs of perforated RWP VGs, the decrease in convection heat transfer coefficient is 5.87% from RWP without holes at a velocity of 2.0 m/s. In the configuration of three pairs of perforated VGs at the highest velocity, the decrease in pressure drop in the CRWP and RWP cases is 30.73% and 13.87% of the VGs without holes, respectively