Thermal-exergetic behavior of triangular vortex generators through the cylindrical tubes (original) (raw)
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Heat transfer augmentation in a circular tube with winglet vortex generators
Chinese Journal of Chemical Engineering, 2015
The article presents the influence of winglet vortex generators (WVG) placed in the core flow area on thermal performance enhancement of a tube heat exchanger. The experiment was carried out in a uniform wall heat-fluxed tube by varying turbulent airflow for Reynolds number ranging from 5300 to 24,000. In the present work, the WVGs with an attack angle of 30 o were inserted into the test tube at four different winglet pitch ratios (R P =P/D) and three winglet-width or blockage ratios (R B =e/D). The experimental results at various R P and R B values were evaluated and compared with those for smooth tube and tubes with twisted tape or wire coil. The measurement reveals that the WVGs enhance considerably the heat transfer and friction loss above the plain tube, wire coil and twisted tape. The Nusselt number and friction factor increase with the increment of R B and Re but with the decreasing R P. The average Nusselt numbers for the WVGs with various R B are in the range of 2.03-2.34 times above the plain tube. The thermal performance for the WVGs is found to be much higher than that for the wire coil and twisted tape and is in a range of 1.35-1.59. Also, a numerical investigation is conducted to study the flow structure and heat transfer enhancement mechanisms in the winglet-inserted tube.
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.
2021
In this research, a novel vortex generator (VG) is presented. The experimental and numerical investigations were carried out to study the micro thermal-hydraulic performance in a heated tube. The numerical results showed that the fluid in the core flow region and the near-wall region was fully mixed because of the longitudinal vortices created by the vortex generators. In addition, the experimental results showed that the heat transfer coefficient (h) decreased with the increasing pitch ratio (PR) value, while the friction coefficient exhibited the opposite trend. With the increasing ration angle (RA) numbers, the h values decreased while the f numbers increased. In addition, the maximum and minimum values of the fraction ratio were 1.66 and 4.27, while these values of the Nusselt number ratio were 1.24 and 1.83. The maximum thermal enhancement factor (TEF) was 1.21 when PR = 0.5, RA = 0° and Re = 9090. The heat transfer enhancement mechanism of the vortex generator is explained fro...
International Conference on Advance of Mechanical Engineering Research and Application (ICOMERA 2018), 2018
Improvement of heat transfer in fin and tube heat exchangers for improving energy efficiency is required to be performed. In the present study, an enhancement in the rate of heat transfer is done by manipulating fin geometry on the fin and tube using longitudinal vortex generators. Perforated concave delta winglet is introduced as the latest longitudinal vortex generator that can improve heat transfer better than previous vortex generators. Experimental study is conducted to investigate the thermal and hydraulic performance of perforated concave delta winglet vortex generators in a rectangular channel. From the results of the study, it is found that the heat transfer rate increases up to 78.9% of the baseline by using three pairs of concave delta winglet vortex generators with three holes. This value is 27.3% higher than using delta winglet vortex generator with three holes. However, this increase in heat transfer rate is also accompanied by an increase in pressure losses in the flow. Pressure drop increases up to five times from the baseline by installing three pairs of three-hole concave delta winglet vortex generators.
Numerical study of winglets vortex generator effects on thermal performance in a circular pipe
International Journal of Thermal Sciences, 2017
Various technologies have been developed to enhance heat transfer and, ultimately, to develop more efficient compact heat exchanging devices. In this research, heat transfer and wall friction in a pipe, with vortex generators (VGs) insert, are numerically investigated. The effects of different attack angles and blockage ratios of VGs fitted inside a smooth pipe are investigated. CFD simulations, with and without VGs insert, were conducted for an air flow with Reynolds numbers in the range 6000e33000 and for a constant heat flux on the pipe model surface. Four VGs are fitted in a circular pattern on the inner surface of the pipe. The different sets of delta winglets were characterized by four attack angles b (0 , 15 , 30 and 45) and three blockage ratios B (0.1, 0.2 and 0.3). The Nusselt number and friction coefficient results show the influence of the VGs insert on thermal performance. The results indicate that the best set of parameters for thermal performance enhancement (TPE) is b ¼ 30 and B ¼ 0.1. The internal flow behavior and the distribution of the Nusselt number, friction coefficient and turbulent kinetic energy, were explored to explain the effects of the VGs, with different configurations, on the overall Nusselt number, friction coefficient and thermal performance enhancement. The extent of the turbulent wake, in the axial direction, was estimated to explain the different performance of the configurations considered.
Heat Transfer, 2020
This experiment was carried out using delta winglet arrays of vortex generators (VG) with inline arrangement in a tube heat exchanger to study enhanced heat transfer and flow behaviour. The experiment was conducted for the turbulent flow (Re = 6000 to 27000). In this experiment, different parameters, pitch ratios (PR = 1.6, 2.4, and 4.8), lengths (L = 10, 15, and 20 mm), and attack angles (B = 0°, 10°, 20°, 30°, and 45°) were studied and then their effect on thermal performance was observed. Results indicate that the PR affected f and Nu significantly. For PR = 1.6, VGs showed the highest f and Nu for all of the cases. Vortex generators with L10 B45 PR4.8 achieved the best TPE with 1.23 at Re = 6000. Attack angle B indicated a significant impact on thermal performance and 45 degree showed the TPE of 1.23 at lower Re. Oil film flow and smoke flow visualization were employed to identify the flow vortices and understand flow mechanism. The oil film flow and smoke flow visua-lization clearly traced longitudinal vortex, and induced vortex, which induced impingement flow and re-circulation zone that lead to significant heat transfer enhancement. K E Y W O R D S delta winglet, flow visualization, inline arrays, longitudinal vortex, thermal performance, vortex generators Heat Transfer. 2020;1-21. wileyonlinelibrary.com/journal/htj
Journal of Mechanical Science and Technology, 2019
The effect of winglet height on the thermal-hydraulic performance of finned tube heat exchanger (FTHE) is investigated numerically. The rectangular winglet pairs (RWPs) having 5° attack angle are placed in common flow up (CFU) manner adjacent to the tubes for analysis. The air-side performance evaluation has been done based on the area goodness factor (j/f). The working fluid (air) is considered as incompressible fluid. Additionally, MOORA (multi objective optimization on the basis of ratio analysis) method is employed to get the best performance order of various configurations by taking Nusselt number (Nu) and area goodness factor (j/f) as beneficial attributes and friction factor (f) as a non-beneficial attribute having equal significances. The present study reveals that the rectangular vortex generators having 60 % of the channel height provides the better thermal hydraulic performance compared to the other considered cases.
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