The Experts below are selected from a list of 8325 Experts worldwide ranked by ideXlab platform
Junmei Wu - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the performance of a novel fin tube air heat exchanger with punched longitudinal Vortex Generator
Energy Conversion and Management, 2012Co-Authors: Junmei Wu, Hua Zhang, Yi WangAbstract:Abstract To enhance the heat transfer of fin-tube surface, two kinds of novel fin-tube surfaces with two rows of tubes in different diameter, arranged in staggered pattern are presented. Along the direction of air flow, the diameter of the first transverse row of tubes is smaller than that of the second. Delta winglet pairs working as longitudinal Vortex Generators are punched only around the first transverse row of tubes in reduced size, with either “common flow up” or “common flow down” orientation. The performances of two new types of air heat exchangers using the novel fin-tube surfaces (referred as SA and SB) and one traditional plain fin-tube heat exchanger (named BL) acting as baseline in contract are experimentally studied under dry-surface conditions. On the condition of the minimum cross velocity in heat exchanger u max = 4.0 m/s, air-side convective heat transfer coefficients of SA and SB increases by 16.5% and 28.2%, respectively, in comparison with that of BL. The air-side pressure drop decreases less than 10% for SA, and slightly decreases for SB, compared with the baseline heat exchanger. The present results show that one can achieve heat transfer enhancement accompanying with a reduction of pressure loss using the strategies of fin-tube surface, longitudinal Vortex Generator design and appropriate placement on the fin-tube surfaces.
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numerical study on laminar convection heat transfer in a channel with longitudinal Vortex Generator part b parametric study of major influence factors
International Journal of Heat and Mass Transfer, 2008Co-Authors: Junmei WuAbstract:Abstract This paper presents the influences of main parameters of longitudinal Vortex Generator (LVG) on the heat transfer enhancement and flow resistance in a rectangular channel. The parameters include the location of LVG in the channel, geometric sizes and shape of LVG. Numerical results show that the overall Nusselt number of channel will decrease with the LVGs’ location away from the inlet of the channel, and decrease too with the space between the LVG pair decreased. The location of LVG has no significant influence on the total pressure drop of channel. With the area of LVG increased, the average Nusselt number and the flow loss penalty of channel, especially when β = 45° will increase. With the area of LVG fixed, increasing the length of rectangular winglet pair Vortex Generator will bring about more heat transfer enhancement and less flow loss increase than that increasing the height of rectangular winglet pair Vortex Generator. With the same area of LVG, delta winglet pair is more effective than rectangular winglet pair on heat transfer enhancement of channel, and delta winglet pair-b is more effective than delta winglet pair-a. Delta winglet pair-a results in a higher pressure drop, the next is rectangular winglet pair and the last is delta winglet-b. The increase of heat transfer enhancement is always accompanied with the decrease of field synergy angle between the velocity and temperature gradient when the parameters of LVG are changed. This confirms again that the field synergy is the fundamental mechanism of heat transfer by longitudinal Vortex. The laminar heat transfer of the channel with punched delta winglet pair is experimentally and numerically studied in the present paper. The numerical result for the average heat transfer coefficient of the channel agrees well with the experimental result, indicating the reliability of the present numerical predictions.
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numerical study on laminar convection heat transfer in a rectangular channel with longitudinal Vortex Generator part a verification of field synergy principle
International Journal of Heat and Mass Transfer, 2008Co-Authors: Junmei WuAbstract:This study presents numerical computation results on laminar convection heat transfer in a rectangular channel with a pair of rectangular winglets longitudinal Vortex Generator punched out from the lower wall of the channel. The effect of the punched holes and the thickness of the rectangular winglet pair to the fluid flow and heat transfer are numerically studied. It is found that the case with punched holes has more heat transfer enhancement in the region near to the Vortex Generator and lower average flow frictional coefficient compared with the case without punched holes. The thickness of rectangular winglet can cause less heat transfer enhancement in the region near to the Vortex Generator and almost has no significant effect on the total pressure drop of the channel. The effects of Reynolds number (from 800 to 3000), the attack angle of Vortex Generator (15°, 30°, 45°, 60° and 90°) were examined. The numerical results were analyzed from the viewpoint of field synergy principle. It was found that the essence of heat transfer enhancement by longitudinal Vortex can be explained very well by the field synergy principle, i.e., when the second flow generated by Vortex Generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient, the heat transfer in the present channels will be enhanced. Longitudinal vortices (LVs) improve the synergy between velocity and temperature field not only in the region near LVG but also in the large downstream region of longitudinal Vortex Generator. So LVs enable to enhance the global heat transfer of channel. Transverse vortices (TVs) only improve the synergy in the region near VG. So TVs can only enhance the local heat transfer of channel.
M Khoshvaghtaliabadi - One of the best experts on this subject based on the ideXlab platform.
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thermal hydraulic characteristics of plate fin heat exchangers with corrugated Vortex Generator plate fin cvgpf
Applied Thermal Engineering, 2016Co-Authors: M Khoshvaghtaliabadi, M Khoshvaght, P RahnamaAbstract:Abstract Plate-fin heat exchangers (PFHEs), after tubular heat exchangers, are the most common types of heat exchange instruments in thermal engineering applications. In the present work, a new design of the plate-fin, namely, corrugated/Vortex-Generator plate-fin (CVGPF), is proposed and studied. It is designed based on the corrugated plate-fin (CPF) and the Vortex-Generator plate-fin (VGPF) configurations. It is anticipated that this enhanced plate-fin can be a great choice in the PFHEs. Influences of the most effective geometrical parameters of CPF, VGPF, and CVGPF on thermal-hydraulic performances of the PFHEs are investigated and appraised. Water/ethylene glycol mixtures (100:0, 90:10, and 75:25 by mass) are selected as working fluid to examine the effects of coolant. The results show that at the same geometrical and operating conditions, the CVGPF channel has the best thermal-hydraulic performances, and the CPF and VGPF channels come in the second and third, respectively. It is also detected that the working fluid with the higher mass fraction of ethylene glycol has lower values of Nusselt number, and the effect of that on the friction factor is not considerable. However, the overall thermal-hydraulic performances of all plate-fins improve, as the mass fraction of ethylene glycol in the working fluid increases.
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an experimental study on Vortex Generator insert with different arrangements of delta winglets
Energy, 2015Co-Authors: M Khoshvaghtaliabadi, O Sartipzadeh, A AlizadehAbstract:Heat transfer enhancement in a tube using the VG (Vortex-Generator) insert with different arrangements of the delta-winglets is investigated. Fourteen VG inserts with the longitudinal and forward arrangement of the delta-winglets are made from the aluminum sheets with a length of 350 mm, a width of 14.5 mm, and a thickness of 0.6 mm. The heat transfer and pressure drop results achieved from the use of the VG inserts inside the tube are compared with those obtained for the plain tube. It is found that at the transitional flow through the plain tube, Notter-Rouse equation predicts the current experimental Nusselt number better than Gnielinski equation. Also, the experimental results reveal that the use of the VG inserts inside the tube yields higher heat transfer coefficient and pressure drop than the plain tube, and these parameters augment with increasing the delta-winglets. The appropriate tradeoff between the enhanced heat transfer and the friction is found by using a special arrangement of the delta-winglets on the VG insert which presents the highest heat transfer coefficient as well as the maximum values of considered PEC (performance evaluation criterion). The maximum PEC of 1.41 is found for this VG insert at Re = 8715.
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performance of a plate fin heat exchanger with Vortex Generator channels 3d cfd simulation and experimental validation
International Journal of Thermal Sciences, 2015Co-Authors: M Khoshvaghtaliabadi, S Zangouei, F HormoziAbstract:Abstract A type of plate-fin channel with rectangular wings as a transverse Vortex-Generator channel was considered. The heat transfer and fluid flow characteristics of the Vortex-Generator channel were systematically analyzed by 3D-CFD simulations. As the first part of project, a precise and reliable experimental setup was designed and fabricated to generate a constant temperature boundary condition. Inlet–outlet bulk and surface temperatures along with flow rate data were acquired by using pt-100 and K series calibrated thermocouples and an ultrasonic flow meter, respectively. Hence, boundary conditions for the CFD simulations were well defined, and data for the validation of a reference model were generated. Comparing the experimental data with the predicted results by CFD simulation implies that the applied CFD approach can properly predict the thermal-hydraulic specifications of the Vortex-Generator channel. In the second part of the project, the influences of seven effective geometrical parameters (i.e. wings height, wings width, channel length, longitudinal wings pitch, transverse wings pitch, wings attach angle, and wings attack angle) for three conventional coolants flow (i.e. water, oil, and ethylene glycol) at the laminar flow regime were evaluated. As the third part of the project, general correlations were derived for Nusselt number of the coolants flow inside the plate-fin heat exchangers with Vortex-Generator channels.
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effects of geometrical parameters on performance of plate fin heat exchanger Vortex Generator as core surface and nanofluid as working media
Applied Thermal Engineering, 2014Co-Authors: M Khoshvaghtaliabadi, F Hormozi, A ZamzamianAbstract:Abstract Forced convective heat transfer with laminar and steady-state flow of copper-base deionized water nanofluid inside the Vortex-Generator plate-fin channels was studied experimentally and also numerically using CFD method. In the experimental section, a setup with capability to provide a constant wall temperature condition was fabricated. Single-phase (homogeneous) and two different two-phase (mixture and Eulerian) models were accomplished for temperature dependent thermo-physical properties in the numerical section. For the case under consideration, the mixture model gives closer predictions of the convective heat transfer coefficient to the experimental data than the homogeneous and Eulerian models. For nanofluids under consideration, the average relative error of Nusselt number between experimental data and CFD results based on mixture model was about 3.0%. Also, it was illustrated that the homogeneous and Eulerian models underestimated Nusselt number. Influences of two operating factors (i.e. Reynolds number and nanoparticles concentration) and seven geometrical parameters (i.e. wing height, wing width, channel length, longitudinal wings pitch, transverse wings pitch, wings attach angle, and wings attack angle) were investigated on performance of a plate-fin heat exchanger with Vortex-Generator channels. Finally, two correlations were developed for Colburn factor and Fanning friction factor variations based on Reynolds number, nanoparticles weight fraction, and geometrical parameters.
Yuwen Zhang - One of the best experts on this subject based on the ideXlab platform.
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numerical study of heat transfer enhancement by punched winglet type Vortex Generator arrays in fin and tube heat exchangers
International Journal of Heat and Mass Transfer, 2012Co-Authors: Y L He, Yuwen ZhangAbstract:Abstract The potential of punched winglet type Vortex Generator (VG) arrays used to enhance air-side heat-transfer performance of finned tube heat exchanger is numerically investigated. The arrays are composed of two delta-winglet pairs with two layout modes of continuous and discontinuous winglets. The heat transfer performance of two array arrangements are compared to a conventional large winglet configuration for the Reynolds number ranging from 600 to 2600 based on the tube collar diameter, with the corresponding frontal air velocity ranging from 0.54 to 2.3 m/s. The effects of different geometry parameters that include attack angle of delta winglets (β = 10 deg, β = 20 deg, β = 30 deg) and the layout locations are examined. The numerical results show that for the punched VG cases, the effectiveness of the main Vortex to the heat transfer enhancement is not fully dominant while the “corner Vortex” also shows significant effect on the heat transfer performance. Both heat transfer coefficient and pressure drop increase with the increase of attack angle β for the side arrangements; the arrays with discontinuous winglets show the best heat transfer enhancement, and a significant augmentation of up to 33.8–70.6% in heat transfer coefficient is achieved accompanied by a pressure drop penalty of 43.4–97.2% for the 30 deg case compared to the plain fin. For the front arrangements of VGs higher heat transfer enhancement and pressure drop penalty can be obtained compared to that of the side arrangement cases; the case with front continuous winglet arrays has the maximum value of j/f, a corresponding heat transfer improvement of 36.7–81.2% and a pressure drop penalty of 60.7–135.6%.
Jiangbo Wu - One of the best experts on this subject based on the ideXlab platform.
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effect of longitudinal Vortex Generator on heat transfer in rectangular channels
Applied Thermal Engineering, 2012Co-Authors: Jiangbo WuAbstract:Abstract Average convective heat transfer on the top and bottom surfaces of a plain plate and four plates with a pair of delta winglet longitudinal Vortex Generator punched directly from the plates at attack angles of 15°, 30°, 45° and 60° respectively, is experimentally and numerically studied in the present paper. The plate fixed horizontally in the center of the tested channel is designed to simulate the forced heat transfer on the both surfaces of a single piece of fin in a fin-tube heat exchanger. Experimental results show that the average Nusselt number on the surfaces of plate increases with the increase of the attack angle of delta winglet pair compared with that of plain plate without delta winglet pair in the test range. The average Nusselt number of the plate with attack angle of 60° is slightly higher than that of plate with attack angle of 45°, yet may bring larger pressure drop. Strong longitudinal vortices are visualized when air flow across the leading-edges of the winglet pair. And a portion of air stream flows into the lower channel through the punched holes on the plates after rushing at the frontal face of delta winglet, and disturbs the flow field of the lower channel further. The heat transfer in the tested channel of five cases is also numerically investigated. Variance of average Nusselt number between the numerical results and experimental results for the five cases are all less than 10%, validating the present models and methods used for the simulation of fin channel flow with punched Vortex Generators feasible and reliable. The computed velocity and temperature fields are analyzed to understand the details of fin channel flow with longitudinal Vortex Generator. The experimental and numerical results reveal that the transverse flow of air stream through the punched holes disturbs the air flow in the lower channel, enhancing the heat transfer on the under surface of fin.
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investigation on laminar convection heat transfer in fin and tube heat exchanger in aligned arrangement with longitudinal Vortex Generator from the viewpoint of field synergy principle
Applied Thermal Engineering, 2007Co-Authors: Jiangbo WuAbstract:3-D numerical simulation results are presented for laminar flow heat transfer of the fin-and-tube surface with Vortex Generators. The effects of Reynolds number (from 800 to 2000), the attack angle (30° and 45°) of delta winglet Vortex Generator are examined. The numerical results are analyzed from the viewpoint of field synergy principle. It is found that the inherent mechanism of heat transfer enhancement by longitudinal Vortex can be explained by the field synergy principle, the second flow generated by the Vortex Generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. In addition, the heat transfer enhancement of delta winglet with the attack angle of 45° is larger than that of 30°, while the delta winglet with the attack angle of 45° results in an increase of the pressure drop, however, the delta winglet with the attack angle of 30° results in a slight decrease.
Anthony M Jacobi - One of the best experts on this subject based on the ideXlab platform.
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heat transfer enhancement by winglet type Vortex Generator arrays in compact plain fin and tube heat exchangers
International Journal of Refrigeration-revue Internationale Du Froid, 2008Co-Authors: Arindom Joardar, Anthony M JacobiAbstract:Abstract The potential of winglet type Vortex Generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of Vortex Generators is compared to a single-row Vortex Generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row Vortex Generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that Vortex Generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.
