Longitudinal Vortex Generators Research Articles

Heat transfer mechanism of different vortex generators arrangements embedded in heat exchange tubes

Heat exchange is widely used in many fields to improve heat transfer efficiency and save energy, while longitudinal vortex generator (VG) is widely used in many heat transfer heat exchangers. In this work, the effect of VGs with different numbers and different pitch ratios (PR) on the heat transfer characteristics in the tube was studied numerically. The results show that when the fluid flows through the VG, the reflux region will be generated, and the fluid velocity in the reflux region will be inhibited, resulting in uneven temperature distribution and increased Nu. When multiple VGs are arranged in a row, the number of vortices is increased, and the area affected is increased. This improves the overall heat transfer performance. With the decrease of PR, the number of VG rows increases, and the heat transfer performance increases first and then decreases with the decrease of PR.

Temperature uniformity analysis and multi-objective optimization of the microchannel heat sink with cavities under longitudinal vortex flow

With the development of electronic devices toward a more centralized direction, there is an urgent need to introduce new technologies in the microchannel heat sink to address thermal deformation or failure caused by uneven temperature distribution. Therefore, microchannels with longitudinal vortex generators (LVGs) and different shapes of cavity structures combination are designed innovatively to address this issue. The laminar flow solver solves for single-phase, steady, and fully developed liquid flows through microchannels in the inlet Reynolds number range of 168–793. Study finds that the longitudinal vortex flow not only mixes the fluid in the mainstream region but also effectively weakens the retention effect in the cavities. Among all microchannels, the microchannel with LVGs and triangular cavities combination (MC-LTC) shows the best performance. Subsequently, multi-objective optimization of the MC-LTC is carried out using Non-dominated Sorting Genetic II Algorithm with the pumping power (Pp) and the temperature uniformity factor (E) as objective functions, and the relative heights (α, β, γ) of the three pairs of LVGs as the three design variables. The optimal solutions set for Pp and E range from 0.706 mW to 1.018 mW and 0.547 to 0.716, respectively. Among the five selected Pareto optimal solution parameters, MC-LTC (α = 0.6001, β = 1.3528, γ = 1.3707) and MC-LTC (α = 0.6001, β = 1.0725, γ = 1.3017) show the best temperature uniformity performance.

Hydrothermal performance of a wavy minichannel heatsink with longitudinal vortex generators

Wavy channels and vortex generators (VGs) are potential heat transfer enhancement methods, and their combination can provide a remarkable hydrothermal performance. In this study, a water-cooled top and bottom walls sinusoidal wavy minichannel equipped with 14 VGs on each of its side walls is experimentally and numerically investigated. The pressure drops and average base temperatures are recorded for the Reynolds numbers (Re) between 500 and 1300 and the obtained experimental data are employed to validate the numerical conjugate heat transfer model. 3 configurations of the wavy channel with inline VGs and 3 with staggered VGs which differ by the attack angle of VGs are numerically investigated. The hydrothermal performances of the cases are studied and compared with a wavy channel without VGs. The Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) are utilized to evaluate the hydrothermal performances. The most significant TPF is found to belong to the wavy channel with staggered VGs, periodically titled for 45° in the direction of the first part of the local curve of the wavy walls. Its TPF is found to be in the range of 1.4–1.46, while the TPF of the wavy channel without VGs is in the range of 1.17–1.36 for the studied Re range.

Effect of the arrangement of longitudinal vortex generators on the performance of a parabolic trough solar collector

Effect of the arrangement of longitudinal vortex generators on the performance of a parabolic trough solar collector

Efficiency Enhancement in Ocean Thermal Energy Conversion: A Comparative Study of Heat Exchanger Designs for Bi2Te3-Based Thermoelectric Generators.

This research focuses on enhancing the efficiency of Bi2Te3-based thermoelectric generators (TEGs) in ocean thermal energy conversion (OTEC) systems through innovative heat exchanger designs. Our comparative study uses computer simulations to evaluate three types of heat exchangers: cavity, plate-fins, and longitudinal vortex generators (LVGs). We analyze their impact on thermoelectric conversion performance, considering the thermal energy transfer from warm surface seawater to TEGs. The results demonstrate that heat exchangers with plate-fins and LVGs significantly outperform the cavity heat exchanger regarding thermal energy transfer efficiency. Specifically, plate-fins increase TEG output power by approximately 22.92% and enhance thermoelectric conversion efficiency by 38.20%. Similarly, LVGs lead to a 13.02% increase in output power and a 16.83% improvement in conversion efficiency. These advancements are contingent upon specific conditions such as seawater flow rates, fin heights, LVG tilt angles, and locations. The study underscores the importance of optimizing heat exchanger designs in OTEC systems, balancing enhanced heat transfer against the required pump power. Our findings contribute to a broader understanding of materials science in sustainable energy technologies.

Enhancing Ocean Thermal Energy Conversion Performance: Optimized Thermoelectric Generator-Integrated Heat Exchangers with Longitudinal Vortex Generators

The effective utilization of renewable energy has become critical to technological advancement for the energetic transition from fossil fuels to clean and sustainable sources. Ocean Thermal Energy Conversion (OTEC) technology, which generates electricity by leveraging the temperature differential between surface and deep ocean waters, enables stable power generation around the clock. In this domain, the combination of thermoelectric generators (TEGs) and heat exchangers has exhibited immense potential for ameliorating the deficiencies of conventional OTEC. This study uses finite element numerical simulation of the COMSOL5.5 software to investigate the fluid dynamics characteristics of heat exchangers with flat fins and different types of longitudinal vortex generators (LVGs) under the same number of fins. This research encompasses heat exchangers with rectangular, triangular, and trapezoidal LVGs. Concurrently, the analysis examines how the vortices generated by the LVGs influence the thermoelectric performance of the TEGs. The results demonstrate that heat exchangers integrating flat fins and LVGs can enhance the power generation efficiency of TEGs. However, the pumping power required by the LVGs constrains the thermoelectric conversion efficiency. Compared to rectangular and triangular LVGs, trapezoidal LVGs achieve a superior balance between output and pumping power. Heat exchangers utilizing trapezoidal LVGs can attain the highest TEG thermoelectric conversion efficiency with a specific seawater flow velocity. Overall, these findings provide valuable reference information for applying TEGs and heat exchangers in OTEC design.

Heat transfer enhancement mechanism of elliptical cylinder for minichannels with delta winglet longitudinal vortex generators

In order to improve the heat transfer performance in the minichannel with delta winglet longitudinal vortex generators and obtain the heat transfer enhancement mechanism, the flow and heat transfer of four basic models (CFD-I, CFD-V, CFU-I and CFU-V configurations) and four enhanced models with elliptical cylinders are numerically simulated in the range of Reynolds number from 2500 to 10,000. The friction factor, Nusselt number and thermal performance factor are evaluated, and the secondary flow intensity and entropy generation rate are analyzed. The main conclusions are as follows: compared with the basic models, the Nusselt number increase by 8.4–14.1 %, 6.1–12.0 %, −1.9-5.0 % and 11.0–14.9 % respectively after adding the elliptical cylinders, and the thermal performance factor of these four models with elliptical cylinders are within 1.05–1.25, 1.00–1.13, 0.97–1.16 and 1.03–1.22, respectively. Compared with the smooth channel, the Nusselt number of CFD-V and CFU-I configurations with elliptical cylinders increased by up to 61 % and 63 %, respectively, and the overall thermal performance increased by up to 25 % and 22 %, respectively. These two configurations are recommended because they make full use of the fluid accelerated by the elliptical cylinder and effectively improve the strength and influence range of the longitudinal vortexes.

Multi-objective optimization of a microchannel heat sink combining cavities and longitudinal vortex generators based on CFD and NSGA-II genetic algorithm

Microchannel heat sink (MCHS) is an innovative cooling device for high-powered integrated circuits. Cavities and longitudinal vortex generators (LVGs) are two kinds of effective heat transfer enhancement techniques for MCHS. It has been demonstrated that cavities can enhance the heat transfer but generate the dead zone of flow, while longitudinal vortex generators (LVGs) have the advantage of low pressure drop. In this paper, an integrated microchannel heat sink combing cavities and LVGs (MC-LVG-C) is proposed. The impacts of geometric parameters of cavities and LVGs on the thermal-hydraulic performance of proposed MCHSs are analyzed and evaluated by CFD when the Reynolds number (Re) ranges from 150 to 325. Further, the multi-objective configuration optimization based on Non-dominated Sorted Genetic Algorithm-II (NSGA-II) is performed at Re=325 to minimize the thermal resistance and pumping power of MC-LVG-C simultaneously. It is found that the proposed scheme (MC-LVG-C) has clear superiority in the thermal-hydraulic performance over MCHS with cavities only (MC-C) and MCHS with LVGs only (MC-LVG). Geometric parameters analysis reveals that the height (hl) and length (L) of LVGs and the spacing (L2) between LVGs and cavities have significant impact on the thermal-hydraulic performance. The NSGA-II optimization indicates that optimal thermal-hydraulic performance values for MC-LVG-C are divided into four design zones. For optimal solutions, better heat transfer can be obtained by increasing hl and L, while smaller resistance can be provided by increasing hl and L2. In practical design, the reasonable geometric parameters can be chosen from the proposed four design zones by the design requirement.

Optimization of the structure and cathode operating parameters of a serpentine PEMFC with longitudinal vortex generators by response surface method

An improved method based on a concept for enhancing heat and mass transfer based on longitudinal vortex system is proposed for optimizing the performance and water-thermal management of proton exchange membrane fuel cells (PEMFCs). A certain number of rectangular plates are added to the cathode channel of the serpentine plate to create the longitudinal vortex to enhance the diffusion of fuel gas, the discharge of water, and temperature distribution uniformity of the fuel cell. A series of numerical studies are conducted employing the response surface method to evaluate the effect of cathode operating parameters on the efficiency and power density of the fuel cell system. The results obviously suggest that the installation of twenty groups of Longitudinal vortex generators(LVGs) in the first four straight flow channels can enhance the mean current density by 5.02 % compared with the condition without LVGs. Meanwhile, LVGs in the cathode flow channel close to the inlet can also enhance the distribution uniformity of membrane temperature by 11.38 %, which can contribute to the diffusion enhancement of oxygen by 36.94 % at the cathode and the improvement of water distribution uniformity by 10.87 %. The main reason for this phenomenon is that the rectangular-plate longitudinal vortex generator can increase the local turbulence intensity of the fuel gas in the cathode channel; therefore, more fuel gas can be transported from the channel to the diffusion layer, leading to a greater current density, in addition to the fact that the generated longitudinal vortex system can assist the exiting of the generated water from the channel. In addition to these, increasing pressure or reducing temperature or relative humidity can enhance power density, while reducing relative humidity is beneficial for improving system efficiency.

Hydrothermal, entropy generation and exergy performances analysis in a mini-channel with combination of longitudinal and transverse vortex generators using Al2O3 nanofluids

With high-tech industrial development, micro/mini-channel heat sinks (MCHSs) are very widely applied for heat dissipation in high-heat-flux devices in these industries. At present, the energy crisis and environmental problems have been restricting human development. Therefore, MCHSs with low energy consumption are urgently designed. In this investigation, a new MCHS with a combined structure of longitudinal and transverse vortex generators is designed and the Al2O3 nanofluid is used as a working medium to further improve various performances of this MCHS. The effects of the transverse vortex generator shape and longitudinal vortex generator angle on the hydraulic characteristic, thermal characteristic, comprehensive performance, entropy generation and exergy efficiency are explored. It is found that the triangular transverse vortex generator is conductive to improve the comprehensive performance and exergy efficiency. Whose performance evaluation criterion is 22.34% on average higher than that of the smooth mini-channel, and the average exergy efficiency reaches 94.30%. On the basis of this, combining the longitudinal and transverse vortex generators can further improve the various performances in mini-channel. The optimal combined structure is the combination of triangular transverse vortex generator and 90°-longitudinal vortex generator and can make mini-channel yield the best comprehensive performance, entropy generation and exergy efficiency. Which obtains the highest performance evaluation criterion (1.36) and exergy efficiency (97.63%) when Reynolds number is 742. Overall, the new MCHS performs a beneficial effect on comprehensive performance improvement in mini-channel to enhance energy efficiency.

Thermohydraulic performance study of the effect of winglet inserts and a corrugated wall in a rectangular channel

This numerical study investigates the enhancement of heat transfer and pressure drop characteristics in rectangular channels with transverse corrugations and longitudinal winglet vortex generators. Numerical simulations cover a range of Reynolds numbers (Re) (5000–20000) using channels with uniform wall heat flux and fixed wavelength. The study evaluates the influence of geometrical parameters (corrugated channel amplitude and winglet length) on flow and temperature characteristics, average Nusselt number (Nu), and pressure drop. Corrugated channels alone create stationary transverse vortices that impede heat transfer. However, integrating winglet vortex generators introduces beneficial longitudinal vortices, disrupting stationary vortices, perturbing the thermal boundary layer, enhancing near-wall turbulence, and improving fluid mixing and heat transfer compared to smooth and corrugated channels. At Reynolds number (Re)20,000, corrugated channels with winglets exhibit 167.7 % and 61.8 % higher Nusselt numbers compared to smooth and corrugated channels, respectively. However, this enhanced heat transfer accompanies increased pressure drop. Both heat transfer and pressure drop rise with higher Reynolds numbers (Re), corrugation amplitude, and winglet length. This study provides insights into heat transfer mechanisms in corrugated channels and the potential for improvement through winglet vortex generators.

Etude numérique de l’effet des générateurs de vortex longitudinaux sur le transfert thermique d’un écoulement laminaire traversant un micro-canal

We conducted, in this work, a three-dimensional numerical study of forced convection heat transfer of a laminar flow of water passing through micro-channels with and without longitudinal vortex generator, using the CFD code “Ansys- Fluent”. This work aimed to elucidate the effect of vortex generators on the dynamic and thermal behavior of the micro-fluidic flow. The results obtained show that the increase in the Reynolds number leads to an improvement in the quality of heat transfer in both cases of the study. Rectangular micro-channel with LVG can improve heat transfer compared to smooth rectangular micro-channel while consuming more pressure drop. In the range of Reynolds numbers between 200 and 1200, a 2-21% increase in the mean Nusselt number was observed for micro-channels with LVG compared to smooth micro-channels. This occurs through better mixing of the fluid, reduction in the thickness of the thermal boundary layer, and increased heat transfer area. In addition, the friction factor has been increased by more than 50% compared to smooth micro-channels, due to the local resistance of LVGs and the presence of secondary flows.

Comparative Analysis of Longitudinal Vortex Generators and Louvered Fins in Enhancing Thermal Performance in Compact Heat Exchangers

Comparative Analysis of Longitudinal Vortex Generators and Louvered Fins in Enhancing Thermal Performance in Compact Heat Exchangers

Influences of operating parameters on uniform mixing behaviors of gas-liquid-solid in novel spouted beds with strengthening components

Influences of integral multi jet(IMJ), swirling blade nozzle(SBN) and longitudinal vortex generators(LVGs) on uniform mixing behaviors of ternary mixture during water vaporization in spouted beds were simulated from the perspective of temperature and velocity fields. To quantitative evaluate the mechanism of water vaporization, temperature uniformity index(Tu), mixing index(IM) and coefficient of variation(CV) were used. Simulation results: the bubble-like distribution of particles caused by LVGs, IMJ and SBN strengthen the gas–solid radial mixing and improve flow “dead zone”. In the upper of system, the promotion of uniformity and mixing quality is SBN > LVGs > IMJ, and LVGs has the most obvious promoting effect on Tu. Moreover, the influences of operating parameters on Tu, IM and mass fraction of H2O(g)(MFH) were investigated. Vgas = 11.2 m/s, Tgas = 520 K, and TWater = 300 K, the liquid–solid mixing quality is the best. In terms of Tu and MFH, Vgas = 11.2 m/s, Tgas = 540 K, and Twater = 400 K have the most obvious effect.

Geometric parametrization of toe-out type vortex generators for energy-efficient capacity augmentation in finned-tube heat exchangers

For compact sizing of finned-tube heat exchangers, improving the gas-side thermal conductance is essential, which is attempted by integrating longitudinal vortex generators. As geometry of the vortex generators is one of the principal design parameters, main thrust of this investigation is to identify their energy-efficient geometric design(s). Since spatial positioning of the generators as well as its attack angle have a strong bearing on the energy-efficiency of the said design, therefore, both are accounted over the entire effective range for a comprehensive and conclusive investigation. For the selection of best geometric designs, regression based phenomenological models are developed, and the selection is conducted based on a detailed thermo-hydraulic trade-off. After identifying the optimal design(s), a study is conducted to assess their robustness by making them perform under varying operating conditions. Although phenomenological models suffice the purpose of design optimization, they do not explain the physics of thermo-hydraulic augmentation. Therefore, a study investigating the effect of geometric variation on the flow and thermal characteristics is also conducted. Since tube wakes in plain finned-tube heat exchangers make a significant heat transfer area virtually unavailable for the stipulated task, a study discussing the effect of generator’s geometry on the thermal management of wake affected surfaces is also reported. It is observed that heat transfer augmentation over the surfaces wetted by the baseline wakes has a dominant role to play whenever energy-efficient compact sizing of the heat exchanger is desirable. For a selected position of generators in the tube aft region, the highest Colburn j-factor augmentation over the wake-affected fin equals 207.1 % at the specified Reynolds number.

Improvement of Plate-Fin Heat Exchanger Performance with Assistance of Various Types of Vortex Generator

A 3-dimensional incompressible laminar flow and heat-transfer in a plate-fin heat exchanger (PFHE) where investigated numerically in this article. The influence of mounting a longitudinal vortex generator (LVG) on the offset rectangular-triangular fin (ORT) in the PFHE, on thermal and hydro-dynamic fields are presented. The novelty of this study is by attaching a LVG to an offset strip fin (OSF) surface. The cases of study for the PFHE are established, by using a built-in rectangular winglet pair type RWP longitudinal vortex generator carried out and fitted on this fin to improve the convective heat transfer of the (ORT) fin while minimizing pressure loss. The upper and lower plates are exposed to constant heat flux and the working fluid is air where chosen under a laminar range of RE (600 to 1400). The laminar flow and heat-transfer are governed by continuity, momentum and energy equations. ANSYS FLUENT (2021 R1) is used to get the numerical results, based on the finite volume method. The performance of the VG is assessed for an optimum winglet attack angle (45°), as well as by modifying the geometrical size parameters, namely the height and placement (L) of the RWP LVG. The result shows that the Nusselt number reaches its optimum enhancement values by using a common flow up CFU built-in rectangular winglet pair type RWP VG with a height and entrance length of (h=1.25mm, L=0.5mm), by 22.23% as compared with base case configuration (ORT). Finally, a two more LVG are tested with the optimum conditions of the RWP, which they are a delta winglet pair (DWP) and trapezoidal winglet pair (TWP). In addition, the temperature fields for the primary and secondary flows were shown in contour and streamline diagrams

Experimental and numerical investigations on the effects of insertion-type longitudinal vortex generators on flow and heat transfer characteristics in square minichannels

Longitudinal vortex generator (LVG) is an effective device for enhancing heat transfer in micro/mini-channel thermal systems. In this study, a new insertion-type LVG (ITLVG) is designed and the effects of length and arrangement of ITLVG on flow and heat transfer characteristics in square minichannel are explored using experimental and numerical methods under Reynolds number of 414–1042. Results show that the vortex flow is generated in both sides of ITLVG and behind ITLVG, thereby intensifying flow disturbance and reducing the thermal boundary layer. The friction factors and Nusselt numbers in the minichannels with ITLVGs increase by 85.5%–246.1% and 39.2%–102.0% on average, respectively, compared to smooth minichannel. The ITLVG arrangement has a significant effect on the flow and heat transfer, while the ITLVG length has a slight effect. The ITLVG with the length of 20 mm and arranged simultaneously in upstream, midstream and downstream shows the highest performance evaluation criterion (PEC) values at most of Reynolds numbers, as well as maximum PEC value reaches 1.50 at the Reynolds number of 1042. Moreover, the correlations for Nusselt number and friction factor are developed. Overall, the new ITLVG performs beneficial effect for comprehensive performance improvement in minichannel to increase energy conversion efficiency.

Thermal performance and exergy analysis in a round tube with louvered trapezoidal winglets

An experiment was performed to investigate the influence of inserting a louver-punched trapezoidal-winglet (LPTW) into a uniform heat-fluxed tube in order to create a longitudinal vortex generator. This research aims to maximize both the thermal performance to increase energy savings, and the relative Nusselt number (NuR) at the optimal performance to reduce heat exchanger sizes. Therefore, the experimental result was emphasized on the thermal and pressure loss characteristics including entropy, and exergy analysis of the turbulent tube flow for Reynolds numbers (Re) that extended from 4760 to 29,280. The LPTWs were arranged by letting V-tip direct downstream with three attack angles (α = 30°, 45° and 60°) and five louver angles (θ1 = 0°, 25°, 30°, 45° and 90°), all at a single relative winglet pitch (PR = 1.0) and height (BR = 0.25). According to the findings, it revealed that the friction factor (f) and Nusselt number (Nu) of the LPTW at α= 60° and θ1 = 0° are, respectively, up to 29.1 and 5.5 times above those of the plain tube. With decreasing Re and θ1, the entropy generation (S˙′gen) was reduced to a lower value and the maximum exergy efficiency (ηEx) was obtained for the LPTW at α = 60° and θ1 = 0° The peak thermal performance around 2.5 together with NuR = 4.68 was found at a= 60°, θ1 = 45° and the lowest Re. However, the optimal condition at α= 60°, θ1 = 30° was preferable because it provides the greatest NuR = 5.04 at TEF = 2.47. Additionally, correlations for f and Nu were derived and presented for the range of parameters that were taken into consideration.

Multiple field synergy mechanism of the desulfurization process in the intensified spouted beds

The semi-dry flue gas desulfurization process in the conventional spouted bed (CSB), integral multi-jet spouted bed (IMJSFB), spouted bed with longitudinal vortex generator (SB with LVG) and swirl blade nozzle (SB with SBN) was simulated using the multi fluid model. Meanwhile, the multiphase reaction system of intensified spouted beds was explored based on the field synergy theory. The analysis of the synergy angle among three fields of the gas phase velocity, temperature, and pressure in the spouted bed shows that adding intensification structures can effectively enhance the gas heat transfer and reduce the gas drag and pressure drop. The intensified spouted beds also had better synergy among the multiphase field of velocity, velocity gradient, and temperature gradient. The desulfurization efficiencies in the CSB, SB with LVG, IMJSFB, and SB with SBN were 77.75 %, 80.85 %, 87.97 %, and 88.81 %, respectively, and the promotion effects in descending order of SBN > multi-jets > LVG.

Experimental and numerical study on the heat transfer and flow characteristics of micro-gap chip with longitudinal vortex generator array

The longitudinal vortex generators (LVGs) are introduced in the 3D stacked chip micro gaps to enhance heat transfer. Experimental and numerical tests on the performance of 3D stacked chip with and without LVGs in the gap are conducted, and the flow and heat transfer performance at various mass flow rate and heating power as well as LVG spacing is investigated. The experimental and numerical results indicate that the LVGs array can effectively improve the cooling performance of the chip with micro gap. Under the experimental condition of q = 41 W/cm2 and Qv = 112 ml/min, the LVGs array can reduce the wall temperature by 14.49 °C compared with smooth channel. Reducing the spacing of the longitudinal vortex array can improve the cooling performance of the micro gap chip since the interaction between the vortexes generated by the LVGs in the pair is enhanced, which also causes the increase of pressure drop. The comprehensive heat transfer performance comparison considering the pump work consumption indicates that the LVGs enhanced chip is more applicable at higher heating power, and chips with smaller spacing are more applicable for conditions with lower flow rate of cooling water.