Swirl Flow Generator Research Articles

Enhancing heat exchanger performance with perforated/non‐perforated flow modulators generating continuous/discontinuous swirl flow: A comprehensive review

AbstractHeat exchangers are crucial in transferring heat and finding applications across various industries. Numerous strategies have been devised to improve and optimize the heat transfer process within these systems. Among these, passive methods have garnered significant attention for their ability to operate without external power consumption. This article examines the recent experimental and computational studies conducted by researchers since 2018 on passive enhancement techniques, especially twisted tape, wire coil, swirl flow generator, and others, to boost the thermal efficiency of heat exchangers and aid designers in adopting passive augmentation methods for compact heat exchangers. Recently, researchers' new class of flow maldistribution devices, referred to as swirl flow devices, has gained attention; which enhances convective heat transfer by introducing swirl into the main flow and disrupting the boundary layer at the tube surface through alterations in surface geometry. Twisted tape inserts are devices that demonstrate better performance in laminar flow compared to turbulent flow. Conversely, other passive techniques like ribs, conical nozzles, and conical rings are generally more effective in turbulent flow than laminar flow. A recent research trend is the utilization of nanofluids in combination with other passive heat transfer enhancement techniques like turbulators, ribs, and twisted tape inserts in heat exchangers, which can reduce exergy losses and improve overall convective heat transfer coefficient and effectiveness of heat exchanger.

Thermo-hydraulic Investigation of a Heat Exchanger Tube Equipped with 3D-Printed Swirl Flow Generators

AbstractHeat transfer capabilities of the heat exchangers require enhancements to save energy and decrease their size. For this purpose, the swirl generators have been widely preferred. However, the swirler inserts have not reached their optimum shape. Thus, this study experimentally and numerically investigates the impact of novel 3D-printed swirler inserts with varying twist angles in the range of 0°–450° on the thermo-hydraulic performance of solar absorber tube heat exchangers under laminar flow (Re = 513–2054) condition. Friction factor, Nusselt number, and performance evaluation criterion (PEC) were used to assess heat exchanger performance, and related correlations are provided. Tangential velocity components were also used to explore fluid flow characteristics in local analysis. Numerical investigation was done by using computational fluid dynamics adopting Finite Volume Method in ANSYS Fluent. Results show that 3D-printed swirlers considerably increase heat transfer compared to plain tube. The swirler with a twist angle of 450° led to the maximum enhancements of nearly 217% in average Nusselt number and around 1630% in friction factor at Reynolds number of 2054. Overall, increasing Reynolds number enhanced Nusselt number. The highest PEC of 1.15 was observed at a Reynolds number of 1031 using the swirler with 150° twist angle. Flow near the swirler has higher tangential velocities, hence contributing to local Nusselt number enhancement up to 453.8% compared to plain tube when swirler with twist angle of 450° utilized. It is anticipated that findings of this study can guide further related research and increase the usage of swirlers in heat exchangers.

Characterization of flow field of swirling flow conveying in bulk grain pipeline based on gas‐solid multiphase coupling

AbstractAn experiment was carried out to study the characteristics of swirling pneumatic conveying of grain particles in horizontal pipeline, which can provide a reference for the design and optimization of swirling pneumatic conveying system of bulk grain pipeline. The numerical simulation of swirling pneumatic conveying under the guidance of vane swirling generator was performed via CFD‐DEM coupling method. The axial velocity of grain particles was symmetrical along the radial direction, and the tangential velocity was symmetrical along the pipe axis. When the blade number of the swirling device was 6–9, the static pressure drop and standard deviation of the flow field were large, the instantaneous energy consumption of the system and the dispersion of particles were high, and the conveying effect was good. When the blade number was six, the spiral distance of the flow field in the pipe was longer with better quality of swirl flow. In accordance with the simulation results, the best effect of swirling conveying is achieved when the equivalent diameter of the grain particles is 4 mm, the multiphase flow conveying speed is 20 m/s, and the spiral blade number of the swirling flow generator with flow deflector is six.Practical applicationIn the practical application, the swirling flow generated by the swirling device can suppress the settlement of particles and the blockage of the pipeline in the straight pipe conveying, and avoid the high speed collision between particles and the pipe wall in the curved pipe conveying, slow down the impact, reduce the particle breakage and the wear of the pipe wall. The generation and maintenance of swirling flow play a key role in the long‐distance conveying of various chemical raw materials, grain, fertilizer and other granular materials. Swirling flow pneumatic conveying has the advantages of simple equipment structure, small occupation space, flexible pipeline layout, easy to automatic control, high production efficiency, recycling, environmental protection, and so on. It has become an important conveying mode in bulk material conveying.

Investigation of novel passive methods of generation of swirl flow in supersonic separators by the computational fluid dynamics modeling

In this paper, three passive methods for the generation of swirl flow in the supersonic separator (3S) were investigated, and their structures were optimized by computational fluid dynamics (CFD) modeling. The influence of the structural and operational parameters on the dew point depression, phase envelope diagram, rate of natural gas liquid (NGL) recovery, and separation efficiency have also been evaluated. The collection efficiency was significantly improved for the nozzle equipped with the passive swirler compared with the simple nozzle. The selection of passive swirler type played a crucial role in the natural gas liquefaction and separation. The side injected swirler, and serpentine swirler showed the most significant improvement in separation efficiency than the U-turn swirler. For the side injected swirler at the optimum injection angle, the maximum collection efficiency was about 89% at the pressure loss ratio (PLR) of 0.2. Besides, the simulation results demonstrated that for the serpentine 3S, with the increase in serpentine twist number, the highest improvement on the collection efficiency of the investigated nozzle was obtained. In addition, it was observed that, when the convergent section profile was designed according to the Witoszynski line-type, a larger refrigeration zone was obtained than other considered profiles.

Thermo-hydraulic performance of tube with decaying swirl flow generators

• Investigation of experimental and numerical study for decaying swirl flow in a pipe are presented. • Pressure drop and heat transfer were evaluated and analyzed for different swirl angle. • Due to the swirl intensity, heat transfer enhances with increasing swirl helical angle. • Performance evaluation criteria is the highest at the lowest swirl angle. • Variation Local Nusselt number along pipe is higher at larger swirl angle. In this study, the influences of swirl generators fixed at the pipe inlet and having different swirl angles (0°, 22.5°, 41°and 50°) on the heat transfer and fluid flow characteristics in a pipe flow were experimentally and numerically studied under a constant heat flux condition in the range of Reynolds ( Re ) number 2400–23000. The axial type passive swirl generator aims to increase the turbulence effect and gives tangential acceleration while increasing the total flow length in the pipe. This study is novel with the aspects of; (i) the number of helical air passage channels employed in the investigated swirl generators and, (ii) 360° rotation of each helical channel at different swirl angles, i.e., lengths of considered swirl generators are different. Experiments were carried out in a smooth aluminum pipe having an inner diameter of 15 mm and a length of 675 mm with and without swirl generators for turbulent airflows. Empirical correlations for the local and mean Nusselt ( Nu ) numbers, and friction factor ( f ) were developed as a function of Re number and swirl angle as well as smooth pipe flow. The obtained experimental results for the heat transfer and friction factor at different swirl angles were compared with the smooth pipe results. The findings showed that the maximum heat transfer rate is achieved at a swirl angle of θ = 50°, and the heat transfer rate increases as the swirl angle and Re number are increased. The decaying swirl flow leads to around 1.1–1.41 times enhancement of Nu and 2.3–6.76 times increase of f compared to the smooth pipe. The maximum value of performance evaluation criteria ( PEC ), around 0.83, is achieved by the decaying swirl flow when the θ = 0° and Re = 2400. The experimental and numerical Nu and f values for swirl flow are in good agreement within the mean deviation ± 7.1% and ± 8.4%.

Effect of the Number of Nozzles of Swirl Flow Generator Utilized in Flat Plate Solar Collector: An Entropic Analysis

The numerical model of the pipes of a flat plate solar collector (FPSC) with several nozzles has been investigated in the present study. Indeed, the effect of the number of nozzles of the swirl generator on the entropic characteristics has been evaluated. The nozzles were applied for improving the performance of FPSC. For evaluating the proposed system based on the entropy concept, the effect of injection angle and mass flow rate has been considered. The selected injection angles were 30°, 45°, 60°, and 90°. Also, the total mass flow rates entered from all of the nozzles were 0.2 kg/s, 1 kg/s, and 2 kg/s. The effect of said variables on frictional and thermal entropy generations was analyzed; then, the overall energetic-entropic performance of the system was predicted using several dimensionless parameters including NE, NS, Nu ∗ , and heat transfer improvement (HTI). Moreover, Witte-Shamsundar efficiency ( η W − S ) was applied to pinpoint the efficiency of the system. The highest value of HTI and η W − S was 1.7 and 0.9 that achieved by “single-nozzle; A90-D50-N12.5-M0.2” and “quad-nozzle; A30-D50-N12.5-M2,” respectively.

Experimental characterization of heat transfer enhancement in a circular tube fitted with Koflo Blade™ inline mixer

This paper addresses the experimental study of heat transfer enhancement of laminar flow in a tube fitted with Koflo Blade™ inline mixer as the swirl-flow generator and under constant surface heat flux. Experiments were carried out with air as heat transfer fluid and two different types of the mixer having blades crossing angles of 90° and 120° The flow swirling in the mixer is mainly due to the centrifugal force induced by the angle between the blades, which is responsible for heat transfer augmentation. The results show that the mixer with 90° blades supplies Nusselt numbers higher than the 120° mixer but, likewise, results in higher pressure drop. The rate of heat transfer in the tube equipped with inserts was augmented up to 78% and 47% for 90°-blades and 120°-blades mixers, respectively. The enhancement in heat transfer was correlated with the Graetz number that supports the experimental data for both mixers by a deviation within ±10%. Furthermore, the tube fitted with a 120°-blades mixer yields higher thermal performance with a maximum value of 1.77. As well, the 120°-blades mixer provides thermal performance factors up to 17% greater than that for 90°-blades mixer for the same pumping power, which implies that heat transfer effects significantly dominate pressure drop effects.

Entropy generation analysis of turbulent convection in a heat exchanger with self-rotating turbulator inserts

Turbulator inserts are commonly applied to enhance the thermal performance of heat exchangers with an accompanying rise in pressure drop due to the generation of the secondary swirl flow. We study the effect of inter-turbulator distance of rotating turbulator inserts on the heat transfer enhancement and entropy generation of forced convection in the turbulent flow region of a heat exchanger. Attributed to the turbulator inserts, the maximum rise of Nusselt number is 360% and 240%, for non-rotating and rotating cases, respectively, while the friction factor is increased significantly in the flow disturbed by the turbulator inserts. The Nusselt number and friction factor are augmented as the inter-turbulator distance is reduced. The partitioning of tube by the turbulator insert induces the swirl flow that leads to the enhancement of forced convection. From the second-law analysis, the entropy generation rate of the non-rotating case increases up to 202% comparing to that of the rotating case. This shows that the rotating turbulator insert is a more thermodynamically advantageous configuration, as it enhances the thermal performance appreciably while reducing the entropy generation significantly.

Enhancing effect of an open pipe exit on the precessing vortex core occurring in confined swirling flows

This paper investigates the effect of an open pipe exit on the dynamic behaviour of the helical precessing vortex core (PVC) occurring in a confined swirling flow after vortex breakdown. This is achieved by carrying out extensive particle image velocimetry and dynamic pressure measurements downstream of an air swirling flow generator in two pipes configurations at two values of swirl number $$S=0.7$$ and $$S=1.1$$ . The first pipe configuration features a diffuser followed by a straight pipe and an open exit. In the second configuration, the open exit is placed closer to the outlet of the swirl generator by removing the straight part. In both configurations, the PVC structural parameters are properly determined by phase-averaging of the instantaneous velocity fields. In the first configuration, a sudden change in the pitch of the helical vortex is observed at both swirl number values downstream of the connection between the diffuser and the straight part. Beyond this transition, the vortex trajectory starts widening as it is getting closer to the open exit of the pipe. The results in the second configuration confirm this enhancing effect of the open exit on the PVC: at both swirl numbers, the vortex trajectory is strongly widened and its radius continuously increases from the swirl generator outlet to the pipe exit, resulting in an increase in the Strouhal number and pressure fluctuations amplitude by 20 $$\%$$ and a factor up to 9, respectively, compared with the first configuration. Finally, based on a dimensional analysis, a linear relation between two dimensionless parameters including the vortex parameters and the pressure fluctuations amplitude is derived and supported by the data obtained in both pipe configurations.

The experimental investigation concerning the heat transfer enhancement via a four-point star swirl generator in the presence of water–ethylene glycol mixtures

In the present study, a new swirling flow generator is studied which aims to enhance the convective heat transfer rate in a heat exchanger tube. This device has a four-point star cross section. The study mainly investigates the effect of swirl generator on heat transfer rate and pressure drop along the test tube which is under a constant and uniform heat flux. The working fluid in the experiments is the water–ethylene glycol mixtures with Prandtl numbers ranging from 5 to 150 at different Reynolds numbers from 12,000 to 27,000. The results clarify the potential of the applied swirl generator to make a significant enhancement in the heat transfer rate with a satisfactory rise in the pressure drop. Based on studies of different cases, it is found that the swirl generator enhances the heat transfer and also the pressure drop up to 75% and 55%, respectively. The results show that the swirl generator is more efficient at lower Reynolds numbers. Moreover, the results lead to this finding that the swirl generator has a better performance for water and consequently for water–ethylene glycol mixtures with lower ethylene glycol percentage. In other words, the swirl generator has a better performance for the working fluids with a lower Prandtl number.

Numerical Study on the Effect of a Novel Swirling Flow Generator for Submerged Entry Nozzle in Tundish

The swirling flow in the submerged entry nozzle (SEN) is found to significantly improve the flow pattern in the mold, as well as the quality of the steel products. However, the devices generating swirling flow designed so far are mostly limited to be applied in the industries due to the cost, lifetime, external facility, and so on. Herein, a novel swirling flow generator (SFG) is intended to be installed in the conventional tundish to generate a swirling flow in the SEN driven by the gravitational potential energy of the molten steel. The computational fluid dynamics (CFD) simulations are performed to investigate the effects of the SFG by comparing the flow pattern in the conventional tundish. The result shows that a swirling flow is produced in the SEN without bringing a serious disturbance to the flow distribution in the tundish. The flow in the SEN becomes much even by adopting the SFG and the swirling velocity is found to decrease with the increasing distance from the bottom of the tundish. A parameter called swirling intensity is proposed to quantitatively evaluate the intensity of the swirling in the SEN.

Numerical Study on the Gas-Solid Flow in a Spouted Bed Installed with a Controllable Nozzle and a Swirling Flow Generator.

The swirling flow technology is adopted on a nozzle of the spouted bed in order to enhance the radial movement of the particles. The hydrodynamic characteristics in a spouted bed with a swirling flow generator installed on the nozzle are numerically investigated based on the two-fluid model (TFM). The traditional spouted bed and spouted bed with an integral swirling blade nozzle (ISBN) are simulated and analyzed. Numerical results show that the dead zone at the cone region of the annulus can be effectively eliminated by using the ISBN. The maximum decrease in particle concentration near the cone region is 72%, and the ISBN structure can significantly improve the comprehensive fluidization degree of the spouted bed when γ equals 86°. The turbulent kinetic energy of gas can be significantly increased by the swirling flow along the radial direction in the spouted bed, especially in the spout region. Also, the swirling flow can promote the radial velocity and granular temperature of the particles in the spouted bed, which is helpful to the radial mixing of particles and gas phase between the central spout and the annulus in the spouted bed. There exists a value of ξ (equals 0.526), which brings the greatest elimination effect of the flow dead zone in the annulus of the limited spouted bed space, and the overall fluidization of the spouted bed has the best performance when ξ = 0.316.

Nanoparticles hydrothermal simulation in a pipe with insertion of compound turbulator analyzing entropy generation

The aim of this investigation is to investigate the H2O turbulent flow according to the nanoparticles, including copper oxide within a pipe outfitted by an innovative swirling flow generator. For the purpose of determining width effect in turbulent flow for Reynolds number, the results are analyzed. Moreover, relationships are obtained to estimate the irreversibility component. It is observed that viscous reduces directly proportional to pumping power. This means that following an increase in inlet velocity, differential pressure rises. Because of higher velocity gradient, by increasing width Sgen,f becomes greater. As turbulator with larger b is used, stronger turbulence intensity will be generated.

Numerical investigation of turbulent heat transfer enhancement using combined propeller-type turbulator and nanofluid in a circular tube

Heat transfer enhancement is an important issue because of environmental effects and also cost reduction in any thermal installation. A combined propeller-type turbulator and Al2O3 nanofluid are considered for heat transfer enhancement in a horizontal circular tube. Three-dimensional governing equations using the two-phase mixture model with SST k–e turbulent model are numerically solved to predict the behavior of different thermo-fluid parameters in a horizontal circular tube. In addition to studying the effects of these, both means on the heat transfer enhancement, an important discussion on their simultaneous effects are also presented. The effects of turbulator on the generation of swirl flow and also on the turbulent kinetic energy are shown and discussed for different nanoparticle volume fractions and different nanoparticle mean diameters. On one hand, the effect of inserting a turbulator on the thermal performance significantly dominates the effect of using a nanofluid. For instance, at the Z/D = 13.5, using combined nanofluid and turbulator the heat transfer coefficient 2.68 times augments while using only a turbulator it is 2.53 times enhanced. On the other hand, turbulator generates a radial gradient on the momentum forces. The latter significantly deteriorates the uniformity of the nanoparticles concentration. A higher nanoparticle concentration at the near-wall region where the sedimentation problem is taken placed is seen. Thus, it is recommended that nanofluid is not a suitable choice for simultaneous consideration with a propeller-type turbulator in such an application particularly when considering its physicochemical stability drawback. However, further experimental investigations must be carried out to verify such a conclusion and recommendation. It should be mentioned that agglomeration and sedimentation of nanoparticles on the wall surface have not been considered on the modeling of nanofluid physical properties.

Simulation of turbulent flow of nanofluid due to existence of new effective turbulator involving entropy generation

In current work, turbulent flow of H2O based nanomaterial flow containing copper oxide inside a pipe fitted with new swirl flow generator was examined. Outputs were examined to find the impact of width tape for the Reynolds number in turbulent regime. In addition, correlations were derived for predicting component of irreversibility. Outcome show that viscous loss has direct relationship with pumping power. Thus, increasing inlet velocity makes the differential pressure to augment. Owing to higher velocity gradient, Sgen,f augments with increasing width. Using turbulator with greater b leads to generate stronger turbulence intensity.

Intensification of convective heat transfer and heat exchanger performance by the combined influence of a twisted tube and twisted tape

Twisted tubes and twisted tapes are swirl flow generators utilized for increasing thermal performance. The combined effects of twisted tubes and twisted tapes on heat transfer, pressure drop and thermal performance were experimentally investigated. Experiments were performed using a trapezoidal shaped twisted tube and twisted tapes having various twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0). Water was used as the test fluid in a turbulent regime (4500 < Re < 16,000). A simulation of velocity, temperature contours and local Nusselt number plots was also performed to gain information about fluid flow and heat transfer. The results of the combined devices are studied with those of a smooth circular tube and a twisted tube alone, for comparison. The experimental results show that at a given Re, the Nusselt number (Nu), friction factor (f) and thermal performance of a twisted tube mounted with a twisted tape are consistently higher than those of the twisted tube alone and a smooth circular tube. Additionally, the heat transfer, friction loss and thermal performance factor increase with a reduction of the twist ratio (y/w) since the tape with a smaller y/w gives stronger and more consistent swirl flow.

A study on the multi-field synergy principle of convective heat and mass transfer enhancement

In this study, a constitutive relation between fluid power flux and pressure gradient was discussed, and a conservative equation of fluid mechanical energy was introduced to describe convectional phenomena that is essential to convective heat and mass transfer. The multi-field synergy relations among velocity, pressure, temperature and component concentration were revealed according to the synergy equations based on the conservations of thermal energy, mechanical energy, component mass and fluid momentum to analyze physical characteristic of enhancing convective heat and mass transfer. A new experimental correlation of Eu number versus Re and Li numbers was obtained for the first time through theoretical derivation and experiment to test hydrodynamic performance of heat transfer tube. A circular tube inserted by longitudinal swirl flow generator with center-connected rectangle rods was investigated through numerical simulation and PIV experiment to validate the synergy relation in convective heat transfer enhancement.

Computational investigations on the hemodynamic performance of a new swirl generator in bifurcated arteries

Hemodynamic behaviour of blood in the bifurcated arteries are closely related to the development of cardiovascular disease. The secondary flows generated at the bifurcation zone promotes the deposition of atherogenic particles on the outer walls. The present study aims at suppressing the development of atherosclerosis plaque by inducing helical flow structure in the arterial passage. To realize this objective a novel swirl generator (stent like structure with an internal groove) has been developed to induce helicity in the bifurcated passage. The functional requirement of the swirl generator is to minimize the relative residence time (RRT) of the fluid layer near the endothelial wall without generating any additional pressure drop. Different configurations of the swirl generator have been tested computationally using large eddy simulation (LES) model. It is observed that the induced helical flow redistributes the kinetic energy from the centre to the periphery. A single rib swirl flow generator proximal to the stent treated passage can generate sufficient helicity to bring down the RRT by 36% without generating any additional pressure drop. The swirl flow adds azimuthal instability which increase vortex formations in the passage. The induced helical flow in the domain provokes more linked vortices, which may act as self-cleaning mechanism to the arterial wall.

Experimental and numerical study on the thermal and hydrodynamic characteristics of non-Newtonian decaying swirl flows

Experimental and numerical investigation has been carried out to determine the effectiveness of three novel inlet swirl flow generators on heat transfer of a non-Newtonian drilling nanofluid under turbulent flow conditions in a constant heat flux heat exchanger. Thermophysical and rheological properties of working fluid were measured and an empirical model for thermal conductivity was proposed. Non-Newtonian temperature dependent power law coefficients for drilling nanofluid were also presented. Experimental Nusselt number and friction factor were evaluated and compared to the numerical model results. Numerical Nusselt number and swirl number were used to predict thermal and hydrodynamic behavior of the flow at different Reynolds numbers from 4000 to 10,000. The outcomes demonstrate that the fluid flow and convective heat transfer are a function of nanofluid concentration, twist angle and Reynolds number. It also has been shown that the hydrodynamic and thermal characteristics of the flow are not necessarily similar in the whole domain.

Research on multi-radial swirling flow for optimal control of dust dispersion and pollution at a fully mechanized tunnelling face

In order to control the high-concentration dust pollution and protect the health of workers at a fully mechanized tunnelling face, numerical simulation on multi-radial swirling flow is performed to control the migration of dust produced by the excavation at a fully mechanized tunnelling face. The result shows that the airflow is in turbulent regime in the fully mechanized rock tunnel with far-pressing-near-absorption (FPNA) ventilation. An evident swirling flow field exists behind the dedusting fan, and the dust produced by the tunnelling face migrates to the entire tunnel. It is difficult to control the dust pollution through single FPNA ventilation. The field test shows that the simulation result is generally accurate. The dust migrates over a shorter distance LD (the distance of dust migration) when the distance between where the multi-radial swirling flow is generated and the tunnelling face, i.e., LG (the distance between multi-radial swirling flow generator and tunnelling face) is relatively long. For LG = 20 m, the multi-radial swirling flow field produced by generator is converted into an effective dust-control air curtain where the tunneller driver is located, and the dust is controlled in front of the driver. For LG > 20 m, LD changes slightly and becomes stable. For QP (the pressurized air volume) = 200 m3/min and QP ≥ 450 m3/min, the dust migrates behind the tunneller driver, and the optimal QP is between 230 m3/min and 400 m3/min.