Swirl Generator Research Articles

Thermohydraulic performance of magnetic nanoparticles via combined upstream and downstream swirl generators in solar heat exchanger tubes

Thermohydraulic performance of magnetic nanoparticles via combined upstream and downstream swirl generators in solar heat exchanger tubes

Swirling flow and heat transfer in a pipe: Decay and transition to axial flow

This paper describes an experimental study of heat transfer, local and total swirl flow parameters in the pipe 80 mm in a diameter and 150 diameters long. The pipe consists of 12 separate pipes of different length, connected to each other using 20 mm ring spacers. These spacers were also used to provide the flow and heat transfer measurements. Overall, eight blade-type swirl generators with central body and profiled according to the power low, are installed at the pipe inlet. The actual swirl intensity S of swirl generators is ranged from 0.38 to 1.29. The profiles of mean axial and tangential velocity, surface heat flux, swirl flow angle, static and total pressure, flow and surface temperature are measured. A few novel scientific results and equations are obtained, including the axial and tangential speed maximum, axial and tangential momentum flux, swirl number decay and energy loss transformation. The common link between the local and total swirl parameters, one-valued correlation between tangential and axial velocity were obtained. The results, presented in the paper led to the conclusion that transition from swirling to axial flow occurs at S ≈ 0.19 in terms of the heat transfer decrease, but at S ≈ 0.10 – in terms of the energy loss reduction.

Geometric factors affecting CO2 separation in a supersonic separator

The current work evaluates a potential carbon separation approach with swirl flows and spontaneous condensation. Euler-Euler model is established to depict the spontaneous condensation. By combining Euler-Lagrange model and Euler-Euler model, the droplet motion behavior is predicted, and the influence of separator structure including swirl generator and gap length on the separation efficiency of CO2 is quantified. The flue gas expands under pressure to create a non-equilibrium system, which leads to the emergence of CO2 condensation nuclei. On the surface of nuclei, metastable molecules aggregate and promote the growth of CO2 droplets. Based on the force on droplets, the droplet behavior can be separated into three categories: impacting the straight tube wall, entering the collector and entering the diffuser. When the angle of swirl generator and gap length rises by 315° and 3.75 mm respectively, the separation efficiency rises by 60.3 % and 48.6 %, respectively.

2D3C Measurement Of Velocity, Pressure And Temperature Fields In A Intake Flow Of An Air Turbine By Filtered Rayleigh Sattering (FRS) And Validation With LDV And PIV

A Filtered Rayleigh Scattering Technique is implemented in two different experimental setups and compared to the established velocity measurement techniques Laser Doppler Anemometry (LDA) and Particle Image Velocimetry (PIV). The Frequency Scanning Filtered Rayleigh Scattering Method employed uses an imagefiber bundle which allows for the simultaneous observation of the flow situation from six independent perspectives, utilizing only one sCMOS camera. A testrig with a nominal diameter of 80 mm was implemented by ILA R&D GmbH. Here measurements with straight pipe flow and a swirl generator were realised, as well as comparisions with LDA. A second experiment utilized Cranfields University’s Complex Intake Facility (CCITF), enabling the simulation of the flow field for an engine intake as observed behind an S-Duct diffuser. The diameter in the measuring plane was 160 mm. Measurements up to a mach number of 0.4 were performed and compared with HighSpeed Stereo-PIV (S-PIV) measurements. Good agreement was achieved in respect to both the absolute magnitude of the velocity measurements as well as to the resolution of complex flow structures. The developed FRS multi-view Setup is able to simultaneously determine the 3D velocity components, the pressure and the temperature on a measurement plane with high resolution and without seeding. After calibration the FRS system yields the pressure and temperature within 3 percent respectively 0.8 percent of the reference values. The measured velocity was within 1-2 m/s of the reference.

Effect of temperature and velocity inlet conditions at the diffusers on the thermal and dynamic behavior of an impacting swirling multi-jet system

This study concerns the numerical simulation of a system of swirling turbulent jets impacting a flat plate, by two numerical models of the closure of the Navier Stokes equations (k-ω sst). The jet impact technique is widely applied in the field of heating, drying and cooling of industrial objects. The experimental test bench comprising a diffuser of diameter D, impacting the perpendicular plate, such that the impact distance H = 4D. The swirl is obtained by a swirl generator, made up of 12 fins arranged at 60° from the vertical, placed just at the outlet of the diffuser. The temperature of the swirling jets blowing on the plate is measured with a VELOCICALC PLUS portable thermo-anemometer device, in different stations. It is noted that this diffuser configuration having balanced inlet temperatures (T, T, T), gives a uniform distribution of temperature and velocity on the surface of the plate. This temperature distribution results from a 95% spread of homogenization of plate heat transfer. The (k-ω sst) model gave temperature and velocity profiles that coincide with those of the experimental results. By way of comparison, the (k-ω sst) model better predicts impacting jets, particularly in fluctuating zones. The latter remains a relatively better numerical simulation tool in terms of quality.

Synergistic effects of a swirl generator and MXene/water nanofluids used in a heat exchanger pipe of a negative CO2 emission gas power plant

The focus on optimizing heat exchangers contributes to improved temperature control mechanisms, ensuring the sustainable operation of innovative power plants working toward negative CO2 emissions. In the realm of oxy-combustion within Negative CO2 Emission Power Plants (nCO2PP), the temperature of combustion products surpasses 3000 ( K ) . Addressing this challenge, the imperative arises to reduce these elevated temperatures to a manageable 1100 ( ° C ) . This critical cooling process is achieved through the injection of water, facilitated by the implementation of heat exchangers. The study delves into the optimization of heat transfer within the heat exchanger pipe, specifically tailored for the context of a nCO2PP. Employing a numerical simulation, the investigation explores the impact of vortex generator geometry, vane angles, single and dual propeller-type swirl generators, and the integration of a novel class of fluid, MXene/water nanofluid. Initially, the study scrutinizes propeller-type geometry at vane angles spanning from 15° to 60°. The enhanced swirl flow associated with lower vane angles leads to improved fluid mixing, fostering more effective heat transfer. Results showed that the 15-degree vane angle, with a wider circumferential coverage, may result in increased wall contact, influencing heat transfer efficiency. Subsequently, at Re = 6000, incremental rates of the Nusselt number ( Nu n − Nu s Nu s %), for θ = 15°, 30°, 45°, and 60° are 175.1, 108.8, 90.7, and 40.3%, respectively. Also, the increment rates of Friction Factor ( f n f s ) for aforementioned vane angle are 38.48, 9.26, 4.08, and 2.42%, respectively. In addition, for ∅ MXene = 0.5 % , the Nusselt number experiences considerable increments of 22.94, 24.17, 24.70, and 24.707% at Reynolds numbers of 6000, 12,000, 18,000, and 24,000, respectively, compared to pure water, emphasizing the potential of MXene to enhance heat transfer efficiency.

Numerical study of a CO2 swirl ejector with lubricating oil

At present, most simulations of ejectors ignore the presence of lubricating oil, which may affect the accuracy of the results. Additionally, there has been less research conducted on the influence of motive nozzles with swirl generators on the performance of ejectors. In this study, a heterogeneous mixture model was developed for a three-phase swirl ejector equipped with a motive nozzle featuring a swirl generator. This article examines the performance of swirl ejectors under supercritical conditions using three-dimensional numerical simulations conducted in ANSYS. The study explores swirl ejectors with varying helical angles of 77°, 64°, 58°, 50°, 37° . The study also takes into account the influence of lubricating oil to enhance the practicality of the research. Firstly, lubricating oil with a volume fraction of 2 % was introduced into both the motive and suction streams, followed by conducting an ejection analysis. The results indicate that the swirl enhances the entrainment ratio, and the swirl strength can be modified by changing the helical angle. A smaller helical angle results in greater swirl strength and a higher entrainment ratio. When the helical angle is 37° and the helical pitch is 20 mm, a swirl number of 0.42, an entrainment ratio of 0.998, and an effective entrainment ratio of 0.863 is achieved. However, when the oil circulation ratio in the suction stream is increased from 2 % to 10 % while keeping the oil circulation ratio of the motive stream constant, the entrainment ratio decreases.

Twisted tape inserts in parabolic trough solar collectors: Assessment of Energy, Exergy, and Environmental impacts

The parabolic trough solar collector is a solar technology extensively employed to focus and harness solar energy for diverse heating purposes. One effective technique to enhance its thermal performance involves the insertion of swirl generators within its absorber tube. In this research, experimental investigation on performance enhancement of parabolic trough solar collector using single twisted tape and dual twisted tape insert across Reynolds number values ranging from 1,000 to 9,000 is performed. Collector efficiency, Nusselt number, friction factor, performance improvement factor, and exergy efficiency are examined for single twisted tape inserts with pitch to width ratios (y/w) of 1, 1.5, 2, 2.5, and 3, and dual twisted tape inserts with y/y0 ratios of 2, 3, and 4. Maximum enhancement in collector efficiency is reported at the lowest flow rate for both inserts. The single twisted tape insert with pitch to width ratio of 1 and the dual twisted tape insert with a pitch ratio of 2 exhibit the most notable enhancements in the evaluated performance parameters. Specifically, at lower flow rates (Re < 4400), the dual twisted tape insert (y/y0 = 2) outperforms the single twisted tape insert (y/w = 1). This dual twisted tape insert configuration provides a thermal efficiency enhancement of 14 %, while the Nusselt number and friction factor enhancement are found to be 372 % and 1600 % compared to bare tube. Additionally, the exergy efficiency exhibits a peak increase of 20.8 % at the lowest flow rate using the dual twisted tape insert (y/y0 = 2). This improvement translates to an annual CO2 reduction between 1.53 tons/year offering a highest enviro-economic benefit of 22.19 US dollars per year.

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.

An experimental investigation on the effects of the vortex tube material, swirl generator material and the tube length to diameter ratio on vortex tube performance

The current research investigates the effects of the swirl generator material, the tube length to diameter (L/D) ratio, and the vortex tube housing material on its performance. Two vortex tube were designed and constructed using either stainless or brass. In addition to testing different materials for the housing, 5 different materials were examined as potential options for the swirl generator, including stainless steel, brass, polyamide, acrylic and wood. All were having nozzle number of 6. The study encompassed three main areas: examining the impact of various L/D ratios on an entirely stainless vortex tube (ESVT) and an entirely brass vortex tube (EBVT), exploring various swirl generator materials at an optimal L/D ratio for the stainless vortex tube and the brass vortex tube, and investigating the influence of an optimal swirl generator material with varying L/D ratios for the stainless and brass vortex tubes. Operating conditions were controlled for all tests, the natural refrigerant, compressed air was used, the inlet pressure was set to 3.0 bar and the cold mass fraction was varied from 0.40 to 0.90. The results revealed that the performance of the ESVT was greater than the EBVT. The best combination was the polyamide swirl generator and brass vortex tube with an L/D ratio of 19.0. This resulted in the maximum isentropic efficiency of 0.27 at a cold mass fraction of about 0.47.

Thermal hydraulic performance of a tubular heat exchanger with in‐line perforated baffle with shutter type saw tooth turbulator

AbstractThis experimental investigation aimed to analyze the impact of a unique design of swirl generator airflow on the performance of a tubular heat exchanger operating with axial flow. To conduct the experiment, we utilized a custom‐built apparatus containing eight sawtooth air deflectors with differing space height ratios (e/h). These deflectors were oriented in a uniform manner (shutter type) and positioned at various inclination angles. Circular baffle plates, housing these deflectors, were equidistantly spaced at different pitch ratios. The arrangement of tubes within the heat exchanger remained constant throughout the study, while the Reynolds number ranged from 16,000 to 30,000. In addition, a consistent heat flux condition was maintained on the surface of the tubes. The research outcomes indicated that incorporating a deflector baffle plate with an inclination angle of 30°, an e/h ratio of 0.4, and a pitch ratio of 1.2 led to an average increase of 1.36 in the thermal enhancement factor when compared to a heat exchanger lacking a baffle plate, tested under similar conditions.

Optimising the Hydro‐Thermal Performance of a Four‐Lobed Swirl Tube by Changing the Post‐Swirl Pipe Length

This study explored the heat transfer performance of a decaying swirl flow generated by a four‐lobed swirl generator with simulations and experiments. In the experimental studies, the thermal performance of a swirl generator was compared with that of a circular tube, indicating that the printed swirl generator provided better heat transfer performance than the printed circular tube. Further experiments were performed over a range of Reynolds numbers with different lengths of post‐swirl, circular pipe to assess the decay of swirl, downstream. Here, for shorter lengths of post‐swirl, circular pipe, the thermal improvement was maintained, but this advantage was lost with longer circular pipe runs. In numerical studies, the effect of various pitch‐to‐diameter (PD) ratios of the swirl pipe, including the actual swirl pipe (in-swirl) as a part of the heat exchanger or excluding it (ex-swirl), and the effect of different post‐swirl section lengths were investigated. The heat transfer rate and pressure drop increased with the reduction of the PD ratio, and the in‐swirl arrangements gave higher thermal enhancement and similar pressure loss compared with the ex‐swirl arrangements. The PD6 in‐swirl arrangement gave the highest thermal enhancement for all the geometries. Applying the swirl intensity and the field synergy principle confirmed these results, showing that any thermal enhancement created by swirl generators disappeared rapidly after exiting the swirl tube. In addition, the field synergy principle was more suited to explain the thermal enhancement effect of the decaying swirl flow instead of swirl intensity. This study demonstrates that by optimising the post‐swirl pipe length, overall heat transfer performance can be increased by around 5% with a pressure drop of less than 16%.

The NexGen burner: Non-Reacting gaseous and spray dynamics

This paper reports the results of a comprehensive investigation to identify turbulent multiphase fluid dynamics through the NexGen burner used for fireworthiness certifications by the Federal Aviation Administration. The burner geometry consists of a draft tube, a stator to swirl the incoming air, a turbulator that is placed immediately downstream of the stator to increase the turbulence intensity of the swirling flow, and a burner cone that exhausts into the atmosphere. A Delavan type-W fuel nozzle, attached downstream of the turbulator injects Jet A into the burner cone, where it mixes with the turbulent swirling air, vaporizes and subsequently burns. The operating conditions consist of air and fuel mass flow rates of 0.0384 kg/s and 2.5 Gph at room temperature and pressure conditions. In this paper, we report on non-reacting fluid dynamics; the reacting flow analysis will be presented in a subsequent manuscript. To systematically analyze the flow configuration, three calculations are conducted. First, to validate our large eddy simulation-based framework, a case without the burner cone is conducted—our results are in reasonable agreement with experimental measurements. In the second configuration, to isolate the effect of liquid injection on turbulent flow physics, simulations are conducted with the burner cone but without fuel spray. Detailed analyses are conducted, including identification of flow structures, swirl generation, and the turbulent kinetic energy budget. Finally, Jet A is injected into the burner, and the spray and gaseous flow fields are quantified and compared with the flow structures developed without spray injection.

Numerical Investigation of Film Cooling Effectiveness and Flow Field Characteristics over a Flat Plate with in-Hole Swirl Generator

Numerical Investigation of Film Cooling Effectiveness and Flow Field Characteristics over a Flat Plate with in-Hole Swirl Generator

Large eddy simulation investigation of S-shaped intake distortion and swirl characteristics

Curvature change of an S-duct wall naturally causes total pressure and swirl distortions in a compressor inlet. In this study, the large eddy simulation (LES) method is used to investigate the internal flow of a continuous variable curvature S-duct without a downstream compressor. A comparison between the numerical results and the experimental data verifies the effectiveness of the LES method in analyzing the internal flow mechanism of an S-duct. Based on the SAE standard, the transient distortion descriptors of the research cross-section are quantitatively analyzed, and the distortion characteristics of the total pressure and swirl in the aerodynamic interface plane (AIP), downstream outlet plane, and their spatial–temporal variation processes are revealed. Furthermore, the proper orthogonal decomposition and sparsity-promoting dynamic mode decomposition methods are used to decompose the flow structures of the AIP velocity fields, and the main coherent structures affecting the flow and their corresponding frequency/attenuation characteristics are obtained. The results indicate that the twin two swirl pattern near the wall annulus of the S-duct is dominant at high Reynolds numbers, and turbulent mixing downstream inhibits the development of distortion and swirl. In addition, some stable low-frequency mode structures exist near the Starboard, exhibiting multi-spiking frequency properties. Thus, this study reveals the generation, development, and evolution mechanisms of distortion and swirl at the upstream of a compressor inlet, and the analysis results of distortion and swirl characteristics can provide important input conditions for subsequent compressor distortion research and influence analysis of mass injection pre-compressor cooling technology.

Effect of the geometrical shapes of the helical-spiral shroud intake valve on swirl generation in cylinder of diesel engine

Improving combustion efficiency for diesel engines is an important requirement to save fuel and lower exhaust gas toxicity. In this study, the effect of the geometric shape of the helical-spiral shroud intake valve (HSSIV) for the swirl generation in a diesel engine cylinder was studied, which has important significance in improving the combustion efficiency in a diesel engine.In this study, helical-spiral shroud (HSS) are classified into convex, flat, and concave types according to the installation angle on the intake valve, and their influence on the swirl generation in the cylinder are comparatively analyzed using the computational fluid dynamics (CFD) method. As a result, it is considered that HSSIV with convex shape generates the best swirl and tumble effect in the engine cylinder. The Model 1 with convex shape has a swirl ratio value of 32.5 which is 3.8 times larger at 80CAD, and the tumble ratio value is 48.2 which is 4.5 times larger at 130CAD, compared to Model 0 with no shroud. The findings and results of this study were applied to the diesel engine, but they can also be applied to gasoline engines, and can also be applied to research subjects that need to generate a swirl in the fluid flow path without additional energy consumption and reduction in the volumetric efficiency of the fluid.

Resonator-like behavior of a wall-bounded precessing vortex core in a diffuser with wall asymmetries

This paper reports a detailed investigation of the interaction between a wall-bounded precessing vortex core (PVC) occurring in swirling flows after vortex breakdown and a wall asymmetry. Experiments are carried out in an axisymmetric diffuser downstream of an axial swirl generator inducing a swirling flow with a swirl number of S = 1.1. Wall pressure measurements and two-component particle image velocimetry (PIV) are conducted for Reynolds numbers (Re) ranging from 20 000 to 76 000 in the initial axisymmetric configuration and several asymmetric configurations, with an additional cylindrical protrusion placed on the diffuser wall at different streamwise and circumferential positions. It is first confirmed that synchronous pressure fluctuations at the PVC frequency are only produced in asymmetric configurations. Furthermore, the analysis of the pressure data in several asymmetric configurations revealed for the first time a resonator-like behavior of a wall-bounded PVC. While a change of the protrusion circumferential position in a given cross section of the diffuser only affects the phase of the synchronous pressure fluctuations, the amplitude of the latter features successive minima (pressure node) and maxima (pressure anti-node) as the protrusion is moved along the diffuser in the streamwise direction. In addition, as the protrusion is moved closer to a pressure node, the phase of the synchronous pressure fluctuations exhibits a sudden variation of ±π. Similar results are observed for all tested values of Reynolds number, whereas the PVC frequency linearly increases with Re. A reconstruction of the PVC helical structure based on PIV measurements showed that these consecutive pressure nodes are spaced by a distance equal to approximately one third of the PVC helical pitch. Finally, it also revealed that two different states are observed, depending on the position of the protrusion along the diffuser: the synchronous pressure component reaches its maximum value as the PVC center is approaching either its closest or farthest angular position with respect to the protrusion. The transition from one state to another one depends on the streamwise position of the protrusion with respect to the pressure nodes. These unprecedented experimental observations pave the way to novel theoretical developments for a better understanding and modeling of synchronous pressure fluctuations induced by wall-bounded PVC in asymmetric geometries.

On the impingement of heat transfer using swirled air jets

Experimental analyses were conducted under identical experimental conditions on the heat transfer between a constant heat flux flat plate and a round air jet for both conventional and swirled jets. Vane-type swirl generators inserted at the nozzle exit were used to produce a swirl. The experimental measurements were performed at a fixed Reynolds number value (Re = 23,000) calculated on the jet tube’s inside diameter. A comparison between conventional air jets and swirl jets with swirl numbers of S = 0, 0.19, 0.42, and 0.72 was presented for the different nozzle-to-plate spacings Z/D = 2, 6, and 10. The results show that heat transfer to the plate decreases when the nozzle-to-plate distance increases. In addition, increasing the swirl number S increases heat transfer uniformity but decreases global heat transfer. At the low plate-to-jet distance Z/D = 2, the point of maximum heat transfer is shifted to a radial position depending on the swirl number. Also, for both Z/D = 6 and 10, the stagnation point and stagnation region heat-transfer enhances only for swirl numbers 0 and 0.19.

A semi-empirical correlation for the swirl number of swirling jets generated by a radial-type swirler

This work presents a semi-empirical correlation for the swirl number of a radial-type swirl generator under different conditions of both the Reynolds number and the angle of the swirler channels used to generate the flow tangential velocities. Quantitative velocity measurements are carried out via stereoscopic particle image velocimetry (PIV) to characterize the three-component velocity field of the swirling jets in the proximity of the nozzle exit for four values of the Reynolds number (i.e., 12,800, 20,800, 31,100 and 41,500) and nine swirl angles ranging from 0° to 20°. Such data is used to estimate the values of the swirl number from different theoretical formulations. Semi-empirical formulas are derived based on the mass and angular momentum conservation laws and analytical approximations of the quantities involved in the definition of the swirl number. These formulas elucidate the dependence of the swirl number on the geometrical parameters of the radial-type swirl generator, in particular on the swirl angle, and include coefficients estimated empirically from the velocimetry data, which essentially depend on the exit velocity distribution. The derived correlations may be useful for design and analysis purposes.

CFD-DEM investigation of gas–solid swirling flow in an industrial-scale annular pipe

Swirling gas-particle flow has been prevalently utilized in many industrial applications due to the obvious advantages of high particle dispersity, small pressure drop and low power consumption. In this work, numerical simulation of the swirling gas–solid two-phase flow in the three-dimensional industrial-scale annular pipe installed with a helical swirler is carried out via computational fluid dynamics coupled with discrete element method. The mixing characteristics of two-axial jets together with the particle-scale information of solid phase are fully investigated. The results show that the high Reynolds number of gas phase is observed above the swirl generator, while high turbulent Reynolds number of gas phase mainly appears in the core region of the mixing zone. The existence of the swirler vorticity in the high-velocity jet increases the strain rate of gas phase. The cross-section distribution of the particles always follows the normal distribution pattern, and the velocity components of the outermost particle are dramatically higher than those in the core region. Due to the entrainment effect of swirling gas flow, the velocity and dispersion width of the particles increase when moving downward. Swirling flow of gas phase obviously impacts the particle velocity and entrained number within the height of the z/H = 0.2 to 0.1 but only affects the particle entrained number in the range of z/H = 0.1 to 0.