Swirl Generator Research Articles

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.

Performance of solar collector with turbulator involving nanomaterial turbulent regime

In current attempt, swirl generator and four-lobed pipe were installed in a solar collector to achieve higher performance not only in view of cooling rate but also available energy. In outputs, components of irreversibility were illustrated for different values of revolution (N), pumping power (Re (Reynolds number)) and width of tapes (D∗(diameter ratio)). Four functions were scrutinized namely; Xd (exergy loss); Sgen,th (thermal irreversibility); Sgen,f (frictional irreversibility); Φs (Augmented irreversibility). Experimental articles were utilized to not only verify the nanofluid modeling but also the correctness of selecting k-ϵ turbulent model. Sgen,th declines with rise of active parameters because of reduction in temperature gradient and highest impact belongs to Re. Although increasing revolution provides stronger secondary flow as well as trend of Re, the influence of N on Sgen,th is lower than that of Re. At lowest values of other factors, Be (Bejan number) declines about 0.016%, 0.004% and 8.2% with enhance of diameter ratio, N and Re. Revolution of tape has lowest impact on Be in comparison to other factors. Be decreases about 1.67% with rise of N at Re = 20000, D∗ = 0.045. The component of ∇T reduces as greater secondary vortex appears. So, augment of inlet velocity, width and revolution of tape makes exergy loss to decline.

EXPERIMENTAL INVESTIGATIONS TO STUDY THE INFLUENCE OF TWISTED TAPE INSERT ON HEAT TRANSFER EQUIPMENTS – AN EXTENSIVE REVIEW

Heat transfer augmentation with compact and effective manner are the recent developments of the heat exchangers. Considering cost reduction, simplicity, compact size etc were the parameters considered for the design and development of heat exchangers. Use of passive techniques like creating fins, rough surface on the flow path, wire coil inserts, generation of swirl on the flow path and mounting inserts like blocks, winglets and twisted tapes were the impressive methods of heat transfer intensification in heat exchanger design. Twisted tape is the technique that supports to enhance the heat transfer in heat exchanging devices. Many investigators involved on the experimentation to enhance the rate of heat transfer employing twisted tapes by varying the twisted tape geometry , twisted tape shape and the size of the duct etc. This extensive review emphases on the argumentation of heat transfer by twisted tape insert with varying twisted tape geometry, is discussed and disclosed in detail. This review revealed the outcomes of the literatures reported for the past decade.

A tool to minimize the need of Monte Carlo ray tracing code for 3D finite volume modelling of a standard parabolic trough collector receiver under a realistic solar flux profile

AbstractThe energy collection element of a parabolic trough collector includes a selective coated metallic receiver tube inside an evacuated glass tube. Perpendicularly incident sun light on the parabolic trough mirror aperture is concentrated on the receiver tube highly nonuniformly along its circular direction. This solar energy is collected as thermal energy circulating a suitable heat transfer fluid (HTF) through the tube. This conjugate heat transfer phenomenon under nonuniform heat flux boundary condition is computationally studied applying 3D finite volume (FV) modelling technique of computational fluid dynamics coupled with Monte Carlo ray tracing (MCRT) optical data. The MCRT model simulates the actual flux profile around the receiver tube. Apart from a FV model, this coupled study requires expertise in, and access to, a suitable MCRT code. A combination of polynomial correlations and user‐defined function (UDF) is introduced in this article in order to minimize the need of MCRT codes from subsequent FV modelling of the receiver tube of the Luz Solar 2 (LS2) collector. The correlations are developed from a verified 3D MCRT model, which is equivalent to the local irradiation data as a function of receiver circular location. The UDF includes two algorithms: one to develop solar flux profile from the correlations around the receiver, and the other to calculate heat loss from the receiver. Interpreting the UDF into ANSYS Fluent, a 3D FV model of the LS2 receiver is developed and validated with experimental results. The effectiveness of the UDF as an alternative to MCRT code is verified. The FV model is capable to investigate the heat transfer characteristics of the LS2 collector receiver at different solar irradiation level, optical properties of the collector components, glass tube conditions, HTFs, inserts or swirl generators, collector length, and internal diameter of the tube.

Entropy generation of turbulent Cu–water nanofluid flows inside thermal systems equipped with transverse-cut twisted turbulators

In the present study, numerical simulations have been carried out on thermal characteristics and second-law analysis of turbulent Cu–H2O nanofluid flow with the nanoparticle volume fraction of $$0 < \phi < 1.5\%$$ inside heat exchangers fitted by transverse-cut twisted tapes (TCTTs) with alternate axis. The transverse-cut ratios are in the range of 0.7 < b/c < 0.9 and 2 < s/c < 2.5, and the Reynolds number is varied between 5000 and 15,000. The impacts of the design variables on the turbulent kinetic energy, temperature distribution, thermal and frictional entropy generations and Bejan number have been evaluated. The simulations show that the TCTTs with b/c = 0.7 generate higher turbulent kinetic energy compared to the b/c = 0.9 due to higher swirl generation and flow disturbance. The additional recirculating flow produced near the alternate edges is another main physical factor for heat transfer augmentation. It is found that raising the nanoparticles volume concentration reduces the thermal entropy generation which is attributed to the thermal conductivity enhancement of nanofluids. Besides, raising the nanoparticles volume concentration from 0 to 1.5% reduces the $${{N}_{\text{g,thermal}}}$$ by 23%.

Characteristics of Flame Stability and Gaseous Emission of Bio-Crude Oil from Coffee Ground in a Pilot-Scale Spray Burner

Coffee ground has been recently considered as a new biomass resource in relation to the increasing coffee consumption worldwide. The bio-crude oil can be produced by fast pyrolysis of coffee ground, and it has advantages of larger heating values in comparison with those from other biomass. But the bio-crude oil from coffee ground has a significantly high viscosity which can hinder the application to conventional burners. In this study, a pilot-scale burner system with a 35 kW capacity with an air-blast atomizing nozzle was developed for the combustion of bio-crude oil from coffee ground with a high viscosity. A downward fuel injection system was adopted to enhance the ignition of fuel spray and the flame stabilization, and a movable block swirl generator was installed for the combustion air. The bio-crude oil was blended with ethanol at the volumetric ratio of 9:1 to enhance the combustion characteristics. The effect of various atomizing air pressures, swirl intensities, and overall equivalence ratios on the flame stability and gaseous emission were investigated to find out the optimum operating conditions for a bio-crude oil burner.

Study on the Influence of Premix Uniformity on NOx Emission Concentration in 9E Gas Turbine Combustion Chamber

In this paper, a numerical simulation is performed on the basis of a combustion chamber of 9E gas turbine, to study the effect of premix uniformity on the NOx emission concentration. The results show that when the 9E gas turbine is working under the baseload with a fuel flow ratio of the primary nozzle R fuel deviates within an optimal interval of 78 % to 84 %, an increment in the number of secondary nozzle fuel injection points leads to a decline in NOx emission concentration. Since purge air nozzles of DLN are placed in upstream of swirl generator while the nozzles are placed downstream of swirl generator in LEC, the impact of the purge airflow rate on the NOx emission in the DLN has an opposite trend with that in the LEC. Besides, the increment of the mixed air proportion R air leads to a distinct enhancement in the local equivalence ratio peak value of the primary combustion zone outlet. Also, the distribution of the equivalence ratio changes. The NOx emission concentration is influenced as a result.

Effect of the Geometry of a Swirl Generator on Energy Loss and Shockwave Position in Arina Nozzle

AbstractTo investigate the effect of the swirl generator (SG) on shockwave position and pressure drop, 3D simulation is conducted and validated by Arina's study. An increase of the blade number, height, and end angle leads to shockwave displacement toward the nozzle outlet. The maximum increment of the shockwave displacement, which is due to enlarging the angle of the blade end, is about 47 %. For this case, the pressure drop share of the SG is nearly half of the total pressure drop, while the residence time of particles is prolonged by about 51 %. As a general finding, increasing the swirl intensity provides a longer residence time to separate adequately the liquid from the gas. However, a higher energy loss is not desirable for the high‐pressure process at the downstream of the 3S separator.

Performance enhancement of axial concurrent liquid\u2013liquid hydrocyclone separator through optimization of the swirler vane angle

Vane angle configuration is considerably affecting the internal flow behavior and separation performance of a concurrent axial inlet liquid–liquid hydrocyclone. This study was carried out to improve the design of the swirl generator by optimizing the vane’s deflection angle in an oil/water axial inlet hydrocyclone separator. Angles ranging from 37° to 75° were examined at various operational conditions, including mixture temperature, mixture flow rate, and water-to-oil ratio. Two analysis techniques have been coupled to achieve the aim. First, design of experiment by the response surface method was utilized to generate a combination of run/boundary conditions of swirler vane angles, inlet mixture temperatures, flow rates, and concentrations. The obtained 15 run/boundary conditions were adopted as cases for computational fluid dynamics simulation to determine the separation efficiency, tangential velocity and pressure drop of each case using ANSYS Fluent software. The optimization results show that the swirl generator with a 45° deflection angle generated slightly higher tangential velocity compared with higher and lower vane deflection angles. The separation efficiency obtained by using the 45° swirl generator was higher than other angles, in spite that the turbulence intensity is slightly higher at 45° compared to other vane angles.

An extensive review of various technologies for enhancing the thermal and optical performances of parabolic trough collectors

A wide range of engineering industrial applications require both the thermal and optical efficiencies of the system to be maximized with a reasonable low penalty for the friction factor and subsequently low losses in pressure. Among the family of concentrated solar power systems, parabolic trough collectors (PTCs), which have recently received significant attention, face similar challenges. The current work presents an extensive review of the PTC systems comparing recent and past technologies, which are widely being used to improve and enhance the thermal and optical efficiencies. Furthermore, the techniques used for single and two-phase flow modeling in numerical simulations, design variables, and experimental processes have been discussed in detail. The article also presents different numerical methods and analytical approaches of implementing the nonuniform solar distribution with different design parameters. Four main technologies are comprehensively addressed to effectively enhance the thermal performance of the PTCs; changing working heat transfer fluids, replacing the working fluids by nanofluids (single and hybrid) that have higher thermal–physical properties than those of base working fluids, inserting different tabulators with various design configurations, and finally combining the advantages of nanofluids and swirl generators in the same application. The article also critically summarizes the studies investigating the enhancement of thermal performance: use of novel design of PTCs and passive heat transfer enhancement techniques. Finally, a wide range of numerical and experimental studies are proposed for the future work related to the aforementioned main technologies.

Numerical investigation of a confined diffusion flame in a swirl burner

In this study, combustion in confined burners, with confinement ratios equal to 1, 1.5, 2, and 3 were numerically investigated. A non-premixed swirling flame was generated by supplying the fuel, i.e. methane or propane, to a central gas outflow while air was supplied through screw-type swirl generator with six opening lobes. Swirling flame was confined inside a long confinement tube with various confinement diameters. Flame structure, fuel–air mixing efficiency, NOx and CO emissions were investigated in wide ranges of equivalence ratios (0.68–0.82), momentum ratios (0.002–0.006), and air flow Reynolds numbers (5400–6450). Fuel–air reaction was modelled using a 2-step reaction approach. The results showed that confinement ratio and momentum ratio played important roles in determining recirculation zone size and shape. For small confinement ratio, the central fuel jet penetrated the central recirculation zone while for confinement ratio equal to 3, this behaviour did not happen. Because of the high confinement and the partial combustion of the fuel, two streams occurred in the confinement tube—an outer stream with high oxygen content and an inner stream with high concentration of CO. It found that propane flame released more NOx and CO emissions than methane flame did, and NOx and CO concentrations at the burner exit were dependent on momentum ratio rather than confinement ratio. Increasing air flow, i.e. increasing Reynolds number, led to a reduction of NOx due to the formation of a stronger recirculation zone.

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.

Effect of Fuel Nozzle Geometry on Swirling Partially Premixed Methane Flames

Abstract This paper presents an experimental study of the effect of fuel nozzle geometry on swirling partially premixed methane flames, where the focus is put on the ensuing flowfield and its role on coherent structures' suppression. The burner consists of a central interchangeable fuel nozzle surrounded by a swirling co-airflow where both discharge into a short mixing tube. The nozzle geometry is classified into two groups, namely, single- and multi-orifice nozzles. The swirling motion of the co-airflow is produced using a radial-type swirl generator with a swirl number of 1.15. The flowfield characteristics and coherent structures are documented using particle image velocimetry (PIV). Flame front dynamics are captured using Mie scattering technique. Quantitative laser sheet (QLS) is used to qualitatively shed light on the mixing characteristics downstream of the mixing tube exit, and laser Doppler velocimetry (LDV) is used to extract the coherent structures' peak frequency from the power spectra. The results revealed that the fuel nozzle geometry significantly affects the mean flowfield, mean, and root-mean-square (RMS) of the flame front location, flame front asymmetry, and coherent structures' amplitude. Higher spread rate and faster decay caused by single-orifice nozzles inside the mixing tube result in divergent flames with higher degree of flame front asymmetry downstream of the mixing tube exit. On the other hand, multi-orifice nozzles mitigate coherent structures, enhance mixing, and hence, promote the most appropriate conditions for coherent structures' suppression.

Effect of an asymmetric flow disturber on an ultrasonic flowmeter

AbstractAn ultrasonic flowmeter used in custody-transfer heat metering applications is subject to several test applications for approval. A flow disturbance test with an asymmetric swirl generator upstream of the device is performed to evaluate its accuracy with and without the swirl generator. This standard asymmetric swirl generator is designed to reproduce the behaviour of applications in the field, such as an out of plane 90° double bend. To assess the compliance of the already approved device (Endress+Hauser Prosonic Flow E Heat) for heat metering applications with the standard asymmetric swirl generator, extensive Computational Fluid Dynamics (CFD) simulations are performed. The steady and transient CFD simulations are carried out on a High-Performance Computer (HPC) for several volume flows. With the developed automated simulation method, a virtual calibration of the device takes place. The calibration curves for the cases of a straight pipe, and an asymmetric flow disturber mounted upstream of the flowmeter are attained from experiments and simulations. The agreement of experiments and simulations is discussed and physical insight for the behaviour of the flow disturber and the flowmeter is gained.

Experimental and Numerical Investigation of Swirling Flow on Triple Elbow Pipe Layout

The secondary flow downstream of a triple elbow layout was studied experimentally and numerically to visualize the flow behavior under swirling inlet flow conditions. The inlet swirling condition was generated by a swirl generator, consisting of a rotary pipe and honeycomb assembly. The experiments were carried out in turbulent water flow condition at Reynolds number Re = 1 × 104 and inlet swirl intensity S = 1. Ultrasonic measurements were taken at four locations downstream of the third elbow. The two-dimensional velocity field of the flow field was measured using the phased array ultrasonic velocity profiler technique to evaluate the flow field with separation. Furthermore, a numerical simulation was performed and its results were compared with the experimental data. The numerical result was obtained by solving three-dimensional, Reynolds-averaged Navier-Stokes equations with the renormalization group k-ε turbulence model. The experimental results confirmed that the swirling flow condition modified the size of the separation region downstream of the third elbow. A qualitative comparison between the experimental and CFD simulation results of the averaged velocity field downstream of the third elbow showed similar tendency on reverse flow.

Studies on the efficacy of helical port design using computationla fluid dynamics

In-cylinder gas motion is the essential parameter that enhances fuel-air mixing and increases the combustion rate and governs the performance and emission of the engine. It also has significant impact on heat transfer. Angling the intake port into various angles is the one of the method to enhance swirl motion inside the combustion chamber. In this project, direct port is converted into helical port to analyze the air motion inside the engine cylinder. In order to analyze the effect of helical port design the various flow parameters such as swirl ratio, flow coefficient, and turbulent kinetic energy are calculated. By angling the intake port, swirl generation during suction stroke is comparatively larger than direct port. A commercial CFD software STAR-CCM is used to analyze the in-cylinder air motion.

Numerical evaluation on the decaying swirling flow in a multi-lobed swirl generator

Accurate predictions of decaying swirling flow behavior in the multi-lobed swirl generator (MLSG) are essential for certain engineering applications. In this study, decaying swirling flow characteristics in an MLSG are examined using the Computational Fluid Dynamics (CFD) technique with a Reynolds stress turbulence model (RSM). The effects of different lobe numbers (n) and pitch length ratios (P/D) on swirl intensity, pressure drop, friction factor coefficient, and decay rate are observed with Reynolds number from 50,000 to 125,000. Combined with the pressure loss, the efficiency of swirl induction is evaluated by introducing a swirl effectiveness (SE) evaluation criterion. The initial swirl intensity is shown to first increases and then decreases as lobe number increases. The maximum value is obtained at lobe number n = 4. The pitch length ratios P/D corresponding to the optimal SE value obtained from different lobe also differ. The optimal SE value is achieved at n = 4 and P/D = 8. The friction factor ratio f s/f p decreases as pitch length ratio increases, but the decreasing trend decelerates over time. Correlations based on the numerical predictions of friction factor ratio f s/f p and decay rate β are presented accordingly.

Augmentation of Nanofluids Heat Transfer in a Circular Pipe with Coiled Tube Insert as Heat Source and Swirl Generator

This research present steady state heat transfer and fluid flow characteristics in concentric pipe with coiled tube insert for turbulent flow regime with metal oxide nanofluid using ANSYS-FLUENT 18.0 where the governing equations of mass, momentum and heat transfer were solved simultaneously, using the k-e two equations turbulence model. Copper was chosen as the as metal for the construction of pipe and the helical tube insert. Coiled tube with curvature to pitch ratio as 1 and 2.5 mm in diameter with 1% volume fractions of TiO2 and CuO Nanofluid with Reynolds number ranged from 4000-16000 were considered in this research. The heat generated from constant water temperature (80 °C) with constant flow rates in helical coil (Re=4000). The Result shows that the heat and friction coefficients conducted by vortex generator raised with Reynolds number and accretion of nanoparticle presence. Furthermore, the maximum rate of heat transfer with significant intension in friction coefficient has been produced TiO2 nanofluid by as compared with CuO and water.

Experimental investigation of the heat transfer and pressure drop characteristics of SiO2/water nanofluids flowing through a circular tube equipped with free rotating swirl generators

The heat transfer and pressure drop characteristics of SiO2/water nanofluids flowing through a horizontal circular stainless steel tube equipped with free rotating swirl generators (FRSGs) at the entrance of a test tube are reported in this article. The experimental studies were performed with a Reynolds number ranging from 3500 to 13,000; volume concentrations of 0.5, 1, and 2 vol%; and inlet temperatures of 25, 30, and 35 °C, where a constant heat flux was imposed on a test tube. FRSGs made from aluminum, with three different twisted angles (30°, 60°, and 90°) and a length of 2.3 cm, were located at the entrance of the test tube. The results indicated that FRSGs had significant effects on heat transfer and pressure drop characteristics for the flow of both water and nanofluids in the tube. The Nusselt number increased with increasing volume concentration, inlet temperature, and Reynolds number. However, the friction factor of nanofluids flowing through FRSGs was significantly greater than that of water when the Reynolds number was lower than 6000. This is because FRSGs do not rotate under the given conditions. A maximum efficiency index of 1.57–1.7 was obtained when using SiO2/water nanofluids with FRSGs at a volume concentration of 2 vol%, inlet temperature of 35 °C, and Reynolds number greater than 7000. On the other hand, the efficiency index value was lower than unity when the Reynolds number was lower than 7000 and with volume concentrations of 0.5 and 1 vol%. No significant differences were found among twisted angles of FRSGs on heat transfer, pressure drop, and efficiency index.

Influence of perforated triple twisted tape on thermal performance characteristics of a tube heat exchanger

One of the challenging tasks in the development of heat exchangers is to select an appropriate geometry that will consume minimum energy. This could be achieved by designing a suitable enhancing device which will boost the thermal performance characteristics of heat exchangers. Twisted tape swirl generator, a heat transfer enhancement device equipped in a tube heat exchanger would induce turbulence and superimposed vortex motion causing a reduction in the hydrodynamic or thermal boundary layer thickness which results in the improvement of convective heat transfer. In this study, a new design of perforated triple twisted tape (PTTT) insert was applied as a swirl flow device with four different porosities (Rp) of 1.2, 4.6, 10.4 and 18.6% to enhance the convective heat transfer of a tube heat exchanger. The effects of porosity (Rp) of PTTT swirl generators on heat transfer, fluid friction and thermal performance characteristics of a tube heat exchanger were experimentally investigated. The experiments were conducted under constant heat flux condition using air as the working fluid in turbulent flow regime for variation in Reynolds number (Re) from 7250 to 49,800. The Nusselt number of the tube installed with PTTT inserts for porosity ranging from 1.2 to 18.6% was found to be 88–320% higher, whereas, the friction factor was achieved to be 112–355% higher in comparison to the plain tube. The highest heat transfer result of 320% was obtained at a porosity of 4.6% with PTTT insert compared to the smooth tube. Despite the significant enhancement in heat transfer, the friction factor was obtained to be 355% higher in comparison to the plain tube at a porosity of 4.6% with PTTT insert. The experimental results demonstrated that Nusselt number, friction factor, and thermal enhancement efficiency (TEE) were increased with decreasing the porosity of the tape inserts except for 1.2%. The heat transfer performance was evaluated based on constant blower power and the values were found to be 1.13–1.5 relative to the plain tube. The maximum TEE of 1.5 was achieved using PTTT insert with a porosity of 4.6%. Based on the experimental data, the empirical correlations of heat transfer, friction factor and TEE were developed in terms of Rp, Re and Prandtl number (Pr) to predict the heat transfer, friction factor and TEE. The optimal design of PTTTs based on the evaluation of thermal performance with suitable porosity could be an excellent heat transfer enhancement device for many industrial applications.