Turbulence Promoters Research Articles

Concurrent arsenic, fluoride, and hydrated silica removal from deep well water by electrocoagulation: Comparison of sacrificial anodes (Al, Fe, and Al–Fe)

Some studies have reported the removal of As (As) and fluoride (F−) using different sacrificial anodes; however, they have been tested with a synthetic solution in a batch system without hydrated silica (SiO2) interaction. Due to the above, concurrent removal of As, F−, and SiO2 from natural deep well water was evaluated (initial concentration: 35.5 μg L−1 As, 1.1 mg L−1F−, 147 mg L−1 SiO2, pH 8.6, and conductivity 1024 μS cm−1), by electrocoagulation (EC) process in continuous mode comparing three different configurations of sacrificial anodes (Al, Fe, and Al–Fe). EC was performed in a new reactor equipped with a small flow distributor and turbulence promoter at the entrance of the first channel to homogenize the flow. The best removal was found at j = 5 mA cm−2 and u = 1.3 cm s−1, obtaining arsenic residual concentrations (CAs) of 1.33, 0.45, and 0.77 μg L−1, fluoride residual concentration (CF−) of 0.221, 0.495, and 0.622 mg L−1, and hydrated silica residual concentration (CSiO2) of 21, 34, and 56 mg L−1, with costs of approximately 0.304, 0.198, and 0.228 USD m−3 for the Al, Fe and Al–Fe anodes, respectively. Al anode outperforms Fe and Al–Fe anodes in concurrently removing As, F− and SiO2. The residual concentrations of As and F− complied with the recommendations of the World Health Organization (WHO) (As < 10 μg L−1 and F− < 1 mg L−1). The spectroscopic analyses of the Al, Fe, and Al–Fe aggregates showed the formation of aluminosilicates, iron oxyhydroxides and oxides, and calcium and sodium silicates involved in removing As, F−, and SiO2. It is concluded that Al would serve as the most suitable sacrificial anode.

Enhancing the Permeate Flux Improvement of Direct Contact Membrane Distillation Modules with Inserted S-Ribs Carbon-Fiber Filaments.

Three widths of manufacturing S-ribs carbon-fiber filaments acting as turbulence promoters were implemented into the flow channel of direct contact membrane distillation (DCMD) modules to augment the permeate flux improvement in the present study. Attempts to reduce the disadvantageous temperature polarization effect were made by inserting S-ribs turbulence promoters in improving pure water productivity, in which both heat- and mass-transfer boundary layers were diminished due to creating vortices in the flow pattern and increasing turbulence intensity. The temperature polarization coefficient ttemp was studied and found to enhance device performance (less thermal resistance) under inserting various S-ribs carbon-fiber thicknesses and operating both cocurrent- and countercurrent-flow patterns. The permeate fluxes in the DCMD modules with inserted S-ribs carbon-fiber turbulence promoters were investigated theoretically by developing the mathematical modeling equations and were conducted experimentally with various design and operating parameters. The theoretical predictions and experimental results exhibited a great potential to considerably achieve permeate flux enhancement in the new design of the DCMD system. The DCMD module with inserted S-ribs carbon-fiber turbulence promoters in the flow channel could provide a relative permeate flux enhancement up to 37.77% under countercurrent-flow operations in comparisons with the module of using the empty channel. An economic consideration on both permeate flux enhancement and power consumption increment for the module with inserted S-ribs carbon-fiber filaments was also delineated.

On the geometry and material stability of tubular PVDF-TiO2 static mixer membrane contactors for photocatalytic ozonation of micropollutants

The prevention of ozone hotspots in ozonation reactors for wastewater treatment is essential for effective degradation of micropollutants without forming harmful by-products. Membrane contactors can provide a bubble-free ozonation process that is able to decrease by-product formation, e.g., bromate formation in bromide-charged wastewater. Furthermore, the geometry of the reactor influences the distribution of dissolved ozone in a membrane contactor. Turbulence promoters can significantly decrease ozone hotspots and increase ozone mass transfer into wastewater. This work presents a fabrication methodology to produce PVDF-TiO2 helical static mixer membranes using the rotation-in-a-spinneret technology. Static mixer membranes combine the functionality of a membrane contactor and a static mixer in a single component. Furthermore, the PVDF matrix is doped with TiO2 particles as photocatalyst. Thus, we present a membrane-based photocatalytic ozonation process to increase the concentration of hydroxyl radicals for degradation of micropollutants under UV radiation. Static mixer membranes increase the ozone mass transfer coefficient by 70% compared to conventional hollow fiber membranes. Furthermore, the specific photocatalytic degradation rate of methylene blue increases by 50% using static mixer membranes. However, this work also reveals a lack of long-term stability of PVDF-TiO2 membranes in the corrosive environment of photocatalytic ozonation. The molecular weight of PVDF decreases by 11% after use in photocatalytic ozonation resulting in a loss of mechanical stability of the membranes. Similar material concepts are required based on ceramic materials which avoid wetting of the porosity.

A comprehensive review on the effect of turbulence promoters on heat transfer augmentation of solar air heater and the evaluation of thermo-hydraulic performance using metaheuristic optimization algorithms

AbstractSolar air heaters are characterized by poor thermal performance due to limited heat transfer capability of air, thereby necessitating the need for design modifications. Among a different system performance augmentation technique, turbulence promotors are widely used owing to its effectiveness. Based on design parameters such as geometry, size, pitch and arrangement of turbulence promoters, varying levels of heat transfer increment with the pressure drop penalty is achievable. This led to the development of new designs which could offer on optimum thermo-hydraulic performance for a wide range of Reynolds number. Such research invariably requires a thorough insight of data related to various design parameters and optimal thermal–hydraulic performance range. This article provides a detailed overview of various turbulence promotor designs and their optimal thermal–hydraulic performance ranges compiled from a wide spectrum of experimental and numerical studies. Apart from outlining the general flow characteristics of each turbulator design, this study also evaluates different metaheuristic optimization algorithm such as bonobo optimization (BO), particle swarm optimization and teaching–learning-based optimization algorithm for enhancing the thermal–hydraulic performance parameter (THPP). The study shows that the BO algorithm does not exhibit local trapping due to its self-adapting nature of the optimized parameters which makes it a promising choice for THPP optimization studies in air heater applications. The extensive review also shows that the arrangement pattern of rib turbulator plays a key role in thermo-hydraulic performance augmentation. Based on the BO optimization analysis, the range of THPP is determined for the optimized geometry of turbulence promoters. In the pool of rib design, transverse prism rib, multi-V-rib, multi-V-shaped rib with staggered rib, sinewave-shaped rib with gap and S-shaped ribs exhibits an optimal THPP range of 2.05–3.32, 2.43–2.94, 3.00–3.61, 1.58–3.40 and 2.05–3.74, respectively. Other turbulence promotor designs such as winglet vortex generator, dimple protrusion in arc shape and multi-V-baffles exhibits optimal THPP range of 1.95–2.2, 2.44–3.68 and 1.75–2.01, respectively. At the end, the study proposes key research gaps such as the use of combined ribs and vortex generators and discrete fin arrays of different geometry as future scope of research. Graphical abstract

ENHANCED FILM COOLING EFFECTIVENESS USING TURBULENCE PROMOTER IN COOLING HOLE

The film cooling is investigated experimentally and numerically for gas turbine blade cooling. Film cooling performance is vital for safe operation of the blades. By calculating the film cooling effectiveness, the effect of wall roughness through a turbulence promoter inside the cooling hole is evaluated. A turbulence promoter of aspect ratio &lt;i&gt;K&lt;/i&gt; &amp;#61; &lt;i&gt;L/h&lt;/i&gt; from 6 to 14, varying pitch &lt;i&gt;L&lt;/i&gt; with constant height &lt;i&gt;h&lt;/i&gt;, is introduced. Blowing ratio range from &lt;i&gt;M&lt;/i&gt; &amp;#61; 0.5 to 2 and fixed mainstream Reynolds number, Re &amp;#61; 2.0 &amp;times; 10&lt;sup&gt;5&lt;/sup&gt; is tested. Smooth cooling hole and flat plate surface with angle of 35&amp;deg; is set up in a wind tunnel to compare the results and validate the CFD approach assessing the turbulence models &lt;i&gt;k-&amp;epsilon;&lt;/i&gt; renormalized group theory (RNG) and Reynolds stress model (RSM). A swirl flow develops inside the cooling hole due to installing the turbulence promoter. The coolant discharge is modified in turbulence parameters improving momentum and heat transfer rates compared to the normal case. This has an impact on the film cooling performance. The results indicate film cooling effectiveness and surface protection enhancement, obtained for the best aspect ratio and blowing ratio. Coolant wall roughness may be used to improve the design of coolant hole and to reduce the number of orifices needed for safe gas turbine blades.

Intensification of the rate of heat and mass transfer at the wall of a stirred tank reactor by integrating a helical coil turbulence promoter with the tank wall

ABSTRACT The influence of a helical coil turbulence promoter on liquid-solid mass transfer rates in a stirred tank was investigated using a technique that involved measuring the rate of diffusion-controlled copper dissolution in acidified dichromate. The study examined the effects of helical coil tube diameter (d), helical coil pitch (p), impeller rotation speed, impeller geometry (axial and radial), the presence of baffles, and solution physical properties. The presence of the helical coil near the reactor wall significantly enhanced mass transfer rates, with a factor ranging from 1.01 to 2.48. This improvement was accompanied by a corresponding increase in the volumetric mass transfer coefficient (kA), ranging from 2.68 to 4.55, depending on operating conditions. Further analysis revealed that the average mass transfer coefficient increased with decreasing coil tube diameter, while coil pitch had a minimal impact. Additionally, radial flow turbines demonstrated superior mass transfer performance compared to axial flow turbines. The presence of baffles also promoted higher mass transfer rates compared to unbaffled reactors. The experimental data were successfully correlated using dimensionless correlations, emphasizing the significance of these correlations in scaleup and design optimization of catalytic stirred tank reactors with efficient cooling systems.

Numerical analysis of thermo hydro-dynamics behavior of solar flat plate collector with square and V-cut twisted tape inserts

Numerical analysis has been conducted for a solar collector with two circular pipes having semi-circular contact with absorber plate. The tubes are analyzed with and without the inclusion of twisted tape inserts of twist ratio Y = 3 and Y = 4. The comparison between the heat transfer and pressure drop characteristics of a plain tube to that fitted with the twisted tape inserts is done and validated against experimental results with good agreement. Additionally, helical twisted tape is modeled with square- and V-cut to analyze its influence on flow and heat transfer phenomenon. V-cut twisted tape inserts act as turbulence promoters, increasing fluid flow and inducing vortex-like motion. As a result, boundary layer around the absorber plate is disrupted with decrease in stagnation temperature, resulting in better heat transfer and more effective absorption and conversion of solar energy. The Nusselt number, friction factor, and heat transfer coefficient variation with the Reynolds number have been studied for the given heat fluxes. It is found that the Nusselt number of the fluid flowing in the plain tube is increased by 76.44% when the tube is fitted with twisted tape inserts. The pressure drop in the tube is found to increase with the presence of the twisted tapes. The average temperature along the length of the circular tube and absorber plate has also been reported.

Investigation of CO2 Absorption Rate in Gas/Liquid Membrane Contactors with Inserting 3D Printing Mini-Channel Turbulence Promoters.

The CO2 absorption by Monoethanolamine (MEA) solutions as chemical absorption was conducted in the membrane gas absorption module with inserting 3D mini-channel turbulence promoters of the present work. A mathematical modeling of CO2 absorption flux was analyzed by using the chemical absorption theory based on mass-transfer resistances in series. The membrane absorption module with embedding 3D mini-channel turbulence promoters in the current study indicated that the CO2 absorption rate improvement is achieved due to the diminishing concentration polarization effect nearby the membrane surfaces. A simplified regression equation of the average Sherwood number was correlated to express the enhanced mass-transfer coefficient of the CO2 absorption. The experimental results and theoretical predictions showed that the absorption flux improvement was significantly improved with implementing 3D mini-channel turbulence promoters. The experimental results of CO2 absorption fluxes were performed in good agreement with the theoretical predictions in aqueous MEA solutions. A further absorption flux enhancement up to 30.56% was accomplished as compared to the results in the previous work, which the module was inserted the promoter without mini channels. The influences of the MEA absorbent flow rates and inlet CO2 concentrations on the absorption flux and absorption flux improvement are also illustrated under both concurrent- and countercurrent-flow operations.

Intensified ultrafiltration process for fouling mitigation during concentration of bioactive compounds from hibiscus (Hibiscus sabdariffa L.) extract: Innovation by using ultrasound and 3D turbulence promoters

Here we evaluated the application of different techniques (turbulence promoter and ultrasound) to mitigate fouling occurrences during ultrafiltration of hibiscus extract. The turbulence promoter was designed as cylindrical pins which were assembled on the membrane surface. The integrated process with the turbulence promoter and ultrasound increased the steady-state flux of hibiscus extract through the 5 kDa membrane from 97.55 ± 0.05 to 367.61 ± 0.74 kg h−1m−2. In addition to the considerable flux increase, the membrane fouling was mitigated due to the application of ultrasound and turbulence promoters. The 5 kDa membrane was able to retain more than 60 % of total phenolic compounds, total anthocyanins, cyanidin-3-glucoside, delphinidin, quercetin, myricetin, and rutin in the hibiscus extract. Thus, the application of turbulence promoter and ultrasound in the ultrafiltration process showed great potential to significantly mitigate the membrane fouling and to improve the permeate flux, without compromising the quality of the permeate extract.

The effect of inlet design and developing flow on local mass transfer in electrolyzers

The mass transfer performance of electrolyzers can vary significantly depending on the type of inlet that is used. Furthermore, significant local effects can occur if the flow is not distributed well by the inlet. In this work, these effects are investigated using segmented electrodes. With a tube inlet, the formation of a jet results in regions of low and high mass transfer. With a conic inlet, significant flow channeling to the sides of the electrolyzer is observed. These local effects were reduced by using a divider inlet, the addition of a calming section, or a turbulence promoter. The type of inlet also determines the flow regime: with the extended conic configuration the flow is developed laminar, whereas with the tube inlet the flow is developing turbulent. The cross-sectional area ratio of the inlet to the channel was found to be an important parameter in predicting the local mass transfer behavior.

Experimental investigation on jet impingement heat transfer analysis in a channel flow embedded with V-shaped patterned surface

ABSTRACT Heating and cooling systems benefit from jet impingement as it increases efficiency while reducing operating costs. The combined methodology, integrating jet impingement and passive heat transfer through the use of roughened surfaces, offers significant potential for improving heat transfer. This research presents the results of an experimental study on a channel flow commonly used for air heating, known as a solar air heater (SAH), with impinging air on the heated surface. The surface is embedded with V-shaped ribs as turbulence promoters, and it receives a continuous heat flow of 1,000 W/m2. Various design combinations were tested experimentally, including streamwise pitch ratio X/Dh = 0.866, spanwise pitch ratio Y/Dh = 0.866, jet diameter to hydraulic diameter ratio Dj/Dh = 0.065, and an angle of attack (α) ranging from 45° to 90°. During these experiments, the Re varied from 3,500 to 18,000. The optimal improvement was observed at values of X/Dh = Y/Dh = 0.866, Dj/Dh = 0.065, and α = 60°. This paper presents novel findings demonstrating that incorporating V-shaped rib patterns in SAHs can yield Nusselt numbers up to 5.2 times higher than those in smooth duct SAHs, offering substantial potential for enhanced energy efficiency. When the entering jet impacts and flows along the ribs of the absorber, the findings suggest that the V-shaped ribs accelerate the flow, resulting in enhanced heat transfer. All datasets were also analyzed for their thermo-hydraulic performance, with the maximum value recorded as 3.301 within the constraint range used in this analysis.

Enhancing ultrafiltration performance for dairy wastewater treatment using a 3D printed turbulence promoter

Dairy factories annually generate an increasing amount of wastewater, which can cause eutrophication due to high concentrations of amino acids and lipids. To address this issue, membrane technology has emerged as a promising solution, but membrane fouling remains a significant challenge, since it can cause decreased flux, decrease membrane rejection performance, and increased energy demand. This study aimed to reduce membrane fouling by integrated a three-dimensional printed (3DP) turbulence promoter into an ultrafiltration dead-end cell and varying stirring speeds. Two mathematical models, Hermia and resistance-in-series, were used to analyze the fouling process. According to both models, the cake layer formation model indicated the most prevalent fouling mechanism. Specific energy demand, permeate flux, membrane rejection, and membrane reversible and irreversible resistances were measured, calculated, and compared. The results suggest that the combination of an integrated 3DP turbulence promoter and high stirring speeds can effectively reduce membrane fouling in a dairy wastewater treatment module.

Novel classification of multistage flash desalination via finite and infinite flashing: Investigating thermofluid dynamics under varying inlet flow rates employing validated multiphase CFD simulations

This research presents a comprehensive investigation into the flashing process within the evaporation zone of a multistage flashing (MSF) desalination chamber. It introduces a novel classification of the flashing process as ideal, finite, and infinite, aiming to advance the understanding of this critical phenomenon. A validated volume-of-fluid (VOF) multiphase computational model is employed to accurately predict the shape of the free surface and elucidate the complex phase change phenomena occurring within the MSF chambers. By systematically varying the inlet brine velocities and rigorously analysing the thermofluid behaviour in the flashing chamber under both finite and infinite flashing conditions, this study provides a comparative analysis of design factors, including flashing rate and maximum bubble nucleation. Additionally, non-equilibrium losses and flashing efficiency are examined as pivotal metrics for evaluating the flashing process. The findings reveal distinct behaviours of the evaporation zone for finite and infinite flashing processes. Intriguingly, alterations in the flow rate lead to simultaneous enhancements and detriments in thermal efficiency due to the intricate interplay of turbulence promotion, improved mixing, and reduced residence time. Furthermore, the study highlights the significant impact of the inlet flow rate on phase change size, flashing rate, and bubble nucleation frequency within the bubble formation region. This investigation emphasizes the critical importance of comprehending the flashing phenomena and its consequential effect on the thermal efficiency of MSF systems. Leveraging advanced computational models, this study provides a solid foundation for identifying innovative methodologies to optimize the flashing process and enhance the overall performance of MSF systems. The ground-breaking insights presented in this research contribute significantly to the scientific understanding of the field and pave the way for future advancements in MSF desalination technology.

Feasibility Study on Liquid Divertor Using Molten Salt Free Surface Flow with Turbulent Promoters

Feasibility Study on Liquid Divertor Using Molten Salt Free Surface Flow with Turbulent Promoters

Review of Turbine Cooling Technologies

Abstract Modern gas turbines operate in very demanding thermomechanical conditions. The operating temperatures are typically higher than material capability, which requires the parts to be cooled. This work aims to provide a concise overview of the current cooling methods and heat transfer mechanisms occurring in modern gas turbines, including different types of turbulence promoters, impingement, film cooling, microcooling, and the impact of recent applications of additive manufacturing.

Exergy and sustainability analysis of a solar heat collector with wavy delta winglets as turbulent promoters: A numerical analysis

This numerical study aims to determine the exergy analysis for a modified solar heat collector (SHC) having wavy delta winglets as turbulent promoters. These winglets disrupt the viscous layer to improve the heat transfer rate from the heat-absorbing surface to the fluid medium in the rectangular channel. The analysis considers following parameters: the relative longitudinal pitch (P/H), number of waves (φ), and flow angle of attack (α0) and flow Reynolds number range of 4000–18000. The maximum exergy efficiency of 29.18% is achieved with a longitudinal pitch of 5, an angle of attack of 60°, and a relative number of waves of 5. To evaluate the system's feasibility and sustainability, the study uses a Sustainability Index (SI), which reflects the system's Waste Energy Ratio (WER) and Improvement Potential (IP). This assessment helps identify opportunities for improvement in the thermal system.

Outstanding productions of peroxymonosulfuric acid combining tailored electrode coating and 3D printing

In this work, the combination of a tailored design of electrode and electrochemical cell to produce peroxymonosulfuric acid (PMSA), also known as Caro's acid, is evaluated. For the electrode, a customized coating of BDD was deposited onto a niobium substrate. This electrode exhibited a good reproducibility and efficiency in the production of PMSA, thus promoting direct oxidation of sulfuric acid into Caro's acid and preventing the action of scavengers. The electrochemical cell was manufactured after the application of computer-aided design (CAD) combined with computational fluid-dynamics (CFD) simulation and 3D printing. The prototype, with an area of 25sqcm and a designed flowrate of 48 L/h, has been characterized with the evaluation of mass transfer coefficients and RDT curves, which demonstrate an outstanding performance with mass transport coefficients over 3·10−5 m s−1 without turbulence promoter. The cell equipped with the electrodes was tested in the production of Caro's acid enabling a remarkable production of 200 mM of peroxymonosulfuric acid in discontinuous operation mode with a coulombic efficiency (57.2 %) and energy Efficiency (10.67 mmolA−1 h−1). These values outperform the previous state-of-the-art works done in the field for undivided cells operated in discontinuous mode. The results obtained were successfully fitted to a phenomenological model for the generation of Caro's acid.

Influence of heat enhancement technique on the thermal performance of solar water heater for sustainable built environment. Start-of-the-art review

Solar water heater (SWH) is important and low-cost technology for transforming solar radiation into heat energy that is utilized for commercial and industrial purposes. However, due to different advantages, this technology still suffers from poor thermal efficiency and thermal losses from the collector. The various reasons responsible for the poor heat transfer rate of SWH are heat losses from the system and different geometrical shapes of hindrance promoters. The researcher is working on various innovative methods to ameliorate the effectiveness of solar water heating systems (SWHS) by using various heat enhancement methods. The solar thermal conversion efficiency is found to be 70% as compared to solar electrical direct conversion system, which is around 17%. The different heat enhancement techniques, like twisted tape turbulator and their shape, etc., play a very remarkable role in ameliorating the effectiveness of SWHS. This review work abridges the previous research work with different heat enhancement techniques, including the coating effect of pipes, collector design, use of PCM, and different geometrical shapes of turbulence promoters. The twisted tape provides better η as compared to other heat enhancement techniques.

Subcritical transition to turbulence in quasi-two-dimensional shear flows

The transition to turbulence in conduits is among the longest-standing problems in fluid mechanics. Challenges in producing or saving energy hinge on understanding promotion or suppression of turbulence. While a global picture based on an intrinsically 3-D subcritical mechanism is emerging for 3-D turbulence, subcritical turbulence is yet to even be observed when flows approach two dimensions, e.g. under intense rotation or magnetic fields. Here, stability analysis and direct numerical simulations demonstrate a subcritical quasi-two-dimensional (quasi-2-D) transition from laminar flow to turbulence, via a radically different 2-D mechanism to the 3-D case, driven by nonlinear Tollmien–Schlichting waves. This alternative scenario calls for a new line of thought on the transition to turbulence and should inspire new strategies to control transition in rotating devices and nuclear fusion reactor blankets.

Exploration of ARC-class reactor vessel and divertor cooling system

ARC (Affordable, Robust, and Compact) is a compact tokamak design proposed by Commonwealth Fusion Systems and the Plasma Science and Fusion Center at the Massachusetts Institute of Technology.ARC features REBCO (Rare Earth Barium Copper Oxide) high temperature superconducting magnets, demountable coils, a replaceable vacuum vessel and a liquid immersion blanket (LIB). The LIB is a Li2BeF4 (FLiBe) molten that provides cooling, tritium breeding, and neutron shielding. The compact dimensions of ARC result in very high heat fluxes on the first wall (0.4MW/m2) and the divertor (10MW/m2). These heat fluxes mandate a high heat transfer coefficient in the cooling channels that cannot be achieved without adopting heat transfer enhancement techniques. The scope of this work is to analyze the FLiBe flows through the vacuum vessel channels, and the exploration of different passive heat transfer enhancement techniques to provide adequate cooling to the vessel, which must withstand considerable heat flux and volumetric power generation. Minimum cooling requirements for vessel and divertor are evaluated, and the performance of different turbulence promoters is compared to find the most advantageous design. In particular, wire coil inserts decrease pressure drops by 39% with respect to twisted tapes inserts while providing the same cooling performance.