Jet Impingement Research Articles

Turbulent impinging air jet for cooling the heated surface

The present work deals with the experimental and numerical study of steadystate conjugate heat transfer during impingement of turbulent air jet over a heated stainless steel. The plate is heated using copper heater located at the middle. The temperature field is measured using an infrared camera and compared with the numerical simulations. Numerical simulations are performed using three-dimensional finite volume based formulation. The turbulence shear-stress transport (SST) is modeled using k−ω model based on the Reynolds averaged Navier Stokes (RANS) equations. The numerical simulations are in good agreement with the experimental data with marginal discrepancy in the steel plate region due to the contact thermal resistance between steel and copper. It is observed that the local Nusselt number increased in the stagnation region with increasing velocity of the impinging turbulent flow and practically unaltered in the region of the steel plate.

Effects of radial fin arrangements on the thermal performance of turbulent liquid jet impingement heat sinks: Experimental and numerical approach

The combination of fins and jet impingement is a highly effective method for enhancing thermal performance in electronic cooling. The arrangement of fins significantly influences the thermohydraulic characteristics of heat sinks. A comprehensive analysis comparing the impact of different radial fin arrangements in confined jet impingement is crucial for a deeper insight into their thermohydraulic performance. This study presents experimental analyses of heat sinks with smooth surfaces and radial straight fins in the Reynolds number ranged from 4300 to 15,500 and the heat flux ranged from 45 to 105 W/cm2. Then a numerical study is conducted on the radial straight and curved fin arrangement to investigate the effects of different radial fin arrangements on the performance of jet impingement heat sinks. The results demonstrate that the use of fins improves heat sink performance by up to 27 % compared to smooth surfaces. The numerical model, employing the SST k-ω turbulent model, shows strong agreement with experimental findings, with a maximum deviation of 9.1 % for the heat transfer coefficient, well within the uncertainty range. Comparing radial straight and curved fin arrangements numerically, the straight fin arrangement exhibits superior thermal performance by up to 9 %. Additionally, the pressure drop for both configurations remains nearly identical. The findings of this research suggest the use of radial straight fin arrangements in annular jet impingement heat sinks over radial curved fin arrangements.

Unveiling the underlying physics of two-phase boiling heat transfer enhancement through shearing of coalescing bubbles

The upcoming energy scarcity problem has driven research toward developing energy-efficient two-phase heat exchangers essential for various cooling applications. This research is rooted in the principles of pool boiling, essential for effective heat transfer in various heat exchangers. A well-known reported problem in heat exchangers is the dry-out phenomena of heated surfaces due to bubble coalescence. To tackle this undesirable problem, an innovative technique has been introduced in this study, which involves the shearing of bubbles through liquid jet impingement over the heated surface. The study has been carried out in a two-dimensional domain numerically, in the wall superheat range of 9–16 K. To study the underlying physics involved in this pool boiling phenomenon, the bubble dynamics parameters such as departure frequency, bubble diameter, cold spot (bubble base) temperature, and vapor volume fraction have been analyzed. The results show that with the jet shearing effect, a maximum enhancement of 25% in heat transfer rate is observed at higher wall superheat. The investigation also highlights that the liquid jet enhances vapor volume fraction, indicating enhanced steam generation, particularly an enhancement of 27% observed at elevated wall superheat. An early onset necking effect is also observed with the shearing effect, which leads to the formation of smaller bubbles with higher departure frequencies. This study is a benchmark to the fundamental physics of enhancing two-phase heat transfer through bubble shearing, offering promising insights for energy conservation in two-phase heat exchanger design, particularly within the context of pool boiling.

Numerical assessment of transient flow and energy dissipation in a Pelton turbine during startup

The Pelton turbine, known for its high application water head, wide efficient operating range, and rapid start-stop capability, is ideal for addressing intermittent and stochastic load issues. This study numerically analyzes the transient two-phase flow and energy dissipation during the startup of a Pelton turbine. Dynamic mesh technology controlled nozzle opening changes, and momentum balance equations managed runner rotation. Findings showed that the runner speed initially increased rapidly and then more slowly, and flow rate matched the nozzle opening variations. Runner torque first rose linearly, then decreased, with the fastest decline during nozzle closing. Hydraulic efficiency peaked early in nozzle reduction but then dropped sharply. Strong vortices formed due to upstream inflow and downstream backflow impact in the distributor pipe. The jet needle and guide vane improved flow in the converging section of nozzle, but flow began to diffuse with increased stroke. Initially, the jet spread fully on the bucket surface, but later only affected the bucket tips. Pressure fluctuations in the water supply mechanism were primarily due to jet needle motion, with higher amplitude during movement and lower when stationary. These fluctuations propagated upstream, weakening over distance. Reynolds stress work and turbulent kinetic energy generation, respectively, dominated energy transmission and energy dissipation, with their maximum contribution exceeding 96% and 70%. High-energy clusters corresponded to jet impact positions, highlighting jet-bucket interference as crucial for energy transport. This study established a performance evaluation method for Pelton turbine startups, supporting further investigation into characteristic parameters, flow evolution, and energy dissipation patterns.

Characterization on the impact load of a local corner region of a liquid tank entering water

This study conducts a detailed examination of the characteristics of impact loads in complex triangular areas within liquid tanks via the volume of fluids (VOF) method, with a general understanding of impact loads. By comparing the numerical results with previous experimental data of oblique wedge impacts on water surfaces, the effectiveness of the VOF method was confirmed. Complex dynamic phenomena such as fluid climbing, jet impact, and air cavity effects in corner areas were analyzed through 3D flow characteristics. By examining two types of impacts (a structure impacting fluid and a fluid impacting structure), the equivalence between them is verified. An in-depth exploration of the load characteristics in different areas is conducted by combining the free surface evolution. The multipeak characteristics of the load and synchronicity of the peak loads at different parts are closely related to the phenomenon of the climbing fluid being obstructed. Bubble flow also plays a crucial role in affecting the load characteristics. Further exploration of the effects of structural motion on load characteristics reveals complex load variability. These findings provide a valuable reference for understanding the impact loads in complex corner areas of liquid tanks.

Enhancing sonothrombolysis outcomes with dual-frequency ultrasound: Insights from an in silico microbubble dynamics study

Sonothrombolysis is a technique that employs the ultrasound waves to break down the clot. Recent studies have demonstrated significant improvement in the treatment efficacy when combining two ultrasound waves of different frequencies. Nevertheless, the findings remain conflicted on the ideal frequency pairing that leads to an optimal treatment outcome. Existing experimental studies are constrained by the limited range of frequencies that can be investigated, while numerical studies are typically confined to spherical microbubble dynamics, thereby restricting the scope of the analysis. To overcome this, the present study investigated the microbubble dynamics caused by the different combinations of ultrasound frequencies. This was carried out using computational modelling as it enables the visualisation of the microbubble behaviour, which is difficult in experimental studies due to the opacity of blood. The results showed that the pairings of two ultrasound waves with low frequencies generally produced stronger cavitation and higher flow-induced shear stress on the clot surface. However, one should avoid the frequency pairings that are integer multipliers of each other, i.e., frequency ratio of 1/3, 1/2 and 2, as they led to resultant wave with low pressure amplitude that weakened the cavitation. At 0.5 + 0.85 MHz, the microbubble caused the highest shear stress of 60.5 kPa, due to its large translational distance towards the clot. Although the pressure threshold for inertial cavitation was reduced using dual-frequency ultrasound, the impact of the high-speed jet can only be realised when the microbubble travelled close to the clot. The results obtained from the present study provide groundwork for deeper understanding on the microbubble dynamics during dual-frequency sonothrombolysis, which is of paramount importance for its optimisations and the subsequent clinical translation.

Influence of nozzle profile on submerged pipe jet impingement heat transfer

ABSTRACT Current work focuses on enhancing the performance of solar air heater by employing vertical submerged pipe jets featuring different profiles: circular, square, triangular, and rectangular. The study investigates parameters including jet diameter ratio d / D h ranging from 0.044 to 0.11 and the jet spacing ratio ( Sj / D h ) varying from 0.108 at 0.433 while keeping the streamwise ( X / D h ) and spanwise Y / D h pitch ratio fixed at 0.867. The Reynolds number Re ranges from 3,000 to 18,000. Initial results for all the profiles were obtained through CFD simulations, indicating that the circular pipe jet demonstrates superior heat transfer and thermo-hydraulic performance parameter (THPP). The experimental validation of circular profile pipe jet showed a maximum THPP of 2.69 achieved at a d / D h of 0.066 and Sj / D h of 0.217, with a Reynolds number of 15,000.

High-Fidelity Simulation of the Light-to-Dense Stratification Transient in the HiRJET Facility

Density stratification in a large enclosure is a crucial phenomenon to heat transfer and sustainable passive heat removal of a sodium fast reactor during reactivity transients. However, engineering turbulence models were identified to have unsatisfactory performance in predicting propagation of a stratified front. Yet, the scarcity of high-resolution data for stratification hampers the development of models. To explor e applications of leveraging direct numerical simulation (DNS) data to support turbulence model development, this work conducted DNS using NekRS to study a long stratification transient in the High-Resolution Jet (HiRJET) experimental facility. This work considers an experiment run where light fluid is injected into a tank containing a denser fluid with a relative density difference of 1.5%. Formation of the stratified layer is identified as impingement of the buoyant jet promoting mixing of the two fluids. Based on the transient statistics, transport of the concentration can be characterized by regions with dominating effects of turbulent mixing, buoyant dissipation, and molecular diffusion, respectively, as moving away from the elevation of jet impingement. Concentration near the stratified front also exhibits oscillation at Brunt-Väisälä frequency. Preliminary validation of the simulation showed encouraging agreement of the concentration distribution with the reference experiment.

Evaluation of film cooling effect in multi-row hole configurations on turbine blade leading edge

The present study evaluated the film cooling performance of turbine blade leading edges with multi-row hole configurations. Numerical models were refined to improve simulation accuracy by adjusting the turbulent viscosity coefficient, enhancing the prediction of jet diffusion in stagnation areas. The film cooling effectiveness distribution was analyzed through pressure-sensitive paint (PSP) experiments, and the numerical method was validated. The Sellers formula, a two-dimensional model, was used to evaluate the impact of upstream jets on downstream film cooling, with comparisons to simulations. The results show that the Sellers formula generally predicts well at low blowing ratios, but strong interactions between the mainstream and secondary jets, along with vortex formation between hole rows, undermine its accuracy at high blowing ratios, creating a concentrated high-effectiveness cooling zone. Changes in hole row layout affect the film cooling effectiveness distribution but have minimal impact on area-average predictions by the Sellers formula. Combining experimental data at high blowing ratios with the Sellers formula provides critical insights for designing leading edge multi-row hole film cooling structures. This study emphasizes the importance of understanding vortex structures and jet interactions to optimize film cooling strategies, offering significant value for engineering designs in turbine blades.

A Study on the Optimization of Water Jet Decontamination Performance Parameters Based on the Response Surface Method

The substrate that adheres between the teeth of the traveling track plate during the operation of a deep-sea polymetallic nodule mining vehicle affects the driving performance, so this study aimed to investigate the effect of the water jet on the cleaning and decontamination performance of the track under different conditions. An optimization design method based on response surface methodology (RSM) is proposed. Based on the Box–Behnken design, the optimization variables of jet pressure, jet target distance, and impact angle, and the target response of jet strike pressure on tracks, were selected, and the numerical simulation method was combined with the response surface method to establish the regression model of the response of each optimization variable to the jet strike pressure on tracks and to determine the optimal parameter combinations. The study findings indicate that the primary factor influencing the pressure of the jet striking the crawler is the jet pressure. The hierarchical order of influence on the pressure of the jet striking the crawler, under the interaction of the three factors, is as follows: jet pressure and impact angle, jet pressure and target distance of the jet, and target distance of the jet and impact angle. The maximum pressure of the jet striking the crawler occurs when the jet pressure is 0.983 MPa, the target distance is 0.14 m, and the impact angle is 89.5°. Overall, the proposed design serves as a systematic framework for parameter optimization in the cleaning and decontamination process, and the research method and results provide theoretical references for the optimal design of mining truck desorption efficiency, which is critical for increasing mining efficiency and lowering energy consumption.

Prediction of heat transfer for a single round jet impingement using the GEKO turbulence model

Two-dimensional Reynolds-Averaged Navier–Stokes simulations are performed to study a single, round impinging jet heat transfer problem, utilizing the generalized k-omega (GEKO) turbulence model as a benchmark. The simulations are performed at a jet Reynolds number of 23,300 and a nozzle-to-plate distance of 2.0 where a second peak in surface Nusselt number is observed. The effects of the three primary (Csep, Cmix and Cnw) and three auxiliary (Cbf,l, Cbf,t and Cnw,sub) GEKO calibration parameters are investigated. The results indicate that Cmix has the most significant impact on the laminar-turbulent transition zone. A deep learning based regression model is developed and trained using the simulation outputs for fast predictions of the heat transfer curve. Using Csep=1.1, Cmix=−0.7, Cnw=2.0, Cnw,sub=2.25 and Cbf,t=3.0 along with laminar-to-turbulent transitional modeling values, provides the best agreement with experimental results from previous studies.

Thermal network for breeding blanket analysis and design in fusion reactor

Achieving carbon neutrality in energy production has become crucial and fusion energy is a promising way to a sustainable energy future. Breeding blanket is a critical component of a fusion reactor, ensuring tritium self-sufficiency and heat recovery for power generation. Breeding blanket needs an effective thermal management system as it operates under the high plasma in fusion reactors and the heat generated by the breeding reaction, which should be collected for power conversion. In this study, a thermal circuit model is used to analyze the design of a breeding blanket cooling system; in this model, each component is regarded as a thermal resistance element. Numerical simulations, empirical correlations, and equations are used to compute each resistance element. The thermal circuit results are then integrated into power conversion system using GateCycle for a basic analysis of power generation efficiency of a breeding blanket. Furthermore, we investigated the modified jet impingement design by changing thermal circuit elements to enhance cooling performance. The use of protrusions enhances the thermal performance of the impinging jet by 11 %, contributing to an overall enhancement in system efficiency. These findings could offer valuable insights for advancing the development of efficient, sustainable fusion energy systems.

Influence of operating parameters on the flow of the molten bath during the swirl-type oxygen lance blowing process

ABSTRACT In top-blowing steelmaking, the flow behaviour of molten steel during supersonic jet impact into the molten bath is crucial for the refining process. In this study, the effects of lance height and operation pressure on velocity distribution and the flow characteristics of the molten bath during the swirl-type oxygen lance blowing process in a 260t converter were explored. The results demonstrate that compared to the traditional oxygen lance, the stirring efficiency of a molten bath with the swirl-type oxygen lance is improved due to the tangential momentum of the jet and the increase in cavity diameter. As the lance height increases, the flow is improved at the bottom and surroundings of the molten bath, and the dead zone volume of the molten bath decreases first and then increases. The best stirring efficiency is achieved at H = 40de. As the operation pressure increases, the impact strength of the jet increases, the flow at the upper zone of the bath is significantly improved, and the dead zone volume decreases.

Thermal and hydraulic characteristics of a single reverse nanofluid jet in a double-wall cooling configuration

AbstractThis work investigates the thermo-hydraulic characteristics of a novel reverse jet impingement cooling 3-D module for high-power systems, entailing a single jet impinging upon a concave hemispherical surface within a double-wall cooling configuration. Water-based nanofluids, with Al2O3 and multi-wall carbon nanotubes (MWCNT), were subject to a comprehensive examination at a range of Reynolds numbers from 10,000 to 40,000. The computational framework utilized the volume of fluid (VOF) model for precise phase interface tracking, along with the $$k-\omega$$ k - ω SST turbulence model. The results demonstrated that nanofluids have remarkable heat transfer enhancement, compared to water. The maximum Nusselt number augmentation reached 61.76% and 77.47% for 2.0% Al2O3 and 0.04% MWCNT nanofluids, respectively. The thermal performance improved when escalating nanoparticle concentration and Reynolds numbers, reaching a cooling module’s thermal resistance of only 0.0266 K W−1. However, mild increments in pressure drop of up to 7.80 and 3.04% were noticed at the lowest Reynolds number for the two nanofluids, respectively. MWCNT nanofluids exhibited superior thermal enhancement over their Al2O3 counterparts despite their lower concentrations. The greatest combined thermo-hydraulic performance was attained with a 0.04% MWCNT nanofluid at a Reynolds number of 20,000, where the energy performance was boosted by 77%, compared to water. The study identified significant conjugate heat transfer effects, demonstrating how temperature gradients within the solid walls directly influenced heat transfer coefficients and thermal resistances within the fluid phase. These findings provide a deeper understanding of thermal management strategies for high-power systems. Graphic abstract

Influence of mass flux ratio and phase difference on impingement heat transfer characteristics of coaxial synthetic jet

The aim of the present study is to introduce and investigate the performance of a novel independently controlled coaxial synthetic jet (CSJ) designed for enhancing impinging heat transfer applications. The CSJ features a unique configuration with two coaxial cavities, each featuring inner and annular orifices of the same hydraulic diameter, all aligned at 0∘ The independently controlled CSJ allows precise manipulation of jet conditions and phase differences between its inner and outer cavities, offering a versatile platform for optimizing heat transfer performance under varying operational scenarios. This capability not only enhances our understanding of the heat transfer characteristics of the CSJ but also underscores its potential as an innovative tool for advancing thermal management in engineering systems. Here, the actuators are operated at a Reynolds number (Re) of 1260 to perform the jet impingement experiment. The study explores mass flux ratios, including 0.5, 1, and 2, to understand how these ratios affect impinging heat transfer characteristics. The investigation also explores the influence of different phase differences (∅) between the inner and outer diaphragms, ranging from 0∘ to 180∘ for different mass flux ratios. It has been observed that the percentage enhancement of the peak stagnation Nusselt number (Nustag) for Mr=0.5 is approximately 30.36░% and 53.68░% compared to Mr=1 and Mr=2, respectively. The peak Nustag enhancement of CSJ operated at Mr=0.5 is approximately 63.9░% and 58.6░% compared to the inner jet and annular jet operated separately. In the far field, when a phase difference of ∅=135∘ is provided, the peak Nustag is enhanced by approximately 17.29░% compared to ∅=0∘ for Mr=0.5. Based on the present study, it is recommended to operate the CSJ at a lower mass flux ratio (Mr=0.5) and a higher phase difference between the actuators (∅=135∘) to achieve maximum cooling effect from the heated plate.

Experimental heat transfer analysis of conical pin configurations in jet impingement cooling with elongated nozzle holes

BackgroundThis study investigates the impact of jet impingement cooling with varying nozzle lengths on the heat transfer performance of smooth and conical pinned target surfaces under turbulent flow conditions. The study focuses on the Reynolds numbers (Re) of 13,000, 26,000, and 39,000, using the liquid crystal thermography (TLC) method to collect experimental data. The dimensionless conical pin heights (Hc/d = 0.00, 0.67, 1.00, 1.33) and target surface-nozzle distances (G/d = 1.0, 2.0, 3.0, 6.0) were analyzed to understand their effects on heat transfer. MethodsThe experimental setup involved measuring Nu numbers and pressure losses in models with elongated nozzles and conical pins. The study examined how the interaction between pin heights and nozzle lengths influences heat transfer in a channel-confined impinging jet flow. The analysis included evaluating heat transfer performance in different jet regions and assessing pressure loss coefficients for various configurations. Significant FindingsResults indicated that for smooth target surfaces, elongated nozzles increased heat transfer in the first two jet regions but decreased it in the last jet regions due to cross-flow effects. In contrast, conical pinned surfaces showed a significant increase in heat transfer, particularly in the stagnation and last jet regions, with lower G/d and higher Hc/d values. Conical pinned surfaces enhanced overall heat transfer by at least 5 % compared to smooth surfaces, with a maximum Nu number increase of 21.87 %. However, configurations with G/d < 2.0 and Hc/d ≤ 0.67 negatively impacted heat transfer. Pressure loss analysis revealed that using conical pins and extended jets together increased pressure loss, with a maximum drop of 5.67 kPa at Re = 39,000. The Thermal Performance Criterion (TPC) ranged from a minimum of 0.97 at Re = 26,000 (G/d = 1.0, Hc/d = 1.00) to a maximum of 1.18 at Re = 26,000 (G/d = 6.0, Hc/d = 1.33).

Boiling heat transfer characteristics of Cu–Al2O3 nanocomposite coating surfaces in distributed jet array impingement

Nanocomposite coating surfaces were electrodeposited on copper substrate at various current densities, deposition times and Al2O3 concentration to experimentally investigate the enhancement of boiling heat transfer of HFE-7100 under atmospheric pressure in a distributed jet array impingement. The surface structure topography and wettability were analyzed to explore their relation to boiling heat transfer enhancement and critical heat flux (CHF). An increase in both current density and deposition time led to a decrease followed by an increase in the wettability of the Cu– Al2O3 surface. Conversely, an increase in Al2O3 concentration resulted in decreased surface wettability. However, unlike pool boiling, jet impingement attenuated the impact of enhanced surface wettability on boiling heat transfer and CHF; instead, the microstructure on the surface was found to be closely linked to boiling heat transfer performance. The nanocomposite coating surfaces exhibited a 70 % higher maximum boiling heat transfer coefficient and 50 % higher CHF than those of smooth surfaces. Excessive Al2O3 concentration weakened the enhancement of heat transfer performance due to the inhibitory effect of Al2O3 nanoparticles on copper growth, leading to reduced micro-nano structures.

Experimental investigation of enhancement heat dissipation in a novel heat sink under simultaneous impact of impingement jet and magnetic field

Experimental investigation of enhancement heat dissipation in a novel heat sink under simultaneous impact of impingement jet and magnetic field

Flow characteristics and thermal fields in fan-coupled jet impingement

Numerical methods are used to analyze the flow properties and thermal fields of a fan-coupled jet impingement. The shear stress transport(SST) k−ω model has been utilized in the numerical simulation conducted in ANSYS CFX. Initially, the study focuses on flow structures that are driven by pressure gradients. Due to the presence of the pressure gradient, there is a tip leakage vortex moving through the tip gap. In the vicinity of the hub, the boundary layer rolls up to form a passage vortex close to the blade. The presence of these secondary flow structures affects the features of the cooling flow provided by the axial fan. Velocity deficit and high turbulence exist in the regions as a result of the secondary flow structures. Furthermore, to demonstrate how the 3D structures affect the performance of the jet impingement, two comparison cases, named LF-Q and LF-curve, are introduced with uniform incoming flow. In the comparison cases, the axial fan is abstracted as a solid body with pressure rise and flow rate. Compared to the counterparts with uniform incoming flow, the fan-coupled jet shows a greater re-circulation and a narrower main jet as a result of the velocity deficit exiting near the hub. In terms of thermal performance, the fan-coupled jet outperforms a uniform impinging jet with the same flow rate by 1.18 times in total heat transfer. The velocity deficit and larger re-circulation have reduced the heat transport in the central target, while the mainstream with high velocity and strong turbulence has enhanced the heat transfer in the outer region. The fan-coupled jet impingement with high velocity in the narrower jet also shows improved local heat transfer, with a peak Nusselt number (Nu) approximately 1.37 times larger than that of the uniform case with the same flow rate.

High-frequency pressure fluctuations in vertical jet impingements: fast pressure-sensitive paint analysis

High-frequency pressure fluctuations in vertical jet impingements: fast pressure-sensitive paint analysis