Impinging Air Jet Research Articles

Experimental and numerical investigations of forced convection impingement heat transfer on plate-fin heat sinks using three different electronic cooling fans

An experimental and numerical study was conducted for plate-fin heat sinks subjected to impinging air jets produced by electronic cooling fans. One axial and two different radial fans were used and their distance to the heat sink was varied. The aluminum heat sinks had either plain fins or fins with sinusoidal surface structures, were heated by heat sources either distributed over the entire base plate or concentrated in the center. In total, temperature measurements for 264 settings were performed, and numerical simulations were carried out for 19 selected cases. The results show that the axial fan outperforms the radial fans for the investigated fan distances, that the structured fins lead to lower base plate temperatures and that significant asymmetries in the heat sink temperature distribution can occur in certain cases. The numerical simulations are used to gain a better understanding of the trends observed in the measurements. Particularly, the impact of the velocity profiles at the fan outlets and the influence of certain geometrical details of the fan design on the heat flux distributions and the airflow into the fin channels are explored. The results highlight practical problems that need to be considered when optimizing heat sink-fan combinations.

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.

Bayesian parameter estimation and evaluation of the K-ω shear stress transport model for plane impinging jets

Numerical simulations with semi-empirical turbulence models are commonly used to model impinging jets, often used for cooling solid surfaces. In this work, the constants in the k-ω shear stress transport model in ANSYS FLUENT are calibrated to experimental velocity and heat transfer data for a plane turbulent impinging air jet to determine if Kennedy-O’Hagan calibration (Kennedy and O’Hagan 2001 J. R. Stat. Soc. B 63 425–64) can improve predictions of near-surface velocities and surface Nusselt numbers for similar flows. Impinging jets have been proposed to cool the target plates of the divertor in future magnetic fusion energy reactors, where simulations are used to estimate divertor performance. The flat-plate divertor (Wang et al 2009 Fusion Sci. Technol. 56 1023–7) uses a plane jet of helium issuing from a B = 0.5 mm slot to cool a surface with radius of curvature of 44B at a distance 4B from the slot. Predictions from the calibrated numerical model are compared with independent experimental data at different flow conditions, as well as surface temperature data for a flat plate divertor test section. The contribution of this work is evaluation of the accuracy of a calibrated turbulence model for modest extrapolations in flow geometry and flow conditions for a plane impinging jet.

Experimental investigation of air jet impingement cooling in car radiator with hollow cone nozzle plate spacing using nanofluids

Experimental investigation of air jet impingement cooling in car radiator with hollow cone nozzle plate spacing using nanofluids

A comprehensive study of air jet impingement on curved surfaces: experimental analysis and correlation development

A comprehensive study of air jet impingement on curved surfaces: experimental analysis and correlation development

Experimental study of convective heat transfer distribution of non-interacting wall and perpendicular air jet impingement cooling on flat surface

An experimental study evaluated heat transfer with perpendicular and wall-impinging air jets on stainless steel foil, for Reynolds numbers Re = 3000, 5000, 8000, and 10000, where the perpendicular jet targets the bottom and the wall jet the top, creating a unique, non-interacting effect. Distances to nozzle diameter ratios for wall jets (S/d = 4, 6, 8, 10) and perpendicular jets (Z/d = 2, 4, 6, 8) were varied. Significant heat transfer increases were noted, with the Nusselt number rising by up to 49.20 % for a Z/d = 6 and S/d = 8 combination at Re = 5000. Improvements ranged from 10.03 % to 49.20 %, peaking when the jets' high heat transfer regions overlapped. Optimal performance for Re = 3000 was at S/d = 10, aligning the wall jet's maximum with the perpendicular jet's stagnation area. For Re = 5000 to 10000, optimal S/d values were 8 and 4 for Z/d = 6, 8 and Z/d = 2, 4, respectively. The Nusselt number increase ranged from 29.21 % to 46.57 % at S/d = 10 for Re = 3000, the highest among all tested values. Wall jet heat transfer downstream increased by 90–105 % over perpendicular jets in corresponding regions. Increasing the wall to perpendicular jet distance improved heat transfer near the stagnation point, suggesting this cooling method for high-density electronics like CPUs and GPUs.

Experimental investigation of effects of convective heat transfer and thermal performance of impinging jet on a metal plate with porous media

This experimental investigation is aimed to evaluate the effects of convective heat transfer phenomena in an aluminium metal flat disc/plate placed below metal foam using a single round jet of air impinging in a confined region. The Jet impingement technique contains pressurized air, which is configured for certain specific application. It is designed to spray the fluid with the help of a nozzle on the surface of the disc or plate which is being heated or is being cooled. To understand the heat transfer phenomena in a metal plate with metal foams facing round air jet impingement; three metal foams of similar geometries but of different porosities and permeabilities are taken for study. Each experiment is performed with seven different flow rates and at two different heights with two different heat flux values. The recorded measurements are temperatures, pressure differences, flow rates, resistance voltages and currents, and time. The outcomes of the experimental data are analysed and compared results of all four distinct kinds of metal foams with different jet to plate height and at different heat fluxes. It is concluded that heat transfer efficiency may or may not increase depending upon the metal foam used. Overall, the conclusions are extremely useful in engineering.

Investigation of Heat Transfer Increment in Electronic System Surfaces by Different Air Jet Impingement Applications

Investigation of Heat Transfer Increment in Electronic System Surfaces by Different Air Jet Impingement Applications

Exergetic performance assesment of a downward solar air heater with impinging air jets - An experimental study

The main objective of the present study is to perform an in-depth exergetic analysis on a downward solar air heater (SAHRR) in two configurations: one incorporating impinging air jets and the other without it utilizing an indoor experimental setup. In the present study, the exergy efficiency is calculated based on the rates of exergy losses to evaluate separately the exergy losses, providing insights into the specific terms that contribute to the highest rates of exergy deterioration for the given SAHRR. This investigation is performed to understand how various parameters, such as mass flow rate(m) and geometric parameters influences the thermal performance of SAHRR. Thermal performance was assessed experimentally by considering several parameters, including average Nusselt number, first law thermal efficiency, thermohydraulic efficiency, and exergy efficiency. The maximum thermohydraulic efficiency of 84.86% was obtained at m equals 0.06 kg/s with geometric parameters of relative jet spacing (H1/HD) of 0.5, relative jet Diameter (DJ/DH) of 0.057. From the investigation, it could be concluded that the predominant origin of exergy loss in both SAHRR configurations is attributed to the exergy losses resulting from the temperature difference between the sun and the SAHRR surface, which constitutes 70% of the overall exergy losses.

Evaluation of air impingement for dry-cleaning nonfat dry milk residues on a stainless-steel surface.

The use of air jet impingement to remove residues from surfaces in food manufacturing operations offers an alternative to the use of water and liquid cleaning agents. During this investigation, air impingement was used to remove nonfat dry milk (NFDM) residues from a stainless-steel surface. The influence of the water activity (aw ) of the residue, the time after the residue reached an equilibrium water activity, and the thickness of residue at the time of removal from the surface have been investigated. All three factors had a significant effect on the time for removal. An increase in the water activity, the time at equilibrium, the sample thickness, or a combination of all three resulted in an increase in the time required to remove the deposits. Visible changes in the structure of deposits were observed as NFDM samples equilibrated to water activities above 0.43. NFDM residues with water activities less than 0.33 were removed within 1s of using air impingement regardless of wall shear stress. When the water activities were greater than 0.50, the thickness of deposit was greater than 1mm, and the time after reaching an equilibrium water activity was over 7days, more than 5min of air impingement with wall shear stress over 9.48Pa was required to remove the residue. The results from these experiments indicated that air impingement has the potential to provide effective cleaning in manufacturing facilities for low-moisture foods. PRACTICAL APPLICATION: The introduction of water in low-moisture food environments is often undesirable due to the possibility of pathogenic microorganism growth. The normal cleaning operations in the food industry use water as a cleaning agent. This study evaluates the application of air impingement technology as a dry-cleaning method.

Impact of air jet impingement technology on the strength of tissue paper

Impinging air jets can be used to dewater, heat, and dry the web of tissue paper. High velocities of the air jets degrade the paper, and appropriate adjustments to the jet velocity and the distance of the nozzle from the surface of the wet web are crucial to obtain the highest quality product. This work investigated the correlation between the velocity of the air jet and the strength of paper subjected to the impingement method. Papers with an initial moisture content of 20% and various pulp mixes were tested, and the physical properties of papers were explored. After impinging an air jet, different tensile strength limits were obtained in the machine and cross directions. The paper had lower apparent density and higher roughness compared to classical pressing. The dependence of tensile strength and roughness on the fibers composition also was determined. Increasing the amount of eucalyptus fibers in impingement dewatered paper resulted in a decrease in its tensile strength and roughness. The value of elongation before breaking was the highest for softwood papers after the impingement method. The maximum velocity of an air jet that can be used to dewater or dry paper without the risk of damage to the papers was determined.

Heat Transfer Augmentation for Impingement of Steady Air Jet under Exponential Heat Flux Boundary Condition

Heat Transfer Augmentation for Impingement of Steady Air Jet under Exponential Heat Flux Boundary Condition

Experimental investigation of the Aero-Acoustics of a rectangular jet impinging a slotted plate for different flow regimes

Impinging jets are found in many industrial applications and specifically in ventilation systems. Mostly, these jets are turbulent and under certain conditions can be a source of discomfort in closed areas due to the high level of noise it can generates. Therefore, it is very important to understand the flow dynamics that is responsible of generating the acoustic field in order to control and reduce such phenomenon. In this paper, an experimental study of a rectangular impinging air jet on a slotted plate is considered for three different Reynolds numbers producing self-sustaining tones (Re = 4100, 5100, and 5900). The sound pressure and spatial velocity field are obtained simultaneously using four microphones located at different locations and SPIV technique. Results show that Re = 5100 correspond to a critical regime where there is a significant drop in the sound pressure level (SPL) that reached 5 dB when compared to a lower Reynolds number Re = 4100. The flow dynamic analysis suggests that this drop in SPL could be contributed to the path followed by the large coherent structure at Re = 5100, where they are deviated in the transverse direction along the wall leading to low energy transfer from the dynamic field to the acoustic one. However, at Re = 4100 and 5900 the peak in SPL could be contributed to the two paths followed by the large coherent structures and particularly to the path where vortices hit the slotted plate before escaping through it. This path is responsible for the optimization of energy transfer from the dynamic field to the acoustic field. Moreover, at Re = 5900 the spectrogram of the instantaneous frequency and instantaneous flow dynamics results show that the acoustic frequencies (160 Hz and 320 Hz) are generated by symmetric and anti-symmetric modes respectively. This unusual aspect is related to the sudden changes in vortex mode.

Thermo-hydraulic and exergetic analysis of rectangular channel with integrated jet impingement and roughness

ABSTRACT This experimental study investigates an innovative approach to enhance surface heat transfer efficiency by employing V-pattern protrusions in conjunction with an impinging air jet. The synergy between surface roughness and the air jet induces heightened turbulence, resulting in significantly improved heat transfer performance. Various parameters on a jet plate, such as relative streamwise spacing (X/Dh), relative spanwise spacing (Y/Dh), and relative jet diameter (dJ/Dh), were systematically explored over a Reynolds number range of 4,000 to 18,000, representing the operational range. Optimal thermo-hydraulic efficiency was achieved at specific parameter values: relative streamwise spacing (X/Dh) of 1.7, relative spanwise spacing (Y/Dh) of 0.86, and relative jet diameter (dJ/Dh) of 0.086. Statistical correlations were established based on experimental data for both Nusselt number and friction factor. Furthermore, an exhaustive exergetic analysis was conducted to evaluate the thermal system’s sustainability, potential for waste heat recovery, and avenues for improvement. This study’s significance lies in its pioneering approach to augmenting heat transfer through the novel integration of V-pattern protrusions and impinging air jets. The results not only delineate optimal parameter configurations for enhancing heat transfer but also provide insights into system sustainability, waste heat recovery potential, and broader applications. By amalgamating distinct techniques, this research advances the existing literature by achieving superior thermal performance.

Influence of inclined unconfined circular air jet impingement on local heat transfer characteristics of smooth flat plate

The influence of inclined unconfined circular air jet impingement on local heat transfer characteristics of smooth flat plate is studied experimentally. The experimental investigation was conducted with jet inclination angles of 45°, 60° and 75°, jet Reynolds number of 12000–28000 and nozzle to target surface distance of 1–6. The Nu characteristics is studied in different radial direction angles on flat plate ranging from θ = 0° to 180° in stagnation and wall jet area for different z/d, Re and jet inclination configurations. The Nu characteristics are obtained by using an IR thermal imaging and thin foil approach. The Nu characteristics of different jet inclination angles (φ = 75°, 60° and 45°) was compared with vertical jet (φ = 90°) for different z/d and Re. Asymmetric in Nu characteristics increases with decrease in jet inclination about the geometric impingement point. With jet inclination, the maximum Nu value shifts away from geometric impinging point towards the uphill area of target plate. The displacement of maximum Nu from geometric impinging point towards the uphill area is highly pronounced at lower z/d and higher Re for a given jet inclination configuration. The isothermal Nu ring is reported at r/d ∼2 from geometric point in wall jet area. Within isothermal ring, Nu increases with radial direction angles from 0° to 180° and reverse behavior is observed outside the isothermal Nu ring. Correlations of Nu are obtained at geometric point and maximum Nu point with maximum deviation of ±10 %. Moreover, correlation for average Nu is also presented with and accuracy of ±3.4 %.

Coupled fluid-thermal-structural analysis during the air cooling for glass tempering

The tempering process of plate glass involves rapidly cooling the high-temperature glass using an array of impinging air jets, inducing desired stress during cooling. Consequently, the formation of tempering stress results from the coupled interaction among flow, heat transfer, and stress. However, most previous studies have commonly neglected the influence of the flow field by assuming a uniform and constant distribution of heat transfer coefficients at different positions on the glass plate, which deviates from actual situations. This study employed a fluid-thermal-structural coupled simulation approach to predict the non-uniform residual stress distribution in tempered glass and investigate the interaction mechanisms among flow, heat transfer, and stress. Simultaneously, to validate the reliability of the method and model, this study experimentally investigated the single-nozzle jet impingement cooling for glass tempering. The study concluded that the simulation results were consistent with the experiment. Subsequently, a comparative analysis was performed between the fluid-thermal-structural coupled simulation results based on real boundary conditions and the thermal-structural coupled simulation results based on ideal uniform heat transfer coefficient boundary conditions. The results revealed non-uniform distributions of both heat transfer coefficient and temperature due to varying localized flow characteristics. Consequently, the ratio of surface compressive stress to internal tensile stress along the width direction of the glass was not a fixed value but ranged from 1.63 to 2.38. Furthermore, significant differences were observed in the stress distribution under the simulations of fluid-thermal-structural coupling and thermal-structural coupling. Therefore, it is recommended to employ the fluid-thermal-structural coupling method when predicting localized stress distribution.

Thermal characteristics of metal foamed flat plate with circular and elliptical impinging jets

ABSTRACT Here, the thermal characteristics of open-cell metal foam (OCMF) integrated stainless steel (SS) foil are investigated experimentally during air jet impingement using circular and elliptical nozzles. The aspect ratio (AR) of the elliptical nozzle is varied from 2 to 4, the Reynolds number (Re) is varied within 5000 - 25,000 and the impinging distance (z/d) is varied within 3–7 during tests. Thin foil thermal imaging infrared thermography has been utilized to record the temperature, and the measured temperature data is used to estimate the performance parameters. The thermal performance is evaluated based on the local, average, and stagnation Nusselt number (Nu) for different configurations. The integration of OCMF with SS foil has been found to significantly enhance heat transfer at the stagnation point in different nozzle configurations. At a Reynolds number (Re) of 5000, the percentage increase in stagnation Nu with foam compared to when there is no foam is found to be 80%, 46%, 38%, and 24% for nozzles with AR of 1, 2, 3, and 4, respectively. The local (0 ≤ x/d ≤2) and average values of Nu for lower impinging distance (z/d ≤5) are found to be higher for the elliptical nozzles, while for z/d ˃ 5, the circular nozzle is found to exhibit better performance. The peak average Nu with nozzle AR = 4 at Re = 25000 is found to be higher than nozzle AR of 3, 2, and 1 by 6.75%, 8.72%, and 23.44%, respectively. Additionally, for the same Re, the peak average Nu of nozzles with AR = 4, AR = 3, and AR = 2 is higher than the circular nozzle by 23.44%, 15.62%, and 13.54%, respectively. New correlations based on experimental results are proposed to determine the local and average Nusselt number as a function of various operating parameters.

A numerical investigation into thermo-fluid characteristics of pulsating jet impingement on a dimpled surface

A two-dimensional axisymmetric numerical model is employed to study the flow and heat transfer attributes of the pulsating air jet impingement on a dimpled surface. The results are compared with the steady jet impingement. The results are examined at a fixed Reynolds number of 5000, over a Strouhal number range of 0.1–0.5, and pulsation amplitude of 15% and 25% for three different nozzle-to-surface separations (z/d = 2, 6, and 10). The pulsation amplitude of 15% has a minor effect on heat transfer from the dimpled surface. However, at 25% pulsation amplitude, significant improvements in the heat transfer rates are obtained in many combinations of jet Strouhal number and jet surface spacing. The value of the optimum Strouhal number provides conditions for the maximum heat transfer rate, which varied with nozzle-to-surface separation distances. Combinations of higher separations and lower Strouhal numbers (and vice versa) produced optimum heat transfer among the cases considered in the present study. The maximum improvement (17.41%) in the average heat transfer over the steady jet was found at z/d = 10 for pulsation at St = 0.1, while at z/d = 6, St = 0.2 provides the highest heat transfer rate. It is urged that the vortices formed in pulse jet close to the natural frequency of vortex formation provide a conducive environment for the vortex growth and their existence, significantly affecting the jet entrainment, mixing, and jet spread, which eventually play the decisive factor in determining the overall heat transfer rates on the dimpled surface.

Heat transfer of movable air jet impingement over flat plate: experimental implementation

Heat transfer of movable air jet impingement over flat plate: experimental implementation

Flow condensation inside a multiport mini channel and a rectangular mini channel with pin fin array

In this paper, an experimental study of flow condensation was carried out of R134a in a multiport mini channel and a mini channel with pin fin array. The former comprised 20 parallel rectangular channels with an equivalent diameter of 0.64 mm. The latter is a narrow rectangular mini channel containing 10 rows of diamond pin fins with a staggered configuration, and height and longitudinal/transverse pitch of 0.5 mm and 2 mm respectively. To acquire the local value of heat flux and heat transfer coefficient, air jet impingement cooling devices were adopted to condense the vapor of refrigerants. The effects of vapor quality, mass flux, heat flux, and saturation pressure on flow condensation heat transfer coefficient were investigated with the operating conditions: vapor quality from 1 to 0, mass flux from 160 to 450 kg/(m2s), heat flux from 10.0 to 39.8 kW/m2, and saturation pressure from 600 to 1500 kPa. The experimental results indicated that the pin fin array significantly improves the condensation heat transfer coefficient up to nearly 186 % compared to the multiport mini channel in the high vapor quality region. For both channels, the local heat transfer coefficient increases with an increase in vapor quality, mass flux, and heat flux whereas decreases with increase in saturation pressure. The influence of heat flux and mass flux on heat transfer coefficient was more pronounced in the high vapor quality region than in the low vapor quality region. A sensitivity analysis was performed at different vapor quality levels. The most influential parameters in the smooth channel and the pin fin array are saturation pressure and mass flux, respectively. The relative contribution of heat flux is more obvious in the high vapor quality region. Some of the existing correlations have good prediction performance for the smooth channel experimental data in this paper, and the corresponding MAD is within 20 %. However, their deviations are much greater for the applications of pin fin array.