Jet Impingement Heat Transfer Research Articles

CFD Simulation of the Slot Jet Impingement Heat Transfer Process and Application to a Temperature Control System for Galvanizing Line of Metal Band

A CFD model to simulate the cooling technique trough slot jet impingement has been developed. Such a technique has been tested on an existing vertical galvanizing industrial line, which initially envisaged a round jet configuration, the subject of a previous work. Two different slot jet configurations have been simulated and compared to the pre-existing one, in order to provide design information for a possible new jet cooler after exploring different solutions. The numerical model has been appropriately calibrated and validated by comparing it with experimental measurements from a literature case. At first, a single slot jet configuration was simulated through a 2D model, then multi slot configurations were calculated using 3D models. Different turbulence models were compared to select the best candidate for the CFD approach. Finally, several configurations with different slots numbers and jet-wall distances were considered. It was possible to understand the physical mechanisms underlying this cooling technique and to be able to select the most promising configuration for the reference industrial cooling process.

Experimental study of jet impingement heat transfer with microencapsulated phase change material slurry

Based on the heat dissipation requirement of high heat flux for electronic chips, this paper establishes a closed-cycle experimental system and investigates jet impingement heat transfer characteristics with a microencapsulated phase change material (MEPCM) slurry as the working fluid. The phase change properties of the MEPCM particles and the thermal properties of the MEPCM slurry are analysed. The effects of several key parameters on the heat transfer and pressure drop of jet impingement are also discussed. Experimental results show that a 10% mass fraction of MEPCM slurry may enhance jet heat transfer by 32.8% compared with water because of the latent heat absorption of the PCM core. The heat transfer enhancement will be limited for higher mass fractions of slurry. The slurry exhibits a high heat transfer efficiency when the jet distance is ΔL/D = 4–9.3. The convective heat transfer coefficient of the slurry first increases and then decreases as the jet inlet temperature increases, and the optimum jet inlet temperature is approximately 12.1 °C lower than the melting peak temperature. Jet temperatures that are too high or too low will lead to deterioration of heat transfer for the slurry. These findings can provide guidance for the design of heat dissipation systems using MEPCM slurries.

REVIEW OF JET IMPINGEMENT HEAT AND MASS TRANSFER FOR INDUSTRIAL APPLICATION

REVIEW OF JET IMPINGEMENT HEAT AND MASS TRANSFER FOR INDUSTRIAL APPLICATION

Numerical analysis of inclined jet impingement heat transfer in microchannel

Abstract The current study focuses on investigating of the performance of inclined microjet array to reduce the temperature of electronic devices. The capacity of the inclined jet arrays has been investigated through a computational fluid dynamics analysis for incompressible laminar flow to find out surface temperature, pressure drop, and flow chaos for the change in jet spacing and diameter, which is related to the number of jets under the constrained heat sink volume. Five different jet arrays consisting of 4, 5, 9, 13, and 16 jets were investigated for different jet diameters. The jet inclination kept constant at 45° to the impingement surface. The results show that the average exit liquid temperature increases with increasing the number of jets. The effects also manifest as the number of jets increases the pressure drop reduces monotonously for all jet diameters under constant mass flow rate in the module. Inclined microjet impingement heat sink having 13 jets showed better potential than the other microjet array configurations.

A review on multiple liquid jet impingement onto flat plate

Multiple jet impingement has been an important industrial application for a long time. Processes like quenching of hot steel surfaces in steel industry utilize the high heat-carrying capacity of liquid multiple impinging jets in order to achieve the uniform temperature of the metallic surface. The objective of this paper is to summarise the state of the art of the process of multiple jet impingement onto flat plate and highlight the future scope of research space in this field. This study focuses on the arrays of impinging liquid jets and to summarize relevant experimental and numerical results on multiple liquid jet impingement heat transfer and hydrodynamic behavior together with the latest developments published in the literature. The present work is limited to the normal impingement of multiple liquid jets on flat surfaces and the physics behind the single and multiple liquid jet configurations are discussed in the paper followed by the experimental studies. The effect of various paprameters like the jet diameter, jet velocity, velocity-profile, jet to target distances, jet to jet distances, and surface boundary conditions. The numerical studies discuss the studies conducted on multiple jet impingement and compare the accuracy of the different numerical methods utilized in the studies. The extrapolation of the results obtained from single liquid jet impingement have been discussed to suggest efficient methodologies for multiple jet impingement studies. It has been found that the study of hydrodynamic characteristics of multiple jet impingement is an important aspect that affects the heat transfer rate due to the jet impingement and needs to be explored further to find a better correlation between heat transfer rate and different hydrodynamic parameters of the flow.

Heat transfer of multi-slot nozzles air jet impingement with different Reynolds number

This study analyzes the heat transfer characteristics of multi-slot nozzles air jets with velocity difference between the adjacent jets. The research content includes the influence of thermal uniformity analysis and heat transfer capacity owing to the existence of adjacent jets. The multi-slot nozzles experiment was carried out under the specified conditions. The heat transfer uniformity of multi-slot nozzles jet heat transfer was improved compared with that of a single-nozzle jet heat transfer. Moreover, the closer the Reynolds number of the adjacent jets, the better the heat transfer uniformity. The existence of adjacent jets would relatively inhibit the heat transfer capacity. Through a single-slot nozzle experiment, an empirical formula for heat transfer characteristics of a single-nozzle jet on this experimental platform is obtained. The empirical formula of multi-slot nozzles is obtained by extending the empirical formula of single nozzle. The accuracy of multi-slot nozzles empirical formula is verified through a multi-nozzle confirmatory experiment, and the application scope of the empirical formula is relatively widened.

Determination of effective heat transfer area on vertical surfaces subject to spray and impinging jet

In this paper a method is introduced to determine the area primarily contributing to heat transfer of spray and jet impingement cooling below boiling point. The setup is based on temperature measurement via an infrared camera. This camera is pointed at the back of a metal plate, whereas the nozzle is spraying from the front. This technique is especially suitable for heat transfer areas with different shapes, as it occurs with different nozzle types. The analysis of the heat transfer area uses a temperature criterion based on the second derivative of the temperature distribution. Using this method the heat transfer areas generated by a full cone nozzle, a hollow cone nozzle and a jet nozzle have been studied. The study focused on the influence of nozzle pressure, nozzle to target distance and nozzle inclination on the heat transfer area. The results show, that the heat transfer area generated by different nozzle types have similar behavior regarding nozzle pressure, but different behavior in terms of distance variation and nozzle inclination.

Jet impingement heat transfer within a hemisphere

Jet impingement heat transfer finds applications where a large heat flux is required between a fluid and a surface. Impinging jets can be implemented in Concentrating Solar Power (CSP) thermal receivers and bayonet tube heat exchangers. A simultaneous outlook on the heat transfer and total pressure loss (performance) characteristics of several jets impinging on a concave hemispherical surface are investigated experimentally and using an axisymmetric Reynolds averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) model. The four equation Transition SST RANS turbulence CFD model demonstrates to be most suitable for this domain with a mean absolute deviation from the experimental results of < 7% for the heat transfer coefficient and < 8% for the total pressure loss. Empirical correlations for the Nusselt number as a function of the nozzle outlet Reynolds number and Prandtl number are fitted. Relatively good agreement is found between the Nusselt correlation and existing literature. An empirical correlation is also presented for the total pressure loss factor for the jet impingement domain in general because it is found that the dominating total pressure loss occurs because of rapid expansion, which occurs in any impinging free jet. The developed empirical correlations and CFD model can be used to estimate the heat transfer and pressure loss characteristics of a bayonet tube heat exchanger, a solar thermal receiver employing impinging jets as well as other jet impingement domains.

Heat Transfer Investigation with Multiple Jet Impingement

An experimental study was carried out to study the effect of multiple jet impingement on a virtual electronic component using water and air as working fluids. It consists of an electrically heated test plate of size 20mm×20mm. Heat flux is varied between 25 to 250W/cm2 was dissipated using 0.25 and 0.5mm diameter jets placed in a 7×7 array with a pitch of 3mm. The difference in temperature between test surface and fluid inlet is within 30 degC for water jets and within 75 degC for air jet experiments. Experiments were conducted by changing the heat flux, flow rate and distance between the test surface and jet exit and [iv] horizontal and vertical positioning of the jets. It was found that heat flux, jet diameter and Reynolds number are important factors in determining the heat transfer. The effects of distance between test surface and jet exit [Z] and positioning of the jets were insignificant. Though the multiple jet impingement heat transfer problem is complex, the heat transfer results could be correlated using a simple relationship in the form of Nu = AqmRen. The constant (m) which indicates the effect of heat flux has the value of 0.8 and 0.9 depending upon the jet diameter and the coolant. The constant (n) which indicates the influence of Reynolds number has the value of 0.25 for both water and air jets. The value of constant (A) is different for water and air jets. The correlation developed in this research work can be effectively used to design multiple water and air jet cooling system for electronic components.

Numerical Investigation of Heat Transfer and Pressure Force from Multiple Jets Impinging on a Moving Flat Surface

In this paper extensive numerical investigation of the heat transfer characteristics and the pressure force of jet impingement from the single row and multiple rows on a fixed and moving flat surface are reported. The computations were carried out over a wide range of parameters: relative nozzle-to-surface distance (H/d) from 0.5 to 6, relative nozzle to nozzle distances (S/d) from 4 to 10, jet angle from 45° to 90°, relative velocity ratio (Vplate/Vj) i.e. ratio of surface velocity to jet velocity from 0 to 1. The jet Reynolds number (Re) of 2,500, 3,400, 10,000, 20,000, and 23,000 and the number of jet rows of 1, 2, 4, and 8 have been used. It was found that the numerical accuracy by SST k-ω model is reasonably high to allow for a discussion of the main flow and heat transfer characteristics. The jet impingement heat transfer performance is generally enhanced with the increase of jet Reynolds number and jet angle and with the decrease of surface distance (H/d), jet distance (S/d) and the relative velocity ratio (Vplate/Vj) within the range examined. The pressure force coefficients on the impingement surface are relatively insensitive to Re number and the velocity ratio within the range examined, while it has highly dependent on H/d, S/d and jet angle. For multiple rows of aligned jet holes, the flow pattern exhibited a different shape due to the different intensity of the interference between adjacent air jets. The effect of multiple rows with regards to the impact on average Nu and pressure force coefficient for different geometry variations such as Re, H/d, S/d, VR and ɵ is negligible compared to the single row by approximately 9 and 13% in average respectively. Based on the computed results, equations of dimensionless parameters are correlated.

Numerical study of the oscillation amplitude effect on the heat transfer of oscillatory impinging round jets

In this study, the effect of oscillation amplitude on the pulsed impinging jets in different nozzle to surface distances and Reynolds numbers investigated. Generally, the heat transfer increases by increasing frequency and amplitude. For distances smaller and longer than the length of the jet potential core the threshold frequency is highly dependent on the amplitude. As the amplitude increases, the threshold Strouhal number decreases, while for nozzle to surface distance near the end of the jet core the threshold Strouhal number is approximately independent from the oscillation amplitude and the Reynolds number and is about Also, although increasing the Reynolds number causes an enhancement in the threshold frequency, but in smaller amplitudes the heat transfer, increased relative to the corresponding steady jet.

RANS Simulation of the Effect of Pulse Form on Fluid Flow and Convective Heat Transfer in an Intermittent Round Jet Impingement

The of effect pulse form (rectangular, sinusoidal and triangular) on the fluid flow and heat transfer of an intermittent jet impingement was studied numerically. It was shown in a non-steady-state jet, both an increase and decrease in heat transfer are possible compared with steady-state jet for all investigated pulse forms. For small distances between the pipe edge and obstacle (H/D ≤ 6) in the pulsed jet, heat transfer around the stagnation point increases with increasing pulse frequency, while for H/D &gt; 8 an increase in frequency causes a heat transfer decrease. A growth in the Reynolds number causes a decrease in heat transfer, and data for all frequencies approach the steady-state flow regime. The numerical model is compared with the experimental results. Satisfactory agreement on the influence of the form and frequency of pulses on heat transfer for the pulsed jet on the obstacle surface is obtained.

A numerical analysis on the heat transfer of jet impingement with nanofluid on a concave surface covered with metal porous block

In this paper, combining the bilayer porous metal block of copper (BPMBC) on the concave heating surface and jet impingement of SiO2-H2O nanofluid is utilized in the flow channel. The k-e turbulent model coupled with Brinkman Forchheimer extended Darcy equations are employed to analyze the effects of the SiO2-H2O nanofluid concentration, porosity in the porous monolayer on concave surface, thickness ratio between the upper and lower porous layer in the bilayer porous metal block as well as the curvature of concave surface on the heat transfer. In comparison with pure water as working fluid, the 5.85% rise of average heat transfer coefficient (HTC) can be obtained while the 3.0% SiO2-H2O nanofluid is utilized in the mode. The combining effects of the porosity in the monolayer porous layer and the curvature of concave surface on the heat transfer are related to the heating surface area and convection between the jet nanofluid and heating surface. More heat transfer occurs in the bilayer porous metal block with a larger porosity in the upper layer and a lower porosity in the bottom layer due to the dominant effects of the convection and thermal conductivity respectively in the different porous layers. The effects of the thickness ratio between the upper and lower layer in the bilayer porous metal block on the heat transfer are related to the influencing portion between the surface area and convection. With an increase in the curvature of concave surface from R/L(ratio of concave radius to chordal length) =0.5 to R/L = 1.1, the average Nusselt numbers go up, and their rise rates decrease by the Reynolds number gradually, but the surface area decreases, which causes the average temperature rise of copper block. Besides, the higher average temperature occurs in the mode with a flat plate than that with a concave surface.

Heat Transfer From a Heated Flat Surface Due to Swirling Coaxial Turbulent Jet Impingement

Abstract Heat transfer from an isothermally hot flat surface due to swirling coaxial turbulent jet impingement is investigated numerically. The coaxial jet construction consists of implanting a thin-walled round tube inside a coaxial outer pipe. Two different fluid streams or jets, having different average velocities, flow through the inner tube, and the annular space between the inner tube and the outer pipe. The ratio of the average velocities of the jets, the ratio of the pipe diameters, the jet exit Reynolds number, the strength of the swirl, and the separation distance from the jet exit to the impingement surface are the main parameters for this flow configuration. The effects of the swirl strength on the jet impingement heat transfer at the target surface are investigated by computing the flow and thermal fields for various combinations of the problem parameters. The presented results contain the plots of the flow streamlines, the contours of the temperature, the contours of the swirl velocity, as well as the distribution of the local and average Nusselt number on the impingement surface. It is found that, compared to the single round jet, the coaxial jet produces enhanced and more uniform heat transfer at the heated surface. The jet-spreading and mixing are affected by the imposed jet swirl which modifies the heat transfer process. Thus, the heat transfer compared to a non-swirling jet is either enhanced or diminished depending on the combination of the problem parameters.

Effects of a triangular guide rib on flow and heat transfer in a turbulent jet impingement on an asymmetric concave surface

In this study, a triangular guide rib (TGR) is designed with the aim of enhancing the heat transfer rate by accelerating a jet impinging downward on an asymmetric concave surface with curvature radii of 8 cm (Cr = 0.15) and 12 cm (Cr = 0.1). An infrared thermometer camera is employed to measure the temperature distribution in the steady-state condition. Predicted Nusselt number profiles by the renormalization group k–ε turbulent model go well with the experimental data. An equilateral triangular rib with each side measuring 12 mm (D/2) is placed in the stagnation region to investigate the effects of the TGR on flow and heat transfer of the asymmetric concave surface. This investigation is carried out for three different Reynolds numbers: 23 000, 35 000, and 50 000. The acceleration of the impinging jet due to the TGR creates a horseshoe-shape in the zone of high Nusselt number values. Numerical results show that the TGR provides higher averaged Nusselt numbers compared to a smooth concave surface.

Effects of Frequency and Jet to Surface Spacing on Synthetic Jet Impingement Heat Transfer

Synthetic jet is a new technique for electronic chip cooling, which combines stagnant air to form a jet resulting from periodic diaphragm oscillations in a cavity. In this work, the heat transfer characteristics of a synthetic jet are investigated experimentally and numerically. A Piston-cylinder arrangement powers the synthetic jet through a circular orifice for the impingement of jet on the heated surface. Air is considered as the cooling medium. The major parameters identified to describe the impinging jet heat transfer are Reynolds number, frequency, ratio of jet spacing to diameter(Z/D) and nozzle geometry. Numerical studies have been carried out using the finite volume based commercial software ANSYS Fluent. The turbulent model used is k-ω model. The dimensionless distance between the nozzle and plate surface is in the range 2 to 16. Numerical results are in fair agreement with experimental results. As the frequency increases the average Nusselt number increases. High frequency synthetic jets were found to remove more heat than low frequency jets for small Z/D ratio, while low frequency jets are more effective at larger Z/D ratio. Nusselt number is maximum at the stagnation point and there occurs a secondary peak at lower Z/D ratios. Synthetic jet with rectangular orifice is more effective as compared to circular and square geometries.

Analytical solution to transient inverse heat conduction problem using Green’s function

A transient inverse heat conduction problem concerning jet impingement heat transfer has been solved analytically in this paper. Experimentally obtained transient temperature history at the non-impinging face, assumed to be the exposed surface in real practice, is the only input data. Aim of this study is to estimate two unknown thermo-physical parameters—overall heat transfer coefficient and adiabatic wall temperature—at the impinging face simultaneously. The approach of Green’s Function to accommodate both the transient convective boundary conditions and transient radiation heat loss is used to derive the forward model, which is purely an analytical method. Levenberg–Marquardt algorithm, a basic approach to optimisation, is used as a solution procedure to the inverse problem. An in-house computer code using MATLAB (version R2014a) is used for analysis. The method is applied for a case of a methane–air flame impinging on one face of a flat 3-mm-thick stainless steel plate, keeping Reynolds number of the gas mixture 1000 and dimensionless burner tip to impinging plate distance equals to 4, while maintaining the equivalence ratio one. Inclusion of both radiation and convection losses in the Green’s function solution for the forward problem enhances the accuracy in the forward model, thereby increasing the possibility of estimating the parameters with better accuracy. The results are found to be in good agreement with the literature. This methodology is independent of flow and heating conditions, and can be applied even to high-temperature applications.

In Memoriam: Professor Ephraim Maurice Sparrow

In Memoriam: Professor Ephraim Maurice Sparrow

An experimental examination of the role of turbulence on flame impingement heat transfer

Turbulence induced by actuators has been widely utilized as a effective means to enhance jet impingement heat transfer (JIHT). Flame impingement heat transfer (FIHT) has parital similarity to JIHT, and thus it is of interest to investigate the role of an actuator-induced turbulence to flame combustion as well as its FIHT. On a Bunsen burner that is incorporable with a ring-type turbulence actuator, a detailed experimental comparison of the flame appearance, reaction zone structure, thermal field and heat transfer of both laminar and turbulent flames under identical bulk flow conditions and equivalence ratios were conducted.Results show that the turbulent flame has a narrower stable-operation range than the laminar couterpart, and thus turbulence reduces the flame stability. A major difference between two flames exists at the reaction zone, which is identified to be a ‘brush’ structure in the turbulent case, instead of being a perfect cone in the laminar case. The flame brush changes the heat release behavior such that the temperature field of the turbulent flame shows lowered peak temperature while enlarged high-temperature zone. The changed heat release or temperature field reults in distinct local heat fluxes in the impinging flames at the stagnation region and near wall jet region. Consequently, the overall heat transfer rate of the turbulent flame becomes higher than the laminar flame. Accordingly, this study proposes that the actuator turbulence can be utilized as a useful technique to promote FIHT.

Performance analysis of different turbulence models in impinging jet cooling

The characteristics of heat transfer from a hot wall surface for the oblique impingement of a free turbulent slot jet have been investigated numerically. Different turbulent models — the [Formula: see text]-[Formula: see text], [Formula: see text]-[Formula: see text], SST [Formula: see text]-[Formula: see text], cubic [Formula: see text]-[Formula: see text] and quadratic [Formula: see text]-[Formula: see text] models — are used for the prediction of heat transfer and their results were compared with experimental results reported in the literature. The comparison shows that the [Formula: see text]-[Formula: see text], quadratic [Formula: see text]-[Formula: see text] and SST [Formula: see text]-[Formula: see text] models give more unsatisfactory results for the investigated configuration, while the cubic [Formula: see text]-[Formula: see text] model is capable of predicting the local Nusselt number in wall-jet region only. The [Formula: see text]-[Formula: see text] model exhibits the best agreement with the experimental results in both stagnation and wall-jet regions. Further, the [Formula: see text]-[Formula: see text] model is applied to analyze the obliquely impinging jet heat transfer problem. The parametric effects of the jet inclination ([Formula: see text], [Formula: see text] and [Formula: see text]), jet-to-surface distance ([Formula: see text], 6 and 8), Reynolds number ([Formula: see text], 15[Formula: see text]000 and 20[Formula: see text]000), and turbulent intensity ([Formula: see text], [Formula: see text] and [Formula: see text]) have been presented. The heat transfer on the upward direction is seen to decrease, while that on the downward direction it rises for the increasing angle. It is to be noted that as the value of [Formula: see text] decreases, the point of maximum Nusselt number ([Formula: see text]) displaces toward the upward direction from the geometric center point as well as its value reduces. The shifting of the [Formula: see text] is found to be independent of Re and [Formula: see text] within the range considered for the study.