Confined Slot Jet Impingement Research Articles

Structure Optimization and Cooling Performance of a Heat Sink With Discontinuous Triangular Ribs Impacted by Hybrid Nanofluid Confined Slot Jet Impingement

Abstract Due to the increased use of high heat flux electronic equipment, improving the heat transfer capacity and surface temperature uniformity of heat sinks have become a major concern. In this study, a novel confined slot jet impingement heat sink with discontinuous triangular ribs (CSJIHS-TR) in the wall impingement zone is proposed. The upper cover plate is angled to improve the ability of the heat sink to dissipate heat. A Cu-Al2O3/water hybrid nanofluid is chosen as coolant. The main structural parameters of CSJIHS-TR are optimized using multi-objective. The optimized CSJIHS-TR is investigated using the Re and φ of the hybrid nanofluid. The results show that the optimized CSJIHS-TR exhibits an improved heat transfer capacity. The optimized CSJIHS-TR achieves a 27.8% improvement in performance evaluation criterion (PEC) and a 91.0% reduction in temperature standard deviation (Tstd) compared to the confined slot jet impingement flat-plate heat sink (CSJIFPHS). As Re of the jet impingement and φ of the hybrid nanofluid increase, the heat transfer capacity and temperature uniformity of the optimized CSJIHS-TR increase; however, the flow resistance of CSJIHS-TR also increases. In addition, compared with the mononanofluid, the temperature uniformity and the heat transfer capacity of the CSJIHS-TR with hybrid nanofluid are significantly improved.

Structure optimization and cooling performance of a heat sink with discontinuous arc protrusions impacted by nanofluid confined slot jet impingement

PurposeThe purpose of this paper is to improve the overall heat transfer performance and the temperature uniformity of the heat sink and to explore the effects of the jet Reynolds number and the nanoparticle volume fraction of the nanofluids on the flow and heat transfer performance.Design/methodology/approachA heat sink with discontinuous arc protrusions in the wall jet region is proposed for confined slot jet impingement. A sloping upper cover plate is added to improve the heat transfer effect in this area. An Al2O3–water nanofluid is selected as the working fluid of the jet for better heat transfer. The Standard k-e turbulence model is used for numerical calculation. The key structural parameters of the heat sink are optimized by the response surface method and a genetic algorithm. The effects of the jet Reynolds number (Re) and the nanofluid concentration (ϕ) on the flow and heat transfer performance of the optimized heat sink are investigated.FindingsThe average Nusselt number of the optimal heat sink is 8.2% higher and the friction resistance is 5.9% lower than that of the initial flat plate heat sink when ϕ = 0.02 and Re = 8,000. The discontinuous arc protrusions and the sloping upper cover plate substantially enhance the heat transfer in the later stage of jet development, improving the temperature uniformity of the heat sink. The maximum temperature difference of the optimal heat sink is 28.1% lower than that of the flat plate heat sink at the same nozzle height. As the jet Reynolds number and the nanofluid particle concentration increase, the Nusselt number of the optimized heat sink and the friction coefficients increase, resulting in a decrease in the evaluation coefficient. However, the overall temperature uniformity of the heat sink is improved under all conditions.Originality/valueThe novel heat sink structure provides a new way to enhance the heat transfer and temperature uniformity of confined slot jet impingement. The flow and heat transfer performance of the heat sink impinged by confined slot jet of nanofluids are obtained. The combination of response surface method and genetic algorithm can be applied to the multi-objective optimization of heat resistance and flow resistance of heat sink.

Numerical investigation on heat transfer performance of a confined slot jet impingement with different MEPCM-water slurries using two-phase Eulerian–Eulerian model

An in-house Fortran-based two-phase Eulerian–Eulerian solver is used to study an impinging jet with microencapsulated phase change material (MEPCM)-water slurry in a minichannel. The heat transfer performance of water based n-eicosane and n-octadecane MEPCM slurries are reported here. The melting pattern of the particles within the minichannel are also reported at different parameters. Figure of merit (FOM) is used to quantify the heat transfer performance of the MEPCM-water slurry taking into account both the thermal and flow characteristics of the slurry. The heat transfer enhancement around 72% is found in the average Nusselt number for a 5%-n-eicosane water slurry, compared to that of pure water at a jet Reynolds number of 200. The melting region of MEPCM particles is found to come closer to the heated walls with an increase in Reynolds number. An increase in the Reynolds number from 100 to 300 has brought an increment of around 81% in the Nusselt number at the jet impinging region, while the increment in the average Nusselt number is around 145%. The figure of merit (FOM), increases from 1.34 to 1.64 with an increase in particle concentration from 1% to 10%, at Re = 300. By comparing the figure of merit values, the best heat transfer performance compared to pure water is obtained for water-based n-eicosane slurry at Re = 100, and εs=1%. A parametric study involving Reynolds number, particle concentration, and channel height to jet width ratio has been reported. Present results are validated with numerical and experimental results available in the literature.

Application and CFD-Based Optimization of a Novel Porous Object for Confined Slot Jet Impingement Cooling Systems under a Magnetic Field

A novel porous object for the control of the convective heat transfer of confined slot nanojet impingement is offered under magnetic field effects, while optimization-assisted computational fluid dynamics is used to find the best working conditions to achieve the best performance of the system. The flow, thermal patterns, and heat transfer characteristics were influenced by the variation in rotational Reynolds number (Rew), Hartmann number (Ha), permeability of the porous object (Da) and its location (Mx). There was a 14.5% difference in the average Nusselt number (Nu) at the highest Rew when motionless object configuration at Ha = 5 was compared, while it was less than 2% at Ha = 25. At Rew = −600, the average Nu variation was 22% when cases with the lowest and highest magnetic field strength were compared. The porous object provides an excellent tool for convective heat transfer control, while the best performance was achieved by using optimization-assisted computational fluid dynamics. The optimal sets of (Rew, Da, Mx, AR) for porous object were (−315.97, 0.0188, −1.456, 0.235), (−181.167, 0.0167, −1.441, 0.2), and (−483.13, 0.0210, −0.348, 0.2) at Ha = 5, 10, and 25, respectively. At the optimal operating point, the local Nu enhancements were 19.46%, 44.86%, and −0.54% at Ha = 5, 10, and 15, respectively, when the no-object case was compared, while the average values were 7.87%, 8.09% and 5.04%.

Hybrid nano-jet impingement cooling of a curved elastic hot surface under the combined effects of non-uniform magnetic field and upper plate inclination

In this study, slot hybrid nano-jet impingement cooling application of a curved elastic surface is considered under the combined effects of non-uniform magnetic field and upper plate inclinations. When magnetic field is present, the local Nusselt number (Nu) peaks are suppressed, but in absence of magnetic field, profound rise of stagnation point Nu is seen with higher Re. The increment amount of the local peak Nu becomes 155.5% and 50.5% at Ha=0 and Ha=20. Significant variations of the local peak Nu locations are obtained when elastic modulus are varied with magnetic field at the highest strength. There is 141% variation of average Nu for the curved elastic part when walls with the lowest and highest elastic modulus cases are compared. There is 7% variations in the average Nu when the amplitude of the magnetic field is varied. The left and right plate inclinations contributed differently to the overall convective cooling performance due to the non-uniform magnetic field effects. Non-uniform magnetic field parameters along with the plate inclinations can be used for cooling performance of confined slot jet impingement system for a surface with curved elastic part.

Numerical Study on Hydrothermal Performance Factor Using Jet impingement and Nanofluid

In this study, thermal-hydraulic performance of a confined slot jet impingement with Al2O3-water nanofluid has been numerically investigated over Reynolds number ranges of 100-1000. Two triangular ribs are mounted at a heated target wall; one rib located on the right side of the stagnation point and another one located on left side of the stagnation point. The governing momentum, continuity and energy equations in the body-fitted coordinates terms are solved using the finite volume method and determined iteratively based on SIMPLE algorithm. In this study, effects of Reynolds number, rib height and rib location on the thermal and flow characteristics have been displayed and discussed. Numerical results show an increase in the average Nusselt number and pressure drop when Reynolds number and rib height increases. In addition, the pressure drop and average Nusselt number increases with decrease the space between the stagnation point and rib. The maximum enhancement of the average Nusselt number is up to 39 % at Reynolds number of 1000, the rib height of 0.3, rib location of 2 and nanoparticles volume fraction of 4%. The best thermal-hydraulic performance of the impinging jet can be obtained when the rib height of 0.2 and rib location of 2 from the stagnation point with 4% nanoparticles volume fraction.

Heat Transfer and Thermal Characteristics Effects on Moving Plate Impinging from Cu-Water Nanofluid Jet

The present article is focused on modelling of flow and heat transfer behaviour of Cu-water nanofluid in a confined slot jet impingement on hot moving plate. Different parameters such as various moving plate velocities, nanoparticles at various concentrations, variation in turbulent Reynolds number and jet nozzle to plate distance have been considered to study the flow field and convective heat transfer performance of the system. Results of distribution of local and average Nusselt number and skin friction coefficients at the plate surface are shown to elucidate the heat transfer and fluid flow process. Qualitative analysis of both stream function and isotherm contours are carried out to perceive the flow pattern and heat transfer mechanism due to moving plate. The results revealed that average Nusselt number significantly rises with plate velocity in addition with jet inlet Reynolds number. Correlations of the average Nusselt numbers are presented.

Numerical investigation on fluid dynamic and thermal behavior of a non-Newtonian Al2O3–water nanofluid flow in a confined impinging slot jet

A numerical investigation of hydrodynamic and heat transfer behaviors for Al2O3–water nanofluids for laminar confined slot jet impingement is presented. This study has been conducted by considering the nanofluid as Newtonian as well as non-Newtonian for a wide range of solid volume fraction (0 ≤ φ ≤ 5%) and Reynolds number range of (25–300). A single-phase fluid approach was used to model the nanofluid and the Ostwald–de Waele model described the non-Newtonian shear thinning nanofluid behavior has been adopted. A comparison with Newtonian and non-Newtonian nanofluid in terms of heat transfer coefficient, Nusselt number, streamlines and isotherms contours has been performed for the same Reynolds number, jet inlet velocity and the same aspect ratio H/W. It has been observed that the rate of heat transfer increases with Reynolds number and solid volume fraction of the nanofluid. Noting that the local Nusselt number is much higher for non-Newtonian nanofluid than Newtonian flow in the entire target surface with a particular enhancement located at the jet axis where a relative increase of 9.8% is evaluated for φ = 5% and Re = 300. However, the pumping power results showed a steep increase with the volume fraction for a Newtonian nanofluid case. In fact, the required PP is 1.32, 1.53, 1.99, 2.11 and 4 times greater than the values calculated in case of pure water at φ = 1, 2, 3, 4 and 5 respectively. At the same value of volume fraction φ, it is noted that the pumping power for a non-Newtonian nanofluid is many times higher than PP required in Newtonian nanofluid case, especially at Re ≤ 200. Lastly, the correlations for stagnation point and average Nusselt number are provided for Newtonian and non-Newtonian nanofluid.

Heat transfer analysis of slot jet impingement using Nano fluid on convex surface

Numerical simulation is performed for investigating the heat transfer performance using nanofluids in a confined slot jet impingement on a convex surface. The impinging jet is water - alumina nanofluids (40 nm average particle size). The aim of this numerical study is to evaluate the augmentation of heat transfer with suspended nanoparticles (in this case Al2O3 - water) using temperature independent nanofluids properties. Different parameters such as various Reynolds numbers, distance between jet to target plate have been considered to investigate the flow behaviour and convective heat transfer performance of the system. Results in the form of distribution of average Nusselt number and convective heat transfer coefficients at the curved surface are shown to elucidate the heat transfer and flow behaviour process. In addition, qualitative analysis of both stream function and isotherm contours is carried out to perceive the flow pattern and heat transfer mechanism due to addition of nanofluids. The results reveal that average Nusselt number and heat transfer coefficient significantly rises with rise in jet inlet Reynolds number. It is also proved that heat transfer is augmented when nano particles are added to a base fluid.

Heat Transfer Augmenation Using Nanofluid of a Confined Slot Impingement Jet on Concave Surface

Numerical investigation of heat transfer process using A12O3-water nanofluid in a confined slot jet impingement on concave surface is performed. The simulation is conducted on a two-dimensional turbulent flow with k –ω SST model for the turbulence computation. A constant heat flux is considered on concave surface. Different parameters such as various Reynolds numbers, and nozzle-to-surface spacing have been considered to study the flow field and convective heat transfer performance of the system. Results in form of distribution of local and average Nusselt number and Convective heat transfer coefficients at the curved surface are shown to elucidate the heat transfer and fluid flow process. In addition, qualitative analysis of both stream function and isotherm contours is carried out to perceive the flow pattern and heat transfer mechanism due to addition of nanofluids. The results reveal that average Nusselt number as well as heat transfer coefficient significantly rises with jet inlet Reynolds number. It is also proved that heat transfer is augmented when nanoparticles are added to a base fluid.

Three-dimensional numerical study of laminar confined slot jet impingement cooling using slurry of nano-encapsulated phase change material

This Article presents a three dimensional numerical model investigating thermal performance and hydrodynamics features of the confined slot jet impingement using slurry of Nano Encapsulated Phase Change Material (NEPCM) as a coolant. The slurry is composed of water as a base fluid and n-octadecane NEPCM particles with mean diameter of 100nm suspended in it. A single phase fluid approach is employed to model the NEPCM slurry.The thermo physical properties of the NEPCM slurry are computed using modern approaches being proposed recently and governing equations are solved with a commercial Finite Volume based code. The effects of jet Reynolds number varying from 100 to 600 and particle volume fraction ranging from 0% to 28% are considered. The computed results are validated by comparing Nusselt number values at stagnation point with the previously published results with water as working fluid. It was found that adding NEPCM to the base fluid results with considerable amount of heat transfer enhancement.The highest values of heat transfer coefficients are observed at H/W=4 and Cm=0.28. However, due to the higher viscosity of slurry compared with the base fluid, the slurry can produce drastic increase in pressure drop of the system that increases with NEPCM particle loading and jet Reynolds number.

Numerical Study of Heat Transfer From Pin-Fin Heat Sink Using Steady and Pulsated Impinging Jets

This paper investigates numerically the heat transfer characteristics of confined slot jet impingement on a pin-fin heat sink. A variety of pin-fin heat sinks is investigated, and the resulting enhancement of heat transfer studied. The distribution of heat transfer coefficient on the top surface of the base plate and that along the fin height are examined. Both steady and pulsated jets are studied. It is observed that for a steady jet impingement on a pin-fin heat sink, the effective heat transfer coefficient increases with fin height, leading to a corresponding decrease in base plate temperature for the same heat flux. In the case of pulsated jets, the influence of pulse frequency and the Reynolds number is examined, and their effect on the effective heat transfer coefficient is studied.

Cooling Performance of Using a Confined Slot Jet Impinging onto Heated Heat Sinks

A series of experimental investigations on the studies related to transient- and steady-state cooling performance from the horizontally heated heat sinks with a confined slot jet impingement have been conducted. The relevant parameters influencing the transient convective cooling performance include the steady-state Grashof number, ratio of jet separation distance to nozzle width, ratio of heat sink height to nozzle width, and jet Reynolds number. The transient heat transfer behaviors such as the temperature distribution, local and average Nusselt numbers on the heated heat sinks have been systematically explored. Two empirical correlations of steady-state local and average Nusselt numbers are presented. Furthermore, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. This empirical correlation obtained by data regression is in good agreement with the experimental data. The maximum and average regression errors are 7.46% and 2.87%, respectively.

Mist/Steam Heat Transfer in Confined Slot Jet Impingement

Internal mist/steam blade cooling technology has been considered for the future generation of Advanced Turbine Systems (ATS). Fine water droplets of about 5 μm were carried by steam through a single slot jet onto a heated target surface in a confined channel. Experiments covered Reynolds numbers from 7500 to 25,000 and heat fluxes from 3 to 21 kW/m2. The experimental results indicate that the cooling is enhanced significantly near the stagnation point by the mist, decreasing to a negligible level at a distance of six jet widths from the stagnation region. Up to 200 percent heat transfer enhancement at the stagnation point was achieved by injecting only ∼1.5 percent of mist. The investigation has focused on the effects of wall temperature, mist concentration, and Reynolds number.

Heat transfer behaviors of a confined slot jet impingement

An experimental study on heat transfer behaviors of a confined slot jet impingement has been systematically performed. The parametric effects of jet Reynolds numbers and jet separation distance on heat transfer characteristics of the heated target surface are explored. With the measurement of jet mean velocity and turbulence intensity distributions at nozzle exit, two jet flow characteristics at nozzle exit, initially laminar and transitional/turbulent regimes, are classified. As for the investigation of heat transfer behaviors on stagnation, local and average Nusselt number, it is evident that the effect of jet separation distance is not significant; while the heat transfer performance increases with increasing jet Reynolds number. Comparisons of the present experimental data with the existing numerical and experimental results are made. Besides, two new empirical correlations for stagnation and average Nusselt numbers on the heated target surface are also reported in the study. Furthermore, a concept of effective cooling length is introduced to evaluate the average Nusselt number on a finite-length target surface, the existing numerical results are reasonably consistent with the present experimental data.

Fluid flow and heat transfer of an extended slot jet impingement

A numerical analysis for fluid flow and heat transfer of a confined slot jet impingement with an extended nozzle is performed. The parametric effects of jet Reynolds number, spacing between the confinement plate and the target surface, and nozzle length on local flow development and heat transfer characteristics of the heated target surface are explored. The viscous boundary-layer thickness at the stagnation line is presented. It may be well predicted by the correlation of a two-dimensional stagnation flow if the lateral velocity gradient just outside the viscous boundary layer is known. This lateral velocity gradient is linearly proportional to jet Reynolds number, while inversely proportional to the ratio of nozzle exit-to-target surface distance to nozzle width in a 0.34 power. In addition, new correlations for stagnation and local Nusselt numbers along the heated target surface are reported in this article. These correlations give satisfactory agreements with theoretical results.