Water Jet Impingement Research Articles

Jet impingement quenching phenomena for hot surfaces well above the limiting temperature for solid–liquid contact

Experiments were conducted to understand the phenomena that happen just after a subcooled free-surface circular water jet impinges on a high temperature surface. A 2 mm-water-jet of 5–80 K subcooling and 3–15 m/s velocity was impinged on the flat surface of a cylindrical steel/brass block that was preheated to 500–600 °C. The transient temperature data were recorded and used to predict the surface temperature by an inverse heat conduction technique. A high-speed video camera was also employed to capture the flow condition. It is found that for a certain period of time the surface temperature remains well above the thermodynamic limiting temperature that allows stable solid–liquid contact. What happens during this period and what makes the surface temperature drop to the limiting temperature are important questions whose possible answers are given in this article. The cooling curves at the center of the impinging surface for different experimental conditions are also explained in relation with the limiting temperature and three characteristic regions having different types of flow patterns are identified.

Experimental investigation of propagation of wetting front on curved surfaces exposed to an impinging water jet

The wetting phenomenon during the cooling of a hot cylindrical specimen exposed to an impinging water jet has been studied experimentally. The Speed of Propagation of Wetting Front (SPWF) and regions of boiling heat that transfer outwards from the jet stagnation point have been investigated using high-speed video images. The effect of various jet parameters (velocity, diameter, water temperature) and the effect of the surface temperature on SPWF have been considered. Experiments were conducted under transient conditions considering initial specimen surface temperatures of 250°C, 500°C and 800°C, water temperatures in the range between 20°C and 80°C, jet velocities of 5 m/s and 7.75 m/s and jet diameters of 3 mm and 4 mm. For all of the jet and surface parameters considered in the study, SPWF was found to correlate well with power functions of time (i.e., instantaneous wetting front radius R&#61a(t)n)). Within the considered range of parameters, the results indicate that SPWF is mostly affected by the initial surface temperature, water temperature and jet velocity. Since control of the product microstructure is the key in determining its mechanical properties, the results of the investigation of the SPWF are used to quench carbon steel (1045) cylinders using different combinations of jet parameters. The results show a great flexibility in achieving various cooling rates, as indicated by the change in the final microstructure of the quenched samples.

Controlled partial embedding of carbon nanotubes within flexible transparentlayers

Applications of carbon nanotubes (CNTs) like field emission displays, super-capacitors, andcell growth scaffolds can benefit from controllable embedding of the CNTs in a material suchthat the CNTs are anchored and protrude a desired length. We demonstrate a simple methodfor anchoring densely packed, vertically aligned arrays of CNTs into silicone layers usingspin-coating, CNT insertion, curing, and growth substrate removal. CNT arrays of 51 and120 µm in height are anchored into silicone layers of thickness 26 and36 µm, respectively. Scanning electron microscopy (SEM) and opticalmicroscopy are used to characterize the sample morphology, a5.5 m s−1 impinging water jet is used to apply shear stress, and a tensile test shows that the siliconelayer detaches from the substrate before the CNTs are ripped from the layer. The CNTsare thus well anchored in the silicone layers. The spin-coating process gives control overlayer thickness, and the method should have general applicability to various nanostructuresand anchoring materials.

Experimental and Numerical Study on Heat Transfer with Impinging Circular Jet on a Convex Hemispherical Surface

In this paper, the experimental and numerical study has been carried out to investigate the water jet impingement on a convex hemispherical surface. The pressure and skin friction coefficient distributions on the impingement surface were analyzed numerically. A great deal of attention was paid to analyze the effects of the jet impingement exit velocity and the nozzle-to-surface distance on the heat transfer characteristics. A comparison of the heat transfer coefficient was performed between the jet impingement on the convex surface and the flat plate. The results show that the Nusselt number for the convex surface is higher than that for the flat surface. The local Nusselt number is decreased monotonically from its maximum value at the stagnation point for lower Reynolds numbers. A secondary maxima occurs for higher Reynolds numbers. The experiment and simulation were performed with the following parameters: the jet impingement Reynolds number of Re = 1947–19478, and the nozzle-to-surface distance of L/D = 2.5–25.

Nucleate boiling on the superhydrophilic surface with a small water impingement jet

In this study, the coating process on the copper surface with titanium dioxide (TiO2) has been introduced. The coated surface exhibits extremely high affinity for water and the solid–liquid contact angle decreases nearly to zero by exposing the surface to ultra-violet light. This superhydrophilic characteristic was applied to nucleate boiling heat transfer of water jet impingement on a flat heated plate. By making use of this special heat transfer surface, the nucleate boiling heat transfer and the critical heat flux (CHF) of a bar water jet impingement on a large flat superhydrophilic surface was experimentally investigated. The experimental data were measured in a steady state. The purified water was employed as the working liquid. Three main influencing factors, i.e., subcooling, impact velocity and the surface coating condition, were changed and their effects on the nucleate boiling heat transfer and the CHF were investigated. The empirical correlations were obtained for predicting the CHF of steady boiling for a small round water jet impingement on a large flat superhydrophilic surface. The experimental results show that the CHF on the superhydrophilic surface is about 30% higher than that on conventional copper surface by decreasing the solid–liquid contact angle.

Physical and Mathematical Modeling of Two-Phase Flows in a HOLLOW JET NOZZLE

The HOLLOW JET NOZZLE (HJN) is a heat exchanger used for the removal of superheat from molten steel between tundish and mold. It is a relatively new technology, developed by CRM, Belgium, through engineering the design of the conventional submerged entry nozzle (SEN) in continuous casting. In the present study, fluid-flow phenomena in a HJN system were investigated experimentally via a 0.23-scale water model, designed and operated on the basis of a Froude scaling criterion. Parallel to such, numerical simulation was carried out via FLUENT 6.1 embodying a turbulent, VOF-based, multiphase flow calculation procedure. These, in general, indicated that the incoming liquid, following its impingement on the solid baffle, spreads radially and flows down as a thin liquid film along the wall of the HJN. A large number of experiments were carried out to determine the radial spread of the impinging water jet and its point of attachment on the wall of the HJN as a function of volumetric flow rate, baffle geometry and dimensions, diameter of HJN, etc. These indicated that baffle geometry and dimensions together with the diameter of the HJN influence the point of attachment (or the corresponding “attachment distance”) most. It was demonstrated that attachment distance and the associated contact area between the flowing liquid and HJN wall can be considerably improved by appropriately modifying the currently employed baffle design. Such experimental findings were corroborated well by the FLUENT-based numerical procedure, which was in general able to capture the intricacies of film flow in the HJN system reasonably accurately. In addition to these, simplified models for attachment distance and film thickness have been developed and proposed for axisymmetrical HJN operation. Based on such, a relatively simple differential heat flow model has been developed for prediction of melt temperature in an industrial HJN system. It is demonstrated that in the absence of any elaborate numerical computation, the simplified models developed in this study provide a reasonable basis for engineering calculations in the axisymmetrical HJN system.

Synthesis and characterization of laser-based direct metal deposited nano-particles reinforced surface coatings for industrial slurry erosion applications

A nano-based material system resistant to the impingement of solid and liquid particles on the solid surfaces was developed by the laser-based direct metal deposition (LBDMD) process. The nano-based materials system contains 5% tungsten carbide (WC) nano-particles that are agglomerated with nickel–tungsten carbide 60 (Ni–Tung 60) by ball mill operation for slurry erosion resistance applications. Slurry erosion tests are performed on the LBDMD processed depositions using the ceramic proppant at different impingement angles using the abrasive water jet erosion testing machine. From these tests the amount of material removed, depth of penetration, and profile of the formed crater are computed as a function of the abrasive water jet impingement angles. The nano-based materials system exhibited better performance for slurry erosion resistance than the monolithic Ni–Tung 60 depositions and 4140 steels. In order to understand the role of the WC nano-particles influence on slurry erosion resistance and to understand the characteristic features of erosion surfaces, sub-surfaces, and the erosion mechanism, different advanced characterization tools are used.

An experimental investigation of free and submerged miniature liquid jet array impingement heat transfer

Liquid water jet impingement cooling was investigated experimentally for both free-surface jet arrays and confined submerged jet arrays. The jet arrays consisted of straight holes of 1.0 mm diameter arranged in rectangular arrays with spacings of 3, 5 and 7 jet diameters between adjacent jets. For the impingement surface area of 780 mm 2, these jet array configurations can be considered well populated, with a total of 21, 45 and 121 jets impinging on the surface. Average heat transfer and pressure drop measurements are presented for volumetric flow rates in the range of 2 L / min ⩽ V ˙ ⩽ 9 L / min and dimensionless jet-to-target spacings between 2 ⩽ H/ d n ⩽ 30. For the submerged jet arrays a strong dependence on both jet-to-target and jet-to-jet spacing is observed and correlations are presented that adequately predict the experimental measurements. The free-surface jets show a non-monotonic change with jet-to-target spacing with a local minimum in the heat transfer coefficient at approximately H/ d n = 10. Here a transition from a submerged to a free jet flow configuration occurs. Once again, a correlating equation is presented that adequately predicts the free-surface jet array heat transfer data. The pumping power required to form the submerged and free jet flows show a different relationship to the heat transfer coefficient. Generally, submerged jets have a higher heat transfer coefficient for a given pumping power requirement.

Maximum heat flux propagation velocity during quenching by water jet impingement

Maximum heat flux propagation characteristics during quenching of hot cylindrical blocks with initial temperature 250–600 °C have been investigated experimentally using a subcooled water jet. When the wetted area starts moving towards the circumferential region, the heat flux reaches its maximum value and the position of maximum heat flux follows the visible leading edge of the wetting front. If wetting starts immediately after the jet strikes the surface, the velocity of this maximum heat flux point increases with the increase of jet velocity and subcooling and decreases with the increase of block initial temperature. These trends are opposite if there is a long delay before movement of the front.

Oblique impingement of circular water jets on a plane boundary

This paper presents the results of an experimental study on the oblique impingement of turbulent water jets of diameter d equal to 50.8, 101.6 and 152.4 mm, placed above a horizontal plate at vertical distances varying from 45 to 255mm and at impingement angles of θ with the plate equal to 15°, 30°, 45°, 60° and 75°, with the velocity of the jet in the approximate range of 3–10 m/s and the jet Reynolds number varying from 380,000 to 720,000. The deflected jet was mostly in the forward direction with very little backward flow for θ < 45°, which increased to an estimated value of about 5–10% for larger angles of impingement. The forward flow in the deflected jet or stream was in the supercritical state. The thickness profile of the deflected jet in the centerplane was similar for all the experiments if plotted in terms of a suitable scale which was either the thickness at the normalized distance from the impingement point x/d = 1.0 or 5.0, for x/d up to about 20. These scales in terms of the jet diameter varied mainly with the angle of jet impingement. The transverse thickness profiles in the deflected jet were also found to be similar. The velocity profiles in the boundary layer of the deflected jet were similar and its thickness δ remained constant for x/d up to about 7.5 as in the case of stagnation flows. The boundary shear stress τ0 appeared to increase first with the distance from the impingement point and then decrease as in the case of the impingement of submerged impinging jets.

Modeling of the Hydroentanglement Process

Mechanical performance of hydroentangled nonwovens is determined by the degree of the fiber entanglement, which depends on parameters of the fibers, fiberweb, forming surface, water jet and the process speed. This paper develops a computational fluid dynamics model of the hydroentanglement process. Extensive comparison with experimental data showed that the degree of fiber entanglement is linearly related to flow vorticity in the fiberweb, which is induced by impinging water jets. The fiberweb is modeled as a porous material of uniform porosity and the actual geometry of forming wires is accounted for in the model. Simulation results are compared with experimental data for a Perfojet ® sleeve and four woven forming surfaces. Additionally, the model is used to predict the effect of fiberweb thickness on the degree of fiber entanglement for different forming surfaces.

High heat-flux accelerator targets: Cooling with liquid metal jet impingement

In order to evaluate the performance of jet impingement for high heat-flux cooling, experimental cooling loops based on water and liquid metal jet impingement were designed and constructed. The current liquid metal system, based on an eutectic alloy of gallium and indium (GaIn) with a melting point of 15.7 °C, employs an annular inductive electromagnetic pump. The experiments showed that it is capable of accommodating a heat flux of about 20 MW/m 2 over an area of 10 −4 m 2. The jet velocity is less than 4 m/s and the required differential pressure from the pump is less than 10 5 Pa. In the present work the experimental section is supplemented by a theoretical one in which the cooling capability of impinging jets of liquid metal is modeled. In particular, turbulent flow in a dead end associated with the rear surface of a high-temperature target, and the corresponding heat-transfer process, are considered. The developed novel analytical model embodies the main peculiarities of the heat-transfer process and agrees fairly well with the experimental data. In addition, a detailed direct numerical simulation was done with the STAR-CD code. The gross underprediction of the turbulent heat transfer rate by the STAR-CD code is attributed to overprediction of the eddy viscosity in liquid metal flows.

A finite element-based model for pure waterjet process simulation

The utilization of abrasive waterjet (AWJ) cutting/drilling, and in particular its application into hard-to-cut materials, is growing. However, the mechanics of AWJ cutting is complex; the material removal process is not fully understood and, consequently, it has not been accurately modeled. In the current study, work was undertaken to mesh in a first stage the waterflow into the waterjet nozzle in order to use the finite element (FE) method to simulate the pure waterjet flow. The main objective is to investigate and analyze in detail the workpiece material behavior under waterjet impingement; a non-linear FE model (using LS-DYNA 3D code) has been developed, which simulates the erosion of the target material caused by the high-pressure waterjet flow. A combination of Eulerian–Langrangian elements is used for the waterjet and the target material, respectively, in order to handle their interaction. Damaged zones can be localized on impinged materials. Elements’ failure is handled by introducing a threshold strain after which Langrangian elements are removed. The results obtained from this numerical simulation (velocity profile, stress, erosion stages) show a good agreement with the results from previous experimental work that is available in bibliography. The next step of the research will be focused on the simulation of the whole procedure using various abrasives.

Quenching of High Temperature Cylindrical Surface with an Impinging Jet (Maximum Heat Flux)

An experimental study has been conducted to understand characteristics of transient heat transfer during quenching a hot cylindrical block with an impinging water jet. The experiment was done at atmospheric pressure for the following condition : an initial block temperature of 250 and 400°C, a subcooling of 20-80 K, a jet velocity of 3-15 m/s, and a nozzle diameter of 2 mm. The surface temperature and heat flux are estimated by applying two-dimensional inverse solution to the measured temperatures in the block during the quench. The surface heat flux is greatly influenced by the position of the wetting front. It reveals that the maximum heat flux appears slightly far from the wetting front and its value decreases with a distance from the jet. The experiment shows that the maximum heat flux in the quecnching is smaller than the critical heat flux (CHF) in the corresponding steady condition depending on a cooling situation, but the trend is similar between the maximum heat flux and the CHF. An equation is proposed to predict the maximum heat flux on a basis of the CHF correlation.

Critical Heat Flux of Steady Boiling for Water Jet Impingement in Flat Stagnation Zone on Superhydrophilic Surface

The nucleate boiling heat transfer characteristics of a round water jet impingement in a flat stagnation zone on the superhydrophilic surface were experimentally investigated. The superhydrophilic heat transfer surface was formed by a TiO2 coating process. The experimental results were compared with those on the common metal surface. In particular, the quantificational effects of the flow conditions, heating conditions, and the coating methods on the critical heat flux (CHF) were systemically investigated. The experimental data showed that the nucleate boiling heat transfer characteristics on the superhydrophilic surface are significantly different from those on the common metal surface. The CHF of boiling on the superhydrophilic surface is greatly increased by decreasing of the solid-liquid contact angle.

Erosion — corrosion of duplex stainless steel under Kuwait marine condition

Erosion — corrosion of stable passive metals like Duplex Stainless Steels (DSS) proceeds by the repeated removal and repair of the oxide film. When sand particles are entrained it can be a problem in marine pumps, piping systems, heat exchangers, and units handling seawater in the Arabian Gulf for use as part of desalination plants. More specifically, sand particles in the presence of seawater enhanced the erosion corrosion problem. If the passive film structure is stable, it will reform spontaneously when it becomes damaged. The erosion-corrosion study is concerned with the application of a jet impingement apparatus to study the behavior of DSS steel of Cr/Ni/Mo/N grade in simulated Arabian Gulf seawater. An interference color imaging technique (ICI) for thickness measurement of the oxide film passivity, pitting, and transpassivity of the surface of DSS has been developed under the effect of well defined hydrodynamic condition and potentiodynamic polarization technique. Electrochemical imaging technique of surface corrosion potential mapping (SCM) was also introduced to measure the rate of repair of the passive film combined poteniodynamic polarization under flowing conditions, both with and without the addition of sand particles. The main aim is to obtain a better understanding of the electrochemistry of DSS alloys in marine erosion–corrosion condition and to examine the viability of SCM and ICI to be used as a diagnostic tool for DSS material evaluation. The results indicated that both techniques gave optimum imaging analysis of DSS steel. Water jet impingement showed higher current densities at the ferrite dissolution potential and austenite pitting potential during the introduction of sand particles.

선상가열시 수냉이 유발하는 막비등 현상을 고려한 판의 변형 예측

From a rapid cooling to a slow cooling in the actual cooling process in shipyards, the phase of steel becomes martensite, bainite, ferrite, and pearlite. In order to simulate the cooling process, heat transfer analysis was performed considering the effects of impinging water jet, film boiling, and radiation. From above simulation it is possible to find the cooling speed at the inherent strain region and volume percentage of all phases in that region. By the suggested method based on the precise material properties calculated from volume percentage of all phases, it will be possible to predict the plate deformations by line heating more precisely. It is verified by comparing with some experimental results that the present method is very effective and efficient.

High heat flux accelerator targets cooling with liquid-metal jet impingement

Accelerator targets for radioisotope production generate very high density of thermal energy in the target material, which absorbs the particles beam. The design of these targets requires efficient heat removal techniques in order to preserve the integrity of the target. Normal average heat fluxes from these targets are around 1kW/cm2 and may reach order of magnitude higher values at hot spots.Few techniques exist to deal with such high heat fluxes. One of them is jet impingement that has been proved to be able to deal with heat fluxes as high as 40kW/cm2 using water as coolant. However, this requires very high jet velocities of more than 100m/s. A few theoretical and experimental studies indicate that liquid-metal coolants (e.g., gallium or gallium alloys) can improve the heat transfer efficiency in this configuration.Experimental cooling loops based on water and liquid-metal jet impingement have been designed and built at Soreq to evaluate this method. For the current liquid-metal system an eutectic alloy of gallium and indium (GaIn) is used. Initial experiments demonstrate that the GaIn cooling system can deal with heat flux of about 2kW/cm2 over an area of 1cm2. The jet velocity is less than 4m/s and the required differential pressure from the pump is less than 1bar.

평면 충돌제트에서 노즐 깃이 단상 및 비등 열전달에 미치는 영향

The water jet impingement cooling is one of the techniques to remove the heat from high heat flux equipments. Local heat transfer of the confined water impinging jet and the effect of nozzle collar to enhance the heat transfer are investigated in the fee surface jet and submerged jet. Boiling is initiated from the farthest downstream and increase of the wall temperature is reduced with developing boiling, forming the flat temperature distributions. The reduction in the nozzle-to-surface distance fur H/W1 causes significant increases and distribution changes of heat transfer. Developed boiling reduces the differences of heat transfer for various conditions. The nozzle collar is employed at the nozzle exit. The distances from heated surface to nozzle collar, Hc are 0.25W, 0.5W and 1.0W. The liquid film thickness is reduced and the velocity of wall jet increases as decreased spacing of collar to heated surface. Heat transfer is enhanced fur region from the stagnation to x/W8 in the free surface jet and to x/W5 in the submerged jet. For nucleate boiling region of further downstream, the heat transfer by the nozzle collar is decreased in submerged jet comparing with higher velocity condition. It is because the increased velocity by collar is de-accelerated downstream.

Machining of nickel-base, Inconel 718, alloy with ceramic tools under finishing conditions with various coolant supply pressures

Machining of Inconel 718 with whisker reinforced ceramic tool gave better performance in terms of tool life under high-pressure coolant supplies up to 15 MPa compared to conventional coolant supplies. The use of 15 MPa coolant supply pressure tend to suppress notching during machining thus improving tool life, while the use of higher coolant supply pressure of 20.3 MPa did not show improvement in tool life due probably to accelerated notch wear caused by water jet impingement erosion. Cutting forces decreased with increasing coolant supply pressure due to improved cooling and lubrication at the cutting interface as well as effective chip segmentation ensured by the momentum of the coolant jet. Surface roughness generated were well below the rejection criteria. This can be attributed to the round shape of the insert which tend to encourage smearing of the machined surface with minimum damage. Microstructure analysis of the machined surfaces show evidence of plastic deformation and hardening of the top layer up to 0.15 mm beneath the machined surface as a result of increase in dislocation density.