Multiple Jet Impingement Research Articles

Computational study on the behaviours of supersonic jets and their impingement onto molten liquid free surface in BOF steelmaking

A mathematical model is proposed to study the impingement of multiple supersonic jets onto the free surface of the liquid bath containing molten slag and metal in a steelmaking converter by means of volume of fluid (VOF) approach. The applicability of the proposed model is verified by the good agreement with measured and calculated results. The model is then used to study the jet hydrodynamic behaviours such as jet profile, impact force, penetration depth and impact area, as well as time-dependent evolution of cavity, with respect to temperature, operating pressure and lance height. The results show that the temperature effect on total impact force is negligible but significant for penetration depth and impact area. A semi-empirical correlation is used to describe penetration depth under the steelmaking condition of high temperature. It is also shown that the proposed model can reproduce the splashing phenomenon on the bath surface.On propose un modèle mathématique pour étudier l’impact de jets supersoniques multiples à la surface libre du bain liquide contenant de la scorie et du métal fondus dans un convertisseur de production d’acier, au moyen de l’approche du Volume de Fluide (VOF). On vérifie l’applicabilité du modèle proposé par l’agrément entre les résultats calculés et les résultats mesurés. On utilise ensuite le modèle pour étudier les comportements hydrodynamiques du jet, comme le profil du jet, la force de choc, la profondeur de pénétration et la superficie de l’impact, ainsi que l’évolution de la cavité en fonction du temps par rapport à la température, à la pression d’opération et à la hauteur de la lance. Les résultats montrent que l’effet de la température sur la force totale de choc est négligeable mais qu’il est important pour la profondeur de pénétration et pour la superficie de l’impact. On utilise une corrélation semi-empirique pour décrire la profondeur de pénétration pour la production d’acier à température élevée. On montre également que le modèle proposé peut reproduire le phénomène d’éclaboussement à la surface du bain.

Optimization of a Multiple Impinging Jets Cavitation Reactor Using Zero‐Valent Iron Powder as Catalyst

AbstractThe effect of a combination of impinging jets and hydrodynamic cavitation technology was investigated by a multiple impinging jets cavitation reactor (MIJCR). Zero‐valent iron (ZVI) powder and rhodamine B were chosen as heterogeneous catalyst and model pollutant, respectively. ZVI addition resulted in more than five times higher decolorization efficiency compared to runs without ZVI. In situ generation of Fenton reagents suggested an advanced Fenton process to explain the enhancing effect of the applied catalyst. Impinging jets and aeration led to significant enhancement of the process, and optimum values of inter‐nozzle distance and initial catalyst concentration favored the decolorization of rhodamine B.

Heat Transfer Enhancement by Jet Impingement on a Flat Surface with Detached-Ribs under Cross-flow Conditions

In this article, the heat transfer augmentation on a flat surface with jet impingement on axisymmetric detached ribs is numerically investigated. Both single and multiple jet impingement with and without crossflow interaction is investigated. Numerical simulations are done using Reynold-averaged Navier–Stokes (RANS) equations with a shear stress transport (SST) model with the commercial CFD code ANSYS-CFX. The influence of jet Reynolds number (7000 ≤ Re j ≤ 78,000), blowing ratio (5.8 ≤ M ≤ 11.5), and jet-outlet-to-target wall distance (2 ≤ H/D ≤ 6) are examined. Results show that the heat transfer is enhanced on the target wall with detached ribs in single and multiple jet impingement at moderate crossflow speeds.

Experimental Investigation to Boiling Heat Transfer on a Heated Surface with Multiple Impinging Jets

On the condition of water multiple jet impingements, a steady-state experimental study had been conducted for boiling heat transfer in an atmospheric pressure. The jet velocity was 0.95~1.59m/s and the sub-cooling degrees of jet fluid were 30~83°C.The results revealed that increasing either jet velocity or sub-cooling degrees would promote the heat flux through heated surface, and the effect was more pronounced in partial boiling regime than fully-developed boiling regime. The heat transfer with multiple jets is enhanced due to disturbance of different impingements. With modification of the factor which related to flow distance of fluid on heated surface, correlation which is applicable to one single impinging jet boiling, can also be used to calculate critical heat flux(CHF) in boiling heat transfer with multiple impinging jets.

Flow Asymmetry in Symmetric Multiple Impinging Jets: A Large Eddy Simulation Approach

A numerical study on in-line arrays of multiple turbulent round impinging jets on a flat heated plate was conducted. The Large Eddy Simulation turbulence model was used to capture details of the instantaneous and mean flow fields. The Reynolds number, based on the jets diameter, was equal to 20,000. In addition to flow features known from single jets, the interaction between the neighboring jets was successfully elucidated. Symmetry boundary conditions were imposed to reduce the computational domain to only a quarter. In accordance with previous numerical and experimental works, the asymmetry in the velocity field near to the impingement plate was also found to exist. LES showed oval imprints of the Nusselt number similar to experiments but with some discrepancies on the symmetry boundaries. The asymmetry, observed in previous experimental and numerical results, in the horizontal planes, parallel and close to the impingement wall, was confirmed. The recirculation zone responsible for asymmetry, known to develop due to the wall jets interaction, was seen in only one side of the diagonal formed by the central and the farthest jets.

Experimental investigation of heat transfer enhancement using impingement of multiple water jets

AbstractThe problem of cooling electronic components has become a subject of special interest in recent years due to the increasing capacity and rapidly decreasing size of electronic components. Direct contact cooling using multiple jet impingement is considered the most effective method. The heat transfer problem is complex and a better understanding of the jet impingement method is essential for the proper application of this method for electronic cooling. Investigations were carried out using an electrically heated test plate. Heat flux in the range of 25 to $200 \ \hbox{W/cm}^{2}$, which is a typical requirement for cooling high power electronic components was dissipated using 0.5‐mm diameter water jets arranged in a 7×7 array with a pitch of 3 mm. Temperature difference between the test plate and water was within $30 \ ^{\circ}\hbox{C}$. Tests were performed in the flow rate range of 22 to 40 ml/min, resulting in a Reynolds number range of 1100 to 1750. Results show a significant increase in the heat transfer coefficient or Nusselt number with an increase in heat flux. The effect of the flow rate or Reynolds number on the heat transfer coefficient is found to be negligible. © 2010 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20291

Enhancement of Impingement Cooling in a High Cross Flow Channel Using Shaped Impingement Cooling Holes

Impingement systems are common place in many turbine cooling applications. Generally these systems consist of a target plate that is cooled by the impingement of multiple orthogonal jets. While it is possible to achieve high target surface heat transfer with this configuration, the associated pressure drop is generally high and the cooling efficiency low. Furthermore, especially in large impingement arrays, the buildup of cross flow from upstream jets can be significant and results in deflection of downstream impingement jets reducing the resultant heat transfer coefficient distribution. This paper presents a computational and experimental investigation into the use of shaped elliptical or elongated circular impingement holes designed to improve the penetration of the impinging jet across the coolant passage. This is of particular interest where there is significant cross flow. Literature review and computational investigations are used to determine the optimum aspect ratio of the impingement jet. The improved heat transfer performance of the modified design is then tested in an experimental rig with varying degrees of cross flow at engine representative conditions. In all cases, a 16% increase in the Nusselt number on the impingement target surface in the downstream half of the cooling passage was achieved. Under the first four impingement holes, a Nusselt number enhancement of 28–77% was achieved, provided no additional cross flow was present in the passage. When appropriately aligned, a significant reduction in the stress concentration factor caused by the addition of a hole can be achieved using this design.

Efficient helium cooling methods for nuclear fusion devices: Status and prospects

Helium-cooled reactors offer several important advantages as the helium is an inert and neutron transparent gas, compatible with high outlet temperatures and all structural and functional materials considered for plasma facing components. On the other hand, during the power plant studies performed up to now it became evident, that the helium pumping power could become very high if standard cooling methods based on hydraulically smooth cooling channels would be applied and that a very high heat flux in the divertor can only be achieved when using sophisticated gas cooling methods. In relation to this the main focus in this paper is on advanced gas cooling technology applications developed at Forschungszentrum Karlsruhe (FZK) for the main in-vessel components blanket/first wall and divertor of future fusion power reactors. Among a large number of considered cooling technologies the V-rib-based surface roughness approach for the first wall and the multiple jet impingement cooling technique for the divertor were identified as suitable and advantageous methods. The paper presents the main parameters to be considered and an evaluation of the achievable cooling performance in both cases.

Heat Transfer during Multiple Jet Impingement on the Top Surface of Hot Rolled Steel Strip

Using a unique pilot facility a series of tests were conducted using three top jets to simulate the heat transfer that occurs during run‐out table (ROT) cooling. Steel samples instrumented with internal thermocouples were tested on this facility and the effect of top jet configuration (nozzle spacing of 40 to 115mm), and water flow rate (15 and 30 1/min) were quantified using moving plate samples. The multiple top jet work indicated that heat transfer across the plate width varies significantly and is high directly under the nozzle but decreases rapidly away from the nozzle in the interaction region. As cooling progresses a much larger wetted region occurs and more uniform cooling is experienced across the plate. Multiple jet cooling experiments have also confirmed that nozzle spacing does have an effect on heat transfer. This effect is predominate in the interaction region where closer nozzle spacing leads to enhanced and more uniform heat transfer in the lateral direction across the plate width away from the nozzle. As expected higher water flow rates led to higher heat transfer both under the nozzle and in the interaction region.

Large-eddy simulation of twin impinging jets in cross-flow

The flow-field beneath a jet-borne vertical landing aircraft is highly complex and unsteady. large-eddy simulation is a suitable tool to predict both the mean flow and unsteady fluctuations. This work aims to evaluate the suitability of LES by applying it to two multiple jet impingement problems: the first is a simple twin impinging jet in cross-flow, while the second includes a circular intake. The numerical method uses a compressible solver on a mixed element unstructured mesh. The smoothing terms in the spatial flux are kept small by the use of a monitor function sensitive to vorticity and divergence. The WALE subgrid scale model is utilised. The simpler jet impingement case shows good agreement with experiment for mean velocity and normal stresses. Analysis of time histories in the jet shear layer and near impingement gives a dominant frequency at a Strouhal number of 0·1, somewhat lower than normally observed in free jets. The jet impingement case with an intake also gives good agreement with experimental velocity measurements, although the expansion of the grid ahead of the jets does reduce the accuracy in this region. Turbulent eddies are observed entering the intake with significant swirl. This is in qualitative agreement with experimental visualisation. The results show that LES could be a suitable tool when applied to multiple jet impingement with realistic aircraft geometry.

Integration of an advanced He-cooled divertor in a DEMO-relevant tokamak geometry

Strong impulses to the development of in-vessel components for near-term fusion reactors like DEMO were given by the recent EU power plant conceptual study (PPCS). Within the PPCS reactor models were developed based on the EU Helium cooled pebble bed blanket (HCPB) concept (reactor model B) and the dual coolant blanket (DC) concept (reactor model C). As a consequence of the study, a design review was carried out in the EU to create a modular HCPB blanket, followed by an effort at Forschungszentrum Karlsruhe (FZK) of a complete in-vessel integration. Also, the development of a gas cooled divertor was launched within the PPCS, with the aim of increasing both safety and the overall plant efficiency. The latest and most advanced divertor concept, which was developed at FZK, is based on a feasible and effective heat transfer enhancement technique, namely the multiple jet impingement cooling technology, while helium was chosen as a gaseous coolant due to its good safety characteristics when used with a Be-containing blanket. A brief description of the divertor design is given with the focus is on reactor integration and target layout.

Determination of heat transfer rates in an industry-like spray quench system using multiple impinging water jets

Liquid jet impingement (LJI) cooling is widely employed in quench systems, the majority of which utilise multiple impinging jets. Successful design and operation of such systems require accurate data of actual heat transfer rates. The present study is concerned with the determination of heat transfer rates during rapid cooling of high temperature surfaces using multiple impinging water jets (MIWJs) in an industry-like arrangement. The effects of jet variables have been investigated. Heat transfer coefficients have been numerically calculated using inverse analysis, utilising experimentally determined temperature profiles. Comparison with heat transfer rates of immersion quenching has been considered. The present study provides important information about heat transfer rates in an industry-like water spray quench system using MIWJs. Results demonstrated that the use of MIWJs offers significant flexibility in controlling cooling rates, which renders this technique most suitable for quench operations requiring wide range of cooling rates.

Predictions of flow and heat transfer in multiple impinging jets with an elliptic-blending second-moment closure

We present numerical computations of flow and heat transfer in multiple jets impinging normally on a flat heated surface, obtained with a new second-moment turbulence closure combined with an elliptic blending model of non-viscous wall blocking effect. This model provides the mean velocity and turbulent stress fields in very good agreement with PIV measurements. The exploration of several simpler closures for the passive thermal field, conducted in parallel, confirmed that the major prerequisite for the accurate prediction of the temperature field and heat transfer is to compute accurately the velocity and stress fields. If this is achieved, the conventional anisotropic eddy-diffusivity model can suffice even in complex flows. We demonstrate this in multiple-impinging jets where such a model combination provided the distribution of Nusselt number over the solid plate in good agreement with experiments. Extension of the elliptic blending concept to full second-moment treatment of the heat flux and its truncation to a quasi-linear algebraic model is also briefly discussed.

04/00758 Socio-economic study of fusion energy at the Japan Atomic Energy Research Institute: Konishi, S. et al. Fusion Engineering and Design, 2003, 69, (1–4), 523–529

Strong impulses to the development of in-vessel components for near-term fusion reactors like DEMO were given by the recent EU power plant conceptual study (PPCS). Within the PPCS reactor models were developed based on the EU Helium cooled pebble bed blanket (HCPB) concept (reactor model B) and the dual coolant blanket (DC) concept (reactor model C). As a consequence of the study, a design review was carried out in the EU to create a modular HCPB blanket, followed by an effort at Forschungszentrum Karlsruhe (FZK) of a complete in-vessel integration. Also, the development of a gas cooled divertor was launched within the PPCS, with the aim of increasing both safety and the overall plant efficiency. The latest and most advanced divertor concept, which was developed at FZK, is based on a feasible and effective heat transfer enhancement technique, namely the multiple jet impingement cooling technology, while helium was chosen as a gaseous coolant due to its good safety characteristics when used with a Be-containing blanket. A brief description of the divertor design is given with the focus is on reactor integration and target layout.

04/00756 Conceptual design of the dual-coolant blanket in the frame of the EU power plant conceptual study: Norajitra, P. et al. Fusion Engineering and Design, 2003, 69, (1–4), 669–673

Strong impulses to the development of in-vessel components for near-term fusion reactors like DEMO were given by the recent EU power plant conceptual study (PPCS). Within the PPCS reactor models were developed based on the EU Helium cooled pebble bed blanket (HCPB) concept (reactor model B) and the dual coolant blanket (DC) concept (reactor model C). As a consequence of the study, a design review was carried out in the EU to create a modular HCPB blanket, followed by an effort at Forschungszentrum Karlsruhe (FZK) of a complete in-vessel integration. Also, the development of a gas cooled divertor was launched within the PPCS, with the aim of increasing both safety and the overall plant efficiency. The latest and most advanced divertor concept, which was developed at FZK, is based on a feasible and effective heat transfer enhancement technique, namely the multiple jet impingement cooling technology, while helium was chosen as a gaseous coolant due to its good safety characteristics when used with a Be-containing blanket. A brief description of the divertor design is given with the focus is on reactor integration and target layout.

Parametric Study of Heat Transfer in Turbulent Gas−Solid Flow in Multiple Impinging Jets

Heat transfer in a dilute gas−particle suspension flow in multiple-slot impinging jets has been numerically investigated using a new Eulerian−Lagrangian method that accounts for conduction heat transfer due to particle−wall collisions. The numerical results are compared with available experimental data. Good agreement between experiment and simulation is obtained only if the additional conduction heat transfer due to particle−wall collisions is considered in the model. The effects of particle diameter, particle material properties and loading ratios, jet Reynolds number, impingement wall temperature, and direction of the gravitation vector on heat transfer are discussed.

An evaluation of gas quenching of steel rings by multiple-jet impingement

Multiple gas jet impingement cooling for quenching is a very promising approach for increasing the heat transfer coefficients ( h) and thus the overall cooling rates in the gas-quenching process. Appropriate correlations for h were selected based on an extensive critical literature review, and used in a numerical heat conduction model and a numerical phase transformation model which were developed and solved for evaluating the quenching capacity of such cooling methods for quenching steel rings. The models allow prediction of the steel phase transformation extent as a function of h, for different ring sizes. An optimization of the jet nozzle dimensions and configuration was performed, and the effects of the jet spent flow and the cooling gas temperature were discussed and estimated. It was also found that while the spent flow effect on h is not adequately known, it tends to lower h, while the cooling gas temperature has minimal effect on h. Validation experiments were performed and show that the predicted trends are reasonable, within the errors of the Johnson–Mehl–Avrami phase transformation model and the experimental method used.

Local Heat Transfer Distributions in Confined Multiple Air Jet Impingement

Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000<Re<20,000), orifice-to-target spacing 0.5<H/d<4, and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Predictive correlations are proposed for single and multiple jet impingement heat transfer.

HEAT TRANSFER AND FLOW FIELDS IN CONFINED JET IMPINGEMENT

Confined jet impingement of air and different liquids is reviewed. The influence of confinement on the heat transfer and fluid mechanics of governing parameters such as jet diameter and geometry, Reynolds number, jet-to-target separation distance, exit velocity profile and turbulence levels, fluid properties, and target size is discussed. This review deals primarily with turbulent jets. Single- and multiple-jet impingement are considered, including predictive correlations for stagnation-point and area-averaged heat transfer. The velocity and turbulence fields in confined jet impingement are also described, with particular reference to their effect on the heat transfer obtained. The important role of flow visualization in understanding confined flow fields is demonstrated. Augmentation of jet impingement heat transfer by employing surface enhancements is also considered. The review includes discussions of numerical modeling efforts.

Heat transfer from pin-fin heat sinks under multiple impinging jets

The enhancement of heat transfer from a discrete heat source using multiple jet impingement of air in a confined arrangement was experimentally investigated. A variety of pin-fin heat sinks were mounted on the heat source and the resulting enhancement studied. Average heat transfer coefficients are presented for a range of jet Reynolds numbers (2000<Re<23000). Two jet-to-jet spacings were investigated and the results were compared to single jets of both the same orifice diameter and orifice area. A total fin effectiveness was computed for the pinned heat sinks relative to the unpinned ones, and was in the range of 3 to 6; the highest value was obtained for the largest nozzle diameter. Results for the average heat transfer coefficient were correlated in terms of Reynolds number, fluid properties and geometric parameters of the heat sinks and the orifice plate.