Detailed Heat Transfer Measurements of Jet Impingement on Dimpled Target Surface Under Rotation

2018 ◽  
Vol 10 (3) ◽  
Author(s):  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Crystal ◽  
Rotational Speed ◽  
Buoyancy Force ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Enhancement ◽  
One Dimensional ◽  
Enhancing Heat Transfer

The present study investigates the effects of Coriolis force and centrifugal buoyancy force on heat transfer due to jet impingement on dimpled target surface (DT). Detailed heat transfer measurements were carried out using transient liquid crystal (LC) thermography, where the target surface was modeled as one-dimensional (1D) semi-infinite solid. Three different configurations of DT surfaces have been studied. The flow and rotation conditions have been kept the same for all the configurations, where the average Reynolds number (based on jet hole hydraulic diameter: Rej) was 2500 and the rotational speed was 400 rpm (corresponding to Roj of 0.00274). Under nonrotating conditions, DT surface showed positive heat transfer enhancements compared to smooth target surfaces. Under rotating conditions, it was observed that rotation was helpful in enhancing heat transfer on leading and trailing sides for smooth target surface. However, for the DT surfaces, rotation proved to be detrimental to heat transfer enhancement.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Effect of Film Extraction on Impingement Heat Transfer Characteristics of Jet Arrays on Spherical-Dimpled Surfaces

2015 ◽  
Author(s):  
Xing Yang ◽  
Zhao Liu ◽  
Zhenping Feng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Film Cooling ◽  
Coupling Effect ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Target Surface ◽  
Local Heat ◽  
Separation Distance ◽  
Plate Spacing

Detailed heat transfer distributions are numerically investigated on a multiple jet impingement target surface with staggered arrays of spherical dimples where coolant can be extracted through film holes for external film cooling. The three dimensional Reynolds-averaged Navier-Stokes analysis with SST k-ω turbulence model is conducted at jet Reynolds number from 15,000 to 35,000. The separation distance between the jet plate and the target surface varies from 3 to 5 jet diameters and two jet-induced crossflow schemes are included to be referred as large and small crossflow at one and two opposite exit openings correspondingly. Flow and heat transfer results for the dimpled target plate with three suction ratios of 2.5%, 5.0% and 12.0% are compared with those on dimpled surfaces without film holes. The results indicate the presence of film holes could alter the local heat transfer distributions, especially near the channel outlets where the crossflow level is the highest. The heat transfer enhancements by applying film holes to the dimpled surfaces is improved to different degrees at various suction ratios, and the enhancements depend on the coupling effect of impingement and channel flow, which is relevant to jet Reynolds number, jet-to-plate spacing and crossflow scheme.

Jet Impingement Heat Transfer Enhancement by Packing High-Porosity Thin Metal Foams Between Jet Exit Plane and Target Surface

2019 ◽  
Vol 11 (6) ◽  
Author(s):  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Metal Foam ◽  
Jet Impingement ◽  
Target Surface ◽  
Metal Foams ◽  
Thin Metal ◽  
High Porosity ◽  
Pumping Power ◽  
Transfer Enhancement

High-porosity metal foams are known for providing high heat transfer rates, as they provide a significant increase in wetted surface area as well as highly tortuous flow paths resulting in enhanced mixing. Further, jet impingement offers high convective cooling, particularly at the jet footprint areas on the target surface due to flow stagnation. In this study, high-porosity thin metal foams were subjected to array jet impingement, for a special crossflow scheme. High porosity (92.65%), high pore density (40 pores per inch (ppi)), and thin foams (3 mm) have been used. In order to reduce the pumping power requirements imposed by full metal foam design, two striped metal foam configurations were also investigated. For that, the jets were arranged in 3 × 6 array (x/dj = 3.42, y/dj = 2), such that the crossflow is dominantly sideways. Steady-state heat transfer experiments have been conducted for varying jet-to-target plate distance z/dj = 0.75, 2, and 4 for Reynolds numbers ranging from 3000 to 12,000. The baseline case was jet impingement onto a smooth target surface. Enhancement in heat transfer due to impingement onto thin metal foams has been evaluated against the pumping power penalty. For the case of z/dj = 0.75 with the base surface fully covered with metal foam, an average heat transfer enhancement of 2.42 times was observed for a concomitant pressure drop penalty of 1.67 times over the flow range tested.

Experimental Investigation on Convective Heat Transfer Enhancement of Laminar Slot Jet Impingement in the Presence of Porous Medium

2016 ◽  
Author(s):  
Sampath Kumar Chinige ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Medium ◽  
Porous Media ◽  
Nusselt Number ◽  
Heat Sink ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Transfer Enhancement ◽  
Porous Obstacle

An experimental study using Liquid crystal thermography technique is conducted to study the convective heat transfer enhancement in jet impingement cooling in the presence of porous media. Aluminium porous sample of 10 PPI with permeability 2.48e−7 and porosity 0.95 is used in the present study. Results are presented for two different Reynolds number 400 and 700 with four different configurations of jet impingement (1) without porous foams (2) over porous heat sink (3) with porous obstacle case (4) through porous passage. Jet impingement with porous heat sink showed a deterioration in average Nusselt number by 10.5% and 18.1% for Reynolds number of 400 and 700 respectively when compared with jet impingement without porous heat sink configuration. The results show that for Reynolds number 400, jet impingement through porous passage augments average Nusselt number by 30.73% whereas obstacle configuration enhances the heat transfer by 25.6% over jet impingement without porous medium. Similarly for Reynolds number 700, the porous passage configuration shows average Nusselt number enhancement by 71.09% and porous obstacle by 33.4 % over jet impingement in the absence of porous media respectively.

Flow and Heat Transfer of Confined Impingement Jets Cooling

2000 ◽  
Author(s):  
Ting Wang ◽  
Mingjie Lin ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Experimental Studies ◽  
Cross Flow ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Transfer Behavior

Experimental studies on heat transfer and flow structure in confined impingement jets were performed. The objective of this study was to investigate the detailed heat transfer coefficient distribution on the jet impingement target surface and flow structure in the confined cavity. The distribution of heat transfer coefficients on the target surface was obtained by employing the transient liquid crystal method coupled with a 3-D inverse transient conduction scheme under Reynolds number ranging from 1039 to 5175. The results show that the average heat transfer coefficients increased linearly with the Reynolds number as Nu = 0.00304 Pr0.42Re. The effects of cross flow on heat transfer were investigated. The flow structure were analyzed to gain insight into convective heat transfer behavior.

Leading Edge Jet Impingement Under High Rotation Numbers

2012 ◽  
Author(s):  
Cassius A. Elston ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rotation Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Cases ◽  
Nusselt Numbers ◽  
Supply Channel ◽  
Cooling Air

The effect of rotation on jet impingement cooling is experimentally investigated in this study. Pressurized cooling air is supplied to a smooth, square channel in the radial outward direction. To model leading edge impingement in a gas turbine, jets are formed from a single row of discrete holes. The cooling air from the first pass is expelled through the holes, with the jets impinging on a semi-circular, concave surface. The inlet Reynolds number varied from 10000–40000 in the square supply channel. The rotation number and buoyancy parameter varied from 0–1.4 and 0–6.6 near the inlet of the channel, and as coolant is extracted for jet impingement, the rotation and buoyancy numbers can exceed 10 and 500 near the end of the passage. The average jet Reynolds number varied from 6000–24000, and the jet rotation number varied from 0–0.13. For all test cases, the jet-to-jet spacing (s/djet = 4), the jet-to-target surface spacing (l/djet = 3.2), and the impingement surface diameter-to-diameter (D/djet = 6.4) were held constant. A steady state technique was implemented to determine regionally averaged Nusselt numbers on the leading and trailing surfaces inside the supply channel and three spanwise locations on the concave target surface. It was observed that in all rotating test cases, the Nusselt numbers deviated from those measured in a non-rotating channel. The degree of separation between the leading and trailing surface increased with increasing rotation number. Near the inlet of the channel, heat transfer was dominated by entrance effects, however moving downstream, the local rotation number increased and the effect of rotation was more pronounced. The effect of rotation on the target surface was most clearly seen in the absence of crossflow. With pure jet impingement, the deflection of the impinging jet combined with the rotation induced secondary flows offered increased mixing within the impingement cavity and enhanced heat transfer. In the presence of strong crossflow of the spent air, the same level of heat transfer is measured in both the stationary and rotating channels.

Numerical Analysis of Heat Transfer in a Laminar, Submerged, Slot Jet Impinging on an Oscillating Wall

2019 ◽  
Author(s):  
Srivathsan Ragunathan ◽  
Douglas J. Goering
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Electronics Cooling ◽  
Jet Impingement ◽  
Target Surface ◽  
Index Method ◽  
Laminar Jet ◽  
Nusselt Numbers ◽  
Grid Convergence Index ◽  
Two Parameters

Abstract Numerical simulation results of flow and heat transfer resulting from a confined, submerged liquid jet impinging on a planar oscillating surface are presented here. Laminar jets are employed in places where space and pumping capacity constraints exist (for example, in electronics cooling). However, in a laminar single jet, the cooled region due to the jet is small and is concentrated in the stagnation zone. One way to potentially enhance the heat transfer in a laminar jet impingement arrangement is by oscillating the heated impingement surface. This work extends the previous fluid dynamics analysis (by the same author) by a description and quantification heat transfer in such an arrangement. The problem is studied with respect to two parameters governing jet impingement :Jet Reynolds Number, distance from the jet inlet to the impinging wall (z/d ratios) and a parameter characterizing oscillation : the oscillatory peak Reynolds Number. OpenFOAM (foam-extend 3.2), an open-source CFD code based on the finite volume method is used to solve the problem. Quantification of discretization uncertainty is done by employing the Grid Convergence Index Method (GCI). The transport of the vortex structures formed due to the confined arrangement of the jets and due to the oscillation of the target wall has a strong influence on the temperature distribution on the target surface. The enhancement in heat transfer is estimated as a ratio of the Nusselt Numbers cases with oscillation to corresponding cases without oscillation. It is shown that the heat transfer enhancement is a strong function of the jet and the oscillatory parameters considered.

Impingement Heat Transfer From a Jet-Array With In-Between Return Holes for the Crossflow

2020 ◽  
Author(s):  
Chen Tang ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Thin Sheet ◽  
Jet Impingement ◽  
Target Surface ◽  
Transfer Rates ◽  
Impingement Heat Transfer ◽  
Acrylic Plate ◽  
High Heat Transfer ◽  
Jet Array

Abstract Jet-impingement heat transfer is commonly used for vane leading edges and end-walls of turbine components for cooling the surfaces. One of the factors that limit high heat transfer rates is the effect of the crossflow which builds up downstream and adversely impacts the jet penetration and the impingement heat transfer rates. The present paper investigates the concept of introducing return holes (RH) for the crossflow to prevent its build-up and therefore reduce its deleterious effects. In the present experimental study, a 3 by 9 jet-array impinging on a target surface is considered with and without return holes. The return holes are located in an in-line pattern between the impingement holes. Experiments are conducted in an impingement channel with closed side walls and for jet-to-target distances (H/D) of 1D to 9D and a jet-Reynolds number of 20,000. Two different crossflow schemes combined with three return hole (RH) configurations are studied. The two crossflow arrangements are: (1) one radial exit and RH’s open for the spent air to exit and (2) all radial exits blocked with the spent air exiting through the RH’s only. Three different area-openings for the RH’s are considered and correspond to 33.3%, 66.7%, and 100% of the total return hole area open. In addition, a baseline case with no RH’s and one radial exit is studied. A transient liquid-crystal based study is conducted using a thin sheet of narrowband Thermochromic Liquid Crystal glued on an acrylic plate serving as the target surface. Local heat transfer coefficients are obtained based on the measured surface temperature and the solution of 1D transient heat conduction in the target acrylic plate. Return holes have significant influence on the crossflow-induced degradation effects at small jet-to-target spacing. The all-blocked crossflow scheme demonstrates good uniformity and axisymmetric Nusselt number distributions.

Liquid Jet Impingement Without and With Heat Transfer

2009 ◽  
Author(s):  
F. A. Jafar ◽  
G. R. Thorpe ◽  
O¨. F. Turan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Liquid Jet ◽  
Substantial Impact ◽  
Plate Spacing ◽  
Numerical Predictions ◽  
Surface Configuration

Equipment used to cool horticultural produce often involves three-phase porous media. The flow field and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships amongst dimensionless groups. This work represents a first step towards the goal of harnessing the power of computational fluid dynamics (CFD) to better understand the heat transfer process that occur in beds of irrigated horticultural produce. The primary objective of the present study is to use numerical predictions towards reducing energy and cooling water requirement in cooling horticultural produce. In this paper, flow and heat transfer predictions are presented of a single slot liquid jet on flat and curved surfaces using a CFD code (FLUENT) for 2-D configurations. The effects of Reynolds number, nozzle to plate spacing, nozzle width and target surface configuration have been studied. Reynolds numbers of 250, 500, 700, 1800 and 1900 are studied where the liquid medium is water. Here, the Reynolds number is defined in terms of the hydraulic nozzle diameter, inlet jet velocity and fluid kinematic viscosity. The results show that Reynolds numbers, nozzle to plate spacing and nozzle width have a significant effect on the flow filed and heat transfer characteristics; whereas the target surface configuration at stagnation area has no substantial impact. The use of a numerical tool has enabled detailed investigation of these characteristics, which have not been available in the literature previously.

Heat Transfer Characteristics of CuO-Water Nanofluids Jet Impingement on a Hot Surface

2016 ◽  
Author(s):  
Sandesh S. Chougule ◽  
Mayank Modak ◽  
Prajakta D. Gharge ◽  
S. K. Sahu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Jet Impingement ◽  
Target Surface ◽  
Test Surface ◽  
Initial Surface ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Heat Transfer ◽  
Hot Surface

In present study, an experimental investigation has been carried out to analyze the heat transfer characteristics of CuO-water nanofluids jets on a hot surface. A rectangular stainless steel foil (AISI-304, 0.15 mm thick) is used as a test surface is electrically heated to obtain the required initial temperature. The distribution of heat flux on the target surface is evaluated from the recorded thermal images during transient cooling. The effect of nanoparticle concentration and Reynolds number of the nanofluids jet impingement heat transfer characteristics is studied. Tests were performed for an initial surface temperature of 500°C, Reynolds number (5000≤Re≤13000), CuO-water nanofluids concentration (Φ= 0.15%, 0.6%) and nozzle to plate distance was l/d= 4.

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