Convective Heat Transfer From Heated Extended Surfaces With a Confined Slot Jet Impingement

2004 ◽  
Author(s):  
L. K. Liu ◽  
M. C. Wu ◽  
C. J. Fang ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Separation Distance ◽  
Nusselt Numbers ◽  
Transfer Behavior ◽  
Extended Surfaces

A series of experimental investigations with stringent measurement methods on the studies related to mixed convection from the horizontally confined extended surfaces with a slot jet impingement have been successfully conducted. The relevant parameters influencing mixed convection performance due to jet impingement and buoyancy include the Grashof number, ratio of jet separation distance to nozzle width, ratio of extended surfaces height to nozzle width and jet Reynolds number. The range of these parameters studied are Grs = 3.77 × 105 – 1.84 × 106, H/W = 1–10, Hs/W = 0.74–3.40 and Re = 63–1383. In the study, the heat transfer behavior on the extended surfaces with confined slot jet impingement such as the temperature distribution, local and average Nusselt numbers on the extended surfaces has been systematically explored. The results manifest that the effect of steady-state Grashof number on heat transfer behavior such as stagnation, local and average Nusselt number is not significant; while the heat transfer performance increases with decreasing jet separation distance or with increasing extended surface height and jet Reynolds number. Besides, two new correlations of local and average Nusselt numbers in terms of H/W, Hs/W and Re are proposed for the cases of extended surfaces. A satisfactory agreement is achieved between the results predicted by these correlations and the experimental data. Finally, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. The comparison of the predictions evaluated by this correlation with all the present experimental data is made. The maximum and average deviations of the predictions from the experimental data are 7.46% and 2.87%, respectively.

Convective Heat Transfer From a Stationary or Rotating MCM Disk With a Unconfined Round Jet Impingement

2005 ◽  
Author(s):  
Y. M. Kuo ◽  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Mixed Convection ◽  
Jet Impingement ◽  
Disk Surface ◽  
Separation Distance ◽  
Heat Flux Distribution ◽  
Disk Rotation ◽  
Nusselt Numbers

A series of experimental investigations with stringent measurement methods on the studies related to fluid flow and transient mixed convection from a horizontally unconfined stationary or rotating ceramic-based MCM disk with unconfined jet impingement have been successfully conducted. The relevant parameters influencing fluid flow and heat transfer performance are (1) mixed convection due to jet impingement and buoyancy: steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter; and (2) mixed convection due to jet impingement, disk rotation and buoyancy: steady-state Grashof number, jet Reynolds number (Rej), rotational Reynolds number (Rer), ratio of jet separation distance to nozzle diameter (H/d). The thermal behavior explored includes the transient temperature distribution on the MCM disk surface, transient heat flux distribution of input power, transient convective heat flux distribution of chips, and transient chip and average heat transfer characteristics on the MCM disk surface. Besides, two new correlations of transient stagnation and average Nusselt numbers in terms of Rej, H/d and t are presented for the cases of stationary MCM disk. For the cases of rotating MCM disk, a new empirical correlation to classify two regimes of heat transfer modes such as disk rotation mode and jet impingement mode is presented; and a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement, disk rotation and buoyancy is proposed. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t > 6 min in the power-on transient period.

Transient Convective Heat Transfer of Air Jet Impinging Onto a Confined Ceramic-Based MCM Disk

2001 ◽  
Author(s):  
W. S. Su ◽  
L. K. Liu ◽  
Y. H. Hung
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Jet Impingement ◽  
Disk Surface ◽  
Separation Distance ◽  
Transient Time ◽  
Nusselt Numbers ◽  
Air Jet ◽  
Transient Experiments ◽  
Transfer Behavior

Abstract Transient heat transfer behavior from a horizontally confined ceramic-based MCM disk with jet impingement has been systematically explored. The relevant parameters influencing heat transfer performance are the steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter. In addition, an effective time, ton, representing a certain transient time when the mixed convection effect due to jet impingement and buoyancy becomes significant relative to heat conduction, is introduced. Both the transient chip and average Nusselt numbers on the MCM disk surface decrease with time in a very beginning period of 0 ≤ t < ton, whereas it gradually increases or keeps constant with time and finally approaches the steady-state value in the period of ton ≤ t < ts. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t ≥ 4 min in the power-on transient period.

Transient Convective Heat Transfer of Air Jet Impinging Onto a Confined Ceramic-Based MCM Disk

2004 ◽  
Vol 126 (1) ◽  
pp. 159-172 ◽  
Author(s):  
Li-Kang Liu ◽  
Wen-Shien Su ◽  
Ying-Huei Hung
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Jet Impingement ◽  
Disk Surface ◽  
Separation Distance ◽  
Transient Time ◽  
Nusselt Numbers ◽  
Air Jet ◽  
Transient Experiments ◽  
Transfer Behavior

Transient heat transfer behavior from a horizontally confined ceramic-based MCM disk with jet impingement has been systematically explored. The relevant parameters influencing heat transfer performance are the steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter. In addition, an effective time, ton, representing a certain transient time when the mixed convection effect due to jet impingement and buoyancy becomes significant relative to heat conduction, is introduced. Both the transient chip and average Nusselt numbers on the MCM disk surface decrease with time in a very beginning period of 0⩽t<ton, whereas it gradually increases or keeps constant with time and finally approaches the steady-state value in the period of ton⩽t<ts. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t⩾4min in the power-on transient period.

Heat Transfer Behavior for a Stationary or Rotating MCM Disk With an Unconfined Round Jet Impingement

2006 ◽  
Vol 129 (4) ◽  
pp. 400-410 ◽  
Author(s):  
C. J. Fang ◽  
M. C. Wu ◽  
Y. M. Kuo ◽  
C. Y. Lee ◽  
C. H. Peng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Steady State ◽  
Mixed Convection ◽  
Jet Impingement ◽  
Disk Surface ◽  
Average Heat ◽  
Nusselt Numbers ◽  
Transient Period ◽  
Transfer Behavior

A series of experimental investigations on the studies related to fluid flow and transient mixed convection from a horizontally unconfined stationary or rotating ceramic-based multichip module (MCM) disk with unconfined jet impingement have been successfully conducted. The fluid flow and heat transfer behavior explored includes the streamwise velocity and turbulence intensity distributions, transient dimensionless temperature distribution on the MCM disk surface, transient heat flux distribution of input power, and transient chip and average heat transfer characteristics on the MCM disk surface. Besides, two new correlations of transient stagnation and average Nusselt numbers in terms of jet Reynolds number, ratio of jet separation distance to nozzle diameter and time elapsed during the transient period, are presented for the cases of stationary MCM disk. For the cases of rotating MCM disk, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement, disk rotation and buoyancy is proposed. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasisteady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t>6min in the power-on transient period.

Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface

2021 ◽  
Author(s):  
Pratik S. Bhansali ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbine ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Rotating Disc ◽  
Disc Surface ◽  
Pin Fins

Abstract Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).

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.

Thermal Optimal Design for Multichip Module Disks With an Unconfined Round-Jet Impingement

2005 ◽  
Author(s):  
C. J. Fang ◽  
M. C. Wu ◽  
C. H. Peng ◽  
Y. C. Lee ◽  
Y. H. Hung
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Steady State ◽  
Thermal Performance ◽  
Jet Impingement ◽  
Separation Distance ◽  
Grashof Number ◽  
Round Jet ◽  
Space Limitation

An effective method for performing the thermal optimization of stationary and rotating MCM disks with an unconfined round-jet impingement under space limitation constraint has been successfully developed. The design variables of stationary and rotating MCM disks with an unconfined round-jet impingement include: the ratio of jet separation distance to nozzle diameter (H/d), steady-state Grashof number (Grs), jet Reynolds number (Rej), rotational Reynolds number (Rer). The total experimental cases for stationary and rotating MCM disks are statistically designed by the Central Composite Design (CCD) method. In addition, a sensitivity analysis, the so-called ANOVA, for the design factors has been performed. In the stationary MCM disk with an unconfined round-jet impingement, the contribution percentage of jet Reynolds number on the thermal performance is 95.86%. The effect of jet Reynolds numbers on chip temperature distribution is more significant than that of the H/d ratio and steady-state Grashof number. In rotating MCM disk with an unconfined round-jet impingement, the effect of jet Reynolds number, which has the contribution percentage of 91.81%, dominates the thermal performance. Furthermore, the comparisons between the predictions by using the quadratic Response Surface Methodology (RSM) and the experimental data are made. The maximum deviations for transient stagnation Nusselt number and transient average Nusselt number for the cases of stationary MCM disk are 10.05% and 11.82%, respectively; and 9.41% and 12.44% for the cases of rotating MCM disk, respectively. Finally, with the Sequential Quadratic Programming (SQP) technique, a series of thermal optimal designs under space limitation constraint H/d≤12 has been efficiently performed. Comparisons between the numerical optimization results and the experimental data are made with a satisfactory agreement.

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.

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