A Novel Microelectronics Cooling Technique Using a Pair of Unsteady Confined Impinging Air Jets

2003 ◽  
Author(s):  
Jorge L. Rosales ◽  
Victor A. Chiriac
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Heat Sources ◽  
Air Jets ◽  
Target Wall

The unsteady laminar flow and heat transfer characteristics for a pair of confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel and aligned with the jets was determined as well as the oscillating jet frequency for the unsteady cases. The present study continues the authors’ previous investigation, which emphasized how single confined jets will remain steady at Reynolds numbers that make side-by-side jets highly unsteady. The nature of this unsteadiness depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region, and the jets “wash” a larger surface area on the target wall. The results indicate that the dual jets become unsteady between a Reynolds number of 200 and 300. Also, in the range of Reynolds numbers studied, a fixed stagnation “bubble” was formed on the target wall between the two jets, which reduced the heat transfer removal from that region, leading in fact to a quasi-independence of the local heat transfer on flow conditions. The stagnant region contains slow moving warm air that forces the cool impinging air jets to flow to the sides of this target wall area. The oscillating frequency of the flow increases with Reynolds number for the unsteady cases. Also, the time-averaged heat transfer coefficient on the heat sources rises as the Reynolds number increases for the steady cases but there is a slight decrease when it transitions to unsteady flow, indicating again that the stagnation “bubble” occurring between the two heat sources affects the local heat transfer.

The Unsteady Characteristics of a Laminar Flow and Heat Transfer of a Pair of Confined Impinging Air Jets

2003 ◽  
Author(s):  
Victor Adrian Chiriac ◽  
Jorge Luis Rosales
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Laminar Flow ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Heat Sources ◽  
Transfer Coefficients ◽  
Air Jets ◽  
Flow And Heat Transfer ◽  
Target Wall

The unsteady laminar flow and heat transfer characteristics for a pair of confined impinging air jets centered in a channel were studied numerically. The time-averaged heat transfer coefficient for a pair of heat sources centered in the channel was determined as well as the oscillating jet frequency for the unsteady cases. The present study continues the authors’ previous investigation [1], which emphasized how the small spacing between the heat sources leads to a reduction in heat transfer when increasing the flow Reynolds (Re) number, particularly in the unsteady regime. It depends on the proximity of the jet inlets, the channel dimensions and the jet Reynolds number. The jet unsteadiness causes the stagnation point locations to sweep back and forth over the impingement region, and the jets “wash” a larger surface area on the target wall. The results indicate that the dual jets become unsteady between a Renumber of 200 and 300. Prior study indicated that in this Re range, a fixed stagnation “bubble” forms on the target wall between the two jets, reducing the local heat transfer and leading to its quasi-independence on flow conditions. In this study, due to the larger space between the heat sources, the “bubble” occurring between the jets is not having a detrimental impact on heat transfer. The oscillating frequency of the flow increases with Re number for the unsteady cases, leading to significant heat transfer enhancement. The time-averaged heat transfer coefficient on the heat sources rises with Re number increase for both steady and unsteady cases. By varying the distance between the heat sources, the “bubble” region does not impact the cooling of the heat sources, as the increase in flow rate leads to increased heat transfer coefficients. Alternative designs and their impact on the heat source thermal performance are further investigated.

Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

1987 ◽  
Vol 109 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J. W. Baughn ◽  
H. Iacovides ◽  
D. C. Jackson ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Pipe Bend ◽  
Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

Detailed Experimental Characterization of Heat Transfer Coefficient Over the Internal Cooling Passages of an Additive Manufactured Turbine Airfoil

2016 ◽  
Author(s):  
Sin Chien Siw ◽  
Minking K. Chyu ◽  
Jae Y. Um ◽  
Ching-Pang Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Scale Model ◽  
Internal Cooling ◽  
Trailing Edge

This report describes the detailed experimental study to characterize the local heat transfer coefficient distribution over the internal cooling passages of a simplified generic airfoil. The airfoil is manufactured through additive manufacturing based on actual geometry and dimensions (1X scale model) of row one airfoil, applicable in large gas turbine system. At the mainbody section, the serpentine channel consists of three passages without any surface features or vortex generators. Both the leading edge and trailing edge sections are subjected to direct impingement. The trailing edge section is divided into three chambers, separated by two rows of blockages. This study employs the well-documented transient liquid crystal technique, where the local heat transfer coefficient on both pressure and suction sides is deduced. The experiments were performed at varying Reynolds number, ranging from approximately 31,000–63,000. The heat transfer distribution on the pressure side and suction side is largely comparable in the first and third pass, except for the second pass. Highest heat transfer occurs at the trailing edge region, which is ultimately dominated by impingement due to the presence of three rows of blockages. A cursory numerical calculation is performed using commercially available software, ANSYS CFX to obtain detailed flow field distribution within the airfoil, which explains the heat transfer behavior at each passage. The flow parameter results revealed that the pressure ratio is strongly proportional with increasing Reynolds number.

Local Heat Transfer and Friction Measurements in Ribbed Channel at High Reynolds Numbers

2021 ◽  
Author(s):  
Igor Baybuzenko
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbine ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Local Distribution ◽  
Heavy Duty ◽  
Heavy Duty Gas Turbine

Abstract The power generation industry is targeting heavy duty gas turbine to increase power and efficiency. Hot gas temperature and massflow are continuously being increased. It brings new challenges for the design of cooling systems for turbine blades and vanes. Up to date most of studies of heat transfer in internal cooling channels were in the range of Reynolds numbers below 80,000 for cooling air flow, for example, experimental series done by J. Chin Han et al. since 1985. Actually the range of Reynolds numbers is increased with the increase of total massflow. Extrapolation of available data is not reliable while local distribution of heat transfer coefficients becomes critical in terms of thermal stresses. Only few recent studies deal with the range of Reynolds number above 80,000, for example, in 2009 J. Chin et. al showed results for 45° angled ribs provided only area averaged values for heat transfer coefficient over one pitch and in 2003 R. Bunker showed local distribution for 45° angled ribs only. Within current study the experimental measurements of local heat transfer and friction in ribbed cooling channel were performed for Reynolds numbers in range of 100,000 – 180,000, what fits the parameters of modern and perspective heavy duty gas turbines. Using thermochromic liquid crystal technology the following rib configurations were tested: angled 45°, 60°, 90° and chevron 45°, 60°; pitch to height ratio of 10; rib turbulator height-to-channel hydraulic diameter ratio of 0.083. Maximum averaged heat transfer value was provided by 60° angled ribs. Comparison of local distribution of heat transfer coefficients for considered configurations was performed. Minimum non-uniformness of heat transfer coefficient was provided by chevron ribs, having maximum friction factor. Conjugated thermal-hydraulic analysis for cooled vane for heavy duty gas turbine was performed in order to quantify the effect of local heat transfer coefficient distribution in ribbed cooling channel. Metal temperature calculation was performed for two cases of air side thermal boundary condition application for wall surface between rib-turbulators: averaged value of heat transfer coefficient and detailed local distribution. Comparison of calculated metal temperature for 2 cases shows that usage of locally distributed air side heat transfer coefficient is important and should increase the accuracy of temperature prediction by 50°C. Consideration of local distribution of heat transfer coefficient is important for cooling design of modern heavy duty gas turbine in order to provide acceptable thermal gradients and consequently reach lifetime targets.

Measurements of Local Heat Transfer Coefficient Over the Full Surface of a Bank of Pedestals With Fillet Radii

1994 ◽  
Author(s):  
Zuolan Wang ◽  
Peter Ireland ◽  
Terry Jones ◽  
S. Toby Kohler
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Gas Temperature ◽  
Transfer Method

Complete distributions of local heat transfer coefficient have been measured over the full surface of a pedestal bank at a number of Reynolds numbers. The transient heat transfer method with thermochromic liquid crystals used as the surface thermometer was used to obtain the data. The pedestal geometry included fillet radii representative of those used in engine blade cooling passages. The heat transfer coefficient distributions are compared to previously reported local measurements made on a bank of plain cylinders. Averaged values based on the local mixed bulk gas temperature are compared to established correlations. The distributions of local heat transfer coefficient show a remarkable periodicity when based on a local temperature. These patterns are discussed in terms of the interpreted flow field. Measurements of pressure drop are also reported and, for a range of engine representative Reynolds numbers, agree with an existing correlation for prismatic pedestals.

Thermal Transport From a Rotating Disk During Partially Confined Liquid Jet Impingement

2007 ◽  
Author(s):  
Jorge Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Interface Temperature

This paper presents a numerical study that characterizes the conjugate heat transfer results of a semi–confined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. The model covers the entire fluid region including the impinging jet on a flat circular disk and flow spreading out downstream under the confined insulated wall that ultimately gets exposed to a free surface boundary condition. The solution is made under steady state and laminar conditions. The model examines how the heat transfer is affected by adding a secondary rotational flow under semi-confined jet impingement. The study considered various standard materials, namely aluminum, copper, silver, Constantan and silicon; covering a range of flow Reynolds number (220–900), under a broad rotational rate range from 0 to 750 rpm, or Ekman number (7.08×10−5 – ∞), nozzle to target spacing (β = 0.25 – 1.0), disk thicknesses to nozzle diameter ratio (b/dn = 0.25 – 1.67), Prandtl number (1.29 – 124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77) and oil (MIL-7808) as working fluids and solid to fluid thermal conductivity ratio (36.91 – 2222). High thermal conductivity plate materials maintained more uniform and lower interface temperature distributions. Higher Reynolds number increased local heat transfer coefficient reducing the interface temperature difference over the entire wall. Rotational rate increases local heat transfer coefficient under most conditions. These findings are important for the design improvement and control of semi-confined liquid jet impingement under a secondary rotation induced motion.

Local Heat Transfer in a Rotating Square Channel With Jet Impingement

1999 ◽  
Vol 121 (4) ◽  
pp. 811-818 ◽  
Author(s):  
S.-S. Hsieh ◽  
J.-T. Huang ◽  
C.-F. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient

The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Rej and ReΩ. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25 percent in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.

Numerical Prediction of 45° Angled Ribs Effects on U-shaped Channels Heat Transfer and Flow under Multi Conditions

2020 ◽  
Vol 37 (1) ◽  
pp. 41-59 ◽  
Author(s):  
Longfei Wang ◽  
Songtao Wang ◽  
Xun Zhou ◽  
Fengbo Wen ◽  
Zhongqi Wang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Narrow Channel ◽  
Aspect Ratios ◽  
Cooling Air Flow

AbstractRibs effects on the heat transfer performance and cooling air flow characteristics in various aspect ratios (AR) U-shaped channels under different working conditions are numerically investigated. The ribs angle and channel orientation are 45° and 90°, respectively, and the aspect ratios are 1:2, 1:1, 2:1. The inlet Reynolds number changes from 1e4 to 4e4 and rotational speeds include 0, 550 rpm, 1,100 rpm. Local heat transfer coefficient, endwall surface heat transfer coefficient ratio and augmentation factor are the three primary criteria to measure channel heat transfer. Ribs increase the heat transfer area and improve heat transfer coefficient of ribbed surfaces significantly, especially in the 1st pass, while the endwall surface contributes more to channel heat transfer because of the larger area and relatively smaller heat transfer coefficient. The wide channel (AR =2:1) owns the better augmentation factor than the narrow channel (AR =1:2) and ribs heat transfer weight increases with an increase of the inlet Reynolds number. Rotating slightly reduces the ribs heat transfer weight in channel and the trailing surface in 1st pass is the main influence object of rotating.

Modeling of Convective Cooling of a Rotating Disk by Partially Confined Liquid Jet Impingement

2008 ◽  
Vol 130 (10) ◽  
Author(s):  
Jorge C. Lallave ◽  
Muhammad M. Rahman
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Liquid Jet

This paper presents the results of the numerical simulation of conjugate heat transfer during a semiconfined liquid jet impingement on a uniformly heated spinning solid disk of finite thickness and radius. This study considered various disk materials, namely, aluminum, copper, silver, Constantan, and silicon; covering a range of Reynolds number (220–900), Ekman number (7.08×10−5–∞), nozzle-to-target spacing (β=0.25–1.0), disk thicknesses to nozzle diameter ratio (b∕dn=0.25–1.67), and Prandtl number (1.29–124.44) using ammonia (NH3), water (H2O), flouroinert (FC-77), and oil (MIL-7808) as working fluids. The solid to fluid thermal conductivity ratio was 36.91–2222. A higher thermal conductivity plate material maintained a more uniform interface temperature distribution. A higher Reynolds number increased the local heat transfer coefficient. The rotational rate also increased the local heat transfer coefficient under most conditions.

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