scholarly journals Design, Fabrication, and Performance Evaluation of a Hybrid Wick Vapor Chamber

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Feng Zhou ◽  
Yanghe Liu ◽  
Ercan M. Dede
Keyword(s):  
Heat Flux ◽  
Waste Heat ◽  
Jet Impingement ◽  
Transportation Systems ◽  
Heat Fluxes ◽  
Air Cooling ◽  
Vapor Chamber ◽  
Power Semiconductors ◽  
Air Jet ◽  
Capillary Limit

The growing electrification of transportation systems is dramatically increasing the waste heat that must be dissipated from high-density power electronics. Transformative embedded heat spreading technologies must be developed in next-generation systems to enable air cooling of power semiconductors with heat fluxes exceeding 500 W/cm2 over large hotspot areas up to 1 cm2. In this study, vapor chamber heat spreaders, or thermal ground planes (TGPs), with customized wick structures are investigated as one possibility. A 10 cm × 10 cm TGP with hybrid wick, which is a blend of a biporous wick with a standard monoporous wick, was designed. The TGP was tested in combination with a straight pin fin heat sink under air jet impingement and a 1 cm2 size heat source. The experimental performance of the hybrid wick TGP was compared under the same air-cooled conditions with an off-the-shelf TGP of the same size from a commercial vendor and a TGP with a biporous wick only. The customized hybrid wick TGP exhibits ∼28% lower thermal resistance compared with a traditional commercial TGP, and the capillary limit heat flux is measured as 450 W/cm2. Technical challenges in extending this capillary limit heat flux value and TGP integration into packaged electronics are described.

Integrated Vapor Chamber Heat Spreader for Power Module Applications

2017 ◽  
Author(s):  
Clayton L. Hose ◽  
Dimeji Ibitayo ◽  
Lauren M. Boteler ◽  
Jens Weyant ◽  
Bradley Richard
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Power Electronics ◽  
Coefficient Of Thermal Expansion ◽  
High Heat ◽  
Heat Fluxes ◽  
High Heat Flux ◽  
Vapor Chamber ◽  
Power Module ◽  
Heat Spreader

This work presents a demonstration of a coefficient of thermal expansion (CTE) matched, high heat flux vapor chamber directly integrated onto the backside of a direct bond copper (DBC) substrate to improve heat spreading and reduce thermal resistance of power electronics modules. Typical vapor chambers are designed to operate at heat fluxes > 25 W/cm2 with overall thermal resistances < 0.20 °C/W. Due to the rising demands for increased thermal performance in high power electronics modules, this vapor chamber has been designed as a passive, drop-in replacement for a standard heat spreader. In order to operate with device heat fluxes >500 W/cm2 while maintaining low thermal resistance, a planar vapor chamber is positioned onto the backside of the power substrate, which incorporates a specially designed wick directly beneath the active heat dissipating components to balance liquid return and vapor mass flow. In addition to the high heat flux capability, the vapor chamber is designed to be CTE matched to reduce thermally induced stresses. Modeling results showed effective thermal conductivities of up to 950 W/m-K, which is 5 times better than standard copper-molybdenum (CuMo) heat spreaders. Experimental results show a 43°C reduction in device temperature compared to a standard solid CuMo heat spreader at a heat flux of 520 W/cm2.

Experimental and Theoretical Studies of Mist Jet Impingement Cooling

1996 ◽  
Vol 118 (2) ◽  
pp. 343-349 ◽  
Author(s):  
K. M. Graham ◽  
S. Ramadhyani
Keyword(s):  
Experimental Data ◽  
Jet Impingement ◽  
Target Surface ◽  
Heat Fluxes ◽  
Heat Sources ◽  
Impingement Cooling ◽  
Jet Cooling ◽  
Air Jet ◽  
Model Predictions ◽  
Experimental And Theoretical Studies

Experimental data and analytical predictions for air/liquid mist jet cooling of small heat sources are presented. The mist jet was created using a coaxial jet atomizer, with a liquid jet of diameter 190 μm located on the axis of an annular air jet of diameter 2 mm. The impingement surface was a square of side 6.35 mm. Experimental data were obtained with mists of both methanol and water. Surface-averaged heat fluxes as high as 60 W/cm2 could be dissipated with the methanol/air mist while maintaining the target surface below 70°C. With the water/air mist, a heat flux of 60 W/cm2 could be dissipated with the target surface at 80°C. Major trends in the data and model predictions have been explained in terms of the underlying hydrodynamic and heat transfer phenomena.

scholarly journals Vaporization Cooling for Gas Turbines, the Return-Flow Cascade

1998 ◽  
Author(s):  
Jack L. Kerrebrock ◽  
David B. Stickler
Keyword(s):  
Heat Flux ◽  
Gas Turbines ◽  
Pressure Ratio ◽  
Self Regulation ◽  
Heat Fluxes ◽  
Return Flow ◽  
Detailed Knowledge ◽  
Air Cooling ◽  
New Paradigm ◽  
Two Phase

A new paradigm for gas turbine design is treated, in which major elements of the hot section flow path are cooled by vaporization of a suitable two-phase coolant. This enables the blades to be maintained at nearly uniform temperature without detailed knowledge of the heat flux to the blades, and makes operation feasible at higher combustion temperatures using a wider range of materials than is possible in conventional gas turbines with air cooling. The new enabling technology for such cooling is the Return-Flow Cascade, which extends to the rotating blades the heat flux capability and self-regulation usually associated with heat-pipe technology. In this paper the potential characteristics of gas turbines that use vaporization cooling are outlined briefly, but the principal emphasis is on the concept of the Return-Flow Cascade. The concept is described and its characteristics are outlined. Experimental results are presented that confirm its conceptual validity and demonstrate its capability for blade cooling at heat fluxes representative of those required for high pressure ratio high temperature gas turbines.

Modelling Heat Transfer Performance of a Thin Bi-Porous Evaporator for a Heat Pipe

2005 ◽  
Author(s):  
Aleksander Vadnjal ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Heat ◽  
Heat Transfer Process ◽  
Heat Fluxes ◽  
Capillary Structure ◽  
Porous Wick ◽  
Capillary Limit ◽  
Porous Capillary Structure ◽  
Selection Of

The evaporator of a heat exchanger is made with a porous, capillary, structure. In the past researchers [7] noticed that the heat flux limits of a bi-porous capillary structure is much greater than that of a mono-porous capillary structure and will be the focus of this work. There are three distinct stages in the heat transfer process in a bi-porous wick. Each of the stages is explored in turn. In the first stage, heat is transferred from the wall across the saturated wick by pure conduction to the evaporating front located on the top of the bi-porous wick. When the boiling limit is reached, bubbles begin to nucleate and the second stage begins. The boiling becomes more and more intensive as the heat flux is increased until all of the liquid from big pores is evaporated, and only small pores remain wetted with liquid. The point reached here is called the capillary limit, which is basically the limit at which the capillary forces are still sufficient to provide the liquid for evaporation into the big pores. The modelling of the different thermal physical processes determining heat transfer within each of the three stages for a bi-porous heat wick are modelled and significant improvement in achievable heat flux is observed. Comparison with experiment is found to be reasonable. Optimal selection of the bi-porous wick characteristics is shown to yield very high heat fluxes.

scholarly journals Performance Analysis of a New Waste Heat Recovery System

2015 ◽  
Vol 12 (1) ◽  
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Heat Recovery ◽  
Waste Heat ◽  
Maximum Energy ◽  
Heat Fluxes ◽  
Low Grade ◽  
Industrial Plants ◽  
Waste Heat Recovery System ◽  
Recovery System

The overall theme of this research is to capture, concentrate and convert some of the waste heat generated at industrial plants to a valuable form of energy. A new system for heat recovery from low grade energy has been built and tested based on a modified heat pipe technology. A single heat pipe used in this research was able to extract 2 kW of energy from waste heat of 250 oC. However a heat pipe can extract 11.5 kW/m2 heat fluxes. The maximum energy extraction by such system from low grad energy can be up to 3 kW. While a heat pipe regardless of its size can have heat flux up to 16.5 kW/m2 from waste heat flow at 250 oC and 12.3 m/s velocity. Also, the system can extract about 1 kW heat or 6.5 kW/m2 heat flux at temperatures as low as 150 oC. However, the system doesn’t function properly at temperatures lower than 150 oC.

Heat Transfer Investigation with Multiple Jet Impingement

2020 ◽  
Vol 12 (3) ◽  
Author(s):  
Niranjan Murthy ◽  
B.K. Naveenkumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Research Work ◽  
Jet Impingement ◽  
Test Surface ◽  
Simple Relationship ◽  
Flux Flow ◽  
Air Jets ◽  
Air Jet

An experimental study was carried out to study the effect of multiple jet impingement on a virtual electronic component using water and air as working fluids. It consists of an electrically heated test plate of size 20mm×20mm. Heat flux is varied between 25 to 250W/cm2 was dissipated using 0.25 and 0.5mm diameter jets placed in a 7×7 array with a pitch of 3mm. The difference in temperature between test surface and fluid inlet is within 30 degC for water jets and within 75 degC for air jet experiments. Experiments were conducted by changing the heat flux, flow rate and distance between the test surface and jet exit and [iv] horizontal and vertical positioning of the jets. It was found that heat flux, jet diameter and Reynolds number are important factors in determining the heat transfer. The effects of distance between test surface and jet exit [Z] and positioning of the jets were insignificant. Though the multiple jet impingement heat transfer problem is complex, the heat transfer results could be correlated using a simple relationship in the form of Nu = AqmRen. The constant (m) which indicates the effect of heat flux has the value of 0.8 and 0.9 depending upon the jet diameter and the coolant. The constant (n) which indicates the influence of Reynolds number has the value of 0.25 for both water and air jets. The value of constant (A) is different for water and air jets. The correlation developed in this research work can be effectively used to design multiple water and air jet cooling system for electronic components.

Investigation of Nanopillar Wicking Capabilities for Heat Pipes Applications

2009 ◽  
Author(s):  
Conan Zhang ◽  
Carlos H. Hidrovo
Keyword(s):  
Heat Flux ◽  
Theoretical Model ◽  
Capillary Flow ◽  
Heat Removal ◽  
Heat Pipes ◽  
Heat Fluxes ◽  
Limiting Factors ◽  
Pillar Array ◽  
Capillary Limit ◽  
Computer Chips

Since Moore’s prediction in 1965, transistor count density on computer chips has grown exponentially and roadmaps for future industry growth still project exponential development for the next decade. With higher transistor densities, greater heat flux dissipation is required in order for performance to keep par with chip development. However, it is theorized that current cooling systems would not be able to cope with heat fluxes of future computer chips. Microchip heat management systems can be either active or passive. Active systems require an external driving component that increases the system’s complexity and ultimately power consumption. Heat pipes are passive fluidic systems, which are more robust and easier to implement than their active counterparts. Recirculation of the coolant in a heat pipe is done passively by means of a wicking structure that induces capillary flow from the condenser to the evaporator. However, there are many limiting factors associated with heat pipes based on the wick dimensions, fluid selection and orientation. At CPU chip operating temperatures the most significant limitation is the capillary limit. This limitation must be addressed in order to meet future computer chip heat dissipation requirements. In order to find an optimal geometry that would maximize the capillary flow, a theoretical model was developed using a rectangular pillar array. Surface tension forces induce a capillary flow that is opposed by viscous stresses from the pillars. Due to the regular and well-defined geometry of the pillar array, an ab initio approach can be used to model this flow, rather than resorting to Darcy’s flow and empirical permeability correlations. Predicted values of maximum flow rate were obtained from this theoretical model. This model and its results are directly applicable to carbon nanotube (CNT) and nanowire (NW) based wick structures. To validate the merit of nanostructure wicks for use in heat pipes, experimental data was collected to show the capillary limits of various nanowicks. The capillary limit of a wick was associated with the heat flux at which the wick cannot sustain the fluid flow necessary for heat removal and burnout occurs. When a baseline wick was experimentally compared to a nanowick, it was found that due to the difference in thickness of the wicks, the baseline wick provided higher flow rates. However, when the data were normalized to produce velocity values, the nanowick was found to have a higher velocity than the baseline wicks.

Air-Cooling Influence on Wire Arc Additive Manufactured Surfaces

2019 ◽  
Vol 813 ◽  
pp. 241-247 ◽  
Author(s):  
William Hackenhaar ◽  
Filippo Montevecchi ◽  
Antonio Scippa ◽  
Gianni Campatelli
Keyword(s):  
Additive Manufacturing ◽  
Coordinate Measuring Machine ◽  
Jet Impingement ◽  
Deposition Efficiency ◽  
Progressive Increase ◽  
Air Cooling ◽  
Heat Accumulation ◽  
Air Jet ◽  
Measuring Machine ◽  
Wire Arc Additive Manufacturing

WAAM (Wire-Arc-Additive-Manufacturing) is an additive manufacturing process which uses arc welding to produce metal parts. This process is prone to heat accumulation, i.e. a progressive increase of the interlayer temperature and molten pool size, having detrimental consequences on the material properties and on the workpiece integrity. This paper investigates the effect of air jet impingement, an active cooling technique, to prevent heat accumulation, on the surfaces of WAAM workpieces. A reference test case was manufactured using traditional free convection cooling and air jet impingement. The workpiece temperature was measured using Ktype thermocouples. The manufactured surfaces were measured using a coordinate measuring machine and compared in terms of deposition efficiency, deposit height and average arithmetical deviation. The temperature results highlight that air jet impingement is effective in preventing the occurrence of heat accumulation. The surface data highlight that air jet impingement increase the deposited height and the surface waviness with a consequent decrease of the deposition efficiency.

scholarly journals Cold Zone Exploration Using Position of Maximum Nusselt Number for Inclined Air Jet Cooling

2017 ◽  
Vol 64 (4) ◽  
pp. 533-549 ◽  
Author(s):  
Sunil B. Ingole ◽  
K. K. Sundaram
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Leading Edge ◽  
Jet Impingement ◽  
Target Surface ◽  
Air Cooling ◽  
Cold Zone ◽  
Jet Cooling ◽  
Air Jet ◽  
Cold Spots

Abstract Inclined jet air cooling can be effectively used for cooling of electronics or other such applications. The non-confined air jet is impinged and experimentally investigated on the hot target surface to be cooled, which is placed horizontally. Analysis and evaluations are made by introduction of a jet on the leading edge and investigated for downhill side cooling to identify cold spots. The jet Reynolds number in the range of 2000 ≤ Re ≤ 20 000 is examined with a circular jet for inclination (Θ) of 15 < Θ < 75 degree. Also, the consequence of a jet to target distance (H) is explored in the range 0:5 ≤ H/D ≤ 6.8. For 45 degree jet impingement, the maximum Nusselt number is widely spread. Location of maximum Nusselt number is studied, which indicates cold spots identification. At a higher angle ratio, the angle is the dominating parameter compared to the Reynolds Number. Whereas at a lower angle ratio, the inclined jet with a higher Reynolds number is giving the cooling point away from leading edge. It is observed that for a particular angle of incident location of maximum Nusselt Number, measured from leading edge of target, is ahead than that of stagnation point in stated conditions.

scholarly journals Cooling Heat Transfer Analysis using Multiple Inline Inclined Air Jet Impingement

2019 ◽  
Vol 9 (1) ◽  
pp. 535-540
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Jet Impingement ◽  
Heat Transfer Analysis ◽  
Present System ◽  
Air Cooling ◽  
Impingement Cooling ◽  
System A ◽  
Air Jet ◽  
Reference Target

Air cooling has its own advantages in packaging technology and such many applications. The analysis of multi-jet impingement cooling process is performed. Air is used as fluid in present system. A simulated component with heater plate is cooled with four jets. All jets are placed inline or considered in a row. The jets are inclined to base and reference target to be cooled. The inclination of each jet is changed according to various configurations from 60 and 120 Degree to make packaging as compact as possible. Different configurations are examined and best combination is selected for study of variation of target to jet distance. Interface of flow from one jet with other is creating turbulence and effect of this on cooling target plate is studied experimentally. The graphs are plotted giving variations of Nusselt number as per Reynolds number in laminar range up to 2000. Jet inclination combination with first jet -inside, second jet - outside, third jet - outside, and fourth jet – inside is considered as giving best results with inclinations as 60-120-60- 120 degree respectively. The laminar flow, with jet position inline, in which jet fluid flow lines gets mixed and creating turbulence gives higher average Nusselt number indicating better cooling performance. Further experiments using various fluids and various jet combinations / inclinations may be performed. The correlation is presented showing variation between Nusselt number and Reynolds number for typical case.

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