Evaporative Thermal Performance of Vapor Chambers Under Nonuniform Heating Conditions

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Je-Young Chang ◽  
Ravi S. Prasher ◽  
Suzana Prstic ◽  
P. Cheng ◽  
H. B. Ma
Keyword(s):  
Heat Flux ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Hot Spots ◽  
Hot Spot ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Nonuniform Heating ◽  
Test Results ◽  
Uniform Heating

This paper reports the test results of vapor chambers using copper post heaters and silicon die heaters. Experiments were conducted to understand the effects of nonuniform heating conditions (hot spots) on the evaporative thermal performance of vapor chambers. In contrast to the copper post heater, which provides ideal heating, a silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The vapor chambers were tested for hot spot heat fluxes as high as 746 W/cm2. The experimental results show that evaporator thermal resistance is not sensitive to nonuniform heat conditions, i.e., it is the same as in the uniform heating case. In addition, a model was developed to predict the effective thickness of a sintered-wick layer saturated with water at the evaporator. The model assumes that the pore sizes in the sintered particle wick layer are distributed nonuniformly. With an increase of heat flux, liquid in the larger size pores are dried out first, followed by drying of smaller size pores. Statistical analysis of the pore size distribution is used to calculate the fraction of the pores that remain saturated with liquid at a given heat flux condition. The model successfully predicts the experimental results of evaporative thermal resistance of vapor chambers for both uniform and nonuniform heat fluxes.

Thermal Performance of Vapor Chambers Under Hot Spot Heating Conditions

2005 ◽  
Author(s):  
Je-Young Chang ◽  
Unnikrishnan Vadakkan ◽  
Ravi Prasher ◽  
Suzana Prstic
Keyword(s):  
Thermal Performance ◽  
Hot Spots ◽  
Hot Spot ◽  
Heat Pipes ◽  
Air Cooling ◽  
Test Results ◽  
Uniform Heating ◽  
One Dimensional ◽  
Localized Heating ◽  
Phase Change Phenomena

Use of heat pipes (or vapor chambers) is considered as one of the promising technology to extend the capability of air cooling. This paper reports the test results of vapor chambers using two different sets of test heaters (copper post heater and silicon die heater). Experiments were conducted to understand the effects of non-uniform heating conditions on the thermal performance of vapor chambers. In contrast to the copper post heater which provides ideal heating condition, silicon chip package was developed to replicate more realistic heat source boundary conditions of microprocessors. The chip contains three metallic heaters: a 10 × 12 mm heater in order to provide uniform heating, a 10 × 3 mm heater in order to simulate a localized heating, and a 400 × 400 μm heater in order to simulate the hot spots on actual microprocessors. In the experiment, the highest heat flux from the hotspot heater was approximately 690 W/cm2. Test results indicated that both conduction heat transfer and phase-change phenomena played key roles in the evaporator. The study found that the evaporator resistance was almost insensitive to non-uniform heating conditions, but was clearly dependent on the amount of power applied over the die area. In addition, a simple one-dimensional thermal model was developed to predict the performance of vapor chambers for non-uniform heating conditions and the results were compared against experiments.

Experimental Study of a Single Microchannel Flow Under Nonuniform Heat Flux

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Ahmed Eltaweel ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Dissipation ◽  
Hot Spot ◽  
Management Strategies ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Nonuniform Heating ◽  
Maximum Heat ◽  
Microchannel Heat Sinks

Abstract Nonuniform heat fluxes are commonly observed in thermo-electronic devices that require distinct thermal management strategies for effective heat dissipation and robust performance. The limited research available on nonuniform heat fluxes focus mostly on microchannel heat sinks while the fundamental component, i.e., a single microchannel, has received restricted attention. In this work, an experimental setup for the analysis of variable axial heat flux is used to study the heat transfer in a single microchannel with fully developed flow under the effect of different heat flux profiles. Initially, a hot spot at different locations, with a uniform background heat flux, is studied at different Reynolds numbers, while varying the maximum heat fluxes in order to compute the heat transfer in relation to its dependent variables. Measurements of temperature, pressure, and flow rates at a different locations and magnitudes of hot spot heat fluxes are presented, followed by a detailed analysis of heat transfer characteristics of a single microchannel under nonuniform heating. Results showed that upstream hotspots have lower tube temperatures compared to downstream ones with equal amounts of heat fluxes. This finding can be of importance in enhancing microchannel heat sinks effectiveness in reducing maximum wall temperatures for the same amount of heat released, by redistributing spatially fluxes in a descending profile.

Investigation of On-Chip Hot Spot Cooling Using Microchannel Heat Sink

2013 ◽  
Vol 455 ◽  
pp. 466-469
Author(s):  
Yun Chuan Wu ◽  
Shang Long Xu ◽  
Chao Wang
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Hot Spots ◽  
Hot Spot ◽  
High Heat ◽  
High Heat Flux ◽  
Microchannel Heat Sink ◽  
Three Dimensional Model ◽  
Spot Cooling ◽  
On Chip

With the increase of performance demands, the nonuniformity of on-chip power dissipation becomes greater, causing localized high heat flux hot spots that can degrade the processor performance and reliability. In this paper, a three-dimensional model of the copper microchannel heat sink, with hot spot heating and background heating on the back, was developed and used for numerical simulation to predict the hot spot cooling performance. The hot spot is cooled by localized cross channels. The pressure drop, thermal resistance and effects of hot spot heat flux and fluid flow velocity on the cooling of on-chip hot spots, are investigated in detail.

Direct Liquid Cooling of High Flux LED Systems: Hot Spot Abatement

2013 ◽  
Author(s):  
Enes Tamdogan ◽  
Mehmet Arik ◽  
M. Baris Dogruoz
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Heat Removal ◽  
Heat Fluxes ◽  
Light Extraction ◽  
Junction Temperature ◽  
System Level ◽  
Design Parameters ◽  
Liquid Cooling ◽  
Wide Range

With the recent advances in wide band gap device technology, solid-state lighting (SSL) has become favorable for many lighting applications due to energy savings, long life, green nature for environment, and exceptional color performance. Light emitting diodes (LED) as SSL devices have recently offered unique advantages for a wide range of commercial and residential applications. However, LED operation is strictly limited by temperature as its preferred chip junction temperature is below 100 °C. This is very similar to advanced electronics components with continuously increasing heat fluxes due to the expanding microprocessor power dissipation coupled with reduction in feature sizes. While in some of the applications standard cooling techniques cannot achieve an effective cooling performance due to physical limitations or poor heat transfer capabilities, development of novel cooling techniques is necessary. The emergence of LED hot spots has also turned attention to the cooling with dielectric liquids intimately in contact with the heat and photon dissipating surfaces, where elevated LED temperatures will adversely affect light extraction and reliability. In the interest of highly effective heat removal from LEDs with direct liquid cooling, the current paper starts with explaining the increasing thermal problems in electronics and also in lighting technologies followed by a brief overview of the state of the art for liquid cooling technologies. Then, attention will be turned into thermal consideration of approximately a 60W replacement LED light engine. A conjugate CFD model is deployed to determine local hot spots and to optimize the thermal resistance by varying multiple design parameters, boundary conditions, and the type of fluid. Detailed system level simulations also point out possible abatement techniques for local hot spots while keeping light extraction at maximum.

Experimental Boiler Tube Burnout as a Function of Downcorner Resistance

1968 ◽  
Vol 12 (01) ◽  
pp. 46-56
Author(s):  
John B. Woodward
Keyword(s):  
Heat Flux ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Boiler Tube ◽  
Average Flow ◽  
Flow Reduction ◽  
Flow Oscillations ◽  
Independent Variable

Experiments to determine the burnout heat flux in a simulated boiler tube are described. The principal independent variable is downcorner resistance to flow, measured by the parameter fL/D, and varied by adjusting a plug cock in the downcorner. The experimental results show an increase in burnout heat flux with increasing downcorner resistance, up to the point at which average flow reduction reverses this trend. The results are explained by the effect of downcorner resistance on the magnitude of flow oscillations, which begin to occur at heat fluxes less than the burnout heat flux, and which tend to promote the onset of burnout.

Numerical Study of Microchannel Heat Sinks With Non-Uniform Heat Flux Conditions

2011 ◽  
Author(s):  
Ling Ling ◽  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Numerical Study ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Bottom Surface ◽  
Nonuniform Heating ◽  
Uniform Heat Flux ◽  
Computational Domain ◽  
Uniform Heating

Higher heat flux is produced by Micro-Electro-Mechanical Systems (MEMS) because of their reduced size and increased clock speed. At the mean time, studies of non-uniform heating conditions which are more practical than uniform heating conditions are inadequate and needed urgently. Four nonuniform heating conditions are simulated in the paper. Three heat sinks with different widths of cross-linked channels locating above the center of hotspots are studied and compared to conventional straight microchannel heat sink. Half of the module geometry is chosen to be the computational domain. Two hotspots are placed at the bottom surface. The coolant is water, whose properties are dependent on temperature. Two inlet velocities, 0.5 m/s and 1 m/s, are tested for each heat sink. Temperature profile at the hotspots, pressure drop and total thermal resistance are selected as criteria of evaluating heat sink performance. All heat sinks have better performance when there is an upstream hotspot or the upstream hotspot is subjected to a higher heat flux. Cross-linked channel width of 0.5 mm has the best benefit to obtain better temperature uniformity without increasing the maximum temperature on the bottom surface.

Analysis of Parallel Microchannels for Flow Control and Hot Spot Cooling

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
Stephen A. Solovitz
Keyword(s):  
Heat Transfer ◽  
Power Law ◽  
Hot Spots ◽  
Hot Spot ◽  
Electronics Cooling ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Cooling Devices ◽  
Parallel Microchannels

Microchannel heat transfer is commonly applied in the thermal management of high-power electronics. Most designs involve a series of parallel microchannels, which are typically analyzed by assuming a uniform flow distribution. However, many devices have a nonuniform thermal distribution, with hot spots producing much higher heat fluxes and temperatures than the baseline. Although solutions have been developed to improve local heat transfer, these are advanced methods using embedded cooling devices. As an alternative, a passive solution is developed here using analytical methods to optimize the channel geometry for a desired, nonuniform flow distribution. This results in a simple power law for the passage diameter, which may be useful for many microfluidic systems, including electronics cooling devices. Computational simulations are then applied to demonstrate the effectiveness of the power law for laminar conditions. At low Reynolds numbers, the flow distribution can be controlled to good accuracy, matching the desired distribution to within less than 1%. Further simulations consider the control of hot spots in laminar developing flow. Under these circumstances, temperatures can be made uniform to within 2 °C over a range of Reynolds numbers (60 to 300), demonstrating the capability of this power law solution.

Experimental Study of a Single Microchannel Flow Under Non-Uniform Heat Flux

2017 ◽  
Author(s):  
Ahmed Eltaweel ◽  
Abdulla Baobeid ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Dissipation ◽  
Hot Spot ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Uniform Heat Flux ◽  
Maximum Heat ◽  
Uniform Heat ◽  
Microchannel Heat Sinks

Non-uniform heat fluxes are commonly observed in thermo-electronic devices that require distinct thermal management strategies for effective heat dissipation and robust performance. The limited research available on non-uniform heat fluxes focus mostly on microchannel heat sinks while the fundamental component, i.e. a single microchannel, has received restricted attention. In this work, an experimental setup for the analysis of variable axial heat flux is used to study the heat transfer in a single microchannel with fully developed flow under the effect of different heat flux profiles. Initially a hot spot at different locations, with a uniform background heat flux, is studied at different Reynolds numbers while varying the maximum heat fluxes in order to compute the heat transfer in relation to its dependent variables. Measurements of temperature, pressure, and flow rates at a different locations and magnitudes of hot spot heat fluxes are presented, followed by a detailed analysis of heat transfer characteristics of a single microchannel under non-uniform heating. Results showed that upstream hotspots have lower tube temperatures compared to downstream ones with equal amounts of heat fluxes. This finding can be of importance in enhancing microchannel heat sinks effectiveness in reducing maximum wall temperatures for the same amount of heat released, by redistributing spatially fluxes in a descending profile.

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.

Inverse Design of Cooling of Electronic Chips Subject to Specified Hot Spot Temperature and Coolant Inlet Temperature

2015 ◽  
Author(s):  
Sohail R. Reddy ◽  
George S. Dulikravich
Keyword(s):  
Heat Flux ◽  
Hot Spot ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Heat Transfer Analysis ◽  
Maximum Temperature ◽  
Fluid Temperature ◽  
Cooling Fluid ◽  
Pin Fin ◽  
The Given

Most methods for designing electronics cooling schemes do not offer the information on what levels of heat fluxes are maximally possible to achieve with the given material, boundary and operating conditions. Here, we offer an answer to this inverse problem posed by the question below. Given a micro pin-fin array cooling with these constraints: - given maximum allowable temperature of the material, - given inlet cooling fluid temperature, - given total pressure loss (pumping power affordable), and - given overall thickness of the entire electronic component, find out the maximum possible average heat flux on the hot surface and find the maximum possible heat flux at the hot spot under the condition that the entire amount of the inputted heat is completely removed by the cooling fluid. This problem was solved using multi-objective constrained optimization and metamodeling for an array of micro pin-fins with circular, airfoil and symmetric convex cross sections that is removing all the heat inputted via uniform background heat flux and by a hot spot. The goal of this effort was to identify a cooling pin-fin shape and scheme that is able to push the maximum allowable heat flux as high as possible without the maximum temperature exceeding the specified limit for the given material. Conjugate heat transfer analysis was performed on each of the randomly created candidate configurations. Response surfaces based on Radial Basis Functions were coupled with a genetic algorithm to arrive at a Pareto frontier of best trade-off solutions. The Pareto optimized configuration indicates the maximum physically possible heat fluxes for specified material and constraints.

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