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.

Thermal Management of Ultra Intense Hot Spots With Two-Phase Multi-Microchannels and Embedded Thermoelectric Cooling

2013 ◽  
Author(s):  
Jackson B. Marcinichen ◽  
Brian P. d’Entremont ◽  
John R. Thome ◽  
Gary Bulman ◽  
Jay Lewis ◽  
...  
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Electrical Current ◽  
Heat Fluxes ◽  
Junction Temperature ◽  
Two Phase ◽  
Flow Through ◽  
Microchannel Cooling ◽  
On Chip ◽  
A Current

This study concerns cooling of electronic components of intense background heat flux with one ultra intense hot spot (e.g. 1000 Wcm−2 on a footprint of 1 cm × 1 cm with 5000 Wcm−2 applied to a 0.02 cm × 0.02 cm region at the center). To manage these extreme heat fluxes and consequently surpass the thermal-hydrodynamic challenges and design paradigms, for example as specified in a recent DARPA request for proposals (Intrachip/Interchip Enhanced Cooling Fundamentals - ICECool Fundamentals [1]), on-chip two-phase multi-microchannel cooling integrated with a superlattice (SL) thin-film thermoeletric cooling (TEC) technology was investigated via computer simulations. The simulations showed that increasing TEC electrical current results in greater enhancement of heat flow through the TEC, but at high currents this benefit is offset by a net addition of heat to the system, which must also be evacuated by the microchannels. When optimized, a minimum peak junction temperature of about 86 °C for a current of about 8 A was found, which represented a reduction of about 4 °C from a maximum allowed 90 °C at the ultra-intense hot-spot, thus potentially significantly capable of exceeding the DARPA [1] requirement, due to the embedded SL TEC within the microevaporator (ME) structure.

Perspiration Nano-Patch for Hot Spot Thermal Management

2007 ◽  
Author(s):  
Shankar Narayanan ◽  
Andrei G. Fedorov ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Hot Spot ◽  
Evaporative Cooling ◽  
Heat Removal ◽  
Heat Fluxes ◽  
Conceptual System ◽  
Sweeping Gas ◽  
Phase Change Heat Transfer ◽  
Latent Heat Of Vaporization

A novel cooling scheme utilizing evaporative cooling for an ultra-thin, spatially confined liquid film is described for meeting the challenge of hot spot thermal management aiming at locally removing heat fluxes in excess of 200 W/cm2. This work presents the conceptual system design and results of performance calculations supporting the feasibility of the proposed cooling scheme. The phase change heat transfer is one of the most efficient means of heat transfer due to an advantage offered by the significant latent heat of vaporization of liquids. Fundamentally, evaporation could be a much more efficient method of heat removal as compared to boiling if certain conditions are met. Theoretically, we demonstrate that if a stable monolayer of liquid can be maintained on the surface and fully dry sweeping gas (e.g., air) is blown at high velocity above this liquid monolayer one can dissipate heat fluxes of the order of several hundreds of Watts per cm2. We also show that a more volatile FC-72 can outperform water in evaporative cooling using stable liquid microfilms.

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.

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.

Forced Convection Boiling in Microchannels for Improved Heat Transfer

2006 ◽  
Author(s):  
Thomas B. Baummer ◽  
Ebrahim Al-Hajri ◽  
Michael M. Ohadi ◽  
Serguei V. Dessiatoun
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
High Heat Flux ◽  
Surface Areas ◽  
Feed Pressure ◽  
Wide Range

This paper presents experimental results from research investigating the heat transfer capabilities of microchannel surfaces using a novel force-fed boiling and evaporation technique. The evaporative surfaces being investigated consist of a series of parallel, high-aspect ratio, open topped microchannels. The different sample surfaces vary in channel density, channel aspect ratio, and channel width and have heat transfer surface areas up to ten times their nominal surface areas. Liquid enters the channels of the evaporative surface from above through a developed system of feed channels. This method organizes a liquid-vapor circulation at the boiling surface that results in dissipation of very high heat fluxes in the boiling/thin film evaporation mode. By using the force-fed boiling technique, nominal area heat transfer rates of 100,000 W/m2-K have been achieved with HFE-7100 as the working fluid [1]. In force-fed boiling, the many very short microchannels are working in parallel; therefore the feed pressure and pumping power are very low. This technique may prove valuable to a wide range of heat transfer applications, particularly for heat removal at high heat flux surfaces.

Removing the Hot-Spots in High Power Devices Using the Thermoelectric Cooler and Micro Heat Pipe

2012 ◽  
Author(s):  
Agat Hirachan ◽  
Dereje Agonafer
Keyword(s):  
Heat Pipe ◽  
Integrated Circuit ◽  
Hot Spots ◽  
Hot Spot ◽  
The United States ◽  
High Heat ◽  
Heat Fluxes ◽  
Thermoelectric Cooler ◽  
Silicon Chips ◽  
Micro Heat Pipe

Due to localized high heat fluxes, hot-spots are created in silicon chips. Cooling of the hot-spots is one of the major thermal challenges in today’s integrated circuit (IC) industry. Many researches have been conducted to find ways to cool hot-spots using different techniques as uniform heating is highly desired. This paper focuses on cooling of hot-spot using conventional thermoelectric cooler (Melcor_CP1.0-31-05L.1) and a micro heat pipe. A chip package with conventional integrated heat spreader and heat sink was designed. Hot-spot was created at the center of the silicon die with background heat at rest of the area. The heat flux on the hot-spot was much greater than rest of the area. Forced convection was used to cool IC package, temperature was observed at active side of the silicon die. After that a copper conductor was used to take away heat directly from the hot-spot of the silicon die to the other end of the conductor which was cooled using the thermoelectric cooler. Finally the conductor was replaced by a heat pipe and a comparison between three cases was done to study the cooling performance using the commercial software, ANSYS Icepak. The effect of trench on silicon die was also studied. In this paper the United States Patent, Patent No. US 6,581,388 B2, Jun. 24 2000 [8] as shown in Fig. 1 (b) was modified by replacing the conductor with a micro heat pipe to solve the hot-spots problem in electronic packaging.

MEMS Enabled Micro Spray Cooling System for Thermal Control of Electronic Chips

2001 ◽  
Author(s):  
S. C. Yao ◽  
C. H. Amon ◽  
K. Gabriel ◽  
P. Kumta ◽  
J. Y. Murthy ◽  
...  
Keyword(s):  
Cooling System ◽  
Surface Texturing ◽  
Thermal Control ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
System Level ◽  
Air Cooling ◽  
Liquid Cooling ◽  
Droplet Impingement ◽  
Dielectric Fluids

Abstract Liquid cooling of electronic devices becomes necessary when the chip-level heat fluxes increase and traditional air cooling encounters ever-increasing difficulties. From all the liquid cooling processes, spray cooling appears more successful due to its high critical heat flux, relatively low liquid flow rates, highly controllable, and the non-existence of boiling incipient hysterisis. This paper describes the development of the EDIFICE project (Embedded Droplet Impingement For Integrated Cooling of Electronics), which seeks to develop an integrated droplet impingement cooling device for removing chip heat fluxes in the range 50–100 W/cm2, employing latent heat of vaporization of dielectric fluids. Micro-spray nozzles are fabricated on silicon using MEMS technology to produce 100 micron droplets with odd shaped nozzles and swirling nozzles. The effects of shape, size, type of fluid, and swirling are tested and discussed. Spray heat transfer on silicon surfaces is studied with various surface texturing on the backside of the chip to promote spreading and evaporation of cold fluids as well as at heated conditions. The effects of configuration and fluids are revealed. Numerical modeling is used to study preliminary designs at both the device and system level. The paper describes progress made in the development of the EDIFICE device.

scholarly journals Molecular Recognition of SARS-CoV-2 Spike Glycoprotein: Quantum Chemical Hot Spot and Epitope Analyses

2020 ◽  
Author(s):  
Chiduru Watanabe ◽  
Yoshio Okiyama ◽  
Shigenori Tanaka ◽  
Kaori Fukuzawa ◽  
Teruki Honma
Keyword(s):  
Amino Acid ◽  
Molecular Recognition ◽  
Hydrogen Bonds ◽  
Hot Spots ◽  
Hot Spot ◽  
Spike Glycoprotein ◽  
Microscopic Mechanism ◽  
S Protein ◽  
Π Interactions ◽  
Wide Range

<div>Due to the COVID-19 pandemic, researchers have attempted to identify complex structures of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike glycoprotein (S-protein) with angiotensin-converting enzyme 2 (ACE2) or a blocking antibody. However, the molecular recognition mechanism - critical information for drug and antibody design - has not been fully clarified at the amino acid residue level. Elucidating such a microscopic mechanism in detail requires a more accurate molecular interpretation that includes quantum mechanics to quantitatively evaluate hydrogen bonds, XH/π interactions (X = N, O, and C), and salt bridges. In this study, we applied the fragment molecular orbital (FMO) method to characterize the SARS-CoV-2 S-protein binding interactions with not only ACE2 but also the B38 Fab antibody involved in ACE2-inhibitory binding. By analyzing FMO-based interaction energies along a wide range of binding inter-faces carefully, we identified amino acid residues critical for molecular recognition between S-protein and ACE2 or B38 Fab antibody. Importantly, hydrophobic residues that attribute to weak interactions such as CH-O and XH/π interactions, as well as polar residues that construct conspicuous hydrogen bonds, play important roles in molecular recognition and binding ability. Moreover, through these FMO-based analyses, we also clarified novel hot spots and epitopes that had been overlooked in previous studies by structural and molecular mechanical approaches. Altogether, these hot spots/epitopes identified between S-protein and ACE2/B38 Fab antibody may provide useful information for future anti-body design and small or medium drug design against the SARS-CoV-2. </div><div><br></div>

Effect of Thermal Contact Resistance on Optimum Mini-Contact TEC Cooling of On-Chip Hot Spots

2009 ◽  
Author(s):  
Viatcheslav Litvinovitch ◽  
Avram Bar-Cohen
Keyword(s):  
Contact Resistance ◽  
Thermal Management ◽  
Hot Spots ◽  
High Performance ◽  
Thermal Contact Resistance ◽  
Hot Spot ◽  
Thermal Contact ◽  
Heat Fluxes ◽  
Thermoelectric Coolers ◽  
On Chip

Shrinking feature size and increasing transistor density, combined with the high performance demanded from next-generation microprocessors and other electronic components, have lead to the emergence of severe on-chip “hot spots,” with heat fluxes approaching — and at times exceeding — 1 kW/cm2. The cost-effective thermal management of such chips requires the introduction and refinement of novel cooling techniques. Mini-contact enhanced, miniaturized thermoelectric coolers (TECs) have been shown to be a viable approach for the remediation of on-chip hot spots, but their performance is constrained by the thermal resistance introduced by the attachment of this thermal management device. This paper uses a detailed finite-element package-level model to examine the parasitic effects of the thermal contact resistance (at the interfaces of the mini-contact and TEC) on the cooling efficacy of this thermal solution. Particular attention is devoted to the deleterious effect of contact resistance on the thermoelectric leg height and the mini-contact size required to achieve the greatest hot spot temperature reduction on the chip. Data from experiments with TECs (with a leg height of 130 μm) combined with several sizes of mini-contact pads, are used to validate the modeling approach and the overall conclusions.

Study of the Hot Spots in Integrated Circuits Cooled by Microfluidic Heatsinks

2007 ◽  
Author(s):  
Alireza Motieifar ◽  
Cyrus Shafai ◽  
Hassan M. Soliman
Keyword(s):  
Fluid Flow ◽  
Integrated Circuits ◽  
Heat Sink ◽  
Hot Spots ◽  
Hot Spot ◽  
Solid Material ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Fem Method ◽  
Spot Temperature

The thermal input into high-power Integrated Circuits (IC) can have local peaks or hot spots with heat fluxes far exceeding 100 W/cm2. In this work, the temperature distribution on a microfluidic heatsink has been simulated using the FEM method. The effects of the fluid flow and thickness of the heatsink on the hot spot temperature have been studied. Simulations have been performed for a 1 cm × 1 cm heat sink loaded with 100 W/cm2 heating power, with a 1 mm hot spot of 1000 W/cm2 and a 3 mm hot spot of 500 W/cm2. Heat sinks fabricated from silicon, nickel, and copper are considered. These results show that the effect of increasing the thickness of the heatsink on the peak temperature of the hot spot depends on the solid material and the fluid flow. Simulations showed that the hot spot temperature rise can be about 40% higher if a nickel heat sink is used instead of a copper heat sink.

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