scholarly journals Micro channels in macro thermal management solutions

2006 ◽  
Vol 10 (1) ◽  
pp. 81-98
Author(s):  
Boris Kosoy
Keyword(s):  
Surface Roughness ◽  
Thermal Management ◽  
High Performance ◽  
Electronic Device ◽  
Three Dimensional ◽  
Thermal Control ◽  
Consumer Products ◽  
Working Fluid ◽  
Channel Height ◽  
Micro Channels

Modern progress in electronics is associated with increase in computing ability and processing speed, as well as decrease in size. Future applications of electronic devices in aviation, aero space and high performance consumer products? industry demand on very stringent specifications concerning miniaturization, component density, power density and reliability. Excess heat produces stresses on internal components inside the electronic device, thus creating reliability problems. Thus, a problem of heat generation and its efficient removal arises and it has led to the development of advanced thermal control systems. Present research analyses a thermodynamic feasibility of micro capillary heat pumped net works in thermal management of electronic systems, considers basic technological constrains and de sign availability, and identifies perspective directions for the further studies. Computer Fluid Dynamics studies have been per formed on the laminar convective heat transfer and pressure drop of working fluid in silicon micro channels. Surface roughness is simulated via regular constructal, and stochastic models. Three-dimensional numerical solution shows significant effects of surface roughness in terms of the rough element geometry such as height, size, spacing and the channel height on the velocity and pressure fields.

High-performance Planar Thermal Diode with Wickless Components

2021 ◽  
Author(s):  
George Damoulakis ◽  
Mohamad Jafari-Gukeh ◽  
Theodore P. Koukoravas ◽  
Constantine Megaridis
Keyword(s):  
Thermal Management ◽  
High Performance ◽  
Building Materials ◽  
Condensed Medium ◽  
Thermal Control ◽  
Electronics Packaging ◽  
Vapor Chamber ◽  
Reverse Mode ◽  
Low Profile ◽  
Specific Direction

Abstract The characterization "thermal diode" has been used to portray systems that spread heat very efficiently in a specific direction but obstruct it from flowing in the opposite direction. In this study, a planar vapor chamber with a wickless, wettability-patterned condenser is fabricated and tested as a thermal diode. When the chamber operates in the forward mode, heat is naturally driven away from the heat source; in the reverse mode, the system blocks heat backflow, thus working as a thermal diode. The low-profile assembly takes advantage of the phase-changing properties of water inside a closed loop comprised of a classical thin-wick evaporator opposing a wickless wettability-patterned condenser, when the chamber operates in the forward (heat-transporting) mode. The wettability patterned plate -when on the cooled side- enables spatial controlled dropwise and filmwise condensation and offers an efficient transport mechanism of the condensed medium on superhydrophilic wedge tracks by way of capillary forces. The same chamber acts as a thermal blocker when the opposing wick-covered plate is on the cool side, trapping the liquid in the pores and blocking heat flow. With this system, thermal diodicities exceeding 20 have been achieved, and are tunable by altering the wettability pattern as needed for different purposes. The present vapor chamber - thermal diode design could be well-suited for an extensive range of thermal-management applications, ranging from aerospace, spacecraft, and construction building materials, to electronics protection, electronics packaging, refrigeration, thermal control during energy harvesting, thermal isolation, etc.

Slip due to Rarefaction, Surface Roughness, and Intermolecular Interactions for Gases and Liquids

2011 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Surface Roughness ◽  
Intermolecular Interactions ◽  
Stokes Equations ◽  
Slip Length ◽  
Wall Slip ◽  
Mean Free Path ◽  
Working Fluid ◽  
Channel Height ◽  
Near Surface ◽  
Accommodation Coefficients

In the present study, slip phenomena are investigated in two different sets of experiments conducted in gases and one Newtonian liquid. Overall, differences in near-surface slip behavior are illustrated for these two different fluid mediums, where the slip is induced surface roughness and rarefaction in the gases, and by surface roughness and intermolecular interactions in the liquid. Within both sets of experiments, flows are induced within micro-fluidic passages by rotation within C-shaped fluid chambers formed between a rotating disk and a stationary surface. When gases are employed, accommodation coefficients are determined in a unique manner from experimental results and analysis based on the Navier-Stokes equations. In all cases, roughness size is large compared to molecular mean free path. When channel height is defined at the tops of the roughness elements, slip is believed to be a result of rarefaction as well as fluid shear. With this arrangement, tangential accommodation coefficients decrease and slip velocity magnitudes increase, at a particular value of Knudsen number, as the level of surface roughness increases. With Newtonian water as the working fluid, hydrophobic roughness is used to induce near-wall slip in the fluid chamber. The magnitudes of slip length and slip velocities increase as the average size of the surface roughness becomes larger. The resulting slip length data show a high degree of organization when normalized using the fluid chamber height, such that experimental data obtained using different chamber heights and different disk roughness magnitudes collapse along a single line, illustrating strong linear dependence of the slip length on the normalized radial-line-averaged shear stress.

Influence of Three-Dimensional Roughness on Pressure-Driven Flow Through Microchannels

2003 ◽  
Vol 125 (5) ◽  
pp. 871-879 ◽  
Author(s):  
Yandong Hu ◽  
Carsten Werner ◽  
Dongqing Li
Keyword(s):  
Surface Roughness ◽  
Pressure Drop ◽  
Roughness Element ◽  
Three Dimensional ◽  
Channel Height ◽  
Roughness Effect ◽  
Microscale Flow ◽  
Roughness Elements ◽  
Pressure Driven Flow ◽  
Pressure Driven

Surface roughness is present in most of the microfluidic devices due to the microfabrication techniques or particle adhesion. It is highly desirable to understand the roughness effect on microscale flow. In this study, we developed a three-dimensional finite-volume-based numerical model to simulate pressure-driven liquid flow in microchannels with rectangular prism rough elements on the surfaces. Both symmetrical and asymmetric roughness element arrangements were considered, and the influence of the roughness on pressure drop was examined. The three-dimensional numerical solution shows significant effects of surface roughness in terms of the rough elements’ height, size, spacing, and the channel height on both the velocity distribution and the pressure drop. The compression-expansion flow around the three-dimensional roughness elements and the flow blockage caused by the roughness in the microchannel were discussed. An expression of the relative channel height reduction due to roughness effect was presented.

Experimental and Numerical Study of Evaporating Flow Heat Transfer in Micro-Channel

2007 ◽  
Author(s):  
HoKi Lee ◽  
C. D. Richards ◽  
R. F. Richards
Keyword(s):  
Heat Transfer ◽  
Latent Heat ◽  
Numerical Study ◽  
Three Dimensional ◽  
Contact Angles ◽  
Numerical Results ◽  
Working Fluid ◽  
Micro Channels ◽  
Flow Heat ◽  
Domain Integration

Experimental and numerical results are presented for steady evaporating flow heat transfer from open top square micro-channels. Radial channels, 40 microns high, and 35, 50 and 70 microns wide with 5 micron wide SU-8 walls are considered. The channels are filled with Fluorinert FC77 working fluid pumped by capillary forces from a reservoir at the outer circumference of the radial channels. An energy balance on the radial channels including heat into the channels, conduction heat transfer radially along the channels and latent heat transfer via evaporation of the working fluid from the channels is experimentally determined. Microphotography is used to visualize the working fluid and the meniscus contact angles in the channels. A three-dimensional finite difference time-domain integration is used to predict sensible heat transfer rates and latent heat transfer/ evaporation rates. Experimental measurements are compared to the numerical results to extract estimates of the liquid thickness in the channels.

FINLESS Heat Sinks, High Performance and Low Cost for Low Profile Cooling Applications

2011 ◽  
Author(s):  
Ed Walsh ◽  
Ronan Grimes ◽  
Patrick Walsh ◽  
Jason Stafford
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
High Performance ◽  
Imaging Techniques ◽  
Low Cost ◽  
Local Heat Transfer ◽  
Consumer Products ◽  
Laminar Flows ◽  
Transfer Coefficients ◽  
Low Profile

The need for low profile, sustainable thermal management solutions is becoming a critical need in electronics from consumer products to server cabinets. This work presents a FINLESS thermal management solution that utilises fluidic structures generated within it to enhance the heat transfer performance. The FINLESS thermal management solution can be manufactured to have a height of ∼5mm or even less when using low profile motors. Particle Image Velocimetry (PIV) combined with Infra-Red (IR) imaging techniques are used to explain the underlying flow physics that results in increased heat transfer rates compared to typical laminar flows. It is found that the local heat transfer coefficients in the finless design are up to 300% greater than those achieved at the same Reynolds number using conventional boundary layer theory. The additional benefits in terms of sustainability of the approach are also highlighted.

Thermal Characterization of Interlayer Microfluidic Cooling of Three-Dimensional IC With Non-Uniform Heat Flux

2009 ◽  
Author(s):  
Yoon Jo Kim ◽  
Yogendra K. Joshi ◽  
Andrei G. Fedorov ◽  
Young-Joon Lee ◽  
Sung Kyu Lim
Keyword(s):  
Thermal Management ◽  
System Integration ◽  
High Performance ◽  
Hot Spot ◽  
Three Dimensional ◽  
Limiting Factors ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Two Phase

It is now widely recognized that three-dimensional (3D) system integration is a key enabling technology to achieve the processing speeds and performance needs of future microprocessor integrated circuits (ICs). To provide modular thermal management in 3D stacked ICs, interlayer microfluidic cooling scheme is adopted and analyzed in this study. The effects of cooling scheme and essential geometry variations on the routing completion and congestion of electrical interconnect are quantitatively analyzed. Also, the thermal and hydraulic performance of several two-phase refrigerants is discussed in comparison with single-phase cooling. The results show that refrigerants in two-phase flow are thermally preferred due to the higher heat transfer coefficients, and relatively constant fluid temperature throughout the microchannel. However, the large internal pressure and pressure drop act as significant limiting factors in realizing the merits of two-phase cooling. It is also concluded that integration of high performance hot-spot thermal management is a key to addressing a challenge of mass flow rate mal-distribution.

Surface Topography Evolution During Long-Run Micro-Stamping of Bipolar Plates (BPPs) and Effects on Corrosion and Contact Resistance Characteristics

2012 ◽  
Author(s):  
M. F. Peker ◽  
Ö. N. Cora ◽  
M. Koç
Keyword(s):  
Surface Roughness ◽  
Contact Resistance ◽  
Coefficient Of Friction ◽  
Mass Production ◽  
Surface Interactions ◽  
Proton Exchange ◽  
Channel Height ◽  
Bipolar Plates ◽  
Forming Process ◽  
Micro Channels

Micro-stamping, as a promising sheet metal forming process for mass production of small parts, can meet the expectations such as durability, strength, surface finish, and low cost for miniaturized metal products and features. The purpose of this research was set to investigate surface interactions during mass manufacturing of micro-stamped sheets, and its consequences; then establish correlations (if any) between surface interactions vs. corrosion and contact resistance of bipolar plates (BPPs) to be used in proton exchange membrane fuel cells (PEMFC). In experimental part of this study, 10,000 SS316L sheet blanks were micro-stamped using a stamping die set with 750 μm-deep micro-channels under 200 kN stamping force, and with a constant stamping speed of 1mm/s. Surface inspections (surface roughness and micro-channel height measurements), corrosion and contact resistance tests were carried out on BPPs. Analysis of variance (ANOVA) technique was utilized to investigate the significance of surface roughness, channel heights, corrosion and contact resistance variations for BPPs. Moreover, three-dimensional (3D) finite element models of micro-stamping process were established to approximate the stress and strain levels as well as coefficient of friction value experienced at contact interface. The results revealed that the roughness values for micro-stamping dies and BPPs followed similar trends during 10,000 micro-stampings. Since surface defects trigger corrosion, the correlation between surface roughness and corrosion resistance of BPPs was found to be direct. Increasing number of surface irregularities (asperities) lowered contact surface area that resulted in increased contact resistance. Finally, comparison of experimental and numerical channel height values showed that the coefficient of friction did not change considerably during the mass production of BPPs, at least within the 10,000 stamping cycle.

Influence of Thermo-Physical Properties on the Flow and Heat Transfer in Rectangular Micro-Channels

2011 ◽  
Vol 347-353 ◽  
pp. 2640-2644 ◽  
Author(s):  
Xue Tao Duan ◽  
Bin Xu ◽  
Hao Luo
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Flow Direction ◽  
Three Dimensional ◽  
Working Fluid ◽  
Fluid Temperature ◽  
Flux Boundary Condition ◽  
Flow And Heat Transfer ◽  
Friction Factors ◽  
Micro Channels

This paper investigated the behaviors of flow and heat transfer of single-phase in rectangular micro-channels with three-dimensional numerical analysis. The single micro-channel is 200μm deep, 50μm wide. Deionized water was used as the working fluid. The fluid physical properties varying with temperature and Re number were studied. Comparisons were made among the results obtained from experiments, numerical simulations, and from those in the literature. The results indicated that the friction factors decreasing along the flow direction were ascribed to the fluid temperature rising under the unified heat flux boundary condition. It was found that influence of viscosity variation with temperature and viscous dissipation effect could be too significant to be neglected.

Lock-exchange release density currents over three-dimensional regular roughness elements

2017 ◽  
Vol 832 ◽  
pp. 793-824 ◽  
Author(s):  
Kiran Bhaganagar ◽  
Narasimha Rao Pillalamarri
Keyword(s):  
Surface Roughness ◽  
Volume Fraction ◽  
Rough Surfaces ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Channel Height ◽  
Density Currents ◽  
Mixing Processes ◽  
Fundamental Study ◽  
Roughness Elements

A fundamental study has been conducted to understand the front characteristics and the mixing in the flow of density currents over rough surfaces. A large-eddy simulation (LES) has been performed for lock-exchange release density currents over rough walls to shed light on the unsteady mixing processes. A volume-penalization method, which is a special case of the immersed-boundary method, has been implemented to realize the bottom-mounted rough topology. In this study, the LES has been conducted in a channel with a lower wall covered with three-dimensional cube- and pyramid-shaped roughness elements, such that all cases have the same base area, but differences in the roughness solidity and volume fraction of roughness. Both cases of identical roughness elements and those with randomness in height have been considered. The maximum roughness height for all cases is kept at a constant fraction (10 %) of the total channel height. The study focuses on the instantaneous mixing processes in lock-exchange release currents over rough surfaces. An important contribution of the work is that qualitative and quantitative analysis has been conducted to demonstrate additional mixing mechanisms due to the presence of surface roughness that enhances dilution of the current. Enhanced mixing due to roughness is related to the strength of the shear layer resulting from the roughness, and hence depends on friction Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$). The combined role of current characteristics and $Re_{\unicode[STIX]{x1D70F}}$ together dictate the mixing processes and extent of dilution in density currents over surface roughness.

scholarly journals Experimental Measurement of Thermal Conductivities in a Thin Heterogeneous Structure of Thermal Diodes

2020 ◽  
Vol 194 ◽  
pp. 01019
Author(s):  
Jieyang Zhou ◽  
Zhe Wang ◽  
Yun Wang
Keyword(s):  
Thermal Management ◽  
Liquid Water ◽  
Thermal Control ◽  
Liquid Water Content ◽  
Working Fluid ◽  
Heterogeneous Structure ◽  
Nylon Mesh ◽  
Printing Paper ◽  
The One ◽  
Thermal Conductivities

Thermal diode has a wide application in the field of thermal management and thermal control. This article reports experimental results about measurement of the thermal conductivities of a novel thin layer (the thickness is about 0.3mm) for thermal diode applications. The layer consists printing paper, nylon mesh and liquid water, which are sealed between two pieces of aluminum, thus has a heterogeneity sublayers structure. It is shown that the thermal conductances are different in the two opposite through-plane directions. At 75 ˚C, the thermal conductivity is 0.457 W/mK in the conductive direction, more than 3 times larger than that in the opposite direction (0.133 W/mK). This phenomenon is due to the one-direction flow of working fluid. The thermal performance is dependent on the operating temperature and liquid water content in the structure.

Sign in / Sign up

Export Citation Format

Share Document