Phase change in microchannel heat sinks with integrated temperature sensors

1999 ◽  
Vol 8 (4) ◽  
pp. 358-365 ◽  
Author(s):  
Linan Jiang ◽  
Man Wong ◽  
Y. Zohar
Keyword(s):  
Phase Change ◽  
Temperature Sensors ◽  
Heat Sinks ◽  
Microchannel Heat Sinks

Design of a Microscale Breather for Two-Phase Thermal Management Devices

2008 ◽  
Author(s):  
B. R. Alexander ◽  
E. N. Wang
Keyword(s):  
Phase Change ◽  
Removal Rate ◽  
Heat Removal ◽  
Design Guidelines ◽  
Heat Sinks ◽  
Two Phase ◽  
Cross Sectional ◽  
Optical Visualization ◽  
Gas Removal ◽  
Microchannel Heat Sinks

Two-phase microchannels promise an efficient method to dissipate heat from high performance electronic systems by utilizing the latent heat of vaporization during the phase-change process. However, phase-change in microchannel heat sinks leads to challenges that are not present in macroscale systems due to the increasing importance of surface tension and viscous forces. In particular, flow instabilities often occur during the boiling process, which lead to liquid dry-out in the microchannels and severely limits the heat removal capabilities of the system. We propose a microscale breather device consisting of an array of hydrophobic breather ports which allow vapor bubbles to escape from the microchannels to improve flow stability. In this study, we use the combination of microfabricated structures and surface chemistry to separate vapor from the liquid flow. We designed test devices that allow for cross-sectional optical visualization to better understand the governing parameters of a breather design with high vapor removal efficiencies and minimal liquid leakage. We examined breather devices with average liquid velocities ranging from 0.5 cm/s to 4 cm/s and breather vacuum levels between 1 kPa and 9 kPa on the maximum gas removal rate through the breather. We demonstrated successful breather performance. In addition, a model was developed that offers design guidelines for future integrated breathers in microchannel heat sinks. The breathers also have significant promise for other microscale systems, such as micro-fuel cells, where liquid-vapor separation can significantly enhance system performance.

OPTIMUM DESIGN OF MICROCHANNEL HEAT SINKS FOR ANNULAR FLOW WITH PHASE CHANGE

2014 ◽  
Vol 21 (4-5) ◽  
pp. 373-395
Author(s):  
Sainaba Jesseela ◽  
Choondal B. Sobhan ◽  
G. P. Peterson
Keyword(s):  
Phase Change ◽  
Optimum Design ◽  
Annular Flow ◽  
Heat Sinks ◽  
Microchannel Heat Sinks

Control of Instabilities in Two-Phase Microchannel Flow Using Artificial Nucleation Sites

2007 ◽  
Author(s):  
Rory J. Jones ◽  
Daniel T. Pate ◽  
Sushil H. Bhavnani
Keyword(s):  
Phase Change ◽  
Flow Regime ◽  
Flow Instability ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
High Speed Photography ◽  
Unstable Flow ◽  
Microchannel Heat Sinks

Microchannel heat sinks offer the promise of an effective and compact technique for heat dissipation from high-powered microelectronics. When combined with phase-change mechanisms, it is possible to extend heat removal capabilities over several future technology nodes on electronics roadmaps. Many studies have documented instabilities in phase-change flows associated with uncontrolled transition from bubbly flows to slug flows at fairly low void fraction. The phase-change thermal transport reported here was carried out on microchannel heat sinks etched in silicon and cooled by the dielectric fluid FC72. Microchannels with a hydraulic diameter of 253 microns were studied. The base of each microchannel is augmented with 20-micron cavities to trigger controlled nucleation activity and help control large-scale instabilities reported in the literature. The cavities significantly impact the flow regime by promoting stable nucleate boiling. Temperature and pressure measurements show stable flow regimes under all combinations leading to saturated channel exit conditions and even for subcooled exit conditions at low-to-moderate heat fluxes. These measurements are confirmed by high-speed photography. Instabilities observed were confined to a sub-set of the subcooled exit flow regime. Within this region, an analysis of the data shows that the frequency of the flow instability is between 8–14 Hz. Instability maps demarcating regions of stable and unstable flow are presented as functions of mass flux (535–2140 kg/m2–s), and inlet subcooling (5–25°C).

Modeling and Numerical Simulations of Vapor-Liquid Flow and Heat Transfer Within Microchannel Heat Sinks

2012 ◽  
Author(s):  
Chengyun Xin ◽  
Jianhua Wang ◽  
Jianheng Xie ◽  
Yuee Song
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Solid Wall ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Flowing Fluid ◽  
Liquid Coolant ◽  
Microchannel Heat Sinks

Microchannel heat sinks have demonstrated the ability to dissipate large amounts of heat flux. This ability can be strongly enhanced by phase change of a liquid coolant. This paper numerically simulates the processes of liquid coolant flow, heat absorption and phase change within a microchannel, which is heated at one side by given heat fluxes. The two-phase flow model widely used in the investigations on heat and mass transfer within porous media is firstly introduced into microchannnel heat sinks by this paper. Experiential equations of the heat transfer coefficients in single phase and boiling region within microchannels are employed to calculate the convective heat exchange between solid wall and flowing fluid by an iterative process. The numerical results of pressure and temperature distributions obtained at different conditions are exhibited and analyzed. The results indicated that the trends predicted by this approach agree well with the previous references. Therefore the modeling is validated in some sense. At the same time, two phenomena, countercurrent flow in two-phase region and special pressure variations near the transition point, are exhibited.

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