scholarly journals Numerically Investigating the Effects of Cross-Links in Scaled Microchannel Heat Sinks

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Minh Dang ◽  
Ibrahim Hassan ◽  
Sung In Kim
Keyword(s):  
Pressure Drop ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Heat Sinks ◽  
Straight Channel ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
Cross Links ◽  
Channel Configuration

Thermal management as a method of heightening performance in miniaturized electronic devices using microchannel heat sinks has recently become of interest to researchers and the industry. One of the current challenges is to design heat sinks with uniform flow distribution. A number of experimental studies have been conducted to seek appropriate designs for microchannel heat sinks. However, pursuing this goal experimentally can be an expensive endeavor. The present work investigates the effect of cross-links on adiabatic two-phase flow in an array of parallel channels. It is carried out using the three-dimensional mixture model from the computational fluid dynamics software, FLUENT 6.3. A straight channel and two cross-linked channel models were simulated. The cross-links were located at 1/3 and 2/3 of the channel length, and their widths were one and two times larger than the channel width. All test models had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm. The results showed that the trend of flow distribution agrees with experimental results. A new design, with cross-links incorporated, was proposed and the results showed a significant improvement of up to 55% on flow distribution compared with the standard straight channel configuration without a penalty in the pressure drop. Further discussion about the effect of cross-links on flow distribution, flow structure, and pressure drop was also documented.

Microchannel Size Effects on Two-Phase Local Heat Transfer and Pressure Drop in Silicon Microchannel Heat Sinks With a Dielectric Fluid

2007 ◽  
Author(s):  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
The Heat Transfer Coefficient

Two-phase heat transfer in microchannels can support very high heat fluxes for use in high-performance electronics-cooling applications. However, the effects of microchannel cross-sectional dimensions on the heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer in microchannel heat sinks. The effect of channel size on the heat transfer coefficient and pressure drop is studied for mass fluxes ranging from 250 to 1600 kg/m2s. The test sections consist of parallel microchannels with nominal widths of 100, 250, 400, 700, and 1000 μm, all with a depth of 400 μm, cut into 12.7 mm × 12.7 mm silicon substrates. Twenty-five microheaters embedded in the substrate allow local control of the imposed heat flux, while twenty-five temperature microsensors integrated into the back of the substrates enable local measurements of temperature. The dielectric fluid Fluorinert FC-77 is used as the working fluid. The results of this study serve to quantify the effectiveness of microchannel heat transport while simultaneously assessing the pressure drop trade-offs.

Experimental Investigation and Theoretical Model for Subcooled Flow Boiling Pressure Drop in Microchannel Heat Sinks

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Jaeseon Lee ◽  
Issam Mudawar
Keyword(s):  
Pressure Drop ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Heat Sinks ◽  
Bulk Liquid ◽  
Two Phase ◽  
Phase Layer ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Microchannel Heat Sinks

This study examines the pressure drop characteristics of subcooled two-phase microchannel heat sinks. A new model is proposed, which depicts the subcooled flow as consisting of a homogeneous two-phase flow layer near the heated walls of the microchannel and a second subcooled bulk liquid layer. This model is intended for conditions where subcooled flow boiling persists along the entire microchannel and the outlet fluid never reaches bulk saturation temperature. Mass, momentum, and energy control volume conservation equations are combined to predict flow characteristics for thermodynamic equilibrium qualities below zero. By incorporating a relation for apparent quality across the two-phase layer and a new criterion for bubble departure, this model enables the determination of axial variations in two-phase layer thickness and velocity as well as pressure drop. The model predictions are compared with HFE 7100 pressure drop data for four different microchannel sizes with hydraulic diameters of 176–416 μm, mass velocities of 670–5550 kg/m2 s, and inlet temperatures of 0°C and −30°C. The pressure drop database is predicted with a mean absolute error of 14.9%.

The Effects of Cross Links on Adiabatic Two-Phase Flow Characteristics in Scaled Microchannel Heat Sinks

2007 ◽  
Author(s):  
Minh N. Dang ◽  
Ibrahim G. Hassan
Keyword(s):  
Flow Regime ◽  
Single Channel ◽  
Flow Characteristics ◽  
Flow Distribution ◽  
Intermittent Flow ◽  
Straight Channel ◽  
Channel Design ◽  
Two Phase ◽  
Cross Links ◽  
The Cross

The effects of cross-links, introduced in the channel core of an array of parallel scaled microchannels, were investigated by comparison of the flow distribution in six different multichannel configurations. A standard straight channel test section and five other test sections, which incorporated cross-links were used. One case includes two cross-links located at 1/3 and 2/3’s of the channel length, with their width varied by one, two, and three times the channel width. Whereas, four and six cross-links were used for the other case. All test sections had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm, and were fabricated from clear acrylic to enhance flow visualization. The flow distribution was monitored at four select channels. The working mixture was air and water with superficial velocities ranging from 0.03 to 9.93 m/s, and 0.04 to 0.83 m/s, respectively. This corresponds to an observed range of flow quality between 0 and 0.25, whereby the mass flux range is from 42 kg/m2s to 834 kg/m2s. The cross-linked designs permit fluid communication between channels, and the results showed that there is a significant impact on flow distribution when compared to the straight channel design. This is due to flow sharing between neighboring channels. Flow patterns were presented in terms of fractional time function, and provided further insight to flow characteristics. Comparing with a single channel flow regime map, the expected intermittent flow regime was observed 84% to 90% of the time for the cross-linked designs, whereas 65% to 80% of that for the straight channel design.

Two-Phase Stacked Microchannel Heat Sinks for Microelectronics Cooling

2005 ◽  
Vol 2 (2) ◽  
pp. 122-131
Author(s):  
Pradeep Hegde ◽  
K.N. Seetharamu ◽  
P.A. Aswatha Narayana ◽  
Zulkifly Abdullah
Keyword(s):  
Finite Element ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Sink ◽  
Two Phase Flow ◽  
Heat Sinks ◽  
Phase Flow ◽  
Pumping Power ◽  
Two Phase ◽  
Microchannel Heat Sinks

Stacked microchannel heat sinks with two-phase flow have been analyzed using the Finite Element Method (FEM). The present method is a simple and practical approach for analyzing the thermal performance of single or multi layered microchannel heat sinks with either single or two-phase flow. A unique 10 noded finite element is used for the channel discretization. Two-phase thermal resistance, pressure drop and pumping power of single, double and triple stack microchannel heat sinks are determined at different base heat fluxes ranging from 150 W/cm2 to 300 W/cm2. The temperature distribution along the length of the microchannel is also plotted. It is found that stacked microchannel heat sinks with two-phase flow are thermally more efficient than two-phase single layer microchannel heat sinks, both in terms of thermal resistance and pumping power requirements. It is observed that the thermal resistance of a double stack microchannel heat sink with two-phase flow is about 40% less than that for a single stack heat sink. A triple stack heat sink yields a further 20% reduction in the thermal resistance and at the same time operates with about 30% less pumping power compared to a single stack heat sink. The effect of channel aspect ratio on the thermal resistance and pressure drop of stacked microchannel heat sinks with two-phase flow are also studied.

Two-Phase Flow and Heat Transfer in Rectangular Micro-Channels

2003 ◽  
Author(s):  
Weilin Qu ◽  
Seok-Mann Yoon ◽  
Issam Mudawar
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Two Phase Flow ◽  
Flow Patterns ◽  
Heat Sinks ◽  
Phase Flow ◽  
Micro Channel ◽  
Two Phase ◽  
Micro Channels

Knowledge of flow pattern and flow pattern transitions is essential to the development of reliable predictive tools for pressure drop and heat transfer in two-phase micro-channel heat sinks. In the present study, experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel having a 0.406 × 2.032 mm cross-section. Superficial velocities of nitrogen and water ranged from 0.08 to 81.92 m/s and 0.04 to 10.24 m/s, respectively. Flow patterns were first identified using high-speed video imaging, and still photos were then taken for representative patterns. Results reveal that the dominant flow patterns are slug and annular, with bubbly flow occurring only occasionally; stratified and churn flow were never observed. A flow pattern map was constructed and compared with previous maps and predictions of flow pattern transition models. Annual flow is identified as the dominant flow pattern for conditions relevant to two-phase micro-channel heat sinks, and forms the basis for development of a theoretical model for both pressure drop and heat transfer in micro-channels. Features unique to two-phase micro-channel flow, such as laminar liquid and gas flows, smooth liquid-gas interface, and strong entrainment and deposition effects are incorporated into the model. The model shows good agreement with experimental data for water-cooled heat sinks.

Transient Analysis of Nonuniform Heat Input Propagation Through a Heat Sink Base

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Srivathsan Sudhakar ◽  
Justin A. Weibel
Keyword(s):  
Heat Source ◽  
Heat Input ◽  
Heat Sink ◽  
Three Dimensional ◽  
Temperature Response ◽  
Flow Distribution ◽  
Temporal Variations ◽  
Step Response ◽  
Dimensional System ◽  
Two Phase

For thermal management architectures wherein the heat sink is embedded close to a dynamic heat source, nonuniformities may propagate through the heat sink base to the coolant. Available transient models predict the effective heat spreading resistance to calculate chip temperature rise, or simplify to a representative axisymmetric geometry. The coolant-side temperature response is seldom considered, despite the potential influence on flow distribution and stability in two-phase microchannel heat sinks. This study solves three-dimensional transient heat conduction in a Cartesian chip-on-substrate geometry to predict spatial and temporal variations of temperature on the coolant side. The solution for the unit step response of the three-dimensional system is extended to any arbitrary temporal heat input using Duhamel's method. For time-periodic heat inputs, the steady-periodic solution is calculated using the method of complex temperature. As an example case, the solution of the coolant-side temperature response in the presence of different transient heat inputs from multiple heat sources is demonstrated. To represent a case where the thermal spreading from a heat source is localized, the problem is simplified to a single heat source at the center of the domain. Metrics are developed to quantify the degree of spatial and temporal nonuniformity in the coolant-side temperature profiles. These nonuniformities are mapped as a function of nondimensional geometric parameters and boundary conditions. Several case studies are presented to demonstrate the utility of such maps.

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