scholarly journals Local heat transfer distribution and effect of instabilities during flow boiling in a silicon microchannel heat sink

2011 ◽  
Vol 54 (15-16) ◽  
pp. 3179-3190 ◽  
Author(s):  
Tailian Chen ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Microchannel Heat Sink

Dependence of Flow Boiling Heat Transfer Coefficient on Location and Vapor Quality in a Microchannel Heat Sink

2011 ◽  
Author(s):  
Ravi S. Patel ◽  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Microchannel Heat Sink ◽  
Vapor Quality

Experiments were conducted to determine the influence of local vapor quality on local heat transfer coefficient in flow boiling in an array of microchannels. Additionally, the variation of local heat transfer coefficient along the length and width of the microchannel heat sink for given operating conditions was investigated over a range of flow parameters. Each test piece includes a silicon parallel microchannel heat sink with 25 integrated heaters and 25 temperature sensors arranged in a 5×5 grid, allowing for uniform heat dissipation and local temperature measurements. Channel dimensions ranged from 100 μm to 400 μm in depth and 100 μm to 5850 μm in width; the working fluid for all cases was the perfluorinated dielectric liquid, FC-77. The heat transfer coefficient is found to increase with increasing vapor quality, reach a peak, and then decrease rapidly due to partial dryout on the channel walls. The vapor quality at which the peak is observed shows a strong dependence on mass flux, occurring at lower vapor qualities with increasing mass flux for fixed channel dimensions. Variations in local heat transfer coefficient across the test piece were examined both along the flow direction and in a direction transverse to it; observed trends included variations due to entrance region effects, two-phase transition, non-uniform flow distribution, and channel wall dryout.

Thermo-Fluidic Characteristics in a Cross-Linked Silicon Microchannel Heat Sink

2007 ◽  
Author(s):  
R. Muwanga ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cross Sections ◽  
Heat Sink ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Significant Difference ◽  
The Cross

This paper presents the flow and heat transfer characteristics in a cross-linked silicon microchannel heat sink. The heat sink is composed of 45 channels, 270 μm wide × 285 μm tall in a silicon substrate formed via deep reactive ion etching. A detailed discussion of the pressure drop data reduction is described, including characterization of the channel cross-sections and methods to account for inlet and exit loss coefficients. No significant difference is observed in the pressure drop measurements between the cross-linked and standard heat sinks flowing air and water. The use of un-encapsulated liquid crystal thermography was successfully utilized to obtain local heat transfer data with FC-72 as the working fluid. The heat transfer results show inflections in the thermal profile due to the cross-links.

scholarly journals Analysis of laminar flow and heat transfer in an interrupted microchannel heat sink with different shaped ribs

2019 ◽  
Vol 140 (3) ◽  
pp. 1259-1266 ◽  
Author(s):  
Wei Wang ◽  
Yongji Li ◽  
Yaning Zhang ◽  
Bingxi Li ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Heat Sink ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Windward Side ◽  
Microchannel Heat Sink ◽  
Flow And Heat Transfer ◽  
Friction Performance

AbstractA numerical study was conducted to investigate the mechanism of laminar flow and heat transfer enhancement in an interrupted microchannel heat sink (IMCHS) with different shaped ribs at Reynolds number ranging from 100 to 900. The global flow features, heat transfer and friction for IMCHS with no ribs, rectangle ribs, triangle ribs and trapezoid ribs are detailed compared. The results show that the local heat transfer and friction performance of IMCHS with ribs show significant increase at the windward side of the ribs. Additionally, the smaller the chamfer of ribs, the larger average heat transfer and friction performance. For IMCHS with rectangle ribs, the maximum increment of Nu and f can reach to 1.81 and 2.59, respectively. Concerning the overall heat transfer performance (PEC), the trapezoid ribs show the best behavior with PEC = 1.65–1.38 at Re = 100–900.

Enhanced Microchannel Heat Sinks Using Oblique Fins

2009 ◽  
Author(s):  
Yong-Jiun Lee ◽  
Poh-Seng Lee ◽  
Siaw-Kiang Chou
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Heat Sinks ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Oblique fins created in a microchannel heat sink can serve to modulate the flow, resulting in local and global heat transfer enhancement. Numerical analysis of laminar flow and heat transfer in such modified microchannel heat sink showed that significant enhancement of heat transfer can be achieved with negligible pressure drop penalty. The breakage of continuous fin into oblique sections causes the thermal boundary layers to be re-initialized at the leading edge of each oblique fin and reduces the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of the smaller oblique channels causes a fraction of the flow to branch into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. The combination of the entrance and secondary flow effect results in a much improved heat transfer performance (the average and local heat transfer coefficients are enhanced by as much as 80%). Both the maximum wall temperature and temperature gradient are substantially decreased as a result.

Hot Spot Mitigating With Oblique Finned Microchannel Heat Sink

2010 ◽  
Author(s):  
Yong-Jiun Lee ◽  
Poh-Seng Lee ◽  
Siaw-Kiang Chou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Sink ◽  
Hot Spot ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Secondary Flows ◽  
High Heat Flux ◽  
Microchannel Heat Sink

Sectional oblique fins are employed in contrast to continuous fins in order to modulate the flow in microchannel heat sink. The breakage of continuous fin into oblique sections leads to re-initialization of boundary layers and generation of secondary flows which significantly enhance the cooling performance of the heat sink. In addition, oblique finned microchannel heat sink has the flexibility to tailor local heat transfer performance by varying its oblique fin pitch. Clusters of oblique fins at higher density can be created in order to promote greater degree of boundary layers redevelopment and secondary flows generation to provide more effective cooling at the high heat flux region. Thus the varying of oblique fin pitch can be exploited for hot spots mitigation. Simulation studies of silicon chip with hot spot shows more than 100% increment in local heat transfer coefficient at the high heat flux region for the variable pitch oblique finned microchannel compared with the conventional microchannel heat sink. Both the maximum temperature and its temperature gradient are reduced by 12.4°C as a result. Interestingly, there is only little or negligible pressure drop penalty associated with this novel heat transfer enhancement scheme in contrast to conventional enhancement techniques.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

Flow Boiling Heat Transfer on Micro Pin Fins Entrenched in a Microchannel

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Axial Distance ◽  
Mass Fluxes ◽  
Pin Fins

Flow boiling of 1-methoxyheptafluoropropane (HFE 7000) in 222 μm hydraulic diameter channels containing a single row of 24 inline 100 μm pin fins was studied for mass fluxes from 350 kg/m2 s to 827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2. Flow visualization revealed the existence of isolated bubbles, bubbles interacting, multiple flow, and annular flow. The observed flow patterns were mapped as a function of the boiling number and the normalized axial distance. The local heat transfer coefficient during subcooled boiling was measured and found to be considerably higher than the corresponding single-phase flow. Furthermore, a thermal performance evaluation comparison with a plain microchannel revealed that the presence of pin fins considerably enhanced the heat transfer coefficient.

Local Heat Transfer Coefficient of Flow Boiling in Microchannels With Artificial Reentrant Cavities

2007 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bubble Generation ◽  
Parallel Microchannels

Flow boiling in parallel microchannels with structured reentrant cavities was experimental studied. Flow patterns, boiling inceptions and heat transfer coefficients were obtained and studied for G = 83 kg/m2-s to G = 303 kg/m2-s and heat fluxes up to 643 W/cm2. The heat transfer coefficient-mass velocity and quality relations had been analyzed to identify boiling mechanism. Comparisons of the performance of the enhanced and plain-wall microchannels had also been made. The microchannels with reentrant cavities were shown to promote nucleation of bubbles and to support significantly better reproducibility and uniformity of bubble generation.

Experimental Study on Flow Boiling of HFC134a in a Multi-Port Extruded Tube

2004 ◽  
Author(s):  
Ken Kuwahara ◽  
Shigeru Koyama ◽  
Kengo Kazari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Rectangular Channel ◽  
Large Diameter ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Inlet Temperature

In the present study, the local heat transfer and pressure drop characteristics are investigated experimentally for the flow boiling of refrigerant HFC134a in a multi-port extruded tube of 1.06mm in hydraulic diameter. The test tube is 865mm in total length made of aluminum. The pressure drop is measured at an interval of 191 mm, and the local heat transfer coefficient is measured in every subsection of 75mm in effective heating length. Experimental ranges are as follows: the mass velocity of G = 100–700 kg/m2s, the inlet temperature of Tin = 5.9–11.4 °C and inlet pressure of about 0.5 MPa. The data of pressure drop are compared with a few previous correlations for small diameter tubes, and the correlations can predict the data relatively good agreement. The data of heat transfer coefficient is compared with the correlations of Yu et al. proposed for relatively large diameter tubes. It is found that there are some differences about two phase multiplier factor of convective heat transfer between the circular channel and rectangular channel.

Numerical Investigation of Flow Boiling in a Manifold Microchannel Heat Sink With Conjugate Heat Transfer

2019 ◽  
Author(s):  
Zhichuan Sun ◽  
Yang Luo ◽  
Junye Li ◽  
Wei Li ◽  
Jingzhi Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Heat Sink ◽  
Conjugate Heat Transfer ◽  
Flow Boiling ◽  
High Heat Flux ◽  
Microchannel Heat Sink ◽  
Two Phase ◽  
Boiling Process ◽  
Manifold Microchannel

Abstract The manifold microchannel heat sink receives an increasing number of attention lately due to its high heat flux dissipation. Numerical investigation of boiling phenomena in manifold microchannel (MMC) heat sinks remains a challenge due to the complexity of fluid route and the limitation of numerical accuracy. In this study, a computational fluid dynamics (CFD) approach including subcooled two-phase flow boiling process and conjugate heat transfer effect is performed using a MMC unit cell model. Different from steady-state single phase prediction in MMC heat sink, this type of modeling allows for the transient simulation for two-phase interface evolution during the boiling process. A validation case is conducted to validate the heat transfer phenomenon among three phases. Besides, this model is used for the assessment of the manifold dimensions in terms of inlet and outlet widths at the mass flux of 1300 kg/m2·s. With different ratios of inlet-to-outlet area, the thermal resistances remain nearly stable.

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