In the present study, fluid flow and heat transfer in microchannel heat sinks with different inlet/outlet locations (I, C and Z-type), header shapes (triangular, trapezoidal and rectangular) and ...microchannel cross-section shapes (the conventional rectangular microchannel, the microchannel with offset fan-shaped reentrant cavities and the microchannel with triangular reentrant cavities) are numerically studied with computational domain including the entire microchannel heat sink. Detailed three-dimensional numerical simulations are useful in identifying the optimal geometric parameters that provide better heat transfer and flow distribution in a microchannel heat sink. Results highlight that flow velocity uniformity is comparatively better for I-type and poor for Z-type. The flow distribution is found to be symmetrical for I-type. It is seen from the header shapes analysis that the rectangular header shapes provides better flow velocity uniformity than the trapezoidal and triangular headers. The fluid flow mechanism can be attributed to the interaction of the branching of fluid and the friction offered by the walls of the header. Effects of microchannel cross-section shapes emphasize that the microchannel with offset fan-shaped reentrant cavities and the microchannel with triangular reentrant cavities of the heat sinks enhance the heat transfer compared to the conventional rectangular microchannel. The heat transfer mechanism can be attributed to the jetting and throttling effect, the additional flow disturbance near the wall of the reentrant cavities and the form drag of the reentrant cavities. The heat sink C has better heat transfer characteristic for qv=150ml/min and is able to prolong the life of the microelectronic devices.
•The location of throat influences the thermohydraulic performance of microchannel.•The performance of MCHS depends on the convergent and divergent angle of the convergent divergent microchannel.•The ...sudden convergence and expansion of the microchannel cross-section enhances the heat transfer performance and recovers the pressure respectively.•Both the heat transfer performance and pressure drop of the channel increases with increase in the number of sudden contraction and expansion of the channel.
Microchannel heat sink (MCHS) is used as an efficient method of thermal management in a miniaturized, high performance electronic devices. However, high pumping power and uneven distribution of temperature are two major limitations of such MCHS. In this work, efforts are made to optimize these limitations through modification of channel geometry. Three sequential computational analyses have been performed for a MCHS. In the first analysis, the channel cross-section reduces to a minimum one (at the throat) and then increases. For five different throat positions are considered for this analysis. None of the channel configuration achieves the overall performance more than 1. Next, sudden contraction and expansion are introduced in the channel passage. Three different cross-sections are used. The sudden expansion recovers the pressure gradually, whereas, at sudden contraction, the pressure drops instantaneously. The overall performance index (OPI) improves when two channel sections with larger cross-sectional area is connected by a channel with smaller cross-section. The OPI of such configuration is found to be greater than 1. Finally, multiple sudden expansion and sudden contraction are introduced sequentially in the channel cross-section. It is observed that the heat transfer performance and pressure drop both increases with increase in number of expansion and contraction.
Electroosmotic flow (EOF) in a fractal tree‐like microfluidic network has wide applications. To reduce the fluid resistance of EOF in the network, this paper numerically studies the influences of the ...branch convergence α, the level convergence κ, the length ratio λ, the branching number N, the maximum branching level M, and the channel height H of a fractal tree‐like convergent microchannel network (FTCMCN) on the EOF flowrate and analyzes the optimal structure of FTCMCN to maximize the EOF transport efficiency. The present paper finds the optimal structure of FTCMCN and its dependence on the various geometric and structural parameters. This work is beneficial to the optimization design of the FTCMCN to achieve the highest EOF transport efficiency.
To enhance the transport efficiency of electroosmotic flow (EOF) within a fractal tree‐like convergent microchannel network (FTCMCN), this paper investigates the influences of the geometric and structural parameters of the FTCMCN on the EOF flowrate. The optimal cross‐section dimensions of the FTCMCN to reach the maximum EOF flowrate under the fixed voltage difference are studied.
In this work, a comparative analysis of innovative microchannel heat sinks such as two-layered and multi-layered microchannel heat sinks (MCHS), or thin films within flexible complex seals and ...cooling augmentation using microchannels with rotatable separating plates, is presented. A compilation of the numbers of layers, main characteristics, setups, advantages and disadvantages, thermal resistance, pumping power in double-layer (DL-MCHS) and multi-layer MCHS (ML-MCHS) is presented. In addition, the thermal resistance is analyzed in order to present a comparison between the single-layer MCHS (SL-MCHS) and multi-layer microchannels. The results of comparison indicates that double-layer and multi-layer MCHS have lower thermal resistance and require smaller pumping power and they resolve the high streamwise temperature rise problem of SL-MCHS.
•Open-ring pin fin microchannels (ORPFM) were developed for advanced microchannel heat sinks.•Both inline and staggered ORPFM presented a small wall superheat for ONB.•Inline ORPFM augmented boiling ...heat transfer, reduced pressure drop compared to staggered ones.•Inline ORPFM mitigated two-phase flow instabilities compared to staggered ones.
A type of open-ring pin fin microchannels (ORPFM) was proposed and developed for advanced microchannel heat sinks. They consist of an internal cavity for bubble nucleation and two inner small and outside large rings with separated and converged flow passages. Two arrangements of open-ring pin fins, inline and staggered ones, were prepared and compared for optimization. Flow boiling experiments were performed to assess the two-phase boiling performance of both inline and staggered ORPFM. Tests were conducted using subcooled deionized water with an inlet subcooling of 10°C and mass fluxes of 200 kg/m2·s and 300 kg/m2·s. Two-phase boiling heat transfer performance, pressure drop and two-phase flow instabilities of the ORPFM were systematically explored. Experimental results indicated that both inline and staggered ORPFM samples presented a small wall superheat of 1-2°C for onset of nucleate boiling (ONB). Nucleate boiling, both nucleate boiling and thin film evaporation, and convective boiling in turn dominated with increasing heat flux and vapor quality for ORPFM. The inline ORPFM generally presented a 10% to 80% augmentation in boiling heat transfer at moderate and high heat fluxes, a 2%-20% smaller pressure drop, and more stable flow boiling process with a mitigation of two-phase flow instabilities than the staggered one. Therefore, the inline ORPFM seemed to be more favorable for high heat flux dissipation of advanced microchannel heat sinks.
Microchannel Plate Nakazato, Masaki; Hirata, Takafumi
Journal of the Mass Spectrometry Society of Japan,
2021/12/01, Volume:
69, Issue:
6
Journal Article
An improved design of wavy microchannel heat sink with changing wavelength or/and amplitude along the flow direction is proposed. The thermal resistance R and the maximum bottom wall temperature ...difference ΔTb,max for the new design are compared with those for the straight and the original wavy design under a constant pumping power. The results show that the new design performance is enhanced significantly with lower R and smaller ΔTb,max when the wavelength of wavy units decreases or the amplitude increases. The enhancement becomes more remarkably when the absolute value of the wavelength difference Δλ or amplitude difference ΔA between two adjacent wavy units increases. The performance can be further improved by simultaneously increasing the absolute values of Δλ and ΔA. Moreover, as compared with the straight and the original wavy microchannel heat sink, the reductions in R and ΔTb,max for the new design is found more significant for the heat sink with a smaller channel aspect ratio. The heat transfer enhancement is attributed to the formation of vortices in the channel cross sections caused by the curved walls, which promotes the coolant mixing and enhances the convective heat transfer between coolant and channel walls.
•A new design of wavy-channel microchannel heat sink is proposed.•The performance of the new design is improved greatly than the original design.•The mechanisms of performance improvement are revealed.
•Simultaneous thermal and hydraulic improvement of double layer MCHS is shown.•Figure of merit is used to consider heat transfer and pressure drop simultaneously.•Optimum designs are revealed at ...different porosities, flow rates, and materials.
Effect of utilizing porous substrates on thermal and hydraulic performance of double-layered microchannel heat sinks (MCHSs) is comprehensively analyzed in this work. Thermal resistance and pumping power of the porous double layer MCHSs are evaluated to find optimized designs which improve heat transfer while requiring lower pumping power compared to conventional MCHSs. Conjugate heat transfer is numerically simulated by developing three dimensional models of porous MCHSs with different solid and porous fin thicknesses at the top and bottom channels. For design optimization, various performance parameters are evaluated and compared to conventional microchannels by changing the porous substrate and solid fin thickness. The results show that for every combination set of geometrical parameters in double-layered MCHS, an optimized porous double-layered MCHS can be found which can enhance thermal and hydraulic performance. Studying the heat transfer effectiveness and pumping power effectiveness of the new porous double-layered MCHSs simultaneously indicate this. The enhancement is shown in all scenarios where the top and bottom channel can have different solid-porous thickness. The superior performance of porous double-layered microchannels is verified for different range of Reynolds number, porosity of substrates, and heat sink material.
•An extensive overview of heat transfer augmentation through various techniques using microchannel heat sink (MCHS).•This review (with more than 300 references) covers the recent developments in the ...area of different cooling technologies in general and MCHS in particular.•The focus has been paid to the research articles since 2010 because of the enormous volume of papers published in this area in the last 10 years.•Extensive studies have been conducted on channels that inherently provide boundary layer interruption, secondary flows, and chaotic advection that promote heat transfer without modest change in pumping power.•Special emphasis has been given to the fractal shaped MCHS due to its inherent property of reducing temperature non-uniformity with an insignificant drop in pressure.
This paper provides an extensive overview of heat transfer augmentation through various techniques using microchannel heat sink (MCHS). Continuous miniaturization of electronic devices due to multifunction, high heat flux over the unit area, and lower package volume has compelled researchers to find advanced and sophisticated heat removal technologies. This review paper (with more than 300 references) covers the recent developments in the area of different cooling technologies in general and MCHS in particular. The focus has been paid to the research articles since 2010 because of the enormous volume of papers published in this area in the last 10 years. Following a brief introduction to the rise of micro-scale devices, as well as conventional cooling technologies and applications, the review first classifies flow channels, as well as the various microchannel fabrication techniques used over the years. The next section provides different methods adopted for heat transfer enhancement that are broadly categorized under active and passive techniques, with the focus on passive devices. The final section provides heat transfer enhancement in MCHS by geometrical modifications. When flow inside a straight channel becomes regular and the boundary layer grows, heat transfer performance deteriorates. So, extensive studies have been conducted on channels that inherently provide boundary layer interruption, secondary flows, and chaotic advection that promote heat transfer without modest change in pumping power. Special emphasis has been given to the fractal shaped MCHS due to its inherent property of reducing temperature non-uniformity with an insignificant drop in pressure. Additionally, comments and perspectives to highlight the notable contributions are presented.
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