Two-Phase Heat Sinks With Microporous Coating

2011 ◽  
Author(s):  
Tadej Semenic ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Porous Coating ◽  
Two Phase ◽  
Small Channel ◽  
Rectangular Channels ◽  
Microporous Coating ◽  
Channel Aspect Ratio

To minimize flow boiling instabilities in two-phase heat sinks, two different types of microporous coatings were developed and applied on mini- and small-channel heat sinks and tested using degassed R245fa refrigerant. The first coating was epoxy-based and was sprayed on heat sink channels while the second coating was formed by sintering copper particles on heat sink channels. Mini-channel heat sinks had overall dimensions 25.4 mm × 25.4 mm × 6.4 mm and twelve rectangular channels with a hydraulic diameter 1.7 mm and a channel aspect ratio of 2.7. Small-channel heat sinks had the same overall dimensions, but only three rectangular channels with hydraulic diameter 4.1 mm and channel aspect ratio 0.6. The microporous coatings were found to minimize parallel channel instabilities for mini-channel heat sinks and to reduce the amplitude of heat sink base temperature oscillations from 6 °C to slightly more than 1 °C. No increase in pressure drop or pumping power due to the microporous coating was measured. The mini-channel heat sinks with porous coating had in average 1.5-times higher heat transfer coefficient than uncoated heat sinks. Also, the small-channel heat sinks with the “best” porous coating had in average 2.5-times higher heat transfer coefficient and the critical heat flux was 1.5 to 2-times higher compared with the uncoated heat sinks.

Optimization Under Uncertainty of Manifold Microchannel Heat Sinks

2012 ◽  
Author(s):  
Suchismita Sarangi ◽  
Karthik K. Bodla ◽  
Suresh V. Garimella ◽  
Jayathi Y. Murthy
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Optimization Under Uncertainty ◽  
Microchannel Heat Sink ◽  
Probabilistic Optimization ◽  
Manifold Microchannel

Conventional microchannel heat sinks provide good heat dissipation capability but are associated with high pressure drop and corresponding pumping power. The use of a manifold system that distributes the flow into the microchannels through multiple, alternating inlet and outlet pairs is investigated here. This manifold arrangement greatly reduces the pressure drop incurred due to the smaller flow paths, while simultaneously increasing the heat transfer coefficient by tripping the thermal boundary layers. A three-dimensional numerical model is developed and validated, to study the effect of various geometric parameters on the performance of the manifold microchannel heat sink. Apart from a deterministic analysis, a probabilistic optimization study is also performed. In the presence of uncertainties in the geometric and operating parameters of the system, this probabilistic optimization approach yields an optimal design that is also robust and reliable. Uncertainty-based optimization also yields auxiliary information regarding local and global sensitivities and helps identify the input parameters to which outputs are most sensitive. This information can be used to design improved experiments targeted at the most sensitive inputs. Optimization under uncertainty also provides a quantitative estimate of the allowable uncertainty in input parameters for an acceptable uncertainty in the relevant output parameters. The optimal geometric design parameters with uncertainties that maximize heat transfer coefficient while minimizing pressure drop for fixed input conditions are identified for a manifold microchannel heat sink. A comparison between the deterministic and probabilistic optimization results is also presented.

Prediction of the Heat Transfer Coefficient in a Small Channel with the Superposition and Asymptotic Correlations

2018 ◽  
Vol 26 (01) ◽  
pp. 1850001
Author(s):  
Yushazaziah Mohd-Yunos ◽  
Normah Mohd-Ghazali ◽  
Maziah Mohamad ◽  
Agus Sunjarianto Pamitran ◽  
Jong-Taek Oh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Experimental Work ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Two Phase ◽  
Forced Convective Heat Transfer ◽  
Small Channel ◽  
The Heat Transfer Coefficient

Heat transfer coefficient as an important characteristic in heat exchanger design is determined by the correlation developed from previous experimental work or accumulation of published data. Although discrepancies still exist between the existing correlations and practical data, several researchers claimed theirs as a generalized heat transfer correlation. Through optimization method, this study predicts the heat transfer coefficient of two-phase flow of propane in a small channel at the saturation temperature of 10[Formula: see text]C using two categories of correlation — superposition and asymptotic. Both methods consist of the contribution of nucleate boiling and forced convective heat transfer, the mechanisms that contribute to the total two-phase heat transfer coefficient, which become as two objective functions to be maximized. The optimization of experimental parameters of heat flux, mass flux, channel diameter and vapor quality is done by using genetic algorithm within a range of 5–20[Formula: see text]kW/m2, 100–250[Formula: see text]kg/m2[Formula: see text]s, 1.5–3[Formula: see text]mm and 0.009–0.99, respectively. In the result, the selected correlations under optimized condition agreed on the dominant mechanism at low and high vapor qualities are caused by the nucleate boiling and forced convective heat transfer, respectively. The optimization work served as an alternative approach in identifying optimized parameters from different correlations to achieve high heat transfer coefficient by giving a fast prediction of parameter range, particularly for the investigation of any new refrigerant. In parallel with some experimental works, a quick prediction is possible to reduce time and cost. From the four selected generalized correlations, Bertsch et al. show the closer trend with the reference experimental work until vapor quality of 0.6.

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.

Forced Convection Computational Fluid Dynamics Analysis of Architected and Three-Dimensional Printable Heat Sinks Based on Triply Periodic Minimal Surfaces

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Oraib Al-Ketan ◽  
Mohamed Ali ◽  
Mohamad Khalil ◽  
Reza Rowshan ◽  
Kamran A. Khan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Transfer Coefficient ◽  
Minimal Surfaces ◽  
Heat Sink ◽  
Three Dimensional ◽  
Heat Sinks ◽  
Triply Periodic Minimal Surfaces ◽  
Triply Periodic

Abstract The drive for small and compact electronic components with higher processing capabilities is limited by their ability to dissipate the associated heat generated during operations, and hence, more advanced heat sink designs are required. Recently, the emergence of additive manufacturing techniques facilitated the fabrication of complex structures and overcame the limitation of traditional techniques such as milling, drilling, and casting. Therefore, complex heat sink designs are now easily realizable. In this study, we propose a design procedure for mathematically realizable architected heat sinks and investigate their performance using the computational fluid dynamics (CFD) approach. The proposed heat sinks are mathematically designed with topologies based on triply periodic minimal surfaces (TPMSs). Three-dimensional CFD models are developed using the starccm+ platform for uniform heat sinks and topologically graded heat sinks to study the heat transfer performance in forced convection domains. The overall heat transfer coefficient, surface temperature, and pressure drop versus the input heat sources as well as the Reynolds number are used to evaluate the heat sink performance. Moreover, temperature contours and velocity streamlines were examined to analyze the fluid flow behavior within the heat sinks. Results showed that the tortuosity and channel complexity of the Diamond solid-networks heat sink result in a 32% increase in convective heat transfer coefficient compared with the Gyroid solid-network heat sink which has the comparable surface area under the examined flow conditions. This increase is at the expense of increased pressure drops which increases by the same percentage. In addition, it was found that expanding channel size along flow direction using the porosity grading approach results in significant pressure drop (27.6%), while the corresponding drop in convective heat transfer is less significant (15.7%). These results show the importance of employing functional grading in the design of heat sinks. Also, the manufacturability of the proposed designs was assessed using computerized tomography (CT) scan and scanning electron microscopy (SEM) imaging performed on metallic samples fabricated using powder bed fusion techniques. A visible number of internal manufacturing defects can affect the performance of the proposed heat sinks.

Two-Dimensional Flow Boiling Characteristics with Wettability Surface in Microgap Heat Sink and Heat Transfer Prediction Using Artificial Neural Network

2021 ◽  
Author(s):  
Anwarul Karim ◽  
Yoon Jo Kim ◽  
Jong-Hoon Kim
Keyword(s):  
Neural Network ◽  
Heat Transfer ◽  
Artificial Neural Network ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Two Dimensional ◽  
Two Phase ◽  
Hydrophilic Surfaces

Abstract As technology becomes increasingly miniaturized, thermal management becomes challenging to keep devices away from overheating due to extremely localized heat dissipation. Two-phase cooling or flow-boiling in micro-spaces utilizes the highly efficient thermal energy transport of phase change from liquid to vapor. However, the excessive consumption of liquid-phase by highly localized heat source causes the two-phase flow maldistribution, leading to a significantly reduced heat transfer coefficient, high-pressure loss, and limited flow rate. In this study, flow-boiling in a two-dimensional microgap heat sink with a hydrophilic coating is investigated with bubble morphology, heat transfer, and pressure drop for conventional (non-hydrophilic) and hydrophilic heat sinks. The experiments are carried out on a stainless steel plate, having a micro gap depth of 170 µm using deionized water at room temperature. Two different hydrophilic surfaces (partial and full channel shape) are fabricated on the heated surface to compare the thermal performance with the conventional surface. Vapor films and slugs are flushed quickly on the hydrophilic surfaces, resulting in heat transfer enhancement on the hydrophilic heat sink compared to the conventional heat sink. The channel hydrophilic heat sink shows better cooling performance and pressure stability as it provides a smooth route for the incoming water to cool the hot spot. Moreover, the artificial neural network prediction of heat transfer coefficient shows a good agreement with the experimental results as data fits within ±5% average error.

scholarly journals Heat Transfer Enhancement of Plate-Fin Heat Sinks with Different Types of Winglet Vortex Generators

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5219
Author(s):  
Jin-Cherng Shyu ◽  
Jhao-Siang Jheng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Vortex Generators ◽  
Airflow Velocity ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

Because the delta winglet in common-flow-down configuration has been recognized as an excellent type of vortex generators (VGs), this study aims to experimentally and numerically investigate the thermo-hydraulic performance of four different forms of winglet VGs featuring sweptback delta winglets in the channel flow in the range 200 < Re < 1000. Both Nusselt number and friction factor of plate-fin heat sinks having different forms of winglets, including delta winglet pair (DWP), rectangular winglet pair (RWP), swept delta winglet pair (SDWP), and swept trapezoid winglet pair (STWP), were measured in a standard wind tunnel without bypass in this study. Four rows of winglets with in-line arrangement were punched on each 10-mm-long, 0.2-mm-thick copper plate, and a total of 16 pieces of copper plates with spacing of 2 mm were fastened together to achieve the heat sink. The projected area, longitudinal and winglet tip spacing, height and angle of attack of those winglets were fixed. Besides that, three-dimensional numerical simulation was also performed in order to investigate the temperature and fluid flow over the plate-fin. The results showed that the longitudinal, common-flow-down vortices generated by the VGs augmented the heat transfer and pressure drop of the heat sink. At airflow velocity of 5 m/s, the heat transfer coefficient and pressure drop of plain plate-fin heat sink were 50.8 W/m2·K and 18 Pa, respectively, while the heat transfer coefficient and the pressure drop of heat sink having SDWP were 70.4 W/m2·K and 36 Pa, respectively. It was found that SDWP produced the highest thermal enhancement factor (TEF) of 1.28 at Re = 1000, followed by both RWP and STWP of similar TEF in the range 200 < Re < 1000. The TEF of DWP was the lowest and it was rapidly increased with the increase of airflow velocity.

Cooling Performances of Perforated-Finned Heat Sinks

2016 ◽  
Author(s):  
Mohammad Reza Shaeri ◽  
Bradley Richard ◽  
Richard Bonner
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Cooling System ◽  
Thermal Characteristics ◽  
Heat Sinks ◽  
Pumping Power ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Cooling performances of perforated-finned heat sinks (PFHS) are investigated in the laminar forced convection heat transfer mode, through detailed experiments. Perforations like windows with square cross sections are placed on the lateral surfaces of the fins. Cooling performances are evaluated due to changes in both porosities and perforation sizes. Thermal characteristics are reported based on pumping power, in order to provide more practical insight about performances of PFHSs in real applications. It is found that at a constant perforation size, there is an optimum porosity that results in the largest heat transfer coefficient. For a fixed porosity, increasing the number of perforations (reducing the perforation size) results in an enhancement of heat transfer rate due to repeated interruption of the thermal boundary layer. The opposite trend is observed for PFHSs with larger perforation sizes. This indicates that there is an optimum perforation size and distance between perforations in order to achieve the maximum heat transfer coefficients at a constant porosity. Also, a PFHS results in a smaller temperature non-uniformity across the heat sink base, as well as a more rapid reduction in temperature non-uniformity on the heat sink base by increasing pumping power. In addition, the advantage of a PFHS to reduce the overall weight of the cooling system is incorporated into thermal characteristics of the heat sinks, and demonstrated by the mass specific heat transfer coefficient.

scholarly journals Analysis of the Two-Phase Heat Transfer Coefficient of Propane in a Small Channel

2017 ◽  
Vol 105 ◽  
pp. 4635-4640
Author(s):  
Yushazaziah Mohd Yunos ◽  
Normah Mohd Ghazali ◽  
A.S. Pamitran ◽  
S. Novianto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase ◽  
Small Channel ◽  
Two Phase Heat Transfer

Heat-Transfer Characteristics and Design Optimization for a Small-Sized Plate-Fin Heat Sink Array

2007 ◽  
Vol 129 (4) ◽  
pp. 518-521 ◽  
Author(s):  
Gaowei Xu ◽  
Yingjun Cheng ◽  
Le Luo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Sink ◽  
Convective Heat Transfer Coefficient ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Fin Thickness

The heat-transfer characteristics of 128 small-sized plate-fin heat sinks in a supercomputer chassis are investigated with CFD simulation. The V-shaped curves of the chip temperature versus fin pitch and fin thickness are derived and a thermal resistance model is built to explore the profile and obtain the convective heat-transfer coefficient of the heat sinks. It turns out that the V-shaped profile arises from the joint action of the thermal conduction and convection of heat sink, which can be attributed to the intricacy of the dependencies of thermal resistances on either fin pitch or thickness. It can be further concluded that Biot criterion is applicable to estimate the Biot number of large-scale plate-fin heat sink but not applicable for the small-sized one. The convective heat-transfer coefficient is a complicated function of fin pitch and fin thickness. The empirical formulas of heat transfer are obtained and the fin pitch and fin thickness are optimized.

Flow Boiling in a Heat Sink Embedded With Hexagonally Linked Minichannels

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Shubhankar Chakraborty ◽  
Omprakash Sahu ◽  
Prasanta Kr. Das
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Vapor Quality ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
The Heat Transfer Coefficient

The thermal hydraulic performance of a miniature heat sink during flow boiling of distilled water is presented in this article. The unique design of the heat sink contains a number of microchannels of 1 mm × 1 mm cross section arranged in a regular hexagonal array. The design facilitates repeated division and joining of individual streams from different microchannels and thereby can enhance heat transfer. Individual slug bubble experiences a typical route of break up, coalescence, and growth. The randomness of these processes enhances the transport of heat. With the increase of vapor quality the heat transfer coefficient increases, reaches the maximum value, and then drops. The maximum heat transfer coefficient occurs at an exit vapor quality much higher than that observed in conventional parallel microchannel heat sinks. Repeated redistribution of the coolant in the interlinked channels and the restricted growth of the slug bubbles may be responsible for this trend.

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