Double-layered Microchannel Heat Sink Research Articles

Performance Enhancement of Double-Layer Microchannel Heat Sink by Employing Dimples and Protrusions on Channel Sidewalls

High-temperature gradient causes thermal stress and is indirectly responsible for other demerits in nonstacked microchannels. High-temperature gradient is overcome by employing double layers in the heat sink. Utilization of dimple and protrusion in such double-layered sink to enhance overall performance is done in the present numerical study. Before placement of dimples and protrusions on sidewalls of the sink, optimum width and depth of channel have been assessed. Microsinks with the protruded-dimpled bottom layer and microsinks with protruded-dimpled layers are investigated. The parameters such as maximum bottom wall temperature difference (ΔTb), Nusselt number ratio (Nu/Nuo), and thermal performance factor (η) have been evaluated. The impact of aligned and staggered arrangements of dimple and protrusion is also compared. Deionized water as a coolant for the range of Reynolds number of 89–924 is examined. It has been realized that aligned models offer higher heat transfer coefficient, maximum Nu, and minimum ΔTb, but in terms of overall performance, staggered sinks are superior. The heat sink with both layers protruded and dimpled, showing Nu/Nuo and η of 1.36 and 1.32, respectively, is observed as one of the optimum sinks which offers an excellent lowest ΔTb of 1.48 K.

Investigation of double-layered wavy microchannel heatsinks utilizing porous ribs with artificial neural networks

Microchannel heatsinks with porous media, wavy and multi-layered configurations introduce compact designs and high efficiencies in cooling applications. Current Computational Fluid Dynamics (CFD) based study bridges the concept by introducing a novel double layered microchannel heatsink with wavy up-down and porous ribs alongside each other. Since Artificial Neural Network (ANN) trained by CFD results reveals designs with better thermal and hydraulic performance with an insignificant computational time, ANN is employed for finding the best performers and effects of waviness on Nusselt number, pressure drop, and maximum temperature difference at the bottom of the microchannel for a Reynold number range of 100 < Re < 800 by defining a thermal efficiency factor. Even though the pressure drop increases in the wavy design, the thermal performance is affected positively. Nusselt number increases more than 55% for Re = 800. The thermal performance increases with the introduction of Dean vortices, especially at higher Re. The best design provides maximum bottom temperature difference of 1.2 °C, with a Thermal Efficiency Factor of 1.34. However, it is observed that better thermal efficiency factors are attained by using a wavy channel at the top layer and keeping the bottom layer straight for the final design.

Heat transfer characteristics of two-phase flow in a double-layer microchannel heat sink

Coolant two-phase flow in microchannel heat sinks can provide efficient and attractive solutions for disposing of high heat fluxes generated in electronic components and other similar engineering devices. Moreover, the coolant flow in double-layer microchannels has been proven as an also more effective way than a single layer. This paper introduces some useful results of an experimental study with coolant two-phase flow conditions in double-layer microchannels. The double layers microchannels were fabricated by end milling using a CNC machine. The effects of the applied heat flux up to 82 W/cm2, the mass flux in the range of 200 to 426 kg/m2.s, and the maximum microchannel depth of 550 μm, on the thermal behaviour and associated coolant pressure drop, were investigated. The study handles ‘in integrated approach’ the important topics of the boiling heat transfer characteristics and hydraulic performance. Among these topics, the flow boiling curve and average boiling heat transfer coefficients have received much attention in the present work. Numerical values of this coefficient were predicted using an accurate mathematical model combined with in-house solution code which was developed and reported in this paper. The coolant two-phase flow good square surface temperature uniformity for the double layer microchannels.

Investigation of Double-Layered Wavy Microchannel Heatsinks Utilizing Porous Ribs with Artificial Neural Networks

Investigation of Double-Layered Wavy Microchannel Heatsinks Utilizing Porous Ribs with Artificial Neural Networks

Header Shape Effect on the Inlet Velocity Distribution in Cross-Flow Double-Layered Microchannel Heat Sinks

Counter-flow double-layered microchannel heat sinks are very effective for thermal control of electronic components; however, they require rather complicated headers and flow maldistribution can also play a negative role. The cross-flow configuration allows a much simpler header design and the thermal performance becomes similar to that provided by the counter-flow arrangement if the velocity distribution in the microchannels is not uniform. The aim of this work is to show the possibility of achieving a favorable flow distribution in the microchannels of a cross-flow double-layered heat sink with an adequate header design and the aid of additional elements such as full or partial height baffles made of solid or porous materials. Turbulent RANS numerical simulations of the flow field in headers are carried out with the commercial code ANSYS Fluent. The flow in the microchannel layers is modeled as that in a porous material, whose properties are derived from pressure drop data obtained using an in-house FEM code. It is demonstrated that, with an appropriate baffle selection, inlet headers of cross-flow microchannel heat sinks yield velocity distributions very close to those that would allow optimal hotspot management in electronic devices.

Experimental and numerical examinations of thermofluids characteristics of double-layer microchannel heat sinks with deflectors

This study employs deflectors to enhance the thermal characteristics of double-layer microchannel heat sinks (DMHS) through both numerical simulations and experimental verifications. The deflectors were introduced into the DMHS to improve the performance of the traditional straight DMHS. Three 3D-printed test samples was manufactured for experiments, and it is found that the numerical simulations are in line with the experimental measurements. The temperature control of the substrate temperature by using deflectors is very obvious, and the highest temperature of the substrate is significantly reduced. The peak value of the temperature on substrate is 7 K lower than that of traditional DMHS. The experimental study and numerical simulation both show that the heat transfer enhancement of the deflector structure is very pronounced. Even though the proposed deflector yields higher pressure drop penalty, the performance factor that combines the influence of heat transfer and pressure drop penalty still shows that the proposed DMHS with deflectors outperforms considerably that of traditional DMHS.

Thermal and electrical performances of actively cooled concentrator photovoltaic system

• Reliable thermal management for CPV is mandatory for efficient/safe operation. • 3D heat transfer/thermal model for DL-MCHS coupled with CPV layers are developed. • Including and ignoring the header of DL-MCHS is considered in the simulation work. • Without headers, CPV/T system attained a lower average and local cell temperature. • With headers, electrical efficiency is improved while pumping power is augmented. The double-layer microchannel heat sink (DL-MCHS) is commonly applied for thermal management of high heat flux surfaces, including electronic chips and concentrator photovoltaic (CPV). However, most of the recent studies neglected the header effect in the simulation of the DL-MCHS. The current study compressively investigated the impact of considering the inlet and outlet headers on the CPV systems' performance. A three-dimensional conjugate heat transfer model of the fluid flow in the DL-MCHS coupled with the CPV layers' thermal model was employed. The thermal performances of DL-MCHS with and without considering the headers were evaluated. Parallel flow (PF) and counter flow (CF) conditions at a solar concentration ratio ( CR ) of 20 suns were studied. The results showed that the header section should be considered in the numerical model for obtaining a more realistic average and local silicon layer temperature profile, especially in the CF operation. For instance, the difference in solar cell temperature between including and ignoring the header section is about 13.86 K for CF operation at CR of 20 and 200 ml/hr coolant flowrate. The predicted pumping power and net gained electric power were also significantly affected by neglecting the headers in the numerical modelling. The electrical efficiency deviation reached about 23.5% at CF, while PF reported almost 4.0%.

Performance Improvement of a Double-Layer Microchannel Heat Sink via Novel Fin Geometry—A Numerical Study

This study proposes a novel design having dense fins with lesser thickness at the upper layer and comparatively spare fins with greater thickness in the lower layer to further improve the overall thermal performance of a double-layer microchannel heat sink. The design can effectively direct more low temperature fluid flow toward the lower layer to improve heat transfer while the sparse fin structure at low layer can ease pressure drop penalty. At the same time, the thicker fins at the lower layer ensure higher fin efficiency to facilitate high heat transfer. Parametric and detailed analysis is conducted for the proposed double-layer microchannel heat sink in comparison with the traditional one. After optimization, the thermal resistance of the proposed double-layer microchannel heat sink at the same pumping power is found to be reduced by 9.42% when compared to the traditional double-layer microchannel heat sink. Yet at the same Reynolds number, the Nusselt number of the proposed design exceeds the traditional value by 13%.

Hybrid nanofluids with temperature-dependent properties for use in double-layered microchannel heat sink; hydrothermal investigation

The forced convection heat transfer through a double-layered microchannel heat sink is simulated by the finite volume method. The simulations are conducted under the conditions of constant Reynolds number and constant flow rate. The Al2O3-Cu/water and Al2O3-SiO2/water hybrid nanofluids with temperature-dependent properties and different volumetric concentrations are considered. The cooling capacities of these nanofluids are compared with that for pure water. The results showed that the base surface temperature is decreased by using both nanofluids compared to the base fluid at constant Reynolds numbers. The Al2O3-SiO2/water nanofluid has a better cooling capacity compared to Al2O3-Cu/water nanofluid as the Reynolds number is constant. At a constant flow rate, nanofluids with different volumetric concentrations do not affect the base surface temperature compared to the base fluid. The Al2O3-SiO2/water nanofluid gives lower thermal resistances compared to the Al2O3-Cu/water nanofluid but it has higher pumping power consumption than Al2O3-Cu/water nanofluid. The Al2O3-SiO2/water nanofluid has better Nusselt numbers compared to the pure water and Al2O3-Cu/water nanofluid. In general, increasing the volumetric concentration of both nanofluids reduces the thermal resistance and raises the pumping power consumption.

Concentrator photovoltaic thermal management using a new design of double-layer microchannel heat sink

The concentrator photovoltaic (CPV) systems commonly endure high cell temperatures, which affect their overall performance. Besides, the high cell temperature could lead to physical damages within the whole system due to the induced thermal stresses. Therefore, an efficient cooling is mandatory to achieve a higher net output power from the CPV and safe operation. The current work's main purpose is to investigate the integration of double-layered microchannel heat sink (DL-MCHS) with CPV cell as thermal management device. A three-dimensional (3D) model is presented to investigate the performance of a CPV cooled by the DL-MCHS to figure out the ability to handle the effective heat dissipation under different terrestrial conditions. The parallel flow (PF) and counter flow (CF) cooling orientations were studied. Ethanol coolant is used to cool the CPV under different concentration ratios (CR) of 5, 10, 15, and 20 suns. The results show that the temperatures remarkably decreases with the inlet flowrate is increased. The counter flow operation (CF) achieved the best temperature uniformity index (Tuni) when the coolant mass flowrate (V̇) ranged between 200 and 1200 ml/hr. Especially at CR 5 suns, the temperature uniformity index, Tuni, enhanced to 99.87% at 1200 ml/hr.

Performance evaluation and optimization of flattened microchannel heat sinks for the electronic cooling application

The present study introduces a microchannel heat sink (MCHS) with a new geometry entitled as flattened, which is used to dissipate heat flux form high heat flux generation devices and evaluates its hydrothermal performance. Three-dimensional conjugate heat transfer problem with the assumptions of laminar and steady-state fluid flow has been solved numerically, based on finite volume method. Silicon and pure water with temperature-independent thermophysical properties form the solid part of the heat sink and the coolant, respectively. The performance of three geometric designs of flattened cross-sectional MCHS including a simple single-layer heat sink (Design-A), a heat sink with an adjustable horizontal separation plate (Design-B), and a double-layer MCHS with truncated upper channels (Design-C), is evaluated based on the changes of six effective parameters in the problem including the number of microchannels (N), wall thickness (Ww), thickness of the separation plate (δ), vertical position of the separation plate (H1), velocity ratio (VR), and the length ratio (LR), and under the thermal and hydrodynamic conditions of a uniform heat flux and four different pumping powers. Creating the lowest thermal resistance and the most uniform temperature distribution are the criteria for selecting the optimal designs. The results show that Design-C with the specifications of N = 72, Ww = 56 µm, δ = 25 µm, H1 = 300 µm, VR = 0.7, and LR = 0.7 has the best performance among the all cases by creating the thermal resistance of 0.1333 kW−1, which also indicates a $$7.9\%$$ performance improvement over similar studies.

Thermal Improvement in Double-Layered Microchannel Heat Sink with Incorporating Wavy Porous Fins

A new configuration of microchannel heat sink with a superior heat removal capability is proposed. The proposed geometry consists of double-layered wavy channels with porosity inserted on the top layer. A conjugate heat transfer numerical solver is employed to compare thermal and hydrodynamic properties of the proposed configuration with other possible double-layered wavy and rectangular geometries with/without porous fins. Even though the rectangular configurations represent lower pressure drop, their thermal performance is generally weaker than their wavy counterpart at the same pumping power. Lowest thermal resistance is achieved by utilizing the proposed design compared to other investigated geometries at the same imposed heat flux and pumping powers. The enhancement in overall thermal performance is attributed to the combined effects of secondary flow induced by the channel waviness and penetration of coolant flow in the top-layer porous fins. Moreover, the impacts of wavelength and amplitude on the thermal resistance of the proposed configuration are examined. It is shown that increasing the wavelength leads to a sharp decrease in thermal resistance at lower wavelengths, followed by a slight rise in higher longitudinal periods. Conversely, increment in amplitude causes a monotonous reduction in thermal resistance.

A study on thermal characteristics of double-layered microchannel heat sink: Effects of bifurcation and flow configuration

A comparative study of flow and thermal characteristics has been performed in a double-layered microchannel with bifurcation under parallel and counter-flow layouts using a finite-volume method based open source package OpenFOAM for Re ranging from 50 to 900. The pressure drop, friction factor, flow structures and temperature distribution are compared for both layouts. The effects of bifurcation plate in double-layered microchannel on the overall thermal performance are analyzed and compared with single-layered microchannel with bifurcation reported in the literature. The results show that the overall thermal resistance for the double-layered microchannel with bifurcation is lower compared to that for the non-bifurcated microchannel by approximately 28%. However, the bifurcation plates act as an obstacle in the flow region and hence offer a large pressure drop and increase the pumping power. It is also observed that Nusselt number is increased by 72% for the parallel-flow over the range of Re considered and it is higher than that for the counter-flow for a fixed value of Re. However, difference in Nusselt number is higher in the parallel-flow than that in the counter-flow at low values of Re and this difference diminishes as the flow rate increases. The counter-flow shows a more uniform temperature distribution of the substrate, which is essential for the reliability of any thermal system. Additionally, thermal enhancement factor is obtained for all the cases considered.

Header impact assessment of double-layer microchannel heat sink in the computational fluid mechanics simulation for CPV thermal management

Thermal management is extremely required for concentrator photovoltaic (CPV) to prevent any thermal stress or physical damage. Yet, offering an adequate, reliable, and practical thermal management system for CPV is still challenging. In this work, the double-layer microchannel heat sink (DL-MCHS) is investigated for CPV cooling. To achieve this objective, a three-dimensional (3D) conjugate heat transfer model for the fluid flow in the DL-MCHS coupled with the thermal model for the solar cell, is done. The assessment of considering the inlet and outlet headers in the computational fluid mechanics (CFD) simulations are highlighted. The results reveal that including headers in the numerical study leads to predicting the accurate thermo-hydraulic performance of the DL-MCHS, especially in the CF. However, slight predicted variations have been obtained when PF operated. Moreover, neglecting the header in the CFD calculations significantly affect the calculated pumping power for both PF and CF operated. The potential of this intensive study demonstrates that there is an obvious difference in the CFD simulation figures when the DL-MCHS attached by headers in the CFD calculations.

Quasi-oppositional-based Rao algorithms for multi-objective design optimization of selected heat sinks

Abstract In this paper, an endeavor is made to enhance the convergence speed of the recently proposed Rao algorithms. The new upgraded versions of Rao algorithms named as “quasi-oppositional-based Rao algorithms” are proposed in this paper. The quasi-oppositional-based learning is incorporated in the basic Rao algorithms to diversify the searching process of the algorithms. The performance of the proposed algorithms is tested on 51 unconstrained benchmark functions. Also, three multi-objective optimization case studies of different heat sinks such as a single-layered microchannel heat sink (SL-MCHS), a double-layered microchannel heat sink (DL-MCHS), and a plate-fin heat sink (PFHS) are attempted to investigate the effectiveness of the proposed algorithms in solving real-world complex engineering optimization problems. The results obtained using the proposed algorithms are compared with the results obtained using the well-known advanced optimization algorithms such as genetic algorithm (GA), artificial bee colony (ABC), differential evolution (DE), particle swarm optimization (PSO), teaching-learning-based algorithm (TLBO), Jaya algorithm, multi-objective genetic algorithm (MOGA), non-dominated sorting genetic algorithm (NSGA-II), real-coded GA (RCGA), direction-based GA, self-adaptive multi-population (SAMP) Rao algorithms, and basic Rao algorithms. The proposed quasi-oppositional-based Rao algorithms are found superior or competitive to the other optimization algorithms considered.

Thermal performance and entropy generation of novel X-structured double layered microchannel heat sinks

A novel X-structured Double layered Microchannel Heat Sink (X-DMHS) is proposed for performance augmentation on the traditional rectangular Double layered Microchannel Heat Sink (DMHS). The overall flow and thermal performances of parallel-flow and counter-flow arrangements on X-DMHSs are studied, and the entropy generation from the second law perspective is also quantitatively analyzed. From the analysis of the pressure drop penalty, thermal performance and entropy generation rate, it is found that the proposed X-DMHSs show much superior performance either from the heat transfer performance or from the second law perspective. The design offers higher entropy generation number and better thermal uniformity on substrate, meaning that proposed X-DMHSs can control the thermal gradients more significantly and lower the highest temperature on the heated substrate more effectively with affordable rise of pumping power as compared with the corresponding traditional DMHS.

Constructal design progress for eight types of heat sinks

This review paper summarizes constructal design progress performed by the authors for eight types of heat sinks with ten performance indexes being taken as the optimization objectives, respectively, by combining the methods of theoretical analysis and numerical calculation. The eight types of heat sinks are uniform height rectangular fin heat sink, non-uniform height rectangular fin heat sink, inline cylindrical pin-fin heat sink (ICPHS), plate single-row pin fin heat sink (PSRPHS), plate inline pin fin heat sink (PIPHS), plate staggered pin fin heat sink (PSPHS), single-layered microchannel heat sink (SLMCHS) with rectangular cross sections and double-layered microchannel heat sink (DLMCHS) with rectangular cross sections, respectively. And the ten performance indexes are heat transfer rate maximization, maximum thermal resistance minimization, minimization of equivalent thermal resistance which is defined based on the entransy dissipation rate (equivalent thermal resistance for short), field synergy number maximization, entropy generation rate minimization, operation cost minimization, thermo-economic function value minimization, pressure drop minimization, enhanced heat transfer factor maximization and efficiency evaluation criterion number maximization, respectively. The optimal constructs of the eight types of heat sinks with different constraints and based on the different optimization objectives are compared with each other. The results indicated that the optimal constructs mostly are different based on different optimization objectives under the same boundary condition. The optimization objective should be suitable chosen based on the focus when the constructal design for one heat sink is performed. The results obtained herein have some important theoretical significances and application values, and can provide scientific bases and theoretical guidelines for the thermal design of real heat sinks and their applications.

An efficient method for the geometric parameters optimization of double-layer micro-channel heat sink

In this study, thermal resistance of a double-layer micro-channel heat sink (DL-MCHS) with different ratio of upper and bottom channel heights in outlet (α=HU/HB) and the angle of channel inclination (θ), was investigated numerically. The advantage of DL-MCHS in reducing thermal resistance compared with single-layer micro-channel heat sink (SL-MCHS) was quantitatively demonstrated. It was confirmed that both α and θ have significant impacts on the heat transfer performance of DL-MCHS. Accordingly, response surface methodology as a time-efficient optimization method was employed to obtain the optimal geometry for DL-MCHS. It turned out that the optimized geometric parameters were α = 2 and θ = 6°. In this case, compared to SL-MCHS, the thermal resistance of DL-MCHS is reduced by 34.6%. Our work should be of practical value for the design of high efficiency micro heat sink with various geometric parameters.

Modeling of double-layer triangular microchannel heat sink based on thermal resistance network and multivariate structural optimization using firefly algorithm

The micro-channel heat dissipation system has minor specifications and good thermal conductivity per unit, which is the best choice for heat dissipation of micro-chips. By optimizing the cross section of microchannel, the heat exchange efficiency and temperature uniformity can be effectively improved. In this article, a double-layer triangular microchannel heat sink is proposed, which uniquely combines triangular cross section and double-layer structure to obtain a better heat dissipation performance. A new thermal resistance network model is established. At the same time, the model of pressure drop in microchannel heat sink is obtained by use of fluid theory. Taking thermal resistance and pressure drop as optimization objectives, the thermal resistance of double-layer triangular microchannel heat sink is 0.284 K/W and the pressure drop is 1386.89 Pa by using the firefly algorithm based on the Pareto optimal solution set, obtaining the optimal structural parameters. The thermal-flow-solid coupling simulation analysis shows that the thermal resistance and theoretical analysis error is 5.19%, and the pressure drop and theoretical analysis error is 9.49%, which can verify the accuracy of the thermal resistance network model. This article has a guiding significance for the thermal resistance analysis and heat dissipation improvement of non-rectangular cross section microchannel heat sinks.

Numerical Analysis of Fluid Flow and Heat Transfer in Micro-Channel Heat Sinks with Double-Layered Complex Structure.

Micro-channel heat sink (MCHS) has been extensively used in various electronic cooling fields. Double-layered MCHS, or DL-MCHS, is regarded as one effective technique for high-heat-flux transfer and is expected to meet the ever-increasing heat load requirement of future electronic device generations. In order to improve the cooling capacity, two new types of the MCHS, with a double-layered matrix structure (DL-M) and double-layered interlinked matrix structure (DL-IM) are proposed and investigated numerically. The two designs are compared with the traditional double-layered rectangular structure (DL-R) and the double-layered triangular structure (DL-T). Different properties of the heat sink are investigated to assess the overall heat transfer performance, for which coolant flow and heat transfer are both evaluated. The numerical results reveal that the periodical slot subchannel in the matrix has a significant effect on fluid flow for heat transfer. In comparison to the DL-R and the DL-T, the DL-M and DL-IM realize a much lower pressure drop and temperature rise at the base surface and also have higher Nusselt number and secondary flow intensity, therefore, manifesting better overall thermal performance. In the DL-M and DL-IM, the coolant flows along the periodical subchannel in one layer and is redirected into the second layer with vortices being induced. The vortices promote the coolant mixing and enhance the mass and heat transfer. These geometric design strategies can provide references for wide heat sink applications.