Thermal Performance Of Microchannels Research Articles

Improving Thermal Performance of Rectangular Microchannel Heat Sinks using Porous Layer: CFD Simulation and Optimization

Microchannel heat sinks are very widely used due to their high heat transfer coefficients and low refrigerant requirements. Nevertheless, microchannel heat sinks still perform sub-optimally when it comes to thermal performance. Therefore, this paper investigates the individual and combined impacts of different characteristics of porous media on the thermal performance of microchannel. Four porosity values are considered: 0.8, 0.85, 0.9, and 0.95. The evaluation is based on three-dimensional computational fluid dynamics simulations. Due to the large number of degrees of freedom in this study, Constructal Theory and Design of Experiments are employed. In this study, the response surface type is Genetic Aggregation, while the Latin Hypercube Sampling algorithm is used for data sampling and Genetic algorithm is used for optimization. Combining porous layers with microchannel heat sinks reduces maximum temperatures about 3K. It is also observed that a lower maximum surface temperature is achieved in the cases with less porosity. Furthermore, the optimal geometry and size of the microchannels with porous layers are determined.

Numerical Investigations of Heat Transfer and Fluid Flow Characteristics in Microchannels with Bionic Fish-Shaped Ribs

Microchannel cooling technology is an effective method to solve local thermal stacking. In this paper, four innovative microchannels with bionic fish-shaped rib arrangements (CM-O, CM-R, CM-H, and CM-G) are designed by imitating geese and fish clusters. The heat transfer and flow characteristics of the microchannels are simulated numerically at different Reynold’s numbers (Re = 200 − 1600). The liquid water temperature and flow field in the four innovative microchannels with bionic ribs are analyzed. The results show that the ribs’ arrangement has an influence on the thermal performance of microchannels. Compared to the smooth microchannel (CM), the of the Nu microchannels with the bionic fish-shaped ribs increases by 33.00–53.26% while the fave increases by 28.63–34.93% at Re = 1200. The vortices around the ribs are clearly observed which improves the temperature gradient. The performance evaluation criterion (PEC) of CM-H is higher than that of the others. This indicates that the rib arrangement of CM-H is superior for heat dissipation application.

Significance of cold cylinder in heat control in power law fluid enclosed in isosceles triangular cavity generated by natural convection: A computational approach

The selection of appropriate geometrical characteristics of enclosure has salient influence on performance of different thermal engineering processes and devices like microelectronics, heat exchangers, power engines, boilers, solar collectors, nuclear reactors and so forth. Specifically, the triangular cavity of different aspect ratios are used to obtain multi-objective optimization and gaining excellence in thermal performance of micro channels. Subsequently, the installation of cold cylinder in a triangular enclosure are extensively used to remove high energy dissipation in micro heat sinks and heat exchangers. So, the purpose of current effort is to probe thermal characteristics of power-law liquid describing features of shear thinning and thickening materials containing applications in lubrication and polymer industry. Heat transfer is generated by the consideration of natural convection process generated due to consideration of cold walls and cylinder with provision of non-uniform heating at base wall. No-slip velocity conditions are supposed at all walls of isosceles triangle cavity. Solution of attained differential system is simulated by capitalizing finite element based COMSOL Multiphysics software (Version 5.6). Domain discretization by distributing into triangular and rectangular elements is conceded and equations at element levels are discretized by executing weak formulation. The validation of adopted numerical procedure is established by making agreement with formerly available works in both statistical and graphical approaches. Streamlines and isotherms are plotted and discussed against various parametric regimes. This study reveals noticeable influence of involved physical parameters on average and local heat flux coefficients, kinetic energy and cutlines against involved physical parameters are also evaluated. It is inferred thorough the analysis that with uplift in Rayleigh number (Ra) produces enrichment in kinetic energy and local heat transfer coefficients whereas reverse pattern is depicted against power-law index.(n).

The Role of Flow Structures on the Thermal Performance of Microchannels With Wall Features

Abstract Innovative design of microchannel heat sinks (MCHS) remains a contemporary research need to meet the increasing cooling demand of modern electronic industries. A transient three-dimensional conjugate heat transfer study has been carried out here for different combinations of constrictors like ribs or protrusions along with cavities on the sidewalls of a microchannel (MC). A facing pair of cavities with circular arc sections, together called a fan-shaped cavity (FC), has been considered. Each in the facing pair of ribs (R) or protrusions (P) is in the form of a part of cylinder or sphere, respectively. The results include the variations of Nusselt number, friction factor, and thermal performance over a range of Reynolds numbers from 140 to 605 in microchannels with rib (MCR), protrusion (MCP), or cavity pairs alone (MCFC), as well as with cavity-rib pairs (MCFCR) or cavity–protrusion pairs (MCFCP). Contrasting the highest thermal performance of 1.6 reported in an earlier study on MCFCR, a value as high as 1.76 has been obtained around Re of 550 for MCFCP with the relative values of cavity length, width, and pitch of 0.015, 0.5, and 0.0625, respectively, along with protrusion length and width of 0.01 and 0.4, respectively. The mechanisms leading to spiraling transverse streamlines in both MCFCR and MCFCP have been explained. The superior performance of MCFCP has presumably arisen from the vortex structure with no interference with the boundary layers at the top and bottom walls.

Heat transfer and flow characteristics of microchannels with solid and porous ribs

The microchannel cooling technology is an effective method to solve heat dissipation problems caused by high power electronic devices. In this work, the heat transfer and flow characteristics of microchannels with solid and porous ribs are comprehensively investigated using numerical approaches. It is reported that the thermal performance of microchannels with solid and porous ribs are significantly better than those without any ribs. The field synergy principle is adopted to analyze the thermal performance, which proves that microchannels with porous ribs show a better synergy effect compared to those with solid ribs. On the other hand, the pressure drops and friction factors for all microchannels with solid ribs are larger than those with porous ribs. When solid ribs are replaced by porous ribs, the pressure drops reduce about 67%, 57% and 12% for the middle, symmetrical and staggered rib configurations, respectively. It can be found that vortices and recirculation flow come into being behind solid ribs. The thermal boundary layers are disrupted and redeveloped due to the intensified fluid mixing in porous regions, which facilitates the convective heat transfer. Finally, the comprehensive thermal and hydraulic performance is evaluated, and microchannels with symmetrical and staggered porous ribs exhibit the best comprehensive thermal and hydraulic performance.

Effect of Microfins on Thermal Performance of Microchannel Using CFD

In the present study, the fluid flow and heat transfer characteristic of microchannel heat sink with microfins are studied numerically at Reynold number ranging from 400 to 1200. The influence of microfins on the Nusselt number and pressure drop are investigated. Five different types of microfins namely cylindrical microfins (Case A), diverge cylindrical microfins (Case B), diverge cylindrical microfins with semi-circle rib (Case C), diverge cylindrical microfins with rectangular rib (Case D) and diverge cylindrical microfins with triangular rib (Case E) are designed. A comparative analysis of these five types of microfins with bare microchannel has been conducted. The result highlighted the extended microfins augmented the heat transfer characteristic by disrupt the thermal boundary layer. The overall thermal performances of microchannel heat sink with microfins are 1.1 – 1.47 times higher compared to bare microchannel.

Hydrodynamic and Thermal Performance of Microchannels With Different Staggered Arrangements of Cylindrical Micro Pin Fins

This study focuses on microheat sinks with different staggered arrangements of micro pin fins (MPFs). A rectangular microchannel with the dimensions of 5000 × 1500 × 100 μm3 (l′ × w′ × h′) was considered for all the configurations while different MPF diameters, height over diameter ratio (H/D), and longitudinal and transversal pitch ratios (SL/D and ST/D) were considered in different arrangements. Using the ansys fluent 14.5 commercial software, the simulations were done for different Reynolds numbers between 20 and 160. A constant heat flux of 30 W/cm2 was applied through the bottom heating section. The performances of the microheat sinks were evaluated using design parameters, namely pressure drop, friction factor, Nusselt number, and thermal-hydraulic performance index (TPI). The effect of each geometrical parameter as well as wake-pin fin interaction patterns were carefully studied using the streamline patterns and temperature profiles of each configuration. The results reveal a great dependency of trends in pressure drops and Nusselt numbers on the wake region lengths as well as the local velocity and pressure gradients. Moreover, the wake region lengths mostly contribute to the increase in obtained pressure drop and Nusselt number with Reynolds number. Although an increase in the H/D and SL/D ratios results in an increase and a decrease in pressure drop, respectively, the effect on the Nusselt number depends on other geometrical parameters and Reynolds number. A larger ST/D ratio generally results in a decrease in the pressure drop and Nusselt number. Finally, while the friction factor decreases with Reynolds number, two different trends are seen for the TPI values of configurations with the H/D ratio of 1 and 2 (D = 100 and 50 μm). While the trend in the TPIs is increasing for Reynolds numbers between 20 and 40, it reverses for higher Reynolds numbers with a steeper slope in the configurations with the ST/D ratio of 1.5.

Hydrodynamic and Thermal Performance of Microchannels With Different In-Line Arrangements of Cylindrical Micropin Fins

This study presents results on the hydrodynamic and thermal characteristics of single-phase water flows inside microchannels (MCs) with different micropin fin (MPF) configurations. Different inline arrangements of micropin fins were considered over Reynolds numbers ranging from 20 to 160. The computational studies were performed using the commercial software ansys 14.5. The hydrodynamic performances of the configurations were compared using two parameters, namely, pressure drop and friction factor while the comparison in their thermal and thermal-hydraulic performances were based on Nusselt number and thermal performance index (TPI). Wake-pin fin interactions were carefully analyzed through streamline patterns in different arrangements and under different flow conditions. The results showed strong dependencies of all four evaluated performance parameters on the vertical pitch ratio (ST/D). Weaker dependencies on height over diameter ratio (H/D), horizontal pitch ratio (SL/D), and minimum available area (Amin) were observed. With an increase in the Reynolds number, extension of the wake regions behind MPFs was observed to be the paramount factor in increasing pressure drop and Nusselt number. Regarding TPI, two adverse trends were observed corresponding to different ST/D ratios, while the effect of SL/D ratio was unique. For friction factors, H/D and SL/D ratios of 1 and 1.5, respectively, led to minimum values, while different ST/D ratios are needed for each diameter size for the maximum performance. Moreover, a twofold increase in Reynolds number resulted in about 40% decrease in friction factor in each configuration.

The Influence of Geometry on the Thermal Performance of Microchannels in Laminar Flow With Viscous Dissipation

Micro heat exchangers may achieve very high heat transfer coefficients thanks to their small dimensions and high area-to-volume ratio even in laminar flow, a highly desirable feature in many industrial applications. The main drawback of these devices is the high frictional losses—especially for liquid flows—that make viscous dissipation no longer negligible. In order to enhance heat transfer, modification of the channels’ cross-section is a viable strategy. In this work the fully developed steady laminar flow of a Newtonian liquid through a microchannel subject to uniform heat flux, uniform peripheral temperature boundary conditions in the presence of viscous dissipation is investigated. Entropy generation numbers and the constrained total heat transfer area performance evaluation criterion are employed to assess the influence of smoothing the corners of an initially rectangular cross section, with an aspect ratio ranging from 1 to 0.03 under four different types of geometrical constraints. The governing equations and the results are expressed in nondimensional form, with the intensity of viscous dissipation being exemplified by the Brinkman number, which is demonstrated to increase its maximum allowable value when corners are smoothed. The results are reported as a function of the nondimensional radius of curvature and aspect ratio and show that smoothing the corners almost invariably brings an improvement for a fixed heated perimeter.

Thermal Performance of Microchannels with Patterned Super-Hydrophobic Surfaces Under Laminar Flow

This article presents the simulation results and the effects of slip length and fractal ratio on patterned super-hydrophobic surfaces in microchannels under laminar flow conditions. The effects of using different slip length ratios and fractal ratios on patterned surfaces were simulated numerically at two Reynolds number values. Dimensionless parameters such as Nusselt number, friction factor, and performance efficiency indicator were used to study the effects of boundary conditions (i.e., surface features) on microchannel thermal performance. The results show that the flow structure within a patterned microchannel experiences flow fluctuations near the wall boundary caused by the super-hydrophobic surface. The results also indicate that patterned surfaces with high slip length enhance heat transfer performance and reduce pressure drop.

Numerical study on drag reduction and heat transfer enhancement in microchannels with superhydrophobic surfaces for electronic cooling

Microchannels with superhydrophobic surfaces are a promising candidate for electric cooling with mild frictional penalty. Frictional and thermal performance of laminar liquid-water flow in such microchannels is numerically investigated for various shear-free fractions and Reynolds numbers. The structures on superhydrophobic surfaces include square posts and holes, transverse and longitudinal grooves. Combined frictional and thermal performance of microchannels is evaluated by a goodness factor, and is compared with that of smooth plain channels. It is found that with increasing shear-free fractions, both friction factor and average Nusselt number deteriorate for four surface patterns; however, goodness factor is improved significantly over smooth plain channels. In general, superhydrophobic surfaces containing longitudinal and transverse grooves exhibit the lowest and highest frictional and thermal performance, respectively; however, combined performance of these two are on opposite. Among four surface patterns, longitudinal grooves have the highest goodness factors, except at high shear-free fractions or high Reynolds numbers where overall performance is surpassed by square posts. At very low or high shear-free fractions, frictional and thermal performance of two-dimensional square posts and holes approaches that of one-dimensional longitudinal or transverse grooves. Our study suggests microchannels with superhydrophobic surfaces as promising candidates for efficient cooling devices.

The influence of viscous dissipation on thermal performance of microchannels with rounded corners

The influence of viscous dissipation on thermal performance of microchannels with rounded corners

Thermal three-dimensional Lattice Boltzmann simulations of suspended solid particles in microchannels

This paper presents a three-dimensional thermal Lattice Boltzmann model to simulate the interaction of suspended solid particles with the flow field and their effects on hydrodynamic and thermal performance of microchannels. A 19-bit single-relaxation-time Lattice Boltzmann method (D3Q19) is used to perform thermal fluid flow, while the Newtonian dynamic equations are solved to investigate the transport of the suspended solid particles. The needed forces in equations of the particle motion are evaluated by the momentum exchange method. The effects of solid spherical particles with various diameters on the fluid flow and heat transfer enhancement in a rectangular microchannel, at different Reynolds numbers, are investigated and discussed. Three cases of stationary, constant velocity and freely moving single particle are investigated which the results show the latter case has the highest heat transfer enhancement and the lowest pressure drop. The particulate flows in the microchannel for both cases of 15 stationary and freely moving particles are also studied and the hydraulic and thermal performances are compared.

Thermal Performance of Microchannels With Wavy Walls for Electronics Cooling

Wavy walls are investigated in this paper as a passive scheme to improve the heat transfer performance of low-Reynolds-number laminar flows in microchannel heat sinks for electronics cooling applications. 3-D laminar fluid flow and heat transfer characteristics in microchannels with wavy walls are numerically studied for a 500-μm hydraulic diameter channel by varying the wavy feature amplitude at different Reynolds numbers (10, 20, 50, and 100). In addition, flow measurements are made using a micrometer-resolution particle image velocimetry technique for understanding the fundamentals of fluid flow in the wavy-walled microchannels for the considered Reynolds numbers. Based on the comparison with straight channels, it was found that wavy channels can provide improved heat transfer performance while keeping the pressure drop within acceptable limits. Accordingly, wavy channels are to found to provide an improvement of up to 26% in the overall performance (which includes the effect of wall waviness on heat transfer, pressure drop, and surface area) compared to microchannels with straight walls for the same pumping power and hence are attractive candidates for cooling of future electronics.