Straight Microchannel Heat Sink Research Articles

A novel center-hybrid pin-fin microchannel heat sink with embedded secondary microchannels for hotspot thermal management

With the rapid advancement of microelectronics technology, the issue of excessive localized heat flux in electronic devices has become increasingly prominent. This study introduces a center-hybrid pin-fin microchannel heat sink (CHPFMHS) for hotspot thermal management, comprising a central hexagonal pin-fin region flanked by two lateral straight microchannel zones located at the inlet and outlet. Furthermore, four types of various secondary microchannels are integrated within the pin-fins of CHPFMHS (Case 1: with no secondary microchannel; Case 2–5: with 3-direction, 4-direction, 6-direction, and vertical intersecting secondary microchannels, respectively) for effective heat dissipation with low pressure drop. The performances of CHPFMHSs and non-hybrid straight microchannel heat sink (NHSMHS) are evaluated with Re = 50–400. For all flow rates, the pressure drops in Cases 2–5 are lower than that in Case 1, with Case 4 exhibiting the lowest pressure drop among all CHPFMHSs. The thermal resistance (Rth) and temperature non-uniformity (δT) of Case 5 with hotspot area (Ah) of 2.25 mm2 and pin-fin region length (Lrpf) of 3 mm are 47.3 % and 30.8 % lower than those of NHSMHS, respectively. Among Case 1–5, the configuration of Case 5 is the most optimal. The impacts of hotspot and the pin-fin region size of the CHPFMHS have also been investigated. As Ah rises to 6.25 mm2, in comparation with NHSMHS, Rth and δT of Case 5 decrease by 52.7 % and 40.2 %, respectively. As Lrpf rises, the values of both δT and Rth, for Case 5, approach their minimum when Lrpf is close to the length of the hotspot. However, they exhibit slight changes as Lrpf continues to increase.

An experimental and numerical investigation of thermofluidic properties on the novel curved microchannel heat sink with slotted section

The current work proposes the development of a novel curved microchannel heat sink by modifying the existing flat microchannel heat sink for enhancing the heat dissipation in the electronic device without significant pressure drop penalty. The inspiration for the curved channel is taken from a NACA airfoil. The microchannel comprises two sections: a curved section and a slotted straight section. Experimental and numerical investigations are performed on the proposed geometry to study the thermofluidic properties for Reynolds number (Re) ranging from 200 to 500 using DI water as working fluid. Fluid flow and heat transfer are analysed by carrying out a full domain numerical simulation in ANSYS Fluent 19.0. The thermofluidic properties of the curved microchannel heat sink (CMCHS) and straight microchannel heat sink (SMCHS) are compared numerically by keeping the geometrical parameters (hydraulic diameter, foot area and fin area) and inlet parameters (inlet velocity and heat flux) identical. The average heat transfer coefficient (havg) of CMCHS is enhanced over SMCHS due to the formation of vorticities in the slotted region owing to the fluid intermixing and boundary layer disruption. The presence of curved section leads to reducing pressure drop penalty pertaining to gravitational effects. Together, the curved section and slotted section enhance the performance factor of CMCHS over SMCHS. The vortices formed increase as the Reynolds number increases, enabling an increase in the heat transfer coefficient. Therefore, the performance factor also increases as the Reynolds number is increased. An enhancement of ≈ 67.6 % in havg is achieved for Re = 500 in CMCHS compared to SMCHS with DI water as the working fluid.

Oblique microchannel merged with circle micro pin-fin as a novel hybrid heat sink for cooling of electronic devices

Recently, the advantages of microchannel and micro pin-fin heat sinks for cooling have become clear. This study delves into the effects of hybrid designs on electronic chip cooling by combining microchannel and pin-fin patterns. The research contrasts the performance of a straight microchannel heat sink (Case Ⅰ), circular pin-fin (Case Ⅱ), straight-circular pin-fin-straight (Case Ⅲ), and oblique grooved straight-circular pin-fin-oblique grooved straight (Case Ⅳ). Results show that Case Ⅳ's Nu number reaches 61 at Re = 1250, surpassing Case Ⅰ, Case Ⅱ, and Case Ⅲ by 517 %, 32 %, and 235 %, respectively. Case Ⅳ also has the highest pressure drop. The study calculates each Case's performance evaluation index (ƞ), highlighting the balance between enhanced Nu numbers and pressure drops. Case Ⅳ's ƞ is notably higher than Case Ⅱ and Case Ⅲ. To achieve a more uniform thermal distribution across the entire heat sink, the orientation of the oblique grooves is modified in Case Ⅳ, resulting in a new design labeled Case Ⅴ. While Cases Ⅳ and Ⅴ have similar Nusselt numbers, Case Ⅴ's design ensures consistent temperature distribution, reducing hotspot risks on the chip.

Three-dimensional numerical investigation of flow and heat transfer performances of novel straight microchannel heat sinks

Four-type novel single crystal diamond (SCD) straight microchannel heat sinks with different shapes (symmetrically inclined, turned symmetrically inclined, V-shaped, and X-shaped) are designed and investigated by the three-dimensional computational fluid dynamics method. These four-type microchannel heat sinks are evaluated in terms of fluid flow and heat transfer capabilities compared to the conventional rectangular straight microchannel (RSMC) heat sink. Our research indicates that the newly designed novel SCD microchannel heat sinks can enhance the heat dissipation effect in comparison to the conventional RSMC heat sink, thereby substantiating its potential for enhancing thermal management in electronic devices. Each V-shaped and X-shaped straight microchannel heat sink has a higher heat transfer capacity than the RSMC heat sink. Among the heat sinks involved in this work, the V-shaped SCD heat sink has the best surface temperature uniformity. The symmetrically inclined heat sink shows the lowest pumping power, with 14.1 % lower than that of the RSMC heat sink. The X-shaped SCD heat sink exhibits a significantly lower thermal resistance, with an 8.5 % reduction compared to the RSMC heat sink. Additionally, it demonstrates a substantially higher Nusselt number, with a 27.6 % increase relative to the RSMC heat sink. The X-shaped SCD heat sink has the highest heat transfer coefficient of up to 1.08 × 105 W/(m2·K), which is 20.4 % higher than that of RSMC heat sink. Owing to the highest performance evaluation criterion of 1.22, the X-shaped straight microchannel heat sink is the most optimal of the designed heat sinks.

Employing the (SWCNTs-MWCNTs)/H2O nanofluid and topology structures on the microchannel heatsink for energy storage: A thermal case study

The present study investigated the increase of heat transfer rate of the microchannel (heatsink) with high heat flux using topology structures and CNTs nanofluids. The heat transfers in the heatsink were studied using a three-dimensional finite volume method (FVM). Four nature-inspired topology structures were used: snowflake shape, honeycomb-shaped, ternate veiny, and spider netted, and their results were compared with straight microchannel heatsink (MHS). For testing the effect of nanoparticle concentration and type on heat transfer of heatsinks, two water-based nanofluids (SWCNT-Water) and (MWCNT -Water) were used. The temperature and pressure contours related to the proposed designs and two nanofluids were presented. The spider netted model had the highest heat transfer coefficient and the highest-pressure changes compared to other designs. For Reynolds number 550, the heat transfer coefficient and pump power (Pp) increased by 56.1% and 46.1%, respectively, when using SWCNT- H2O nanofluid. Based on the thermo-hydraulic performance of the models, spider netted increased heatsink performance by an average of 50.2%. The results also showed that nanofluids with a concentration of 5% significantly increase the heat transfer coefficient and pump power in the heatsink.

A critical review of the straight and wavy microchannel heat sink and the application in lithium-ion battery thermal management

As demand for high-performance heat transfer increases, interest in microchannel heat sinks as a viable solution for heat flux removal in thermal devices has grown significantly. Microchannel heat sinks with straight and wavy designs are the two main varieties that have been the focus of extensive research in this field. The current paper provides beneficial information regarding the different designs and methods for heat enhancement and overall thermal performance in straight and wavy microchannel heat sinks. Besides using nanofluids, modified designs improve heat transfer performance due to incorporating secondary flow. Moreover, utilizing microchannels as indirect cooling methods in lithium-ion battery thermal management is discussed in this review. This study discusses current issues and future research directions.

A Critical Review of the Straight and Wavy Microchannel Heat Sink and the Application in Lithium-Ion Battery Thermal Management

A Critical Review of the Straight and Wavy Microchannel Heat Sink and the Application in Lithium-Ion Battery Thermal Management

Heat transfer optimization based on finned microchannel heat sink

The straight microchannel heat sink is relatively low in heat transfer efficiency due to the influence of the thermal boundary layer, and the thermal requirements of which may fail to be met under high heat flux conditions. In this paper, the fins were introduced to form a secondary channel to optimize the heat dissipation effect of the microchannel heat sink. Combined with CFD method, the structure parameters (the angle, lateral spacing and vertical spacing) and arrangement ways (the aligned, staggered) of internal fins in microchannel were analyzed. At the same time, CFD method is verified by experiments, and the relative errors are within 2%. Under the mass flow rate of 3.5 gs−1, compared with the straight microchannel heat sink, the maximum temperature and average temperature of optimized model are reduced by 3.04 K (6.67%), 2.86 K (6.75%), respectively. And the uniformity of temperature also is increased by 0.005 (8.47%). The pressure drop is reduced by 226.5 Pa (13.33%). At same time, the value of the performance evaluation can reach 1.285. In actual design and application, appropriate mass flow rate can be selected by the heating power to ensure the cooling effect of the microchannel heat sink and the power loss of the pump.

Optimization of permeable membrane microchannel heat sinks for additive manufacturing

The design freedom brought by additive manufacturing (AM) can be leveraged in the design of microchannel heat sinks to improve their cooling performance. The permeable membrane microchannel (PMM) heat sink geometry was inspired by the ability of powder bed AM processes to fabricate partially porous metal parts having small internal flow features on the order of the powder size. The design routes coolant through a parallel array of thin permeable membranes arranged in a single-layer-manifold configuration. The permeable membranes provide effective heat exchange surfaces and the manifold configuration yields a low flow resistance across the PMM heat sink, all incorporated in a single layer by the use of AM. Past work has introduced the PMM heat sink concept, but the optimal geometric feature sizes were not explored or identified. The n current study is first to explore design optimization of the PMM heat sink to identify target feature sizes for AM fabrication, assessment of the conditions under which the PMM geometry outperforms other standard microchannel heat sink designs, and inspection of the ability of metal 3D printing process to produce the optimal features. To this end, a reduced-order PMM heat sink model is developed, a gradient-based-multi-objective optimization is performed to identify the optimal feature sizes for different coolants (water and 48/52 water/ethylene glycol mixture) at different flow rates (100–500 mL/min), footprint areas (49–900 mm2), and channel heights (0.5–2.5 mm). The optimization results are benchmarked against an optimized straight microchannel (SMC) heat sink design. Optimized PMM designs offer up to 68% lower thermal resistance at a set pressure drop compared to optimized SMC designs. A pair of SMC and PMM heat sinks optimized for the same operating conditions are 3D printed using direct-metal-laser-sintering (DMLS) of AlSi10Mg. X-ray microtomography is used to characterize the geometry of the 3D-printed parts. The model identifies that optimal membrane gap sizes on the order of ~ 10 s μm are required for the PMM to realize performance advantages compared to SMC heat sinks under the same operating conditions. The performance is predicted to be highly sensitive to this pore size, and even though DMLS is shown to produce parts with gaps as small as 26.7 µm, morphological deviations between the design and as-printed part are shown to lead to noticeable performance differences. Albeit excellent performance potential reinforced by this work, these findings call for further AM process development to ensure reliable, as-predicted PMM heat sinks to realize this potential.

A Numerical Study on Heat Transfer Performance in a Straight Microchannel Heat Sink with Standing Surface Acoustic Waves

There has been a remarkably increasing interest in applying acoustofluidics in micro-electro-mechanical systems and lab-on-a-chip systems in the past decades. This paper investigated the heat transfer performance in a straight microchannel heat sink which applies standing surface acoustic waves (SSAW) to disturb the flow. Two-dimensional numerical simulations of the SSAW-driven flow are performed by employing perturbation theory on basis of COMSOL platform. The elasticity of microchannel material is taken into account by applying the impedance boundary conditions. Parametric effects on heat transfer performance including the SSAW wavelength and the dimensions of microchannel heat sink are investigated. It is found that the introduction of SSAW can greatly enhance the overall heat transfer. Moreover, with a constant channel height, shorter SSAW wavelength and narrower microchannel are found to be more beneficial to the overall thermal performance. Keeping both the microchannel width and the SSAW wavelength unchanged, a “wide” configuration of the microchannel cross section is recommended to achieve higher heat transfer efficiency. Finally, we elucidate the underlying mechanisms of heat transfer enhancement peculiar to the excitation of SSAW in microchannel, which is attributed to the appearance of acoustic vortices and the disruption of thermal boundary layer induced by acoustic streaming.

Topology optimization of microchannel heat sinks using a homogenization approach

Topology optimization for heat sink devices typically relies on penalization methods to ensure the final designs are composed of strictly solid or open regions. In this work, we formulate a homogenization approach wherein the partial densities are physically represented as porous microstructures. This formulation allows design of thermal management components that have sub-grid features and leverages additive manufacturing techniques that can produce such partially porous regions within the build volume. Topology optimization of a liquid-cooled microchannel heat sink is presented for a hotspot over a uniform background heat input. The partial densities are represented as arrays of pin fins with varying gap sizes to achieve sub-grid-resolution features. To this end, the pin fins are modeled as a porous medium with volume-averaged effective properties. Height-averaged two-dimensional flow and non-equilibrium thermal models for porous media are developed for transport in the pin fin array. Through multi-objective optimization, the hydraulic and the thermal performance of the topologically optimized designs is investigated. The pin fin thickness is chosen based on the minimum reliable printing feature size of state-of-the-art direct metal laser sintering machines, and the gap sizes between the pin fins are optimized. The resulting topologies have porous-membrane-like designs where the liquid is transported through a fractal network of open, low-hydraulic-resistance manifold pathways and then forced across tightly spaced arrays of pin fins for effective heat transfer. The effects of the grid resolution and the initial design guess on the resulting topologies and performances are reported. The topologically optimized designs are revealed to offer significant performance improvements relative to the benchmark, a straight microchannel heat sink with features optimized under the same multi-objective cost function. The work demonstrates that representing partial densities as porous microstructures results in nearly resolution-independent performance at sufficiently-small grid sizes through the use of sub-grid features.

Thermal analysis of high concentrator photovoltaic module using convergent-divergent microchannel heat sink design

The dense-packed high concentrator photovoltaic module (DP-HCPVM) is normally exposed to a very high heat flux concentrated from sunlight. The resultant high module operation temperature drops the overall performance and reduces the module life expectancy. Consequently, the provision of powerful cooling is compulsory for such structures. In this study, a complete three-dimensional (3D) model was developed to investigate the performance of a DP-HCPVM under the active cooling scheme to figure out its ability to attain effective heat dissipations. A new cooling convergent-divergent microchannel heat sink cases were numerically investigated and compared in terms of temperature distribution and electrical efficiency of a DP-HCPVM. The influence of heat sink design and inlet mass flowrate on the cooling performance of the heat sink device were examined. The same external dimensions are considered, and the flow was laminar with the inlet temperature of 25 °C for all designs for a reasonable comparison. The concept of variation flow direction by changing the inlet and outlet arrangement is adopted. The comparison between all studied designs was highlighted concerning surface average temperature, surface temperature uniformity, and pressure drop across the heat sink. The results indicated that the new convergent-divergent microchannel heat sink design achieved better effectiveness and heat transfer rate compared to the conventional straight microchannel heat sink design for DP-HCPVM thermal management, as it decreased the average cells temperature and temperature non-uniformity by 11.4% and 37.8%. Moreover, it was found that the electrical efficiency and Nusselt number were improved by 0.35% and 21.9% at the maximum studied inlet mass flowrate.

Comparative Study of the Flow Boiling Performance of the Hybrid Microchannel-Microgap Heat Sink with Conventional Straight Microchannel and Microgap Heat Sinks

In this study, the flow boiling performance of the hybrid microchannel-microgap heat sink (Hybrid 1:1), developed for improved boiling stability, is benchmarked against a conventional straight microchannel heat sink (SMC) and microgap heat sink (MG) having identical footprints of 25mm x 25mm, and microchannel and microgap dimensions of 300μm (Wmc) x 600μm (Hmc), and 25000μm (Wmg) x 600μm (Hmg) respectively. Experiments along with flow visualization are performed using deionized water as the coolant under heat fluxes and mass fluxes in the ranges of 0-128 W/cm2 and 100-399 kg/m2s respectively. SMC experiences the greatest degree of flow instabilities owing to the rapid bi-directional expansion of vapor slugs within the confined flow passages. In comparison, Hybrid 1:1 improves boiling stability particularly under low mass flux conditions on account of the expanding flow configuration that promotes forward expansion of vapor slugs. Similarly, MG also offers a comparable degree of boiling stability as Hybrid 1:1. However, SMC shows the most superior heat transfer performance at all mass fluxes followed by Hybrid 1:1 and MG. Although Hybrid 1:1 stabilizes boiling, the reduced wetted area towards the downstream compromises its heat transfer performance. Whereas the larger wetted area of SMC offsets the degrading effects of boiling instabilities. With the smallest wetted area, MG shows the most inferior heat transfer performance with severe partial dry-out conditions at high heat flux leading to early CHF, particularly under low mass flux conditions. Pressure drops of the heat sinks are in order of the extent of channel confinement, with the highest being for SMC followed by Hybrid 1:1 and MG.

Thermodynamic Assessment of Microchannel Heat Sinks with Novel Sidewall Ribs

An inadequate cooling associated with a straight microchannel heat sink for electronic components requires an improved thermal management with an acceptable cost of hydrodynamic deterioration by extending the effective heat transfer area. The present study is an attempt to numerically investigate the heat transfer and fluid flow characteristics in a microchannel heat sink having novel sidewall ribs configurations. The investigated geometric profiles include symmetrical ellipse-, trapezoid-, hydrofoil-, and rectangular-shaped ribs. A thermodynamics-based assessment has been conducted involving various evaluation parameters that include a friction factor ratio, a Nusselt number ratio, a thermal enhancement factor, transport efficiency, and entropy generation rates for a Reynolds number in the range of 100 to 1000. The predicted results supported the motivation of adding sidewall ribs to a microchannel heat sink with a significant heat transfer enhancement and a reasonable increase of pressure drop. The increased pressure drop leads to a higher pumping requirement for the flow system design, and is therefore assessed carefully with the evaluation parameters to yield a favorable configuration based on the overall performance for range of the Reynolds number . The results show that the sidewall ribs of a hydrofoil configuration are the best performers, yielding the least augmented entropy generation rates among all considered configurations.

Numerical investigation of heat transfer enhancement and fluid flow characteristics in a microchannel heat sink with different wall/design configurations of protrusions/dimples

The convective cooling associated with Microchannel heat sink (MCHS) devices for electronic components with high power density is a recent topic of cutting-edge research. However, thermal improvement with minimum degradation in hydrodynamic characteristic by extending the effective heat transfer area of different walls of MCHS is still a major challenge. In this regard, the heat transfer enhancement and fluid flow behavior of MCHS with protrusions, dimples and their different wall, geometric and design combinations are numerically studied in the present study. The wall configurations considered for the present analysis includes: Base wall protrusions/dimples (BWP/D), Side wall protrusions/dimples (SWP/D) and all walls protrusions/dimples (AWP/D). While for design configurations, the (AWP/D-Aligned), (AWP/D-staggered) and all wall protrusions and dimples mix (AWPD-Mix) cases are considered. The governing equations are discretized and solved across the computational domain using commercial computational fluid dynamics code with three-dimensional conjugate laminar flow model. The numerical model is then validated with experiment and theory in the literature and reasonable agreement in the results of average Nusselt number (Nuavg) and apparent friction factor (fapp) are observed. The effect of geometric parameters i.e. protrusion/dimple’s diameter (Dfr = 200 - 230 μm) and Pitch (Sfr = 400 - 1200 μm), operating parameters i.e. Reynolds number (Re = 100–1000) and Heat flux (qw = 50–100 W/cm2) on the heat transfer and fluid flow characteristics are examined to provide a better physical understanding of the energy management. The results indicate that the addition of protrusions/dimples to different walls of MCHS significantly improves the heat transfer with reasonable increase in pressure drop. The fluid flow pattern with the addition of the protrusions/dimples to different walls is improved through better mixing and lower pumping power augmentation to transport the same heat load than Straight MCHS. The favorable configuration along with geometric and operating parameters in terms of better thermal and hydrodynamic performance is suggested based on thermal enhancement factors (ƞ) and entropy generation rates ($$ {\dot{\mathrm{S}}}_{\mathrm{gen}} $$). Among the proposed wall configurations, AWP demonstrates superior thermal performance by resulting in maximum improvement of 82% in ƞ compared to BWP configuration. When compared to the straight MCHS, AWP-aligned MCHS achieved maximum enhancement of 115% in Nuavg at the cost of 152% higher fapp at same operating conditions of Re = 1000 and qw = 100 W/cm2 for design configurations. Furthermore, the outcomes of this study is expected to provide some important guidelines for the future experiments on such MCHS devices for energy saving and management.

Experimental study of flow boiling in a hybrid microchannel-microgap heat sink

A stable flow boiling operation is key to enhancing the two-phase cooling performance of microchannel heat sinks. To this end, a novel heat sink is developed which integrates a 300 μm × 600 μm straight microchannel array in the upstream region with a 25 mm × 600 μm microgap channel in the downstream region of a 25 mm × 25 mm copper heat sink. Flow boiling experiments are conducted using de-ionized water at 5 different mass fluxes in the range of 100–399 kg/m2 s, supplied at a fixed inlet temperature of 85.5 °C. The downstream heat transfer coefficient in the microgap section shows an M-shaped profile with increasing heat flux and vapor quality. Stable boiling conditions are prevalent across a large span of operating heat flux. Instabilities are experienced only for a short range of low heat flux following ONB. The stabilizing effect is attributed to the larger flow cross-section area offered by the downstream microgap section that allows expanding vapor bubbles to evacuate with lesser hindrance. Flow visualization reveals that a stable annular flow regime is established at moderate to high heat flux during which the stable boiling operation is observed. Thin film evaporation taking place during annular flow conditions results in an increasing trend in the downstream heat transfer coefficient from moderate to high heat flux. Pressure drop associated with the hybrid heat sink is found to be modest and reaches a maximum of 6 kPa at the highest mass flux of 399 kg/m2 s. A brief comparison of this heat sink is made with its straight microchannel and microgap heat sink counterparts. The hybrid heat sink shows a heat transfer performance that is superior to the microgap heat sink while poorer than the straight microchannel heat sink although it offers a better boiling stability than the straight microchannel heat sink. It however lowers the pressure drop compared to the straight microchannel heat sink.

Thermohydraulic performance of microchannel heat sinks with triangular ribs on sidewalls – Part 2: Average fluid flow and heat transfer characteristics

Triangular ribs mounted in the microchannel heat sink generally result in higher heat transfer coefficient, but are usually accompanied by higher pressure drop per unit length. In order to obtain some insight into the effect of geometry parameters of triangular ribs on laminar flow and heat transfer characteristics, three-dimensional conjugated heat transfer models taking account of the entrance effect, viscous heating and temperature-dependent thermophysical properties are conducted, and four non-dimensional variables related to the width, height, converging-diverging ratio and spacing of the triangular rib for both aligned and offset arrangements are designed. Effects of the geometry and arrangement of triangular ribs on thermohydraulic performance are examined by the variations of average friction factor and Nusselt number for Reynolds number (Re) ranging from 187 to 715. The studied microchannels have the same width (Wc) of 0.1 mm and same depth (Hc) of 0.2 mm in the constant cross-section region. The geometric parameters of aligned or offset triangular ribs are ranged in 0.025–0.4 mm for width (Wr), 0.005–0.025 mm for height (Hr), 0.2–5 mm for spacing (Sr) and 0–1 for the width ratio of converging region to a single rib (Wcon/Wr). Based on the total 660 computational cases of the microchannel heat sinks with triangular ribs, the correlations of average friction factor and Nusselt number are proposed, respectively for aligned and offset arrangements. For the studied Reynolds number range and geometry parameters of flow passage, the microchannel heat sinks with aligned triangular ribs present 1.03–2.01 times higher of average Nusselt number and 1.06–9.09 times larger of average friction factor, and those with offset triangular ribs show 1.01–2.16 times higher of average Nusselt number and 1.04–7.43 times larger of average friction factor, compared with the reference straight microchannel heat sink. Proposed heat transfer and friction factor correlations show good agreements with the computational results for the microchannel heat sinks within the parameter ranges of 187 ≤ Re ≤ 715, 0.25 ≤ Wr/Wc ≤ 4, 0.05 ≤ Hr/Wc ≤ 0.25, 0 ≤ Wcon/Wr ≤ 1, and 2 ≤ Sr/Wc ≤ 50.

Thermohydraulic performance of microchannel heat sinks with triangular ribs on sidewalls – Part 1: Local fluid flow and heat transfer characteristics

Triangular ribs are mounted on the parallel sidewalls of microchannels in order to reinitialize the thermal boundary layer and improve the mixing of cold and hot fluids. This paper presents a detailed numerical study on local laminar fluid flow and heat transfer characteristics in microchannel heat sinks with tandem triangular ribs for Reynolds number of 443. Three-dimensional conjugate heat transfer models considering entrance effect, viscous heating, as well as temperature-dependent thermophysical properties are employed. Water and silicon are respectively used as fluid and solid for the computational domain. Triangular ribs are attached in microchannels with either aligned or offset arrangement. Four non-dimensional geometry parameters relative to the width, height, converging-diverging ratio and spacing of triangular ribs are proposed to investigate the influence on local fluid flow and heat transfer characteristics. Velocity contour, pressure and temperature distributions are examined to demonstrate the basic fluid flow and heat transfer mechanism. Local pressure and temperature profiles are studied to show the influence of the triangular ribs on fluid flow and heat transfer process. Local friction factor and Nusselt number for different non-dimensional geometry variables are further investigated to comprehensively indicate the impact of triangular ribs. Results shows that the triangular ribs can significantly reduce the temperature rise of the heat sink base and efficiently prevent the drop of local heat transfer coefficient along the flow direction, but also result in higher local friction factor than the straight microchannel. For the studied operation conditions and geometry parameters of flow passage, the heat sink base temperature varies in the range of from 301.90 to 324.31 K, the computed pressure drop and heat transfer coefficient fluctuate from one triangular rib to the next and their amplitude and wavelength significantly depend on the geometry and arrangement of triangular ribs. Compared to the reference straight microchannel heat sink, a superior configuration considered in this paper can yield an improvement of up to 2.15 times higher of average Nusselt number.

Numerical investigation into the thermo-fluid performance of wavy microchannels with superhydrophobic walls

As an efficient cooling method, wavy microchannel heat sink (W-MCHS) with superhydrophobic walls is suggested as an alternative to a straight microchannel heat sink (S-MCHS) with conventional walls. Navier-Stokes and Energy equations with slip boundary conditions (velocity slip and temperature jump) are solved to study the hydraulic and thermal performances of the microchannels. It is observed that based on the “goodness factor” criterion, the overall performance of the new heat sink design is improved by 47.3%. In fact, the pressure drop reduction accompanying the use of superhydrophobic walls outweighs the thermal performance degradation due to the presence of trapped layers of air. It is also observed that with an increase in the waviness of the channel (either by an increase in the wave amplitude or a decrease in the wavelength), the pressure drop reduction by the use of superhydrophobic walls intensifies as the maximum velocity shifts from the centre of the channel towards the crest regions. This, in turn, increases the velocity gradient at the wall which excites the velocity slip and results in a better hydraulic performance. On the other hand, the thermal performance is deteriorated to a greater extent (compared to the hydraulic improvement) when the channel waviness increases, due to the elongated flow path and the related increase in the trapped layers of air. As a result, as long as the cooling performance of the heat sink with superhydrophobic walls is concerned, microchannels with lower waviness are desirable.

Heat Transfer Characteristics and Flow Visualization during Flow Boiling of Acetone in Semi-Open Multi-Microchannels

ABSTRACTExperimental results of flow boiling characteristics and flow patterns with acetone in two different microchannel heat sinks are presented in this paper. A semi-open microchannel heat sink and a straight microchannel heat sink with 19 parallel microchannels each were designed and tested. The semi-open microchannels have a channel width of 0.8 mm, fin width of 0.4 mm, and pedestal height of 0.2 mm and the straight microchannels have a rectangular cross section of 0.8 mm × 1 mm. The experimental heat fluxes ranged from 0 to 90 kW/m2, vapor quality ranged from 0.05 to 0.5, mass fluxes ranged from 4.34 to 15.62 kg/m2·s and the inlet temperatures were 20 and 30°C, respectively. Compared to those in the straight microchannels, flow boiling heat transfer coefficients can be improved by up to 36.2%. Furthermore, flow patterns were observed with a speed video camera. The flow boiling heat transfer mechanisms are analyzed according to the observed flow patterns.