Wavy Microchannel Research Articles

Thermal and hydrodynamic characteristics of microencapsulated phase change materials slurry flow in wavy microchannels

Thermal and hydrodynamic characteristics of microencapsulated phase change materials slurry flow in wavy microchannels

Enhancement of heat transfer characteristics in wavy microchannel heat sinks with streamlined micropins within convergent-divergent flow passages

In the current study, the heat transfer characteristics of a novel design microchannel with a wavy sinusoidal convergent-divergent wall structure featuring streamlined pins have been numerically investigated under laminar flow conditions. Various amplitudes, wavelengths, pin heights, and Reynolds numbers are considered as parameters. The thermal and hydraulic characteristics are analyzed in terms of Nusselt number, Fanning friction factor, and Performance Evaluation Criteria number (PEC), which evaluates the heat transfer enhancement against the associated pressure drop. It is revealed that increasing the amplitude and decreasing wavelength, along with moderate pin heights, significantly augment heat transfer. The streamlined pins effectively direct the flow, and the resulting secondary flow and chaotic advection considerably enhance heat transfer in the designed configuration. The study demonstrates that the heat transfer can be improved by a factor of 4.79 compared to a straight microchannel. Under these geometric and flow conditions, the pressure drop increases by a factor of 9.87, and the PEC is found to be around 2.23. A multi-objective optimization study using the Non-dominated Sorting Genetic Algorithm (NSGA-II) is conducted with Genetic Aggregation Response Surface Methodology to evaluate the impact of various parameters on thermal-flow performance and to identify the optimal design with material quantity variation. According to the optimal results, a 5 % increase in material can augment thermal-flow performance by approximately 206.6 % compared to traditional microchannels. Finally, practical correlations for the Nusselt number and friction factor, accounting for various parameters, have been developed to facilitate in designing of microchannel cooling systems.

Optimal design of a wavy Micro-Channel based on Multi-Objective genetic algorithm

With the increase of heat generation in electronic equipment, microchannel heat sinks (MCHS) have been widely adopted as a solution for heat dissipation under high heat flux conditions. This study aims to optimize the thermal resistance (θ) and the pressure drop (Δp) of a wavy MCHS through a multi-objective optimization method. The channel shape of the MCHS is controlled by adjusting the coordinates of seven nodes (Si) evenly distributed along the flow direction. The genetic algorithm and CFD software COMSOL Multiphysics are combined to determine the Pareto front with the optimal θ and Δp. The Pareto front suggests that gradually increasing the channel width in the inlet section can enhance the comprehensive performance, by appropriately introducing perturbations in the middle and rear sections. The Spearman’s correlation is adopted to reveal the relevance between Si and objective functions, which also indicates that downstream nodes have a higher correlation. Furthermore, a multi-objective decision-making algorithm is employed to identify OptimalTOPSIS as the best compromise solution. Compared to the straight-through channel, OptimalTOPSIS not only reduces Δp by 40.8% with almost unchanged θ, but also improves the uniformity of the substrate temperature by 4.2%.

A numerical study on a hybrid battery thermal management system based on PCM and wavy microchannel liquid cooling

With the emerging development of electrical vehicle, the efficient thermal management of the lithium-ion battery is becoming a critical point for its wide application and normal operating. Hence, based on the advantages of liquid cooling and PCM, a novel hybrid cooling system using PCM coupled with wavy microchannel cooling plate (PCM-WMCP) was proposed in this paper, and a numerical study was carried out to investigate its performance. It's found the hybrid cooling system with PCM and microchannel cooling plate showed much lower battery temperature than individual PCM and air cooling systems, moreover, among the hybrid cooling systems, the novel PCM-WMCP exhibited 2 K lower maximum battery temperature than PCM-SMCP (straight microchannel cooling plate) type at 1C, and increased potential in utilizing PCM for heat dissipation. The PCM was further modified to composite PCM (CPCM) by adding expanded graphite, which was found to realize a further lower maximum battery temperature and more uniform battery temperature field, with graphite mass fraction of 10 %. Besides, facing thermal runaway, the CPCM-WMCP cooling system showed a better temperature control ability compared to CPCM-SMCP, with temperature suppressed to below 318 K, and the maximum temperature difference at about 1.6 K.

Modeling of Metal Matrix Concentrated Solar Receivers for sCO2 Power Blocks

Abstract Supercritical CO2 power blocks for Concentrating Solar Power (CSP) with novel metal matrix solar receivers have the potential to reduce operating expenses while improving overall system efficiencies. These concentrated solar receivers integrated with a metal matrix-based phase change (PCM) thermal storage medium provide the compounding effect of an efficient heat exchanger while also integrating thermal storage within the receiver. Detailed numerical modeling of such devices with enthalpy-porosity-based formulation for phase change and turbulent convective heat transfer for the sCO2 microchannels is described in the current work. With sCO2 power blocks operating at temperatures and pressures beyond 800°C and 200 bar, different high-temperature PCMs are studied. A detailed steady charging followed by discharge and charging transients is simulated to analyze the thermal performance of these devices. In the current work, the energy storage density of PCMs is studied, followed by an analysis of the movement of the melt-pool interface over the streamwise length of a high corrugation wavy microchannel. A scaling analysis is carried out to estimate the heat transfer coefficients while compare them with the numerical model predictions. The results from the current work can be utilized for sizing and detailed design of integrated solar receivers for high-temperature sCO2 power block applications.

Simulation study of flow and heat transfer in wavy microchannel heat sink with manifolds and secondary channels composite

With the continuous increase in power density of electronic devices, traditional cooling methods have gradually shown their limitations. Microchannel heat sinks (MCHSs) have enormous potential in thermal management for electronic devices due to their excellent heat dissipation performance. To improve the flow and heat transfer performance of MCHSs, a numerical study was conducted on 56 types of wavy microchannel heat sinks with manifolds and secondary channels composite (WMCHS-MSCs). The results indicate that compared to the original manifold wavy microchannel heat sink (MWMCHS), the optimal WMCHS-MSC increases the thermal enhancement factor by 45.1 % when the inlet volume flow rate Q = 1.0 × 10−6 m³/s. At the same time, the overall thermal resistance, the maximum temperature difference on the bottom wall, and the pressure drop of the optimal WMCHS-MSC are reduced by 7.6 %, 21.9 %, and 10.6 %, respectively. Compared to the original MWMCHS, the increase in Q for WMCHS-MSCs results in an overall trend of increased thermal performance, decreased temperature non-uniformity and hydraulic performance, and initially increased and then decreased overall performance. The flow field distribution of the secondary channels of WMCHS-MSCs intuitively demonstrates the improved hydraulic and thermal performance brought about by disrupting the thermal boundary layer and mixing the flow. The study presents a novel approach for the design of wavy MCHSs, potentially paving the way for enhanced thermal management solutions in electronic devices.

Comparative study of two-phase flow approaches for modeling conjugate heat transfer in a three-dimensional wavy microchannel-heat sink with CuO-water nanofluid

This study aims to numerically investigate the conjugate heat transfer (CHT) and the changes in the hydraulic and thermal terms of laminar flow (300 ≤ Re ≤ 800) in a 3-D wavy microchannel heat sink (MCHS). The obtained results from different nanofluid flow simulated models will be compared. The numerical simulation approaches used include single-phase, mixture, Eulerian, DPM, and DDPM. The effect of adding 1%, 3%, and 6% concentration of CuO nanoparticles (100 nm) in deionized water as the base fluid is examined on various parameters such as local and axial temperature, heat transfer convective coefficient, friction factor, Nusselt number (Nu), velocity distribution, and thermal and hydraulic boundary layer parameters. The substrate surface, due to its larger area surface and the amplitude of the sinusoidal wave, has a greater impact on the nanofluid flow as a channel bottom conjugate surface compared to others. The results obtained from the different models show close agreement with each other for various cases. For example, at Re = 304, the average Nu and friction factor for pure water are approximately 10.43 and 0.0260, respectively. For water with 0.01 concentration of CuO nanoparticles, Nu is found to be in the range of 10.43–10.78, and the friction factor ranges from 0.260 to 0.290, depending on the approach used for simulation. This shows a 2% increase in Nusselt number compared to a 0.05% increase in the friction factor. Moreover, these values increase by approximately 5.7% and 11.3% on average with an increase in CuO nanoparticle concentration to 0.06. Additionally, the DPM and DDPM models show a 15% difference in the scattering of CuO nanoparticles compared to the Eulerian-Eulerian models. The single-phase model presented in this study yields similar results to the multiphase approaches. Furthermore, the PEC parameter increases by about 1.9% with the addition of CuO nanoparticles at a concentration of 0.06.

Effect of Wire-EDM textures on corrosion performance of Bio-Degradable Mg alloy

Magnesium (Mg) is the most suitable material for biodegradable implant applications owing to its nontoxic behaviour and comparable Young’s modulus to human bone. However, poor corrosion resistance limits its application. Therefore, surface texturing can be a more suitable and cost-effective technique to mitigate these issues. Hence, wire electric discharge machining (WEDM) is used to create various textures (wavy texture, microchannels, and micro-pillars) and investigate their influence on the corrosion resistance of Mg-Zn-Ca alloy. The results revealed that micropillar texture exhibited significantly lower surface roughness (Ra = 1.049 µm) and a higher contact angle indicative of hydrophobicity (130.3°), resulting in superior corrosion resistance (corrosion rate: 0.816 mm/year) compared to other textures and standard WEDM surfaces. These findings suggested that textured surfaces generated through WEDM hold the potential for enhancing the corrosion resistance of biodegradable Mg implants.

Surface charge-dependent slip length modulates electroosmotic mixing in a wavy micromixer

This study explores electroosmotic mixing in microfluidic channel with predefined surface topology, mainly focusing the effect of surface charge-dependent slip length on the underlying mixing dynamics. Our analysis addresses the need for precise control of flow and mixing of the participating fluids at microscale, crucial for medical and biomedical applications. In the present work, we consider a wavy microchannel with non-uniform surface charge to explore the electroosmotic mixing behavior. To this end, adopting a finite-element approach, we numerically solve the Laplace, Poisson–Boltzmann, convection–diffusion, and the Navier–Stokes equations in a steady-state. The model is validated by comparing the results with the available theoretical and experimental data. Through numerical simulations, the study analyzes electroosmotic flow patterns in microchannels, highlighting the impact of surface charge-dependent slip lengths on mixing efficiency. For example, at a diffusive Peclet number of 200, mixing efficiency drops from 95.5% to 91.5% when considering surface charge-dependent slip length. It is established that the fluid rheology, characterized by Carreau number and flow behavior index, non-trivially influences flow field modulation and mixing efficiency. Increased Carreau numbers enhance flow velocity, affecting overall mixing of the constituent fluids in the chosen fluidic pathway. For instance, by increasing the Carreau number from 0.01 to 1.0, a discernible trend emerges with higher flow line density and accelerated velocity within the microchannel. The study also examines the effect of diffusive Peclet numbers on the mixing efficiency, particularly in the convective regime of underlying transport. These insights offer practical guidance for designing microfluidic systems intended for enhanced mixing capabilities. Additionally, the study explores the likelihood of particle aggregation under shear forces, vital in biological non-Newtonian fluids, with implications for drug delivery, diagnostics, and biomedical technologies.

Thermo‐hydraulic analysis of wavy microchannel heat sinks with porous fins based on field synergy principle

AbstractIn order to enlarge the area and intensity of convective heat transfer among the coolant and heated surface, the vertical fins of microchannel heat sinks (MCHSs) with microencapsulated phase change material slurry (MPCMS) as coolant are arranged into wavy porous channels to realize more heat being dissipated to the outside. The phase transition of microencapsulated particles in laminar flow state is described, and the Brinkman–Forchheimer–Darcy model based on volume average approach and the energy equation for local heat equilibrium are adopted to portray flow and heat transfer in porous medium. The impacts of geometrical parameters on flow and heat transfer behaviour of wavy porous MCHS are numerically analyzed, and performance evaluation factor (PEF) is defined to estimate the thermo‐hydraulic capability of heat exchanger. The numeric outcomes match well with the experiments. Results indicate that MPCMS has a significant heat transfer improvement in the newly designed channel configuration compared with the coolant fluid flowing in the straight microchannel. Based on field synergy principle, the comprehensive capability enhancement mechanism of MPCMS in new MCHS is explored, and its superior thermal performance can be attributed to the improvement of the synergistic degree among flow and temperature fields, and its reasonable structural design can effectively improve the heat rejection capacity in the limited space.

Evaluation of the mixing index in a micromixer of side feeds in a conical chamber

This study delves into the investigation of mixing efficiency in microdevices by augmenting angular momentum within a truncated cone-shaped micromixer through side-feedings. While microchannel flows are typically dominated by molecular transport, characterized by parallel streamlines, this hinders rapid responses in mixing quality. To address this, we evaluate a micromixer featuring side-feedings coupled to a 2D truncated cone, followed by a wavy microchannel. The research assesses the impact of feed arrangement in the entrance section, Reynolds number (Re), and the curvatures of bumps in the wavy microchannel. Symmetrical lateral feeds promote homogeneous mixing in the inlet section where streamlines intersect. At the device outlet, all bump curvatures contribute to a mixing index exceeding 0.90 within a Reynolds number range of 20 to 40. Additionally, lower Reynolds numbers (Re = 0.1) yield a mixing index above 0.90, but with a slower and predominantly diffusive flow. Notably, a sharper curvature geometry results in smaller pressure drops while maintaining a comparable mixing index to other geometries, indicating it as a promising choice for bump curvature.

The influence of micro-channel shape filled by nanofluid on heat transfer characteristics: Numerical and experimental study

The integration of nanofluid effects and channel shape effects in a heat sink, which exhibits both variable and constant cross-section, has gained significant traction as an efficient cooling method for thermal devices, particularly microelectronic devices. This research presents an experimental and numerical analysis to compare the performance of microchannel heat sink designs (straight, zigzag, wavy, and circular cavities). In addition, the study dealt with the use of pure water and nanofluid (CuO-H2O) with volumetric concentrations of (0.01, 0.02, and 0.03) as coolants. COMSOL Multiphysics was used for numerical analysis to simulate and solve the problem of fluid and heat flow in 3D. The bottom wall of the four microchannels is subjected to a steady heat flux of 170 kW/m2. The simulations were only performed within the laminar domain, encompassing a spectrum of Reynolds numbers ranging from 50 to 150. The influence on the microchannel's wall temperature, thermal resistance, pressure drop, and friction factor is exhibited. According to the findings, the wavy and zigzag microchannel heat sink cooled by nanofluid displays higher performance in terms of heat transmission and dissipation in comparison to the heat sink that was cooled by distilled water. as evidenced by a 12% increase in mussel number at volume concentrations of 0.03%.

Thermal analysis and structure optimization of wavy microchannel with combining ribs of porous layer and solid wall in multi objective genetic algorithm

The combining rib of porous layer and solid wall is set in wavy microchannel heat sink to enlarge heat transfer area and convection with smaller increase in flow resistance, in which the consumption of pump power relates to the ratios of wave amplitude to length or to width and the thickness of porous layer due to vortices generation while coolant passing through channel. The local thermal equilibrium occurs in porous layer, and the Forchheimer-Brinkman-Darcy relations were used to describe the flow inside porous ribs. The effects of channel-to-pitch width ratio, width ratio of porous layer to pitch and microchannel height on its cooling performance are investigated, and the parameter of figure of merit (FOM) is defined to evaluate thermo-hydraulic performance in wavy microchannel. Besides, the multi objective genetic algorithm method is employed to optimize structure parameters in wavy microchannel to obtain better performances, in which the increase in thermal resistance from 0.062 K/W to 0.166 K/W together with consumption of pump power decreasing from 0.00416 W to 0.00185 W can be obtained in the Pareto front set, and it relates to the heat dissipation in convection between coolant and bottom surface or vertical side ribs. Compared to wavy microchannel with solid rib, the 37.61% and 16.67% decreases respectively in thermal resistance and consumption of pump power occur in the case with optimal combining rib of porous layer and solid wall.

An In-Depth Comparison of Straight and Wavy Microchannel Heat Exchangers

Abstract This paper presents extensive fluid flow and Heat-Transfer studies conducted using a commercial computational fluid dynamics (CFD) package known as CFD-ACE® to elaborate and expand on the reference studies available for ceramic-compact counterflow microchannel heat exchangers (MCHEs). The computational 3D model was developed using an experimentally tested MCHE and validated with experimental data with 3–5% variation for hot fluid and 6–12% variation for cold fluid for the entire design of experiments (DoEs). This study aimed to identify the performance of novel microchannel shapes using numerical analysis. The MCHE has good heat exchange properties, a compact design at industrial throughput, and a lower inner volume. During the study and identification of novel channel shapes, the segmented wavy MCHE was evaluated. The results were compared with those of the same volume and area straight MCHE baseline design under various identical operating conditions. Although the performance in terms of effectiveness is increased up to ∼12–25% in wavy MCHE with respect to straight MCHE simultaneously, the pressure drop is also increased by ∼60–80% under the same operating conditions. Therefore, performance and trade-offs are required to make the correct decision regarding feasibility. The effectiveness of the heat-transfer enhancement was also evaluated by plotting the heat-transfer coefficient ratio with respect to the pressure ratio of the two designs under identical operating conditions. This numerical study clearly indicates that wavy channels are better from the thermal performance point of view, whereas straight channels are better from the pumping power point of view, and the quantitative values are presented in graphical form.

An Experimental and Numerical Study of the Effect of Microchannels Geometry on Heat Transfer of Nanofluids

The use of micro-channel heat exchangers is widespread across a variety of different industrial sectors. This study presents both an experimental and a numerical analysis to compare the performance of four different designs of microchannel heat sinks. The study dealt with using pure water and nanofluid (Al2O3, CuO, and TiO2–H2O) with volumetric concentrations of (0.01- 0.03) as coolants. The software Comsol Multiphysics was employed for conducting numerical analysis in order to simulate and resolve the issue pertaining to fluid and heat flow in a three-dimensional domain. A constant heat flux of 170 kW/m2 is applied to the lower wall of the four microchannels. The simulations were exclusively conducted within the laminar regime, covering a range of Reynolds numbers spanning from 50 to 150. The impact on the temperature of the microchannel's wall, thermal resistance, pressure drop, and friction factor is demonstrated. Based on the results obtained, it is evident that the utilization of nanofluid in the cooling process of a wavy and zigzag microchannel heat sink yields superior performance in terms of both heat transfer and dissipation, as compared to the implementation of pure water as the cooling medium for the heat sink.

Thermal performance improvement in wavy microchannels using secondary channels

PurposeThis study aims to minimize the pressure drop across wavy microchannels using secondary branches without compromising its capacity to transfer the heat. The impact of secondary flows on the pressure drop and heat transfer capabilities at different Reynolds numbers are investigated numerically for different wavy microchannels. Finally, different channels are evaluated using performance evaluation criteria to determine their effectiveness.Design/methodology/approachTo investigate the flow and heat transfer capabilities in wavy microchannels having secondary branches, a 3D conjugate heat transfer model based on finite volume method is used. In conventional wavy microchannel, secondary branches are introduced at crest and trough locations. For the numerical simulation, a single symmetrical channel is used to minimize computational time and resources and the flow within the channels remains single-phase and laminar.FindingsThe findings indicate that the suggested secondary channels notably improve heat transfer and decrease pressure drop within the channels. At lower flow rates, the secondary channels demonstrate superior performance in terms of heat transfer. However, the performance declines as the flow rate increased. With the same amplitude and wavelength, the introduction of secondary channels reduces the pressure drop compared with conventional wavy channels. Due to the presence of secondary channels, the flow splits from the main channel, and part of the core flow gets diverted into the secondary channel as the flow takes the path of minimum resistance. Due to this flow split, the core velocity is reduced. An increase in flow area helps in reducing pressure drop.Practical implicationsMany complex and intricate microchannels are proposed by the researchers to augment heat dissipation. There are challenges in the fabrication of microchannels, such as surface finish and achieving the required dimensions. However, due to the recent developments in metal additive manufacturing and microfabrication techniques, the complex shapes proposed in this paper are feasible to fabricate.Originality/valueWavy channels are widely used in heat transfer and micro-fluidics applications. The proposed wavy microchannels with secondary channels are different when compared to conventional wavy channels and can be used practically to solve thermal challenges. They help achieve a lower pressure drop in wavy microchannels without compromising heat transfer performance.

Thermo-capillarity of immiscible binary fluids within serpentine micro-confinements

The thermocapillary flow of multiple liquid layers over contoured substrates finds applications in many industrial phenomena via micro-electromechanical systems/nano-electromechanical systems devices. This study theoretically explores the thermocapillary transport of binary-liquid layers in a wavy microchannel with serpentine wall profiles. Sinusoidal profiles are considered for the microchannel walls' temperature and surface topology. Patterned slip conditions at the walls are also accounted for in the analysis to make the problem more realistic. We semi-analytically solve the energy and momentum equations to understand the system's thermal and hydrodynamic characteristics for the limiting conditions of Ma, Re, and Ca. The leading- and higher-order solutions of the temperature and flow field are separately shown to demonstrate the advection terms' contribution to the transport equations. The circulatory flow obtained due to periodic thermal stimuli can be used to enhance the mixing efficiency of the system. We also present how the parameters like phase difference between the thermal stimulus, relative thermal conductivity, and relative film thickness ratio of the liquid layers can be altered to control the flow characteristics to obtain the most potent thermocapillary effect.

Numerical investigation of fluid flow and heat transfer within multilayer wavy microchannels

Numerical investigation of fluid flow and heat transfer within multilayer wavy microchannels

Heat Transfer of Air-Water Flow in Wavy Microchannels

Effective cooling of the electronic devices is of great importance to their performance. Of particular interest is when the size of the equipment has scaled down to micro level. Despite a continuous improvement over the years, there is only a handful information on gas-liquid flow in wavy microchannels. This paper presents an experimental study of the air-water two-phase flow in a wavy microchannels heatsink typically used for cooling of electronic devices. The heatsink was made from copper with 26 wavy channels. The width and the depth of each channel were 800 and 500 μm, respectively. Two cartridge heaters were used to generate a constant heat flux. Pressure and temperatures of the working fluid at the inlet and outlet of the test section were measured using a pressure transducer and thermocouples. To evaluate the benefit of using the wavy microchannels, experiment was performed using water as the working fluid. The results showed that the wavy microchannels could elevate the Nusselt number by up to 112% compared to that obtained from the straight microchannels. Experiments at various air and water flowrates in the wavy microchannels suggested that the advantages of using the air-water flow would be obvious at the liquid Reynolds number above 379.

Thermal management of an asymmetrical wavy microchannel heat sink via Ag/water nanofluid

The ever-increasing demand for electronic systems to enhance their performance and processing speed has exponentially increased their heat generation, especially those containing microstructures with reduced surface area. Tackling these complex thermal management challenges creates an urgent need to design and model compact efficient cooling systems. In this investigation, a unique design of a microchannel heat sink with sinusoidal and absolute sinusoidal wavy walls with/without nanofluid is proposed. Heat transfer enhancement and fluid flow characteristics are numerically investigated by developing a two-dimensional finite element model for Reynolds numbers 5, 100, and 500. The periodicity of the wavy section and the different volume fractions of silver nanoparticles ranging from 0 to 4% in water are further considered. The entropy generation is analyzed using the Bejan number. The findings revealed that while the entropy generation rises in the absolute sinusoidal channel, it has a better heat transfer performance by 10.3%, 15.8%, and 16.6% than a straight microchannel for the ascending Reynolds numbers. Interestingly, the channel's heat transfer and thermal efficiency decrease when an unnecessary number of sinusoidal periods are used. The thermal efficiency improves by 3.35% compared to the straight microchannel by employing only one absolute sinusoidal wavelength along the channel.