Multilayer Microchannel Research Articles

Experimental investigation on the discharge and suction gas performance in the multilayer insulation microchannels

The use of cryogenic propellants is prioritized for powering Mars lander propulsion systems. To provide thermal protection for these cryogenic propellants, a combination of multilayer insulation (MLI) and foam is commonly employed. However, during the Mars lander ascent, space travel, and reentry, unique phenomena such as transient venting and suction of gas occur within the MLI, significantly compromising its insulation performance. In the current study, an experimental platform was developed to investigate the discharge and suction of rarefied gas in MLI microchannels. Based on the perforation MLI results, the residual gas pressure in the innermost layer reaches below 10 Pa after over 100 h of evacuation. Baked MLI exhibits favorable discharge gas performance, with an average pressure value (the sum of the interstitial pressure in MLI divided by the total number of layers) 30.85% lower than that of the original MLI. Evacuation rates are improved by 11.87% when the MLI is flushed with nitrogen (N2). The baking condition does not significantly affect suction gas properties. The thermal conductivity of residual helium (He) is much higher than that of air and N2. These findings offer valuable insights for the design of cryogenic propellant tanks, aiding in optimizing their insulation performance.

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

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

Numerical investigation of a hybrid double layer microchannel heat sink with jet impingement

This study investigates numerically, with experimental verification, the performance of a hybrid multilayer microchannel heat sink with jet impingement. The three-dimensional fluid flow and heat transfer processes were solved using the finite volume method using Fluent CFD Solver. The surface temperature distribution and pressure drop across the system were monitored under a range of designs and operating conditions including different flow rates, channel aspect ratios, jet spacings, and distribution of the flow rate between the jets and the channels. Our results show that increasing the number of jets minimizes the pressure drop, yet, results in higher surface temperatures. Increasing channel height decreased the pressure drop and enhanced the temperature uniformity. Using a double-layer heat sink instead of a single-layer one resulted in a decrease of 7.5% in surface temperature with a considerable reduction in pressure drop. Nevertheless, adding copper fins/posts in the lower channel layer is essential to help conduct the heat to the top layer and improve the heat removal rate. We also studied dividing the total flow rate between the jets and the main cooling channel and found that it can reduce the average temperature on the hot surface even though it did not improve the temperature uniformity. We verified our simulation results with experimental measurement for a single-layer hybrid heat sink with jet impingement and results matched with a temperature difference below 5 °C. Based on our simulations, the DL-hybrid module can remove high heat fluxes while maintaining an acceptable pressure drop.

Optimization analysis of multi-layered microchannel heat sink

Microchannel heat sinks with a large specific surface area are widely applied to the heat dissipation of microelectronic devices. In this work, a multi-layered microchannel heat sink with a size of was proposed based on the microchannel of the Printed Circuit Heat Exchanger (PCHE). The thermal resistance network model was established for the multi-layered heat sink with a semi-circular cross-section microchannel. Then, the Genetic Algorithm(GA) was employed to optimize the structure and operation parameters of the heat sink based on the thermal resistance network model. The optimized parameters and the corresponding thermal resistance under various power consumption were obtained. The optimization results show that the thermal resistance decreases rapidly with the increase of power consumption. When the power consumption is large, the trend of thermal resistance reduction is gradually flat. When the power consumption increases to 0.8 W, the optimal value of channel layers is up to 12, and the thermal resistance of the heat sink is 0.322 °C/(W/cm2). As the power consumption further increases from 0.8 W, the optimal value of layers remains constant at 12, and the ratio of the channel radius to the plate thickness remains at about 0.56. Three-dimensional numerical simulation is performed to verify the thermal resistance network model, and the results of the thermal network model agree well with the simulation.

不同直径和流量对层叠式微通道散热器热性能的影响研究

不同直径和流量对层叠式微通道散热器热性能的影响研究

Thermal Performance Optimization of the Three-Dimensional Integrated Circuits Employing the Integrated Chip-Size Double-Layer or Multi-Layer Microchannels

Abstract The chip-size integrated double-layer microchannels (DLMCs) and multilayer microchannels (MLMCs) are investigated to optimize the thermal performance of three-dimensional integrated circuits (3D ICs). The chip-size integrated DLMCs without a heat spreader and a heat sink reduce the hotspot temperature by almost 15 K for a nominal 3D IC structure. Meanwhile, the size is significantly smaller than the copper heat sinks, and the weight of the chip-size integrated DLMC is reduced by 99.9%. Furthermore, two chip-size integrated DLMCs lower the hotspot temperature by another 6.77 K compared with utilizing just one integrated DLMC on top of the chip structure. The results also show that the MLMCs have a great effect on reducing the hotspot temperature. We have established that the optimal layout is four layers. The hotspot temperature is reduced by 21 K and 102 times lighter in weight compared to nominal 3D IC structure. The proposed structure and results presented in this study pave the way for major innovations in resolving the thermal issues for the 3D ICs.

Engineering a monolithic 3D paper-based analytical device (μPAD) by stereolithography 3D printing and sequential digital masks for efficient 3D mixing and dopamine detection

Stereolithography 3D printing and digital masks in sequence are used herein to manufacture 3D µPAD in a monolithic layer of paper within 1 s. Multiple experiments were systematically conducted to further understand the fundamentals and limitation of this manufacturing process, and a novel 3D mixer and a fluorescent chemosensor assay used to determine dopamine concentration at high-alkaline pH conditions were successfully demonstrated. Experiment results showed: (1) the 3D mixer is superior than conventional 2D mixer regarding mixing performance and repeatability, (2) dopamine detection and pH indicator can be realized with fewer operation steps and shorter processing time, (3) a truly 3D µPAD, including multilayer microchannels within a monolithic paper substrate, can be created with fewer reagent loss and higher transportation efficiency, (4) a smallest microchannel, 100 µm wide microchannel, can be successfully created on µPAD. These results clearly proved that this proposed 3D µPAD is not only a novel format of µPAD, but it can also simplify the operation steps for an analytical assay while improving the mixing phenomenon via 3D mixer and using minimum sample volume. • Using SLA 3D printing and multiple digital masks to manufacture monolithic 3D µPAD. • 3D mixer is superior than 2D mixer regarding mixing performance and repeatability. • A truly 3D µPAD can result fewer reagent loss and higher transportation efficiency. • Dopamine detection and pH indicator can be realized with fewer operation steps. • A smallest microchannel, 100 µm wide microchannel, was successfully created.

Research on coupling performance of heat transfer and throttling of microchannel J-T effect cryocoolers

• Printed Circuit Board (PCB) technology is applied to the J-T cryocooler. • The steady-state model for J-T cryocooler is developed and verified. • The coupling performance of heat transfer and throttling in cryocooler is analyzed. • A new parameter η jt is proposed to evaluate the utilization rate of J-T effect. To solve the shortcomings of small cooling capacity of the current Joule-Thomson (J-T) cryocooler, a multi-layer microchannel J-T cryocooler is designed and fabricated by printed circuit board technology. The characteristic of the cryocooler is that there exists heat transfer while throttling. The coupling effect of heat transfer and throttling affects the overall performance of cryocooler. Therefore, the steady-state model was established for each part of the cryocooler. The P-h diagram of N 2 was calculated by the model. Considering the variation of J-T coefficient ( μ jt ) in the process, the coupling performance of heat transfer and throttling in the J-T cryocooler were analyzed. A new parameter, J-T efficiency ( η jt ), was proposed to evaluate the J-T effect. Additionally, according to the dependence of μ jt with temperature and pressure, the refrigeration performance of the cryocooler under different working conditions was simulated. The results show that the heat transfer in the throttle can enhance the throttling effect. When the inlet temperature is 285.0 K and the inlet pressure increases to 18.00 MPa, the N 2 temperature at the cold end reaches 116.3 K, and the gross cooling capacity is 4.55 W. When the inlet pressure is 6.00 MPa and the inlet temperature reduces to 195.0 K, the temperature at the cold end can reach to the saturated temperature of 103.2 K, and the maximum gross cooling capacity is 7.68 W. For the two groups of working conditions, the heat transfer in the throttle can enhance the J-T effect. η jt reaches 95.87% and 94.76%, the proportion of temperature drop caused by J-T effect is 56.10% and 68.03% of the total temperature drops, respectively. Finally, the variation laws of inlet temperature and η jt are analyzed when N 2 reaches saturated temperature under different pressures to guide the selection of inlet parameters.

Analytical Study of the Electroosmotic Flow of Two Immiscible Power-Law Fluids in a Microchannel

The multilayer microchannel flow is a promising tool in microchannel-based systems such as hybrid microfluidics. To assist in the efficient design of two-liquid pumping system, a two-fluid electroosmotic flow of immiscible power-law fluids through a microtube is studied with consideration of zeta potential difference near the two-liquid interface. The modified Cauchy momentum equation in cylindrical coordinate governing the two-liquid velocity distributions is solved where both peripheral and inner liquids are represented by power-law model. The two-fluid velocity distribution under the combined interaction of power-law rheological effect and circular wall effect is evaluated at different viscosities and different electroosmotic characters of inner and peripheral power-law fluids. The velocity of inner flow is a function of the viscosities, electric properties and electroosmotic characters of two power-law fluids, while the peripheral flow is majorly influenced by the viscosity, electric property and electroosmotic characters of peripheral fluid. Irrespective of the configuration manner of power-law fluids, the shear thinning fluid is more sensitive to the change of other parameters.

Experimental and numerical analysis of the multilayer distributed Joule‐Thomson cooler with pillars

SummaryThe conventional Joule‐Thomson cooler is not compact in heat exchanger and insufficient in cooling capacity, which is limited in applying integrated electronics. However, microchannels with pillars are effective in increasing the area to volume ratio and enhancing heat transfer through the presence of vortex. Besides, multilayer microchannels are essential to enlarge the mass‐flow rate in the cooler. In this study, a multilayer distributed J‐T cooler with pillars is investigated. A new mathematical model of the cooler is developed and validated against the experimental data; the relative errors of the temperature and mass‐flow rate are both within 5%. Furthermore, the distribution of temperature and pressure in the microchannel is analyzed by the model calculation. Numerical results show that the temperature of the high‐pressure fluid decreased slightly under the influence of the heat exchange and distributed J‐T effect. When the inlet pressures are 3.00, 4.00 and 5.40 MPa, the cold‐end temperatures are 233.0, 185.8 and 161.2 K, respectively, with the cooling capacity reaching 2.25, 3.40 and 3.87 W, respectively. In addition, the influences of the axial heat conduction and heat leakage on the cooling performance are analyzed by using the models. The temperature rise of the cold end increases by 6.8 and 6.2 K at 5.40 MPa, respectively, considering the above two factors. The simulation model provides a useful tool for the J‐T cooler.

Effect of Channel Arrangement on the Thermal Hydraulic Performance of Multilayer Microchannel Arrays

Thermal hydraulic performance of microchannel device is affected mainly by its geometrical parameter. The purpose of this study is to investigate the effect of multilayer microchannel arrangement to the thermal hydraulic performance of microchannel arrays. Numerical analysis was conducted to simulate three different microchannel arrangements by varying mass flow rate and heat flux imposed on the microchannel device. The simulation model is a simplified version which consists of eight microchannels in a single row and contains four layers for model one while model two has an arrangement of eight-seven-eight-seven microchannels in four layers and model three has an arrangement of seven-eight-seven-eight microchannels in four layers. The boundary condition that was set for heat flux ranged between 200 W/cm2 to 1000 W/cm2 while mass flow rate that flow into the device was varied between 20 kg/h to 80 kg/h. From the simulation result, it is shown that certain arrangement of microchannel in multilayer channels contribute to the enhancement of heat transfer and at the same time reducing the pressure drop of the system.

Numerical and Experimental Study on Mixing in Chaotic Micromixers with Crossing Structures

AbstractTwo chaotic micromixers (Models A and B) based on the split‐and‐recombine principle using multilayer microchannels are proposed and the mixing performance was analyzed numerically and experimentally for a wide range of Reynolds numbers. The fluid flow and mixing performance were numerically analyzed by solving Navier‐Stokes equations. Micromixers were fabricated using a soft‐lithography technique. As working fluids, water and a dye/water mixture were used. Quantitative and qualitative analyses were performed using confocal scanning microscopy and image processing techniques. The micromixers could enhance the mixing performance by expanding the interfaces between the working fluids to be mixed. The results confirm the superior mixing index of Model B compared to that of Model A.

Indoor and outdoor characterization of concentrating photovoltaic attached to multi-layered microchannel heat sink

Concentrating Photovoltaic technology is a promising option in power generation using the photovoltaics compared to the conventional flat PV system. This study investigates the performance of a high concentrated photovoltaic single solar cell module attached to a multi-layered microchannel heat sink. The system has been tested the first time experimentally both at indoor and outdoor conditions. The indoor characterization of the system investigated the effect of varying the number of the layers of the heat sink and the flow rate of the fluid electrically and thermally. The experiments show that varying the number of the heat sink layers from 1-layer to 3-layers increase the maximum electrical generation by 10% and reduces the cell temperature by 3.15 °C under the same fluid flow rate of 30 ml/min. The outdoor experiments show the maximum output electrical generation of the system of 4.60 W and the short circuit current of 1.96 A. The maximum solar cell temperature was maintained below 61 °C where the extracted heat of the system was 12.85 W which represents of 74.9% of the total generated power.

Multi-layering of SU-8 exhibits distinct geometrical transitions from circular to planarized profiles.

The negative tone photoresist SU-8 permits the creation of micrometer-scale structures by optical lithography. It is also the most used photoresist in soft lithography for the fast-prototyping of microfluidic devices. Despite its importance, the effect of capillary forces on SU-8 multi-layering onto topographical features has not been thoroughly studied. In particular, the profile of the added layer has not been examined in detail. The overlaying process exhibits a set of distinct behaviors, or regimes, depending on the relative thickness of the overlay and the underlying rectangular pattern. We demonstrate how capillary effects control the profile of multi-layer microchannels in a predictable manner. We derive a simple static model to describe the evolution of the overlay as a function of dimensionless geometric parameters. Our study provides a critical understanding of the parameters that govern multi-layer spin coating.

Experimental and Numerical Thermal Analysis of Multi-Layered Microchannel Heat Sink for Concentrating Photovoltaic Application

Concentrating photovoltaic has a major challenge due to the high temperature raised during the process which reduces the efficiency of the solar cell. A multi-layered microchannel heat sink technique is considered more efficient in terms of heat removal and pumping power among many other cooling techniques. Thus, in the current work, multi-layered microchannel heat sink is used for concentrating photovoltaic cooling. The thermal behavior of the system is experimentally and numerically investigated. The results show that in extreme heating load of 30 W/cm2 with heat transfer fluid flow rate of 30 mL/min, increasing the number of layers from one to four reduces the heat source temperature from 88.55 to 73.57 °C. In addition, the single layered MLM heat sink suffers from the highest non-uniformity in the heat source temperature compared to the heat sinks with the higher number of layers. Additionally, the results show that increasing the number of layers from one to four reduces the pressure drop from 162.79 to 32.75 Pa.

Secondary bonding of PMMA micromixer with high-pressure

This paper studies the process to fabricate a micromixer by bonding the PMMA sheets after CO2 laser processing microchannel. It has been widely used in analysis chemical and detection as its low cost. Chemical analysis chips are commonly produced using low-pressure bonding. The bonding strength of the micromixer is improved by secondary bonding with high-pressure, which can meet the requirements of the chemical analysis with higher flowing rate and higher pressure. The effects on the single-layer and multi-layer microchannels are compared with high-pressure and low-pressure bonding. The deformation of the width and height at low pressure and high pressure of the single-layer channel are 12.4 μm, 23.5 μm and 17.1 μm, 54.1 μm, respectively. The multi-layer channels are 43.44 μm, 23.7 μm and 78.1 μm, 27.7 μm. The influence on the height of the V-shaped microchannel is greater when the single-layer micromixer is performed with high-pressure bonding, and when multi-layer bonding with high-pressure, the effect on the width of the rectangular microchannel is obvious. In the process of secondary bonding and pressurization, the chip position can be appropriately adjusted to avoid deformation caused by uneven force on the chip during manual operation. Since high-pressure bonding has an effect on the shape of the microchannel, different bonding methods can be selected according to different requirements of the chemical analysis chips on microchannel quality and bonding strength.

Constructal Design of Circular Multilayer Microchannel Heat Sinks

Abstract Based on the constructal theory concepts, an investigation is carried out to optimize circular multilayer microchannels embedded inside a rectangular heat sink with different numbers of layers and flow configurations. The lower surface of the heat sink is uniformly heated, while both pressure drop and length of the microchannel are fixed. Also, the volume of the heat sink is kept fixed for all studied cases, while the effect of solid volume fraction is examined. All the dimensions of microchannel heat sinks are optimized in a way that the maximum temperature of the microchannel heat sink is minimized. The results emphasize that using triple-layer microchannel heat sink under optimal conditions reduces the maximum temperature about 10.3 °C compared to the single-layer arrangement. Further, employing counter flow configuration in double-layer microchannel improves its thermal performance, while this effect is less pronounced in the triple-layer architecture. In addition, it is revealed that the optimal design can be achieved when the upper channels of a multilayer microchannel heat sink have bigger diameters than the lower ones. Finally, it is observed while using two layers of microchannels is an effective means for cooling improvement, invoking more layers is far less effective and hence is not recommended.

Image Reconstruction Under Contact Impedance Effect in Micro Electrical Impedance Tomography Sensors.

Contact impedance has an important effect on micro electrical impedance tomography (EIT) sensors compared to conventional macro sensors. In the present work, a complex contact impedance effect ratio ξ is defined to quantitatively evaluate the effect of the contact impedance on the accuracy of the reconstructed images by micro EIT. Quality of the reconstructed image under various ξ is estimated by the phantom simulation to find the optimum algorithm. The generalized vector sampled pattern matching (GVSPM) method reveals the best image quality and the best tolerance to ξ. Moreover, the images of yeast cells sedimentary distribution in a multilayered microchannel are reconstructed by the GVSPM method under various mean magnitudes of contact impedance effect ratio |ξ|. The result shows that the best image quality that has the smallest voltage error UE = 0.581 is achieved with measurement frequency f = 1 MHz and mean magnitude |ξ| = 26. In addition, the reconstructed images of cells distribution become improper while f < 10 kHz and mean value of |ξ| > 2400.

Fabrication of 3D Microfluidic Channels and In‐Channel Features Using 3D Printed, Water‐Soluble Sacrificial Mold

AbstractRecent advent of additive manufacturing potentiates the fabrication of microchannels, albeit with limitations in resolution of printed structures, freedom of geometry, and choice of printable materials. Herein, a method is developed by sacrificial molding to fabricate microchannels in various polymer matrices and geometries. This method allows for rapid fabrication of 3D microchannels and channels harboring intricate in‐channel features. The method uses commercially available fused deposition modeling 3D printer and filament made of polyvinyl alcohol (PVA). Mechanically stable molds are fabricated for 3D microchannels that can be completely removed in water. Importantly, the PVA mold is stable and resilient in hydrogels despite being hygroscopic. Perfusion channels are fabricated in biocompatible substrates such as gelatin and poly(ethylene glycol) diacrylate. Fabrication of the network of 3D multilayer microchannels is demonstrated by preassembling sacrificial molds from modular pieces of molds. Intricate staggered‐herringbones grooves (SHGs) are also fabricated within microchannels to produce micromixers. The versatility and resilience of the method developed here is advantageous for biological and chemical applications that require 3D configurations of microchannels in various matrices, which would not be compatible with fabrication by direct 3D printing and softlithography.

High-voltage nanofluidic energy generator based on ion-concentration-gradients mimicking electric eels

Although rapid advances have been made in micro/nano-scale devices, there is still a lack of clean and sustainable power source for them. Here we propose a high voltage nanofluidic energy generator inspired by electrical eel using ion-concentration gradients, which converts Gibbs free energy into electricity without any pollutants. The high voltage can be induced by alternatively multi-stacking cation and anion-exchange nanochannel network membranes (CE-NCNMs and AE-NCNMs) in a confined microscale space. These membranes were constructed by in situ self-assembled nanoparticles with hydroxyl and amine groups, respectively. The multiple stacks of CE-NCNMs & AE-NCNMs were successfully realized by precisely guiding the nanodrops with the suspended positively or negatively charged nanoparticles into the desired positions in the multilayered microchannel platform. The performance of the proposed nanofluidic energy generator was quantitatively investigated by changing nanoparticle species, intermembrane distance (IMD), and environmental temperature. Interestingly, we found that our optimized IMD (~80µm) is very similar to the inter-cell membrane distance of electrocytes in natural electric eels and the diffusion potential of a single full cell at this IMD (~138mV) is also similar to the net potential across a single electrocyte (~150mV). This optimized IMD is verified through not only electrical measurement but also by fluorescent tracing and numerical analysis using multiphysics simulation. The high voltage of up to 1 V achieved by stacking 20 full cells is, to the authors’ knowledge, the highest value yet obtained by microfluidic systems harnessing ion-concentration gradients.