Liquid Microchannel Research Articles

Controlling gas–liquid segment length in microchannels using a high-speed valve

Segmented flow, one of the most important flow patterns in microchannels, has been widely employed in gas–liquid microreactor systems because it enhances mass transfer through the biphasic interface. The segment length is determined by the channel parameters (e.g., size, material type), fluid flow rate, and fluid properties. Thus, it is difficult to manipulate the gas–liquid segment length without affecting the residence time of the fluid. In this work we successfully achieved regularly segment length control by introducing a high-speed valve into a gas–liquid microchannel system while varying the frequency of the valve installed in the gas-phase tube to allow gas and liquid segment lengths to be controlled within a large range. In contrast, the segment lengths were almost constant under the same conditions without the high-speed valve. Furthermore, a gas/liquid flow rate ratio in the range of 0.7–1.2 was deemed necessary for steady segmented flow. Finally, a correlation was proposed to predict the segment length using parameters such as valve frequency and fluid flow rate, and it matched the experimental data well. This segment length control strategy will improve the performance of gas–liquid reactions in microreactors and advance the design of microreactor systems.

Design of Flexible Pressure Sensor Applied to Mechanical Gripper

Flexible electronic devices have emerged as a novel and popular research direction in the field of artificial intelligence, in which flexible sensor is an indispensable branch of flexible devices. In this article, a flexible pressure sensor is developed based on a liquid metal microchannel, which has the advantages of convenient measurement and easy integration. The sensor adopts Dragon skin 20 as the sensor matrix and Ga-In-Sn alloy as the conductive liquid. Meanwhile, there are two kinds of sensor structures are introduced which are the sensor only has a sensing layer and the sensor with an amplification layer. Through comparison of mechanical simulation models, the results suggest that adding the amplification layer structure can make the channel deformation more obvious, and the resistance change will be larger under the identical pressure, which indicating that adding amplification layer can effectively improve the sensitivity of sensor. We further demonstrate the basic characteristics of the sensor, and finally, it is proved by experiments that it can be installed on the mechanical gripper used to sense the pressure. This indicates that the flexible pressure sensor has relatively high sensitivity and the resistance value of sensor can well change with the size of pressure, which also indicates that the flexible pressure sensor has the possibility of applying in orchard manipulator picking for grasping force sensing to prevent peel breakage.

Research on Intelligent Distribution of Liquid Flow Rate in Embedded Channels for Cooling 3D Multi-Core Chips.

A numerical simulation model of embedded liquid microchannels for cooling 3D multi-core chips is established. For the thermal management problem when the operating power of a chip changes dynamically, an intelligent method combining BP neural network and genetic algorithm is used for distribution optimization of coolant flow under the condition with a fixed total mass flow rate. Firstly, a sample point dataset containing temperature field information is obtained by numerical calculation of convective heat transfer, and the constructed BP neural network is trained using these data. The “working condition–flow distribution–temperature” mapping relationship is predicted by the BP neural network. The genetic algorithm is further used to optimize the optimal flow distribution strategy to adapt to the dynamic change of power. Compared with the commonly used uniform flow distribution method, the intelligently optimized nonuniform flow distribution method can further reduce the temperature of the chip and improve the temperature uniformity of the chip.

Liquid Cooled Microchannel Heat Sink Based Peltier Solar Atmospheric Water Generator

To maintain the high RH value near dry air vent, increase the efficiency of Peltier with proper ventilation that is to make the heat escape easily, to provide more surface area for heat sink to cool down the air more effectively. Mass of the body is reduced, and durability is improved. RH value is maintained with the help of dry air vent. We can get benefits from a liquid cooled micro channeled heat sink which needs only a little space. It is suitable for the high flux heat dissipation and also gives a better result compared to generic convection method. It is used without reacting with the body frame. It is portable with help of 12V DC solar 10W. This system solves water scarcity in rural areas. We can especially use at hill stations as the humid conditions are the best.

Open-channel microfluidics via resonant wireless power transfer

Open-channel microfluidics enables precise positioning and confinement of liquid volume to interface with tightly integrated optics, sensors, and circuit elements. Active actuation via electric fields can offer a reduced footprint compared to passive microfluidic ensembles and removes the burden of intricate mechanical assembly of enclosed systems. Typical systems actuate via manipulating surface wettability (i.e., electrowetting), which can render low-voltage but forfeits open-microchannel confinement. The dielectric polarization force is an alternative which can generate open liquid microchannels (sub-100 µm) but requires large operating voltages (50–200 VRMS) and low conductivity solutions. Here we show actuation of microchannels as narrow as 1 µm using voltages as low as 0.5 VRMS for both deionized water and physiological buffer. This was achieved using resonant, nanoscale focusing of radio frequency power and an electrode geometry designed to abate surface tension. We demonstrate practical fluidic applications including open mixing, lateral-flow protein labeling, filtration, and viral transport for infrared biosensing—known to suffer strong absorption losses from enclosed channel material and water. This tube-free system is coupled with resonant wireless power transfer to remove all obstructing hardware — ideal for high-numerical-aperture microscopy. Wireless, smartphone-driven fluidics is presented to fully showcase the practical application of this technology.

Design and Optimization of a Novel Microchannel Battery Thermal Management System Based on Digital Twin

In order to avoid high-temperature and large rate discharge impact on the performance of battery modules, a microchannel liquid cooling battery thermal management system (BTMS) and BTMS virtual model of the microchannel structure based on digital twin (DT) is proposed. On the basis of accurate virtual simulation model, the computational fluid dynamics (CFD) model and the Gaussian process regression algorithm were combined to drive the optimization process in order to improve the cooling capacity of the system. The results show that the microchannel plates can greatly enhance the cooling capacity of the direct cooling system and effectively improve the uniformity of the coolant. The width of the microchannel plates and the side spacing actually represent the amount of coolant flowing through the inside and outside of the battery module, which significantly impacts the maximum temperature and maximum temperature difference. Increasing the coolant flow can only effectively improve the cooling capacity of the module to a limited extent. Gaussian process regression based on the DT virtual model is more suitable for analyzing the interaction between multiple factors and obtaining global optimization results. After optimization, the maximum temperature and the maximum temperature difference of the system are reduced by 4.02 °C and 5.05 °C, respectively. The proposed structure and method are expected to provide insights into the design and development of battery thermal management systems.

Flow and Heat Transfer Performances of Liquid Metal Based Microchannel Heat Sinks under High Temperature Conditions.

Developments in applications such as rocket nozzles, miniature nuclear reactors and solar thermal generation pose high-density heat dissipation challenges. In these applications, a large amount heat must be removed in a limited space under high temperature. In order to handle this kind of cooling problem, this paper proposes liquid metal-based microchannel heat sinks. Using a numerical method, the flow and heat transfer performances of liquid metal-based heat sinks with different working fluid types, diverse microchannel cross-section shapes and various inlet velocities were studied. By solving the 3-D steady and conjugate heat transfer model, we found that among all the investigated cases, lithium and circle were the most appropriate choices for the working fluid and microchannel cross-section shape, respectively. Moreover, inlet velocity had a great influence on the flow and heat transfer performances. From 1 m/s to 9 m/s, the pressure drop increased as much as 65 times, and the heat transfer coefficient was enhanced by about 74.35%.

New correlations for heat transfer in parallel-plate ducts at low Peclet number

Calculations of heat transfer in duct flows generally neglect the effect of axial heat conduction within the fluid. However, in some situations, this effect must be taken into account. The decision on whether or not to consider this phenomenon is driven by the value of the Peclet number. A low value, with 100 commonly considered the threshold, indicates that axial conduction, i.e., conduction parallel to the flow, should be accounted for in the calculations. Microfluidic devices, systems using liquid metal coolant or microchannel heat exchangers are some examples of applications where low Peclet flow conditions may be encountered. While exact analytical solutions exist for such cases, they are often impractical to use for common engineering design purposes due to their mathematical complexity. The present work proposes three new correlations for the estimation of the fully developed Nusselt number, thermal entry length and local Nusselt number in the entrance region of a laminar flow within a parallel-plate duct with constant wall temperature. These correlations allow the simple and accurate evaluation of useful engineering quantities, thus avoiding lengthy and complex calculations. They were developed using rational approximation theory and are effective on a wide range of Peclet numbers and axial coordinates. Accuracy of under 1% relative error is achieved with each of the three correlations when results are compared against exact analytical series solution values.

Study of the performance of an integrated liquid cooling heat sink for high-power IGBTs

• An integrated heat sink was manufactured. • The performance of three common heat sinks were compared. • The cooling water temperatures have effect on the performance of the integrated heat sink. • The installation angles have effect on the performance of the integrated heat sink. To address the challenge of heat management for high-power IGBTs, a type of microchannel liquid cooling heat sinks integrated vapor chamber (VC integrated heat sink) was developed. Firstly, it compared with the VC separate heat sink and the simple microchannel heat sink under the same conditions. The experimental results showed that the VC integrated heat sink had less thermal resistance than the VC separated heat sink, and the relatively simple microchannel heat sink could significantly improve the temperature uniformity. The influence of the cooling water flow rate, temperature and inclination angle on the VC integrated heat sink was further studied. Reductions in the cooling water temperature led to decreases in the heat source temperature but did not improve temperature uniformity. The inclination angle had a significant influence on the performance of the VC integrated heat sink. The performance of the VC integrated heat sink was optimal when the inclination angle was 60°.

Coupling management optimization of temperature and thermal stress inside 3D-IC with multi-cores and various power density

A three-dimensional integrated circuit (3D-IC) is representative of technologies that have achieved the “beyond Moore's Law” concept. However, a 3D-IC suffers from the thornier problems of local overheating and thermal stress concentration as a result of its higher integration. Herein, a 3D-IC model with a real microprocessor structure to explore the temperature and thermal stress distributions under a closed microchannel liquid cooling condition. Finally, the effects of the structural parameters, flow direction of the cooling water, and core area overclocking on the maximum temperature, thermal stress distribution, and total pressure drop inside the 3D-IC model were investigated. The numerical results indicated that a mixed arrangement of micro-pin fins in the bottom microchannel and in-line arrangement in the upper microchannel was beneficial for balancing the maximum temperature and pressure drop. Moreover, the maximum thermal stress decreased by 34% after parallel flow and an optimized upper microchannel structure were adopted in the 3D-IC. Furthermore, the reliability of the chip with the optimized structure was governed by the thermal failure risk instead of thermal stress. Therefore, to balance the reliability and pumping power consumption of chips, maintaining the maximum temperature at 333 K could be a reference for 3D-IC coupling management.

Microchannel cold plate heat transfer and flow resistance characteristics calculation and structure optimization

This paper designs a microchannel liquid cold plate suitable for array multi-chip cooling. The influence of aspect ratio of rectangular cross section on heat transfer and flow performance of microchannel cold plate was studied by numerical analysis. The optimal ratio of height to width of rectangular section is selected and its structure is optimized. The results show that when the equivalent diameter of rectangular cross-section is fixed, the friction coefficient f and Nusselt number Nu increase with the increase of aspect ratio of rectangular cross-section; after optimizing the structure of the channel, the microchannel cold plate exhibits good heat transfer characteristics of low pressure drop, realizing effective heat dissipation and meeting the requirements of pressure drop.

Minimizing the Effects of On-Chip Hotspots Using Multi-Objective Optimization of Flow Distribution in Water-Cooled Parallel Microchannel Heatsinks

Abstract The industry shift to multicore microprocessor architecture will likely cause higher temperature nonuniformity on chip surfaces, exacerbating the problem of chip reliability and lifespan. While advanced cooling technologies like two phase embedded cooling exist, the technological risks of such solutions make conventional cooling technologies more desirable. One such solution is remote cooling with heatsinks with sequential conduction resistance from chip to module. The objective of this work is to numerically demonstrate a novel concept to remotely cool chips with hotspots and maximize chip temperature uniformity using an optimized flow distribution under constrained geometric parameters for the heatsink. The optimally distributed flow conditions presented here are intended to maximize the heat transfer from a nonuniform chip power map by actively directing flow to a hotspot region. The hotspot-targeted parallel microchannel liquid cooling design is evaluated against a baseline uniform flow conventional liquid cooling design for the industry pressure drop limit of approximately 20 kPa. For an average steady-state heat flux of 145 W/cm2 on core areas (hotspots) and 18 W/cm2 on the remaining chip area (background), the chip temperature uniformity is improved by 10%. Moreover, the heatsink design has improved chip temperature uniformity without a need for any additional system level complexity, which also reduces reliability risks.

Liquid metal microchannels as digital sensors in mechanical metamaterials

This report explores a synthesis of principles from liquid metal-based flexible electronics and mechanical metamaterials. In such new platforms, mechanical deformation couples with liquid metal microchannels to govern electrical conduction by constriction and release of liquid metal embedded in the soft material. The mechanisms that influence the ability to induce such discrete switch electrical phenomena are identified through studies focused on mechanical design, liquid metal oxidation, and stress thresholds. Through strategic selection of such factors, repeatable switch ability is retained for many stress cycles on the metamaterial, although aging of the phenomena is evident through switch thresholds that reduce with cycles prior to potential failure. These discoveries provide new foundations for self-sensing mechanical metamaterials that leverage an interface of liquid metal coalescence and local mechanical deformation to lead to digital signaling abilities in continuously stressed metamaterials.

A 3D inlet distributor employing copper foam for liquid replenishment and heat transfer enhancement in microchannel heat sinks

The application of two-phase flow boiling to microchannel heat sinks has attracted increasing attention owing to the compact design and high efficiency of dissipating heat. However, undesirable heat transfer deterioration and premature critical heat flux are commonly encountered in real-life applications of two-phase flow cooling devices. One significant challenge in utilizing two-phase flow boiling in microchannels lies in preventing the thin liquid film and in-time liquid replenishment from being interrupted by the rapid bubble elongation and chaotic vapor-liquid interface in the channel. In the present work, a 3D inlet distributor employing copper foam is proposed as an extra liquid feeding path to facilitate continuous liquid wetting of the boiling surface and improve the heat transfer performance. A physical heat transfer model accounting for the differences in microchannel void fraction and liquid film thickness caused by the copper foam layer (CFL) has been proposed to describe the working mechanism. The validity of the proposed 3D inlet distributor in heat transfer enhancement was verified using a series of flow boiling tests, employing deionized water as the working fluid. It was found that the local overheating of the microchannel heat sink was demonstrably reduced for all the heat flux values (q) in the tests after adopting the CFL, with a maximum reduction of 14 K at q = 397.6 kW/m2, where local dry-out was successfully inhibited. The heat transfer coefficient of the microchannel heat sink with the CFL was improved by approximately 1.7 times compared to the case without the CFL and could be maintained at 41 kW/m2K during elongated bubble flow and annular flow patterns. In addition, the proposed distributor was capable to resist gravity and long-term severe boiling, thus achieving superior and reliable performance under various orientations as well as during long operating hours.

Coupled prediction model of liquid-cooling based thermal management system for cylindrical lithium-ion module

In this paper, a micro-channel liquid cooling battery thermal management system (BTMS) of electric vehicle (EV) battery module was studied. A computational model for coupled heat transfer from electrochemical-thermal prediction for cell unit to the calculation of the whole battery module was established. The predicted performance of a single battery and a battery module were validated. A Tesla Model S battery module was numerically simulated using the established coupled model. The results showed that the distribution of temperature in the micro channels was quite regular, while the non-uniformity of the temperature in the battery stack was noticeable. These indicated the possibility of improving the heat management for the cell stack by enhancing the mixing of the cooling flow. A modification to improve the cooling by adding baffles in the micro-channels was proposed. Simulation results confirmed the effectiveness of such strategy. Convection heat transfer in the cooling channels was enhanced, while the non-uniformity in the cell stack was reduced. Such modification was at an affordable cost of pressure drop in the cooling system. The mechanism of the flow in the micro-channels for improving the cooling efficiency was analyzed.

Liquid metal MHD effect and heat transfer research in a rectangular duct with micro-channels under a magnetic field

The liquid metal blanket of a fusion reactor acts the role of tritium multiplication and energy transportation in a strong magnetic field environment. Liquid metal in fusion blanket is different from traditional flow and heat transfer due to magneto hydrodynamics (MHD) effects. A numerical simulation is employed to investigate the convection heat transfer between liquid metal and micro-channels heated surface under an external magnetic field. It can be found that under the influence of magnetic field, liquid metal can produce strong jet near the wall which drives the liquid metal flow together inside the channel. The MHD Hunt flow effect is intensified with the enhancement of the magnetic field and the results indicate that the magnetic field is beneficial to the energy transport and conversion of liquid metal blanket due to the jet flow on the wall that caused by the magnetic field. From the point of view of enhanced heat transfer, 32% of the heat transfer enhancement under the influence of strong magnetic field provides a new way to solve the heat transfer with high heat flux density. The expression is fitted between Nu number with Re number, the magnetic interaction number and flow distance, which can be used to predict the change of heat transfer intensity between the liquid metal and the micro-channels heated plate with the magnetic field intensity.

Experimental investigation of heat transfer for pulsating flow of GOPs-water nanofluid in a microchannel

The effects of mass fraction (φ) of graphene oxide particles (GOPs) and pulsating frequency (f) on heat transfer and pressure drop in a microchannel with arrayed pin-fins were experimentally investigated. Five different mass fractions of graphene oxide nanofluids were prepared and used as working fluids. Experiments were performed under the condition that the pulsating frequency was from 1 to 5 Hz, the mass fractions was from 0.02% to 0.2% and the average Reynolds number was 272, 407 and 544. The results show that the heat transfer is enhanced significantly when the frequency is in the range of 2 to 5 Hz. For the frequency of 1 Hz, the pulsating flow has a negative effect on temperature uniformity. With the increase of mass fraction, the heat transfer performance is improved while no significant change is found in pressure drop. The pulsating flow leads to a significant enhancement of pressure drop for frequency at 2 Hz. The combination of pulsating and nanofluid can obtain higher heat transfer efficiency under limited size of microchannel heat sink and low inlet Reynolds numbers. This study has a certain guiding significance for the development of microchannel liquid cooling technology.

Predicting entropy generation of a hybrid nanofluid containing graphene–platinum nanoparticles through a microchannel liquid block using neural networks

This study investigates the characteristics of first and second laws of thermodynamics including the convective heat transfer coefficient, entropy generation rate, and Bejan number for the hybrid nanofluid having graphene–platinum nanoparticles through a cylindrical microchannel liquid block. The geometry contains thirty-six microchannels having hydraulic diameter of 564 μm. The maximum values of the convection heat transfer coefficient, thermal entropy generation, and frictional entropy generation are obtained as 7653 W/m2K, 9.7 × 10−5 W/K, and 6.2 × 10−6 W/K, respectively. With increase of the particle concentration, the heat transfer coefficient and frictional entropy generation increase whereas the thermal entropy generation reduces. Furthermore, by increment of the heat load, the entropy generation due to the heat transfer increases, whereas the entropy generation due to the friction reduces. The influence of Reynolds number on the entropy production rates is more noticeable than the effect of particle fraction. Also, the entropy generation due to the heat transfer diminishes by raising the Reynolds number, while the entropy generation due to the friction intensifies. Furthermore, the Bejan number reduces with increment of the particle fraction and Reynolds number. Eventually, the entropy generation is modeled in terms of the Reynolds number, particle fraction, and heat flux by a neural network.

Highly Sensitive and Wearable Liquid Metal-Based Pressure Sensor for Health Monitoring Applications: Integration of a 3D-Printed Microbump Array with the Microchannel.

Wearable pressure sensors capable of sensitive, precise, and continuous measurement of physiological and physical signals have great potential for the monitoring of health status and the early diagnosis of diseases. This work introduces a 3D-printed rigid microbump-integrated liquid metal-based soft pressure sensor (3D-BLiPS) for wearable and health-monitoring applications. Using a 3D-printed master mold based on multimaterial fused deposition modeling, the fabrication of a liquid metal microchannel and the integration of a rigid microbump array above the microchannel are achieved in a one-step, direct process. The microbump array enhances the sensitivity of the pressure sensor (0.158 kPa-1 ) by locally concentrating the deformation of the microchannel with negligible hysteresis and a stable signal response under cyclic loading. The 3D-BLiPS also demonstrates excellent robustness to 10 000 cycles of multidirectional stretching/bending, changes in temperature, and immersion in water. Finally, these characteristics are suitable for a wide range of applications in health monitoring systems, including a wristband for the continuous monitoring of the epidermal pulse rate for cuffless blood pressure estimation and a wireless wearable device for the monitoring of body pressure using a multiple pressure sensor array for the prevention of pressure ulcers.

Directly 3D-printed monolithic soft robotic gripper with liquid metal microchannels for tactile sensing

One of the most valuable contributions robotics can offer is support to daily human activities, yet rigid robots often fail to comply with safety regulations in the proximity of humans. Soft robotics takes inspiration from living organisms’ ability to adapt to their environment using flexible structures. These systems have to generate mechanical forces and simultaneously sense their environment. We developed a soft gripper with integrated sensing microstructures by monolithically 3D printing the structure. The rubber gripper mimics the versatile sensing and actuation abilities of living organisms. This is done using stereolithographic printing technology, rubber material, and resistive, pressure sensitive EGaIn microchannels. Printed microscale pressure sensing cavities are filled with liquid metal and act as resistive pressure sensors. They imitate human haptic perception and provide a sensitivity of 0.5% kPa−1. Simultaneously, a soft-robotic actuator design, which is derived from pneumatic networks, delivers a force of 2.5 N with 16 kPa of actuating pressure and an average efficiency of 0.56 mW kPa−1. Monolithically 3D printed systems promise numerous advantages since the compliance matching between multi-modal capillary sensing networks and actuators enables scale production of smart soft manipulators. Potential applications include collaborative manufacturing and medical support systems such as exoskeletons.