Session X33: Industrial Applications: General

Mixing and oxygen transfer in a rocking bioreactor for cultivated meat production

In the cultivated meat industry, rocking bioreactors have emerged as a promising solution for large-scale cell cultivation, offering advantages such as disposability, cost-effectiveness, and scalability. To ensure proficient cell growth, it is essential to optimize mixing and oxygen transfer while minimizing shear stresses. However, the performance of the rocking bioreactor is still not well understood due to their short history in the market and wide range of geometries and operating conditions. In this study we explore the detailed flow features and their influence on the degree of mixing, oxygen transfer coefficient and shear stresses inside the bioreactor under various operating conditions, using the Basilisk open-source platform to develop a versatile direct numerical simulation toolkit. While intuition might suggest that increased agitation should lead to enhanced transport, we find numerous exceptions to this strategy, which we pinpoint to specific characteristics of the induced fluid flow. We are also able to identify the transitional regime from laminar to turbulent flow, the latter of which may be generally undesirable for cultivated meat production. Our findings are expected to provide guidelines for designing and operating bioreactors for the cultivated meat industry.   

An Optimised Multi-physics Model for Hydrogen Production in Alkaline Water Electrolysers

Alkaline water electrolysers are commonly employed for industrial-scale production of low-carbon hydrogen. Operating at high current densities leads to enhanced hydrogen production, but reduced cell efficiency, partly due to ohmic losses from bubble coverage of the electrode and reduced electrolyte conductivity. To gain further insights into the flow in electrochemical cells we carry out three-dimensional transient multi-physics simulations over a range of flow rates and current densities with the OpenFOAM libraries. We simulate the bubbly flow with a multi-fluid Eulerian model and consider electrochemistry, heat transfer, and bubble coalescence. Through a variance-based sensitivity analysis, we examine the impact of numerical parameter selection, with a focus on turbulence and interphase momentum-coupling models, and select a set of optimal parameters. The turbulent dispersion coefficient emerges as the parameter with the highest sensitivity index in all operating conditions, followed by the turbulence and drag models. Second-order sensitivity indices, which represent the sensitivity to parameter interactions, are significant for the bubble diameter and turbulence model. To address the uncertainty associated with the turbulence model and dispersion coefficients, we perform large-eddy simulations, allowing us to bridge the gap with RANS simulations typically used in industry.   

High-heat-flux processor cooling using a novel microgap device

Advancements in computer processing have become increasingly dependent on similar improvements in processor cooling. Liquid cooling by way of microgaps has proven to be a promising, more efficient alternative to established methods, such as liquid cooling using microchannels or air cooling by way of finned heat sinks. To investigate its potential, a novel microgap device was developed (Hinton and Mydlarski, US Patent No. US 11,507,153 B2, 2022). The device forms a microgap over the heated surface such that the coolant flows directly across the latter, thus eliminating multiple layers of thermal resistance. The modular nature of the design permits multiple flow configurations, such as cross flow and split flow (i.e., flow from the centerline to the edges), as well as the ability to interchange 3D-printed microgap plates, which facilitates parametric studies and the comparison of different heat transfer enhancement methods within the microgap. Experiments with a split flow microgap demonstrate an improvement in the heat transfer when compared to established methods, and this is further extended with enhancements to the microgap.   

Liquid atomization in a microfluidic channel for electrodeposition coating process of commercial vehicle

Liquid chemicals for cleaning or surface preparation that remain in the gap between two panels joined by spot welding have a serious impact on the quality of the electrodeposition process. To solve this problem, we present a liquid emptying technology with acoustic excitation which can atomize the remaining liquid in wide microfluidic channels with a height of tens to hundreds of micrometers. A microfluidic channel chip fabricated to mimic the vehicle panel gap and piezoelectric transducer capable of generating ultrasonic wave with various frequency were used. For understanding the unwanted filling of the liquid inside the microfluidic channel, the fabricated chip is repeatedly immersed in the liquid medium at various tilting angles, and liquid filling behavior is observed. To evaluate liquid emptying performance, we conducted an liquid atomization experiment by changing not only the electrical signal applied to the transducer but also the channel height and tilting angle. This in-channel droplet atomization technology with ultrasonic excitation is expected to be applied to a variety of industries that require the removal of liquids from precise structures.   

Can you clean this pipe? 3-D CFD modeling of compressed-air cleaning of large pipe networks

This study was conducted to improve the methods for modelling compressed-air cleaning of large complex piping systems. The current industry standard is to model the cleaning operation as an inviscid 1-D gas expansion. This work proposes using Computational Fluid Dynamic software for 3-D viscous turbulent flow. The simulation results were compared with actual industrial cleaning operations. Cleaning is measured by the ratio of the gas flow kinetic energy during the cleaning operation to the kinetic energy of normal operation. Cleaning force ratios (CFR) above 1.5 are acceptable. In one case, a simulation was performed on a 1000-foot, 8-inch pipe with four 90⁰ elbows. The simulation yielded a CFR of 16 near the pipe inlet and a CFR of 2 at the pipe exit. This was an 87.5% overall reduction in CFR along the pipe; however, with the minimum CFR above 1.5, the pipe cleaning should still be effective. Not surprisingly, at each elbow there was a noticeable reduction in total energy and velocity. The proposed model shows improved fidelity and accuracy in predicting the CFR and energy losses in these complex piping systems compared to the current industry model.   

Study of repeated damage-recovery of hydrophobic coatings for EWOD devices

The degradation of the hydrophobic coatings used in electrowetting-on-dielectric (EWOD) device is inevitable due to the external environmental factors. The single damage-recovery cycle of the hydrophobic coating has been studied by other research groups. However, there is a lack of research demonstrating the possibility of multiple damage-recovery cycles. Hence, this paper investigates the changes in the driving performance of an electrowetting device due to repeated damage-recovery cycles of CYTOP (CTX-809SP2) coatings. Samples were damaged by water droplet impacts one drop per second at a fixed height for 10 days. Contact angle(CA) and contact angle hysteresis(CAH) of samples were measured on a daily basis. The damaged samples were then heat-treated at 200 degrees celcius in an oven for 24 hours for recovery. CA and CAH of heat-treated samples were measured to demonstrate the recovery of the CYTOP coatings. After two times of damage-recovery cycles, it found that EWOD actuation performance has been significantly degraded. To analyze the reasons, the surface morphology of the CYTOP coatings was observed using atomic force microscopy (AFM). This study is expected to be useful for future applications of hydrophobic coatings in EWOD devices.   

Development of super-slippery silicone-based gel coating for anti-biofouling and drag reduction.

In the face of severe global climate change, reducing energy consumption, particularly in the maritime industry, is critical. Surface friction and marine biofouling significantly impede vessels' fuel efficiency, prompting the shipbuilding industry to develop functional coatings for drag reduction and anti-biofouling. This study presents a Long-chain Entangled PDMS (LEP) gel coating that continuously restores a low-viscosity oil layer, creating an super-slippery, waterproof surface. This coating effectively prevents bacterial adhesion, maintaining a clean surface even in environments infested with red algae for 12 weeks. Its performance remains unaffected under high shear flow conditions, demonstrating sustainable slippery property. To address the lubricant depletion issues common in conventional slippery surfaces, we integrated carbon nanotubes (CNT) onto the LEP gel surface. The micro/nanoscale structures formed by the CNTs maximize capillary force and significantly improve lubricant retention. The industrial practicality of the developed surfaces is currently being assessed through long-term exposure in real marine environments. We anticipate that the LEP gel coating will excel in other engineering applications, including anti-corrosion and anti-icing.   

A computational study of the break-up of a complex liquid ligament in a turbulent crossflow

The use of complex liquids in industrial spray processes is wide ranging and is a crucial component in areas such as food and pharmaceutical manufacturing. In these processes, the complex liquid is subjected to turbulent flow conditions causing the fluid to undergo rapid shearing and deformation causing the fluid to continually breakdown into sheets, ligaments, and droplets. While the process of atomization itself is quite complex, the use of complex fluids results in an additional layer of complexity because of the polymers and particulates that give these fluids an inherent microstructure. This microstructure gives rise to complex behavior such as high effective viscosity, shear-thinning and viscoelasticity not found in Newtonian fluids and ultimately alters the atomization behavior of the liquid. Because the process of atomization is highly multi-scale, this work simplifies the flow configuration to look at a single isolated liquid ligament in a turbulent crossflow to examine how this intrinsic complex behavior impacts the fundamental physics - Rayleigh-Plateau and Rayleigh-Taylor instabilities - that drive atomization. This study uses the volume-of-fluid method to transport the liquid-gas interface. It will begin by looking at the impact of high viscosity on break-up and then incorporate shear-thinning using the Carreau fluid model and FENE style viscoelastic models to include elastic stresses in the governing equations.   

Pigment stability in water using a toolbox for stability

Well-suspended and stabilized pigment is critical to ensure the long-term stability of many commercial products, including paint formulations as well as food and cosmetic products. Here, we discuss the effect of pH and pigment grade on pigment stability in water. We studied pigment stability using a novel 'stability toolbox' that consisted rheological measurements, zeta potential, and quantifying sedimentation/coalescence by light transmission and scattering. We show that each of these techniques provide unique information, enabling us to map out the structure-property-performance relationships of pigments in water. We showed that for inorganic pigments in water, electrostatic interactions dominate the rheological response and the sedimentation behavior. This stability toolbox can be broadly applied to colloidal as well as polymeric suspensions.   

Newtonian Fluid Dynamics in a Misaligned Parallel-Plate Rheometer

A rheometer is a fluid viscosity measurement device in which a fluid is commonly placed in between two parallel plates, and one of the plates rotates relative to the other in order to induce a shear on the fluid of interest. By measuring the torques and forces applied on the plates by the fluid as a function the rotation rate of the moving plate, the viscosity of the fluid can be characterized. Many studies and experiments are conducted under the assumption that the two plates of the rheometer are perfectly parallely aligned; however, unintentional misalignment in the plates can commonly occur through small errors in the manufacturing process. To examine the effect that misalignment plays on viscosity measurements taken by a rheometer, we derive a theoretical model for the behavior of a general Newtonian fluid in a rheometer with misaligned plates. We show that this misalignment can produce additional secondary velocity components and pressures in the fluid, which can greatly affect the forces and moments present in the rheometer and lead to underestimation of the viscosity of the fluid, especially at small rheometer gap heights. We also perform 3D numerical simulations of the system using OpenFOAM to validate the theoretical results, and these simulations provide additional detail to the flow structure inside the rheometer.   

Measuring the Casting Rate of Molten Iron Discharged from a Blast Furnace via Digital Imaging

Estimating the real-time casting rate of molten iron released from the taphole of a blast furnace is crucial to maintaining a steady and efficient iron-producing operation. This research is dedicated to developing a real-time, non-contact method for measuring the casting rate without interrupting the normal operation of the blast furnace. The images of the released iron jet are initially recorded via a machine vision camera. Then the key parameters such as jet velocity and cross-sectional area are extracted through a real-time image processing algorithm. Lastly, the volume flow rate is estimated based on the gathered information, and a calibration process considering the viewing angle, image distortion, and jet profile is employed to ensure precise measurements. A laboratory experiment using a simulated water jet is performed to validate the accuracy and reliability of the proposed method. Furthermore, the designed measurement system has been successfully tested at a blast furnace which shows its potential for practical industrial implementation.   

Improvement of liquid-based electrical insulation via electrohydrodynamic flow control

In liquid dielectrics, smart use of charge injection to improve electrical breakdown strength has been demonstrated in previous works. The bottleneck of this approach is the controllability of charge injection. The objective of this work is to numerically study a new design of charge injecting electrodes using electrohydrodynamic flow. In our needle-plane configuration, the needle electrode has a nozzle connecting its interior to the outside, both filled with the same dielectric liquid. The strong inhomogeneous electric field is able to drive liquid flow through the nozzle, during which the liquid jets will be carrying the charge with the same sign as the electrode. In this work, we build the electrohydrodynamic model and develop a numerical program to simulate this process. Our model couples incompressible flow with electric field and current continuity equations. The steady-state simulation results confirm that the hollow electrode with microchannels can effectively inject homocharges which enhance the electrical conductivity and lower the electric field in the region near the electrode surface. The flow may also help circulate the liquid and drive impurities away from electrode surface area. We explore a new way to improve electrical breakdown threshold of materials, which may have impact on the electric power industry and other technologies.