In recent years, advancements in computational hardware have enabled massive parallelism that can significantly reduce the duration of many numerical simulations. However, many high-fidelity simulations use serial algorithms to solve large systems of linear equations and are not well suited to exploit the parallelism of modern hardware. The Tri-Diagonal Matrix Algorithm (TDMA) is one such example of a serial algorithm that is ubiquitous in numerical simulations of heat transfer and fluid flow. Krylov subspace methods for solving linear systems, such as the Bi-Conjugate Gradients (BiCG) algorithm, can offer an ideal solution to improve the performance of numerical simulations as these methods can exploit the massive parallelism of modern hardware. In the present work, Krylov-based linear solvers of Bi-Conjugate Gradients (BCG), Generalized Minimum Residual (GMRES), and Bi-Conjugate Gradients Stabilized (BCGSTAB) have been incorporated into the SIMPLER algorithm to solve a three-dimensional Rayleigh-Bénard Convection model. The incompressible Navier-Stoke’s equations, along with the continuity and energy equations, are solved using the SIMPLER method. The computational duration and numerical accuracy for the Krylov-solvers are compared with that of the TDMA. The results show that Krylov methods can improve the speed of convergence for the SIMPLER method by factors up to 7.7 while maintaining equivalent numerical accuracy to the TDMA.

In this study, the impact of the cannula geometry on the formation of the depot in subcutaneous tissue is investigated when injecting insulin using an insulin pump. The simulations have been conducted using the Computational Fluid Dynamics (CFD) software ANSYS Fluent. The study is focusing on rapid acting insulin analogues typically used in insulin pump therapy, which enter the bloodstream very shortly after administration. A previously developed 2-dimensional simulation has been transferred into a 3-dimensional case in order to simulate cases with non-axisymmetric geometries. The tissue has been modeled as a homogeneous anisotropic porous media by the use of different porosity values in the parallel and perpendicular direction with respect to the skin surface. The process of absorption is implemented into the model by the use of a locally variable species sink term. The basic case, simulated with a solid cannula, has been compared to other cannula geometries in order to evaluate if the delivery of insulin in the tissue can be improved. The geometries under consideration are the addition of circumferential holes in the wall of the cannula as well as using an array of cannulas instead of a single cannula. The depot formation is analyzed simulating a standard bolus injection of 0.05ml of insulin using an injection time of 25 seconds. It is observed that the addition of multiple holes in the wall of the cannula or using an array of cannulas can alter the shape of the depot quite significantly. The impact of the depot shape on the diffusion of insulin in the tissue has been evaluated by measuring the total volume of the depot after injection.

In this study a numerical model of the insulin depot formation and absorption in the subcutaneous adipose tissue is developed using the commercial Computational Fluid Dynamics (CFD) software ANSYS Fluent. A better understanding of these mechanisms can be helpful in the development of new devices and cannula geometries as well as predicting the concentration of insulin in the blood. The injection method considered in this simulation is by the use of an insulin pump using a rapid acting U100 insulin analogue. The insulin is injected into the subcutaneous tissue in the abdominal region. The main composition of the subcutaneous tissue is blood vessels and adipose cells surrounded by interstitial fluid. The numerical simulation is conducted in a 2D-axisymmetric domain where the tissue is modeled as a fluid saturated porous media. Due to the presence of channel formation in lateral direction in the tissue, an anisotropic approach to define the permeability is studied having an impact on the viscous resistance to the flow. This configuration is resulting in a rather disk shaped depot following recent experimental findings. The depot formation is analyzed running Bolus injections ranging from 5–15 Units of insulin corresponding to 50–150μl. The depot formation model has been extended implementing the process of absorption of insulin from the depot to be able to run the simulation over longer timeframes where absorption starts playing an important role.

In recent years, the forced convection cooling for the heat dissipation of electronic components has become a significant area of research. Many high-end computing applications, from consumer gaming to scientific research, encounter performance limitations due to heat generation in micro-electronic components. Micro heat exchangers can offer an ideal cooling solution for these applications due to their compact size and heat dissipation characteristics. Single-phase heat exchangers are widely used in both industry and consumer applications, but are limited by operational temperature ranges as well as the working fluid’s thermo physical properties. Two-phase, convection cooling systems, however, can further increase the capabilities of micro-heat exchangers. In the present study, a model has been created to investigate bubble growth and the values of wall superheat, contact angle, and Reynolds number that cause instability at the liquid-vapor interface during microchannel flow boiling. The results show how bubble instability is caused by the transfer of heat being restricted by the liquid-vapor interface.

In recent years, heat dissipation in micro-electronic systems has become a significant design limitation for many component manufactures. As electronic devices become smaller, the amount of heat generation per unit area increases significantly. Current heat dissipation systems have implemented forced convection with both air and fluid media. However, nanofluids may present an advantageous and ideal cooling solution. In the present study, a model has been developed to estimate the enhancement of the heat transfer when nanoparticles are added to a base fluid, in a single microchannel. The model assumes a homogeneous nanofluid mixture, with thermo-physical properties based on previous experimental and simulation based data. The effect of nanofluid concentration on the dynamics of the bubble has been simulated. The results show the change in bubble contact angles due to deposition of the nanoparticles has more effect on the wall heat transfer compared to the effect of thermo-physical properties change by using nanofluid.

Water management still remains a challenge for proton exchange membrane fuel cells. Byproduct water formed in the cathode side of the membrane is wicked to the air supply channel through the gas diffusion layer. Water emerges into the air supply channel as droplets, which are then removed by the air stream. When the rate of water production is higher than the rate of water removal, droplets start to accumulate and coalesce with each other forming slugs consequently clogging the channels and causing poor fuel cell performance. It has been shown in previous experiments that rendering the channels hydrophobic or super-hydrophobic cause water droplets to be removed faster, not allowing time to coalesce, and therefore making channels less prone to flooding. In this numerical study we analyze water droplet growth and detachment from a simulated hydrophobic air supply channel inside a proton exchange membrane (PEM) fuel cell. In these numerical simulations the Navier-Stokes equations are solved using the SIMPLER method coupled with the level set technique in order to track the liquid-vapor interface. The effect of the gravity field acting in the −y, −x, and +x directions was examined for an array of water flow rates and air flow rates. Detachment times and diameters were computed. The results showed no significant effect of the gravity field acting in the three different directions as expected since the Bond and Capillary numbers are relatively small. The maximum variations in detachment time and diameter were found to be 8.8 and 4.2 percent, respectively, between the horizontal channel and the vertical channel with gravity acting in the negative x direction, against the air flow. Droplet detachment was more significantly affected by the air and water flow rates.

The preferable cooling solution to the problem of thermal management of modern electronics for increasing power dissipation could be micro heat exchangers based on forced flow boiling. Nanoparticle deposition can affect nucleate boiling heat transfer coefficient via alteration of surface thermal conductivity, roughness, capillary wicking, wettability, and nucleation site density. It can also affect heat transfer by changing bubble departure diameter, bubble departure frequency, and the evaporation of the micro and macrolayer beneath the growing bubbles. In this study, flow boiling was investigated using degassed, deionized water, and 0.001 vol% aluminum oxide nanofluids in a single rectangular brass microchannel for one inlet fluid temperature of 63°C, one flow rate of Re = 100, and two heat fluxes of 130 kW/m 2 and 300 kW/m 2 . High speed images were taken periodically for water and after durations of 25, 75, and 125 minutes of nanofluid flow boiling. The change in regime timing revealed the effect of nanoparticle suspension and nanoparticle deposition on the Onset of Nucelate Boiling (ONB) and the Onset of Bubble Elongation (OBE). Single phase flows at the channel outlet were recorded and compared for different durations of nanofluid flow boiling. The addition of nanoparticles was found to stabilize bubble nucleation and growth and increase heat transfer in the thin film regions of the evaporating menisci.

Thermal analysis is a critical function in the design of electric machinery. While the core design discipline is electro-magnetics, other classic mechanical engineering expertise is required to create state of the art electric machines. Various components of electric machines present the thermal design engineer with obvious applications of classic, well-known solutions. These would include simultaneous thermal and hydro-dynamically developing flow when considering the long, narrow cooling ducts placed between stator laminations. However, the cooling of end windings of a formed, lap-wound electric machine is more challenging. This area features insulated copper coils that extend out of the stator or rotor and return to another section of the machine to complete the loop of a single coil. Effective thermal and flow analysis of this basket-like shape does not easily lend itself to well-known solutions. The present study explores the current literature of this type of machine end-windings as related to thermal and flow solutions. Simple correlations are proposed to aid machine designers that would accelerate the design process. These correlations can be used in thermal and fluid network programs to quickly predict flows and temperatures in a machine. Recent work to characterize heat transfer performance from the pressure drop in heat exchangers using the Generalized Leveque Equation can be of particular value for this effort. Finally, simple Computational Fluid Dynamics (CFD) analysis is presented for a simple geometry similar to a single, isolated stator bar.

The trends of decrease in size and increase in power dissipation for micro-electronic systems present a significant challenge for thermal management of modern electronics. The preferable cooling solution could be micro heat exchangers based on forced flow boiling. Nanoparticle deposition can affect nucleate boiling heat transfer coefficient via alteration of surface thermal conductivity, roughness, capillary wicking, wettability, and nucleation site density. It can also affect heat transfer by changing bubble departure diameter, bubble departure frequency, and the evaporation of the micro and macrolayer beneath the growing bubbles. In this study, flow boiling was investigated for 0.001 vol% aluminum oxide nanofluids in a brass microchannel and compared to results for regular water. For the case of nanofluid flow boiling, high speed images were taken after boiling durations of 25, 75, 125, and 150 min. Bubble growth rates were measured and compared for each case. Flow regime oscillation was observed and regime duration was split into two periods: single-phase liquid and two-phase. The change in regime timing revealed the effect of nanoparticle suspension and deposition on the Onset of Nucelate Boiling (ONB) and the Onset of Bubble Elongation (OBE). The addition of nanoparticles was shown to stabilize bubble growth as well as the transition of flow regimes between liquid, two-phase, and vapor.

Water, a byproduct of the chemical reaction in a Proton Exchange Membrane Fuel Cell (PEMFC), is removed by the air flowing over the cathode. However, when water production rate is more than its rate of removal, water may flood the fuel cell cathode, cutting off the air supply and stopping the reaction. A bio-mimetic solution to the water management problem was proposed in an earlier work where micronized wax was introduced along with the air that would help encapsulate the water droplets facilitating their quick removal from the fuel cell. Based on earlier results, further investigation is done to study different bi-polar flow field designs for effective water management, using bio-mimetic micronized wax. The different flow field designs studied in this work consists of parallel and single serpentine channels on graphite plates under simulated fuel cell load conditions. The effect of micronized wax on the two-phase flow regimes at different flow field orientations is also analyzed. It is clearly observed that the presence of micronized wax significantly helps in water movement in all air flow channels designs and orientations. It is hypothesized that introduction of micronized wax along with the air flow will allow the use of parallel flow field bi-polar plate designs in operating fuel cells with significantly reduced air side pressure drop instead of the prevalent single serpentine channel flow field designs.

Water management in Proton Exchange Membrane Fuel Cell (PEMFC) is an important issue that needs to be addressed appropriately at all loads. Water is formed as a product of reaction, which is removed by airflow at the cathode. However, at part load operations, when the required airflow is less, water can build up inside the cell resulting in reduction of fuel cell output. A bio-mimetic solution to this problem is proposed where a minute amount of powdered wax is introduced along with the incoming air into the gas distribution channel of a bipolar plate. The bi-polar plate is covered with a transparent plexi-glass and water is introduced using a syringe pump through a minute hole on the cover at a location downstream of the air inlet. The air and water flow rates are varied simulating the different load conditions observed in a typical PEMFC. The movement of water inside the serpentine channel is recorded using a high-speed camera. Presence of micronized wax resulted in significant increase in water movement inside the channels.

There is a strong need for a transformative curriculum to train the next generation of engineers who will help design, construct, and operate fuel cell vehicles and the associated hydrogen fueling infrastructure. In this poster we discuss how we integrate fuel cell and hydrogen technology into the project-based, hands-on learning experiences in engineering education at Michigan Technological University. Our approach is to involve students in the learning process via team-based interactive projects with a real-world flavor. This project has resulted in the formation of an “Interdisciplinary Minor in Hydrogen Technology” at Michigan Technological University. To receive the 16 credit minor, students are required to satisfy requirements in four areas, which are: • Participation in multiple semesters of the Alternative Fuels Group Enterprise, where students work on hands-on integration, design, and/or research projects in hydrogen and fuel cells. • Enrolling in a fuel cell course. • Enrolling in a lecture or laboratory course on hydrogen energy. • Enrolling in discipline-specific elective courses.

The present study deals with experimental investigation of cooling of machining tools, by water flowing through a microduct at the tip of the tool. The microduct is of diameter of around 200μm and the flow takes place at turbulent Reynolds number. The outer wall temperature of microduct and the temperature of water at inlet and exit have been measured. The convective heat transfer coefficient is calculated at different wall temperatures and varying liquid mass flux. The experimental results shows that the average Nusselt numbers for the short micro-duct are higher than those predicted by conventional correlations for large diameter ducts. A correlation has been proposed to compute convective heat transfer during turbulent flow through a short microduct of a particular geometry for a range of Reynolds and Prandtl numbers.

Micro heat exchangers are emerging as one of the most effective cooling technologies for high power-density applications. The design of micro heat exchangers is complicated by the presence of alternating flow regimes, which give way to flow boiling instability. Bubble formation inside microchannels can be correlated directly to flow boiling instability and can regulate flow characteristics and wall heat transfer when the bubbles grow to reach the microchannel hydraulic diameter. In this study, the growth of vapor bubbles in a single microchannel was examined using an experimental setup capable of measuring coolant flow rate, inlet and outlet liquid temperatures, and channel wall surface temperature. Liquid flow rate and wall heat flux were systematically varied while a high-speed camera was used to capture images of vapor bubbles forming in the channel. These images were used to compare bubble growth rates for a constant flow rate. The results provide fundamental understanding of the bubble growth process.

Examination of metastable states of fluids provides important information pertinent to cavitation and homogeneous nucleation. Homogeneous nucleation, in particular, is an important topic of research. Molecular Dynamics simulation is a well-endorsed method to simulate metastabilitites, as they are limited to mesoscopic scales of length and time and this life-time is essentially zero on a laboratory time scale. In the present study, a molecular dynamics code has been used in conjunction with MOLDY to investigate phase change in a Lennard-Jones liquid. The Lennard-Jones atoms were subjected to different temperatures at various number densities and the pressure was recorded for each case. The appearance of a change of phase is characterized by the formation of clusters or formation of voids as described by the radial distribution function.