Self-assembly of sub-micron particles suspended in a water film is investigated numerically. The liquid medium is allowed to evaporate leaving only the sub-micron particles. A coupled CFD-DEM approach is used for the simulation of fluid-particle interaction. Momentum exchange and heat transfer between particles and fluid and among particles are considered. A history dependent contact model is used to compute the contact force among sub-micron particles. Simulation is done using the open source software package CFDEM which basically comprises of two other open source packages OpenFOAM and LIGGGHTS. OpenFOAM is a widely used solver for CFD related problems. LIGGGHTS, a modification of LAMMPS, is used for DEM simulation of granular materials. The final packing structure of the sub-micron particles is discussed in terms of distribution of coordination number and radial distribution function (RDF). The final packing structure shows that particles form clusters and exhibit a definite pattern as water evaporates away.

In this work, we numerically study the effects of turbulence intensity at the fuel and oxidizer stream inlets on the soot aerosol nano-particles formation in a kerosene fuel-based combustor. In this regard, we study the turbulence intensity effects specifically on the thermal performance and nano-particulate soot aerosol emissions. To construct our computer model, we simulate the soot formation and oxidation using the Polycyclic Aromatic Hydrocarbons PAHs-inception and the hydroxyl concept, respectively. Additionally, the soot nucleation process is described using the phenyl route, in which the soot inception is described based on the formations of two-ringed and three-ringed aromatics from acetylene, benzene, and phenyl radical. We use the two-equation soot model in which the soot mass fraction and the soot number density transport equations are solved considering the evolutionary process of soot nanoparticles, where all the nucleation, coagulation, surface growth, and oxidation phenomena are suitable considered in calculations. For the combustion modeling part, we benefit from the flamelets library, i.e., a lookup table, considering a detailed chemical kinetic mechanism consisting of 121 species and 2613 elementary reactions and solve the transport equations for the mean mixture fraction and its variance. We take into account the turbulence-chemistry interaction using the presumed-shape probability density functions PDFs. We apply the two-equation high-Reynolds-number k -ε turbulence model with round-jet corrections and suitable wall functions in performing our turbulence modeling. Solving the transport equations of turbulence kinetic energy and its dissipation rate, the turbulence closure problem can be resolved suitably. Furthermore, we take into account the radiation heat transfer of soot and gases assuming optically-thin flame, in which the radiation heat transfer of the most important radiating species is determined locally through the emissions. To evaluate our numerical solutions, we first solve an available well-documented experimental test, which provides the details of a kerosene-fueled turbulent nonpremixed flame. Then, we compare the achieved flame structure, i.e., the distributions of mean mixture fraction, temperature, and soot volume fraction, with those measured in the experiment. Next, we change the turbulence intensities of the incoming fuel and oxidizer streams gradually. So, we become able to evaluate the effects of different turbulence intensities on the achieved temperature and soot aerosol concentrations. Our results show that using moderate turbulence intensities at both fuel and oxidizer stream inlets would effectively increase the maximum temperature inside the combustor and this would reduce the exhaust gases temperature. It also reduces the concentrations of soot in the combustor and its emission to the exhaust gases effectively.

Recently in our research studies, ferroferric oxide magnetic micro particles were used as magnetic seeds combining with adsorbent materials during post hemodialysis (HD) nutrition recovery process. The combined particles were designed as magnetic adsorbents to selectively take back nutritional substances from waste dialysate solution, and then, these substances can be further chemically released to blood. To allow a better adsorption performance, these particles should be trapped inside their working area. So, a gradient magnetic field was designed accordingly. Instead to use a permanent magnet which could accumulate magnetic particles, the field was produced by multiple-level magnetic solenoid coils. This paper outlined the design method for the multiple-level solenoid field. And then, the measurement results for the magnetic intensity at different axis locations inside the solenoid field were compared with the numerical computation results. The computation results also showed that, near the axis area of the multiple-level solenoid, the magnetic intensity is smoothly developed. This feature allows the easy movement of magnetic particles since an abrupt gradient tends to accumulate the particles.

Particulate fouling at elevated temperature is a crucial issue for microchannel heat exchangers. In this work, a microfluidic system is designed to experimentally study on the deposition of micro-particles suspended in microchannels, which simulates the working fluid in microscale heat exchangers. We have directly measured the deposition rate of microparticles and found that the number density of deposited particles was monotonically increased with solution temperature when constant flow rate of samples was maintained. Moreover, our results show that pulsatile flow, which was generated by a piezoelectric unit, could mitigate the particulate fouling in microchannels, and the deposition rate was decreased with increasing the frequency of pulsation within a low frequency region. Our findings are expected to gain better understanding of thermally driven particulate fouling as well as provide useful information for design and fabrication of microchannel heat exchangers.

The effect of ethanol in the binary solution sessile droplet is investigated on the flow field, nanoparticle motion and nanoparticle deposition pattern. It is found that the droplets with ethanol exhibited three distinct flow regimes through the Particle Image Velocimetry (PIV) analysis on the flow field of droplets suspended with fluorescent microspheres. Regime I features furious flows and vortices which transport particles to the liquid-vapor interface and make them aggregate. In regime II, the aggregates of particles move towards the central area of the droplet dominated by Marangoni flow led by non-uniformity of ethanol along the droplet surface. As the droplet enters regime III, most ethanol has evaporated and it is dominated by the drying of the remaining water. The loading of ethanol in the solution prolongs the relative durations of regimes I and II, resulting in the variety of the final drying pattern of nanoparticles.

The confined jet array impingement cooling using NEPCM (nano-encapsulated phase change material) slurry was investigated numerically using a homogeneous model based on effective heat capacity method. The nanofluids consists of the carrier fluid of polyalphaolefin (PAO) and the NEPCM particles of Polystyrene shell and paraffin core. The distributed slot jet array with the jet width W=100 μm, confinement height H=300 μm, jet-to-jet distance S=400 μm was investigated at first under different jet velocity, inlet temperature and NEPCM volumetric concentration. It was found that for a fixed jet velocity, there is an optimal NEPCM volumetric concentration and an optimal inlet temperature to achieve the maximum average heat transfer coefficient. The larger the jet velocity, the higher the optimal NEPCM concentration and the closer the optimal inlet temperature to the midpoint of melting temperature range of PCM where the peak of effective heat capacity achieves. The local heat transfer on the heating surface under the exit slot is the weakest, because of stagnant zone formed by the head-to-head collision of the two adjacent jets. The pressure drop and average heat transfer coefficient of six jet arrays with different H/W (=2, or 3) and S/W (=3, 4 or 5) were also compared.

As the use of MEMS-based devices and systems are continuously increasing, the understanding of their correct characteristics becomes so serious for the related researches. In this study, the supersonic rarefied gas flow over microscale hotwires is investigated using the Direct Simulation Monte Carlo (DSMC) method. Indeed, the DSMC has been accepted as a powerful method to study the rarefied gas flow especially in transitional regime. Therefore, it can be considered as a reliable method to investigate the rarefied supersonic flow over microscale objects including the microscale hotwires. In this work, we study the effective parameters, which affect the performance of these sensors at constant sensor surface temperature conditions. We use our developed DSMC code to perform our investigation. This code uses the DSMC algorithm to solve the rarefied gas flow on unstructured grid distributions. To validate our developed DSMC code, we solve the supersonic rarefied gas flow and heat transfer in microchannel considering different Knudsen number magnitudes. Comparing the achieved flow and heat transfer solutions with other available results and data reported on microchannel studies, we verify the accuracy of achieved results. Next we focus on hotwire sensor, which often consists of the combinations of different long narrow circular cylinders. We study the effects of grid resolution, time step size, and the number of simulated particles on the obtained results. We further study the effects of sensor temperature and sensor diameter on the sensor thermal performance. The achieved results indicate that the surface heat flux performs very similarly in different studied cases. For example, the achieved local Nusselt number distributions around the circular sensor show that the surface heat flux would gradually increase from the sensor stagnation point to its rear end as the temperature gradient increases. It reaches to a maximum magnitude and it then starts decreasing resulting in effective heat flux reduction. Finally, there is a low pressure zone at the rear side of cylinder, which is not considerably affected by the flow properties. The results also show that if the wire surface temperature increases, the Nusselt number would reduce. However, the amount of Nusselt Number reduction rate would decrease as the temperature increases. Furthermore, the results show that the Reynolds number decreases and the Knudsen number increases as the sensor diameter decreases, which is due to the transitional regime behavior. As is known, the flow at boundaries change the condition from the slip to transitional regime when the Knudsen number increases sufficiently; and the flow become rarefied. There is a reduction in the total heat flux rate as the sensor diameter is reduced.

In this paper, we present a novel design of bilayer polydimethylsiloxane (PDMS) microchannel formed by bifurcated junction, from which each curved branch lies on the upper and lower layer, respectively. With this 3D platform, we aim to investigate droplet formation and subsequent fission in a multiphase system using non-Newtonian fluids, which are ubiquitous in daily life and have been widely used in industrial applications including biomedical engineering, food production, personal care and cosmetics, and material synthesis. Numerical model has been established to characterize the non-Newtonian effect to droplet fission and associated breakup dynamics when droplet flows through 3D bifurcated junction, where droplets can deform significantly on account of the confining geometric boundaries, and the flow of the surrounding non-Newtonian liquid, both of which control the deformation and breakup of each mother droplet into two daughter droplets. Dispersions of sodium carboxymethyl cellulose in water, and dispersions of polyvinylchloride in dioctylphthalate have been used as model fluids in the study, with the former one possessing shear-thinning behaviour, while the latter one possessing shear-thickening behaviour. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation when non-Newtonian fluids are involved. The model systems in the study can be further developed to investigate the mechanical property of emulsion templated particles such as drug encapsulated microcapsules when they flow through complex media structures, such as blood capillaries or the porous tissue structure, which feature with bifurcated junction.

In this article, the heat transferring property of the copper-water nanofluids in self-exciting mode oscillating flow heat pipe under different laser heating power is experimented, as well as is compared with that of the distilled water medium in self-exciting mode oscillating flow heat pipe under same heating condition. The objective of this article is to provide the heat transfer characteristics of Cu-H 2 O nanofluids in self-exciting mode oscillating-flow heat pipe under different laser heating input, and to compare with the heat transfer characteristics of the same heat pipe with distilled water as working fluids. The SEMOS HP used in this experiment is made of brass tube with 2mm interior diameter, which is consisted of 8 straight tubes with 4 turns’ evaporation section and 12 turns’ condensation section. The heat resource for the evaporation zone is eight channel quantum pitfall diode array semi-conductor laser heater with 940nm radiation wave length, while the radiation power of each channel is changeable within 0–50W and the facular size is 1×30mm 2 . The condensation section is set in a cooling water tank in which water is from another higher tank. The actual transferring rate could be calculated by the flow rate of the cooling water and the change of the temperature. The change of the temperature of the heat pipe wall is measured by those thermo-couple fixed in different section in the heat pipe and data is collected by a data acquisition. In the heat pipe the fluid filling rate is 43%, the pressure is 2.5×10 −3 Pa, and the heat pipe inclination angle is 55° while the size of the brass particle in the nanofluids is less than 60nm and volume proportion is 0.5%. In this paper, the particularity of heat transfer rate of the SEMOS heat pipe with Cu-H 2 O fluid has been experimentally confirmed by changing the proportion of working fluid and Cu nonsocial particles in the heat pipe. By comparing the experimental result of these two different medium in the SEMOS HP, it is shown that the heat transferring rate with brass-water nanofluids as medium is much better than that with distilled water as medium under same volume proportion.

The diffusion-limited cluster aggregation (DLCA) model has been implemented in a three-dimensional (3D) domain with a shape of an approximately spherical cap for simulating the drying process of a sessile nanofluid droplet. The droplet evaporation is investigated with the pinned three-phase line, resulting in shrinking contact angle and outward capillary flow. The cluster-cluster aggregation between the particles is taken into account in the model, and the transition from the uniform deposition to the coffee-ring pattern is established by altering the sticking probability parameter. The results of the simulation turn to be consistent with the experimental observation. The influence of the parameters, such as particle volumetric concentration and relative domain size, are studied.

The current study is focused on thermal radiation interaction with the natural convection of atmospheric brown cloud (ABC). The current study puts emphasis on ultra fine carbon-black particle suspension of several nano meter range along with some pollutant gas mixture with atmospheric air. The numerical simulation of double diffusive thermo-gravitational convection of ABC is done with Hide and Mason laboratory model for atmosphere. The effect of flow circulation is simulated by setting different value of buoyancy ratios. The effect of participating media radiation has been investigated for various values of optical depth. The governing equations, describing circulation of ABC are solved using modified Marker and Cell method. Gradient dependent consistent hybrid upwind scheme of second order is used for discretization of the convective terms. Discrete ordinate method, with S 8 approximation is used to solve radiative transport equation. Comprehensive studies on controlling parameters that affect the flow and heat transfer characteristics have been addressed. The results are provided in graphical and tabular form to delineate the flow behavior and heat transfer characteristics.

While particles smaller than the thickness of the diffusion film have been known to enhance rates of interfacial mass transfer [1], a relatively new result is the discovery that nanoparticles in suspension show enhancements that far exceed the earlier reported enhancements, and without any apparent adsorptive or reactive effects[2]. Different mechanisms for the enhancements have been speculated upon, but there is a paucity of data on different nanoparticulate materials, collected in a systematic way on model contactors so that rational comparisons may be made. In this work, enhancement in Carbon dioxide absorption in water has been studied using SiO 2 and TiO 2 nanoparticles using the same capillary tube apparatus for which previous results of Fe 3 O 4 were reported. For 0.4% silica particles and 0.0118% TiO 2 nanoparticles, 165% and 155% enhancement was observed respectively. A phenomenological convective diffusion model has been proposed to explain the observed effects of particle size, holdup and material density. The model accounts for the overall effect of the Brownian (and any diffusiophoretic) motion of the nanoparticles on the surrounding fluid in terms of an ‘effective’ convective velocity, which is determined from the experimental data and correlated to the modified Sherwood Number proposed earlier [2], volume fraction of Nanoparticles and a solid Reynolds number R p . This model provides a good fit to the data from wetted wall column and capillary tube experiment for iron oxide from the previous literature, as well as for the data on silica and Titanium dioxide nanoparticles from this work, the average error being 8.3%.

It is well known that a phase transition from liquid to vapor occurs in the thermal boundary layer adjacent to a nanoparticle that has a high temperature upon irradiation with a high-power laser. In this study, the mechanism by which the evaporated layer adjacent to a laser-irradiated nanoparticle can grow as a bubble was investigated. The pressure of the evaporated liquid volume due to heat diffusion from the irradiated nanoparticle was estimated using a bubble nucleation model based on molecular interactions. The bubble wall motion was obtained using the Keller-Miksis equation. The density and temperature inside the bubble were obtained by solving the continuity and energy equations for the vapor inside the bubble. The evaporation of water molecules or condensation of water vapor at the vapor-liquid interface and the homogeneous nucleation of vapor were also considered. The calculated bubble radius -time curve for the bubble formed on the surface of a gold particle with a diameter of 9 nm is close to the experimental result. Our study reveals that an appropriate size of the evaporated liquid volume and a large expansion velocity are important parameters for the formation of a transient nano-sized bubble. The calculation result suggests that homogeneous condensation of vapor rather than condensation at the interface occurs.

The knowledge of the flow fields inside of microsized ionic wind pumps has become more important as the need for smaller and more efficient heat removal devices has increased. Understanding these flow fields will help optimize the ionic wind pump performance. Non-intrusive microscale particle image velocemity (PIV) utilizing a microscopic objective lens is used to obtain the flow field inside of the ionic wind pump. Atomized olive oil droplets are used as seed particles with air as the flow medium. Voltages ranging from 1700 to 2000 V are used, as well as seeded flow rates of 1.5 and 2.0 L/min. Computational models, developed using COMSOL Multiphysics, are used to qualitatively verify the flow fields. The effects of voltage and seed flow rate are also compared. The computational and PIV flow fields are shown to be very similar. It is shown that as the voltage applied to the ionic wind pump increases the maximum velocity inside of the ionic wind pump, ranging from 1.71 m/s to 3.19 m/s. The average mass flow rate inside of the device also increases as the voltage is increased, ranging from .0009 g/s to .0019 g/s. It is also shown that the seed flow rate has little effect on the PIV flow field obtained.

Washing, separation and concentration of bioparticles are key operations for many biological and chemical analyses. In this study, the simulation of an integrated microfluidic device is studied. The proposed device has the capability to wash the bioparticles (transferring the bioparticles from one buffer solution to another), to separate the particles based on their dielectric properties and to concentrate the bioparticles. Washing and concentration of bioparticles are performed by acoustophoresis and the separation is performed by dielectrophoresis. For simulating the flow within the microchannel, a computational fluid dynamics model using COMSOL Multiphysics software is implemented. In order to simulate the particle trajectories under ultrasonic and electric field, point-particle assumption is chosen using MATLAB software. To account for the size variation of the bioparticles, particles with normal size distributions are used inside the microchannel. The effect of the key design parameters such as flow rate, applied voltage etc. on the performance of the device is discussed.

Polyalcohols such as neopentyl glycol (NPG) undergo solid-state crystal transformations that absorb/release sufficient latent heat. These solid-solid phase change materials (PCM) can be used in practical thermal management applications without concerns about liquid leakage and thermal expansion during phase transition. In this paper, microcapsules of NPG encapsulated in silica shell were successfully synthesized with the use of the emulsion technique. The size of the microcapsules was in the range of 0.2–4 μm, and the thickness of the silica shell was about 30 nm. It was found that the endothermic event of the phase change behavior of these NPG-silica microcapsules was initiated at around 39 °C and the latent heat was about 96.0 J/g. A large supercooling of about 43.3 °C was observed in the pure NPG particles without shell. The supercooling of the NPG microcapsules can be reduced to about 14 °C due to the heterogeneous nucleation sites provided by the silica shell. These NPG microcapsules were added into heat transfer fluid PAO to enhance its heat capacity. The effective heat capacity of the fluids can be increased by 56% by adding 20 wt. % NPG-silica microcapsules.

Microfluidic particle separation technologies are useful for enriching rare cell populations for academic and clinical purposes. In order to separate particles based on size, deterministic lateral displacement (DLD) arrays are designed assuming that the flow profile between posts is parabolic or shifted parabolic (depending on post geometry). The design process also assumes the shape of the normalized flow profile is speed-invariant. The work presented here shows flow profile shapes vary, in arrays with circular and triangular posts, from this assumption at practical flow rates (10 < Re < 100). The root-mean-square error (RMSE) of this assumption in the circular post arrays peaked at 0.144. The RMSE in the triangular post array peaked at 0.136. Flow development occurred more rapidly in circular post arrays when compared to triangular post arrays. Additionally, the changes in critical bumping diameter (D CB ) the DLD design metric used to calculate the size-based separation threshold were examined for 10 different row shift fractions (F RS ). These errors correspond to a D CB that varies as much as 11.7% in the circular post arrays and 15.1% in the triangular post arrays.

Disturbing the flow with a particular pulsating frequency alters the thermal and hydrodynamic boundary layer thus affecting the inter-particle momentum and energy exchange. Due to this enhanced mixing, augmentation in the heat transfer is expected. Obviously, the parameters like pulsating frequency vis-à-vis viscous time scales and the imposed pulsating amplitude will play an important role in the enhancement of the heat transfer. Several numerical heat transfer and fluid flow studies on pulsating flows have been reported in the literature but the conclusions are not coherent. Lack of experimental study in hydrodynamics as well as in heat transfer of laminar pulsating flows attracts to revisit this problem especially, in mini-channels. Technological developments in measurement and instrumentation have enabled to experimentally investigate the thermo-hydrodynamic study of laminar pulsating flows in mini-channels as an augmentation technique for heat transfer. In this work, we have undertaken the experimental measurements of heat transfer of single-phase laminar pulsating flow in square mini-channel of cross-section 3 mm × 3 mm. The study is done at two different pulsating frequency 0.05Hz and 1Hz (Womersley number, Wo = 0.8 and 3.4 respectively). These two values are chosen because velocity profile exhibits different characteristic for Wo > 1 (annular effect, i.e., peak velocity near the wall) and Wo < 1 (conventional parabolic profile). The heat transfer study has been done in a square channel of made on polycarbonate sheet with one side heating. Heater (made of SS, 70 microns thin strip, negligible thermal inertia) itself is one of the walls of the square channel making constant heat flux thermal condition and its instantaneous temperature is measured by using pre-calibrated InfraRed camera. Fluid bulk mean temperature has been determined by energy balance and one K-type thermocouple is also placed in the fluid at the outlet cross-section. By using these temporal data, space averaged instantaneous Nusselt number has been obtained. It is observed that for measured frequency range, the overall enhancement in the heat transfer is not attractive for laminar pulsating flow in comparison to steady flow of same time-averaged flow Reynolds number. It is found that the change in species transport is either marginal or highly limited and is primarily occurring in the developing length of the channel/ plate. Enhancement of species transport due to such periodic pulsatile internal flows, over and above the non-pulsatile regular flow conditions, is questionable, and at best, rather limited.

Phase change microencapsules are the microsized particles made of phase change materials (paraffin wax ect.) sealed by the thin shell (polymer ect.) via the methods of microencapsulation. During last decade, due to the large amount of melting/solidifying heat, much attention have been paid on their application in environmental control, building, textiles and electronics ect. Also the novel thermal fluids by phase change microencapsules suspending in the traditional thermal fluids have shown their superior heat storage density and convective heat transfer performance, which can behave as heat storage media and heat transfer media simultaneously. However, the density difference between the phase change microencapsules and tranditional unitary fluid would lead to the unstable suspending states which seriously affect the heat storage and heat transfer performance. Binary mixtures such as alcohol-water etc have already played the important roles in the heat transfer equipments. In this paper, binary propanol-water mixtures of various proportion were formulated as the base fluids, and their stabilities were studied. The result shows that binary propanol-water mixtures with the desity of 941kg/m 3 showed the best stability and no stratification was found after standing for 48 hours. The morphology and diameter distribution of the microencapsule particles were tested by the scanning electron microscope (SEM) and Malvern Nanosizer respectively, and the result show that the diameter of the particles is in the range of 10–80μm with the average value of 26.4μm. The phase change enthalpy and the effective heat capacity of phase change microencapsule suspensions with the concentration of 10–40wt% were measured by the differencial scanning calorimeter (DSC) and it was found the phase change enthalpy of the phase change microencapsule is 152.8J/g and the undercooling is only 7.3°C. The effect of concentration and temperature on the rheological behavior and viscosities of suspensions were experimentally studied by the TA DHR-G2 rheometer. The result shows that the suspensions behave as Newtonian fluids even when the concentration is as high as 40wt% and the viscosities fit well with Vand model. By the Hot Disk 2500S thermal constant analyzer (Sweden), the thermal conductivities of 0–40wt% suspensions were tested at 20–70°C and the variation was analyzed further. The concentration and expansion of MPCM particles during the phase change period were found to affect the thermal expansion coefficient of the MPCM suspensions obviously. The above experimental result and analyzation of stability and thermophysical properties will provide a complete and important data for the application in heat storage and heat transfer.

In this work, the reusable Lab-on-a-Chip or LOC was fabricated and developed to reduce its investment cost and to ease its operations. A sandwiched acrylic set was chosen to assemble the PDMS LOC which was aimed to investigate biological samples, especially the samples from animals. Chicken and sheep blood were chosen as the samples to implement two-phase flows with different red-blood-cell shapes. The chicken blood flow represented the viscous two-phase flow with the oval shape particles while the sheep blood flow represented the inadhesive samples with the round particles. The LOC electrodes from different materials as the sputtered nickel plate, the aluminium foil, the copper plate, and the gold foil were examined. Ratios between the anticoagulant solution and the biological samples were studied to find their effects on sample velocities and to find the best image to characterize the RBC flow behaviors. Since it was hard to characterize the particle flow in the inadhesive flows, the result pictures were analyzed and presented in terms of color intensities per unit area by using a computer program called “ImageJ”. The sheep-blood-flow results were validated with the hematology results which were the hematocrits to find their relationships between the hematocrits and the RBC flows. Among different LOC electrodes, the sputtered nickel electrodes were the most suitable electrodes in this current application. We found that the suitable anticoagulant-sample ratios for chicken and sheep samples were 5:1 and 1:1 by volume, respectively. The normal-health-condition sheep with the standard hematocrits higher than 28% showed the average-different-color intensities per unit area between cathode and anode at 39.485 pixels per unit area while the lower standard hematocrit samples, the hematocrits were lower than 28%, showed the average-different-color intensities at 14.641 pixels per unit area, the lower intensity the lower hematocrit. So the LOC coupled with “ImageJ” exhibited their capabilities to investigate the sheep blood conditions, especially, this coupled technique consumed less time than the traditional hematology process.