Bio-Inspired Engineering: Self-Healing Materials

The objective of this study was to develop a composite metallic material with self-healing capabilities. A developed heterogeneous metal/ceramic composite is able to self-heal at temperatures as high as 1,200 °C.

Analytical Model for the Deformation of Viscoelastic Non-Newtonian Drops Undergoing Secondary Atomization

While there is no single analytical model that accurately predicts all stages and modes of secondary atomization, many groups have developed models that predict deformation and oscillation of a single, isolated drop. The TAB (Taylor Analogy Breakup) model was chosen for this investigation, mainly due to its widespread use by Liu and Reitz [1], Hwang et al. [2], Tanner [3], and Lee and Reitz [4], among others. Since the TAB model is also the foundation for many other analytical models, it will also be used here as a starting point for the development of a viscoelastic non-Newtonian model to predict droplet deformed radii, droplet deformation time, and velocity at deformation time for viscoelastic xanthan gum - DI water solutions. Three additional improvements are made to this viscoelastic TAB model: the first is a change to a TAB coefficient; the second to the equation for the drag coefficient, and the third modification is to the breakup criterion. This model uses Carreau rheology and Zimm relaxation time. Non-dimensional drop diameter and initiation times are plotted against We; model results are compared to experimental results for a range of xanthan gum solution concentrations. Results show fair agreement between experimental results and model results for non-dimensional drop diameter, with the best match at low XG concentration and low-to-medium We (10–30). It was also noted that increased viscoelasticity seems to increase this drop diameter. Good agreement between experimental data and model results has been seen for initiation time, with increased viscoelasticity increasing this parameter as well.

The Effect of Gas Evolution on Hydrodynamic Characteristics of Fluid Flow in Pipeline

A relative motion of different phases leads to formation of certain forces at the interface of transported fluid and pipe walls. In the non-isothermal flow case a thermal interaction between the phases will affect the flow velocity, the pressure and the temperature distributions in variable cross section pipes. Laboratory experiments were conducted in order to study the effects of the gas generation at the pipe walls on the hydrodynamic characteristics of the two-phase oil/gas flow. It is shown that a throughput capacity of the pipe is affected by the temperature difference between the oil and the pipe walls. At certain temperature difference value (∼3°C) the pipe capacity reached a maximum value.

Effects of Stator Configurations on the Flotation Performance of Induced Gas Flotation Machine

Induced Gas Flotation (IGF) vessel is used for water treatment of plant industries such as oil sand and chemical plants. An understanding of the interaction between the stator and rotor is essential for the design of IGF with consideration of geometric blade configuration is essential for the design of IGF. In this study, the effect of the number of stator blades on flotation performance was numerically investigated using the commercial code, ANSYS CFX ver. 16.1. The two-phase (water and air) flow characteristics in the forced-air mechanically stirred Dorr-Oliver flotation cell were considered. The flotation performance was evaluated on the basis of the correlations among the number of stator blades (8, 12, 16, 20, 24), power number and void fraction. By comparing the result of each case, the newly designed model with 12 stator blades which had the highest flotation performance was derived.

The Numerical Simulation of Turbulent Flow in Semi-Closed Rotor-Stator Cavity

The present work numerically considered the turbulent flow in a semi-closed rotor-stator cavity with a superimposed throughflow based on Reynolds Stress Model (RSM). The mean flow structure and turbulent field in the semi-closed cavity (SC) were identified by comparison with the flow in open cavity (OC) and closed cavity (CC). Then the effects of rotation Reynolds number, ranging from 1 × 106 to 4 × 106, on the flow in SC were investigated. The superimposed flow noticeably decreases the tangential velocity, resulting that the pressure difference between central hub and periphery in SC is greater than the OC but less than the CC. The flow in SC belongs to Stewartson type in the region between inlet and outlet, but to Bachelor type between outlet and periphery. Around the outlets, the flow is greatly affected, especially for turbulent field, where the turbulence intensities maintain at higher levels outside the two boundary layers. With the increase of Reynolds number, the tangential velocity goes up, resulted the attenuation of jet impinging effects, the shrinking of affected zones by outlets and the enlargement of pressure difference. Moreover, with the Bödewadt layer moving toward the central hub, the turbulence intensities increase inside two boundary layers but decrease outside them. Consequently, the flow is transited to Stewartson and then Batchelor type.

Viscosity Prediction of Water-Based Silver Nanofluid Using Equilibrium Molecular Dynamics

Nanofluids containing silver (Ag) nanoparticles have been used in three dimensional ink-jet printing (3DP) in recent years. Rheological properties of the nanofluids, for example, viscosity, play significant roles during the application. In this paper, viscosity of Ag-water nanofluid has been predicted using the equilibrium molecular dynamics method. The influencing factors of the viscosity, including temperature, nanoparticle size, nanoparticle concentration and nanoparticle aggregation, have been investigated. By screening the existing water models, TIP4P/2005 model is found the most suitable for viscosity calculation under the temperature range. The weight fraction of the nanoparticles, which proves more appropriate, is used during the study of the concentration effect instead of volume fraction. The results show that the viscosity of the nanofluid goes up by decreasing temperature or increasing nanoparticle concentration. Furthermore, as the nanoparticles get smaller, or aggregate, the viscosity increases slightly.

The Critical Velocity With Minimum Momentum Change in Pushing a Droplet Through a Constriction Channel

Models of squeezing a droplet through a constrictions have wide applications in nature and engineering. In the present research, we found the minimum impulse required (momentum change) to squeeze a droplet through at different velocities. Our theoretical work result in an analytical expression of the critical velocity with minimum impulse. At this expression, we found a force balance between the average surface tension and the dynamic pressure loss at the channel inlet and outlet. Finally, we also compared the analytical results with numerical simulations. These results are important to understand some biological process and design of microscale filters.

Experimental Investigation of Ventilation Effectiveness in an Airliner Cabin Mockup

Frequent air travel and long flight duration makes the study of airliner cabin environmental quality a topic of utmost importance. Ventilation effectiveness is one of the more crucial factors affecting air quality in any environment. Ventilation effectiveness, along with the overall ventilation rate, is a measure of the ability of the air distribution system to remove internally generated pollutants or contaminants from a given space. Because of the high occupant density in an aircraft cabin, local variations in ventilation are important as a passenger will occupy the same space for the duration of the flight. Poor ventilation in even a small portion of the cabin could impact multiple people for extended time periods. In this study, the local effective ventilation rates and local ventilation effectiveness in an eleven-row, full-scale, Boeing 767 cabin mockup were measured. These measurements were completed at each of the 77 seats in the mockup. Each seat was occupied by a heated mannequin. In order to simulate the thermal load inside the cabin, the mannequins were wrapped with a heating wire to generate approximately 100 W (341 BTU/hour) of heat. Carbon dioxide was used as a tracer gas for the experiments and the tracer gas decay method was employed to calculate the local effective ventilation rate and local ventilation effectiveness. The overall ventilation rate, based on total supply air flow, was approximately 27 air changes per hour. Local ventilation effectiveness ranged from 0.86 to 1.02 with a mean value of 0.94. These ventilation effectiveness values are higher than typically found in other indoor applications and are likely due to the relatively high airspeeds present in the aircraft cabin and the high degree of mixing they provide. The uniformity is also good with no areas of particularly low ventilation effectiveness being identified. No clear patterns with respect to seat location, window versus center versus aisle, were found.

Comparison of Inlet Curved Disk Arrangements for Suppression of Recirculation in Centrifugal Pump Impellers

The present work aims to numerically study the inlet flow recirculation and modified impeller interaction in a centrifugal pump. An optimization of modified shrouded impeller with curved disk arrangement to suppress the unsteady flow recirculation is pursued. This modification will enhance the impeller characteristics with a wider operation range at both low and high flow rates in a high speed centrifugal pump type. The unstable flow in the centrifugal pumps is a common problem that leads to damage in the pump’s internal parts, consequently increases the operating cost. At certain flow rates, generally below the Best Efficiency Point (BEP), all centrifugal pumps are subject to internal recirculation occurs at the suction and discharge areas of the impeller. For decades, experimental work has been done to investigate the complex three-dimensional flow within centrifugal pumps impellers, before computational work gains momentum due to advancement of computing power and improved numerical codes. In this study the impeller with a curved disk arrangement has been investigated by using a three-dimensional Navier-Stokes code with a standard k-ε turbulence model. The purpose is to evaluate and select the optimum impeller modification that would increase the pump suction flow rate range. Three-dimensional numerical Computational Fluid Dynamics (CFD) tools are used to simulate flow field characteristics inside the centrifugal pump and provide critical hydraulic design information. In the present work, ANSYS v.16.1 Fluent solver is used to analyze the pressure and velocity distributions inside impeller suction and discharge passages. The ultimate goal of this study is to manufacture and validate the most optimized and efficient centrifugal pump impeller with a curved disk. The best case curve identifies the highest increase of total pressure difference by 22.1%, and highest efficiency by 92.3% at low flowrates.

CFD Simulation of Jet Mixing With Asymmetric Co-Flows in a Down-Scaled Rotary Kiln Model

Rotary kilns used in the iron pellet production in the grate-kiln pelletizing process normally have two asymmetric secondary air channels. The primary jet is ejected from a burner located in the middle of a back plate. As a consequence of the high flow rates and irregular-shaped secondary air channels, the aerodynamics in the kiln is strongly connected to the combustion and sintering performance. In this work a Computational Fluid Dynamics study is performed on a downscaled, simplified kiln model established in earlier numerical and experimental work. Comparisons are made with the experiment and among three turbulence models, the standard k-ε model, a k-ε model modified for turbulent axisymmetric round jets and Speziale-Sarkar-Garski Reynolds Stress Model (SSG-RSM hereafter). Recirculation regions with negative axial velocity are found at the upper side of the kiln and behind the back plate. Results from the standard k-ε model have the best fit to the experimental data regarding the centerline decay and the jet spreading of the velocity. The spreading rate of the scalar concentration calculated from the results with the modified k-ε model and the SSG-RSM fit better with the experiment, but they both underestimate the centerline decay and the spreading of the velocity. The modified k-ε model yields a more physical and realistic flow field compared to the standard k-ε model, and the results are close to those obtained with the SSG-RSM. Unlike the isotropic development of the jet predicted with the standard k-ε model, the modified k-ε model and the SSG-RSM show different development of the jet in the horizontal and vertical directions.