Solid fuel combustion experiments in microgravity using a continuous fuel dispenser and related numerical simulations

The conventional way of determining the flammability characteristics of a material involves a number of tedious single-sample tests to distinguish flammable from non-flammable conditions. A novel test device and fuel configuration has been developed that permits multiple successive tests for indefinite lengths of thin solid materials. In this device, a spreading flame can be established and held at a fixed location in front of optimized diagnostics while continuous variations of test parameters are made. This device is especially well-suited to conducting experiments in space (e.g. aboard the International Space Station) where the limited resources of stowage, volume, and crew time pose major constraints. A prototype version of this device was tested successfully in both a normal gravity laboratory and during low-gravity aircraft trials. As part of this ongoing study of material flammability behavior, a numerical model of concurrent-flow flame spread is used to simulate the flame. Two and three-dimensional steady-state forms of the compressible Navier-Stokes equations with chemical reactions and gas and solid radiation are solved. The model is used to assist in the design of the test apparatus and to interpret the results of microgravity experiments. This paper describes details of the fuel testing device and planned experiment diagnostics. A special fuel, developed to optimize use of the special testing device, is described. Some results of the numerical flame spread model are presented to explain the three-dimensional nature of flames spreading in concurrent flow and to show how the model is used as an experiment design tool.     

A wire-woven cellular metal: Part-II, Evaluation by experiments and numerical simulations

Wire-woven bulk Kagome (WBK) is a new truss-type cellular metal fabricated by systematic assembly of helical wires in six directions. In Part-I of this work, analytic solutions for equivalent material properties, such as yield stress and elastic modulus of WBK under compression and shear were derived. The load capacities of a WBK-cored sandwich panel under bending were predicted for various failure modes, and optimal designs of the WBK-cored sandwich panel were determined. In this work, the overall performance of a WBK-cored sandwich panel under shear and bending loads were evaluated in more detail by experiment and finite element (FE) simulation. Using comparisons with our experimental and numerical results, we show that the simple analytic solutions obtained in Part-I gave effective and accurate solutions. Hence, the model optimally designed on the basis of the analytic solutions gave the expected results. Furthermore, the WBK-cored sandwich panel showed excellent performance in terms of load capacity, energy absorption, and deformation stability after the maximum load point.     

Failure of cemented granular materials under simple compression: experiments and numerical simulations

We investigate the strength and failure properties of a model cemented granular material under simple compressive deformation. The particles are lightweight expanded clay aggregate beads coated by a controlled volume fraction of silicone. The beads are mixed with a joint seal paste (the matrix) and molded to obtain dense cemented granular samples of cylindrical shape. Several samples are prepared for different volume fractions of the matrix, controlling the porosity, and silicone coating upon which depends the effective particle–matrix adhesion. Interestingly, the compressive strength is found to be an affine function of the product of the matrix volume fraction and effective particle–matrix adhesion. On the other hand, it is shown that particle damage occurs beyond a critical value of the contact debonding energy. The experiments suggest three regimes of crack propagation corresponding to no particle damage, particle abrasion and particle fragmentation, respectively, depending on the matrix volume fraction and effective particle–matrix adhesion. We also use a sub-particle lattice discretization method to simulate cemented granular materials in two dimensions. The numerical results for crack regimes and the compressive strength are in excellent agreement with the experiments.     

Mechanistic investigation of mixing and segregation of ordered mixtures: experiments and numerical simulations

Pulmonary delivery of cohesive and micronized drugs through dry powder inhalers (DPIs) is traditionally achieved through the formation of ordered mixtures. In order to improve the mechanistic understanding of formation of ordered mixtures, the system consisting of micronized lactose (AZFL, representative of an active pharmaceutical ingredient) and a coarse particle carrier (LH100) is investigated as a function of different process and material variables in a high shear mixer (HSM) and in a low shear double cone (DCN) blender, using both experimental and numerical methods. Process insight is developed using a Discrete Element Method (DEM) based numerical model which could predict the formation of ordered mixtures in the two blenders and was verified against experimental determinations. Spatial and temporal evolution of granular flow are visualized and quantified in silico to reveal distinguishing features of both blenders to aid in rational selection of blenders and process parameters.     

Sediment transport over a flat bed in a unidirectional flow: simulations and validation

A discrete particle model is described which simulates bedload transport over a flat bed of a unimodal mixed-sized distribution of particles. Simple physical rules are applied to large numbers of discrete sediment grains moving within a unidirectional flow. The modelling assumptions and main algorithms of the bedload transport model are presented and discussed. Sediment particles are represented by smooth spheres, which move under the drag forces of a simulated fluid flow. Bedload mass-transport rates calculated by the model exhibit a low sensitivity to chosen model parameters. Comparisons of the calculated mass-transport rates with well-established empirical relationships are good, strongly suggesting that the discrete particle model has captured the essential elements of the system physics. This performance provides strong justification for future interrogation of the model to investigate details of the small-scale constituent processes which have hitherto been outside the reach of previous experimental and modelling investigations.     

Synthesis and characterization of PbSe nanoparticles obtained by a colloidal route using Extran as a surfactant at low temperature

Lead selenide nanoparticles (PbSe NPs) have been obtained through an easy and low cost route using colloidal synthesis in aqueous solution. The synthesis was carried out at room temperature using Extran (Na?P?O??, NaOH and H?O) as surfactant. Hydrochloric acid (HCl) was used to eliminate the generated by-products. The size of PbSe NPs was varied by changing the Pb:Se molar concentration. The PbSe NPs were characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDAX), high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The XRD measurements showed that the PbSe NPs have the face-centered cubic phase structure. The crystal size was found to be between 14 and 20 nm as calculated from the XRD patterns and these values were corroborated with SEM and TEM. Additionally, HRTEM micrographs showed crystalline planes at (200), (220) and (111) of the PbSe NPs, in agreement with the XRD results.     

Quantifying drying performance of a filter dryer: Experiments and simulations

Drying is one of the most commonly used unit operations in the preparation of dry granules by thermally removing volatile solvent from the wet solid. The study focuses on the quantitative investigation of heat transfer in a filter dryer in the quest to determine the optimum drying conditions. Consequently, contact drying kinetics of glassbeads–ethanol and lactose–ethanol system is investigated using an agitated filter dryer (Charles Thompson). Discrete element method is employed to simulate granular flow, mixing and heat transport in the vessel. Typical system with glass beads is numerically simulated using appropriate material properties and validated by the experimental findings. A parametric study for both simulations and experiments is performed to assess the effect of various conditions of wall temperature, fill level and impeller speed on the drying performance in the filter dryer. A high wall temperature showed an increase in the drying rate and a sharp rise in the average bed temperature, thereby decreasing the total time for drying operation. An increase in fill volume (bed depth) at constant wall temperature and speed resulted in a decline in the drying rate. The rotational speed had a nominal impact on drying of glass beads. Hence low rotational speeds seemed optimal for contact drying.     

Study of using a capillary tube in a heat pump dishwasher with transient heating

For competitive purposes, manufacturers of household appliances need to produce appliances that use less electricity. One way of doing this for a dishwasher is to add a heat pump system. Previous studies using R134a as refrigerant have shown that the addition of a heat pump can reduce total electricity consumption by about 24%. This paper reports on the use of a capillary tube in a heat pump dishwasher during the transient heating period. Working with an available compressor, the mass of R600a and the length of a 0.9 mm capillary tube were varied in order to find the configuration with the lowest electricity consumption. Three methods of calculating the length of the capillary tube were used to determine five lengths for evaluation. The results show that using a single capillary tube throughout the transient heating period yields similar electricity consumption to a variable expansion device which occurred by switching the capillary tube between two or three different lengths during the heating period.     

Self-organization of colloidal particles during drying of a droplet: Modeling and experimental study

Formation of structurized micro/nanoparticle aggregates in spray drying process is analyzed theoretically and experimentally. Colloids of mono- and bimodal particle size distribution are used as the precursors to demonstrate different patterns of particle self-organization inside the drying droplet. In case of monodisperse primary particles their self-organization in the final aggregate results in either a hollow or a full (packed) spherical structure. For primary particles with bimodal size distribution, either the layered structure of aggregates is formed (with smaller particles forming outer layer and the bigger particles captured inside) or the ordering of bigger particles on the aggregate surface is observed, depending on process parameters. Numerical investigations allow to predict and explain the conditions at which self-assembling of particles within powder aggregates takes place.     

Two-dimensional turbulent film condensation of vapours flowing inside a vertical tube and between parallel plates: a numerical approach

Film condensation of vapour flowing inside a vertical tube and between parallel plates is treated. A methodology is presented to determine numerically the heat transfer coefficients, the film thickness and the pressure drop. The analysis is based on the resolution of the full coupled boundary layer equations of the liquid and vapour phases and does not neglect inertia and convection terms in the governing equations. Turbulence in the vapour and condensate film is taken into account using mixing length turbulence models. An explicit method and an implicit finite difference procedures are described. The calculated results for the condensation of steam in a 24 mm diameter tube are compared with those obtained from Chen's correlation. The heat flow rate for the condensation of R123 flowing between parallel plates obtained from numerical solution are compared with experimental values. The mean heat transfer coefficients for the condensation of vapour mixture R123/R134a are also presented.     

Nonlinearly elastic membrane model for heterogeneous plates: a formal asymptotic approach by using a new double scale variational formulation

This paper is concerned with the asymptotic analysis of plates with periodically rapidly varying heterogeneities. The asymptotic analysis is performed when both the material properties and the thickness of the plate are of the same orders of magnitude. We consider a plate made of Saint Venant-Kirchhoff type materials then we justify a new two-scale variational formulation. We assume that both the data and the displacement field admit a formal asymptotic expansion with a negative order of the leading term. We then prove that the lowest order term of the displacement field must be of order zero. Finally, we consider the particular case of a laminated plate clamped along its lateral boundary and we show that this term satisfies a two-dimensional nonlinear membrane model.     

δ25 Crack opening displacement parameter in cohesive zone models: experiments and simulations in asphalt concrete

Recent work with fracture characterization of asphalt concrete has shown that a cohesive zone model (CZM) provides insight into the fracture process of the materials. However, a current approach to estimate fracture energy, i.e., in terms of area of force versus crack mouth opening displacement (CMOD), for asphalt concrete overpredicts its magnitude. Therefore, the δ₂₅ parameter, which was inspired by the δ₅ concept of Schwalbe and co‐workers, is proposed as an operational definition of a crack tip opening displacement (CTOD). The δ₂₅ measurement is incorporated into an experimental study of validation of its usefulness with asphalt concrete, and is utilized to estimate fracture energy. The work presented herein validates the δ₂₅ parameter for asphalt concrete, describes the experimental techniques for utilizing the δ₂₅ parameter, and presents three‐dimensional (3D) CZM simulations with a specially tailored cohesive relation. The integration of the δ₂₅ parameter and new cohesive model has provided further insight into the fracture process of asphalt concrete with relatively good agreement between experimental results and numerical simulations.     

A study on numerical simulations and experiments for mass transfer in bubble mode absorber of ammonia and water

An absorber is a major component in the absorption refrigeration systems, and its performance greatly affects the overall system performance. In this study, both the numerical and experimental analyses in the absorption process of a bubble mode absorber were performed. Gas was injected into the bottom of the absorber at a constant solution flow rate. The region of gas absorption was estimated by both numerical and experimental analyses. A higher gas flow rate increases the region of gas absorption. As the temperature and concentration of the input solution decrease, the region of gas absorption decreases. In addition, the absorption performance of the countercurrent flow was superior to that of cocurrent. Mathematical modeling equations were derived from the material balance for the gas and liquid phases based on neglecting the heat and mass transfer of water from liquid to gas phase. A comparison of the model simulation and experimental results shows similar values. This means that this numerical model can be applied for design of a bubble mode absorber.     

Implementation and validation of a triaxiality dependent cohesive model: experiments and simulations

A recently formulated triaxiality dependent cohesive model for plane strain is implemented and its versatility is tested in simulation of ductile fracture of mild steel at different states of stress. The triaxiality dependent model was implemented as linear displacement formulation based elements whose constitutive behaviour was dependent on the stress-state of the neighbouring continuum element. By comparing the experimental data and predictions of corresponding plane strain simulations, the model parameters are estimated. The model is shown to be effective in reproducing characteristic features of the macroscopic response of both pre-cracked as well as geometries without a preexisting nominal defect. Since the model parameters are held constant for simulations at different stress-states, they are effectively material constants.     

Microneedle-assisted transdermal delivery of Zolmitriptan: effect of microneedle geometry,in vitro permeation experiments,scaling analyses and numerical simulations

Objective: The present study was aimed to investigate the effect of salient microneedle (MN) geometry parameters like length, density, shape and type on transdermal permeation enhancement of Zolmitriptan (ZMT).

Methods: Two types of MN devices viz. AdminPatch^® arrays (ADM) (0.6, 0.9, 1.2 and 1.5?mm lengths) and laboratory fabricated polymeric MNs (PM) of 0.6?mm length were employed. In the case of PMs, arrays were applied thrice at different places within a 1.77?cm² skin area (PM-3) to maintain the MN density closer to 0.6?mm ADM. Scaling analyses was done using dimensionless parameters like concentration of ZMT (C_t/C_s), thickness (h/L) and surface area of the skin (Sa/L²).

Results: Micro-injection molding technique was employed to fabricate PM. Histological studies revealed that the PM, owing to their geometry/design, formed wider and deeper microconduits when compared to ADM of similar length. Approximately 3.17- and 3.65-fold increase in ZMT flux values were observed with 1.5?mm ADM and PM-3 applications when compared to the passive studies. Good correlations were observed between different dimensionless parameters with scaling analyses. Numerical simulations, using MATLAB and COMSOL software, based on experimental data and histological images provided information regarding the ZMT skin distribution after MN application.

Discussion: Both from experimental studies and simulations, it was inferred that PM were more effective in enhancing the transdermal delivery of ZMT when compared to ADM.

Conclusions: The study suggests that MN application enhances the ZMT transdermal permeation and the geometrical parameters of MNs play an important role in the degree of such enhancement.