DETERMINATION METHOD OF VARIABLE DIFFUSION COEFFICIENTS OF HYGROSCOPIC MATERIAL FROM DRYING RATE CURVES OF THE SINGLE PARTICLE

ABSTRACT

The concentration dependency of diffusion coefficients of hygroscopic materials can usually only be calculated by cumbersome experimental techniques.

Taking the diffusion rate in the fictious steady state with the same mean moisture concentration as in the regular regime of the drying process of a spherical hygroscopic particle (which means the drying period not influenced by initial moisture distributions) into account, a simple method is proposed to estimate the dependency of diffusion coefficients on the moisture concentration for hygroscopic materials from drying rate curves of the single particle.     

Huggins' constant and unperturbed parameter of dilute polymer solutions

A novel method developed to evaluate the unperturbed parameter K_θ from the viscometric data of dilute polymer solutions can be considerably simplified by making the reasonable assumption that the Huggins' constant under theta conditions, k_Hθ, is equal to ½ for a number-average degree of polymerization of over about 2000. Two linear equations are derived pertaining to the present analysis, one to deal with the experimental data, and the other specially to estimate the intrinsic viscosity [η]θ which corresponds to κ_Hθ. All calculations were done by the linear least-squares method. The K_θ was computed by the Mark–Houwink–Sakurada equation. It is shown that reliable results on K_θ can be obtained for polystyrene and poly(vinyl acetate).     

Subnational nutrient budgets to monitor environmental risks in EU agriculture: calculating phosphorus budgets for 243 EU28 regions using public data

This paper presents a method to estimate soil surface phosphorus (P) budgets for 243 subnational regions in EU28. This is about the maximum spatial resolution that can be achieved mainly using international datasets that are regularly updated. Similar subnational budgets could be established for nitrogen (N) with some additions to this method. Increasing the spatial resolution from national to subnational is one way to address the well-known issue that national nutrient budgets sometimes mask considerable heterogeneity, i.e., regional surpluses and deficits that are not seen in national averages. Our results indeed show how a rich structure of different P budgets emerges when moving from national to subnational level. Another approach is to exclude the most extensively managed areas from the budgets, to better represent the surplus in intensive agriculture areas. Here, we show that both approaches are useful and sometimes important as they can affect P surplus estimates by about 10 kg P ha^??1 y^??1 or more. The choice of spatial resolution is a trade-off between accuracy and precision. National budgets are the most accurate thanks to good data coverage, but they sometimes fail to identify considerable P surpluses and deficits at subnational level. Increasing the precision (spatial resolution) gradually reveals this heterogeneity but comes at the cost of growing data gaps, which we discuss in detail. These subnational P surpluses represent a middle ground which may prove useful as one indicator among others to monitor the development of environmental risks and resource problems over time.

     

Differences and limits in estimates of persistence length for semi-flexible macromolecules

Persistence length of (bio)macromolecules plays an increasingly important role in macromolecular science, especially in emerging fields like macromolecular biophysics. It is shown that using established approximate relations for the estimation of persistence length for semi-flexible macromolecules leads to differences between different methods or even to a modified behavior, especially at high chain stiffness. The approximate estimate obtained from the average bond angle (B) performs better than the estimate from the decay of bond orientation correlation (C) in chain but close to the coil-to-rod transition starts to fail. This approximate estimate is close to the estimate from the definition of persistence (D) (with minimum approximations) not only in the theta state or the random coil but also in the good solvent. The value of persistence from the decay of bond orientation correlation along the macromolecule is underestimated when compared to the exact value. The persistence obtained from the worm-like chain model (W) is close to the exact result in the coil regime (also in the good solvent) but near at and above the transition produces the largest values of all approximations. In systems with interactions this model starts to underestimate the persistence on decreasing temperature. We advocate using the estimate (D) of persistence length generally since it avoids limitations mentioned above and at the same time does not pose additional requirements on the evaluation itself.     

Methodology to Estimate the Transfer Function of Individual Differential Mobility Analyzers

A method to estimate the nonideal features of the transfer function of individual differential mobility analyzers (DMA) was developed and tested experimentally. This was up to now an unsolved problem, which is important for the precision in DMA measurements. The method involves three DMAs of unknown characteristics, which are used in three rounds of experiments with two DMAs according to a fixed schedule. The width of the transfer functions of the three DMAs is obtained in a single fitting procedure where one parameter is fitted to each DMA transfer function and the particle losses in each DMA are calculated in direct relation to that parameter and parameters known from the experiment. It was shown that the proposed method could solve the apportioning problem and unambiguously estimate the transfer function width and the particle losses in each of the DMAs.     

Characterization of the mass transfer of lyophilized products based on X-ray micro-computed tomography images

ABSTRACT

This paper proposes a systematic work process for the rapid determination of resistance to vapor flow given by the products being freeze-dried. This approach couples mathematical modeling and 3D nondestructive X-ray imaging to reconstruct the internal structure of lyophilized samples. Knowledge of the internal structure is fundamental to better understand the relationship between freezing and within-product heterogeneity as well as between freezing and the drying behavior of the product being lyophilized. The method was validated upon mannitol-based formulations using various freezing protocols. This stepwise approach was demonstrated to be helpful to lyophilization professionals for the control of within-product heterogeneity and for the optimization of the cycle.     

Microwave Drying of Grapes in a Single Mode Cavity at 2450 Mhz - 11: Quality and Energy Aspects

ABSTRACT

Drying studies were conducted to optimize process parameters (air temperature T. microwave power density P and air velocity u) for quality and energy in microwave drying of grapes using a single mode cavity applicator at 2450 MHz. Thc quality was assessed by several attributes like colour. damage, darkness, crystallized sugar, stickiness and non-uniformity. Colour and damage attributes provided more preeise predietability when compared to the other quality attributes. Microwave dried raisins were lighter in colour and hence were superior to hot air dried samples. Quality attributes were sipnificantlv dependent on T. P and u. Increase in air velocitv resulted in better Quality raisins where as P and T had the opposite effect. Optimum selection of T, P and u was found to be critical to achieve an energy efficient process for a quality product. Response surface models in terms of temperature m d micowave power were obtained for each of the quality attributes. Process optimization of the operating variables through response surface method was performed by imposing certain constraint levels on quality attributes     

Effect of nanoclay on mechanical and thermal properties of triblock SBS (styrene–butadiene–styrene) and its binary blend nanocomposites: comparison between polyethylene and polystyrene

ABSTRACT

In this study, the effect of organo-modified nanoclay (OMMT) on the mechanical and thermal properties of SBS and its blend with low-density polyethylene (LDPE) and polystyrene was investigated. The effect of nanoclay content in the presence of LDPE or PS on the final properties of SBS was studied by tensile tester, dynamic mechanical thermal analysis (DMTA), thermal gravimetric analysis (TGA), X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Addition of nanoclay affected the mechanical and rheological properties. From X-ray and DMTA results, it was found that due to more affinity between the nanoparticles and the SBS/PE blend, the 2 theta characteristic peak of nanoclay shifted to lower angles. SEM studies showed better dispersion and lower inter-particle distance of nanoparticles in SBS/PE composites in comparison with SBS/PS and SBS composites, confirming the XRD and DMTA results. It can be concluded that nanoclay acts as a compatibilizer in the SBS/LLDPE blend. TGA studies showed higher stability of SBS/PS composites compared to SBS and SBS/PE ones.     

Theoretical Modeling of Filtration by Nonuniform Fibrous Filters

Modeling commercial filter media using classical theories results in incorrect filter pressure drop and efficiencies and this is attributed to media inhomogeneity. The use of an arbitrary inhomogeneity factor is seen to be inadequate in accounting for the effect of operating conditions on the performance of inhomogeneous filter media. A simplistic theoretical modeling approach is described here to account for the variations in filter packing densities and to estimate their effect on the media particle capture characteristics. The theoretical modeling results are used in obtaining an equivalent filter packing density distribution from media local efficiency measurements. Considering this variation in the theoretical models is seen to result in better prediction of media performance over a wide range of operating conditions. The observed deviation of experimental efficiencies from the theory at smaller Peclet numbers can be explained from the results of the theoretical analysis.     

Structure of Nylon-6 from Analysis of Viscoelastic Properties

Abstract

A method is outlined to study the structure property relationship in semicrystalline fibers involving (a) the characterization of structure in terms of the two phase amorphous-crystalline model (size, concentration and orientation of the crystallites, etc.), (b) the analysis of viscoelastic responses in terms of Takayanagi models, and (c) the analysis of diffusion assuming that crystals are essentially impermeable to large dye molecules. The method, which does not require an accurate estimate of the properties of a “completely” amorphous polymer, is applied to a series of oriented nylon 6 fibers. The study, which confirms the validity of the derived equation to describe the diffusion process in semi-crystalline polymers above the glass transition temperature, leads to a quantitative representation of the “efficiency” of crystal reinforcement as a function of the degree of crystallinity.     

AN EXPLICIT NEARLY UNBIASED ESTIMATE OF THE AR(1) PARAMETER FOR REPEATED MEASUREMENTS

Abstract. It is assumed that n ( n ≥ 1) independent time series, each of length T. have the same autocorrelation function of the AR(1) type, but they may differ in mean value, with the mean value of the i th series equal to a linear combination of a set of covariates associated with the series. To estimate the common autoregressive parameter, Daniels' method is extended to the present case. As, for small T , this gives a severely biased estimate, a formula for its mean value is obtained. A modified estimate which has a substantially smaller bias is found using this formula.     

Assessment and validation of a hygroscopic growth model with different water activity estimation methods

Abstract

Hygroscopic growth models are currently of interest as aids for targeting the deposition of inhaled drug particles in preferred areas of the lung that will maximize their pharmaceutical effect. Mathematical models derived to estimate hygroscopic growth over time have been previously developed but have not been thoroughly validated. For this study, model validation involved a comparison of modeled values to measured values when the growing droplet had reached equilibrium. A second validation process utilized a novel system to measure the growth of a droplet on a microscope coverslip relative to modeled values when the droplet is undergoing the initial rapid growth phase. Various methods currently used to estimate the water activity of the growing droplet, which influences the droplet growth rate, were also compared. Results indicated that a form of the hygroscopic growth model that utilizes coupled-differential equations to estimate droplet diameter and temperature over time was valid throughout droplet growth until it reached its equilibrium size. Accuracy was enhanced with the use of a polynomial expression to estimate water activity relative to the use of a simplified estimate of water activity based on Raoult’s Law. Model accuracy was also improved when constraining the film of salt solution surrounding the dissolving salt core at saturation.

Copyright © 2020 American Association for Aerosol Research     

Conformation of Styrene-Isoprene Block Copolymers in Dilute Solution

Abstract

Viscosity, gel permeation chromatography and light scattering data for two-and three-block copolymers of styrene and isoprene of various compositions and molecular weights have been determined in methylisobutyl ketone at 35°, a near theta solvent for both polystyrene and polyisoprene. The three techniques show that the molecular dimensions of the copolymers are only slightly larger than the sum of the unperturbed dimensions of individual sequences. Such results are interpreted in favour of a nearly segregated conformation with a limited number of heterocontacts.     

Long term durability of crosslinked polyethylene tubing used in chlorinated hot water systems

Abstract

The objectives of the present research are to understand better the degradation of crosslinked polyethylene tubing subjected to pressurised, hot chlorinated water in flow through systems (e.g. home plumbing) and to estimate its service lifetime. Crosslinked polyethylene tubing was subjected to pressure testing with flowing hot, chlorinated water at elevated temperatures from 90 to 120°C, with chlorine levels between 0 and 5 ppm. The combined effects of free chlorine, pH, and metal ion content on the time to failure were found to correlate better with the oxidation–reduction potential than with the free chlorine content directly. Consumption of the antioxidant was analysed using the oxidation induction time as a function of fraction of the time to failure in the tests, with the antioxidant being found to be completely consumed in less than half the time to failure at 115°C. Fractographic observations made using a scanning electron microscope indicated no degradation until the antioxidant was completely consumed. The nature of the damage at failure was investigated using highly polished cross-sections of pipe, which failed by a pinhole leak.     

WATER - CORN EQUILIBRIUM: TEMPERATURE DEPENDENCY OF THE G.A.B. MODEL PARAMETERS AND CALCULATION OF THE HEAT OF SORPTION

ABSTRACT

By using sorption data for com in the range of 4.4-60°C, the temperature (T) variations of the GAB. model parameters (M_m, C_B and k) were studied. As only the monolayer moisture (M_m) varied (decreased) with temperature, a generalized GAB equation of four total parameters was obtained. This, together with the Clapeyron equation allowed a method to calculate the heat of sorption (L_b) as a function of T and moisture content (M). For each temperature, Lb presented a maxinuin some 30% above the heat of vaporization of water (L_f), which occurred around the M_m, in congruence with the sorption theory. A similar behavior of L_b was found using the Othmer method. In contrast, the Gallaher equation predicted an ever increasing L_b up to 3 L_f at very low moistures. The GAB-Clapeyron method is then proposed to calculate L_b as a function of M and T.     

Extraction and Purification of Fullerenes: A Comprehensive Review

Abstract

This review summarizes the advances of the last four years in the field of fullerenes purification. Purification involves extraction from soots, which may be considered as a prepurification step, and separation by liquid chromatography, where the different stationary phases tested are listed. We also describe other purification techniques, like elution on molecular sieves or activated charcoal, gel permeation, and supercritical fluids purification. Our purpose is to show the reader the general trends for obtaining pure C₆₀ and C₇₀. We conclude that no technique is better than another, but that each purification method may offer its own qualities, depending on the application.     

Steady-State Characteristics of Lithium Isotope Separation by a Circuit of Continuous Displacement Chromatography

Abstract

Height equivalent to a theoretical plate (HETP), which is an important factor to determine separation performance, is experimentally obtained for lithium isotope separation by a circuit of continuous displacement chromatography. The values of HETP are related to the flow rates and concentrations of the displacement reagents. A new equation to estimate HETP is derived and shows good agreement with the experimental data. Diffusion in the resin is found to be the major resistance for the isotope exchange reaction, and liquid mixing in the columns also strongly influences the value of HETP.     

A New Method to Measure Aerosol Particle Bounce Using a Cascade Electrical Low Pressure Impactor

The phase state of secondary organic aerosol (SOA) in the atmosphere is of scientific interest as it can impact SOA growth and reactivity. For this purpose, a simplified method is described herein to estimate SOA bounce factor to gain an improved understanding of the phase state of atmospheric aerosols. This new method involves the use of a multistage electrical low pressure cascade impactor operating with either smooth or sintered impaction plates. Measurement of the raw current on smooth and sintered plates allows one to calculate the bounce factor, eliminating the need for a scanning mobility particle sizer to independently measure the SOA aerodynamic size distribution. The proposed method provides the temporal resolution necessary to measure phase changes in a continuously evolving SOA parcel.

We validate our method by measuring the bounce factor of solid and liquid aerosols, namely ammonium sulfate (AS), dioctyl sebacate (DOS), oleic acid (OA) and ozonized OA, and also present bounce factor evolution of aging α-pinene-derived aerosols. The results suggest that the new method can be used to understand the phase state of amorphous and crystalline substances, as well as distinguish between liquid and nonliquid particles.

Copyright 2015 American Association for Aerosol Research     

Further Theoretical Studies on Rotary Drying Processes Represented By Distributed Systems

ABSTRACT

Mathematical tools for studying panicle transpon in rotary drying and cooling processes are developed in this paper. In contrast to conventional approaches aimed at deriving empirical or xmi-empirical correlations, a rigorous mathematical analysis which employs dilferential calculus and analytical geometry is emphasis4 in the current research. These developments allow accurale computations of solid flowrate, retention time and particle holdup in rotary dryers with arbilrary flight configurations. Consequently, optimal dryer configuration design in terms of drum dimension, flight number and geometry can be achieved through a better understanding of the mathematical insight of rotary drum performance.

Techniques developed using this method are applied to the distributed parameter model eslablished earlier by the authors (Wang el al., 1993) to replace out-dated correlations for the determination of retention Lime and solid holdup. As a result of the new developments, the distributed parameter approach to the dynamics of rotary drying processes becomes more general and more reliable.     

A Note on the Aging Properties of the Run Length of Markov-Type Control Charts

Abstract

A change in a production process must be detected quickly so that a corrective action can be taken. Thus, it comes as no surprise that the run length (RL) is usually used to describe the performance of a quality control chart.

This popular performance measure has a phase-type distribution when dealing with Markov-type charts, namely, cumulative sum (CUSUM) and exponentially weighted moving average (EWMA) charts, as opposed to a geometric distribution, when standard Shewhart charts are in use.

In this article, we briefly discuss sufficient conditions on the associated probability transition matrix to deal with run lengths with aging properties such as new better than used in expectation, new better than used, and increasing hazard rate.

We also explore the implications of these aging properties of the run lengths, namely when we decide to confront the in control and out-of-control variances of the run lengths of matched in control Shewhart and Markov-type control charts.