Obtaining more,and better,information from simple ramped temperature screening tests

Thermal screening of materials is a vital part of hazard assessment in the chemical industry. There is the need to identify the worst potential hazards and to further investigate these scenarios. Several screening methods are presented, and the subject of ramped temperature screening tests is studied in detail. Methods for the detection of exothermic reaction 'onset' temperatures are given. It is shown that, under some circumstances, the temperature data obtained during a simple controlled ramp heating experiment can be used to estimate the expected temperature rise that would occur under adiabatic conditions and the heat of reaction. The use of the data to obtain n^th order kinetic parameters is also demonstrated. Data obtained using the Thermal Screening Unit (TS^U) are compared to those obtained using other forms of apparatus. Heats of reaction and kinetic data have also been calculated and compare very well with data obtained using much more sophisticated adiabatic calorimeters. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature effects in capillary electrophoresis. 1: Internal capillary temperature and effect upon performance

Summary In isothermal CE the migration velocity of analytes and the number of theoretical plates delivered are expected to be proportional to the field strength. In reality ohmic heating of the capillary causes distortions: the migration velocity increases more rapidly while the plate count increases less rapidly, and may even fall at high values of the field. These distortions are worse the larger the bore of the capillary and the higher the concentration of buffer. A detailed investigation of these effects using capillaries cooled by natural convection has confirmed that self heating of the capillary is indeed largely responsible. The extent of self heating has been determined by three independent methods and to a first approximation is proportional to the power dissipation in the capillary. Decreasing viscosity with temperature is responsible for the nonlinearity of the dependence of velocity upon field strength while increase in the diffusion coefficient of analytes is responsible for the poorer than expected performance at high field strengths.     

Determination of 2-methylisoborneol and geosmin in aqueous samples by static headspace-gas chromatography-mass spectrometry with ramped inlet pressure

A method for determining the earthy and musty odors 2-methylisoborneol (2-MIB) and geosmin in drinking water using static headspace-GC-MS is described. To achieve lower detection limits, split ratio was optimized with ramped inlet pressure for large headspace sampling volume. The ramped inlet pressure, which held higher pressure (higher column flow rate) only during injection, allowed us to inject 3-mL volume to GC with very low split ratio (2:1). Although sequential analysis with a stainless steel ion source often changed the mass spectrum of 2-MIB, this spectral change was eliminated by using an inert ion source with a 6 mm drawout plate. The detection limits of this method were 0.36 and 0.14 ng/L, respectively, for 2-MIB and geosmin. The repeatabilities (n = 30) were 6.6 and 4.8%, respectively, at 1 ng/L for 2-MIB and geosmin.     

Chemical reaction and Soret effect on an unsteady MHD heat and mass transfer fluid flow along an infinite vertical plate with radiation and heat absorption

In the current investigation, it is anticipated to examine the influence of heat absorption and radiation on an unsteady transient MHD heat and mass transfer natural convective flow of an optically thin non-Grey Newtonian fluid through an abruptly started infinite vertical porous plate with ramped wall temperature and plate velocity in the presence of Soret and chemical reaction of the first order is solved precisely. Using the similarity variables, the governed PDE's are converted into dimensionless governing equations and they are solved numerically by employing the finite element technique. Numerical calculations and graphs are used to illustrate the important features of the solution on fluid flow velocity, heat, and mass transfer characteristics under different quantities of parametric circumstances entering into the problem. Moreover, we computed the physical variables such as the coefficient of drag force, rate of heat, and mass transfer. The findings indicate that when the thermal radiation parameter increases, the thermal boundary layer becomes thinner. To establish the veracity of our present results, we compared them to previously published research and found substantial concordance.     

Numerical model of non-isothermal pervaporation in a rectangular channel

A numerical model of non-isothermal pervaporation was developed to investigate the development of the velocity, concentration and temperature fields in rectangular membrane module geometry. The model consists of the coupled Navier–Stokes equations to describe the flow field, the energy equation for the temperature field, and the species convection-diffusion equations for the concentration fields of the solution species. The coupled nonlinear transport equations were solved simultaneously for the velocity, temperature and concentration fields via a finite element approach. Simulation test cases for trichloroethylene/water, ethanol/water and iso-propanol/water pervaporation, under laminar flow conditions, revealed temperature drop axially along the module and orthogonal to the membrane surface. The nonlinear character of the concentration and temperature boundary-layers are most significant near the membrane surface. Estimation of the mass transfer coefficient assuming isothermal assumption conditions can significantly deviate from the non-isothermal predictions. For laminar conditions, predictions of the feed-side mass transfer coefficient converged to predictions from the classical Lévêque solution as the feed temperature approached the permeate temperature.     

Insights into stretching ratio and velocity slip on MHD rotating flow of Maxwell nanofluid over a stretching sheet: Semi-analytical technique OHAM

Main core part of the research is to develop a novel mathematical model of MHD-Maxwell nanofluid over a stretching and shrinking surface. The stretching ratio, velocity slip and convective boundary conditions are also incorporated. The PDE's with associative boundary conditions are deduced into coupled highly non-linear ODE's by utilizing suitable transformations. The deduced dimensionless sets of Ordinary differential equations are solved by Optimal-Homotopy Analysis Method (OHAM). Behavior of pertinent parameters on the velocity, temperature and concentration fields as well as important aspects skin friction, Nusselt number and Sherwood number are recorded in Table 2. Outcomes declared that role of stretching ratio plays a prominent role in stretching surfaces its clearly recorded in Table 1(a & b).     

Characterization of Simultaneous Heat and Mass Transfer Phenomena for Water Vapour Condensation on a Solid Surface in an Abiotic Environment—Application to Bioprocesses

The phenomenon of heat and mass transfer by condensation of water vapour from humid air involves several key concepts in aerobic bioreactors. The high performance of bioreactors results from optimised interactions between biological processes and multiphase heat and mass transfer. Indeed in various processes such as submerged fermenters and solid-state fermenters, gas/liquid transfer need to be well controlled, as it is involved at the microorganism interface and for the control of the global process. For the theoretical prediction of such phenomena, mathematical models require heat and mass transfer coefficients. To date, very few data have been validated concerning mass transfer coefficients from humid air inflows relevant to those bioprocesses. Our study focussed on the condensation process of water vapour and developed an experimental set-up and protocol to study the velocity profiles and the mass flux on a small size horizontal flat plate in controlled environmental conditions. A closed circuit wind tunnel facility was used to control the temperature, hygrometry and hydrodynamics of the flow. The temperature of the active surface was controlled and kept isothermal below the dew point to induce condensation, by the use of thermoelectricity. The experiments were performed at ambient temperature for a relative humidity between 35?C65% and for a velocity of 1.0?ms^?1. The obtained data are analysed and compared to available theoretical calculations on condensation mass flux.     

Effect of temperature on the separation of chlorophenoxy acids and carbamates by capillary high-performance liquid chromatography and UV (or diode array) detection

In this work, the effect of temperature in isothermal and programmed modes on several chromatographic parameters such as retention factor, selectivity, resolution and plate number has been discussed. A critical comparison of isocratic/isothermal, gradient/isothermal and isocratic/program temperature modes has been made. Two representative families of pesticides have been selected for this study. One includes ionisable chlorophenoxy acids and two of their esters, some of which show similar polarities. The other one contains several weakly polar carbamates. Analysis was carried out using a reversed-phase capillary high-performance liquid chromatography (HPLC) system and focusing technique with UV or diode array detection (DAD).     

Thermal Marangoni Convection of a Fluid Film Coating a Deformable Membrane

The thermal Marangoni instability of a fluid film coating a deformable membrane has been investigated by taking into account the deformation of the fluid free surface. Numerical calculations for different thermal boundary conditions are presented. The prestressed membrane is supposed to be very thin and therefore its behavior is similar to that of an isothermal fluid free surface with a surface tension but with a different mechanical boundary condition; that is, the fluid should stick on its surface and thus the fluid velocity is zero. An important assumption is that the membrane has no temperature dependence and therefore that only one Marangoni number exists for the free surface of the fluid. Numerical results are presented for stationary and oscillatory thermocapillary instability in both the sinuous and the varicose modes. It is shown that membrane deformation has important implications on the Marangoni instability of the fluid layer for positive and negative Marangoni numbers. Copyright 2001 Academic Press.     

Prediction of theoretical plate number in isothermal gas chromatographic analysis on capillary columns

A method for the prediction of the efficiency of gas chromatographic analysis in isothermal conditions by using experimental data of 1-alcohols and n-alkanes measured on capillary columns filled with polar and non-polar stationary phases in isothermal and isobaric conditions is described. The theoretical plate height trend indicates the change of separation efficiency as a function of inlet pressure and column temperature. By evaluating the variation of the diffusion coefficients of the analysed compounds into the mobile and stationary phase it is possible to predict the column efficiency and the number of theoretical plates at any temperature.     

Numerical treatment of Casson nanofluid Bioconvectional flow with heat transfer due to stretching cylinder/plate: Variable physical properties

PurposeThe purpose of the current framework is to scrutinize the two-dimensional flow and heat transfer of Casson nanofluid over cylinder/plate along with impacts of thermophoresis and Brownian motion effects. Also, the effects of exponential thermal sink/source, bioconvection, and motile microorganisms are taken.Methodology/ApproachThe resulting non-linear equations (PDEs) are reformed into nonlinear ODEs by using appropriate similarity variables. The resultant non-linear (ODEs) were numerically evaluated by the use of the Bvp4c package in the mathematical solver MATLAB.FindingsThe numerical and graphical illustration regarding outcomes represents the performance of flow-involved physical parameters on velocity, temperature, concentration, and microorganism profiles. Additionally, the skin friction coefficient, local Nusselt number, local Sherwood number, and local microorganism density number are computed numerically for the current presented system. We noted that the velocity profile diminishes for the rising estimations of magnetic and mixed convection parameters. The Prandtl number corresponds with the declining performance of the temperature profile observed. The enhancement in the values of the Solutal Biot number and Brownian motion parameter increased in the concentration profile.OriginalityIn specific, this framework focuses on the rising heat transfer of Casson nanofluid with bioconvection by using a shooting mathematical model. The novel approach of the presented study is the use of motile microorganisms with exponential thermal sink/source in a Casson nano-fluid through a cylinder/plate. A presented study performed first time in the author’s opinion. Understanding the flow characteristics and behaviors of these nanofluids is crucial for the scientific community in the developing subject of nanofluids.     

Comparison of Different Compositions of Mixed Pentane/1,4-Dioxane Mobile Phases in SFC

Abstract

The effective plate number has been chosen for a comparison between different mixed mobile phases composed of pentane and 1,4-dioxane. A column packed with unmodified silica gel and pyrene as the analyte was used. The dependence of the effective plate number on pressure and composition for a constant temperature, or a constant reduced temperature, both at constant mass flow, are shown in three dimensional network plots. The same dependence is shown at constant temperature and constant linear velocity.

For a detailed discussion, the dependence of the effective plate number on pressure, composition, capacity ratio, and other chromatographic parameters is given in two dimensional graphs. The main result for the present chromatographic system is that a Financial support by the Arbeitsgemeinschaft Industrieller Forschungsvereinigungen (AIF) is gratefully acknowledged.     

Untypical Surface Properties of the System Caprylic Acid + n-Propyl Acetate

The surface tensions of nonaqueous solutions of n-propyl acetate in caprylic (n-octanoic) acid were measured between 273 and 303 K using the Wilhelmy plate method. Complicated concentration dependences were obtained, different from any previously reported. In addition, independent volumetric and acoustic (sound velocity and absorption) methods were applied. The results are interpreted in terms of formation of weak complexes in the bulk as well as at the surface.     

Optimization strategies in micellar electrokinetic capillary chromatography. Optimization of the temperature of the separation capillary

Summary The influence of the temperature of the capillary on the separation of small molecules by micellar electrokinetic chromatography with buffers containing sodium dodecyl sulfate was examined. Investigated parameters were the electroosmotic velocity, the migration velocity of the micelles, the strength of the electric current, retention factors and plate numbers. Thermodynamic parameters associated with micelle solubilization were evaluated from the variation of the retention factor with temperature. An investigation was carried out as to whether the dependence of the electroosmotic velocity and the migration velocity of the micelles are mainly due to the decrease in viscosity and dielectric constant with increase in temperature. The temperature of the capillary strongly affects the plate numbers for various solutes obtained with the same chromatographic system. In order to exclude secondary effects by alteration of the instrumental band broadening and the electroosmotic velocity with temperature, a method is presented that permits the development of chromatograms in MEKC at various temperatures with constant injected plug length and constant electroosmotic velocity. The results are discussed from the point of view of minimizing the analysis time and optimizing the resolution.     

On the evaporation and motion of a volatile droplet near a volatile liquid surface

A problem concerning the free evaporation or condensation growth of a droplet near an infinite planar surface of the same liquid is solved. The behavior of the droplet is considered at vapor temperature and concentration gradients preset at an infinite distance from it. The boundary conditions take into account effects that are linear with respect to the Knudsen number. Equations are derived for the rate of variations in the radius of the droplet and the velocity of its steady motion induced by nonuniform temperature and concentration of the vapor. Dependences of the rate of variations in the radius and the velocity of the steady motion of the droplet on the distance from the planar surface are presented for a droplet 1 ??m in radius suspended in air.     

Contribution to the time balance in gas-liquid chromatography new definition equations of the retention times and retention volumes

The numerous research groups and researchers, as well as IUPAC, that during the last half century have dealt with different theoretical and practical problems in gas-liquid chromatography (GLC), including its nomenclature, have failed in giving an exact definition equation of the net retention time. Using our earlier results and starting from a time balance of GLC we have solved this problem by introducing the so-called acceleration time, t(ac), in the absence of which, the theoretical plate number concept, including the stationary phase transfer, is misinterpreted. The measurements were carried out both on support coated and on wall-coated open tubular columns with apolar and polar stationary phases. Different relationships of t(ac) with some solute properties and the column temperature for a series of n-alkanes on an apolar stationary phase under isothermal conditions were tested. The results obtained are presented in different tables and mathematical relationships.     

Photophoresis of an aerosol sphere normal to a plane wall

A combined analytical-numerical study is presented for the quasisteady photophoretic motion of a spherical aerosol particle of arbitrary thermal conductivity and surface properties exposed to a radiative flux perpendicular to a large plane wall. The Knudsen number is assumed to be so small that the fluid flow is described by a continuum model with a temperature jump, a thermal slip, and a frictional slip at the surface of the radiation-absorbing particle. In the limit of small Peclet and Reynolds numbers, the appropriate equations of conservation of energy and momentum for the system are solved using a boundary collocation method and numerical results for the photophoretic velocity of the particle are obtained for various cases. The presence of the neighboring wall causes two basic effects on the particle velocity: first, the local temperature gradient on the particle surface is enhanced or reduced by the wall, thereby speeding up or slowing down the particle; second, the wall increases viscous retardation of the moving particle. The net effect of the wall can decrease or increase the particle velocity, depending upon the relative conductivity and surface properties of the particle as well as the relative particle-wall separation distance. In general, the boundary effect of a plane wall on the photophoresis of an aerosol particle can be quite significant in some situations. In most aerosol systems, the boundary effect on photophoresis is weaker than that on the motion driven by a gravitational field.     

甲醛-苯氧乙酸树脂对金属离子的交换性能研究

研究了甲醛-苯氧乙酸树脂对重金属离子铅、镉、汞的交换性能,并考察了温度、pH值、浓度等因素对交换性能的影响。结果表明,树脂对3种重金属离子的等温交换过程均符合Langmuir交换等温式,交换受液膜扩散控制;其交换容量可分别达1.85mmol/g、1.73mmol/g、1.13mmol/g。     

Chromatographic terminal band lengths

A terminal band length is defined here as the length of a dispersed solute band as it emerges from the chromatographic column. The number of terminal band lengths per column can be used in the same way that the number of theoretical plates per column is used to measure and compare chromatographic efficiencies, but with greater insight since the proposed unit of measure is an easily visualized, real entity. In addition, the height equivalent to a theoretical plate (HETP) can be regarded as a ratio of the terminal band lenght to sixteen times the number of equivalent terminal band lengths that could be contained in tandem in the column. This concept offers another approach to understanding the meaning of the term, HETP. The terminal band length of a series of homologues is constant and independent of retention time above a certain solute molecular size and column capacity ratio. Within those conditions the correlation between the recorded peak width and retention time during isothermal analysis occurs primarily as a result of change in solute velocity.     

A calculation method for the prediction of effective plate height in capillary gas chromatography

The effective plate height, h_eff, is considered to be a better measure of the efficiency of capillary column than the conventional plate height, h, in isothermal conditions. By using experimental data of 1-alcohols and n-alkanes, 2-ketones and 1-alkenes measured on capillary columns coated with non-polar stationary phases in isothermal and isobaric conditions, the peak width at half height is predicted with a function similar at that of adjusted retention time. The results obtained under different analytical conditions as the head pressure and the temperature of the column confirm the validity of the model, whose parameters are linear, and as a consequence a unique solution is obtained.