Non-isothermal tests

Dynamic properties ASTM D4065-90 ASTM D4473-90 Viscoelastic properties Cure effects on viscosity Dynamic properties of supported and unsupported resins Isothermal and non-isothermal tests... 

The effects of cure on the viscosity of thermoset resins are monitored on the catalysed resin and are associated with the late injection, packing and curing cycles of a thermoset process. There are essentially two types of test methods, namely isothermal and non-isothermal tests, which are usually performed in dynamic or steady shear. 

Yu et al. (2011) studied rheology and phase separation of polymer blends with weak dynamic asymmetry ((poly(Me methacrylate)/poly(styrene-co-maleic anhydride)). They showed that the failure of methods, such as the time-temperature superposition principle in isothermal experiments or the deviation of the storage modulus from the apparent extrapolation of modulus in the miscible regime in non-isothermal tests, to predict the binodal temperature is not always applicable in systems with weak dynamic asymmetry. Therefore, they proposed a rheological model, which is an integration of the double reptation model and the selfconcentration model to describe the linear viscoelasticity of miscible blends. Then, the deviatirMi of experimental data from the model predictions for miscible... 

A very fast testing of polymer stability is based on non-isothermal experiments (DSC, chemiluminescence) where the whole plot of the parameter followed may be visualized over a large temperature interval. The transfer of non-isothermal data to isothermal induction times involves a variety of more or less sophisticated approaches such as published in Ref. [8] or discussed later. 

The final test of the proposed nonlinear robust controllers to be presented in this chapter is its implementation in a highly nonlinear reactor an non-isothermal homopolymerization carried out in a CSTR. In this case, we develop a multivariable version of the nonlinear regulator, in contrast to the SISO versions used in the previous examples. 

Many apparent discrepancies can be found in the experimental results reported in literature for NSRC operation. They are usually caused by inconsistent experimental conditions, which have to be taken into account carefully (cf. Burch, 2004). Actual temperature, non-isothermal conditions in the test reactor, the composition of the gas mixture (presence of C02 and H20, ratio of NO/N02 at the inlet, the used reducing components), transport limitations and dynamics of the measurements are the most important ones. 

The importance of adsorbent non-isothermality during the measurement of sorption kinetics has been recognized in recent years. Several mathematical models to describe the non-isothermal sorption kinetics have been formulated [1-9]. Of particular interest are the models describing the uptake during a differential sorption test because they provide relatively simple analytical solutions for data analysis [6-9]. These models assume that mass transfer can be described by the Fickian diffusion model and heat transfer from the solid is controlled by a film resistance outside the adsorbent particle. Diffusion of adsorbed molecules inside the adsorbent and gas diffusion in the interparticle voids have been considered as the controlling mechanism for mass transfer. 

The proposed model for non-isothermal sorption kinetics can quantitatively describe uptake0data for adsorption of i-octane on 13X and n-pentane on 5A zeolites. The study indicates that the principal resistance to mass transfer for these systems may be confined at the surface of the zeolite crystals. It is also found that the internal thermal resistance of the assemblage of the micron size zeolite crystals used in the kinetic test is significant which produces a substantial thermal gradient within the assemblage and slows down the heat dissipation from it. 

In a recent survey [19] it was noted that a realistic model for catalytic oxidation reactions must include equations describing the evolution of at least two concentrations of surface substances and account for the slow variation in the properties of the catalyst surface (e.g. oxidation-reduction). For the synchronization of the dynamic behaviour for various surface domains, it is necessary to take into consideration changes in the concentrations of gas-phase substances and the temperature of the catalyst surface. It is evident that, in the hierarchy of modelling levels, such models must be constructed and tested immediately after kinetic models. On the one hand, the appearance of such models is associated with the experimental data on self-oscillations in reactors with noticeable concentration variations of the initial substances and products (e.g. ref. 74) on the other hand, there was a gap between the comprehensively examined non-isothermal models with simple kinetics and those for the complex heterogeneous catalytic reactions... 

Specifically, a stoichiometric reaction mixture was studied at a pressure of 20 Torr and a residence time of 8 s. Both isothermal and non-isothermal models were considered for a range of temperatures between 500 and 2311 K. The third body M is assumed to be made up from the molecular species H2, O2 and H2O with relative efficiencies of 1 0.4 6, respectively, for all third-body reactions [105]. Although the chemistry is derived from the original Dougherty and Rabitz scheme, the rate data were updated and, where possible, obtained from the CEC evaluation tables [26]. The sources for other reaction rate data are shown in Table 4.3. Oscillating ignition reactions constitute a particularly stringent test of mechanism... 

The analysis described in Section 4.6.1 was then applied over a range of ambient temperatures and reaction times for both the isothermal and non-isothermal model. Calculation of the 5, values revealed H2O2 and O3 to be redundant species for both models and at all reaction conditions tested. Table 4.4 shows examples of redundant species calculations from the full non-isothermal scheme at differing parts of the oscillatory trace... 

The application of the basic ideas to real combustion systems is then taken up in Chapters 6 and 7. In Chapter 6, experimental and modelling studies are described which link the mechanistic observations of Chapter 1 to combustion characteristics of fuels studied under laboratory conditions. The experimental emphasis is initially on global combustion phenomena - ignition and oscillatory cool-flames - for a range of hydrocarbons. Section 6.5 then addresses the distribution of products in hydrocarbon oxidation this discussion differs from that in Chapter 1 where the conditions were optimized to allow the investigation of specific reactions. The focus is now on studies of oxidation products over a range of isothermal and non-isothermal conditions, the interpretation of the results in terms of elementary reactions and the use of the experimental data as a detailed test of combustion models. The chapter provides an overview of the success of detailed models in describing combustion phenomena and combustion... 

An important effort in this investigation was the thermal decomposition study of the shales. Considerable effort has been made to find a simple kinetic model which will accurately describe the weight loss curves for non-isothermal pyrolysis at various heating rates. In the past, many researchers have proposed and tested theoretical kinetic models for this reaction Q-4), however, most attempts at finding a suitable model have been focused on finding a very accurate fit to experimental data. Successive studies have increasingly emphasized microscopic details (i.e., diffusion models, exact chemical composition, etc.) in an attempt to find a precise model to fit the weight loss curves. In this... 

The work of several authors (Peters et al, 1993, Halley et al, 1994) has demonstrated the use of non-isothermal dynamic sweep tests to examine the combined effects of shear rate and curing on the chemoviscosity of a highly filled epoxy resin simultaneously. These tests use a selected temperature ramp with repeated dynamic rate sweeps to investigate the effects on the chemoviscosity. The advantage of these tests is that the effects of shear rate and cure are not separated, which is similar to processing conditions. 

K. Ellstrom and H. Nyqvist, Non-isothermal stability testing of drug substances in the solid state, Acta Pharm. Sueu. 24, 115-122(1987). 

This paper presents a numerical simulation of the swellin shrinking processes using the numerical model RF-TH/M - a fully coupled thermo-hydraulic model with mechanical coupling - which has been developed for the purpose of modelling non-isothermal multiphase flow in swelling porous media. In this paper details of the mathematical and numerical multiphase-multicomponental formulation for bentonite, as well as code implementation are described. As an example a test case is investigated. 

Up to now two-phase two-component flow under non-isothermal conditions and coupled THM (one-phase flow) have been implemented in this code and validated against different experimental results. For the modelling of water penetration into unsaturated bentonite or clay, a swelling model is available in the code. If the test sample is confined within a constant volume, then a swelling pressure will build up which causes changes to the pore structure and reduces the porosity. A small change in porosity can, however, create a considerable reduction in permeability. 

To test the coupling in the storage terms of the flow equation, five test cases were used for verification purposes 1) Isothermal Undrained Test (UTT), 2) Isothermal Drained Test (DIT), 3) Isothermal Injection Test (INI), 4) Non-isothermal Undrained Test (UNT) and (5) Non-isothermal drained test (DNT). 

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