A kinetic study of pyrolysis process of Parthenium hysterophorous is carried out by using thermogravimetric analysis (TGA) equipment. The present study investigates the thermal degradation and determination of the kinetic parameters such as activation E and the frequency factor A using model-free methods given by Flynn Wall and Ozawa (FWO), Kissinger-Akahira-Sonuse (KAS) and Kissinger, and model-fitting (Coats Redfern). The results derived from thermal decomposition process demarcate decomposition of Parthenium hysterophorous among the three main stages, such as dehydration, active and passive pyrolysis. It is shown through DTG thermograms that the increase in the heating rate caused temperature peaks at maximum weight loss rate to shift towards higher temperature regime. The results are compared with Coats Redfern (Integral method) and experimental results have shown that values of kinetic parameters obtained from model-free methods are in good agreement. Whereas the results obtained through Coats Redfern model at different heating rates are not promising, however, the diffusion models provided the good fitting with the experimental data.

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We present a local stability analysis to investigate the effects of differential diffusion between momentum and density (quantified by the Schmidt number $Sc$) on the three-dimensional, short-wavelength instabilities in planar vortices with a uniform stable stratification along the vorticity axis. Assuming small diffusion in both momentum and density, but arbitrary values for $Sc$, we present a detailed analytical/numerical analysis for three different classes of base flows: (i) an axisymmetric vortex, (ii) an elliptical vortex and (iii) the flow in the neighbourhood of a hyperbolic stagnation point. While a centrifugally stable axisymmetric vortex remains stable for any $Sc$, it is shown that $Sc$ can have significant effects in a centrifugally unstable axisymmetric vortex: the range of unstable perturbations increases when $Sc$ is taken away from unity, with the extent of increase being larger for $Sc\ll 1$ than for $Sc\gg 1$. Additionally, for $Sc>1$, we report the possibility of oscillatory instability. In an elliptical vortex with a stable stratification, $Sc\neq 1$ is shown to non-trivially influence the three different inviscid instabilities (subharmonic, fundamental and superharmonic) that have been previously reported, and also introduce a new branch of oscillatory instability that is not present at $Sc=1$. The unstable parameter space for the subharmonic (instability IA) and fundamental (instability IB) inviscid instabilities are shown to be significantly increased for $Sc<1$ and $Sc>1$, respectively. Importantly, for sufficiently small and large $Sc$, respectively, the maximum growth rate for instabilities IA and IB occurs away from the inviscid limit. The new oscillatory instability (instability III) is shown to occur only for sufficiently small $Sc<1$, the signature of which is nevertheless present with zero growth rate in the inviscid limit. The Schmidt number is then shown to play no role in the evolution of transverse perturbations on the flow around a hyperbolic stagnation point with a stable stratification. We conclude by discussing the physical length scales associated with the $Sc\neq 1$ instabilities, and their potential relevance in various realistic settings.

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The Distributed Activation Energy Model (DAEM) or Multiple Reaction Model (MRM) applies either to the total amount of volatiles released or to the amount of an individual volatile constituent like carbon monoxide or tar (Howard, 1981). It is also called the Distributed Rate Model, and uses Vand's treatment of independent parallel processes (Vand, 1943) in modelling the resistance of metallic films. The detailed study includes the total amount of volatiles released during the pyrolysis process (Howard, 1981;Donskoi and McElwain, 1999). Originally, the coal devolatilization, however, was considered first to develop the Distributed Activation Energy Model (Pitt, 1962), yet the DAEM also applies to the pyrolysis of other materials, including biomass, residual oils, resin char (Teng and Hsieh, 1999), and kerogen (Lakshmanan and White, 1994). Calculations of solutions to this model involve evaluations of double integrals, which vary rapidly and hence create significant numerical difficulties. In order to tackle the integral complication, asymptotic expansion has been adopted for the accurate approximation to our problem. The solution for the DAEM model is given by Eq. (1): (1) where:-the time varying absolute temperature of the biomass R -the universal gas constant E -the activation energy k 0 -the pre-exponential or frequency factor β (β >0) -the scale parameter of initial distribution function respectivelyThe aim of this paper is to use asymptotic methods to make accurate approximations to the integrals and thereby evaluate the influence of relevant parameters on the biomass pyrolysis. Asymptotic expansionThe relationship between the DAEM and the single first order reaction model have been explored by Niksa and Lau (1993), which is based on the approach of holding the activation energy fixed, and defining an effective or nominal rate constant (Niksa and Lau, 1993). They also gave an analytical approximations to the DAEM for the exponentially and the linearly varying temperature profiles. The basis of approach lies on exploiting the rapid changes occurring in the double exponential term in Eq. (1). The procedure adopted by Niksa and Lau (1993) provides accurate approximations to the DAEM for all the relevant parameters for the kinetic mechanism of biomass pyrolysis. The modification done by them is simply refinement of the concept applied by Suuberg (1983), who used unit step function approximation to Double exponential term (DExp) (Howard, 1981;Vand, 1943;Pitt, 1962). In the subsequent sections, a more accurate approximation to DExp has been developed, which is implemented in the two different types of distribution cases (Narrow and Wide distribution). Acta Technologica Agriculturae 3 Nitra, Slovaca Universitas Agriculturae Nitriae, 2017, pp. 78-84 ApproximAtions to the non-isothermAl DistributeD ActivAtion energy moDel for biomAss pyrolysis using the rAyleigh Distribution This paper deals with the influence of some parameters relevant to biomass pyrolysis on the numerical solutions of the nonisothermal n th ...