Iranian Journal of Mechanical Engineering Transactions of ISME
Volume:19 Issue: 2, Sep 2018

The inherent nonlinearities in the kinetics and heat transfer models of biomass pyrolysis have led to the applications of various numerical methods in solving the nonlinear problems. However, in order to have physical insights into the phenomena and to show the direct relationships between the parameters of the models, analytical solutions are required. In this work, approximate analytical solutions for the nonlinear integrated kinetics and heat transfer of pyrolysis of biomass particle under isothermal and non-isothermal heating conditions are presented using differential transformation method. Also, the results of the analytical solutions are compared with the numerical and experimental results in literature. Good agreements are established between the present results and the past works. Thereafter, parametric studies are carried out on the effects of heating conditions, heating rates, thermo-geometric parameters, boundary conditions, particles shape and size on the pyrolysis kinetics and thermal decomposition of biomass particles. It is therefore expected that this study will enhance the understanding of the pyrolysis by giving physical insights into the various factors and the parameters affecting the thermochemical process.

In this paper natural convection heat transfer within a two-dimensional, horizontal, concentric cam shape cylinders that is partially filled with a fluid saturated porous medium has been investigated. both cylinder are kept at constant and uniform temperatures with the outer cylinder being subjected relatively lower than the inner one. In addition the forchheimer and brinkman effect are taken into consideration inside the porous sleeve. furthermore, the local thermal equilibrium condition is take into account. the porosity factor is considered to be uniform and constant with ε = 0.9. the main objective of this study is to examine the effects of stream line shape, thermal conductivity ratio (ks/kf) and the porous layer thickness on the bouyancy induced flow motion under steady state condition. these effects are studied using the following dimensionless parameters: Ra = 104-106, Da = 10-3-10-5. The results show’s that Nusselt number is affected mostly by porous sleeve thickness and Rayleigh number respectively.

A FGM layer sandwiched between two isotropic layers weakened by several interface cracks under antiplane loading is studied. This paper examines the modelling of cracks by distribution of strain nuclei along crack lines. In this investigation, the Volterra-type screw dislocation employed between FGM and an elastic layer. To solve the dislocation problem, the complex Fourier transform is applied. One merit of this technique is the possibility to determination of the stress intensity factors for multiple cracks. The system of equations is derived by considering the distribution of line dislocation on the crack. These equations are of Cauchy singular type at the location of dislocation, which can be solved numerically to obtain the dislocation density on the faces of the cracks. Several examples are solved and the stress intensity factors are obtained. The effect of the properties and cracks geometries on the mode III stress intensity factor are studied and the validity of analysis is checked.

Indentation is a new method for estimating residual stress. The plastic behavior of the materials under study can affect indentation parameters and, thus, influences the results of residual stress measurement. In this paper, the effect of yield stress and work-hardening exponent on the accuracy of residual stress measurements in steels and aluminums was studied.
Results showed that, for materials with a low strain-hardening exponent and yield strain, Lee’s model is applicable; for materials with relatively high amounts of strain-hardening exponent and yield strain, Wang’s model is more accurate; and for materials with a medium range of strain-hardening exponent and yield strain all three models can be applied. It was also found that the stresses being tensile or compressive can affect the accuracy of the calculated results for each model. The applicable range of each model is represented in the article.

This paper sheds more light on the co-rotational element formulation for beams with uniform cross-section. The co-rotational elements are commonly used in problems in which a structure undergoes a large deformation. In this study, the foregoing element obeys the Euler-Bernoulli beam assumptions. Unlike the formulations presented in the literature, in this paper, a number of local nodal coordinates are employed which makes the kinematic description of the deformed beam much easier without the need of expressing any complicated relations. In this regard, via a clamped planar beam as a case study, the methodology is implemented step-by-step, and the results are compared with the ones calculated analytically and by means of elliptic integrals. Then, the methodology is briefly formulized for 3D cases as well. At the end, as a second case study, the large deformation analysis is conducted on a simply supported planar beam as well.

In the present work, the critical heat flux measurements were performed for the subcooled flow boiling of pure water and magnetic nanofluids (i.e., water + 0.01 and 0.1 vol.% Fe 3O4) in a vertical tube. The effect of applying an external magnetic field on the CHF variation was studied experimentally as well. The obtained results indicated that the subcooled flow boiling CHF in the vertical tube is increased by using the nanofluid as the working fluid, especially in lower volume concentration of nanoparticles. The nanoparticles deposition on the tube inner surface and consequently improvement of the surface characteristics such as nucleation site density, wettability and re-wetting properties could be mentioned as the main reasons of this incident. Moreover, it was seen that applying the magnetic field leads to the additional enhancement in the CHF of ferrofluids. It could be clarified as the attraction of the nanoparticles into the magnets and increasing the surface wettability resulted in the CHF enhancement.