Sharif Digital Repository

For the production of synthesis gas utilised in Midrex direct reduction plants, catalytic steam/CO2 hydrocarbon reforming in tubular reformer is the major process. Owing to the high heat input through the Midrex reformer tube wall, the endothermic nature of reforming reactions, low mass velocity of feed gas and large tube diameter, the catalyst bed is exposed to considerable axial and radial temperature gradients. These radial concentration and temperature gradients may create local areas with potential for carbon formation. To investigate this phenomenon, a rigorous two-dimensional model is developed for simulating the operation of a Midrex reformer which applies a dual catalyst loading... 

This article applies a novel non-Boussinesq numerical algorithm to solve the free-convection problem in a wide range of thin to thick vertical cavities subject to different side-wall temperatures. In this regard, the compressible flow equations are solved using a primitive incompressible method. No Boussinesq approximation and low Mach number consideration are included in the formulation. To implement the compressibility effect, the density field is calculated via the equation of state for gas. The temperature gradient is suitably varied to generate different low to high thermobuoyant fields, where the Boussinesq approximation may or may not be valid. Contrary to published works on the thin... 

This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing... 

One important heat transfer application in engineering is to predict the flow behavior and heat transfer rate in thin vertical air layers. There are numerous applications in engi- neering where high temperature gradients exist between the slot walls. In such cases, the methods based on simple Boussinesq approximations do not provide reliable predictions. Unfortunately, the compressibility effect in heat transfer rate through thin vertical slots has not been much investigated by the past investigators. In this work, a compressible algorithm is properly developed and utilized to solve compressible natural convection in vertical air layers. The current technique employs discretization equations... 

A numerical analysis has been performed to investigate the ground effects on the main parameters of a two-phase unconfined cloud of fuel and air to study its detonability. Equivalence ratio, turbulence intensity, cloud shape and volume, uniformity, temperature gradient and delay time distribution are the most important factors that affect the detonability of a vapor cloud. The effects of the altitude of the dispersing device from the ground on these significant factors have been demonstrated. A modified KIVA-based program has been employed to carry out the computations. A finite volume method is used to solve the equations describing the gas phase. A discrete particle technique is applied to... 

The application of the multi-component Fe-based filler metals (FMs) for transient liquid phase (TLP) bonding of AISI 304 austenitic stainless steel has been overshadowed by dissimilar interlayers merely due to their shorter isothermal solidification time. However, the latter usually suffers from low efficiency in terms of mechanical properties even after homogenization of heat treatment. This study shows that by imposing a temperature gradient across the bond line during the TLP bonding process (TG-TLP), it is possible to reduce the isothermal solidification time significantly. This renews the interest in utilizing multi-component Fe-based FMs. In this regard, the TG-TLP bonding process was...