In this paper, the effects of baffle on thermal characteristics of combined convection-radiation heat transfer in laminar flow adjacent to an inclined backward facing step (BFS) in a horizontal duct are investigated. A baffle is mounted on the top wall of channel downstream side of step. In this study, the fluid is treated as a gray, absorbing, emitting and scattering medium; therefore, in the energy equation besides the convective and conductive terms, radiation term is also presented. The radiative transfer equation (RTE) is solved numerically by the discrete ordinates method (DOM) to find the divergence of radiative heat flux distribution inside the radiating medium. The blocked off method is employed for both fluid mechanic and radiation problems to simulate the presence of both step and baffle. The effects of height, width and location of baffle in channel and also the effects of radiative parameters on the fluid flow and heat transfer are investigated by plotting the variations of streamlines, Nusselt number and mean bulk temperature along the flow. It is revealed that, baffle and radiative parameters have great influences on flow and the thermal behaviors of systems with combined convection-radiation heat transfer. تفاصيل المقالة

In this research, the coupling between non-gray radiation and separation convection flow in a duct is investigated numerically. Distributions of absorption coefficients across the spectrum are obtained from the HITRAN2008 database. The full-spectrum k-distribution method is used to deal with the non-gray part of the problem, while the gray radiation calculations are performed using the Planck mean absorption coefficient. To find the divergence of radiative heat flux distribution, the radiative transfer equation (RTE) is solved by the discrete ordinates method (DOM). The effects of radiation-conduction parameter, scattering coefficient and wall emissivity on thermal behaviors are investigated for both gray and non-gray mediums. In addition, the results of gray medium are compared with non-gray results as a real case. The results show that in many cases, use of gray simulations is not acceptable and leads to significant errors, especially in non-scattering medium with high values of radiation-conduction parameter and wall emissivity. تفاصيل المقالة

The present manuscript gives the description of findings which took importance during the design and analysis of the structure of heavy duty hauler machine ordered by Gol-e-Gohar iron ore complex in Iran. Stress and deformation analysis was indeed the heart of the project and the key of its success. The challenging problem of evaluation of value and behaviour of active loads was taken under consideration precisely and all participated external forces were included in analysis. Since the present case is a moving structure, the loading evaluation should be included in all critical experienced conditions through the operation. The inertial forces due to acceleration and road bump have the governing role and have been evaluated and considered in analysis. After precise and complete evaluation of external loads and applying the correct boundary conditions, the simulations for stress analysis have been performed in ANSYS. The main findings of the present study were the optimized decision for the geometry of several important load carrying elements and appropriate reinforcement of the risky positions which was the result of the correct knowledge of the mechanics of problem. Finally, the structure was manufactured with the total weight of about 38 ton and load carrying capacity of 120 ton including the dynamic effects. After succeeding in the initial loading, the operational loading in real conditions in mine ramp has been carried out gradually and the machine is currently working in desired predicted form. تفاصيل المقالة

In the current research, interaction influences of obstacle shape and top wall velocity on the hydrothermal behaviours of the turbulent mixed convection flow in a trapezoidal cavity are numerically simulated. To achieve this goal, three different shapes of the obstacles including semicircular, triangular, rectangular are considered. Dimensions of these obstacles are chosen so that the environment around all three of them is same. The RNG model is chosen to simulate the turbulent flow. To model the inclined or curved walls of trapezoidal cavity and obstacles, the improved blocked-off method is applied. Results show that the obstacle shape and top wall velocity have a significant influence on the thermal and hydrodynamic behaviours. In fact, the highest magnitude of heat transfer rate along the bottom wall occurs in the cavity with the rectangular obstacle and for the highest magnitude of top wall velocity; whilst its lowest magnitude is related to the pure free convection and for the cavity with the semicircular obstacle. Besides, the lowest and highest magnitudes of temperatures fields occur for the cavities with rectangular and triangular obstacles, respectively. تفاصيل المقالة