This work presents a numerical study to investigate the heat transfer characteristics of a 2-D rectangular composite porous radiant burner (CPRB). In the construction of porous burner, the porous layer is considered to be of composite type consisting of upstream and downstream layers with equal thickness but with different physical and radiative properties. In the present work, a two dimensional rectangular model is used to solve the governing equations for porous medium and gas flow.  In order to analyze the thermal characteristics of the CPRB, the coupled energy equations for the gas and porous medium are solved numerically and the discrete ordinates method is used to obtain the distribution of radiative heat flux in the porous media. Finally, the effects of various factors on the performance of CPRB are determined. Computational results show that high porosity and low scattering coefficient for downstream porous layer are desirable for maximizing the CPRB efficiency in comparison to a homogeneous one. Present results prove to be compatible with results obtained from previous studies. پرونده مقاله

This work presents the heat transfer characteristics of a new type of porous radiant air heater that operates on the basis of effective energy conversion method between flowing gas enthalpy and thermal radiation. At each layer, the gas and solid phases are considered in non-local thermal equilibrium, and combustion in the porous radiant burner is modeled by considering a non-uniform heat generation zone. The homogeneous porous media, in addition to its convective heat exchange with the gas, may absorb, emit, and scatter thermal radiation. In order to determine the thermal characteristics of the proposed porous radiant air heater, a two-dimensional model is used to solve the governing equations for porous medium and gas flow, moreover discrete ordinates method is employed to obtain the distribution of radiative heat flux in the porous media. In order to validate the applied numerical method at the present analysis, the results are compared with some reported theoretical and experimental results of other investigators, where good agreement is observed. پرونده مقاله

Abstract: This work presents a numerical study to investigate the heat transfer characteristics of a 2-D rectangular composite porous radiant burner (CPRB). In the construction of porous burner, the porous layer is considered to be composite consisting of upstream and downstream layers with equal thickness but with different physical and radiative properties. In the present work, a two dimensional rectangular model is used to solve the governing equations for porous medium and gas flow.  In order to analyze the thermal characteristics of the CPRB, the coupled energy equations for the gas and porous medium are solved numerically and the discrete ordinates method is used to obtain the distribution of radiative heat flux in the porous media. Finally, the effects of the various factors on the performance of CPRB are determined. Computational results show that the high porosity and low scattering coefficient for downstream porous layer are desirable for maximizing the CPRB efficiency in comparison to homogeneous one. Comparison between the present results with those obtained by other investigators shows a good agreement. پرونده مقاله

In this paper, fluid flow between two parallel flat plates that are partially filled with two-dimension porous media is investigated numerically using single relaxation time (SRT) lattice Boltzmann method (LBM) at pore scale. The considered obstacles are random, circular, rigid and granular with uniform diameters. Single component and single-phase viscous Newtonian fluid are considered as working fluid. There are no overlaps between obstacles. It supposed incompressible, steady and laminar flow and no chemical reaction performed in porous media. Velocity vectors and streamlines in this domain depicted. The effect of varying Reynolds number on the pressure drop or pressure gradient and Darcy drag are studied. Dimensionless permeability calculated as a function of porosity and Knudsen number. To vary porosity, obstacles diameter changed but their places considered constant. With increasing Knudsen number, the dimensionless permeability is increased. In addition, effect of domain resolution on pressure gradient investigated. The results demonstrate that lattice Boltzmann method will be very useful in fluid flow simulation through porous media. پرونده مقاله

Radiative heat transfer has an important role in many industrial equipment; i.e. furnaces, boilers and high temperature heat exchangers. In this paper, combination of Weighted Sum of Gray Gas Method (WSSGM) and Discrete Ordinate Method (DOM) are used together in order to numerically study the radiative heat transfer behavior in a non-gray participating medium. Moreover, the concept of Blocked-off region for irregular geometries is used to simulate the T-shaped furnace. The effect of different radiative parameters, i.e. scattering coefficient and wall emissivity on thermal behavior and wall heat fluxes is investigated and compared for both gray and non-gray media. The results show thatwhen scattering coefficient increases, more radiation is scattered in the medium and therefore less heat flux reaches the walls such that by increasing scattering coefficient from 1.0 to 5.0, the incident radiative heat flux decreases up to 15% in some parts of bottom wall. It is seen that by increasing wall emissivity from 0.5 to 1.0, wall heat flux increases more than 60%. Moreover, results show that, by increasing the temperature, the maximum error strongly increases which indicates that in many engineering problems, the gray medium assumption leads to great error in results. پرونده مقاله

اخیرا با استفاده از محیط های متخلخل نوع جدیدی هوا-گرمکن طراحی شده است که اصول کارکرد آنها بر پایه تبدیل انرژی بین آنتالپی گاز وانرژی تابشی استوار است. در کار حاضر رفتار حرارتی یک هوا – گرمکن متخلخل چهار لایه مورد تجزیه و تحلیل تئوریک قرار گرفته است . به علت عدم تعادل حرارتی بین گاز و محیط متخلخل دو معادله انرژی جداگانه برای فاز گاز و جامد در نظر گرفته شده است که شامل هدایت گرمایی در دوفاز، انتقال حرارت جابجایی بین دو فاز و تشعشع در محیط متخلخل می باشد که به صورت عددی در میدان دو بعدی مستطیلی حل می شوند. برای محاسبه تشعشع گرمایی از مدل جهات مجزا که برای محاسبات چند بعدی دقت بسیار بالایی دارد استفاده می شود. همچنین رفتار حرارتی سیستم مورد نظر و تأثیر پارامترهای مختلفی از قبیل ضخامت لایه متخلخل و نسبت پخش لایه بر عملکرد آن مورد بررسی قرار گرفته است.جهت بررسی صحت روش بکار گرفته شده، نتایج عددی کار حاضر با داده های تئوری وتجربی محققین دیگرمقایسه شده وانطباق قابل قبولی مشاهده شده است. پرونده مقاله