On the forced convective flow inside thermal collectors enhanced by porous media: from macro to micro-channels

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Maziar Dehghan ◽  
Zahra Azari Nesaz ◽  
Abolfazl Pourrajabian ◽  
Saman Rashidi
Keyword(s):  
Porous Media ◽  
Velocity Distribution ◽  
General Model ◽  
Convective Flow ◽  
Three Dimensional ◽  
Momentum Equation ◽  
Distribution Profile ◽  
Content Type ◽  
Forced Convective Flow ◽  
Drag Term

Purpose Aiming at finding the velocity distribution profile and other flow characteristic parameters such as the Poiseuille (Po) number, this study aims to focus on the three-dimensional forced convective flow inside rectangular ducts filled with porous media commonly used in air-based solar thermal collectors to enhance the thermal performance. The most general model for the fluid flow (i.e. the non-linear Darcy–Brinkman–Forchheimer partial differential equation subjected to slip and no-slip boundary conditions) is considered. Design/methodology/approach The general governing equations are solved analytically based on the perturbation technique and the results are validated against numerical simulation study based on a finite-difference solution over a non-uniform but structured grid. Findings The analytical velocity distribution profile based on exponential functions for the above-mentioned general case is obtained, and accordingly, expressions for the Po are introduced. It is found that the velocity distribution tends to be uniform by increasing the aspect ratio of the duct. Moreover, a criterion for considering/neglecting the nonlinear drag term in the momentum equation (i.e. the Forchheimer term) is proposed. According to the sensitivity analysis, results show that the nonlinear drag term effects on the Nusselt number are important only in porous media with high Darcy numbers. Originality/value A general analytic solution for three-dimensional forced convection flows through rectangular ducts filled with porous media for the general model of Darcy–Brinkman–Forchheimer and the general boundary condition including both no-slip and slip-flow regimes is obtained. An analytic expression to calculate Po number is obtained which can be practical for engineering estimations and a basis for validation of numerical simulations. A criterion for considering/neglecting the nonlinear drag term in the momentum equation is also introduced.

Application of agent model in the optimal design of AIG for SCR-DeNOx system

2019 ◽  
Vol 36 (9) ◽  
pp. 3016-3028
Author(s):  
Na Li ◽  
Han Wang ◽  
Hui Xu ◽  
Mingfeng Miao
Keyword(s):  
Velocity Distribution ◽  
Flue Gas ◽  
Three Dimensional ◽  
Optimization Method ◽  
Geometric Parameters ◽  
Cfd Modeling ◽  
Input Device ◽  
Content Type ◽  
Agent Model ◽  
Ammonia Injection

Purpose Ammonia injection grid (AIG) is used as an input device for ammonia which reacts with NOx in the selective catalytic reduction (SCR) reactor. However, non-uniform concentration distribution of ammonia could produce partially poisoning or deposits of the catalyst. In this work, for making ammonia widely distributed throughout the flue gas and fully mixed, an optimization method of AIG is proposed. Design/methodology/approach Depending on the complexity of fluid flow, the relation between the concentration distributions of ammonia and the geometric parameters of AIG is nonlinear. Based on a certain amount of AIG samples, the computational fluid dynamics (CFD) simulations are applied to propose the agent model which describes the functional relation of the deviation of ammonia concentration and the geometric parameters of AIG. The optimization model of AIG based on the agent model is established. The optimized AIG based on the agent model can be used to produce uniform concentration distributions of ammonia, especially in the case that velocity distribution of flue gas is non-uniform. Findings For qualitatively confirming this optimization method, the three-dimensional CFD simulation of the optimized AIG is carried out. The results reveal that the diffusion process of ammonia gas is consistent with the development of the local vortices, which have a certain relation with the velocity distribution of the flue gas. The unequal ammonia injection designed by the optimization based on the agent model promotes a better mixing of ammonia and flue gas. Originality/value In this work, first, the method for optimizing AIG based on the agent model is proposed. Second, the three-dimensional CFD modeling and simulation of the optimized AIG is carried out, and the mixing effects of ammonia and flue gas are presented.

Numerical study on convective flow and heat transfer in 3D inclined enclosure with hot solid body and discrete cooling

2020 ◽  
Vol 30 (10) ◽  
pp. 4649-4659 ◽  
Author(s):  
Ali S. Alshomrani ◽  
S. Sivasankaran ◽  
Amer Abdulfattah Ahmed
Keyword(s):  
Heat Transfer ◽  
Convective Flow ◽  
Energy Transport ◽  
Numerical Study ◽  
Three Dimensional ◽  
Thermal Engineering ◽  
Content Type ◽  
Nusselt Numbers ◽  
Inclination Angles ◽  
Inclined Enclosure

Purpose This study aims to deal the numerical simulation on buoyant convection and energy transport in an inclined cubic box with diverse locations of the heater and coolers. Design/methodology/approach The left/right walls are cooled partially whereas the other walls are kept adiabatic. In the left/right walls, three different locations of the cooler are examined, whereas heater moves in three locations in the middle of the enclosed box. The governing models are numerically solved using the finite-element method. Findings The simulations are done on several values of the Rayleigh number and cavity inclination angles and different locations of the heater and coolers. The results are presented in the form of streamlines, isosurfaces and Nusselt numbers for different values of parameter involved here. It is recognized that the inclination of the box and the locations of the coolers strongly influence the stream and energy transport inside the enclosed domain. Research limitations/implications The present investigation is conducted for steady, laminar, three-dimensional natural convective flow in a box for different locations of cooler and tilting angles of a cavity. The study might be useful to the design of solar collectors, room ventilation systems and electronic cooling systems. Originality/value This work examines the effects of different locations of cooler and tilting angles of a cavity on convective heat transfer in a 3D cavity. The study is useful for thermal engineering applications.

Numerical simulation of methane spreading in porous media after leaking from an underground pipe

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Ji Wang ◽  
Yuting Yan ◽  
Junming Li
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Numerical Model ◽  
Natural Gas ◽  
Three Dimensional ◽  
Ground Surface ◽  
Air Transportation ◽  
Water Evaporation ◽  
Content Type ◽  
Gas Leak

Purpose Natural gas leak from underground pipelines could lead to serious damage and global warming, whose spreading in soil should be systematically investigated. This paper aims to propose a three-dimensional numerical model to analyze the methane–air transportation in soil. The results could help understand the diffusion process of natural gas in soil, which is essential for locating leak source and reducing damage after leak accident. Design/methodology/approach A numerical model using finite element method is proposed to simulate the methane spreading process in porous media after leaking from an underground pipe. Physical models, including fluids transportation in porous media, water evaporation and heat transfer, are taken into account. The numerical results are compared with experimental data to validate the reliability of the simulation model. The effects of methane leaking direction, non-uniform soil porosity, leaking pressure and convective mass transfer coefficient on ground surface are analyzed. Findings The methane mole fraction distribution in soil is significantly affected by the leaking direction. Horizontally and vertically non-uniform soil porosity has a stronger effect. Increasing leaking pressure causes increasing methane mole flux and flow rate on the ground surface. Originality/value Most existing gas diffusion models in porous media are for one- or two-dimensional simulation, which is not enough for predicting three-dimensional diffusion process after natural gas leak in soil. The heat transfer between gas and soil was also neglected by most researchers, which is very important for predicting the gas-spreading process affected by the soil moisture variation because of water evaporation. In this paper, a three-dimensional numerical model is proposed to further analyze the methane–air transportation in soil using finite element method, with the presence of water evaporation and heat transfer in soil.

The 3D job description

2015 ◽  
Vol 34 (4) ◽  
pp. 406-420 ◽  
Author(s):  
Beáta Sz. G. Pató
Keyword(s):  
Human Resource Development ◽  
General Model ◽  
Early Stage ◽  
Three Dimensional ◽  
Job Descriptions ◽  
Job Description ◽  
Horizontal Structure ◽  
Content Type ◽  
Organizational Goals ◽  
The People

Purpose – The purpose of this paper is to present the necessary accessories for creating a job description, through a model. The model concentrates on the person and a job description document, which is capable of connecting and synchronising the organizational goals. The author introduces a tool that assists in creating job descriptions. Design/methodology/approach – In the present paper the author integrates the conclusions of the authors on the subject and her own research results, on the basis of which she creates a three dimensional (3D) job description model. This 3D model could be used as a resource in the human resource development field. Findings – The elements of the resulting job description document: the method specific accessories of the job descriptions. The content specific accessories of the job descriptions. The person specific accessories of the job descriptions. Research limitations/implications – The 3D job description, which is presented in the study, was preceded by the development of a general model. The very first application of the general model was in connection with competence tests, which have gained popularity lately. Competences can be classified in different ways. Each aspect of classification corresponds to a face of a tetrahedron, five of which comprise the model. This model is also adaptable for other kinds of research used at research centres, educational institutions and companies. Practical implications – The 3D job description being presented was developed as a special, multi-dimensional data model. The model allows us to discover and present the causal relationships and the connections between the parts and the whole of job description elements. It demonstrates the interacting factors clearly due to the fact that the tetrahedrons can be rolled over one another, and it is adaptable for the mapping of the connections between these factors. Social implications – The model is capable of defining the central elements. In this case, the people and the organization of work are in the centre. The 3D job description is adaptable for modelling by the exploration of logical links, so it can show what kind of “whole” is generated by the given elements and what parts it consists of. Therefore the model can be interpreted as a network of connections, which is capable of illustrating the vertical and horizontal structure, due to the special form of tetrahedrons. The model is perfect for the demonstration of the connections between contents on the faces of the tetrahedrons, due to their form and movability. Originality/value – The elaboration and presentation of the general model, protected by design patent (90 806 D0500121) in Hungary, was stimulated by the fact that during different kinds of research and analyses it is an important task to explore the influencing factors, elements and their connections. This is of primary importance especially at the early stage of research and analysis, because the negligence of these in the early stages results in the fact that those particular factors can be taken into account only during a repeated analysis.

Generalized periodic surface model and its application in designing fibrous porous media

2015 ◽  
Vol 32 (1) ◽  
pp. 7-36 ◽  
Author(s):  
Wei Huang ◽  
Sima Didari ◽  
Yan Wang ◽  
Tequila A.L. Harris
Keyword(s):  
Porous Media ◽  
Geometric Modeling ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Field Method ◽  
Surface Model ◽  
Periodic Surface ◽  
Content Type ◽  
Modeling Methods ◽  
Fibrous Porous Media

Purpose – Fibrous porous media have a wide variety of applications in insulation, filtration, acoustics, sensing, and actuation. To design such materials, computational modeling methods are needed to engineer the properties systematically. There is a lack of efficient approaches to build and modify those complex structures in computers. The paper aims to discuss these issues. Design/methodology/approach – In this paper, the authors generalize a previously developed periodic surface (PS) model so that the detailed shapes of fibers in porous media can be modeled. Because of its periodic and implicit nature, the generalized PS model is able to efficiently construct the three-dimensional representative volume element (RVE) of randomly distributed fibers. A physics-based empirical force field method is also developed to model the fiber bending and deformation. Findings – Integrated with computational fluid dynamics (CFD) analysis tools, the proposed approach enables simulation-based design of fibrous porous media. Research limitations/implications – In the future, the authors will investigate robust approaches to export meshes of PS models directly to CFD simulation tools and develop geometric modeling methods for composite materials that include both fibers and resin. Originality/value – The proposed geometric modeling method with implicit surfaces to represent fibers is unique in its capability of modeling bent and deformed fibers in a RVE and supporting design parameter-based modification for global configuration change for the purpose of macroscopic transport property analysis.

Dynamics and modeling of nonlinear forced convective flow of Carreau-fluid (non-Newtonian fluid) with Marangoni convection

2021 ◽  
pp. 095440622098726
Author(s):  
M Ijaz Khan ◽  
Yu-Ming Chu ◽  
Sumaira Qayyum ◽  
Shahid Farooq ◽  
A Aldabesh
Keyword(s):  
Nusselt Number ◽  
Convective Flow ◽  
Momentum Equation ◽  
Eckert Number ◽  
Bejan Number ◽  
Carreau Fluid ◽  
Thermal Equation ◽  
Fluid Parameter ◽  
Nonlinear Mixed Convection ◽  
Forced Convective Flow

This paper deals with Marangoni convective flow of Carreau fluid. Boundary condition for momentum equation is considered to be Marangoni type. Thermal energy produces when current passes through the electrical conductor and this process is called Joule heating. Viscous dissipation is also applied in thermal equation. Nonlinear mixed convection for temperature is considered. Governing equations of PDE's are converted to ODE's by implementation of transformation. ND-Solve MATHEMATICA method is used to solve the equations. Parameters result against temperature, velocity, entropy rate, Bejan number, Skin friction and Nusselt number is examined via graphs. Due to increase in fluid parameter velocity of the fluid reduces while increasing impact is seen for temperature. Temperature is increasing function of Eckert number. Entropy generation also shows rising impact via fluid parameter while Bejan number decays. Drag force of surface decays via fluid parameter. Nusselt number is in direct relation with Prandtl and Eckert number.

Sign in / Sign up

Export Citation Format

Share Document