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In this paper, the capacity of a natural circulation loop for transferring heat from a heat source to a heat sink has been analyzed. It is concluded that the capacity of the natural circulation loop depends on the conversion efficiency of the thermal energy from the heat source to the driving force for the circulation of the flow. The low conversion efficiency leading to weak driving force in such loops has been demonstrated analytically and validated through simulation results. This issue has resulted in a low heat transfer capacity in the circulation loop. To increase the heat transfer capacity, one has to improve this efficiency. To meet such a need, a novel efficiency booster has been developed in this paper. The booster essentially increases the flow driving force and hence significantly improves the overall heat transfer capacity. Design and analysis of this booster have been performed in detail. The performance has been examined through extensive computer simulations. It is concluded that the booster can indeed drastically improve the heat transfer capacity of the natural circulation loop. [ABSTRACT FROM AUTHOR]

In the numerical simulation of heat transfer and fluid flow problems, residual is often adopted as a convergence criterion. Since residual is susceptible to several factors, such as the property of physical problems, the expression form of discretized equations, the scale of grid and the nondimensionalization of governing equations, the converged value differs greatly in different cases. Thus, it is hard to set a specific residual value in a specific numerical calculation. To give a universal convergence criterion in this paper, a residual based on normalization idea is proposed. Range of specified values of this improved convergence criterion for general heat transfer and fluid flow problems is also given in this paper. Numerical simulation results indicate that the improved convergence criterion based on normalized residual is much more reasonable than the one based on traditional residual. [ABSTRACT FROM AUTHOR]

The Partially-Averaged Navier–Stokes (PANS) method is intended to provide the optimum fidelity on any given numerical grid while varying seamlessly between the Reynolds-Averaged Navier–Stokes (RANS) model and direct numerical simulation (DNS). This method belongs to so called bridging or seamless methods. The PANS method has been more often used in the research community but also in the industry in last years. This is probably due to its simplicity, robustness and recent theoretical extensions as well as due to the detailed validations on the number of complex cases presented in many publications. As for any relatively new modeling approach, the list of validation cases should be further extended. Therefore, an additional test case is included in this paper. The PANS method is validated here for the fluid flow and heat transfer in a matrix of surface-mounted cubes. The ζ-f variant of PANS was used and compared with its RANS counterpart. The calculation procedure, which now includes the energy equation as well, is explained. A brief description of on-going developments and possible next improvements is also given in this paper. [ABSTRACT FROM AUTHOR]

• Fully resolved simulations of fluid-particle systems. • Surface reaction with significant heat effects. • Temperature-dependent reaction rates determined by the Arrhenius equation. • Simulation parameters adopted from realistic POX reaction. In this paper, an efficient ghost-cell based immersed boundary method (IBM) is used to perform direct numerical simulation (DNS) of reactive fluid-particle systems. With an exothermic first order reaction proceeding at the exterior particle surface, the solid temperature rises and consequently increases the reaction rate via an Arrhenius temperature dependence. In other words, the heat and mass transport is dependently coupled through the particle thermal energy equation and the Arrhenius equation, and they offer dynamic boundary conditions for the fluid phase thermal energy equation and species equation respectively. The fluid-solid coupling is enforced at the exact position of the particle surface by implicit incorporation of the boundary conditions into the discretized momentum, species and thermal energy conservation equations of the fluid phase. Different fluid-particle systems are studied with increasing complexity: a single sphere, three spheres and a dense array consisting of hundreds of randomly generated particles. In these systems the mutual impacts between heat and mass transport processes are investigated. [ABSTRACT FROM AUTHOR]

Abstract This paper aimed to develop a computational fluid dynamics simulation for an industrial boiler. The industrial boiler is used for the sulfuric acid production. A numerical model is carried out using the commercial code "ANSYS-FLUENT". The simulations are developed for the case of the industrial boiler and a new proposed design. A clear understanding of the combustion phenomenon and the fluid flow within the boiler is provided from the simulations. The local characteristics of the fluid flow and the heat transfer such as the temperature; the velocity magnitude and the density distributions are presented and analyzed. The comparison between the numerical results and the experimental data is performed and a good agreement is found. Highlights • A numerical simulation is developed for an industrial boiler. • The fluid flow and the heat transfer characteristics are analyzed and discussed. • The numerical model is validated by comparison between numerical results and industrial measurements. [ABSTRACT FROM AUTHOR]

A fully coupled heat transfer model at pore-scale of volumetric solar receiver is established in this paper. The X-ray computed tomography technique is applied to reconstruct the porous structure. By generating the voxel mesh and coupling with the Monte Carlo Ray Tracing method, the energy source due to the solar radiation could be determined and then added to the unstructured CFD mesh. The governing equations are solved by the commercial CFD software FLUENT. The results show that the details of the fluid flow and heat transfer in volumetric solar receiver are successfully captured. The pressure drop correlation corresponds satisfactorily to the previous study. The local convective heat transfer coefficient varies in a small range along the inlet fluid flow direction inside volumetric solar receiver and the average Nusselt number could be correlated to a power function of the Reynolds number. The radiation transfer inside the porous media is visualized and thermal radiation loss is evident at the entrance of the solar receiver. The proportion taken by radiation in the total heat transfer is determined as a function of the average temperature of porous skeleton. [ABSTRACT FROM AUTHOR]

In selective laser melting, there are two different laser scan pattern including point exposure scan and continuous exposure scan. Different laser scan pattern has a significant effect on the thermal behavior and fluid flow of molten pool. In this paper, under the same energy input, the effects of laser scan pattern on the temperature evolution behavior, molten pool dimensions, fluid flow and cooling rate are thorough studied by method of numerical simulation. Experiments for point exposure are carried out which are in a good agreement with the numerical results. [ABSTRACT FROM AUTHOR]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [ABSTRACT FROM AUTHOR]

Various fundamental studies based on a turbulent duct flow have gained popularity including heat transfer, magnetohydrodynamics as well as particle-laden transportation. An accurate prediction on the turbulent flow field is critical for these researches. However, the database of the mean flow and turbulence statistics is fairly insufficient due to the enormous cost of numerical simulation at high Reynolds number. This paper aims at providing available information by conducting several Direct Numerical Simulations (DNS) on turbulent duct flows at Re τ = 300 , 600 , 900 and 1200 . A quantitative comparison between current and previous DNS results was performed where a good agreement was achieved at Re τ = 300 . However, further comparisons of the present results with the previous DNS results at Re τ = 600 obtained with much coarser meshes revealed some discrepancies which can be explained by the insufficient mesh resolution. At last, the mean flow and turbulent statistics at higher Re τ was presented and the effect of Re τ on the mean flow and flow dynamics was discussed. [ABSTRACT FROM AUTHOR]

The effect of an imposed magnetic field on Rayleigh–Bénard convection in a constricted 2-D geometry is numerically simulated in this paper. The enclosure is heated from below and the top wall is kept cooled while the two side walls are kept thermally insulated. The magnetic field is imposed horizontally or vertically in separate cases. The middle section of the enclosure is smoothly constricted in some simulations. It is observed from the results that for an increase in the Hartmann number or constriction ratio the motion of the fluid is suppressed and hence the Nusselt number decreases. The number of convection rolls increases with increase in the constriction ratio. The flow solution abruptly turns from steady state to oscillatory flow as the Rayleigh number increases from Ra = 8000 to Ra = 10 , 000 for the case of no constriction. The magnetic field along the horizontal direction shows nearly the same effect as the vertical magnetic field and the Nusselt number decreases with increase in Hartmann number in both cases. At Hartmann number Ha = 20 , the motion is completely suppressed irrespective of the constriction, for the Rayleigh numbers we have studied. [ABSTRACT FROM AUTHOR]

Based on numerical simulations using the immersed boundary method (IBM), results for natural convection in a rhombus enclosure with an inner circular cylinder and a Prandtl number Pr = 0.7 are presented. This simulation spans four decades of Rayleigh number Ra, from 10³ to 107. The inner circular cylinder's location is vertically changed along the rhombus enclosure's centerline. We investigate the effects of both the inner cylinder's location in the rhombus enclosure and buoyancy-induced convection on heat transfer and fluid flow. With respect to the cylinder's location and the Rayleigh number, the thermal and flow field is categorized into three regimes: steady-symmetric, steady-asymmetric, and unsteady-asymmetric. The map of thermal and flow regimes is presented as a function of the cylinder's location and of the Rayleigh number. Detailed analysis results for the distribution of streamlines, isotherms, and Nusselt numbers are also presented in this paper. [ABSTRACT FROM AUTHOR]

This paper reviews the use of direct numerical simulation (DNS) models for the study of mass, momentum and heat transfer phenomena prevailing in dense gas-solid flows. In particular, we consider the DNS models as the first important step in a multiscale modeling strategy. Both the merits and the limitations of different DNS methods are discussed, in particular for the field of fluidized bed modeling. The importance of the closures for interfacial transfer of mass, momentum and heat, obtained from DNS and applied in coarser scale models, is demonstrated with illustrative examples. Finally, we present our view on required future developments of DNS models for the investigation of various chemical engineering problems. [ABSTRACT FROM AUTHOR]

In this paper we report the extension of an earlier reported DNS method (Deen et al., 2012; Deen and Kuipers, 2013) based on a novel Immersed Boundary Method (IBM) which incorporates the fluid-solid coupling at the level of the discrete field equations. The extended method is used to study coupled mass and heat transport in dense fluid-particle systems where the coupling arises as a consequence of an exothermal chemical reaction proceeding at the exterior surface of the particles. Following a detailed verification (using an independent numerical technique) and validation (using established empirical correlations) we apply our DNS technique to study coupled mass and heat transfer in a dense fluid-particle system. In addition a comparison is made with results obtained from a simple one-dimensional (1D) heterogeneous reactor model which uses empirical closures for the fluid-particle mass and heat transfer coefficients. The main features of the complex transient temperature profiles obtained from our DNS agree quite well with the corresponding profiles obtained from the 1D heterogeneous reactor model. [ABSTRACT FROM AUTHOR]