Search results for "Convection"
showing 10 items of 332 documents
Onset of convective rolls in a circular porous duct with external heat transfer to a thermally stratified environment
2011
A horizontal circular duct filled with a fluid saturated porous medium is studied. The external wall is assumed to exchange heat with an external environment thermally stratified in the vertical direction. The external heat transfer is modeled through a third kind boundary condition, and a Biot number associated with the external heat transfer coefficient is defined. The linear stability of the basic state where the velocity field is zero is studied numerically. The condition of neutral stability is determined, by solving the system of elliptic governing equations for the disturbances through a Galerkin finite-element method. The neutral stability curves, together with the critical values o…
Numerical and Experimental Analysis of Convection Transfer During Melting by a Mono-Pulsed Laser
2010
This paper presents a comparison between simulation and experimental results of the melting process of metallic material by a pulsed laser source Nd-YAG. Variations of the thermophysical properties were considered. Furthermore, the model included the effects of the surface-tension gradient on the fluid surface and the buoyancy force. The keyhole effect induced strong surface deformations and often formed cavities, which arre undesirable in the surface treatment process. An experimental study of the surface profile of the melted zones was also conducted to seek a relationship between the so-called keyhole effect and the laser triangulation measurements. The predicted Laser Melted Zone (LMZ) …
Simulation of turbulent metal flows
2007
Comprehensive knowledge of the heat and mass transfer processes in turbulent metal flows is required to realize efficient and reliable melting and casting processes. Experimental and numerical studies of the melt flow in induction furnaces show that the flow pattern, which comprise several vortexes of the mean flow, and the temperature distribution in the melt are significantly influenced by low-frequency large scale flow oscillations. Two- and three-dimensional hydrodynamic calculations of the melt flow, using two-equation turbulence models based on Reynolds Averaged Navier-Stokes approach, do not predict the large scale periodic flow instabilities obtained from the experimental data. That…
The Effect of Intense Air Drying on Material Distribution and Quality in Coated Papers
2003
Abstract The aim of this study was to find out what will happen to paper coating quality and material gradients if coating is dried in one air dryer at a high convection rate (150 kg/m2h). Different printing papers were coated, calendered and printed with pilot machines. The binder and pigment gradients of the coated, and also printed, samples were analyzed with LIPS (Laser Induced Plasma Spectrometry). It was found that drying affects the migration of starch, but not latex. Total air drying can be used to dry printing papers, if air temperature, velocity and moisture content can be separately controlled. The control of web temperature is more important for paper quality formation in a coat…
Geoid effects in a convecting system with lateral viscosity variations
1992
The geoid signal and the flow patterns of two-dimensional steady state convection models with exponential temperature- and depth dependent viscosity are compared with results for an equivalent stratified viscosity structure. In analogy to Richards and Hager [1989], the latter are computed by a “dynamic response” approach. The flow fields obtained with this approach are quite different from the full solution; the geoid signals are similar but the amplitudes differ significantly. The differences are analysed in the horizontal wavenumber domain and in the spatial domain. They may lead to an overestimation of the viscosity contrast of the earth's mantle derived by modeling the earth's geoid wit…
Comparing calculated microphysical properties of tropical convective clouds at cloud base with measurements during the ACRIDICON-CHUVA campaign
2016
Abstract. Reliable aircraft measurements of cloud microphysical properties are essential for understanding liquid convective cloud formation. In September 2014, the properties of convective clouds were measured with a Cloud Combination Probe (CCP), a Cloud and Aerosol Spectrometer (CAS-DPOL), and a cloud condensation nuclei (CCN) counter on board the HALO (High Altitude and Long Range Research Aircraft) aircraft during the ACRIDICON-CHUVA campaign over the Amazon region. An intercomparison of the cloud drop size distributions (DSDs) and the cloud water content derived from the different instruments generally shows good agreement within the instrumental uncertainties. The objective of this s…
Optical saturation, diffusion and convection effects in thermal lens spectrometry
1995
Abstract In thermal lens spectrometry (TLS) the intense pump radiation can lead the chromophore to partial optical saturation conditions in which the ground state is depleted and the population of an intermediate excited state increases. A model in which the excitation process competes with both the decay processes and diffusion and convection of the species in the excited and ground states is developed. The model is used to explain the variations of the TLS/spectrophotometry sensitivity ratios found for a series of phthalein and azo dyes in aqueous media.
Heat transfer calculation in a free convection air solar collector
1998
This paper deals with the free convective air flow developing in a vertical channel with a rectangular cross-section heated on one side. The channel geometric and physical properties are such as to simulate an air solar collector suitable for building heating. A calculation method that can be applied to the transient combined heat transfer by conduction through the wall and by convection from the wall to the air stream is presented. The conduction across the wall is computed with a one-dimensional, time-dependent finite difference scheme, with convective boundary conditions at both wall surfaces. For the free convective flow along the channel, the air flow rate and the mean convective coeff…
Study of a water-cooled convective divertor prototype for the DEMO fusion reactor
2000
The plasma facing components of a fusion power reactor have a large impact on the overall plant design, its performance and availability and on the cost of electricity. The present work concerns a study of feasibility for a water-cooled prototype of the convective divertor component of the DEMO fusion reactor. The study has been carried out in two steps. In the first one thermal-hydraulic and neutronic parametric analyses have been performed to find out the prototype optimized configuration. In the second step thermo-mechanical analyses have been carried out on the obtained configuration to investigate the potential and limits of the proposed prototype, with a particular reference to the ma…
Fronts propagating with signal dependent speed in limited diffusion and related Hamilton-Jacobi formulations
2021
We consider a class of limited diffusion equations and explore the formation of diffusion fronts as the result of a combination of diffusive and hyperbolic transport. We analyze a new class of Hamilton-Jacobi equations arising from the convective part of general Fokker-Planck equations ruled by a non-negative diffusion coefficient that depends on the unknown and on the gradient of the unknown. We explore the main features of the solution of the Hamilton-Jacobi equations that contain shocks and propose a suitable numerical scheme that approximates the solution in a consistent way with respect to the solution of the associated Fokker-Planck equation. We analyze three model problems covering d…