Showing papers on "Schmidt number published in 1994"
TL;DR: In this paper, exact solutions for the heat and mass transfer in a hydromagnetic flow of the visco-elastic fluid over a stretching surface were obtained for different parameters, such as the modified Prandtl number P*r, the magnetic parameter M, the surface temperature index S, and the modified Schmidt number S*c.
87 citations
TL;DR: In this article, the authors measured three-dimensional concentration fields in the self-similar region of natural or unexcited, circularly excited and weakly buoyant round jets of Reynolds number based on nozzle diameter of 1000 to 4000 at a spatial resolution of the order of the Kolmogorov length scale.
Abstract: The virtually instantaneous three-dimensional concentration fields in the self-similar region of natural or unexcited, circularly excited and weakly buoyant round jets of Reynolds number based on nozzle diameter of 1000 to 4000 are measured experimentally at a spatial resolution of the order of the Kolmogorov length scale. Isoconcentration surfaces are extracted from the concentration field. These surfaces along with their geometrical parameters are used to deduce the structure and modal composition of the jet. The concentration gradient field is calculated, and its local topology is classified using critical-point concepts.Large-scale structure is evident in the form of ‘clumps’ of higher-concentration jet fluid. The structure, which has a downstream extent of about the local jet diameter, is roughly axisymmetric with a conical downstream end. This structure appears to be present only in fully turbulent jets. The antisymmetric two-dimensional images previously thought to be axial slices of an expanding spiral turn out in our data to instead be slices of a simple sinusoid in three dimensions. This result suggests that the helical mode, when present, is in the form of a pair of counter-rotating spirals, or that the +1 and −1 modes are simultaneously present in the flow, with their relative phase set by initial conditions.In terms of local structure, regions with a large magnitude in concentration gradient are shown to have a local topology which is roughly axisymmetric and compressed along the axis of symmetry. Such regions, which would be locally planar and sheet-like, may correspond to the superposition of several of the layer-like structures which are the basic structure of the fine-scale passive scalar field (Buch & Dahm 1991; Ruetsch & Maxey 1991).
62 citations
TL;DR: In this article, the free convection boundary-layer flow near a stagnation point driven by catalytic surface heating is considered and the case without fuel consumption is treated first, and it is shown that the steady state equations admit multiple solutions.
Abstract: The free convection boundary-layer flow near a stagnation point driven by catalytic surface heating is considered. The case without fuel consumption is treated first, and it is shown that the steady state equations admit multiple solutions. Explicit expressions can be obtained for these solution branches and it is found that a hysteresis point occurs when the activation energy parameter e = 1/5. The effect of fuel consumption is seen to be characterized by the dimensionless parameter α and numerical results are obtained for a range of values of α and e, as well as Prandtl number σ and Schmidt number Sc. Multiple solutions are again observed and analytic expressions for the bifurcation points can be found when σ = Sc. For σ ≠ Scthese have to be determined numerically.
45 citations
01 Jan 1994
TL;DR: In this article, a method of determining eddy transport coefficients of turbulence is used to study how the turbulent Prandtl number depends upon the molecular PrandTL number and turbulence conditions and a comparison between the theoretical prediction and the relevant experimental data is made.
Abstract: The method of determining eddy transport coefficients of turbulence is utilized to study how the turbulent Prandtl number Prturb depends upon the molecular Prandtl number Pr and turbulence conditionsA comparison between the theoretical prediction and the relevant experimental data is made
29 citations
TL;DR: In this article, the axial dispersion of non-Newtonian power law fluids in a circular curved tube for low Dean number was studied and a spectral model that calculates the solutions effectively for large values of Dn 2 Sc (where Dn is Dean number and Sc is Schmidt number) was chosen to obtain realistic results.
29 citations
TL;DR: In this paper, the authors examined the performance of random flight and closure models in predicting turbulent scalar transport rates in the near field and the far field of plumes, respectively, and found that the plumes are seriously distorted due to the inappropriateness of gradient transport in modeling the streamwise flux rate.
Abstract: Direct numerical simulations of scalar fields produced by uniform and line sources in channel flow are used as the basis for examining the accuracy of random flight and closure models in predicting turbulent scalar transport rates. Closure models of gradient form with an anisotropic eddy diffusivity tensor perform well for the uniform source flow and the far field of plumes. In the near field, the plumes are seriously distorted due to the inappropriateness of gradient transport in modeling the streamwise flux rate. Random flight models are most successful in producing a qualitative rendering of the near field of plumes, but are subject to significant quantitative inaccuracies for the low Reynolds and Schmidt number flows considered here. Ensembles of particle paths having common end points are used to explore the physics of the scalar transport correlation. For plume flows, transport in the near field is found to be primarily due to the average effect of the meandering of the turbulent fluid over the sour...
26 citations
TL;DR: In this paper, a linear stability analysis is performed on the interface formed during the directional solidification of a dilute binary alloy in the presence of a weak, time-dependent flow.
22 citations
TL;DR: In this paper, a least-squares finite element method (LSFEM) was developed to investigate the phenomenon of natural convection caused by temperature and concentration buoyancy effects in rectangular enclosures with different geometric aspect ratios.
Abstract: SUMMARY A least-squares finite element method (LSFEM) has been developed to investigate the phenomenon of natural convection caused by temperature and concentration buoyancy effects in rectangular enclosures with different geometric aspect ratios. The time dependent Navier-Stokes equations, the energy and the mass balance equations for an incompressible, constant property fluid in the Boussinesq approximation are reduced into a first-order velocity-pressure-vorticity-temperature-heat flux-concentration-mass flux (u-p-ω-T-q-C-J) formulation. The coupled system is discrelized by backward differencing in time. For the case of heat and mass transfer from side walls, results for both augmenting and opposing flows are obtained with Prandtl number Pr = 0.7, Schmidt number Sc = 0.6 and 0.7 (Le = 1), Grashof number Gr up to 106, buoyancy ratio χ = − 0.2 to − 5.0 and geometric aspect ratio of 1. For the case of heating from below, we test the LSFEM with two Rayleigh-Benard convection problems. Then the LSFEM algori...
19 citations
TL;DR: In this article, the axial distribution of the local mass transfer coefficients at both the inner rod and the outer wall of an annular test section in decaying annular swirl flow generated by axial vane-type swirl generators were measured using an electrochemical technique.
Abstract: This paper describes an investigation of local mass transfer behaviour at the inner rod and outer pipe wall of an annular test section in decaying annular swirl flow generated by axial vane-type swirl generators. Four swirl generators with vane angles of between 15–60° to the axis of the duct were used. The experiments were carried out in the Reynolds number range 3300–50 000 and at a Schmidt number of 1650. The axial distribution of the local mass transfer coefficients at both the inner rod and the outer wall were measured using an electrochemical technique. Current fluctuations were also recorded to gain information on the turbulence characteristics in the vicinity of the local electrodes.
15 citations
TL;DR: In this paper, a numerical study was made to investigate the laminar mixed convection heat and mass transfer in inclined rectangular ducts using the vorticity-velocity method, three-dimensional Navier-Stokes equations, the energy and concentration equations were solved simultaneously.
12 citations
TL;DR: In this paper, a hydrodynamic model of crystal growth from solution is analyzed, where the spatial distribution of solute concentration and of temperature, the average velocity and maximum velocity of fluid, and the growth rate of crystal are calculated with only the variation of the solution density caused by the temperature change taken into account.
TL;DR: In this article, the influence of the Schmidt number on the wall-to-liquid mass transfer in a packed bed reactor has been studied and it is shown that use of the classical dimensionless group Sh·Sc -1 3 and the particle Reynolds number ReL as a means of taking the effects of Schmidt number into account was not appropriate.
Abstract: The influence of the Schmidt number on the wall-to-liquid mass transfer in a packed bed reactor has been studied. It is shown that use of the classical dimensionless group Sh·Sc -1 3 and the particle Reynolds number ReL as a means of taking the effects of Schmidt number into account was not appropriate. The dimensionless group Sh' · φ · Sc−0.41 · √β and ReLW, based on an appropriate characteristic length and wall porosity were found to represent the wall mass transfer correctly as well as the wall heat-transfer coefficients obtained with different organic liquids.
TL;DR: In this paper, a modified turbulent kinetic energy balance is used to define eddy viscosity and eddy diffusivity in the viscous sublayer of the benthic boundary layer.
Abstract: A near-wall turbulence model is applied to the benthic boundary layer to analyze the diffusive transfer of dissolved substance across the sedimentwater interface. A modified turbulent kinetic energy balance is used to define eddy viscosity and eddy diffusivity in the viscous sublayer. The limiting behavior of turbulence quantities very near the bed is expressed as a power of z, the distance from the sediment-water interface. The predicted flux rate over a wide range of the Schmidt number and dissolved oxygen concentration profile near the bed are in good agreement with observations using microelectrodes.
TL;DR: In this article, a study of diffusion controlled corrosion of smooth and rough pipes under single phase liquid flow and two phase gas-liquid flow using the diffusion controlled dissolution of copper in acidified FeCl3 was performed using a recirculating batch tubular reactor.
Abstract: Rates of diffusion controlled corrosion of smooth and rough pipes were studied under single phase liquid flow and two phase (gas–liquid) flow using the diffusion controlled dissolution of copper in acidified FeCl3. The study was carried out using a recirculating batch tubular reactor through which acidified FeCl3 solution was circulated. The mass transfer coefficient of the dissolution of the copper pipe in the solution was obtained from FeCl3 concentration–time data. Variables studied were solution velocity, gas velocity, and peak to valley height of the rough pipe. For single phase fully developed flow, the mass transfer coefficients of the smooth uncorroded pipes were correlated for the conditions 3000 < ReL < 18 000 and 1688 < Sc < 1899 by the equation Sh = 0·054ScO·33ReL0·79, where ReL is the liquid Reynolds number, Sc is the Schmidt number, and Sh is the Sherwood number. For single phase flow in rough pipes, the data were correlated for the conditions 5 < e+ < 52·5, 3000 < ReL < 18 000, and ...
Journal Article•
TL;DR: In this article, a hydrodynamic model of crystal growth from solution under microgravity is analyzed using the law of similarity, where the spatial distribution of solute concentration and of temperature, the average velocities and maximum velocity of fluid, and the growth rate of crystal are calculated with the variation of the solution density only caused by the temperature change taken into account.
Abstract: A hydrodynamic model of crystal growth from solution under microgravity is analyzed using the law of similarity. The spatial distribution of solute concentration and of temperature, the average velocities and maximum velocities of fluid, and the growth rate of crystal are calculated with the variation of the solution density only caused by the temperature change taken into account. The effects of the values of the Rayleigh number Ra, the Prandtl number Pr and the Schmidt number Sc on the fluid convection, the concentration distribution, the temperature distribution, and the growth rate of crystal are analyzed.
01 Jan 1994
TL;DR: In this paper, a computer simulation model was developed predicting the mass transfer in terms of turbulent diffusion for high molecular weight substances, which involves a numerical solution of the time averaged equations of motion with a spatial resolution down in the very thin concentration boundary layer appearing in turbulent wall boundary layers.
Abstract: A computer simulation model have been developed predicting the mass transfer in terms of turbulent diffusion for high molecular weight substances. The method involves a numerical solution of the time averaged equations of motion with a spatial resolution down in the very thin concentration boundary layer appearing in turbulent wall boundary layers.
TL;DR: In this article, the effect of opposing thermal and concentration gradients on the Nusselt and Sherwood numbers is analyzed for horizontal prismatic cavities of trapezoidal section having a hot horizontal base, a cool inclined top and insulated vertical walls.
Abstract: Heat transfer driven by temperature gradients and simultaneous temperature and concentration gradients has been studied numerically for horizontal prismatic cavities of trapezoidal section having a hot horizontal base, a cool inclined top and insulated vertical walls. Results are presented for a cavity with width-to-mean height ratio of 4, thermal and concentration Rayleigh numbers up to 106 and 5.105 respectively, and top surface inclinations from 0 to 15 deg to the horizontal. The Prandtl and the Schmidt number used are 0.71 and 0.6 respectively. The governing equations are expressed in terms of stream function and vorticity and body-fitted coordinates are used for mapping the sloping top wall. As the inclination of the top surface is increased, the Nusselt and Sherwood numbers decrease. The effect of opposing thermal and concentration gradients on the Nusselt and Sherwood numbers is however more important than the effect of the inclination of the top surface. Theoretical Nusselt and Sherwood numbers ar...
01 Mar 1994
TL;DR: In this article, a methodology for simulation of molecular mixing and the resulting velocity and temperature fields has been developed, applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility.
Abstract: A methodology for simulation of molecular mixing, and the resulting velocity and temperature fields has been developed The ideas are applied to the flow conditions present in the NASA Lewis Research Center Planar Reacting Shear Layer (PRSL) facility, and results compared to experimental data A gaussian transverse turbulent velocity distribution is used in conjunction with a linearly increasing time scale to describe the mixing of different regions of the flow Equilibrium reaction calculations are then performed on the mix to arrive at a new species composition and temperature Velocities are determined through summation of momentum contributions The analysis indicates a combustion efficiency of the order of 80 percent for the reacting mixing layer, and a turbulent Schmidt number of 2/3 The success of the model is attributed to the simulation of large-scale transport of fluid The favorable comparison shows that a relatively quick and simple PC calculation is capable of simulating the basic flow structure in the reacting and nonreacting shear layer present in the facility given basic assumptions about turbulence properties