Flow Peclet Number Research Articles

Heat Transfer of Power Law Fluid at Low Peclet Number Flow

An exact solution is presented for the temperature distribution and local Nusselt number of power law fluid in conduit at low Peclet number flow by considering axial conduction in both the upstream and the downstream regions while keeping the wall at constant temperature. Solutions are also reported for the parallel plate geometry for the aforementioned heat transfer condition and for constant wall heat flux boundary condition. The order of importance of axial conduction is established for different geometries and different boundary conditions. The effect of axial conduction is more significant when power law model index, s, increases for constant wall heat flux case, but the effect changes with Peclet number for constant wall temperature case.

Diffusive, Electrostatic, and Gravitational Deposition of Suspensions in the Entrance of a Nozzle

An analytical investigation of the mechanics of deposition affected by gravity, electrostatic charge, and Brownian motion in an effuser from the nozzle inlet to a distance where incompressible effects are still valid has been made and a mathematical model developed for the deposition process. The analysis was restricted to laminar flow of dilute, nonreactive suspensions contained within an incompressible, viscous carrier. The results show that increasing the nozzle angle causes a decrease in deposition rate regardless of the diffusive Peclet number and gravity flow parameter. Furthermore, an increase in gravity field causes an increase in bottom deposition rate and decrease in top deposition rate.

Comment on “Review of flashback reported in prevaporizing/premixing combustors”

Flame flashback attributed to combustion induced vortex breakdown (CIVB) is a major design challenge for swirl stabilized burner combustors. This paper presents an experimental investigation of combustion induced vortex breakdown (CIVB) flashback propensity for flames yielded from Hydrogen (H2)–Carbon Monoxide (CO) fuel blends and actual synthesized gas (syngas) mixtures. A two-fold experimental approach, consisting of a high definition digital imaging system and a high speed PIV system, was employed. The main emphasis was on the effect of concentration of different constituents in fuel mixtures on flashback limit. In addition, the effect of Swirl Number on flashback propensity was discussed. The percentage of H2 in fuel mixtures played the dominant role when CIVB flashback occurred. For a given air mass flow rate, the mixture containing a higher percentage of H2 underwent flashback at much leaner conditions. Flashback maps for actual syngas fuel compositions showed a distinct behavior when various concentrations of diluents were introduced in the mixture. For the two major diluents tested, carbon dioxide (CO2) and nitrogen dioxide (NO2), CO2 was more dominant. The effect of Swirl Number on the flashback propensity was also tested and showed a decrease with an increase in Swirl Number. The final portion of this paper also provides an analysis of flow field of reacting flames which revealed complex vortex–chemistry interactions leading to vortex breakdown and flashback. Based on the experimental results a parametric model similar to Peclet Number approach was developed employing a flame quenching concept. A value of the quench parameter, Cquench was obtained from the correlation of flow Peclet Number and flame Peclet Number, which was observed to be dominated by the fuel composition rather than Swirl Number.

The drag of a body moving transversely in a confined stratified fluid

The slow motion of a body through a stratified fluid bounded laterally by insulating walls is studied for both large and small Peclet number. The Taylor column and its associated boundary and shear layers are very different from the analogous problem in a rotating fluid. In particular, the large Peclet number problem is non-linear and exhibits mixing of statically unstable fluid layers, and hence the drag is order one; whereas the small Peclet number flow is everywhere stable, and the drag is of the order of the Peclet number.

Effects of transpiration and changing diameter on heat and mass transfer to spheres

AbstractMass transfer to spheres suspended in an agitated liquid has been studied both experimentally and theoretically. Finite‐difference solutions are obtained for mass transfer from a sphere to a fluid flowing past it in steady viscous flow. The effects of a transpiration velocity at the surface of the sphere and of a continuously changing sphere diameter are included. A normalized presentation of these effects is quite insensitive to the bulk flow Peclet number. When these theoretical corrections for transpiring and shrinking spheres are applied to the mass transfer data for ice spheres that are melting in an agitated brine bath, the corrected mass transfer coefficients are brought into agreement with a generalized correlation published elsewhere. This agreement suggests that the theoretical results apply, with reasonable accuracy, to a shrinking and transpiring sphere that is suspended in a turbulent liquid.

Decompositional burning of a droplet in a small Peclet number flow.

Asymptotic results for chemical-reaction and forced-convection effects on the quasi-steady adiabatic vaporization of a rigid uniform spherical droplet immersed in an unbounded expanse of gas are obtained by inner-and-outer expansions. The zeroth-order approximation is the radially symmetric solution yielding the classical logarithmic mass transfer rate. The perturbation introduces the corrections arising from 1) first-order decompositional burning for reaction rates small relative to flow rates (small first Damkohler similarity parameter); and 2) the possible wake-generating role of a slight relative flow past the droplet (small Peclet number). For tractable closed-form solution the flow is taken as incompressible with constant properties; the Lewis number is restricted to unity in the perturbational analysis. The first perturbation to the Sherwood number (normalized mass transfer rate) is found to be independent of Schmidt number, but dependent on the reaction rate. The first modification to the Stokes drag (owing to mass transfer) is found to be independent of the reaction rate, but dependent on the Schmidt number. For indefinitely large Schmidt number the Stokes drag is always increased because of mass transfer, and streamlines display no wake; for orderunity Schmidt number entirely different results are anticipated.

An analytical study of heat and mass transfer in multiparticle systems at low Reynolds numbers

AbstractThis investigation was undertaken to obtain an analytical solution to the problem of predicting particle‐to‐fluid heat and mass transfer rates in multiparticle systems at low Reynolds numbers. The energy equation based on the free surface model was solved by expanding the fluid temperature distribution in even powers of the spherical angle and by assuming that the fluid properties remain relatively constant with temperature. Solutions were obtained for Peclet numbers between 0.1 and 100 and fractional void volumes between 0.4 and 1.0. They show that the average Nusselt or Sherwood number in a bed of particles is a function of both the fractional void volume and the Peclet number, the effect of Peclet number decreasing as the bed becomes more concentrated in the low Peclet number range. A plot of the results in terms of the j factor vs. the Reynolds number shows good agreement with published experimental mass and heat transfer data and indicates that the j factor is not independent of the Schmidt or Prandtl numbers at low Reynolds number, low Peclet number flow.