Showing papers on "Natural convection published in 1972"
TL;DR: In this article, the complex nature of the natural convection phenomena in enclosures is discussed and the boundary value problem is formulated, assuming that the motion is two-dimensional and steady, the fluid is incompressible and frictional heating is negligible.
Abstract: Publisher Summary This chapter discusses the complex nature of the natural convection phenomena in enclosures. It discusses the two basic configurations of natural convection— that is, a rectangular cavity and a horizontal circular cylinder. In rectangular cavities, consideration is given to the two-dimensional convective motion generated by the buoyancy force on the fluid in a rectangle and to the associated heat transfer. The two long sides are vertical boundaries held at different temperatures and the short sides can either be heat conducting or insulated. Particular attention is given to the different flow regimes that can occur and the heat transfer across the fluid space between the two plane parallel vertical boundaries. Although heat transfer by radiation may not be negligible it is independent of the other types of heat transfer and can be fairly accurately calculated separately. To formulate the boundary value problem that describes this phenomena it is assumed that: (a) the motion is two-dimensional and steady, (b) the fluid is incompressible and frictional heating is negligible, and (c) the difference between the hot wall and cold wall temperatures is small relative to the absolute temperatures of the cold wall. In horizontal circular cylinder, consideration is given to the large Rayleigh number flow with the Prandtl number large and the Grashof number of unit order of the magnitude.
382 citations
TL;DR: In this paper, a numerical and experimental investigation of the developing laminar free convection heat transfer in vertical parallel plate channels with asymmetric heating is presented, where the Nusselt number characterizing the total heat transfer to the fluid is found to be related to the Rayleigh number very nearly by a universal curve for all ratios of wall temperature differences.
330 citations
242 citations
TL;DR: In this article, the instability of convection rolls in a fluid layer heated from below is investigated for stress-free boundaries in the limit of small Prandtl number, and it is shown that the two-dimensional rolls become unstable to oscillatory three-dimensional disturbances when the amplitude of the convective motion exceeds a finite critical value.
Abstract: The instability of convection rolls in a fluid layer heated from below is investigated for stress-free boundaries in the limit of small Prandtl number. It is shown that the two-dimensional rolls become unstable to oscillatory three-dimensional disturbances when the amplitude of the convective motion exceeds a finite critical value. The instability corresponds to the generation of vertical vorticity, a mechanism which is likely to operate in the case of a variety of roll-like motions. In all aspects in which the theory can be related to experiments, reasonable agreement with the observations is found.
211 citations
TL;DR: In this article, the authors measured energy transport at Rayleigh numbers up to 675 times the critical (linear stability theory) value in a layer of dilute electrolyte bounded horizontally by two rigid planes of constant and equal temperature; Joule heating by an alternating current passing horizontally through the layer provides the volumetric energy source.
Abstract: Energy transport at Rayleigh numbers up to 675 times the critical (linear stability theory) value is measured in a layer of dilute electrolyte bounded horizontally by two rigid planes of constant and equal temperature; Joule heating by an alternating current passing horizontally through the layer provides the volumetric energy source. Horizontally averaged temperature profiles are determined optically. Mean temperature distributions are asymmetric at elevated Rayleigh numbers, the energy transport at the upper boundary being more than twice that at the lower boundary. Three regimes of flow are identified and discrete transitions in the energy transport appear to exist when the flow is turbulent. Extrapolation of the data to the conduction value of the Nusselt number yields a critical Rayleigh number which is within + 10·7% of linear theory values. No subcritical convection is observed when finite amplitude disturbances are introduced into the fluid at a Rayleigh number between the critical values predicted by the linear stability theory and energy theory respectively.
176 citations
TL;DR: In this paper, the burning rates of hexadecane droplets 0.5 to 1 mm in diameter, suspended on quartz fibers in room-temperature air, at pressures from 1 to 0.1 atm.
174 citations
TL;DR: In this article, an algorithm was developed for the finite-difference computation of hydrodynamic stability and natural convection in non-Newtonian fluids heated from below, and the results were found to be independent of the assumed initial state.
Abstract: An algorithm was developed for the finite-difference computation of hydrodynamic stability and natural convection in non-Newtonian fluids heated from below. Test calculations were carried out for fluids whose viscosity characteristics are described by the Ostwald-de Waele (power-law) and Ellis models and for roll-cells with both rigid and dragless vertical boundaries. The effects of time-step and grid-size were tested thoroughly. The results were found to be independent of the assumed initial state. The computed values of the Nusselt number and the critical Rayleigh number for Newtonian fluids agree well with prior experimental results. The computations for the Ostwald-de Waele model indicate that the approximate solution of Tien, Tsuei, and Sun may underestimate the critical Rayleigh Number.
131 citations
TL;DR: In this article, a finite difference solution of the equations describing transient natural convection in porous media is presented, and the linearized equations are solved to provide an estimate of the number of possible convective modes as a function of the Rayleigh number.
112 citations
TL;DR: In this paper, a numerical study of the transient laminar two-dimentional motion of a fluid between two heated vertical plates, the motion being generated by a temperature gradient perpendicular to the direction of the body force, is described.
104 citations
TL;DR: In this article, the heat transfer properties of a vertical array of heated cylinders are obtained in steady state natural convection, showing that the surface temperature increases with elevation in the array for closely spaced arrays, but decreases with elevation when the spacing is sufficiently large.
103 citations
TL;DR: In this paper, the initiation of natural convection in a fluid confined above and below by rigid perfectly conducting surfaces and laterally by rigid, perfectly insulating vertical walls that form a rectangular shape is examined.
TL;DR: In this article, the effects of uniform blowing and suction on the free convection boundary layer on a vertical plate are considered, and a numerical solution of the full boundary layer equations is obtained in both cases.
TL;DR: In this article, the authors deal with natural convection heat transfer from a non-isothermal vertical flat plate immersed in a temperature stratified environment and show that approximations based on the local temperature difference can introduce large errors into the prediction of surface heat transfer rates.
TL;DR: In this article, the authors considered the natural convection flow over a horizontal, isothermal and semi-infinite surface, generated by the combined buoyancy effects of surface heating and diffusion of chemical species.
TL;DR: In this article, the effects of single scattering albedo, optical thickness, and conduction-to-radiation parameter on temperature distribution in the boundary layer and heat transfer at the wall were investigated.
TL;DR: In this paper, three modes of heat removal are identified for the monotonic curve and described analytically: a natural convection mode, a mixed film boiling and a pure film boiling mode.
TL;DR: In this paper, an experimental investigation of free convection heat transfer from heated spheres to water is reported, and the experimental data extend over a wide range of Rayleigh number, thus covering the laminar, transition, and beginning of the turbulent regimes.
TL;DR: In this article, the effect of component size on convective heat transfer from small devices (with surface areas between 2·00 and 0·01 sq cm) was investigated analytically and experimentally.
TL;DR: In this article, a quasi-two-dimensional, free convection heat transfer from a heated horizontal plate of Rayleigh number of the order of 107 in air has been made, and the velocity and temperature fields near the downward-facing surface have been measured.
TL;DR: In this article, the formation and growth of horizontal layered convection cells in a density stratified solution of salt water subject to an impulsively applied lateral temperature gradient is investigated with physical and numerical experiments.
Abstract: The formation and growth of horizontal layered convection cells in a density stratified solution of salt water subject to an impulsively applied lateral temperature gradient is investigated with physical and numerical experiments. Results indicate that lyers are induced by two mechanisms. One is the successive formation of layers due to the presence of the top and bottom boundaries. The other is the spontaneous occurrence of layers when a suitably defined Rayleigh number exceeds a critical value. It is found that well established layers are homogeneous in temperature and salinity and are separated by sharp gradients in density. Lateral heat transfer is of a periodic nature. Numerical experiments were carried out for finite and infinite geometry cases. For the finite geometry case, convection cells are generated successively inward from the horizontal boundaries. For the infinite geometry case, periodic conditions in the vertical direction are assumed. With continuous input of small perturbations,...
TL;DR: In this paper, a model of thermal convection of a Boussinesq fluid in an equatorial annulus of a rotating spherical shell is presented, where the convection induces and maintains differential rotation and meridian circulation.
Abstract: We present extensive numerical calculations for a model of thermal convection of a Boussinesq fluid in an equatorial annulus of a rotating spherical shell. The convection induces and maintains differential rotation and meridian circulation. The model is solved for an effective Prandtl number P = 1, with effective Taylor number T in the range 102
TL;DR: In this article, the authors measured the time-dependent mass transfer rates in the transition and turbulent regimes, and the measured local laminar mass transfer coefficients agreed with analytical predictions, both for vertical and inclined surfaces.
TL;DR: In this paper, the authors modeled natural convection in a porous medium by writing force mass and energy balances on a differential element of porous medium and solved numerically after the introduction of a pseudo-stream function.
Abstract: Natural convection in a porous medium was mathematically modelled by writing force mass and energy balances on a differential element of porous medium. The resultant set of partial differential equations, which accounts for temperature-dependent physical properties, was solved numerically after the introduction of a pseudo-stream function. This method of treating emperature-dependent fluid properties, which is also applicable to other fluid flow problems, resulted in an efficient solution algorithm. Good agreement has been obtained between theoretical and experimental results. Theoretical calculations show that under certain conditions variation of fluid properties with temperature has a significant effect on convective motions.
TL;DR: In this article, a model of thermal convection under a central force field has been constructed using a strong alternating electric field gradient in a dielectric liquid, which is governed by an electrical Rayleigh number.
Abstract: A laboratory model of thermal convection under a central force field has been constructed using a strong, alternating electric field gradient in a dielectric liquid Both the electric field gradient and a temperature gradient are maintained between concentric vertical cylinders The onset of thermal convection is detected by heat transfer and temperature measurements It is governed by an electrical Rayleigh number, in which the electric force replaces gravity Marginal stability analysis gives a critical electrical Rayleigh number in agreement with the experimentally determined value
TL;DR: In this paper, the effects of gas-phase convection on crystal growth are reviewed. But the existing literature in this field is not well documented, the author has attempted to use the limited space available for this review to provide a bibliography (though by no means an exhaustive one) of the field rather than to treat one aspect of the subject in detail.
TL;DR: In this article, the authors present the results of an experimental and theoretical study of heat transfer during film and transition boiling on vertical surfaces, where the theoretical analysis is confined to natural convection saturated film boiling, while the experimental work shows the effect of bulk liquid velocity with saturated and with subcooled methanol.
TL;DR: In this paper, the structure of finite-amplitude thermal convection within a self-gravitating fluid sphere with uniform heat release was determined for a fixed-surface boundary condition.
Abstract: Finite-difference calculations have been carried out to determine the structure of finite-amplitude thermal convection within a self-gravitating fluid sphere with uniform heat release. For a fixed-surface boundary condition, single-cell convection breaks up into double-cell convection at a Rayleigh number of 30,000, at a Rayleigh number of 500,000 four-cell convection is observed. With a free-surface boundary condition only single cell convection is obtained up to a Rayleigh number of 5,000,000.