Showing papers on "Combined forced and natural convection published in 1972"
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 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 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
89 citations
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.
81 citations
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.
73 citations
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.
66 citations
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.
61 citations
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, 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, experimental results are given concerning stationary heat and mass transfer in the laminar boundary layer of a vertical cylinder placed in still air, and the combined effect is considered as well as the two separate effects.
Abstract: In this paper experimental results are given concerning stationary heat and mass transfer in the laminar boundary layer of a vertical cylinder placed in still air. The combined effect is considered as well as the two separate effects.
TL;DR: In this article, a theoretical analysis of haline convection induced by the freezing of sea water is made for a turbulent ocean, and the nonlinear equations for two-dimensional flow are solved using the mean field approximation and expanding the variables in Fourier series.
Abstract: A theoretical analysis of haline convection induced by the freezing of sea water is made for a turbulent ocean. The nonlinear equations for two-dimensional flow are solved using the mean field approximation and expanding the variables in Fourier series. It is found that, when the depth of the mixed layer is sufficiently large, the convective process is independent of depth. Expressions for the horizontal spacing of convection cells, maximum vertical velocity, and time required for manifest convection to develop are derived for a range of Schmidt numbers appropriate for the ocean. The analysis is applied to conditions that may be typical of freshly frozen polynyas or leads in the Weddell Sea, and it is concluded that haline convection is probably an effective process as a precursor to Antarctic Bottom Water formation.
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.
TL;DR: In this article, the authors extended the theory to cover the case of the inclined cell and the vertical cell and showed that convection must be initiated for any temperature gradient to be established between the absorber plate and the glass cover plate.
TL;DR: In this article, the problem of combined forced and free-convection heat transfer from a thin needle in a uniform external stream is considered, and the series and local similarity solutions have been discussed.
Abstract: The problem of laminar combined forced and free‐convection heat transfer from a thin needle in a uniform external stream is considered. The series and local similarity solutions have been discussed.
01 Jan 1972
TL;DR: The development of helium I forced-convection heat transfer systems can be an important key to solving some of the problems that superconducting magnet designers are now facing as discussed by the authors.
Abstract: The development of helium I forced-convection heat transfer systems can be an important key to solving some of the problems that superconducting magnet designers are now facing. Some of the advantages compared with conventional systems are (1) high heat transfer coefficients, (2) simple cryostat design, (3) modest refrigeration requirements (refrigerator directly coupled to magnet coils), (4) cooldown operations considerably simplified, and (5) electrical insulation problems eliminated (due to a more rigid construction).
TL;DR: In this article, a variational analysis of combined free and forced convection through vertical noncircular ducts is carried out using a VAE technique, where the condition of uniform peripheral heat flux is utilized in deriving the variational expression.
Abstract: Analysis of combined free and forced convection through vertical noncircular ducts is carried out using a variational technique. Fully developed flow with uniform axial heat input and uniform peripheral heat flux is assumed. All fluid properties are considered invariant with temperature except the variation of density in the buoyancy term of the equation of motion. The condition of uniform peripheral heat flux is utilized in deriving the variational expression. This procedure releases the thermal boundary condition from satisfying exactly the condition at the wall. A finite-difference procedure is carried out. For pure forced convection case, a particularly simple variational expression is presented. Nusselt numbers for combined free and forced convection are computed for rectangular, rhombic and elliptical ducts. An exact solution is presented for laminar forced convection through elliptic ducts. Variational results are in agreement with this exact solution. The present results are compared with those in the published literature wherever possible, and good agreement is obtained.
TL;DR: In this article, Solute convection is experimentally considered in two ways: through the influence of solute convection on thermal convection and through the combined thermal and solute gradient conditions for complete liquid mixing throughout the liquid zone.
TL;DR: In this article, a new method of accounting for the influence of property variation on heat transfer by forced convection from heated surfaces to liquids is presented, which is used in conjunction with new experimental data to develop a correlation equation for forcing convection heat transfer from cylinders to liquids in crossflow.