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The contribution of the macroscopic mobile phase velocity profile in a paper or thin-layer strip to longitudinal dispersion in chromatography was investigated. For this purpose the dependence of the plate height on the breadth of the paper or thin-layer strip, scanned by the densitometer, was determined using Whatman W2 paper and Camag D cellulose powder. As longitudinal dispersion depends on transversal (convective and diffusive) dispersion, the latter was determined for both chromatographic techniques.

For the laminar flow of a fluid with constant properties in a uniformly heated rectangular duct with no viscous dissipation and internal heat release, an exact solution for the fluid temperature field is presented in the form of rapidly convergent infinite series. Expressions are subsequently derived for the variation of limiting Nusselt number, based on unweighted and weighted mean temperature differences, with duct aspect ratio. It is shown that previously published approximate solutions for the weighted Nusselt number—determined using numerical techniques—are in agreement with the more versatile exact solution to better than 1 per cent.

Laminar convection in vertical systems is affected by buoyancy so that it becomes a combination of natural and forced convection. In downflow the buoyancy forces oppose the main flow. The problem has previously been studied for flows in vertical circular tubes and is here extended to flows in vertical annuli with uniformly heated inner surfaces. This configuration retains the simplicity desirable for both analysis and experiment, but also represents quite closely certain practical systems such as flow in nuclear reactors in which cylindrical components are placed axially in vertical coolant channels. Buoyancy forces opposing the main flow cause the fluid to be slowed down near the heat transfer surface until it is eventually reversed. In simple theory this flow reversal is associated with a decrease in heat transfer performance. An experimental study has been performed in a vertical annulus of ¾ in inner and 2¼ in outer diameter using water. Flow visualization by dye injection indicates that while small reversed flows may occur in a stable form, higher buoyancy forces give rise to radial components of the flow. These radial components cause the reversed flow regime to become unsteady and the Nusselt numbers to be higher than those predicted by laminar convection analysis.

Experimental data are presented from studies of turbulent heat transfer at high fluxes to water flowing in vertical tubes at supercritical pressures. A comparison of data for upward and downward flows indicates an effect of natural convection.

One of the main problems with heat transfer research in the critical region is the lack of accurate thermodynamic and transport property data. This lack of information makes the actual heat transfer performance very difficult to correlate, whilst the extreme property variations produce other effects, which are also dependent on the heating surface geometry. Three fluids, carbon dioxide, nitrous oxide, and chlorotrifluoromethane, were therefore tested with a view to establishing whether they had similar regions of heat transfer and whether any similarity with boiling existed. The results show that in the critical region the normal convective heat transfer is augmented by a process to give results which look very like the lower portion of the normal boiling curve. Finally the authors show evidence to support the theory that there are preferential areas of heat transfer in the supercritical region.

Murray's equation (53) for the velocity of rise of a three-dimensional (spherical) bubble of diameter dB can be written where the unassigned coefficient c enters Murray's analysis in the linearization of the convective momentum term in the momentum equation for the solids (17). (Equations (53) and (17) are as numbered in Murray 1965b.) This compares with the expression used by Rowe & Partridge (1965), who determined the velocity coefficient, K, for several fluidized systems by measuring bubble diameter and velocity from X-ray cine photographs. Values of c calculated from the measured values of K are listed in table 1, from which it is seen that the coefficients are not truly constant. The observed values of Murray's c are also appreciably less than c = 1 or c = ⅗, the two values tentatively suggested by mathematical reasoning, and Murray's figure 13, based on earlier velocity measurements over a limited range of particle sizes, is not a critical test of the value of the constancy of c.

Measurements of liquid-water content in cumulus clouds were made with a device which records changes of conductivity of a paper tape with changes of wetness. One series of measurements was made in tropical cumuli; another was made in clouds over the Central United States. Examples of the variability of liquid water in convective clouds and typical values are given. It was found that the high values of liquid-water content occurred in clouds in which precipitation formed. Comparisons of the observed values of liquid water with theoretical values based on an assumption of moist-adiabatic air ascent, without mixing, lead to the conclusion that clouds with precipitation contain regions where the liquid water exceeds the theoretical amounts.

The following paper is occupied by an attempt to investigate the distribution of the electric and magnetic forces which are called into play when certain electro­magnetic systems are made to move with uniform velocity through the ether. Maxwell’s theory will be employed throughout, and will be applied to th e exact solution of several problems, and to the establishment of some results of a general nature. Professor J. J. Thomson was, I believe, the first to consider a problem of this sort, his paper giving the solution for the motion of a single electrical point-charge at a speed small compared with that of light. Mr. Oliver Heaviside next considered the question, and in his paper obtained an exact solution for the motion of a point-charge. He got the solution by means of the “vector potential” of the convection current formed by the moving charge. The mathematical analysis is of the symbolical kind, but it is shown that the result obtained by means of it satisfies all the necessary conditions. By integrations Mr. Heaviside obtains solutions for the motion of some simple cases of electrical distribution.

Two wavevector filters were designed for investigating the nature of the pressure field induced on a flat boundary by a highly subsonic turbulent boundary layer. The wavevector filters were designed specifically for investigation in the spectral range where the spectral density of the pressure field is high. Preliminary experiments have been carried out, and the results relating to the convection velocity are reported. The major objective of the paper is, however, to present an analysis that makes it possible to properly interpret the results and allows for a more satisfactory comparison between the results reported in the paper and the available data in the literature.

This paper is concerned with the effects of nonlinear eddy coefficients on rising, dry fine thermals. The base atmosphere in which these thermals are embedded is hydrostatic, horizontally homogeneous, nearly neutral, and without an ambient wind. By identifying the turbulent transfer terms with the subgrid–scale motions, a nonlinear formulation, based upon the worn. of Lilly and Smagorinsky, is obtained for the eddy coefficients. The mixing length in these terms is based upon a vorticity formulation rather than the size of the numerical grid used in the computations. Using numerical techniques based upon the work of Arakawa, and Adams and Bashforth, we tested these formulations by following the evolution of rising line thermals. We concluded that the eddy formulation used in this paper is more realistic than using constant coefficients throughout the field of computation. In addition, we found that the density stratification is important if the convective layer is deeper than 3 km.

This paper presents a surface renewal based formulation for convective heat transfer for hydrodynamically and thermally fully developed turbulent flow in a tube. Based on the modeling concept presented in this paper, turbulent pulsatile flow is categorized according to the hydrodynamically unsteady mean residence time, τ(t).

This paper (part II) is the second of two papers dealing with cumulus and broader scale flow interaction. The first (part I) is a companion paper that deals with this topic from broad-scale considerations. The second (part II) deals with this topic from the cumulus scale point of view. A numerical model of individual convective clouds has been used to investigate the effects of a typical population of cumulus clouds on the large-scale features of a tropical disturbance or cloud cluster. The typical cloud population has been determined from U.S. Navy aircraft reconnaissance radar data in the tropical Atlantic Ocean. This study shows that the detrainment of cloud mass from the population produces net cooling of the air around the clouds. This occurs because the cooling produced by the evaporation of the detrained cloud liquid water over-compensates for the detrainment of sensible heat excess. A heat and moisture budget for a steady-state tropical cloud cluster has been computed using the typical cl...

The purpose of this paper is to describe apparatus and instrumentation whereby the sequence of events in confined burning of explosives can be followed. These events are pressure buildups, formation of a convective flame front, formation of a detonation front, or a pressure rupture of the confining tube. Furthermore, although a convective front has been observed in every reported case of transition from deflagration to detonation in granular explosives, we find that it also occurs (at about the same driving pressures and traveling at about the same velocity) in explosives unable to exhibit a transition in this apparatus. Data are presented from the confined burning of ammonium picrate at several compactions and of 95/5 TNT/Wax. Burning these relatively shock-insensitive explosives produces a mild pressurization of the confining tube which leads, after a period of instability, to the formation of a convective flame front and, eventually to tube rupture. The rapid pressure buildup necessary for a transition to detonation is absent. Confined burning of explosives which do exhibit transition is described in a companion paper.