Neil S. Berman

The interfacial turbulence in falling film absorption: effects of additives

Abstract The results of vertical falling film experiments on the absorption of water vapor to aqueous lithium bromide solutions with an additive, 2-ethyl-1-hexanol, are reported. During the absorption, the film becomes highly turbulent. Consequently, the heat and mass transfer is significantly enhanced by turbulent mixing. In addition, the instability mechanisms are detailed. In the vicinity of water absorption, surface-tension gradients due to the lower LiBr concentration, the lower additive concentration, and the higher temperature at the interface, can favor instability of the falling film.

Absorption of water vapour into falling films of aqueous lithium bromide

Abstract In this study, experiments have been performed for water vapour absorption into 50 and 60 mass% aqueous lithium bromide solution films flowing down a vertical surface to investigate the effects of liquid diffusivity values, molecular properties of the concentrated solutions and non-absorbable gases. The experimental results for wavy films over a film Reynolds number range of 15–90 indicate larger dimensionless mass transfer rates than for strictly laminar flow when the diffusivity of water in a concentrated lithium bromide solution is less than that in a dilute solution. The complete set of results shows that the physical property data for lithium bromide solutions including the diffusivities measured by Kashiwagi are sufficient to explain mass transfer behavior.

Drag reduction of the highest molecular weight fractions of polyethylene oxide

The analysis of drag reduction produced by high molecular weight fractions of Polyox shows that the slope of the drag reduction curve on a von Karman plot for a narrow fraction is proportional to concentration and molecular weight. Polydisperse polymer solutions have drag reduction curves characteristic of the high molecular weight tail alone. Experimental results are presented on the shape of the distribution and the drag reduction of cumulative fractions containing the highest molecular weights.

VELOCITY FLUCTUATIONS IN NON-HOMOGENEOUS DRAG REDUCTION

Non-homogeneous drag reduction is obtained by injecting a polymer solution thread into the center of a turbulent pipe flow. Under the proper conditions the magnitude of this non-homogeneous drag reduction is much larger than that for the same polymer molecules uniformly distributed in the flowing solvent. In this work the axial velocities and velocity fluctuations near the wall were examined in such a non-homogeneous drag reduction and also in the flow of a homogeneous (pre-mixed) solution of poly(ethylene oxide). The drag reduction and the Reynolds number were the same for both fluids. Significant differences were found in the velocity profile and in the statistical analysis of the velocity fluctuations. The skewness profile for the non-homogeneous case remained positive to a much greater distance from the wall than the skewness profile for the premix solution. In the injection case the velocity fluctuation spectra had the same sharp peak at 5−10 Hz for y + between 11 and 50. This peak corresponded to th...

Flow time scales and drag reduction

The effects of the flow time scales on the onset and magnitude of drag reduction in turbulent pipe flow were studied using comparatively low molecular weight samples of water soluble polymers in glycerine‐water mixtures and in two different pipe sizes. The results show that onset depends only on the time scale νuτ2 with no Reynolds number dependence. The magnitude of drag reduction after the molecules are extended was found to increase with pipe diameter. A correlation with the lifetime of large eddies or the mean period of turbulence production is suggested.

Effect of roughness on drag reduction for commercially smooth pipes

Les solutions de polymere, reductrices de trainee presentent un maximum de reduction de trainee si on fait des essais sur un domaine de nombre de Reynolds suffisamment grand. On montre que ce maximum correspond a la transition du comportement lisse au comportement rugueux

Solubility of oxygen in aqueous lithium bromide using electrochemical technique

Abstract The solubility of oxygen in aqueous Lithium Bromide for concentrations from 0 to 60 percent by weight was measured using a commercially available electrochemical device. Henrys law constant was also estimated theoretically. When the experimental results were corrected for the activity of oxygen assuming the activity was similar to that for water, the theoretical results agreed with the corrected experimental results.

Large Eddies and Polymer Strings

The Doppler shift of forward scattered light from particles and the fluorescence intensity at 90 degrees from the incident light forming the same probe volume were measured simultaneously to study the interaction of injected polymer strings with the flow. In drag reducing turbulence when clusters of strings are observed, the velocity fluctuations are damped, but isolated strings appear to have no effect on the flow.

A Qualitative Understanding of Drag Reduction by Polymers

The interaction of turbulent flow containing regions of high strain rate and high shear rate with polymer molecules can involve both individual molecules and polymer structures. The results of this interaction lead to suppressions of the small scale motions and to production of some large scale motions that do not contribute to turbulent diffusion. Experimental results are interpreted in terms of the interaction of molecules near the wall and movement of the polymeric large scale structures in the center of pipe flows.

Measurements of Large Disturbances in Laminar Pipe Flow Using a Laser‐Doppler Flowmeter

Large axisymmetric disturbances were generated in a pipe using a sleeve oscillating at the wall. Downstream decay of the fluctuating velocities measured by a laser‐Doppler velocimeter show slower rates of decay than for small disturbances.