Laminary Flow Research Articles

Heat transfer during natural circulation and laminary flow of liquid through vertical and inclined tubes

We present the results of an investigation of the effect the inclination angle has on heat transfer during natural circulation and a laminar flow of liquid through vertical and inclined heated tubes. It is revealed that the maximum heat transfer is reached at inclination angles (with respect to a vertical line) ranging from 15° to 45°.

Characterization of Fibres and Fibre Collectives with Common Laser Diffractometers

The method described utilises the effect that in many commercially available laser diffractometers a laminary flow of the suspension medium in the measurement cell exists. However, data analysis carried out using commercially available laser diffractometers is normally based upon the assumption that there is a statistical orientation of the particles in the measurement volume. The resulting diffraction patterns are, therefore, assumed to be centrosymmetric and ring-shaped. As a consequence, the detectors commonly used only record parts of the diffraction patterns. Based upon these assumptions, it is accepted that grain size analysis of fibrous particles gives an equivalent diameter between length and diameter. First experiments carried out using a Malvern Mastersizer X showed that fibres align in the flow direction. Analysis of the entire diffraction pattern should, therefore, provide information about the length and diameter of the fibres.

Velocity measurement based on bolus tracking with the aid of three-dimensional reconstruction from digital subtraction angiography.

The problem of blood flow measurement in x-ray angiography using measurements of the leading edge of the contrast bolus as it traverses the vascular bed is considered. A new technique for velocity measurement is presented based upon the ratio of the temporal derivative to the spatial derivative of the contrast bolus in the direction of flow. With the addition of a small correction factor, the value obtained is shown to reflect the transport velocity, or the velocity at which the contrast is transported down the vessel of interest. Most blood flow measurements based on bolus tracking techniques are actually using the contrast transport velocity to represent the blood flow velocity. Because of the streaming that occurs due to laminary flow conditions, the measured transport velocity is found to be somewhere between the average and the peak (central) fluid velocities for measurements taken during the traversal of the bolus leading edge. The spatial and temporal variation of the transport velocity are found to be consistent with the bolus motion expected in the presence of laminar flow. From x-ray images of contrast passage through simple tubes, we find that the derivative method measures the transport velocity during passage of the bolus leading edge. In most cases of laminar blood flow, the leading edge transport velocity can be 20%-40% higher than the average blood velocity.

Sampling and Analytical Methods for the Determination of Trace Metals in Surface Seawater

New recently implemented techniques and sample strategies for the determination of trace metals in seawater are discussed. It is shown that only with the highest precautions to prevent contamination, reliable results can be obtained. These precautions start already with the preparation of the sample bottles and sampling equipment in the laboratory. A rubber boat, Go-Flo samplers and a specially designed teflon-coated winch with Kevlar rope is used to collect the samples. At sea, the prevention of contamination of the samples is the highest priority. This implicates the use of a clean air van or at least a laminary flow bench. Acids have to be subboiling distilled in a quartz still and stored in teflon bottles. Preconcentration of the samples on board or in the home laboratory has to be done in clean rooms. This paper gives an account of current procedures used for sampling and analysing seawater for trace metal determinations.

Photosynthetic membranes. VI. Characterization of ultrafiltration membranes prepared by photografting zeolite-epoxy-diacrylate resin composites onto cellulose

Water permeability measurements were carried out at 20°C through membranes prepared by photochemically grafting an epoxy-diacrylate copolymer or one of its zeolite composites onto cellulose. A correlation between mean pore diameter and water flux per unit applied pressure drop has been established, the latter being in turn related to membrane thickness. In Poiseuille's laminary flow regime, with a normal Kozeny-Carman constant indicating a regular packing of isometrically shaped particles in the microporous medium, surface areas of zeolites 3A, 5A, and 13X could be evaluated as 628, 482, and 403 m 2-g − respectively, while a value of 102 m 2-g −1 resulted for the polymeric membrane. Rejection characteristics for poly(ethylene glycol) (PEG) polymers dissolved in water have been investigated. Linear relationships between water flux per unit applied pressure drop and molecular weight of PEG polymers at constant solute rejection have been obtained, independent of the kind of photosynthetic membrane, whether polymeric zeolite free or composite. Characterization of asymmetric membranes, prepared photochemically, by the methods used, gives consistent results as regards structural parameters and geometric configuration of these membranes.

On the theory of dispersion of a solute during laminar flow in tubes

The problem of the diffusion of a solute during laminar flow through a circular tube is solved. A new method of the approximate solution of the corresponding diffusion equation is used. The analytical solution found is compared to previous ones. It is shown that this solution involves the well-known solutions of Taylor-Aris and Maron. The dispersion of a radioactive solute was found which differs from that known in Maron's model. The solution of the problem is also given for the case of the flow between plane parallel walls. 1. Many papers bave been devoted to the study of diffusion of a solute in laminary flow through a circular tube (for a review see [1]). The solution of this problem may be useful for the study of fluid flow (e.g. of blood flow in arteries), it may be applied to chromatography, fluid filtration through porous media and to other fie]ds. An important characteristic, for practical purposes, is the dispersion of soluble matter. The dispersion makes it possible to determine the mixture domain dimensions and the e-~

Evidence that prednisolone is inhibitory to the cyclooxygenase activity of human rectal mucosa

The effect of prednisolone on prostaglandin (PG) synthesis by rectal biopsies in organ culture was investigated using laminary flow bioassay and radioimmunoassay (RIA) of PGE 2. Prednisolone was consistently found to inhibit basal synthesis in cultures whose duration ranged from 2–40 hours. This appeared to be both time and dose dependent. The ability of biopsies homogenised at the end of culture to transform exogenous arachidonic acid into PGE 2 under defined conditions was also investigated and operationally designated cyclooxygenase activity. Prior treatment with prednisolone resulted in a reduction in cycloxygenase activity. This inhibition occurred with a longer latency and to a lesser extent than inhibition of overall basal synthesis. These results suggest that corticosteroids, in addition to their known (indirect) inhibitory action on phospholipase activity, also affect cyclooxygenase activity. The most likely mechanisms are either a repression of synthesis of fresh cyclooxygenase enzyme or induction of an endogenous inhibitor of cyclooxygenase activity.

Fluorescein angiographic findings in retinal venous thromboses (author's transl)

In addition to documenting pathologic vessel changes fluorescein angiography also makes it possible to show hemodynamic changes in retinal thrombosis. An interruption of laminary flow can be seen in the fluorescein angiogram at arteriovenous intersections. The retinal circulation time can be an aid to prognosis. If the interval does not exceed four seconds the prognosis is generally favorable but when it is considerably longer the prognosis with regard to visual acuity is generally poor and, furthermore, sequelae such as rubeosis iridis and secondary glaucoma must be expected. The therapeutic efficacy of laser coagulation can be judged more accurately by photographic and fluorescein angiographic documentation of the course.

The study of flow by pulsed nuclear magnetic resonance. I. Measurement of flow rates in the presence of a stationary phase using a difference method

An analysis is presented of the effect of plug flow and laminar flow on spin-echo amplitudes in a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence, including the rf field distribution of the transmitter/receiver coil. A difference method is described for the measurement of flow rates of flowing fluid in the presence of stationary fluid. Experiments have been carried out on a capillary system with flowing and stationary water, simulating a plant stem. The results are in agreement with a laminary flow in the capillary and a Gaussian shape of the rf field distribution. A discussion is given of the application of the spin-echo difference method to the determination of flow rates in plant stems.

Theory of Light Scattering by Thin Rodlike Macromolecules in a Liquid Subjected to Shear

The light scattering by thin rodlike particles in a liquid subjected to shear is calculated on the basis of the Rayleigh-Gans treatment. The calculations are made for both unidirectional laminary flow and for flow of periodically alternating direction. The calculation is carried out by two methods: the interference factor P is expressed in terms of a power series of G/D, where G and D are the rate of shear and the rotatory diffusion constant, respectively, of the rod rotating around its minor axis. This treatment is applicable to sufficiently low G/D values. The result for a very wide range of rate of shear is obtained by using the Peterlin distribution function of particle axis. Numerical calculation shows that both results agree in a region of G/D below about two if the axial ratio is large enough. The theoretical results appear to agree with the experimental ones.

Heat transfer in laminary flow between parallel plates

Heat transfer in laminary flow between parallel plates

Heat transfer in laminary flow between parallel plates

The heat transfer in a liquid when it passes in Poiseuille flow from a hot tube into a cold tube of the same diameter is known as Graetz' problem. The analogous problem with plane parallel plates substituted for the cylindrical tube wall is solved here by the introduction of a set of eigenfunctions y n satisfying the Sturm-Liouville equation y″+E(1−x 2)y=0. This solution is compared with the solution of Graetz' problem.