Tokuro Mizushina

Turbulence structure in stably stratified open-channel flow

The effects of stable stratification on turbulence structure have been experimentally investigated in stratified open-channel flow and a theoretical spectral-equation model has been applied to the stably stratified flow. The measurements were made in the outer layer of open-channel flow with strongly stable density gradient, where the wall effect was small. Velocity and temperature fluctuations were simultaneously measured by a laser-Doppler velocimeter and a cold-film probe. Measurements include turbulent intensities, correlation coefficients of turbulent fluxes and coherence–phase relationships. These turbulent quantities were correlated with the local gradient Richardson number and compared with the values calculated using a spectral-equation model and with other laboratory measurements. In stable conditions, turbulent motions approach wavelike motions, and negative heat and momentum transfer against the mean temperature and velocity gradient occurs in strongly stable stratification.

EDDY DIFFUSIVITY NEAR THE FREE SURFACE OF OPEN CHANNEL FLOW

Abstract Eddy diffusivity near the free surface was determined by heat-transfer experiments ( Pr ≈ 3) in broad open channel flow with high heat flux at the surface. It decreases to zero in proportion to Y s . A new model is developed, assuming that the damping of turbulence near the surface can be represented by that of the surface wave motion with a wave length equal to the integral scale of turbulence. It represents the experimental result well throughout the cross section. Its limiting relation close to the free surface is well confirmed by gas absorption data of rivers, open channels and liquid films.

Reduction of eddy diffusion for momentum and heat in viscoelastic fluid flow in a circular tube

The velocity profile, longitudinal turbulent intensity profile, and bursting period in drag reducing pipe flow were measured using a laser Doppler technique. The temperature distribution and heat transfer coefficient were measured with thermocouples in the same system. The results of the decrease in eddy diffusivities of momentum and heat near the wall, the gross flow measurements, and the velocity distribution were shown to be in a good agreement with the predictions of the eddy diffusivity model for viscoelastic fluids previously proposed. A simple method based on the eddy diffusivity model to calculate the rate of heat transfer in the fully developed pipe flow of viscoelastic fluids is proposed, and is ascertained to be effective by the previous experiments.

An experimental study of vertical turbulent jet with negative buoyancy

A jet discharged upward into an ambient of higher temperature than that of the jet fluid was investigated experimentally.The width of the upflow spread linearly to the distance from the nozzle exit, whereas the width of the whole jet was almost constant. The height of top of jet varied in proportion to the square root of the discharge Froude number.The time-averaged velocities and temperatures as well as the intensities of their fluctuations at the jet axis were well correlated with the same scaling law as that used for the buoyant jet. The radial distributions showed no similarity profiles for the timeaveraged velocities and temperatures, and the intensities of their fluctuations.ZusammenfassungEin Freistrahl, der in eine Umgebung mit höherer Temperatur als die der Strahlflüssigkeit ausströmt, wurde experimentell untersucht. Die Breite der Aufwärtsströmung nahm linear mit der Entfernung der Düse zu, während die Breite des ganzen Strahls nahezu konstant war. Die maximale Eindringhöhe des Strahls war proportional zur Quadratwurzel der Abström-Froude-Zahl. Sowohl die mittleren Geschwindigkeiten und Temperaturen als auch die Intensitäten der Schwankungsgeschwindigkeiten und-temperaturen in der Achse wurden mit dem ähnlichkeitsgesetz gut korreliert, das auf den Auftriebsstrahl angewandt wurde. Die radialen Verteilungen zeigten keine ähnlichkeitsprofile für die mittleren Geschwindigkeiten und Temperaturen sowie für die Intensitäten der Schwankungsgeschwindigkeiten und -temperaturen.

Turbulent heat and mass transfer between wall and fluid streams of large Prandtl and Schmidt numbers

Abstract The expression for eddy diffusivity in a previous analysis was revised. By using the revised expression, good agreement was obtained between the predicted and experimental results for mass transfer at Schmidt numbers between 800 and 15,000. Both the predicted and experimental results showed that the Sherwood number varies with 1 3 power of the Schmidt number and about 0·9 power of the Reynolds number at Sc = 800−15,000 and Re = 3000−80,000.

Turbulence structure in unstably‐stratified open‐channel flow

The buoyancy effects on the turbulence structure in unstably‐stratified shear flow generated by cooling the top of the layer in an open channel were investigated. Measurements were made of the characteristics of the turbulent fluctuations; turbulence intensities, correlation coefficients, joint probability density functions, and coherence‐phase relationships. The results show that the buoyancy‐driven motions cause substantial changes in the turbulence structure. Of the buoyancy‐driven motions, the intermittent downward motion contributes mainly to the turbulent transport of heat in the vertical direction. A parameter which characterizes the stability dependence of the turbulence structure is the local gradient Richardson number Ri, and the turbulence quantities are well correlated with Ri. A theoretical spectral equation model is applied to the stratified flow and well compared with the experimental results.

Application of laser Doppler velocimetry to turbulence measurement in non-isothermal flow

In order to apply laser Doppler velocimetry to turbulence measurement in non-isothermal flows, an experimental method is proposed for estimating and correcting the effect of interaction of the laser beams with turbulent temperature fluctuations along the beam paths. This is applied to turbulence measurement in fully developed stratified flow in an open channel and the effect of the interaction on the turbulence power spectra and turbulence intensities in the longitudinal and the vertical directions is discussed.

Effect of radial electric field on heat and momentum transfers in dielectric organic liquid for laminar flow through concentric annuli

Abstract Experiments were conducted to investigate changes in convective heat transfer in flows of dielectric organic liquids in annuli between copper tube and concentric wires. Also investigated was longitudinal pressure drop in the flow which could be induced by applying electric fields of direct current between the wall of the tube and the central wire electrode. In the laminar range of Reynolds number, heat transfer rates at the outer wall increased in the thermally well-developed region, and the thermal development was advanced. On the other hand, pressure drops were also increased in liquids of small Prandtl number. In the transitional and turbulent range, however, neither changes of heat nor momentum transfer were noticeable. To express these results in the low Reynolds number range a semi-empirical formulation in non-dimensional terms was derived from the similarity principle.

TETRAFLUOROETHYLENE COATINGS ON CONDENSER TUBES

heat-transfer coefficient of condensing vapour [kcalim*hdegC]; EDWARDS and Doolittle [I], Le Fevre and Rose [?.I, and Butcher and Honour [3] have discussed the promotion of combined conductance of tube wall and resin coating [kcal!m2 hdegC] ; dropwise condensation of steam with tetrafluoroethylene coatings. Their data shows that the overall heat-transfer heat-transfer rate [kcal/m* h] ; coefficient for dropwise condensation is increased from 16

Momentum and heat transfers from fully developed turbulent flow in an eccentric annulus to inner and outer tube walls

An analysis and measurement were made of momentum and heat transfers from fully developed turbulent flow in an eccentric annulus to inner and outer tube walls. The eddy diffusivities of momentum and heat obtained in the turbulent flow in a circular tube were applied to the annular flow in the analysis. The result indicates that the calculated friction factor and average Nusselt numbers on the inner and outer tube walls are in fairly good agreement with the measurements.ZusammenfassungEs wurden Messungen und eine Analyse über den Impuls- und Wärmetransport von einer vollentwickelten turbulenten Strömung in einem exzentrischen Ringspalt an die innere und äußere Rohrwand durchgeführt. Die turbulenten Austauschgrößen von Impuls und Wärme, wie sie für die Strömung in einem Zylinder bekannt sind, wurden in der Analyse auf die Ringströmung angewandt. Die Ergebnisse zeigen, daß die berechneten Werte von Reibungsfaktor und mittlerer Nusselt-Zahl auf der inneren und äußeren Wand des Ringspalts in ausreichend guter Übereinstimmung mit den Messungen sind.