Search

The features of nonstationary heat transfer of one layer of balls of the same size were studied in a fixed layer of liquid. The experiments were carried out in a cylindrical thermostat with a diameter of 128.9 mm filled with glass balls of 8.9 and 16.0 mm diam and polyoxymethylene balls of 9.0 mm diam with the highest possible packing density. The ball packing was filled with distilled water to a level of 0.1-0.2 mm higher than the ball diameter. The temperature of the ball packing surface was measured using a NEC 7100 thermal imager with a step change in temperature at the outer boundary of the packing. It is shown that, for a monolayer of balls of the same size in a stationary liquid, the temperature field is symmetrical relative to the packing center and the value of the effective thermal conductivity coefficient is constant over the packing cross section, both during heating and cooling. It has been found that the heat transfer coefficient and the time for establishing thermal equilibrium of a ball packing in a layer of stationary liquid at the same temperature difference depend on the heat flux direction at the packing boundary. The numerical values of the characteristic time of thermal equilibrium establishment in the heating and cooling regimes differ from each other by several times; whereas in the water layer without balls, this difference does not exceed 30%.

The non-isothermal absorption and thermo-capillary convection in lithium bromide solution with a variable absorbent depth is investigated experimentally. The experiments were carried out with an aqueous solution of lithium bromide with an initial mass concentration of salt in the solution 57.8 wt % and with a solution to which the surfactant was added n-octanol concentration 50 ppm. It is shown that during absorption of water vapor by lithium bromide solution without surfactant thermocapillary convection does not develop at any absorbent depth. Adding n-octanol to an aqueous solution of lithium bromide (LiBr) develops thermally concentrated convection on the surface of the solution for a long time, and it is also the cause of the “dry spots” at liquid depth of less than 1.1 mm.

Dynamics of a single vapor cavity, moving under gravity in a vertical tube of a small diameter, has been studied. The experiment was carried out in water and aqueous LiBr solution in a tube with the length of 400 mm and diameter of 16 mm. Experiments have shown that dynamics of the rising vapor cavity after-the-fact boiling-up of aqueous LiBr solution in a vertical tube of a small diameter for some initial conditions differs qualitatively from dynamics of a gas bubble rising in a pool. Dynamics of the vapor cavity in aqueous LiBr solution and in water demonstrates quantitative but not qualitative differences. During bubble rising in a small diameter tube to time dependence for volume and mass of the vapor bubble, the regimes with pulsations were detected.

The flow of rivulets and droplets over the bottom side of inclined hydrophobic surface was studied in this work. Interacting of two nearby draining rivulets is investigated. Distilled water was used as the working liquid. The experiments were carried out on the bottom side of a smooth plate with the width of 440 mm and length of 1400 mm. The angle of plate surface deviation from the vertical was 14°. The switching centre consisted of two nozzles with diameter of 0.8 mm. Tubes placed perpendicularly plate surfaces on distance of 10 mm from each other. The experiments were carried out at the flow rates from 0.1 to 1.0 ml/s, and flow rate supported constant. The flow patterns were recorded video with the speed of 1200 fps. It was shown at a constant liquid flow rate at the nozzle exit the direction of and shape of the rivulet depend on maldistribution of the liquid flow rate along the rivulet. It is shown, that the regime of flow rivulet can be changed by interacting with another rivulet. Change regime of flow of rivulet occurs according to the laws defining character of a current of a liquid in rivulet.

Experimental studies have been carried out to reveal the peculiarities of the influence of the arrangement of the curved ring on the flow regimes of a liquid film along a cylindrical surface. Regimes under which the estimated thickness of the gap between the flowing film and the cylinder may not be sufficient. Recommendations are given to determine the minimum value of the distance between the ring and the surface along which the film flows, so that at any flow of liquid there is no contact between the liquid and the ring.

The experimental research of hydrodynamic stability of a dome-shape film of liquid for the conditions, when it flows around a thin plate has been carried out. Experiments have been executed for a case of Savart "water bell". An axisymmetrical film has been formed by the impact of a liquid jet with the width of 10 mm on a solid disc with the diameter of 14.5 mm. The width of the thin plate, streamlined by a dome-shape water film, was varied from 0.05 to 3.5 mm. The wide side of the plate was located at two angles relative to the direction of the flow velocity vector in a film: along and across, at various distances from the disc. Stability of the "water bell" surface has been considered and general stability criterion showing its sensitivity to the angle of plate orientation has been derived. The critical Weber number, above which the discontinuity of bell surface appears, and threshold value of the Weber number, below which it coalescences, have been defined. It was shown, that the critical and threshold Weber numbers depend on the Reynolds number.

The experimental research of hydrodynamic stability of a dome-shaped film liquid at a flow around a thin plate has been carried out. Experiments were carry out with a film in shape a «water bell». The film was formed by a leak-in jet of water width 10 mm on a hard disk with diameter 14.5 mm. The width of a plate ζ changed from 0.05 to 3.5 mm. The plate placed along or across relative to the vector of velocity of a liquid in a film. Experiments have shown, that stability of a film of liquid at a flow around the plate is defined by velocity of water and a thickness of a film δ in front of the rod. It is shown, that for the appointed value of Reynolds number Re δ probably continuous flow at a flow around the plate, if Weber number We ζ less than threshold value. The criterion of steadiness a film of the «water bell» by a surface destruction at a flow around the rod is determined on the transverse size of the rod relative to the vector of velocity of a liquid.