Measurements of pitch-off diameter of gas bubbles in liquid metal

To determine the separation diameter of bubbles in a liquid metal melt, an original technique based on the conductivity method is proposed. A thin electrode is installed in the center of the outflow channel, and the separation of bubbles is determined by closing and opening the electrical circuit. In this way, the separation frequency of the bubbles and their volume can be determined. Additional studies are carried out on a transparent liquid (water). It is shown that the presence of an electrode has little effect on the process of bubble detachment. The processing data of high-speed video filming and the proposed method in a transparent liquid coincide with high accuracy. Measurements of the frequency of bubble detachment in melts of the Rose and lead alloy are carried out. The results obtained are used to tune two-phase flow models when simulating fast neutron reactors with heavy liquid metal coolants.

Quality estimation of the nozzle spray by measuring the brightness of the reflected light

This paper presents the results of the laboratory and numerical experiments performed to measure the sizes of transparent liquid droplets sprayed in air. The results of the laboratory experiments were mainly obtained using the Glare Point Technique (GPT) which gave information about the droplet size and the brightness of the light reflected by drops. The relationship between the brightness of the light reflected from the surface of droplets and their sizes was analyzed. Theoretically, the brightness of light scattered by a single spherical drop is proportional to the drop surface area and, accordingly, to the square of the drop diameter. It has been observed experimentally and verified numerically that the theoretical dependence obtained is relevant only for the brightest droplets because of nonuniform illumination. The results of the numerical experiments with a random sample of drops indicated the dependence of the total brightness of reflected light on the effective droplet size. It is shown that, for a fixed total volume, the total brightness of light reflected by drops is proportional to the droplet Sauter mean diameter.

A Single-Camera Synthetic Schlieren Method for Measuring Two-Dimensional Liquid Surfaces

A single-camera synthetic Schlieren method is introduced here to measure two-dimensional topography and depth of dynamic free liquid surfaces. The method is simple and easy to implement. Because of light refraction (following Snell’s law), markers on a flat bottom which are seen through the surfaces of a transparent liquid are virtually displaced. This leads to a governing equation that the liquid surface depth (and its topography) is associated with the marker displacement. In the equation, the refractive index of the liquid (e.g. water) can be obtained by a refractometer (or from a technical reference), and the displacements of the markers can be obtained by a cross-correlation method which is usually used in particle image velocimetry. In the equation, the only unknown, the depth of the surface, can be obtained by solving the governing equation with boundary conditions. Unlike free-surface synthetic Schlieren (FS-SS) of Moisy et al. (Exp. Fluids, 1021, 46, 2009), our method does not require a reference depth (which is obtained before or after experiments), so that flows with temporally evolving depth can be measured. Experiments of liquid ripples and dam-break flows were performed to test the method. The results agree well with those obtained with FS-SS and visualization measurements.

Determination of spray droplet size by wavelet analysis of interferometric images

The problem of size droplet determining by the Interferometric Particle Imaging (IPI) in a spray of an optically transparent liquid is considered. The measurements were carried out using the example of a fuel injector flame. A new method for analyzing the IPI image of a droplet using a continuous wavelet transform is proposed. The spatial distribution of wavelet coefficients is used to introduce an integral measure similar to the spectral density of the signal. As a reliable estimate of the droplet size, we considered the results by the Glare Point Technique (GPT), which were applied simultaneously. A comparative analysis of the sizes obtained using GPT and IPI showed that the application of the wavelet transform to IPI images, in comparison with the Fourier method, significantly reduces the frequency of occurrence of a systematic error in determining the size, which is most specific for large droplets. It was found that the false maxima in the Fourier spectrum causing these errors are due to the appearance of distortions at the boundary of the interferometric image of the droplet. The wavelet transform allows one to separate these distortions from the main maximum in the vicinity of the droplet center.