We observe sounds associated with continuous bubbling in fluid in daily lives. We call them ‘Buku-buku’ sounds. Because similar processes occur at active volcanoes, ‘Buku-buku’ phenomena provide good Kitchen Earth Science subjects. This study investigated bubble sounds using hair-gel solutions with two viscosities. Various waveforms were observed in the air and in the liquid. We focused on two types of airwaves. The one was observed with the relatively low-viscosity fluid and generated by bubble oscillation on the surface. The other was observed with the higher viscosity and generated by bubble opening at the surface. Both types of waves showed frequency gliding from low to high, for which we proposed models. Scaling issues and implications for volcano acoustics are discussed.

The Earth's mantle is chemically heterogeneous and includes primordial material inherited from early planetary processes, which probably led to an initial depth-dependent composition of radioactive elements. One consequence is that its internal heat sources are not distributed homogeneously. Mantle convection induces mixing, such that the flow pattern, the distribution of heterogeneities and the thermal structure are continuously evolving. We studied these phenomena in the laboratory using a unique microwave-based experimental set-up for convection in internally-heated systems. We characterize the development of convection and the progression of mixing in an initially stratified fluid made of two layers with different physical properties and heat production rates. In analogy to the Earth's mantle, the upper layer is thicker and depleted in heat sources compared to the lower one. Two different convection regimes are identified, a dome regime and a stratified regime. In the dome regime, large domes of lower fluid protrude into the upper layer and remain stable for long time-intervals due to their enhanced heat production. In the stratified regime, cusp-like upwellings develop in association with deformation of the interface separating the two fluids. Upwellings are similar in size and morphology to those that would be generated by heating through the tank base, implying that mantle plumes are not necessarily due to heating by the Earth's core. These plumes are made of heated upper layer fluid and enriched lower fluid in variable proportions giving rise to a range of plume compositions. Mixing proceeds by two mechanisms: shearing of thin slivers by viscous coupling at the interface between the two fluids, and trapping of upper fluid within the lower fluid through folding. Empirical scaling law for the mixing rate allows extrapolation to planetary mantles.

Many spacecraft in various countries have succeeded in exploring planets, satellites, and small bodies so far, and the time has come when a large amount of data can be viewed easily by friendly tools. An approach that simulates the morphologies on other celestial bodies by accessible kitchen experiments may facilitate the understanding of them by the public as well as by experts. In this article, we will introduce the fluidized ejecta craters on Mars and the kitchen experiment on the interaction between a vortex ring and a particle layer.

In our previous study, we measured the radial and axial temperature distributions of steam-air mixture in a vertical circular pipe (diameter, 49.5 mm; cooling height, 610 mm) and the cooling water in the annulus gap (8.5 mm) outside the pipe, and the temperature gradients in the pipe wall (thickness, 5.5 mm) between the steam-air mixture and cooling water. From the temperatures, we evaluated condensation heat fluxes q_c, and derived an empirical correlation. In this study, we have calculated the heat transfer coefficient of the condensate film h_f with the Nusselt equation and evaluated the condensation heat transfer coefficient h_c from q_c and the measured temperature distributions. We also compared h_c with h_c correlations based on the heat and mass transfer analogy and the diffusion layer model. Results from both correlations agreed relatively well with the h_c data, but the correlations underestimated h_c for high h_c near the inlet with a thin thermal boundary layer and overestimated h_c for low h_c.

We have been developing the ultrasonic liquid film sensor to measure the liquid film thickness under high-temperature and high-pressure conditions of Boiling Water Reactors (BWRs), focusing on thin film thickness in pre-/post-dryout. The liquid film sensor utilizes Time-of-Flight (ToF) detection based on the ultrasonic pulse-echo method. To detect the ToF from output ultrasonic signal of the liquid film sensor, the waveform subtraction in the time domain has been used as conventional method. However, subtracting signals in the time domain has some concerns for the ToF detection under actual steam-water conditions; e.g. a calibration test is forced to be carefully conducted in the single-phase flow. In the present study, we improved signal-processing performance for the liquid film measurement using cepstral subtraction method. In this method, the ToF was directly detected from convoluted waveforms by calculating cepstrum from Fourier transform and logarithm spectrum. Moreover, avoiding noise effect on the cepstrum was achieved by subtracting mean cepstrum in the qufrency domain; because multiple waveforms were acquired from repetition pulsing of ultrasonic signals at the same experiment, the noise effect could be removed due to unsteady characteristics of liquid film flow. In this study, the basic principle of the cepstral subtraction method was confirmed by a calculation test using simulated ultrasonic signals. Assuming the additive white Gaussian noise with average noise power of -90dB, the maximum error between input thickness and output thickness was 21% in the range of liquid film thickness of 0.008-0.300mm. Furthermore, the time-series liquid-film thickness was measured from actual signals acquired under BWRs’ operating conditions at temperature of 286℃ and pressure of 7MPa. Comparing to the thickness processed from the conventional time-domain subtraction method, the processed results of cepstral subtraction method showed good agreement. Consequently, we confirmed appropriateness of the cepstral subtraction method for the liquid film sensor under high-temperature and high-pressure conditions.

Ultrafine bubbles (UFBs), which are smaller bubbles than 1 μm in diameter, have some unique properties and are being applied in various fields. It is necessary to develop the UFB generation methods more suitable for various applications and industries. The optimal equipment design and operating conditions should be clarified to obtain the required UFB number concentration. In this study, we developed a novel UFB generation method that repeats pressurization and depressurization operations in shaking container, utilizing the pressure dependence on gas solubility in water. Mean bubble size of the generated UFBs was around 90 nm and was constant regardless of operating conditions. UFB number concentration increased as the number of repetitions of the compression and decompression shaking operation increased. The generated UFBs were confirmed to be stable in water for a month. It was presumed in this study that the promotion of bubble nucleation and suppression of bubble growth caused with rapid solubility change due to the pressurization / depressurization with shaking operation produced more UFBs in water.