[Show abstract][Hide abstract] ABSTRACT: The pulse widths of light from sonoluminescing air bubbles in various solutions were measured by a time-correlated single photon counting (TC/SPC) method to investigate the effect of density on sonoluminescence characteristics. The measured values of the pulse width were about 150˜190 ps. No appreciable difference in the pulse width and the bubble behavior for the sonoluminescing air bubbles in various solutions was found even though they have quite different density values varied from 1000 kg/m3 to 1800 kg/m3.
Full-text · Article · Jan 2010 · Journal of Fluid Science and Technology
[Show abstract][Hide abstract] ABSTRACT: The pulse widths of light from sonoluminescing gas bubbles in various solutions having quite different densities were measured by a time-correlated single-photon counting (TC/SPC) method. The measured values of the pulse width were found to be in the range of 150 ps to several ns. No appreciable difference in the measured pulse width and the bubble behavior for the sonoluminescing air bubbles in various solutions was found. The measured results for the pulse width of sonoluminescence (SL) in various solutions suggest that light is emitted from the core region where the temperature is almost uniform. In addition, the theoretical estimation for the pulse widths with thermal bremsstrahlung as emission mechanism for SL provides reasonable results.
[Show abstract][Hide abstract] ABSTRACT: The pulse widths of sonoluminescing gas bubbles in a sulfuric acid solution were precisely measured by using the time-correlated single-photon counting method, which has not been attempted previously. The pulse widths, which are dependent on the size of the bubble at the collapse point were measured and found to be in the range of 165 ps to several ns. The value of the pulse width calculated by assuming thermal bremsstrahlung as the emission mechanism of the sonoluminescence was found to be larger than the observed value by an order of magnitude.
Full-text · Article · Mar 2008 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: Exergetic and thermoeconomic analysis were performed for a 200-kW phosphoric acid fuel cell plant which offers many advantages for co-generation in the aspect of high electrical efficiency and low emission. This analytical study was based on the data obtained by in-field measurement of PC25C fuel cell plant to find whether this system is viable economically. For 100% load condition, the electrical efficiency obtained, 43.7% turned out to be much better than that for the 1000-kW gas turbine co-generation plant. However, the calculated unit cost of electricity with the initial investment cost per power of fuel cell plant of 3000 $/kW, 0.068 $/kWh turned out to be 125% higher than the cost obtained for the 1000-kW gas turbine co-generation plant. This fuel cell system may be viable economically when the initial investment cost per power is reduced to the level of the gas turbine co-generation plant of 1500 $/kW.
[Show abstract][Hide abstract] ABSTRACT: Possibility of upscaling for single bubble sonoluminescence by reducing the driving frequency was tested experimentally. The maximum bubble radius and the expansion ratio obtained from an air bubble at a driving frequency of 12.926 kHz and driving amplitude of 1.33 atm at a water temperature of 23.5°C are considerably less than the predicted ones by the Rayleigh-Plesset equation so that the upscaling of SL cannot be achieved very much with this method. Observed bubble behavior under ultrasonic field may be explained as ``relaxation motion'' of a gas bubble to the characteristic time of the applied ultrasound.
Full-text · Article · Mar 2003 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: Thermosyphon cooling modules, to cool multichip modules (MCMs), were designed and tested. The cooling module consists of a cold plate with microfinned channels and a plate-type integrated condenser. A separate flow model was employed to predict the mass flux and the pressure drop in the channel of the cold plate. The local and average convective boiling heat transfer coefficients and the corresponding wall superheat were calculated using the Chen's correlation. Experiments were performed to find out how the thermal performance of the cooling module was affected by the condenser size and the amount of charging fluid. Great emphasis was placed on the transient characteristics of the cooling module. For an allowable temperature rise of 58 ° C on the surface of the heater, the cooling module can handle a heat flux of as much as 2.5 W/cm2. No boiling retardation was observed inside the cold plate, which resulted in smooth transition from the transient state to the steady one. It was also found that the appropriate size of the condenser and the adequate amount of charging liquid are crucial factors affecting the performance of a closed two-phase thermosyphon device.
Full-text · Article · Mar 2001 · Heat Transfer Engineering
[Show abstract][Hide abstract] ABSTRACT: Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at
chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving
the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made
by two parallel rectangular plates was carried out in this study for possible application of the direct immersion cooling.
Fluorinert FC-72 as a working fluid was used in this experiment. Asymmetric heated channel of open periphery with gap size
of 1, 2, 4 and 26 mm and uniformly heated vertical tubes with diameter of 9, 15 and 20 mm were boiled at saturated condition.
The boiling curves from tested surfaces exhibited the boiling hysteresis. It was also found that the gap size is not a significant
parameter for the thermosyphonic boiling heat transfer with this Fluorinert. Rather pool boiling characteristics appeared
for larger gap size and tube diameter. The heat transfer coefficients measured were also compared with the calculation results
by Chen’s correlation.
Key WordsBoiling Hysteresis-Immersion Cooling-Thermosyphon Boiling
Full-text · Article · Jan 2001 · Journal of Mechanical Science and Technology
[Show abstract][Hide abstract] ABSTRACT: Accurate measurement of the radius of a sonoluminescing gas bubble by a light scattering method was suggested. This can be achieved because of the remarkable stability of a sonoluminescing gas bubble, which has the same shape variation sequence in every oscillation cycle with only 50 ps jitter in the time between flashes, which enables sequential measurement of the bubble radius by the light scattering method and direct imaging technique for the first time. The measured light scattering data with an appropriate proportionality index value can be well fitted to the direct observation for the bubble radius-time curve. However, the observed value of the proportionality index is different from the one predicted by the Mie scattering theory.
Full-text · Article · Mar 2000 · Japanese Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: A mechanism of light emission from a single bubblesonoluminescence (SBSL) was formulated by assuming that the source forthe light emission is bremsstrahlung in partially ionized gases. Thisemission mechanism turns out to be same as the black body radiationwith finite absorption, which confirms that the principal mechanism ofSBSL is bremsstrahlung with slight black body emission nature. Alsothe spectrum was measured and the observed results were compared withthe calculated ones. Calculated and experimental results yield commonspectral behavior in the visible region: the spectral radiance showspower-law dependence on wavelength with an exponent of -2.5. TheSBSL spectrum which is characterized by the continuous one with nomajor peaks has been confirmed experimentally. The bubble dynamicsmodel proposed also takes account the afterpulse characteristics ofSBSL.
Full-text · Article · Jan 2000 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: Behavior of a gas bubble trapped under ultrasound was studied by the light scattering method. With fixed frequency of the ultrasound, the stability of bubble motion was investigated by increasing the driving sound pressure. It has been found that a selective bifurcation instead of period doubling occurs when the driving pressure is increased and the bubble gains extreme stability after the cascade occurrence of such bifurcation. It has also been found that very higher harmonic components in the Fourier spectrum of the bubble motion appear at the sonoluminescing regime, the absolute stable condition.
Full-text · Article · Apr 1999 · Journal of the Physical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: The shock pulse emanating from a sonoluminescing gas bubble was calculated by using the analytical solutions of the conservation equations for the gas inside the bubble and the Kirkwood-Bethe hypothesis for the outgoing wave. The rise time and the magnitude of the pulse signal are in good agreement with the observed values, which may provide the approximate value of the gas pressure at near the collapse of the sonoluminescing gas bubble.
Full-text · Article · Sep 1997 · Journal of the Physical Society of Japan