Masahide Murakami

Correlation to predict heat transfer characteristics of a closed-end oscillating heat pipe at normal operating condition

This paper describes the effect of dimensionless parameters on the characteristics of heat transfer in a closed-end oscillating heat pipe (CEOHP). The parameters studied in this paper are; (i) Bond numbers, (ii) Froude numbers, (iii) Weber numbers, (iv) Prandtl numbers and (v) Kutateladze numbers. Experiments were conducted to find out their effects on the heat transfer rates of copper CEOHPs with inner diameters of 0.66, 1.06 and 2.03 mm. The lengths of the evaporator, adiabatic and condenser sections were equal and changed to 15, 10 and 5 cm. The total lengths of the CEOHPs were 15, 10 and 5 m. R123, ethanol and water were used as the working fluids with a filling ratio of 50%. The evaporator was heated by hot water, while the condenser section was cooled by a solution of water and ethylene glycol with a 1:1 mixing ratio by volume. The angle of the CEOHPs used in the experiments was set at 0° (horizontal mode) with a controlled vapor temperature of 50 °C. When the system reached the steady state, the temperature and the flow rate of the cooling substance was recorded in order to calculate the heat transfer rate of the CEOHP. It was found from the experiment that when R123 was used, the inner diameter affected the heat flux. The results of the experiment showed that when the inner diameter was larger, so was the heat flux. The result for ethanol showed the opposite; when the inner diameter increased, the heat flux decreased. Because of insufficient data obtain from using water as working fluid, the heat flux could not be reliably measured. The evaporator section lengths also affected the heat flux. The evaporator length of 15 cm gave the lowest value of heat flux. When the number of turns decreased, the heat flux increased and when n is equal to 14, heat flux is still increasing with an decrease in n. The results of the experiment also showed that the correlation equation could be used to predict the heat flux and that the operation map could predict the operational range and the inner diameter.

Flight Performance of the AKARI Cryogenic System

We describe the flight performance of the cryogenic system of the infrared astronomical satellite AKARI, which was successfully launched on 2006 February 21 (UT). AKARI carries a 68.5 cm telescope together with two focal plane instruments, Infrared Cameras (IRC) and Far Infrared Surveyor (FIS), all of which are cooled down to cryogenic temperature to achieve superior sensitivity. The AKARI cryogenic system is a unique hybrid system, which consists of cryogen (liquid helium) and mechanical coolers (2-stage Stirling coolers). With the help of the mechanical coolers, 179 L (26.0 kg) of super-fluid liquid helium can keep the instruments cryogenically cooled for more than 500 days. The on-orbit performance of the AKARI cryogenics is consistent with the design and pre-flight test, and the boil-off gas flow rate is as small as 0.32 mg/s. We observed the increase of the major axis of the AKARI orbit, which can be explained by the thrust due to thermal pressure of vented helium gas.

Aerodynamic force data for a V-style ski jumping flight

To determine the flight of a ski jumper it is essential to know what aerodynamic forces are acting on the ski jumper. However, few data on this are available, especially for a V-style ski jumping flight. We have measured the aerodynamic forces during the free flight phase for a V-style, as well as a parallel-style, ski jump by employing a full-size model in a wind tunnel. The aerodynamic force data, (drag, lift and pitching moment) were obtained to create an aerodynamic database. These forces are given in polynomial form as functions of the angle of attack, the body-ski (forward leaning) angle and the ski-opening (V-style) angle. Using the polynomial form database is a convenient way of obtaining the aerodynamic forces. Moreover, the wind tunnel was equipped with a ground effect plate to measure the aerodynamic forces during the landing phase. It was found that the difference between the lift with and without the ground effect plate increases with the ski-opening angle. The longitudinal stability in the pitching motion of a body-ski combination is also discussed on the basis of the pitching moment data. This indicates that a stable pitching oscillation of the body-ski combination may arise around an equilibrium point in the angle of attack, the trim angle of attack, during flight.

Soft x-ray spectrometer (SXS): The high-resolution cryogenic spectrometer onboard ASTRO-H

We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.

Optimal flight technique for V-style ski jumping

This paper describes the results of a numerical study to determine the optimal flight technique for V-style ski jumping. We attempt to answer the question of how a jumper should fly in order to increase their flight distance in a V-style posture. The index of performance in this optimization study is the horizontal flight distance, which is mathematically equivalent to the total flight distance, and the control parameters are the ski-operning angle and the angle of forward lean that the jumper employs (the body-ski angle). The flight trajectory is simulated on the basis of an aerodynamic database constructed from wind tunnel test data. It is found that the ski-opening angle should be increased in the first half of the flight, and then maintained at a constant value during the rest of the jump. Optimal control of the ski-opening angle when there is either a headwind or tailwind is also discussed. It is found that the jumper needs to control the skiopening angle over a wider range in the case of a headwind than in the case of a tailwind. The jumpers skill in controlling the ski-opening angle is very important for increasing the flight distance, especially in the case of a tailwind.

Flow visualization study of thermal counterflow jet in He II

Abstract A method of flow visualization in superfluid helium has been developed by the use of solid H 2 D 2 particles and hollow glass spheres as neutrally buoyant tracers to follow the normal component flow. It is applied to the study of a thermal counterflow jet based on pattern recognition of jet profiles and on measurement of mean normal velocity. Traceability of both kinds of tracers is satisfactory up to a few cm s −1 . The evolution of jet pattern is found to vary widely depending on the Reynolds number, quite similar to usual viscous fluid jets, ranging from laminar to fully turbulent ones. The large-scale vortical motion and the entrainment of the surrounding He II into jet are clearly seen in fully developed turbulent-like jets. The calculation of the total momentum flux from the normal fluid velocity profiles seems to indicate that the zero-relative-velocity situation between the normal and super components is reached in jets as suggested in previous experiments.

Application of laser holography interferometer to heat transport phenomena near the critical point of nitrogen

A laser holography interferometer is applied to investigate heat transport phenomena near the critical point of nitrogen. The very high thermal compressibility and small thermal diffusion near the critical point of fluids affect thermal energy propagation, lead to the formation of weak acoustic waves as carriers of thermal energy. This heat transfer phenomenon is called the piston effect. The piston effect in supercritical nitrogen is investigated using a laser holography interferometer. Natural convection due to gravity interferes with the piston effect under terrestrial conditions. Therefore, we attempt to suppress the generation of natural convection by creating stable density stratification in the cell. The experiment consisted of two different procedures. In the first, heat was added from the bottom of the experimental cell, while in the second, heat is added from the top of the cell. From the two results, we successfully extracted the heat transfer phenomenon, the piston effect, which is considered to be the fourth mechanism of heat transfer.

Comparison of cavitation flows in He I and He II

Abstract This paper describes some of the results of an experimental study on the cavitation phenomena in He II and He I by the visualization and the measurements of the pressure and the temperature. The cavitation flow is generated in liquid helium driven by a bellows pump in the downstream region of the throat in a Venturi channel with a rectangular cross section. It is found that there are some definite differences in the appearance of cavitation between He I and He II flows, and that the λ-phase transition from He I to He II is sometimes induced because of the temperature drop in cavitating He I flow. In addition, the expression for the relation between the amount of the temperature drop induced by cavitation and the void fraction was described, which was found to be qualitatively in good agreement with the experimental result.

Visualization study of film boiling onset and transition to noisy film boiling in He II

The transient boiling phenomena occurring on a planar heater in He II are visually studied to investigate the onset condition and the bifurcation criterion. The whole flow field is visualized with the aid of Schlieren and shadowgraph optics. After step-wise heating, local boiling sites appear and develop, eventually covering the heater surface, followed by the onset of film boiling. The state may further proceed to noisy boiling if the hydrostatic pressure is sufficiently large. A distinctive feature between the noisy and silent boiling states is visually confirmed in the present experiment. The onset time of film boiling as a function of heat flux is obtained via a transparent heater. It is found that there is some distinction between cases with large and small q values in the functional relationship for the onset time on q, presumably originating from different states of the precursor nucleate boiling before film boiling.

An experimental study of heat transfer characteristics of a two-phase nitrogen thermosyphon over a large dynamic range operation

Heat transport characteristics of a cryogenic two-phase nitrogen thermosyphon have been experimentally investigated in this study. The thermal resistance and the maximum heat transfer rate were mainly investigated over a wide dynamic range from near the triple point to the critical point. The experimental data suggests that the nominal thermal resistance does not have pressure dependence in the high pressure and high temperature region. The present experimental result is well explained by the theoretical prediction. From the experimental result of the operating limit of the thermosyphon, it is found that the maximum heat transfer rate is governed by the interaction between the vapor flow and the returning liquid film flow along the wall in the evaporator section, even near the critical point.