A. Iwamoto

H. Nakai

M. Murakami

N. Kimura

R. Maekawa

T. Haruyama

T. Mito

National Institute for Fusion Science (NIFS-Repository)

LightSourcePressur Sensor .....- ......H1CH2 '----t-.....,DigitalOscilloscope101.10 2.10'iii \Q. 101.05 2.05C -l0 CD(b) +l 3'C'0 CDen 101.00 2.000e CD::Jenen 100.95 .. 1.95 ........va:(a)Fig. 1 Block diagram ofthe experimental set-up.100.90 [ 1.900.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35Time(sec)Fig. 2 Experimental results obtained from a test section atP= 101 kPa, T=1.9K, q=10 W/cm2 and a heating time of0.2s. (a) Left: a boiling fIlm formed on the surface of thetransparent heater, Right; a schematic illustlation of thefIlm.(b) Pressure and temperature waves at the boiling.of the pressure and temperature was reciprocal to thepressure. Thus, we consider that the reason why theoscillations of the pressure and temperature were notdetected at atmospheric pressure is that the SIN ratio of theoutput signal of the sensor was lower than that at thepressure ofthe saturated region.4. SummaryThe study of the heat transfer in He IIp was carried outusing a visualization method and a pressurized superfluidhelium cryostat with an optical window. Using thisexperimental apparatus, we found that the measurements forthe action of the boiling film formed on the transparentheater and for their pressure and temperature are possible. Inthe next few years, we plan to improve the SIN ratio of thesensor signal and to obtain experimental data on the heattransfer of the heater surface in more detail. We expect thatwe can get a new insight on the effect of the flow behavior inthe He IIp cooling channels to the heat transfer.1. IntroductionIn the second phase of LHD project, the cooling ofpressurized superfluid helium (He IIp) in a helical coil hasbeen planned. For such a purpose, study of the heat transferof pressurized helium in cooling flow channels has beenrequired to examine the stability of the helical coil. Thepresent work is aimed at understanding the heat transfer andboiling phenomena of He IIp in cooling flow channelsqualitatively by direct observation using a visualizationmethod and quantitatively by measurement using ahighly-sensitive high-resolution sensor. In the fIrst year ofthe project, a test section, the combination of a transparentheater, temperature and pressure sensor was devised andexperiments using it were carried out.2. Experimental set-upIn Fig. 1, a block diagram of the experimental set-up usedin this work is shown. In the experiment, a transparent heater(25 mm x 25 mm) was heated by amplifying rectangularvoltage waves with a high-speed power amplifIer. Also, tomake the measurements synchronized with the start time ofheating, a trigger signal from a wave generator was used asthe measuring start signal for a high-speed video camera anddigital oscilloscope. The action of a boiling fIlm formed onthe heater surface was observed by a high-speed videocamera, and the data measured by the superconductivitytemperature sensor and pressure sensor set over the heaterwere shown by a digital oscilloscope. The experiment wasmade at several pressures from the subcool region of 101kPa to the saturated region of 5.04 kPa. The experimenttemperature was 1.9 K.3. Experimental resultsFig. 2 shows the experimental results for He II atatmospheric pressure (P = 101 kPa). Fig. 2(a) shows anoverview of the boiling fIlm formed on the surface of thetransparent heater, which took a quadrangular pyramidalstructure. Also, it was found that the top of the structurefluctuated. Fig. 2(b) shows the pressure and temperaturewaves at the boiling state. For He IIp at the atmosphericpressure, the oscillation of the temperature and pressure werenot detected at a significant level. Also, during heating, itwas found that a stable temperature region was formed onthe heater surface. On the other hand, in an experiment withHe IIp at a pressure of 5.04 kPa, oscillation of the pressureand temperature was detected, and the temperature of theheater surface was lower than that for the experiment atatmospheric pressure. The fact shows that the heat transfer inthe saturated region is raised compared with that atatmospheric pressure. Also, the amplitude of the oscillationKimura, N., Nakai, H., Haruyama, T. (High EnergyAce. Research Orga.)Murakami, M. (Univ. Tsukuba)Mito, T., Iwamoto, A., Maekawa, R.§ 29. Study on Heat Transfer of PressurizedSuperfluid Helium in a Flow ChannelUsing a Visualization Method121

Study on Heat Transfer of Pressurized Superfluid Helium in a Flow Channel Using a Visualization Method

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