[en] Heat transport characteristics in a pressurized He II channel have been studied, using two-dimensional numerical code that is based on the two fluid model. In general, He II heat transport performance gets worse in a either long or narrow channel. If a porous medium is used as a part of the channel to transfer heat to a next channel, it will be expected to improve the heat transport in the channel. In this study, numerical model was based on the channel formed by two FRP plates in parallel and a spacer was inserted in the middle of the channel to divide into two regions. A heater was placed in one of FRP plate to input heat to the channel. Two kinds of spacers were used in the analysis to compare heat transport characteristics; (1) porous spacer, (2) FRP spacer. The temperature distribution and flow velocity vectors of He II in the channel were calculated with a steady state heat input. According to the calculated results, the temperature increase of He II in the heated channel was suppressed in the case of a porous spacer. In addition, the mass flow induced by the thermo-mechanical effect of He II enhanced heat transport capability. The paper also discusses the He II flows within the channel. (author)

[en] Nanofluid is the liquid with dilute dispersion of nano-meter sized solid particles. It is know that the critical heat flux in pool boiling is usually enhanced and the heat transfer coefficient changes rather complicatedly in the nanofluid comparing with the pure liquid. At present, it is believed that the CHF enhancement can mainly be attributed to the nano-particle layer formed on the heated surface during nucleate boiling. Since nano-particles are often agglomerated in the base liquid, it is expected that the dispersion condition of nano-particles in the base liquid has some impact on the formation process of the nano-particle layer and consequently the value of CHF. In this experimental work, systematic investigation was carried out for the effect of the particle dispersion condition in the base liquid on the CHF and the heat transfer coefficient in nucleate pool boiling of water-based nanofluids. In the present experiments using TiO_2 nanofluids as the test fluid, the CHF was not influenced significantly by the particle dispersion condition whilst noticeable deterioration of the boiling heat transfer took place only in the case of fine particle dispersion. (author)

[en] In High Temperature Engineering Test Reactor (HTTR) of 30 MW, the generated heat at reactor core is finally dissipated at the air-cooler by way of the heat exchangers of the primary pressurized water cooler and the intermediate heat exchanger (IHX). The heat exchangers in the main cooling system of HTTR must satisfy two conditions, that is, achievement of reactor coolant outlet temperature 850degC/950degC and removal of reactor generated heat 30 MW. Therefore, the heat exchanges have to have the same performance as these in the design. In this report, heat exchange performance of the IHX in the main cooling system was evaluated with the rise-to-power-up test and the in-service operation data. Moreover, the validity of the IHX thermal-hydraulic design method was confirmed by comparison of evaluated data with designed value. (author)

[en] A physical model with consideration of the radiative heat transfer was proposed to evaluate analytically the heat transfer and the steam temperature in the dispersed flow regime during reflood in LOCA. This model was used to predict Semiscale Mod-1 Test S-03-8 and FLECHT-SET Test 3105B instead of a purely empirical correlation which was included in the current reflood code. Comparison of the prediction by the model with those experimental data indicated that the model presented a good agreement with turnaround time, maximum temperature and steam temperature of the data. Comparison between the predictions by the model and the current code indicated that the model presented the approximately similar prediction and specially at a higher elevation of a core rod presented a better prediction of turnaround time and maximum temperature, and that the model can be applied to a reflood analysis instead of the empirical correlation. But detailed studies on physical models for the inverted annular flow regime and the quenching are indispensable to obtain a better prediction all over the core area. (author)

[en] In an actual boiling channel, the circumferential heat flux may not be constant. Then the investigation results obtained under uniform heat flux condition may not be used in these systems. Of course, so many investigations with non-uniform heat flux conditions have been done, so far. But, owing to the difference of the main target, to adapt those results to the small conventional boiler condition should pay attention. In the case of the small conventional boiler, the systems are operating under low pressure and low mass-flux condition with large diameter tubes, and the influence of the non-uniformly heating may appear strongly. In this investigation, the CHF experiment under non-uniform heat flux condition was investigated under downward flow condition. CHF value obtained in this investigation decreased than that of the uniformly heating condition. Moreover, the CHF characteristic was quite a difference compared with the similar investigation of upward flow condition. (author)

[en] Surface measurements of sensible heat flux (H) over rice paddies were made for several days using a Larger Aperture Scintillometer (LAS) operating in the near-infrared. At such wavelengths temperature (T) normally dominates refractive fluctuations and humidity (Q) fluctuations are considered insignificant. However, under conditions of low Bowen ratio β, as encountered over rice paddies the combined effects of temperature and humidity fluctuations are theoretically shown to contribute to the refractions and may be a consideration when calculating H from scintillation data. Bacause of low β and overcast skies daytime fluctuations in the refractive index structure parameter (10^-16 m^-2/3 < C_n² < l0^-14m^-2/3) were smaller on average than nocturnal values but greater than the LAS signal-to-noise figure (10^-17 m^-2/3 rms). Corrected half hourly scintillometer data for enhanced Q fluctuations did not improve the H_sc comparison to the eddy correlation H_ec which tended to underestimate for unstable but overestimate for stable conditions over a small dynamic range of data (-100< H< 100 Wm^-2 ). (author)

[en] Recent advances in the field of boiling heat transfer under natural convection (pool boiling and boiling in confined channels) for helium-I are reviewed. The published experimental data are compared with some of the proposed correlations. It would appear that the data of nucleate boiling are widely scattered, whereas the film boiling regime can be predicted successfully. The works on channel boiling mostly deal with critical heat flux to establish its empirical correlation. (auth.)

No abstract available

No abstract available

[en] We investigated surface wettability and Leidenfrost condition using oxide metals irradiated by γ-rays. The result showed that the wet length and the duration of contacting increased, and the contact angle decreased, after the irradiation. The liquid-solid direct contact after the irradiation producted vigorous heating transfer between the droplet and heating surface. (author)