Akira Kurosawa

Critical heat flux of forced convection boiling in an oscillating acceleration field — I. General trends

Abstract The influence of periodically varying acceleration on critical heat flux (CHF) of Freon-113 flowing upward in a uniformly heated vertical annular channel has been studied experimentally. The freon loop was oscillated vertically to determine the ratio of CHF in the oscillating acceleration field to the corresponding stationary value. The amplitude of inlet flow oscillation induced by variation of acceleration, which causes early CHF, is proportional to the acceleration amplitude. The dependence of inlet flow rate on the oscillating acceleration decreases with increasing inlet subcooling, and no oscillation of inlet flow is observed in the case of negative exit quality (subcooled boiling). Nevertheless the degradation of CHF is more remarkable in the low quality region. This result suggests the necessity to introduce an other mechanism of early CHF than flow oscillation.

Critical heat flux of forced convection boiling in an oscillating acceleration field—II. Contribution of flow oscillation

Abstract Critical heat flux (CHF) with forced convection generally decreases under an oscillating acceleration condition. Contribution of flow oscillation on the decrease in CHF was investigated experimentally and theoretically. The experiments were performed with a Freon-113 boiling loop. The results showed that, in the high exit quality region deteriotation of CHF could almost wholly be attributed to the variation of inlet flow rate induced by motion. The amplitude of flow oscillation for a given acceleration variation could be predicted from a transfer function derived with linearization technique. Prediction of the transient CHF on the basis of “local-conditions hypothesis” gave conservative values.

Critical heat flux of forced convection boiling in an oscillating acceleration field — III. Reduction mechanism of CHF in subcooled flow boiling

To investigate the effect of variation in acceleration on the critical heat flux (CHF) in subcooled flow boiling, a photographic study was made. The test section was an internally heated vertical annulus with a glass shroud, in which Freon-113 flowed upwardly. The observation was made at a pressure of 3 bar, a mass flux of 920 kg/m2s, an inlet subcooling 45 K and a slightly lower heat flux level than steady CHF. The vertical acceleration was oscillated with amplitude of 0.3ge and a period of 6 s. At low apparent gravitational acceleration, bubbles generated on the heated surface moved longer along the surface without detachment and coalesced with other bubbles to form large vapor slugs. This causes early CHF, the mechanism of which is dry-out of the liquid film existing between the heated surface and vapor slugs.

THERMO-HYDRAULIC MODEL TEST OF THE FIRST NUCLEAR SHIP REACTOR IN JAPAN

Abstract A series of thermo-hydraulic model tests were carried out to confirm that the first nuclear ship reactor in Japan was properly designed. The major test models were a half-size core structural model, a full-size fuel assembly model and a half-size steam generator plenum model. The measured results were compared with the design calculation of the reactor. Most of the calculated results were found to be in good agreement with experiment. However, the pressure drop in the reactor vessel was found to be overestimated, and a necessary correction was made on the system design. Also flow velocity distribution was found to be much more distorted than expected in the fuel assembly, and an appropriate design modification was made in the lower end plate. Flow coastdown in the primary loop and coolant mixing in the fuel assembly are also discussed.

Visualization study on temperature and flow fields of natural convection in a parallelepiped box

The purpose of this study is to investigate thermo-hydraulic behavior of a fluid region confined in a parallelepiped cavity equiped with a heater and a cooler. A completely transparent experimental test section was made to visualize temperat-ure and flow behavior using the liquid-crystal suspension method. Thermal plumes from the heater and cooler, global natural circulation in the cavity and thermal startifications were observed and combined to form complicated distributions.

Environmental and on-board tests of the instruments

Abstract The performance tests of nuclear measuring instruments and the radiation monitoring system were carried out by simulating the ships conditions and the environmental conditions which would be encountered in the ocean. The pendulum type clinometer was trially made and the same tests were performed. Furthermore, some tests were done on board. As a result, some problems on the manufacture of those facilities on the first nuclear ship in Japan and on the adaptability for use were clarified.