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Evaporation heat transfer from hot water flow to cold air flow in a horizontal duct was examined. Experiments were performed for turbulent condition. The test flow channel was rectangular. The width, height and length were 40 mm, 20 mm and 1,000mm. The length of heat transfer surface was 140 mm. In experiments, hot water was in the range of 40 °C ∼ 60 °C. Cold air was approximately at 20 °C. The air velocity was varied from 1.61 m/s ∼ 10.5 m/s. Heat transfer rate from hot water flow to cold air flow became large with an increase in air velocity. The higher the water temperature was, the larger the heat transfer rate was. When total heat flux from water to air flow was divided into two terms; the evaporation term and the forced flow convection term, the evaporation term dominate main part and that was about 60 ∼ 80 % of the total heat flux. Water surface temperature drop from bulk water temperature was confirmed. However, the temperature drop was less than 5 °C. The surface temperature drop had little effect on the evaporation heat flux and the convection heat flux. The measured evaporation heat flux was lower than the value predicted with the mass transfer correlation that was developed through analogy between heat transfer and mass transfer. The measured convection heat flux was higher, approximately twice, than the value that was calculated with the correlation for turbulent flow heat transfer probably because of bottom heating. The method to predict the heat transfer from the hot water flow to the cold air flow with the evaporation was developed by modifying the turbulent flow mass transfer correlation and the turbulent forced convection heat transfer correlation. Good results were obtained.

Experiments of counter-current two-phase flow of upward steam flow and condensing downward film flow in a pipe were performed. The experiments were intended to examine water accumulation in steam generator U-tubes during intermediate and small break loss-of-coolant accidents of a pressurized water reactor. The inner diameter and the length of a test flow channel used in the experiments were 18 mm and 4 m, respectively. Experiments were performed at higher steam velocity a little than the velocity that was expected just after scram as the first trial. There was no water drainage form the test pipe to the lower plenum. All condensed water was entrained by steam to flow out from the top of the test pipe to the upper plenum. The test pipe was filled with the water lump and the water film, then these were blown up upward and the inner wall of the test pipe became dry. Again the test pipe was filled with the water lump and the water film, then these were blown up upward and the inner wall of the test pipe became dry. This process was iterated at short intervals. The flow state in the test pipe is highly chaotic and agitated. Condensed water flows up and down at high frequencies. It is indicated that to examine the time averaged void fraction and the two-phase pressure drop of the counter-current flow are required.

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