讲座题目： STUDY ON WAVY INTERFACE BEHAVIOR AND DROPLET ENTRAINMENT OF ANNULAR TWO-PHASE FLOW IN ROD-BUNDLE GEOMETRY WITH SPACER
Measurements have been conducted to simultaneously consider both liquid films and droplets of the annular flow on a 3X3 simulating BWR fuel rod-bundle test-section with spacers. The optical system of a high speed camera and a tele-microscope was used to record the backlight images at the gap between a corner rod and a side rod of the bundle at high time and space resolutions. The data at high time and space resolutions provided the detailed descriptions of the gas-liquid interface behaviors at the region close to the inlet as well as further downstream. The formation of the "singlet disturbance-crest" near the inlet which is suggested to be the first form of the disturbance wave was observed. An explanation on the mechanism of this formation process was proposed. Obtained images of three types of the entrainment process (bag break-up, ligament break-up, and droplet impingement) not only agreed with the previously proposed mechanisms but also included the information about wavy behaviors right before and after these events and the created droplets. In addition, the side-view images of the disturbance waves at different stages of development were presented. These data can be used to evaluate other measuring techniques applied to the study of this type of waves. The data obtained from the liquid film showed that the mean film thickness, wave height, power spectral density, and wave velocity at the corner rod are larger than those at the side rod, and that the influences of the spacer are different in the cases of low and high gas superficial velocities. Simultaneously, the data containing size and spatial distributions as well as the axial velocity distribution of liquid droplets were obtained. In the case of lower gas flow rates, the spacer generates not only a large number of small droplets but also big droplets whose size exceeds the maximum droplet diameter at upstream. At further downstream, the spatial distribution of the droplets indicates an asymmetry characteristic, which emphasizes the contribution of the droplet impingement mechanism to the entrainment phenomena. Moreover, a close-up observation at right up- and downstream of the spacer was conducted to describe the interactions between the two-phase flow and this structure. By using these new experimental arrangements, the interaction mechanisms among the wavy liquid film, droplets and spacer are discussed.
讲座题目： MULTISCALE DIRECT NUMERICAL SIMULATION STUDIES ON BOILING PHENOMENA
A direct numerical simulation of the boiling phenomena is one of the promising approaches in order to clarify its heat transfer characteristics and discuss the mechanism. During these decades, many DNS procedures have been developed according to the recent high performance computers and computational technologies. In this paper, the state-of-the-art of direct numerical simulation on the pool boiling phenomena during mostly two decades is briefly summarized at first, and then, the non-empirical boiling and condensation model proposed by the authors is introduced into the MARS (Multi-interface Advection and Reconstruction Solver developed by the authors). On the other hand, in order to clarify the boiling bubble behaviors under the subcooled conditions, the subcooled pool boiling experiments are also performed by using a high-speed and high-spatial-resolution camera with a highly magnified telescope. Resulting from the numerical simulations on the subcooled pool boiling phenomena, the numerical results obtained by the MARS are validated by comparing to the experimental ones and the existing analytical solutions. The numerical results regarding the time-evolution of the boiling bubble departure process under the subcooled conditions show in very good agreement with the experimental results. In conclusion, it can be said that the proposed non-empirical boiling and condensation model combined with the MARS has been validated. This paper is an extended version of the previous reviews by Kunugi et al (2012, 2014).
Tomoaki Kunugi，日本京都大学教授，核工程系主任，名古屋大学兼职教授，是国际多相流与传热方面的专家。日本机械工程学会、日本传热学会理事委员会委员和期刊编委，日本原子能学会计算科学部主席，日本多相流学会实行委员会委员和学科促进委员会主席，日本热能工程技术奖励委员会委员，The Open Thermodynamics Journal编委，7个国家的政府组织和工业企业的顾问。发明了一种新的沸腾强化换热方法，通过在沸腾面涂抹纳米多孔介质层，可以强化沸腾换热而不增加流动阻力。 2002年获国际SFT奖，2004年获日本传热学会学术奖。已发表论文200余篇。