Session: 15-13

Paper Number: 139623

139623 - The Effect of Liquid and Wall Properties Toward the Increase of Wetting Velocity in the Case of Using Multiple Plates in the Top-Reflood Vertical Surfaces 

Abstract: 

Rewetting is an important mechanism in the quenching process, particularly in case of nuclear reactor safety. In the location near the wetting front, heat transfer coefficient (HTC) increases, and the quenching rate also occurs rapidly. On the other hand, the study of wetting velocity by previous studies surface, meanwhile the Emergency Core Cooling System (ECCS) of nuclear reactor comprise of multiple rods.

The mechanism of wetting velocity on the multiple surfaces are assumed to be different compared to the case of 1 (one) plate. This study is based on the case of top-reflood in Boiling Water Reactor (BWR) using vertical surfaces to compare the wetting velocity using 2 (two) plates and 1 (one) plate. On the dry region where the wetting front takes place, cooling mechanism comprises of the heat conduction within the surface as well the convective heat transfers occur in the droplets and vapor phase. In this region, several heat exchange mechanisms occur involving the heat transfer among gas phase, the liquid droplets, and the wall. This hypothesis is further investigated during the research to integrate the droplets impact on the wetting velocity model.

The test section consists of two metal plates which are used as the heat transfer surface. Each of up and down edges of the metal plates (brass or copper) was sandwiched by the brass block columns. The block columns are set to heat the plate until the temperature of 250-300 °C. Meanwhile, distilled water with adjusted temperature is pumped from the storage tank and sprayed through the nozzle onto one or two plates. Furthermore, wetting velocity is calculated using the video captured by infra-red camera FLIR^TM to observe the liquid motion on the heated wall.

Several parameters are being observed, including the effect of mass flux, initial wall temperature, thermal conductivity, wall thickness, and subcooled degree. The wetting velocity in the case of using 2 (two) plates is higher compared to 1 (one) plate in almost all cases observed during the experiment. As the flowrate, wall thickness, and thermal conductivity increases, they contribute to the higher wetting velocity in the case of using multiple plates. Meanwhile, the effect of initial wall temperature is inversely proportional with the increase of wetting velocity in the case of 2 (two) plates. It is shown that the increase of wetting velocity in the case of using multiple plates is influenced by the droplets impact on cooling the wall, particularly in the case of higher mass flux, lower thermal conductivity, and lower thickness. These findings will be useful to inegrated the mechanism of heat transfer between droplets impact and the wall into existing wetting velocity model.  

Presenting Author: Akbari - The University of Electro-communications

Presenting Author Biography: I am the doctoral student in the University Electro-communications and Department of Mechanical and Intelligent Systems. My research is focused in thermal hydraulics safety, particularly to avoid boiling transition in the fuel rods of Emergecy Core Cooling Systems (ECCS) in the nuclear power plants.

Authors:

Akbari - The University of Electro-communications
Hiroyuki Umebayashi The University of Electro-communications
Tomio Okawa The University of Electro-communications