Marijus Seporaitis

Design and Tests of a Device for the Generation of Controlled Condensation Implosion Events

A test facility has been constructed of which the purpose is to explore the characteristics of a thermo-hydraulic component (a “pulser”) where condensation implosion events can be initiated in a controlled and reproducible manner. This paper summarizes experiments conducted in a horizontal cylindrical pulser. For design purposes, a modified Jakobs number criterion was defined. It is an index measuring the capability of the pulser water to condense all of the initial pulser steam that takes into account the heat capacity of the pulser metal and heating of water by condensation. The tests showed that in order to achieve a rapidly growing condensation rate that exceeds the inertial time constant of the vapor phase, the modified Jakobs number has to approach a value of 5. For a 0.027 m3 volume cylindrical pulser, this can be achieved when the steam contains residual amounts of air (on the order of 0.02 to 0.03 mole fraction). The paper presents experimental results characterizing the dynamic response of the pulser as a function of the liquid side turbulence.

The Concept and RELAP5 Model of Thermal-Hydraulic System, Employing a Rapid Condensation for Coolant Circulation

The rapid condensation event is mostly considered a dangerous and undesirable side effect in thermal-hydraulic systems. This work demonstrates a different viewpoint, where condensation implosion is employed to perform mechanical work. Previous experimental study of the condensation implosion event, briefly presented in this article, showed that condensation implosion can be induced intentionally. These results were used as the basis for further investigations. In this work, a concept of the thermal-hydraulic system has been developed, where condensation-implosions-generated pressure difference could be used as a driving force. Numerical study has been performed to investigate the operation of the developed conceptual thermal-hydraulic system. A thermal-hydraulic computer code RELAP5 was selected for modeling the system operation. The RELAP5 code was found not able to predict the condensation implosion; therefore, a modified heat transfer model was implemented into the code. This modification allowed simulating the condensation implosion artificially in the thermal-hydraulic system and modeling the system response to the event. Final results show that a proposed circulation principle is possible and such a thermal-hydraulic system can operate.

Study of Controlled Condensation Implosion Events

At LEI (Lithuanian Energy Institute) an experimental program has been initiated to investigate the ‘condensation implosion’ phenomena that can occur for horizontally stratified liquid-vapour flow conditions. The goal is understand the critical boundary conditions sufficiently so that the phenomenon can be controlled and initiated at will. After a reliable ‘pulser’ is developed, the follow up goal is to implement this unique component in a thermal-hydraulic system designed to perform certain tasks, e.g. to pump water or to transport energy passively in a downward direction. Experimental data obtained to data has shown that pulsers can be designed in which the vapour-liquid interface perturbation required for the initiation of condensation implosions is generated internally and depends solely on the rate at which liquid is supplied to the pulser. Data is presented which documents the conditions required for transition from a smooth to a wavy interface, and subsequently to an exponentially increasing surface distortion that culminates in a ‘condensation implosion’. The importance of the shear-stress generated by the condensation rate is illustrated.Copyright

Experimental Investigation and RELAP5 Modeling of Two-Phase Flow in Horizontal Rectangular Channel

The investigation of steam, water, and air flow characteristics in horizontal channel is a part of major investigations program at the Lithuanian Energy Institute. The objective of this program is to identify condensation effects on two-phase flow stability and to predict conditions when rapid condensation could be induced in two-phase condensable flow. This article presents investigation of steam–water and air multiphase flow in nearly horizontal rectangular channel. The experimental data for pressure drop and interfacial and wall shear stresses in the channel with uniform distribution of void fraction are presented in this paper. Overall channel dimensions are length = 1.2 m, width = 0.02 m, height = 0.1 m; however, the test section was about 0.84 m in length. Three different flow types were analyzed at atmospheric pressure: (1) single-phase air flow (height of the channel was reduced to 0.075 m); (2) non-condensable air–water two-phase flow at void fraction of 0.75; (3) two-phase steam–water flow at almost saturation conditions, and void fraction of 0.75. RELAP5 Mod3.3 code was selected to model test cases. Modeling results and experimental measurements show good agreement with each other. The developed model will be used for calculating different cases of the process.