Study Of Local Bubble Behavior And Boiling Heat Transfer Characteristics Under Ocean Condition

The boiling heat transfer devices inside the nuclear power system is influenced by the variation of the acceleration field induced by the ocean condition.The purpose of the present study is to explore and explain the way,degree and mechanism of the effects of ocean condition on the bubble behavior and heat transfer characteristics in the subcooled flow boiling channel.Bubble behavior under the influence of ocean condition in a subcooled flow boiling channel is researched by using the high speed visualization technology and digital image processing technology.And the data of the subcooled flow boiling heat transfer is also obtained.The test section is a single side heated up-flow rectangular visualization channel and the working fluid is deionized water.In the present study,the range of the system pressure,mass flow rate,wall heat flux and the inlet subcooling degree are 0.1⁰.6MPa,250⁷50 kg/m²s,50⁵00k W/m² and 4³6?,respectively.Bubbles in the subcooled flow boiling channel are divided into two types based on the previous researches and the captured bubble images of the present study.A parameter is defined to quantify the bubble types and a method for the predication of this parameter are also obtained.Basic parameters for the two types of bubbles are summarized,which are bubble maximum diameter,the time of bubble maximum diameter,bubble lift-off diameter,bubble sliding velocity,bubble nucleation site density and bubble nucleation frequency for the first type bubbles.The basic parameters for the second type bubbles includes bubble mean diameter,bubble contact diameter,bubble sliding velocity and bubble number density.Effects of thermo-hydraulic parameters on the two type bubbles are analyzed and a series of new models and correlations are proposed for the predication of the above basic bubble parameters.After examining the bubble data under inclination and rolling condition,it is found that the obtained models and correlations are applicable for the predication of bubble parameters under the effects of inclination and rolling condition.Subcooled flow boiling heat transfer models are proposed for the two type bubbles respectively and the error for the predication of wall heat flux is less than 35%.Different heat transfer mechanisms of the bubbles are caused by the discrepancy between the basic characteristics of the two type bubbles.The transient conduction heat transfer induced by the movement and lift-off of the bubble is dominant in the subcooled flow boiling heat transfer.The proposed heat transfer model is also applicable for the ocean condition after comparing the heat transfer data under subcooled flow boiling.Effects of ocean condition on the nuclear reactor thermo-hydraulic system is systematical and synthetical.The ocean condition can change the characteristics of the subcooled flow boiling heat transfer though exerts an influence on bubble behavior.The influence of ocean condition on bubble behaviors can be caused by the direct influence of acceleration field,marginal of the thermo-hydraulic condition and unsteady factor.For the systems of the present study,the effects of ocean condition is mainly attribute to the variation of thermo-hydraulic marginal,while the direct influence of the variation of acceleration field and the unsteady effects can be ignored.