Research On Pressure Drop Characteristics Of Flow Boiling In Narrow Rectangular Channel In Rolling Motion

Recent advances in the microelectronics system and the compact heat exchanger greatlyboost the development of enhanced heat transfer technology in which narrow channel is usedextensively due to its high efficient heat removal capacity. Besides, flow boiling heat transferin narrow channel draws widespread attention. However, two-phase flow characteristics innarrow channel are significantly different from that in conventional one, especially in theocean condition, many changes of which will be emerged. So in this paper, flow boilingresistance in vertical narrow rectangular channel was investigated in the rest and the rollingmotion using deionized water as the working media. The experimental loop was installed on aplatform which can roll around its central shaft, and experiments were performed in a visibleand an invisible test sections.Onset of significant vapor point was studied through the visualization experiments, andthe Sun Qi model was verified with a mean deviation of8.2%. Rolling motion has weak effecton the position of onset of significant vapor point.Flow boiling resistance experiments in the invisible test section and analysis results ofthe experimental data under rest condition show that mass quality, mass flux and systempressure have significant effects on the flow boiling pressure drop. Further, severalstate-of-the-art correlations for the two-phase frictional pressure drop were evaluated againstthe experimental data, among which the Chisholm C and the Lee-Lee correlations arerelatively better with mean deviations of34.8%,38.3%, respectively. Others poorly predictthe results, especially, the Martinelli-Nelson and the Chisholm B correlations developed forconventional channel are no longer applied to narrow channel. A better correlation based onthe Lockhart-Martinelli model was developed for calculating the two-phase frictionalmultiplier with a lower mean deviation of24.7%.Rolling motion almost has no effect on the averaged two-phase frictional pressure drop.Spacial position change of the system due to the rolling motion results in the periodicalfluctuation of transient pressure drop when the critical outlet mass quality is exceeded. Andthe amplitude of pressure drop fluctuation is dominated by mass quality, mass flux, systempressure as well as rolling period and amplitude, so the instable boundary and the relevant affecting factors were proposed and it is showed that increasing system pressure anddeceasing flow flux, rolling amplitude and period are in favor of the stabilization of system.Furthermore, the correlation for calculating transient flow boiling pressure drop was proposedwithin the specified parameter ranges, and it could be applied to the rolling condition.