Experimental Research For Effect Of Rolling Motion Upon The Characteristics Of Flow Boiling Heat Transfer

Experimental and theoretical investigations on the boiling heat transfer characteristics ofnarrow rectangular channel under vertical, incline and rolling conditions were carried out inthis paper. The working fluid is deionized water.The validation work of the measure instruments and its measuring ranges was conductedby isothermal experiment. Comparisons of frictional coefficient were made to the experimentvalue and the classical correlation, and the agreement was satisfactory and hence thereliability of experimental set up and data acquisition system was guaranteed. By performingthermal experiment, the experiment value of single-phase heat transfer coefficient wascompared with the value calculated by the Gnielinski correlation, and good agreement wasachieved. By performing both isothermal and thermal experiment, foundations were set up forthe subsequent flow boiling heat transfer experiment and data processing.The thermal parameters almost do not fluctuates in vertical and incline conditions. Whenthe heating power is relative low, the quality in the rectangular channel is not much high, theexperimental phenomenon in rolling motion is almost the same as that in vertical and inclineconditions. With increasing heating power, as the quality in the rectangular channel reaches acertain level, the rolling motion causes the thermal parameters fluctuates periodically. Underthe same experiment conditions, the boiling heat transfer coefficient under vertical conditionsis always higher than that under incline conditions. The time-averaged boiling heat transfercoefficient in rolling motion is the same as that in vertical condition, while the instantaneousboiling heat transfer coefficient is affected by the rolling motion, and the variations ofdifferent parameters indicate different tendency. Different correlations for calculating theboiling heat transfer are adopted to analyze the experimental data. The results show thatLiu&Winterton and Lee-Lee correlation can well predict the experimental value, while theKandilikar, superimposed Chen and enhanced Kenning&Cooper correlations fail to predictthe experimental data. Theoretical analysis is performed and it is found that the boiling heattransfer in rectangular channel is affected by both nucleate boiling and convectivevaporization. Modification works considering the two influencing factors are conducted basedon Liu&Winterton correlation, and the agreement of the modified correlation and the experimental results is satisfactory.The time-averaged boiling heat transfer coefficient in rectangular channel in rollingmotion is almost the same as that in vertical condition, while the variations of instantaneousboiling heat transfer is remarkably influenced by rolling motion. analysis show thatperiodically condensation and vaporization occurs in rolling motion, inducing the variation ofthe quality in the channel, therefore, a certain amount of gas is the premise of rolling motioninducing the fluctuation of thermal parameters. Calculations show that the inertial forcesinduced by rolling motion have no effect on boiling heat transfer, the variation of the loopspatial position is the key factor that introducing the fluctuation of thermal parameters. Theexperiment results also indicate the effect of rolling period on instantaneous boiling heattransfer coefficient amplitude is more notable than that of the maximum rolling angle.