Experimental Investigation On Pressure Drop Of Flow Boiling In Rectangular Narrow Channel Under Rolling Conditions

Experimental and theoretical studied of flow boiling resistance of force circulation in rectangular narrow channel under rest and rolling motions. The experiments were conducted in the rolling platform using deionized water as working fluid.Comparison and discussion of numerous void fraction models were carried out and the effects of void fraction model on two-phase pressure drop were presented by using the two-phase experimental data of forced circulation flow boiling in the rest condition. The results reveal that the void fraction rapidly increases with the increasing of mass quality when the mass quality is less than 0.1, while almost keeps constant when the mass quality is more than 0.2. The results also indicate that most of the slip ratio models and the Lockhart-Martinelli parameter based models give results close to each other. The drift flux void fraction models give small values which are incompatible with other models making it inapplicable for narrow rectangular channel. In addition, the alteration of void fraction models has an inconspicuous effect on two-phase frictional pressure drop, while obvious effects on two-phase acceleration pressure drop.The results of flow boiling resistance experiment under rest condition show that thermal hydraulic parameters of mass flux, mass quality and system pressure have significant influence on flow boiling pressure drop. Several correlations for two-phase frictional pressure drop based on homogeneous model or separated model were evaluated against the experimental data, among which the Mishima-Hibiki and Gronnerud correlations give the relatively better prediction with the mean absolute error of 33.1% and 33.5%, respectively.The two-phase viscosity model which based on the homogeneous model has significant effect on the two-phase frictional pressure drop and the effect shows a dependence on the mass quality. Considering the effects of mass flux, channel size, surface tension and gravity, a modified Mishima-Hibiki method is proposed for flow boiling frictional pressure drop in rectangular narrow channel with a mean absolute error of 20%.The results of flow boiling resistance experiment under rolling motions show that the rolling motions almost have no influence on the averaged two-phase pressure drop. The rolling motions result in the periodical fluctuation of transient two-phase frictional pressure drop once the critical mass quality reaches a certain value. The period of pressure drop fluctuation is in accordance with the rolling period. And the amplitude of pressure drop fluctuation is affected by the mass quality, system pressure drop, mass flux significantly,while the rolling angle and period have inappreciable effect on the amplitude. The special position change of the system due to the rolling motion results in bubble coalescence periodically at the condenser's entry and then lead to the loop blocking,thus the pressure,boiling intensity varies accordingly. Therefore,the transient frictional pressure drop fluctuates periodically. The correlation for frictional pressure drop applied to the rest condition is also valid for that under rolling motions for it mainly depending on the mass quality.