Effects Of Dynamic Load And Heating Orientation On Critical Heat Flux Of Two-phase Flow In A Rectangular Groove

Due to its high efficiency,two-phase heat transfer in a narrow channel is widely used in the refrigeration system of the aerospace field. The critical heat flux is an important limiting parameter in two-phase boiling heat transfer, and the hypergravity is often created in advanced aircraft maneuver. Therfore the flow boiling critical heat flux characteristics of the distilled water in a narrow rectangular channel with single-side heating were investigated under hypergravity condition and different orientations in this thesis.Selecting the experimental data as the test section arranged in the circumferential direction on an unmoved platform, the characteristics of fluid critical heat flux and flow resistance in narrow channel under different heating orientations were investigated. The experimental data were compared with the calculated values based on the several state-of-the-art correlations, which shows that Sudo correlation and Katto correlation were not suitable to the present experiment conditions. The predicting values with Ivey-Morris correlation and Wojtan correlation agree well with the experimental data as the orientation angel is at 0°, and their relative deviations are within 30%. However the predicting values are greater than the experimental data under other orientations.Experimental investigation into the effects of dynamic load and heating orientation on the critical heat flux of flow boiling in a narrow rectangular groove were performed on a rotational platform. The change trends of mass velocity, the pressure drop in test section and its outlet wall temperature before and after reaching critical heat flux were obtained. The effects of dynamic load and heating orientation on flow boiling critical heat flux were discussed, and the flow instability was also briefly analyzed. The results show that in addition to the wall temperature rising rapidly, the effective heat flux decreases after the critical heat transfer occuring. The effects of dynamic load and heating orientation on critical heat flux are obvious. Critical heat flux values increase with increasing channel aspect ratio. Not soon before and after the critical heat transfer occurs, the back flowing vapor increases the inlet fluid temperature, which enhances the flow instability. Based on the present experimental data at the orientation angels of 0° and 180° under side load, using genetic algorithms, a new correlation is proposed by modifying the Qu-Mudawar correlation, which shows excellent accuracy in predicting the present critical heat flux.