(An) experimental investigation of the effets of the sudden contraction on single-and two-phase pressure dropin vertical air-water flow = 공기와 물의 수직 유동에 있어유로의 급격한 축소가 단상 및 이상 유동의 압력 강하에 미치는 영향에 관한 실험적 연구
An experimental investigation of the effects of the sudden contraction of flow channel on single-and two-phase pressure drop in vertical air-water flow has been carried out, for the adequate prediction of single-and two-phase pressure drops through a sudden contraction of flow channel is one of the important parts performed in the hydraulic analysis of the primary coolant system in normal and accidental conditions of nuclear power plants. In the present work, a total of 172 measurements were made for four different entrance shapes of sudden contraction. The two-phase flow pattern examined was bubbly flow of air-water mixture. The measured pressure drops were compared with pressure drops predicted by existing models for single-and two-phase flow. From single-phase experimental data, the contractional loss coefficients were determined. Based on these loss coefficients and two-phase experimental data, pressure drops were calculated and compared with the pressure drops predicted by analytical models for two-phase flow. For single-phase flow, there were some discrepancies between experimental data and predictions, and the results show that single-phase contractional loss coefficient for specific entrance shape must be determined experimentally. In the case of two-phase flow, the predicted twophase pressure drops using Hoopes`` model were within $\pm 10\%$ of measured data, whereas the homogeneous model overpredicted the measured data as much as 15\%. In addition, the effects of void fraction and liquid-phase mass velocity on the two-phase pressure drop through a sudden contraction of flow channel were also investigated.