(An) experimental study of solitary wave transition characteristics for countercurrent stratified air-water flows in a horizontal pipe

Abstract

Interfacial waves resulting from turbulent gas shear, which are an intrinsic characteristic of stratified two-phase flow, greatly influence the interfacial transport phenomena and stability of the system especially in safety related problems of the water cooled reactor. The objective of the present experimental study is to provide the fundamental solitary wave transition characteristics. To investigate the solitary wave transition characteristics for the horizontal countercurrent stratified air-water flows, a series of systematic experimental studies has been performed. The experiments are carried out in a horizontal channel with dimensions 4 m in length and 102 mm in inner diameter. The water and air superficial velocities vary from 0.0004 to 0.0204 and from 0 to about 6 m/s, respectively. The instantaneous water thickness is measured by parallel-wire conductance probe, and the wave field is recorded by high speed video camera. Also, to evaluate the wave effects on interfacial friction factors, the pressure drop is measured. Statistical data analysis is accomplished in order to obtain the fundamental wave parameters such as wave amplitude, length, and velocity. Especially, from the statistical analysis, the "Spatial Growth Factor(SGF)" is derived to objectively quantify the wave regime transition boundary. Four wave regimes, a pebbly, 2-D, solitary, and flooding regimes are observed as air velocity increases. From high speed video imaging, it is found that the solitary waves are originated from two modes; continued growth of 2-D waves and the coalescence of 2-D waves. The observed transition boundaries are verified by the different nature of the statistical parameters, and especially the variation of SGF is physically consistent with the onset of the solitary waves. As the waves grow, the interfacial friction factor increases linearly with $j_g$ in pebbly and 2-D wave regions. However it increases drastically in the solitary wave region. It is noted that the i...