Experimental investigation on rapid filling of a large-scale pipeline

This study presents results from detailed experiments of the two-phase pressurized flow behavior during the rapid filling of a large-scale pipeline. The physical scale of this experiment is close to the practical situation in many industrial plants. Pressure transducers, water level meters, thermometers, void fraction meters and flow meters were used to measure the two-phase unsteady flow dynamics. The main focus is on the water-air interface evolution during filling and the overall behavior of the lengthening water column. It is observed that the leading liquid front does not entirely fill the pipe cross section; flow stratification and mixing occurs. Although flow regime transition is a rather complex phenomenon, certain features of the observed transition pattern are explained qualitatively and quantitatively. The water flow during the entire filling behaves as a rigid column as the open empty pipe in front of the water column provides sufficient room for the water column to occupy without invoking air compressibility effects. As a preliminary evaluation of how these large-scale experiments can feed into improving mathematical modeling of rapid pipe filling, a comparison with a typical one-dimensional rigid-column model is made

Emptying of large-scale pipeline by pressurized air

Emptying of an initially water-filled horizontal PVC pipeline driven by different upstream compressed air pressures and with different outflow restriction conditions, with motion of an air-water front through the pressurized pipeline, is investigated experimentally. Simple numerical modeling is used to interpret the results, especially the observed additional shortening of the moving full water column due to formation of a stratified water-air tail . Measured discharges, water-level changes and pressure variations along the pipeline during emptying are compared using Control Volume model results. The CV model solutions for a non-stratified case are shown to be delayed as compared with the actual measured changes of flow rate, pressure and water level, but by considering water-column mass loss due to the water-air tail and residual motion, the calibrated CV model yields solutions that are qualitatively in good agreement with the experimental results. A key interpretation is that the long air-cavity celerity is close to its critical value at the instant of minimum flow acceleration. The influences of driving pressure, inertia and friction predominate, with the observed water hammer caused by the initiating downstream valve opening not significantly influencing the water-air front propagation. Keywords: Air-water interactions, Drainage, Experimentation, Pipes, Transient flow, Unsteady flo