GAS DRIVEN CIRCULATION IN AN AIR-WATER LOOP

An experimental research with water driven by air injected at the inlet of the vertical riser in an adiabatic air -water loop has been carried out. The experimental apparatus consists essentially of two vertical plexiglass tubes 3.8 m long, 0.08 m I.D., that are connected at the bottom by a horizontal pipe and at the top by a large open tank. Air is injected into the riser through a nozzle provided with several small radial holes. The test facility is equipped with differential pressure transducers and two quick closing valves to measure the pressure drops and the average void fraction respectively. The pressure drop across the liquid single phase region has been changed by inserting calibrated orifices into the horizontal region. The data show the effect of the air flow rate and pressure losses on the liquid flow rate, void fraction, flow pattern, and recirculation ratio. The air pumping power has been experimentally estimated versus the liquid flow rate and the pneumatic efficiency has been evaluated. A model has been developed to evaluate the liquid flow rate as a function of the gas flow rate. The model gives a good prediction of the test results and allows the predictions for different conditions.