1,721,007 research outputs found
Gas driven circulation enhancement in an adiabatic air-water loop
No full textThe gas driven circulation enhancement in an adiabatic air -water loop has been investigated. The experimental facility consists of two vertical plexiglas pipes 3.8 m long, 0.08 m I.D. 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 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 experimental results and allows to perform predictions for different condition
Fluiddynamics in a windowless symmetrical target for accelerator driven hybrid nuclear reactors
No full textTwo-phase flow pressure losses in a horizontal impacting T-junction
No full textThe present paper reports further analyses of the two-phase pressure drops experimental data obtained in a horizontal impacting T-junction. A mixture of air and water at ambient temperature and pressures up to 1.5 bar is generated inside a mixer, which is fed by a compressed air system and a centrifugal pump. Superficial velocities of air and water in the inlet pipe are varied up to a maximum of 35 m/s and 3.5 m/s respectively. Each branch has got four pressure taps which can be connected to both differential and absolute pressure transducers. These measurements allow us to determine the pressure behaviour along the pipes and to extrapolate the pressure losses between the inlet and the branches. Pressure drops, that are extrapolated in the junction, are analysed and the irreversible component (pressure loss) is evaluated. The two-phase pressure losses are compared with the Chisholm two - phase multiplier and with the prediction of the El-Shaboury et al. model, and several correlations for the pressure loss coefficients are tested: the loss coefficients are expressed as a function of the Reynolds number, as in the El-Shaboury et al. approach, and the dependence of loss coefficients on the inlet void fraction, flow quality and Martinelli parameter is also analysed
Criteria for Predicting Deteriorated Heat Transfer Conditions for Water at Supercritical Pressure = Criteri per la previsione del deterioramento dello scambio termico per acqua a pressione ipercritica
No full textThe conditions of occurrence of the deteriorated heat transfer for water at supercritical pressure are investigated. The most widely accepted correlations for the deteriorated heat transfer regimes prediction are compared with the experimental data obtained by several authors
Regimi di deflusso e separazione delle fasi in una giunzionea T orizzontale con deflusso di miscele aria-acqua
No full textExperimental Study on the Flow Patterns and Two-phase Pressure Drops in a Horizontal Impacting T- Junction
Full text linkThe present paper analyzes the experimental results concerning the flow patterns and pressure drops in two-phase flow through an horizontal impacting T-junction, whose outlet pipes are aligned and perpendicular to the inlet pipe. The test section consists of plexiglass pipes with inner diameter of 10 mm. A mixture of water and air at ambient temperature and pressures up to 2.4 bar flows through the T-junction, with different splitting of flow rates in the two outlet branches; superficial velocities of air and water in the inlet pipe are varied up to a maximum of 35 m/s and 3.5 m/s respectively. The flow patterns occurring in the inlet and branch pipes were compared with the predictions of Baker’s and Taitel – Dukler’s maps. The pressure drops along the branches have been measured relatively to different splitting of the flow rate through the two branches and the pressure loss coefficients in the junction have been evaluated. Friction pressure drops have allowed us to evaluate two-phase friction multipliers, which have then been compared to the predictions of Lockhart-Martinelli, and Friedel correlations. Local pressure drops were extrapolated at the junction centre and analyzed; the two-phase multiplier has been evaluated and compared with the predictions of Chisholm correlation; the value of the empirical coefficient that minimizes the discrepancies has also been evaluated
Gas Driven Circulation in an Adiabatic Air-Water Loop With Reference to Accelerator Driven Systems
No full textIn order to investigate the fluid dynamic mechanisms of the gas driven circulation, with reference to the accelerator driven systems (ADS), an experimental research with water driven by air injected at the inlet of the vertical riser in an adiabatic test rig has been carried out. The present experimental apparatus consists essentially of two vertical plexiglass pipes 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. The test rig is equipped with differential pressure transducers and two quick closing valves to measure the pressure drops and the average void fraction. The air flow rate ranges up to 5000 Nl/h, at 7 bar pressure, and the liquid flow rate can reach the value of more than 5 kg/s. The research aim is to investigate the effect of the superficial gas velocity on the superficial liquid velocity, on the void fraction and on the pressure drops, for a given geometry. The test data have been compared with some two-phase pressure drops and void fraction correlations. The geometry effect has been investigated too
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