[en] In view of the importance of obtaining unsteady local void fraction and interface velocities in liquid-vapor two-phase flows, an optical probe with a controlled tip geometry was developed and is described. In order to minimize the disturbances caused to the flow field by the presence of the probe, its dimensions have been miniaturized. The electronic and hydrodynamic response of the probe were investigated experimentally. The probe was found to be sensitive to both the interface velocities and the phase present at the probe tip. A possible explanation for the behavior of the probe is presented. Within the velocity range checked and with proper calibration, the optical probe developed can be used to determine both local void fractions and interface velocities

[en] The objective of the BNL Light Water Reactor Development Program is to obtain measurements of the volumetric vapor generation rates in flashing steam-water flows under steady and transient conditions of interest in accident analysis. Instrumentation in support of this activity was developed and constructed to obtain both local and global measurements of the appropriate information, i.e., void fraction and phase velocities. The methods described include local instruments (optical and r-f probes) that provide local information and a global densitometer using γ attenuation techniques. A minicomputer based data acquisition and data analysis system was also developed including a block signal analysis system with the proper time and frequency domain data manipulation software. This presentation summarizes the current status of the work and the accomplishments

[en] An optical probe capable of measuring local void fraction and interface velocities in water-air or water-steam environments was developed, constructed and calibrated in an air-water loop. The probe was found to be sensitive to both the interface velocities as well as the phase present at the probe tip. A possible explanation for the dependence of the output on the bubble velocity was related to a thin water film left on the probe tip during the passage of the bubble, and whose thickness was increasing with the bubble velocity. In order to study the various probe tip geometry response characteristics, a computer program was developed

[en] The current state of the art of void fluctuation dynamics and measurement techniques is briefly reviewed. New and improved measurement techniques which have been developed are described including two local probes which both have the capability of being responsive to phase presence and interfacial velocity. It is shown that the dynamics of a thin liquid film on optical probes have strong effects on the response not heretofore recognized

[en] A radio frequency (r-f) probe that can provide local void fraction and interface velocity measurements in a gas-liquid two-phase flow was developed. The probe response to bubble passage was investigated with single bubble controlled experiments. For fixed geometry, the probe response was dependent on the dielectric constant of the medium surrounding the probe tip, (air or water), and on the frequency of the carrier signal supplied to the probe. Bubble lengths (< 1 cm) and average bubble approach velocities (< 160 cm/sec) were independently measured by two light sources and detectors placed at a known distance from each other and sensing the passage of each bubble. By choosing a sensitive probe tip length of 2.75 - 3 mm, the r-f probe output provided enough information to determine the bubble length and velocity. The results obtained by the two independent methods show reasonable agreement

[en] The two objectives of the BNL light water reactor thermohydraulic development program are as follows: first, analytical expressions for the non-equilibrium vapor generation rates under circumstances of interest in accident analysis were developed; second, the experimental program consists of measuring the actual vapor generation rates in flashing flows. In order to support this effort, both global and local instruments were developed and calibrated to provide the necessary information. At the same time, suitable methods were devised for handling and analysis of the signals and data derived from the various instruments

[en] A major area of interest to reactor safety technology is the prediction of actual vapor generation rates under conditions of thermal nonequilibrium as would be encountered during a loss-of-coolant accident (LOCA) in a light water reactor. In support of the development of advanced codes dealing with LOCA induced flashing, analytical models of the nonequilibrium vapor generation processes of interest have been formulated, and an experimental facility has been constructed to provide data to verify these models. This facility is known as BNL Heat Transfer Facility. The experimental facility consists of a flow loop, test section and the data acquisition and analysis system. The main portion of the flow loop is constructed from three inch nominal (7.6 cm) stainless steel pipe. High purity water is circulated through the loop using a centrifugal pump rated 1500 l/min at 600 kPa. Very close and stable control of all loop parameters is required since flashing is sensitive to very small changes in such parameters as flow rate, subcooling, and pressure

[en] A steady water loop with well controlled flow and thermodynamic conditions was designed, built, and made operational to measure the net vapor generation rates under nonequilibrium conditions. The test section consists of a converging-diverging nozzle with 49 pressure taps and observation windows at the exit. First pressure distributions and photographic observations were recorded under various flashing conditions. The effect of the various parameters such as inlet pressure, inlet temperature, mass flux, and back pressure on the pressure distributions and flashing regimes have been investigated and are reported here. Under specific flashing conditions, a sharp increase in pressure (condensation shock) was observed in the diverging section (which accomodates the high back pressures). The experiments are being continued with a γ densitometer to measure the void fraction distributions needed in the vapor generation rate calculations

[en] In view of the importance of obtaining unsteady local void fraction and interface velocities in liquid--vapor two-phase flows, an optical probe with a controlled tip geometry was developed and is described. In order to minimize the disturbances caused to the flow field by the presence of the probe, its dimensions have been miniaturized. The electronic and hydrodynamic response of the probe were investigated experimentally. The probe was found to be sensitive to both the interface velocities and the phase present at the probe tip. A possible explanation for the behavior of the probe is presented. Within the velocity range checked and with proper calibration, the optical probe developed can be used to determine both local void fractions and interface velocities

[en] The two objectives of the BNL light water reactor thermohydraulic development program are as follows: first, analytical expressions for the non-equilibrium vapor generation rates under circumstances of interest in accident analysis were developed; second, the experimental program consists of measuring the actual vapor generation rates in flashing flows. In order to support this effort, both global and local instruments were developed and calibrated, to provide the necessary information. At the same time, suitable methods were devised for handling and analysis of the signals and data derived from the various instruments