The authors deal with a measuring technique for low flow rate measurements. They describe a sensor that uses a laser-Doppler anemometer as the basic measuring technique to yield instantaneous flow rate information. The principle of the measuring device is explained and it is shown that the axial velocity of a pipe flow can be utilised to obtain the volumetric flow rate. If information on the velocity profile shape is readily available, no calibration of the instrument is required. Using this measuring principle in conjunction with the high measuring precision of laser-Doppler anemometry allows a highly precise instrument to be designed and built for flow rate measurements. The authors show that this instrument has also the capability to carry out instantaneous flow rate measurements. Time-averaged and instantaneous flow rates can both be measured, the latter up to a limiting frequency given by the pipe diameter and the viscosity of the fluid.
A method is described for estimating temperature profiles in the lower troposphere during conditions including a surface-based or elevated inversion layer. The method uses acoustic energy transmitted over paths of the order of 10 km in length. Measurements are made at approximately l-kin intervals extending radially outward from the transmitter. The vertical temperature profile is modeled as two constant temperature gradient layers. The first layer extending from the surface to height H1 has a temperature gradient T•' (usually negative upward). The second-layer temperature gradient T2' is strongly positive upward. For temperature profiles of this type, ray paths arrive with a high intensity at a caustic, and no rays return to earth between the source and the caustic. The method requires that H1 be determined by some other means such as vertical acdar sounding. The Ti' and T2' are then simultaneously determined by measuring the range to the caustic and the wave propagation time. Even if the propagation time cannot be measured, useful estimates of T•' can be obtained from observations of H1 and the caustic distance. For a
Generally, studies investigating the treatment efficiency of tank structures for storm water or waste water treatment observe pollutant flows in connection with conditions of hydraulic loading. Further investigations evaluate internal processes in tank structures using computational fluid dynamic (CFD) modelling or lab scale tests. As flow paths inside of tank structures have a considerable influence on the treatment efficiency, flow velocity profile (FVP) measurements can provide a possibility to calibrate CFD models and contribute to a better understanding of pollutant transport processes in these structures. This study focuses on tests carried out with the prototype FVP measurement device OCM Pro LR by NIVUS in a sedimentation tank with combined sewer overflow (CSO) situated in Petange, Luxembourg. The OCM Pro LR measurement system analyses the echo of ultrasonic signals of different flow depths to get a detailed FVP. A comparison of flow velocity measured by OCM Pro LR with a vane measurement showed good conformity. The FVPs measured by OCM Pro LR point out shortcut flows within the tank structure during CSO events, which could cause a reduction of the cleaning efficiency of the structure. The results prove the applicability of FVP measurements in large-scale structures.
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