Experimental investigation of gas flow in pipes with recesses for ultrasonic transducers

Abstract

In this paper measurements capabilities and results of local flow velocity components in the ultrasonic flowmeters recesses are described. It was described that, the construction of transducers recesses depend on the diameter of transducer, the gap between the transducer housing and the holder of transducer, also from angle between centreline of the pipe and acoustical axis of the transducer. The calculations for variable angles and various diameters of the transducers were performed. The large angle gives small depth of the recess, but it do not provide high accuracy of flow meters. It was determined using of the metallic grid decrease flow in the recess near by the surface of transducer, when flow velocity in the tube is less than 2 m/s. Grid decrease flow velocity near by the surface of the transducer approximately 0,2 m/s. This decreasing depends on the density of the grid. There are differences between flow velocity in the upstream and downstream recesses. Near by the surface of transducer the flow velocity is more than two-time bigger in the upstream recess. However in far away from the surface of the transducer, the flow velocity is bigger in the downstream recess. In this region the maximal value achieves 50% of the flow velocity in the pipe. Dependencies of the flow velocity in the recess have complicated shape. They depend on the flow velocity in the pipe and from aerodynamic properties of the recess space. The first maximum of the flow velocity in the recess is near by the transducer, if the measurements are performed along acoustical axis of the transducer. After that follows the flow minimum at 4 mm away from the surface of transducer. The last maximum of the flow velocity in the upstream recess (at boundary recess and pipe) shows the process passing from the laminar to the turbulent flow.