The tracer method has been adopted to study stratified-dispersed flow in a horizontal pipe, 80 mm in diameter and 50 m long, operating at 5 Bar with nitrogen-water mixtures. The use of the tracer method in a horizontal pipe required the development of a specially designed test section, the
related electronics and a data acquisition system. The test section consists of a short pipe made of a non-conducting material installed in a flow rig designed to operate at an appreciable pressure (40 Bar). The flow loop is made of metallic pipes connected to the electrical ground. The conductance probes are made of three parallel, rigid wires spaced along the flow direction and have been used to measure the height or the electrical conductivity of the liquid layer. The three-electrode geometry is aimed at minimizing current
losses toward ground. The simultaneous operation of all the probes of the array, without multiplexing, allows a substantial reduction of current dispersion and a good circumferential resolution of film thickness or conductivity
measurements. The probe geometry may generate an appreciable
disturbance to the gas-liquid interface. This aspect of the proposed method has been studied with an experimental and numerical investigation relative to free falling liquid layers.
It has also been necessary to develop a tracer injection system, which has been designed in order to obtain uniform tracer concentration in the liquid film immediately after its injection. The main flow parameters which can be measured with the present experimental set-up are the circumferential distribution of the film height, flow rate and tracer concentration, the rates of droplet entrainment and deposition and the split of the liquid phase between the wall layer and the entrained droplets. The average tracer concentration data have been interpreted with a new three-field model of
the liquid phase in the stratified-dispersed flow pattern. In the present formulation, the model holds for steady, fully developed flow conditions and is based on a one-dimensional description of the flow system. The data cover a limited number of flow conditions
