Evaluation of bubble/drop velocity and slip velocity by a single normal hot-film probe placed in a two-phase flow

This paper describes a new method of evaluating the bubble/drop velocity us ing the signal from a hot-film probe placed in either a liquid-gas two-phas e flow or a mixture flow of two immiscible liquids. In previous works the dispersed phase velocity was measured by dual optical or resistance probes, while hot-film probes were used to measure the volum e fraction and statistical velocity parameters of the continuous phase. Thi s paper describes the extension of the hot-film technique to velocity measu rements of both the continuous and dispersed phase with a single hot-film s ensor. This technique was found to be beneficial in terms of direct slip ve locity measurements. Experimental tests were mainly carried out using kerosene-water flow and ad ditional tests were performed for water-air flows. These were interface tes ts simulating the arrival of a bubble/drop front at the sensor location, an d drop tests in still water and in a large-scale recirculating vertical ker osene-water pipe flow. Three features of the 'U'-shaped signal corresponding to the passage of a b ubble/drop were investigated: (i) the voltage overshoot at the bubble/drop arrival, (ii) the corresponding maximum (negative) slope and (iii) the 'ker osene' voltage value at the bottom of the 'U'-shaped signal. This paper pre sents the applicability/limitations of these methods for bubble/drop veloci ty evaluations.