An apparatus for measuring a flow rate of a two-phase fluid flowing within a conduit includes a chamber having at least one transparent wall in fluid communication with the conduit; a high-speed imaging system in visual communication with the at least one transparent wall; a thermocouple and a pressure transducer for obtaining a temperature value and a pressure value of the two-phase fluid flowing within the conduit; and a processor for determining the flow rate of the two-phase fluid by analyzing the images obtained by the high-speed imaging system, and from the temperature and pressure values for the two-phase fluid flowing within the conduit. A process is provided for determining the flow rate of a two-phase fluid flowing within the conduit.