An apparatus for measuring the volumetric rate of flow of a liquid through a conduit, said apparatus comprising the following components: a) a heating element in thermal contact with said liquid in said conduit, said heating element adapted to deliver pulses of thermal energy comprising a known quantity of heat to said flowing liquid; b) a temperature sensor adapted to measure the instantaneous temperature of said heating element; and c) a control system that comprises a processor, a memory unit, and at least one of the following components: input means, display devices, and output means, wherein: i) said processor of said control system is configured to activate said heating element to deliver said known quantity of heat beginning at time t 1 and ending at time t 2; ii) said processor of said control system is configured to receive an initial measurement of the instantaneous temperature T i of said heating element and a final measurement of the instantaneous temperature T j of said heating element from said temperature sensor; iii) said memory unit comprises calibration data relating flow rates to values of T j -T i, wherein said calibration data is specific for said conduit, said liquid in said conduit, said apparatus and the value of heat energy delivered to said flowing liquid between measurements of T i and T j; and iv) said processor of said control system is configured to retrieve from said memory unit said pre-stored calibration data relating changes in the temperature of said heating element to known flow rates of said liquid; characterized in that said apparatus is configured to measure T i after t 1 and said apparatus is configured to measure T j before t 2 and said processor of said control system is configured to use said known quantity of heat delivered to said flowing liquid between measurements of T i and T j, said values of T j -T i, and said pre-stored calibration data to determine the volumetric flow rate. a) a heating element in thermal contact with said liquid in said conduit, said heating element adapted to deliver pulses of thermal energy comprising a known quantity of heat to said flowing liquid; b) a temperature sensor adapted to measure the instantaneous temperature of said heating element; and c) a control system that comprises a processor, a memory unit, and at least one of the following components: input means, display devices, and output means, wherein: i) said processor of said control system is configured to activate said heating element to deliver said known quantity of heat beginning at time t 1 and ending at time t 2; ii) said processor of said control system is configured to receive an initial measurement of the instantaneous temperature T i of said heating element and a final measurement of the instantaneous temperature T j of said heating element from said temperature sensor; iii) said memory unit comprises calibration data relating flow rates to values of T j -T i, wherein said calibration data is specific for said conduit, said liquid in said conduit, said apparatus and the value of heat energy delivered to said flowing liquid between measurements of T i and T j; and iv) said processor of said control system is configured to retrieve from said memory unit said pre-stored calibration data relating changes in the temperature of said heating element to known flow rates of said liquid; characterized in that said apparatus is configured to measure T i after t 1 and said apparatus is configured to measure T j before t 2 and said processor of said control system is configured to use said known quantity of heat delivered to said flowing liquid between measurements of T i and T j, said values of T j -T i, and said pre-stored calibration data to determine the volumetric flow rate. i) said processor of said control system is configured to activate said heating element to deliver said known quantity of heat beginning at time t 1 and ending at time t 2; ii) said processor of said control system is configured to receive an initial measurement of the instantaneous temperature T i of said heating element and a final measurement of the instantaneous temperature T j of said heating element from said temperature sensor; iii) said memory unit comprises calibration data relating flow rates to values of T j -T i, wherein said calibration data is specific for said conduit, said liquid in said conduit, said apparatus and the value of heat energy delivered to said flowing liquid between measurements of T i and T j; and iv) said processor of said control system is configured to retrieve from said memory unit said pre-stored calibration data relating changes in the temperature of said heating element to known flow rates of said liquid;