Calorimetric flow meters work on the principle of heat transfer by the flow of fluid. This is also known as thermal mass flow meter and hot wire anemometer. Typically calorimetric flow meters are situated along the direction of the flow.

A heating of element is placed in the flow. As sensor is positioned to measure the temperature of the device, a second measuring device reads the temperature of the flow downstream from the heater.

Here as T2 and T1 RTD is used to measure temperature.

The rate of flow is determined by the difference in the two temperatures with a constrain power in put this difference in temperature is a linear function of the mass flow and the heat capacity. The flow meter can then be calibrated to indicate directly in mass flow units.

Applications of thermal flow meters are limited to use with fluids that have known heat capacities. Usually they are clean gases or clean mixture of pure gases of known composition. Liquid applications are less common; because liquids are generally contain more impurities than gases.

Most of the thermal flow meter designs have temperature range between 100 and 150 degree Celsius. Conductive surfaces of a thermal flow meter can become contaminated and should be routinely cleaned to maintain the performance levels. These devices are generally not applied to abrasive fluid services.

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