Calibration of Capillary Type Thermal Mass Flowmeter

Abstract

In the capillary type thermal mass flow meter the sensor is a small diameter stainless steel or constantan capillary, heated by an electric current. The heat is supplied either at the central point or over the whole length of the tube. In the absence of gas flow, the temperature profile is symmetric about the mid point. Gas flow through the capillary tube cools the entry section while heating the exit. This introduces an asymmetry in the temperature profile, which is a measure of the fluid flow rate. The asymmetry is measured in terms of difference of temperature between two suitably chosen points on the capillary tube, which are equidistant from the mid point on opposite sides. This temperature difference is a function of the direction and rate of mass flow of the fluid. The focus of this dissertation is to experimentally characterize thermal mass flow meters so as to properly understand their functioning, and to create an adequate knowledge base on the subject. It will significantly facilitate further understanding and development of these devices. Performance a capillary type thermal mass flow meter has also been studied in terms of the different operating parameters.