Measurement of transient fluid temperature

An inverse method to determine transient fluid temperature with high accuracy is proposed. Thermometer housing is modelled as a solid cylinder. The temperature of the fluid is determined based on a transient temperature measured at the cylinder axis. To determine the temperature and heat flux on the surface of a cylinder a space marching method is used. Using the finite volume method, the heat balance equations are written for all control volumes into which the cylinder is divided. Then, the temperature in the control volume nodes is calculated sequentially, starting from the centre of the cylinder and then marching toward to its outer surface. The transient fluid temperature is calculated from the energy balance equation written for the node located at the outer surface of the cylinder. The heat transfer coefficient on the cylinder surface is determined from the experimental correlation based on the measured fluid mass flow rate or fluid velocity. Test calculations and experiments were carried out to validate the method. In the experimental study, the temperature of the superheated steam in the header was determined using three thermometers with different diameters: 7, 15 and 20 mm the mass flow rate of the steam flowing through the header was measured. Transient steam temperature was calculated using the method presented in the paper and compared with the actual steam temperature, which is known for measured pressure and enthalpy of the steam.