Thermal Response Characterization and Low Fluid Velocity Measurements Using Specialized In-Situ Thermocouples Via The Loop Current Step Response Method

In this study, a specialized balanced-leads thermocouple was developed to perform in-situ thermal response characterization via the LCSR test method. Thermal response characterization of installed thermocouples is essential in order to obtain accurate positional temperature data in rapid transient applications. An analytical model is presented that fully describes the thermocouple system based on a first-principles approach to the heat transfer physics of the sensor. In conjunction with the LCSR test, the full model presented yields quantifiable characterization parameters useful for determining accurate positional temperature data. It is necessary to employ a balanced-leads thermocouple for this experimental procedure in order to ensure that the thermocouple bead and its leads are at the same initial temperature, when performing the LCSR test. If the installed thermocouple is in a fluid domain, it has been demonstrated that the LCSR test data may be calibrated against the fluid velocity. This finding was verified by comparison of the present experimental data with forced convection correlations obtained by previous researchers. The next task to improve the work of this study is to construct a balanced-leads thermocouple with a lead temperature ratio of unity. This new balanced-leads thermocouple will more closely satisfy the assumptions made for applying the full model to the thermocouple system. For this study, the data obtained was compared with previous researchers’ convection correlations to demonstrate a proof of concept. Lastly, the thermocouple sensor should be calibrated carefully over a wider velocity range before it can be implemented in an industrial application. This calibration procedure must be repeated for each individual thermocouple sensor to be installed. If these additional tasks are performed, a balanced-leads thermocouple characterized via the LCSR test method could become a valuable and versatile temperature-velocity probe for industrial processes.