Conduction and Inertia Correction for Transient Thermocouple Measurements. Part II: Experimental Validation and Application

Abstract

Thermocouples are often used for temperature measurements. Under transient conditions, measurement errors can occur due to capacitive inertia and heat conduction along the stem of the thermocouples. To correct such errors, a method is presented in Part I [1] of this paper, which uses a simplified analytical approach and a numerical solution. In the present work, this method is applied to temperature measurements. Several experiments with different thermocouple designs were performed to investigate different conditions such as installation depth, thermocouple type and transient temperature rises. In all cases, two thermocouples were placed so that they are exposed to the same fluid temperature. They are installed with short or long immersion length, respectively. It is shown that only the short thermocouple experiences a thermal conduction error, but both are subject to thermal inertia. The importance of compensating for these effects is shown by quantifying the errors in a typical heat transfer experiment when they are neglected. It is shown, which parameters are necessary for a re-calculation of fluid temperatures when two thermocouples are present at the same measuring position. Furthermore, a simplified method is described, which can be applied if the instrumentation of only one thermocouple is possible.

Conduction and Inertia Correction for Transient Thermocouple Measurements. Part I: Analytical and Numerical Modelling

“…Nevertheless, the material properties represented as numerical model coefficients remain unknown until an experimental calibration is executed. Such one is shown in rough outlines and its application will further be demonstrated in Part II [24].…”

“…The models confirm the significance of the necessary corrections and the good agreement with theoretical considerations. In part II [24], the models are applied and validated experimentally.…”

“…The preceding section demonstrated that all unknown model parameters can be determined and the model, thus, works from a theoretical point of view. Part II of this [24] continues at this point by addressing the practical application of the model for real experimental investigations.…”