A study of fin effects in the measurement of temperature using surface-mounted thermocouples

The present study addresses the effects of thermocouples on the measured temperature when such thermocouples are mounted directly on the surface of the object. A surface-mounted thermocouple is a very convenient way of measuring the surface temperature. However the heat conduction into/from the thermocouple wire changes the local temperature at the thermocouple junctions along with the immediate vicinity of the thermocouple. As a consequence, the emf appearing at the thermocouple terminals does not correspond to the actual surface temperature. In this paper we first discuss the general characteristics of the enhanced heating/cooling due to the so-called fin effects associated with the surface-mounted thermocouples. An embedded computational model is then developed so that the model can be used in conjunction with a regular FEM model for the multidimensional calculation of the heating or cooling of a part. The embedded computational model is shown to offer very accurate calculation of the temperature at the junction of thermocouple wire. The developed computational model is further used in the inverse heat transfer calculation for a Jominy end quench experiment.