A novel surface-integrated spray-on thermocouple for heat transfer measurements

A novel manufacturing process for surface-integrated thermocouples is presented and its potential for heat transfer experiments is demonstrated. The presented manufacturing approach allows finely structured and reproducible thermocouples produced as part of the object under study. Therefore a fine channel is milled inside the investigated Perspex wall and gradually filled with conductive paints using spray cans of copper and nickel paint. High flexibility in adapting the sensor design to the requirements of a given experiment is offered by this approach as it involves only low-cost materials and standard manufacturing machinery. The paper details the characteristics and performance of such sensors, i.e. durability, reliability and operational range. Furthermore, an analytical, one-dimensional heat conduction model is used to describe the two layer arrangement of the sensor and underlying support substrate. For a step change in fluid temperature, this model in combination with a multipoint optimization procedure allows to determine the local heat transfer coefficient and the corresponding reference temperature. It is shown that this is possible without knowledge of the thermal properties of the sensor resulting in no additional calibration requirements. The obtained results are validated against measurements with thermochromic liquid crystals and commercial thermocouples. Deviations are within the uncertainty of the reference showing that the new device is competitive to state of the art techniques. Potential applications are seen for all kind of heat transfer experiments, especially when optical access for conventional techniques is restricted. Another possible field is the in-situ calibration of planar measurement techniques such as infrared thermography or thermochromic liquid crystals.