Single element thermal sensor for measuring thermal conductivity and flow rate inside a microchannel

Abstract

The increasing development of continuous-flow applications in the field of microfluidics generates demand for in-line monitoring methods. The thermal conductivity (K) of a liquid has been proven to be a valuable measurand for quality control, process monitoring, and analytical testing. However, most available methods for measuring K of microliter-sized samples are limited for use on stagnant samples. In this work, a novel method and associated prototype device for measuring K under flow conditions is presented. The so-called Transient Thermal Offset (TTO) method requires only a single metal resistive structure that is excitated with direct current (DC) pulses. To demonstrate the working, proof-of-principle experiments are performed on liquids with various K under different flow rates. The results show that, after calibration, the presented microfluidic device can be used for accurately measuring K of liquids under flow, as well as for determining the flow rate of liquids with a known K. Within the explored ranges, both parameters can be determined with an average error of approximately 2.6%. The results confirm that, also under flow conditions, uncertainties concerning probing depth are eliminated with the TTO method. (c) 2021 Elsevier B.V. All rights reserved.