Modelling and characterization of a multiparameter hot disk sensor for determination of fluid mixture ratios

• A low-cost sensor to determine fluid mixture ratios and flow rate is developed.
• The mathematical modelling of the sensor principle is presented.
• Measurements of different fluid mixtures with and without fluid flow are shown.
• Measurements are compared with the developed mathematical model.

The mathematical modelling of a thermal sensor principle based on the transient hot disk method to measure the mixture ratio and flow rate of binary fluid mixtures simultaneously is presented, which helps to predict and understand the sensor response. Measurements of methanol/water-mixtures are shown with and without an applied fluid flow, while the measurement results are compared with the theoretical model. Using this sophisticated hot disk sensor and if no fluid flow is present, multiple thermal properties of the fluid mixture are determined, allowing a self-test of the sensor and the detection of a possible deception. The latter aspect is of interest especially for characterization of aqueous urea solutions used in selective catalytic reduction (SCR) systems to reduce exhaust emissions of diesel engines.