Liquid crystal thermography in a new microfluidic device

Since the early 1980s, attention has turned to the investigation of more complex microfluidic devices such as micro-reactors and micro-heat exchangers, due to the significantly increased transport capacity and efficiency when compared to their conventional macro counterparts [1]. Microfluidic geometries with small hydraulic diameters and high surface-to-volume ratio have been considered as most promising alternatives for various process engineering applications, especially in the field of Measuring, Sensing and Control, Aerospace and Energy. Moreover, further research has witnessed a prompt growth and uncovered exciting opportunity for new applications, especially in bio-medical and chemical engineering [2, 3]. However, due to its complexity, there are still some flow regimes, like churn or annular flows which appear in gas-liquid mixtures, that are not entirely understood. In particular, with the increasing interest in successful implementation of micro-flows, separation techniques and chemical reactions, it is necessary to obtain deeper knowledge of the underlying transport phenomena of heat and multi-phase fluid flows in micro-scale systems. To investigate these phenomena, obtaining local process parameters such as pressure, temperature, and flow velocity at such small scales with high accuracy is of high importance for further improvements. It is particularly important to enhance techniques for measuring local surface and fluid temperatures developed without affecting the flow phenomena, so that the analytical models can be validated at a local level