Measurement Techniques

This chapter focuses on measurement techniques for single-phase and two-phase flow in microchannels. Experimental measurements and flow visualizations are crucial in understanding the fundamental mechanisms of flow and heat transfer in microchannels. Furthermore, theoretical and numerical models need to be validated using accurate and reliable experimental measurements. The small length scales present in microchannels and the desired micron-scale spatial resolution in measurements poses challenges for the measurement of flow and temperature fields using conventional techniques. Moreover, quantities commonly measured in two-phase flow are different from those in single-phase flow; hence different measurement methods need to be developed and utilized in each system based on the existing phases.

A bulk of the experimental work on microchannel flows has utilized conventional measurement techniques such as thermocouples for local temperatures, and the measurement of overall flow rates and pressure drops. More recently, sophisticated, non-intrusive visualization and optical techniques and microfabricated sensors have become available for localized measurements of velocity, shear stress, temperature, and heat flux in microchannels with small spatial resolutions, resulting in more precise local measurements.