High-brightness, high-power LED-based strobe illumination for double-frame micro particle image velocimetry

Abstract

There is a need for more practical, cost-effective and adaptive flow measurement instruments. Unfortunately, most of the current equipment still has to employ bulky and expensive laser systems for flow illumination. In this work we explore the practicability of using high-brightness high-power light-emitting diodes (LED) as a strobe-light illuminator within a double-frame micro particle image velocimetry (microPIV) system. A compact, cost-effective, and controllable LED driver was designed and applied to study the optical and spectral behavior of green and blue family direct-color single chip LEDs, which have excitation wavelengths corresponding to the most widely used fluorescent micro particles. To achieve strobe illumination, LEDs were subjected to high current double-pulsed operating regimes (up to 35A at 20μs pulse duration), which are much beyond their physical damage thresholds. We have witnessed that the blue family LEDs are more suitable for the fluorescence based microPIV experiments as they exhibit more stable spectral behavior at the double-pulsed high currents compared to the green colored LEDs. Specifically, we have observed that the spectral wavelength shift of blue family LEDs due to the high current is less severe and still enough to excite particles than that of green LEDs. Also, we have studied the relation between the pulse duration (as a means of parameter controlling signal-to-noise ratio) and the motion blur effect that arises due to the prolonged pulse durations. As a result, adequate pulse durations for most widely used microPIV experimental conditions were calculated. The feasibility and robustness of the developed double-pulsed LED illumination system was validated through a series of microPIV experiments with real flows inside two different topology microchannels, where the measured velocity was in good agreement with the corresponding analytical solutions. Overall, we can conclude that the high-brightness LED devices are promising candidates to replace their laser counterparts in the microPIV systems.