Experimental investigations on thermal and hydrodynamic entrance regionis in microchannels using oPIV and TLC techniques

摘要

Micro-systems are expected to have abundant applicability in the biomedical industry, where operations such as medical diagnostics or DNA synthesis and sequencing, could potentially be carried out on a hand-held device. Fully integrated micro-systems consist of several processes needed to carry out the analysis, such as mixing, reaction, and detection. These systems are projected to have significant advantages over traditional testing methods, such as smaller footprint areas, portability, and shorter analysis times. Micro-systems are comprised of micro-devices, which perform the desired processes. Micro-devices themselves, such as micromixers or micro-heat exchangers, are an arrangement of microchannels, which span only a fraction of a millimeter. Consequently, microchannels have recently received much attention in the research community. Essential for advanced design applications are flow and heat transfer analyses of microchannels, which are used to transport fluid within micro-systems and their integrated components. The entrance region of a channel, where the flow is hydrodynamically, thermally, or simultaneously developing, is very important since the flow and heat transfer mechanisms are enhanced due to the developing nature of the flow. Through the use of state-of-the-art optical measurement techniques of micro-Particle Image Velocimetry (oPIV) and un-encapsulated Thermochromic Liquid Crystal (TLC) thermography, the hydrodynamic and thermal entrance regions in microchannels are experimentally investigated. New experimental data is obtained for both laminar and turbulent single-phase flow regimes, in microchannels ranging in hydraulic diameter from 100 om to 1 mm. To investigate the effects of dimensional scaling, the results are compared to the physical mechanisms, observations, and existing data for developing flows in conventionally-sized ducts and pipes. In addition, new empirical laminar entrance length correlations are proposed for microchannels. In microfluidic devices and systems, channel lengths are expected to be extremely short, in which case developing flow may dominate the flow field over the entire microchannel length. The present study broadens the knowledge into the mechanisms of developing flow and heat transfer in microchannels. With further understanding of micro flows through experimental evidence, the applicability of complete microfluidic systems can be realized on a practical level