Experimental Investigation On The Characteristics Of Flow At Low Reynolds Numbers In Mini-channels

The characteristics of flow in mini-channels at low Reynolds numbers are one of the essential components for the design of MTE (Micro Turbine Engine). In order to execute this research, the experimental equipment that can fulfill the requirements of the regions of Reynolds numbers in MTE was built. Two new measurement techniques, mini-size static pressure hole and mini-type pressure probe were presented. With the favor of these techniques, the static pressure distribution along the length and the velocity profile at the mini-channel exit were obtained. With the data of more than 500 flow states based on 13 kinds of mini straight rectangular channels that their heights were 0.5mm and 1.0mm, the effects of characteristic scale, surface roughness and the aspect ratio of rectangular on the characteristics of flow resistance of mini straight channels were studied.The results showed that the behavior of flow was still in agreement with the macro-scale predictions when the height of mini-channel is 1.0mm. When the Reynolds numbers was little, the static pressure distribution along the length and the friction-resistance characteristics of laminar flow were completely the same with the macro-scale theoretic value. The velocity profile was also in accord with routine flow. But in the instance of 0.5mm, some evident micro-scale effects were realized. The friction factor of laminar flow has decreased into about 3/4 of the theoretic value, and the static pressure distribution along the length was nonlinear. When the Reynolds numbers became larger, the results of all the mini-channels showed evident compressible effect on the flow.The flow characteristics of laminar flow in different width-height ratio (the height stayed at 1.0mm) also varied, which were determined by the characteristic scale (such as equivalent diameter). Compared with the laminar theoretic value, the experimental friction factor reduced when the scale dropped down. It will become less than the theoretic value and the difference between them will augment with the increase of Reynolds numbers. The transition to the turbulent flow happened when the Reynolds numbers (based on the height of mini-channel) were between 1200 and 1400. And it was found that the critical Reynolds numbers became larger when the friction-resistance factor got smaller.