A WAY TO REDUCE PRESSURE DROP IN ONCE-THROUGH MICRO-EVAPORATORS

作者：Rops C^*; Oosterbaan G; van der Geld C

来源：Experimental Heat Transfer, 2014, 27(4): 329-339.

DOI：10.1080/08916152.2013.849183

• flow boiling
• microfluidics
• pressure drop reduction
• microchannels

This investigation explores the possibilities to reduce the pressure drop of a single-channel micro-evaporator. The availability of micro-technology to create three-dimensional structures at a micro-meter scale opens opportunities to better control process conditions in once-through boilers. However, process miniaturization possesses some inherent drawbacks as well. Among others, the relatively large pressure drop in a micro-system makes it rather unsuitable for low-pressure applications. Especially in phase-change processes, the pressure drop may become large due to the expansion in small-sized channels. To address this drawback, flow boiling relations for small diameter tubes are first studied. These relations show a general form of the empirical correlations. Using this formulation, reduction factors could be deduced for the momentum pressure drop and friction pressure drop in case of a conical channel. These theoretically derived reduction factors show that the total pressure drop can be reduced significantly. The momentum pressure drop completely vanishes for outflow/inlet diameter ratios of 6.3 in the case of water. The friction pressure drop is reduced by a factor of ten at an outflow/inlet diameter ratio larger than four. An experimental comparison using a five-times diameter increase shows that the estimated reduction factor approaches the theoretically derived value for higher water supplies.

• 出版日期2014-7-1