Abstract
Microfluidic systems have witnessed rapid development in recent years. As one of the most common structures, the micro-orifice is always included inside microfluidic systems. Hydrodynamic cavitation in the micro-orifice has been experimentally discovered and is harmful to microfluidic systems. This paper investigates cavitating flow through a micro-orifice. A rectangular micro-orifice with a l/d ratio varying from 0.25 to 4 was selected and the pressure difference between the inlet and outlet varied from 50 to 300 kPa. Results show that cavitation intensity increased with an increase in pressure difference. Decreasing exit pressure led to a decrease in cavitation number and cavitation could be prevented by increasing the exit pressure. In addition, the vapor cavity also increased with an increase in pressure difference and l/d ratio. Results also show the pressure ratio at cavitation inception was 1.8 when l/d was above 0.5 and the cavitation number almost remained constant when l/d was larger than 2. Moreover, there was an apparent difference in cavitation number depending on whether l/d was larger than 1.
Highlights
As a significant branch of micro-electro-mechanical systems (MEMS), microfluidic systems have received growing interest in many fields, including fuel cells, medicine, chemical or biomedical analysis, and drug delivery [1,2,3,4,5]
There are experimental and numerical investigations demonstrating that a microfluidic system with micro-orifices may suffer from the influences of cavitation, there are only a few that concentrate on cavitation inside a microfluidic system until now [16,17,18,19,20,21]
The pressure ratio between the inlet and outlet of the microchannel was studied and results showed that cavitating flow pattern was different to macroscale orifices, which were affected by the size of the micro-orifice and microchannel
Summary
As a significant branch of micro-electro-mechanical systems (MEMS), microfluidic systems have received growing interest in many fields, including fuel cells, medicine, chemical or biomedical analysis, and drug delivery [1,2,3,4,5]. The common microfluidic systems include micropumps, micromixers, microvalves, and lab-on-chip systems [6,7,8,9] In these microfluidic systems, microchannels—especially micro-orifices—are often encountered and can be used to prevent instabilities and keep a uniform flow distribution or act as network connections, for example, in microchannel evaporators or in corrosion studies [10,11]. The pressure ratio between the inlet and outlet of the microchannel was studied and results showed that cavitating flow pattern was different to macroscale orifices, which were affected by the size of the micro-orifice and microchannel. It should be noted that existing studies of cavitation inside micro-orifices were under a laminar flow state, while in microfluidic systems, such as micropumps and microvalves, the flow state is turbulent and the Reynolds number in the orifice can reach up to 25,000 [10,11,32]. The intent of this work is to provide useful insights for designing MEMS and other microchannels containing micro construction
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