Chapter 17

Hydraulic Resistance

17.1 Introduction

In microfluidics fluids are probed through channels with small cross-sections. Depending on the material the channel is made of the initial filling may either be facilitated or hindered by capillary effects. This is dependent on the wetting angle of the fluid on the material of the microchannel (see section 21). However, once the channel is filled with the fluid forces must be applied onto the fluid in order to move it. We know intuitively that it requires a certain amount of pressure in order to squeeze a liquid through a tiny orifice such as a microfluidic channel. A good example are squirt guns where the distance the water will travel depends on the velocity of the liquid upon exiting the ...

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