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Micro-fluid engineering

0104101-109

**[DEFINITION]**

Fluid engineering for the microscopic world of micromachines.

**[DESCRIPTION]**

Micro-fluid dynamics is characterized by smaller scales of length
and velocity than in the ordinary world. In the microscopic world, based on the scale effect, the
forces needed to move fluids are thought to be mainly surface force rather than body forces, that is,
viscous force rather than inertial forces. The ratio of inertial force-to-viscous force is
evaluated by the Reynolds number. If the Reynolds number is equal, other flows with different
dimension are considered to be similar. Generally, the Reynolds number in the microscopic world
tends to much smaller than that in the macroscopic world. Therefore, the use of ordinary propulsion
equipment such as propellers, screws, and turbines requires special consideration in the microscopic
world, because the law of similarity cannot be applied.

**[References]**

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**[Related Terms]**