**2. Microchannel and micro pin-fin heat sinks**

The difference between macro-, mini-, and microchannels remains a lack of complete definition. However, it is fair to say that these differences can be classified into two groups; phenomenology and dimensions. Forces and phenomena play an essential role in micro-scale rather than macro-, mini scales [7]. Channel classification is based on hydraulic diameter as a simple guide to examine the desired dimensional range. Kandlikar and Grande [8] presented a general scheme based on the channel dimensions shown in **Table 1**.

In **Table 1**, D is the hydraulic diameter of the channel. In non-circular channels, it is recommended to use the smallest channel dimension in place of hydraulic diameter (e.g., the short side of a rectangular cross-section) [8]. Also, multiple microfluidic fabrication techniques have been developed, such as photolithography


**Table 1.** *Channel classification [8].*
