Effects of truncated and offset pin-fins on hydrothermal performance and entropy generation in a rectangular microchannel heat sink with variable fluid properties

A rectangular microchannel with truncated and offset pin-fins is designed, and investigated using numerical simulation. The width (W-c) and height (H-c) of a single smooth microchannel are 0.1 mm and 0.2 mm, respectively. The pin-fin length, width and height (H-r) are 0.06 mm, 0.03 mm and 0-0.2 mm, respectively. The offset value (W-r) of two adjacent pin-fins in width direction of microchannel ranges from 0 to 0.07 mm. The effects of relative height (H-rc = H-r/H-c) and relative offset value (W-rc = W-r/W-c) on hydrothermal performance and entropy generation are analyzed. Results show that increasing pin-fin height usually results in both higher thermal enhancement and flow resistance. Increasing pin-fin offset value properly can enhance heat transfer, but extremely larger offset value leads to decrease of thermal enhancement. The microchannel with H-rc = 0.75 and W-rc = 0.6 yields the maximum overall thermal performance factor of 1.43. The minimum augmentation entropy generation number of 0.31 is obtained in microchannel with H-rc = 0.75 and W-rc = 0.4. From comparison of variable and constant fluid properties, variable fluid properties significantly affect flow and heat transfer performance. Particularly, fluid viscosity plays a key role in fluid properties while others have unobvious effect.