Investigation on Flow Through Staggered Micro Pin Fin Arrays with Variable Longitudinal Spacings Using Micro-PIV

ABSTRACT

In this study, the flow behavior of deionized water through the staggered circular micro pin fin arrays with three longitudinal spacings (S_L = 2D, 3D and 4D) is investigated using flow visualization technology of micro particle image velocimetry (micro-PIV) in the range of Re = 100–800. The streamline distribution and velocity field in the three micro pin fin arrays are obtained. Experimental results indicate that the longitudinal spacing has considerable effect on both the extension of the wake region and velocity field around pin fins. The small longitudinal spacing hinders the extension of the wake region behind the pin fin and delays the vortex shedding. The micro pin fin array with S_L = 2D provides maximum velocity span and transverse velocity, indicating intense local fluid mixing. The flow and heat transfer characteristics in the microchannel with a single circular micro pin fin are also studied. By comparison, the feature of the wake region in the micro pin fin array with a large longitudinal spacing is similar to that in the flow past a single micro pin fin. Moreover, vortex shedding occurs in the micro pin fin array at higher Reynolds number. The correlation between velocity field and temperature field around the pin fin is investigated. The belt zone with enhanced heat transfer around the pin fin is consistent with the distribution of fluid with high velocities. Vortex shedding can obviously enhance the heat transfer downstream of the micro pin fin.

KEYWORDS:

• Micro pin fin array
• vortex
• velocity field
• heat transfer enhancement

Nomenclature

A cross-section area of the microchannel away from the pin fin, m²

A_min cross-section area of the microchannel at the pin fin, m²

D diameter of pin fin, m

H height of the pin fin, m

I_i gray scale of snapshot i

L length of the microchannel, m

L₁distance between the inlet of the microchannel and the pin fin near the inlet, m

L_vortex length of the vortex, m

L* dimensionless length of the vortex

$\overline{L^{\ast }}$ average dimensionless length of the vortex

L_c distance between the vortex center and the lag point of micro pin fin, m

L_c* dimensionless distance between the vortex center and the lag point of micro pin fin

$\stackrel{‾}{{L_{\mathrm{c}}}^{\ast }}$ average dimensionless distance between the vortex center and the lag point of micro pin fin

N total snapshots acquired for each operating condition

n number of pin fins in a row

q_v volume flow rate, m³/s

Re Reynolds number

S_T transverse fin spacing, mm

S_L longitudinal spacing, mm

U total velocity, m/s

U_max maximal flow velocity in the flow channel, m/s

U_avg averaged flow velocity in the microchannel, m/s

u streamwise velocity, m/s

v transverse velocity, m/s

W width of the microchannel, m

Greek symbols

μ dynamic viscosity, N·s/m²

ρ fluid density, kg/m³

Subscripts

min minimum

c vortex center

vortex vortex

v volume

T transverse

L longitudinal

max maximum

avg average

Acknowledgments

The authors acknowledge the financial support of Shandong Provincial Natural Science Foundation (ZR2021ME079), National Natural Science Foundation of China (52076113), Science and Technology R & D Projects of Shandong Academy of Sciences (2020KJC-GH04, 2020QN007).

Disclosure statement

The authors declared that they had no interest conflict.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by Shandong Provincial Natural Science Foundation [ZR2021ME079]; the National Natural Science Foundation of China [52076113]; Science and Technology R & D Projects of Shandong Academy of Sciences [2020KJC-GH04, 2020QN007].