Flow dynamics characteristics of flow boiling in minichannels with distributed pin fin structures

Abstract

Bubble dynamics and flow dynamics are crucial for understanding the heat transfer mechanisms in small-scale flow boiling and can be manipulated with surface modification to enhance performance. While numerous investigations have been conducted on minichannels with pin fins, there are few research efforts on bubble dynamics and flow characteristics. Motivated by this fact, this study covers flow boiling experiments using five pin-fin structured configurations with low (1 mm) to high (3 mm) pin-fin heights and distribution (circular) to reveal the flow characteristics and bubble behavior in mini channels with pin fin structured surfaces. Pressure drops (ΔP) were obtained at effective heat flux values ranging from 18 to 175 W/cm2 and mass fluxes from 125 to 325 kg/m2s. The visually obtained images were also presented and discussed in terms of bubble growth, departure time, and departure frequency. The effect of elliptical pin fins and distributed pin fins, along with the consideration of tip clearance, was evaluated. According to the results, three different boiling patterns could be detected over the configurations: bubbly, intermittent, and wavy-annular flow. Elliptical pin fins resulted in a higher pressure drop penalty. In contrast, the distribution pin fins offered a more uniform flow distribution and decreased pressure drop, particularly for low tip clearances (<35 %).