Enhanced model for annular flow in micro-channel heat sinks, including effects of droplet entrainment/deposition and core turbulence

Abstract

This study investigates pressured drop and heat transfer characteristics for saturated flow boiling in a micro-channel heat sink specific to the annular flow regime. A theoretical control-volume-based model is presented, which relies on new relations for liquid droplet entrainment and deposition. While prior models have been attempted for annular flow, these models were based on simplified depictions of the vapor core based on average velocity. On the other hand, the present model provides detailed assessment of turbulence effects in the core, enabling the development of detailed cross-sectional profiles for momentum diffusivity, velocity, and shear stress. Predictive accuracy of the model is assessed against experimental data for R134a using a 609.6-mm long and 203.2-mm wide micro-channel heat sink containing 100 of 1 × 1-mm2 flow channels. The model shows good accuracy against 69 experimental pressure drop data points, with mean absolute error (MAE) of 16.22%, and 97.10% and 100.0% of the data predicted within 30% and 50%, respectively. It also shows very good accuracy against 388 data points for local two-phase heat transfer coefficient, evidenced by a MAE of 8.35%, and with 98.45% and 99.74% of the data predicted within 30% and 50%, respectively.