Numerical investigation of hydraulic and heat transfer characteristics of two-phase ice slurry in helically coiled tubes

Abstract

The helically coiled tubes (HCT) with ice slurry as the cooling medium plays an essential role in reducing the energy consumption of heating, ventilation, air-conditioning, and refrigeration (HVAC&R) systems. However, the hydraulic and heat transfer behavior of ice slurry in HCT has not been fully understood. Therefore, the thermo-fluidic characteristics of ice slurry in HCT are numerically investigated in this study based on Eulerian-Eulerian model. The research revealed that the velocity near the outer wall is larger than that near the inner wall due to the presence of secondary flow, and the high ice concentration region shifts towards the inner wall. As increasing the inlet ice volume fraction and velocity, the ice concentration distribution in vertical radius direction of the cross-section gradually tends to be uniform. The pressure drop increases with increase of the coil radius, while the coil pitch has little influence on the pressure drop. During heat transfer process, the secondary flow causes the ice volume fraction near the inner wall to decline faster than that near the outer wall. At the entrance section, the local heat transfer coefficient decreases sharply from 9320.05 W/(m2·K) to 3002.11 W/(m2·K) and then increases slowly along the flow direction. With increasing Reynolds number, the local heat transfer coefficient enhances linearly. The increase of ice particle diameter and coil radius leads to the enhanced local heat transfer coefficient. In contrast, increasing coil pitch does not bring a significant change of local heat transfer coefficient. In addition, the correlation of local Nusselt number and flow resistance coefficient is proposed.