An Investigation of Ice Forming Behavior in Gravitational Vertical Flows Inside a Tube and an Annular Tube

In tubular ice machines, water flows gravitationally through tubes, while refrigerant flows through the shell side. The tube configuration and the water flow velocity are important parameters affecting the ice production rate. In this study, the flows in a 39 mm diameter tube and in an annular tube with a 39 mm outer diameter and a 10 mm inner diameter were investigated. The experiments were carried out for Computational Fluid Dynamic (CFD) model validation. The CFD simulation was performed for initial velocities ranging from 0.03 to 0.45 m/s. The results showed that the flow through the annular tube resulted in a lower ice thickness (δ) and ice growth rate (G), but a higher initial ice growth rate. This is because the annular tube has a higher heat transfer coefficient. G increases as the flow velocity decreases and decreases as time progresses. When the initial velocities exceeded the critical velocities of 0.40 and 0.35 m/s for the tube and the annular tube, respectively, the flow passages were filled with ice incompletely. For ice production, the flow velocity should be kept as low as possible. Annular tubes proved unsuitable for tubular ice machines.