THREE-DIMENSIONAL VISUALIZATION OF FLOW CHARACTERISTICS USING A MAGNETIC RESONANCE IMAGING (MRI) IN A LATTICE COOLING CHANNEL

摘要

Flow structures in lattice cooling channels are investigated experimentally by measuring three-dimensional velocity components over entire duct. The lattice cooling structure is formed by crossing two sets of parallel inclined ribs. Heat transfer is enhanced when coolant flows through the narrow sub-channels between the ribs. According to the past literature, longitudinal vortex structures are formed inside the subchannels due to interactions between crossing flows. In this study, three-dimensional velocity field measurement is performed using MRI scanner to clarify the flow mechanism. The rib inclination angle is varied from 30 to 60 degrees. Reynolds number is set at approximately 8,000 based on the whole duct inlet hydraulic diameter and bulk velocity. Working fluid is 0.015mol/L copper sulfate aqueous solution. Measured results show that coolants in the upper and lower sub-channels interact not only at the both ends of the duct, but also at diamond-shaped openings formed by opposite sub-channels. The exchange of momentum between the upper and lower sub-channels occurs at the openings, leading to sustained longitudinal vortex in each sub-channel as mentioned in the literature. When the ribs are arranged with obtuse angle, a large vortex spreads across the contact surface, while the vortex structure independently stays in each sub-channel for acute rib angle. The measured velocity fields are compared with numerically-simulated ones using a RANS solver. Overall flow pattern is captured, but flow interaction between the upper and lower sub-channels is underestimated.