Abstract
The present study explores heat removal capability of a two-phase natural circulation loop with microchannel evaporator. The four main devices of the natural circulation loop includes microchannel evaporator, microchannel condenser and final replaced by a 1L water tank with cooling channel, riser and downcomer. The main driving force of the loop flow is the density difference between hot fluid in the evaporator and riser side and the cold fluid in the vertical downcomer. The microchannel evaporator in this research is developed in our lab, which is made from a 4-inches silicon wafer through micro-fabrication processes with dimension of 20mm x 20mm. There are 18 parallel diverging microchannels with depth of 200 µm and length of 10.5mm. The width of the diverging microchannel is from 250 µm to 350 µm. The channels are covered with Pyrex glass 7740 by anodic bonding to enable flow visualization. Our previous research results revealed that a diverging cross section design significantly reduces the instability in the process of boiling. The riser is a circular tube with diameter of 4 mm and length of 150 mm. On the other hand, the vertical downcomer is also a circular tube with diameter of 4 mm and length of 190 mm. While the lower horizontal part is circular tube with diameter of 4 mm and length of 100 mm. The present experimental results indicate that the highest base heat flux could achieved is about 105 kWm-2 with no sign of dry-out. Therefore, it has great potential to have higher heat flux. Moreover, it is found that the loop instability can be suppressed if the input power is higher than 20W. We used the CCD to capture the flow patterns in the evaporator and riser. The flow visualization reveals similar flashing phenomenon to that observed in a big-scale natural circulation loop.