Experimental Investigation on Pool Boiling Heat Transfer Enhancement by Using Interlaced Wettability Surfaces on a Copper Cylinder

This study used sol-gel method and tape as a mask to fabricate the heterogeneous wettability surface on a copper tube with 25mm in diameter. There are two wettabilities on the heterogeneous surface. One is plain surface with its contact angle equal to 90° after baking process. However, it is worth mentioning that the contact angle of the plain surface without baking is equal to 77°. The other one is the superhydrophilic surface modified with silica nanoparticles and the contact angle of the superhydrophilic surface is smaller than 10°. On the copper surface, the strip with one wettability will follow with the strip with the other wettability to form an “interlaced wettability” surface. This study performed pool boiling experiments with surfaces of interlaced wettability. There are two parameters in this study, including the ratio of superhydrophilic surface area and the number of the interlaced line. Before performing experiments with interlaced wettability, this study investigated the effect of measuring location on a copper cylinder. From present results, wall superheat increases with the decrease of inclined angle. On this basis, the heating surface was split into two surfaces. One is the upper surface facing up and the other one is the lower surface facing down. Experimental results showed that heat transfer coefficient of the upper surface is higher than it of the lower surface. Move on to experimental results of interlaced wettability. First, the number of the interlaced line was fixed to examine the effect of the ratio of superhydrophilic surface area. Experimental results showed that the ratio of superhydrophilic surface area won’t affect pool boiling curves when the number of interlaced line is lower than 7. However, at the condition of 15 interlaced lines, although the pool boiling curve of 30% case was similar to it of 50%. The pool boiling curve of 70% case had a shift to left because bubbles on the interlaced line could not only merge with bubbles beside them but also combine with bubbles in front of them. Due to this phenomenon, the surface of 70% case could have better heat transfer performance. Second, the ratio of superhydrophilic area was fixed to examine the effect of the number of interlaced line. From experimental results, wall superheat decreased with the increase of number of interlaced line among 30%、50% and 70% conditions.