マイクロテクスチャリング表面における霜成長過程のその場SEM 観察と表面設計指針

Abstract

In general, frost generation on cooled surfaces have a harmful influence on prevention of heat exchange as well as falling frosts can cause contamination of some medical or daily products. The countermeasure of frost growth on the surfaces achieve by heating those surface by electronic heaters even if it is refrigerator. To enhance eco-friendly electronic devices which have heat exchanger, the surface design to prevent or detach frost from itself is highly required. In the current study, micro-texturing and wettability of the surface were hypothesized to have significant influence on growth process of frost. Several surfaces were prepared such as a lotus leaf which is famous material for natural texturing, and line and space type texturing which was manufactured on the silicon wafers. In the environmental scanning electron microscope equipped peltier device behind of sample can generate frost on the specimen surface, hence, in-situ SEM observation of micro frost was conducted. In the case of hydrophilic surface, frost quickly grew on everywhere with low contact angle to the surface, and then the observation area was covered by frost. On the other hand, if we conducted same procedure to obtain frost on hydrophobic surface, the contact angle toward the surface was higher than hydrophilic one and growth speed of frost was lower than hydrophilic surface. From the observation, the frost on hydrophobic surface grew without enhancing their contact area between frost and the lotus surface. In the case of frost grew on hydrophobic surface, the frost did not grow with widen the contact area between lotus leaf. To determine the accommodate micro-texture design, different width and depth of texturing was applied to observe, then the appropriate gap was determined between 2 to 8 μm. The gap could minimize a contact area between frost and cooled surface which could decrease adhesion force.