Dropwise condensation on biphilic surface in pure steam condition : Supersaturation effect on heat transfer coefficient

Abstract

Dropwise condensation, which has significantly enhanced performance compared with conventional filmwise condensation, has been studied after observed by schdmit et al. in 1930. As objective of improving the performance of dropwise condensation, the fast removal of condensate is necessary. From this point of view, the coalescence-induced jumping phenomena has numerous attentions because of its smaller departure radius characteristics (~um).

Taeyang Han et al. proposed the new condensing surface which made up for the shortcomings that superhydrophobic surface has small coalescence frequency. The surface realized the rapid droplet coalescence through spontaneous movement used micro zigzag structure (Called as SH-Zigzag). Furthermore, the self-arrange method was used for hydrophilic material patterning (Called as Bi-Zigzag). From this unique method, the superhydrophobic surface could have heterogeneous wettability that has an advantage of nucleation density and zigzag activation rate. However, for extensive application of proposed condensing surface, the performance should be evaluated at various condensing conditions (i.e supersaturation).

In this studies, customized chamber was designed for measuring the condensation heat transfer coefficient. Through the customized chamber, various condensing condition (supersaturation, NCG fraction etc.) could be make intentionally. At this studies, supersaturation effect was evaluated at various surface. From the result, Bi-Zigzag surface, which intentionally arranged the hydrophilic polymer in the zigzag structure to increase the zigzag activation rate, showed a 250% enhancement in data compared to the SH or SH-Zigzag surface under low supersaturation condition (S~1.015).

Proposed Bi-Zigzag surface has effective performance at low heat flux region (~70kW/m2). In this point of view, the dehumidification, hot spot cooling using the vapor chamber, which designed for magnifying the effective condensing area can be applied at engineered surface.