Heat transfer model of dropwise condensation and experimental validation for surface with coating and groove at low pressure

Abstract

It is well known that dropwise condensation corresponds to a high heat transfer coefficient. The high performance enhancement of dropwise condensation in comparison to filmwise condensation is attributed to the ability of non-wetting droplets to be shed from the surface by gravity, therefore reducing the overall thermal resistance. The common treatments to carry out the hydrophobic surface for dropwise condensation are coating and structure. The improvement of heat transfer efficiency by combination of surface treatments with coating and groove structure has been proved compared of surface with single surface treatment by coating or groove structure. Based on this result, in this study presents a model developed to predict the heat transfer efficiency of dropwise condensation for surface with coating and groove structure features. The model is established by heat transfer though a single droplet with the drop size distribution. The heat transfer of single drop is not only analyzed as combination of thermal resistances, but also considered capillary effect of droplet due to groove geometry and properties of surface. In addition, the model results are validated with experimental data which is investigated by varied modification of vapor side metallic surface properties at low absolute pressure. It can be a reference to design industrial condensers of heat exchangers in the future. Further to optimize the surface properties and improve the higher heat transfer performance of dropwise condensation

Direct Simulations of Biphilic-Surface Condensation: Optimized Size Effects

“…This method predicts the results for high droplet nucleation density, by dividing the total simulation into two parts. One is the simulation for the large droplets starting with relatively large radius r p (called patch radius), where the sweeping effect is included using the departure radius of 1 mm for copper substrate coated with gold (Lu, et al, 2015). The other is for the small droplets starting with the initial radius of 0.5 µm and ending with the r p (using the cut method).…”

“…The cut and patch methods discussed above are used to simulate DWC with gold-coated copper substrate of variable domain size WD (Lz = WD) from micrometer to meter. The conditions are: θ c = 90°, droplet departure radius of 1 mm (Lu et al, 2015), liquid-vapor interfacial conductance (G/A) lg = 5×10 6 MW/m 2 -K, and the constriction resistance of 20% of the total resistance which is significant for the large droplets (Carey, 1992).…”

“…In practice, various interfacial, constriction and other resistances can shift the droplet distribution, causing a reduction in the DWC heat transfer coefficient. To promote the DWC, micro/nano surface structures (Shang et al, 2018 andZarei et al, 2018), as well as inorganic (gold) coatings Wilkins et al, 1973, hydrophobic porous membranes (Hu and N. Chung, 2018) and hydrophobic organic (polymers (Lu et al, 2015), self-assembled monolayers (Modak et al, 2019)), wick structure in pipe (Yunus and S. Alsoufi, 2019) have been used. To further enhance the heat transfer coefficient, bilphilic (patterned hydrophobic and hydrophilic) surfaces have been created with onedimensional (1-D) (Peng et al, 2015) and two-dimensional (2-D) (Van Dyke et al, 2015) patterns.…”

Dropwise Condensation on Advanced Functional Surfaces – Theory and Experimental Setup

“…Coatings without fluorinated compounds that have been investigated in the context of DWC include: non‐fluorinated organic polymers , amorphous hydrogenated carbon coatings , and self‐assembled monolayers of organic material , . Preston et al reported that chemical vapor‐deposited graphene coatings can also promote DWC.…”

“…The design approaches of DWC experiments reported in the literature vary with regard to the measurement method of heat flux and surface temperature, the geometric dimensions of the sample, and the method of cooling the sample. Common condensation surface geometries include vertical walls , , and horizontal tubes , . In most experimental setups, the condensation surface is cooled through forced‐convection water cooling , , , .…”