Condensation on Surfaces With Biphilic Topography: Experiment and Modeling

Abstract

Optimization of the efficiency of the condensers via different surface engineering techniques is a subject of interest due to its wide range of application in thermal management for aerospace vehicles, power generation systems, and etc., which will further result in considerable savings in annual investments and operating costs by millions of dollars. However, the current technologies are lacking either the necessary condensation enhancements or cost-effective, large-scale fabrication method. In this work, we present a new surface topography to enhance drop-wise condensation at low manufacturing costs. These surfaces consist of macro-scale hydrophobic patterns on hydrophilic structures. Due to their high wettability contrast, the biphilic surfaces enhance drop-wise condensation with long-term functionality, and more importantly, they can be easily manufactured in large-scale using conventional methods as no nano-or micro-features are needed.

Condensate droplet size distribution and heat transfer on hierarchical slippery lubricant infused porous surfaces

“…The theoretical surface heat flux, q'' (kw/m 2 ), can be calculated from coupling the individual droplet heat transfer function of their radius, q d (r), to the droplet number density N(r) as: [2,71]. Since typically during dropwise '' = ∫ ( ) ( ) condensation droplet growth takes place via direct condensation for small droplet with radius below the transition radius r e (r < r e ) and via droplet coalescence for droplets with radius above r e (r > r e ), the total heat flux for dropwise condensation without taking into account droplet shedding or sweeping is expressed as [19,79]: On one hand, the droplet size distribution above the transition radius N(r) can be extracted from Figure 5 or from the different coefficients reported in Table 2, while the droplet size distribution for droplets below the transition radius n(r) can be estimated from the expressions proposed by Graham and Griffith [8], Tanaka [73], Kim and Kim [19], Miljkovic et al [81], Wen et al [71], Chavan et al [18], and Alizadeh-Birjandi [82], amongst others. Nonetheless, in order to solely rely on our experimental data avoiding the use of empirical correlations, in this work we only make use of the N(r) reported in Figure 5 for droplets bigger than r e .…”

Quantification of Nucleation Site Density as a Function of Surface Wettability on Smooth Surfaces

“…Computational models of condensation and heat transfer rely on an accurate estimate of N s , and to date have relied on approximations based on theoretical models, and a minimal range of experimental values as shown in Table 1. [51][52][53][54] It is therefore important to have access to reliable and reproducible experimental values obtained under controlled conditions. Graham & Griffith 1973 [44] Copper tube Not specified Not specified Not specified 2 × 10 13 Tanasawa 1991 [45] Copper tube Not specified Not specified 1-3 °Ca) 1 × 10 15 Briscoe & Galvin 1991 [46] PE film…”

The Effect of Macroscopic and Microscopic Patterns of Stainless Steel Surface on the Efficiency of Dropwise Condensation and Precipitation

“…Biphilic surface-a surface topography of a combination of hydrophobic patterns on hydrophilic structures has been developed and proved to be useful for enhancing dropwise condensation (Fig. 3 (a-d)) with long-term functionality and possible for large scale production (15). A combination of the hydrophobic surface with super hydrophilic grooves on stainless steel showed better condensation heat transfer than each of them separately (Fig.…”

“…This hybrid surface showed effective control of droplet sizes with an optimum grid spacing of a super hydrophilic network. (15). (e) growth, movement, and sweeping of droplets on Hydrophobic SS surface with super hydrophilic grooves.…”

“…The images are taken every 10 min. The biphilic substrate shows better droplet nucleation and removal throughout the experiment(15). (e) growth, movement, and sweeping of droplets on Hydrophobic SS surface with super hydrophilic grooves.…”