انتقال حرارت چگالش قطره ای – نواری
Abstract
Graphic abstract
Nomenclature
۱٫ Introduction
۲٫ Numerical simulation
۳٫ Results and discussion
۴٫ Conclusions
CRediT authorship contribution statement
Declaration of Competing Interest
Acknowledgements
Appendix. Supplementary materials
Research Data
References
Abstract
Condensation heat transfer on biphilic surface is investigated. The surface periodically populates hydrophobic stripes each having a coating layer thickness δp and a width WDWC, and hydrophilic stripes each having a width WFWC. The proposed model includes dropwise condensation on hydrophobic stripe, filmwise condensation on hydrophilic stripe, and droplet detachment radius rmax criterion for heat-mass coupling between the two wettabilities regions. The rmax is the minimum of detachment radii determined by droplet removal modes of double-sides-suction DSS, one-side-suction OSS and sliding, where DSS is a special case of OSS for droplet located at hydrophobic stripe centerline. Simulation results matched the measured heat transfer data well. Optimal width of hydrophobic stripe Wo DWC is found to be dominated by δp and WFWC, but other parameters weakly influence Wo DWC. Interfaced by a δp−WFWC transition curve, a heat transfer regime map is presented to contain Regime I for possible heat transfer enhancement and Regime II for heat transfer deterioration. Regime I enhances heat transfer if WDWC approaches Wo DWC, but may deteriorate heat transfer if WDWC deviates Wo DWC too much. The maximum heat transfer enhancement ratio is 1.67 compared with purely hydrophobic surface. Regime II always deteriorates heat transfer. Our work provides a general guideline to design biphilic surface for performance improvement.
Introduction
Condensation heat transfer enhancement is important to reduce equipment size, metallic consumption and investment cost of condensers. Condensation includes filmwise condensation (FWC) on hydrophilic surface and dropwise condensation (DWC) on hydrophobic surface. The liquid film thickness plays important role on FWC [1]. Various methods have been proposed to decrease liquid film thickness to enhance FWC [2–۴]. Heat transfer coefficient of DWC is one or two magnitudes higher than that of FWC [5]. For DWC, the droplet detachment radius rmax greatly affects heat transfer [6], noting that rmax is also the maximum radius of droplet that can stay on hydrophobic surface. When a droplet reaches rmax, the droplet can be detached. DWC can be enhanced by reducing rmax. The value of rmax depends on droplet detachment modes. Xie et al. [7,8] investigated droplet detachment modes on uniform wettability surfaces, including sliding, rolling and jumping. For contact angle θ<126ο, droplet detaches the surface by sliding mode. For θ>147ο, droplet detaches the surface by rolling mode. Besides, the droplets-coalescence-induced-jumping can occur on nanostructured superhydrophobic surface, decreasing rmax [9]. Such surface is expected to enhance DWC. Many studies have been reported about DWC on superhydrophobic surface.