Flow condensation heat transfer on surfaces with different wettability in mini-channel
【Abstract】The hydrophobic surface embedded with arrayed hydrophilic dots was prepared on a copper surface with mesh screen and Teflon solution. Completely hydrophilic copper surface, completely hydrophobic Teflon-coated surface and hydrophilic/hydrophobic hybrid surface are taken into consideration which serve as the bottom heat transfer area of rectangular mini-channels (1.5 mm hydraulic diameter). In this experiment, the vapor mass velocity ranges from 10 kg·m−2·s−1 to 60 kg·m−2·s−1, while the vapor quality from 0.3 to 1. According to the experimental investigation, the steam condensation heat transfer coefficient on hybrid surface is about 454.6% higher than that of the completely hydrophilic surface and 107.3% higher than the completely hydrophobic surface at most. A high-speed camera provides the photos of two-phase flow pattern, especially the periodic behavior of the droplets nucleation, coalescence and flush which can explain the mechanism of heat transfer enhancement.
【Keywords】 condensation; hydrophilic/hydrophobic surface; mini-channel; heat transfer coefficient;
(Translated by REN XF)
 SHARMA C S, TIWARI M K, ZIMMERMANN S, et al. Energy efficient hotspot-targeted embedded liquid cooling of electronics [J]. Applied Energy, 2015, 138: 414–422.
 UCKERMAN D B, PEASE R F W. High-performance heat sinking for VLSI [J]. IEEE Electron Device Letters, 1981, 2 (5): 126–129.
 CHO H J, PRESTON D J, ZHU Y, et al. Nano-engineered materials for liquid–vapour phase-change heat transfer [J]. Nature Reviews Materials, 2016, 2 (2): 16092.
 FLETCHER N H. Size effect in heterogeneous nucleation [J]. Journal of Chemical Physics, 1958, 29 (3): 572–576.
 KIM S, KIM K J. Dropwise condensation modeling suitable for superhydrophobic surfaces [J]. Journal of Heat Transfer, 2011, 133 (8): 081502.
 DANIEL A, CHRISTOPHE F, BETZ A R, et al. Surface engineering for phase change heat transfer: a review [J]. MRS Energy & Sustainability—A Review Journal, 2014, 1: 1–40.
 MILJKOVIC N, ENRIGHT R, WANG E N. Effect of droplet morphology on growth dynamics and heat transfer during condensation on superhydrophobic nanostructured surfaces [J]. ACSNano, 2012, 6 (2): 1776–1785.
 NAM Y, KIM H, SHIN S. Energy and hydrodynamic analyses of coalescence-induced jumping droplets [J]. Applied Physics Letters, 2013, 103 (16): 161601.
 PARKER A R, LAWRENCE C R. Water capture by a desert beetle [J]. Nature, 2001, 414: 33–34.
 HOU Y, YU M, CHEN X, et al. Recurrent filmwise and dropwise condensation on a beetle mimetic surface [J]. ACS Nano, 2015, 9 (1): 71–81.
 BOREYKO J B, HANSEN R R, MURPHY K R, et al. Controlling condensation and frost growth with chemical micropatterns [J]. Scientific Reports, 2016, 6: 19131.
 XIE J, XU J, HE X, et al. Large scale generation of micro-droplet array by vapor condensation on mesh screen piece [J]. Scientific Reports, 2017, 7: 39932.
 WANG Y, ZHANG L, WU J, et al. A facile strategy for the fabrication of a bioinspired hydrophilic–superhydrophobic patterned surface for highly efficient fog-harvesting [J]. Journal of Materials Chemistry A, 2015, 3 (37): 18963–18969.
 CHATTERJEE A, DERBY M M, PELES Y, et al. Condensation heat transfer on patterned surfaces [J]. International Journal of Heat & Mass Transfer, 2013, 66 (66): 889–897.
 CHATTERJEE A, DERBY M M, PELES Y, et al. Enhancement of condensation heat transfer with patterned surfaces [J]. International Journal of Heat & Mass Transfer, 2014, 71 (4): 675–681.
 CHEN X, DERBY M M. Combined visualization and heat transfer measurements for steam flow condensation in hydrophilic and hydrophobic mini-gaps [J]. Journal of Heat Transfer, 2016, 138 (9): 091503.
 FANG C, STEINBRENNER J E, WANG F M, et al. Impact of wall hydrophobicity on condensation flow and heat transfer in silicon microchannels [J]. Journal of Micromechanics & Microengineering, 2010, 20 (4): 045018.
 DERBY M M, CHATTERJEE A, PELES Y, et al. Flow condensation heat transfer enhancement in a mini-channel with hydrophobic and hydrophilic patterns [J]. International Journal of Heat & Mass Transfer, 2014, 68 (1): 151–160.
 KUMAGAI S, TANAKA S, KATSUDA H, et al. On the enhancement of filmwise condensation heat transfer by means of the coexistence with dropwise condensation sections [J]. Experimental Heat Transfer, 2007, 4 (1): 71–82.
 PENG B, MA X, ZHONG L, et al. Experimental investigation on steam condensation heat transfer enhancement with vertically patterned hydrophobic–hydrophilic hybrid surfaces [J]. International Journal of Heat & Mass Transfer, 2015, 83: 27–38.
 GARIMELLA M M, KOPPU S, KADLASKAR S S, et al. Difference in growth and coalescing patterns of droplets on bi-philic surfaces with varying spatial distribution [J]. Journal of Colloid & Interface Science, 2017, 505: 1065–1073.
 BAI H, WANG L, JU J, et al. Efficient water collection on integrative bioinspired surfaces with star-shaped wettability patterns [J]. Advanced Materials, 2014, 26 (29): 5025–5030.
 MACNER A M, DANIEL S, STEEN P H. Condensation on surface energy gradient shifts drop size distribution toward small drops [J]. Langmuir the ACS Journal of Surfaces & Colloids, 2014, 30 (7): 1788–1798.
 GHOSH A, BEAINI S, ZHANG J, et al. Enhancing dropwise condensation through bioinspired wettability patterning [J]. Langmuir the ACS Journal of Surfaces & Colloids, 2014, 30 (43): 13103–13115.
 HOLMAN J P, GAJDA W J. Experimental Methods for Engineers [M]. 4th ed. New York: McGraw-Hill, 1994
 KIM S M, MUDAWAR I. Universal approach to predicting heat transfer coefficient for condensing mini/micro-channel flow [J]. International Journal of Heat & Mass Transfer, 2013, 56 (1/2): 238–250.
 CAREY V P. Liquid–vapor Phase-change Phenomena [M]. 2nd ed. CRC Press, 2007: 169–172.
 MA X H, LAN Z, WANG K, et al. Dancing droplet: interface phenomena and process regulation [J]. CIESC Journal, 2018, 69 (1): 9–43 (in Chinese).
 WANG H, LIAO Q, ZHU X, et al. Mechanism of liquid droplet movement on surface with gradient surface energy [J]. Journal of Chemical Industry and Engineering (China), 2007, 58 (9): 2313–2320 (in Chinese).
 XIE J, LIU Q, HE X T, et al. Dimensionless critical criterion for the sliding of droplet on tilt surface in shear flow [J]. Journal of Engineering Thermophysics, 2017, 38 (5): 1033–1038 (in Chinese).