Scale Effect on Dropwise Condensation on Superhydrophobic Surfaces
By Ching-Wen Lo, Chi-Chuan Wang and Ming-Chang Lu Journal: ACS Applied Materials & Interface Year of Publication: 2014 Imapct Factor: 5.900
Abstract Micro/nano (two-tier) structures are often employed to achieve superhydrophobicity. In condensation, utilizing such a surface is not necessarily advantageous because the macroscopically observed Cassie droplets are usually in fact partial Wenzel in condensation. The increase in contact angle through introducing microstructures on such two-tier roughened surfaces may result in an increase of droplet departure diameter and consequently deteriorate the performance. In the meantime, nanostructures roughened surfaces could potentially yield efficient shedding of liquid droplets, whereas microstructures roughened surfaces often lead to highly pinned Wenzel droplets. To attain efficient shedding of liquid droplets in condensation on a superhydrophobic surface, a Bond number (a dimensionless number for appraising dropwise condensation) and a solid-liquid fraction smaller than 0.1 and 0.3, respectively, are suggested.
Solar-Thermal Energy harvesting Scheme: Enhanced heat capacity of molten HITEC salt mixed with Sn/SiOx core-shell nanoparticles
By Chih-Chung Lai, Wen-Chih Chang, Wen-Liang Hu, Zhiming M. Wang, Ming-Chang Lu, and Yu-Lun Chueh Journal: Nanoscale Year of Publication: 2014 Imapct Factor: 6.739
Abstract We demonstrated enhanced solar-thermal storage by releasing the latent heat of Sn/SiOx core-shell nanoparticles (NPs) embedded in a salt eutectic. The microstructures and chemical compositions of Sn/SiOx core-shell NPs were characterized. In-situ heating XRD provides dynamic crystalline information of Sn/SiOx core-shell NPs during cyclic heating processes. The latent heat of ~29 J/g for Sn/SiOx core-shell NPs was measured, and the 30 % enhanced heat capacity was achieved from 1.57 to 2.03 J/gK for the HITEC solar salt without and with, respectively, a mixture of 5 % Sn/SiOx core-shell NPs. In addition, an endurance cycle test was performed to prove a stable operation in practical applications. The approach provides a method to enhance energy storage in solar-thermal power plants.
Graphical Abstract
Spatial Control of Heterogeneous Nucleation on the Superhydrophobic Nanowire Array
By Ching-Wen Lo, Chi-Chuan Wang and Ming-Chang Lu Journal: Advanced Functional Materials Year of Pulication: 2013 Impact Factor: 10.439
Abstract We report the ability to spatial control heterogeneous nucleation on a superhydrophobic surface by manipulating the free energy barrier to nucleation through parameterizing regional roughness scale on the Si nanowire array-coated surface. Water vapor preferentially condenses on the designed microgrooves on the Si nanowire surface and continuous shedding of the drop-wise condensate is observed on the surface. The nucleation site density can also be manipulated by tailoring the density of the microgroove on the surface. Moreover, the cycle time on the Si nanowire array with microgrooves is approximately ten times smaller than that on a plain Si surface. This suggests that potentially high heat and mass transfer rates can be achieved on the surface. The insight from this study has implications in enhancing energy efficiency in a wide range of thermal energy conversion systems.