A novel silicon bi-textured micropillar array to provide fully evaporated steam for a micro-Rankine cycle application

• Published in: Journal of physics. D, Applied physics Applied physics, 2014-11, Vol.47 (47), p.475301-7
• Main Authors: Azarkish, H, Behzadmehr, A, Fanaei Sheikholeslami, T, Sarvari, S M H, Fréchette, L G
• Format: Article
• Language: English
• Subjects: Arrays; Droplets; Evaporation; fully evaporated steam flow; Liquids; Microstructure; phase change; Pulsation; Reactive ion etching; rough-smooth microstructures; Silicon
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/47/47/475301

In the present work, a novel silicon micropillar array with rough and smooth sections is introduced as a microstructured evaporator to provide a stable flow of fully evaporated steam without any pulsations or liquid droplets. Two mechanisms are proposed to increase the performance of a micro-evaporator. The first one consists of increasing the water spreading over the evaporator area by creating rough surfaces at the base of the micropillars, which also tends to increase the surface for thin film evaporation. The second mechanism is to prevent the formation of water droplets over the micropillar array with a higher surface energy barrier created by a smooth portion at the top of the pillars. The rough-smooth micropillar arrays were fabricated using deep reactive ion etching over a 1 cm2 membrane with through holes to continuously provide the liquid. Experimental measurements and observations show that the maximum rate of fully evaporated steam is increased by 52% to 122%, for a surface temperature range of 95 to 125 °C, by using the proposed rough-smooth microstructures instead of only smooth silicon microstructures.