Condensation Phenomena in Modified Micro/Nano-Scale Functional Surfaces

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

Peterson, G.P. 'Bud' Rensselaer Polytechnic Institute "Condensation Phenomena in Modified Micro/Nano-Scale Functional Surfaces" The structural and physical properties of a surface can have a significant effect on the condensation/evaporation phenomena that occurs on solid-vapor or solid-liquid interfaces. Modern micro/nano fabrication and other surface modification techniques make it possible to develop a series of multifunctional surfaces that can enhance or suppress the condensation/evaporation by modifying the property characteristics of the surface. Investigation of the condensation phenomena, in or on functionally specified surfaces, has practical applications in many fields, including phase change heat transfer devices such as heat pipes or capillary pumped loops, microelectronics, biochemical devices, nuclear reactors, bioreactors, capillary transport systems for spacecraft thermal control systems, fuel cells, MEMS devices and geothermal applications. Through a better understanding of the mechanisms that govern the fundamental transport phenomena in these micro/nano scale porous structures, new techniques it may be possible to develop new improved technologies for utilization in these fields and devices. Numerous theoretical and experimental investigations have been conducted on surfaces modified either to promote dropwise condensation or to improve filmwise condensation. The surface-modifying methods utilized include lowering the surface energy to obtain dropwise condensation and changing the geometric shape of the surface to reduce the thickness of a condensate, thereby enhancing the heat transfer coefficient. In addition, the condensation/evaporation on or in porous media has received increasing levels of interest in recent years. However, research on the thin film condensation phenomena in or on micro/nano-porous surfaces is not currently available. Because of the small-scale structures and the special surface modifying methods employed, these modified micro/nano-porous surfaces have novel properties related to the wetability, surface tension and capillarity. The condensation phenomena that occur in these modified micro-porous surfaces are not clearly understood and require intensive study from both a theoretical and experimental perspective. The objective of the proposed research is to develop multifunctional surfaces and investigate the condensation phenomena occurring in and on those surfaces. Analytical models describing the capillary condensation and fluid flow, coupled with the characteristic parameters of the micro/nano-porous structures, surface energy, interface tension, wetting characteristics and disjoining pressure, will be established to predict the condensation heat transfer performance. A unique experimental system, in which capillary phenomena is employed to pump the working fluid and thereby maintain a thin condensate film, will be established to evaluate the condensation performance. A series of micro/nano-porous surfaces, which will be fabricated by sintering, chemical vapor deposition, or glancing angle deposition techniques and modified by advanced technologies developed in recent years such as dynamic ion-beam mixed implanting, low temperature plasma polymerization, self-catalyzed chemical deposition, physical vapor deposition and plasma enhanced chemical vapor deposition, will be investigated to examine the effect of micro-structural and physical properties of the surface on the condensation and the induced fluid flow. The results of the experimental investigation will then be compared with the theoretical predictions in order to determine the fundamental parameters governing the condensation phenomena occurring in and on the surfaces. State-of-the-art measuring techniques will be used to monitor the formation of droplets or thin liquid films in the micro/nano-porous cells, and to measure the physical parameters such as characteristic length, porosity, permeability, surface energy and wetability of the micro-porous surfaces, which all have a significant effect on the condensation/evaporation phenomena and using the above methodologies are all controllable. By carefully controlling the physical parameters, the resulting thermophysical parameters, such as interface instability, thermocapillary flow, and contact angle variation can also be adjusted, allowing variations in the disjoining pressure, frictional shear stress, curvature of liquid film and wetting characteristics. The broader impacts of the proposed research consists of (1) advancing the discovery and understanding of the fundamental mechanisms of the transport phenomena in and on micro/nano-porous surfaces and the integration of this information through the research and education of graduate and undergraduate students; (2) establishing collaborations between engineering, advanced surface science, transport phenomena and physics due to the interdisciplinary nature of this research project and the sharing of multidisciplinary research facilities and technologies; (3) disseminating the results of this investigation through the conventional distribution methods, which include publication of refereed journal articles, conference proceedings and presentations, invited lectures, and periodic progress reports distributed to the NSF and the associated agency facilities, and placing information on the Two-phase Heat Transfer Website at http://twophaseheat.rpi.edu/ in which the latest research results on past and ongoing projects underway in Two-phase Heat Transfer Laboratory are presented; (4) development of extensive practical applications in many fields such as the thermal control of microelectronic devices/system, capillary transport and thermal control systems of aerospace, biochemical devices, nuclear reactors, bioreactors, fuel cells, MEMS devices and geothermal applications.