Surface Engineering for Phase Change Heat Transfer: A Review

Among numerous challenges to meet the rising global energy demand in a sustainable manner, improving phase change heat transfer has been at the forefront of engineering research for decades. The high heat transfer rates associated with phase change heat transfer are essential to energy and industry applications; but phase change is also inherently associated with poor thermodynamic efficiencies at low heat flux, and violent instabilities at high heat flux. Engineers have tried since the 1930's to fabricate solid surfaces that improve phase change heat transfer. The development of micro and nanotechnologies has made feasible the high-resolution control of surface texture and chemistry over length scales ranging from molecular levels to centimeters. This paper reviews the fabrication techniques available for metallic and silicon-based surfaces, considering sintered and polymeric coatings. The influence of such surfaces in multiphase processes of high practical interest, e.g., boiling, condensation, freezing, and the associated physical phenomena are reviewed. The case is made that while engineers are in principle able to manufacture surfaces with optimum nucleation or thermofluid transport characteristics, more theoretical and experimental efforts are needed to guide the design and cost-effective fabrication of surfaces that not only satisfy the existing technological needs, but also catalyze new discoveries

Electrospinning: A study in the formation of nanofibers

Electrospinning is a technique to produce nanofibers more efficiently. In electrospinning, electricity spins fibers by extracting the polymer from the solvent and stretching it, all in one continuous electric field. Basics of electrospinning are discussed in sequence from simple homogenous fibers through a single nozzle to heterogeneous core-shell fibers from double, concentric nozzles. Experimental set-up is described and the effect of different variables in the process of electrospinning on nanofiber quality is illustrated. Formation of carbon nanotube fibers with porous walls from polyethylene oxide/polyacrylnitrile (PEO/PAN) core-shell fibers is the definitive objective.Zipped LaTex file</jats:p