New discoveries presented in the last decade for enhancing boiling performance utilizing nanoscale structures on surfaces are critically examined in this paper. Since the mechanism for such a phenomenon is not fully understood, this review mainly focuses on the experimental studies reported in the literature on the boiling phenomena on nanostructures, and implementation of nanostructures on various substrates. The paper also focuses on the interpretation of underlying phenomena for enhancing the boiling performance. The main influencing parameter in controlling is seen as the change in the surface energy of the boiling surface, which is characterized by the contact angle of the liquid and vapor phase interface at the heating surface. The nanostructures are seen to alter the contact angle. Design consideration and theoretical developments are also discussed, followed by practical aspects of nanostructure manufacturing. The issues related to performance, ease of fabrication, and durability (whenever available) are reviewed and recommendations are made for future research in this emerging area.
1 January 1999 in Journal of Microelectromechanical Systems
A microhand, approximately in fist diameter, has been developed with microelectromechanical systems technology to mimic the human hand in microscale. The hand has multiple microfingers, composed of silicon phalanges and polymer-balloon joints. By pneumatically inflating and deflating the balloon joints, the microfingers perform the motions of flexion and extension. This device possesses attractive characteristics: (i) gentle but strong holding, (ii) out-of-plane enclosure, (iii) active grasping, (iv) being inert to surroundings, and (v) reliable monolithic construction. It operates in both air and aqueous environments, as well as demonstrates grasping, stretching, and detaching of soft objects in submillimeter scale for biological applications.
A new technique utilising electrochemical deposition with the assistance of porous alumina membranes as the fabrication template is developed to directly grow metallic nanowires on different substrates. To emphasise the nanowire application in boiling enhancement, Cu nanowire (CuNW) has been successfully fabricated on Si, Au and Cu substrates with improved thermal properties and mechanical reliability. Several process parameters to control the CuNW growth have been discussed. The nanowire structures applied in pool boiling enhancement are further investigated and significant enhancements are observed with all the surfaces with nanowire structures.
25 September 2012 in Journal of Micromechanics and Microengineering