Phase change heat transfer at the micro and nano scales has been a topic of much interest for over two decades. In addition to fundamental studies of evaporation, boiling and condensation, new interesting directions have started to emerge in the past few years. These topics include novel enhancement and manipulation techniques, e.g., electric field-based control, better instrumentation techniques, e.g., plasmonic sensing, and less explored phase change heat transfer processes, e.g., frosting and liquid/liquid phase separation. This special issue attempts to capture some of these advancements and insights. It also aims to supplement and expand on the previous special issue published in Nanoscale and Microscale Thermophysical Engineering, 18 (3), 2014.
Financial support from federal agencies in the United States for research and development pertinent to convective heat transfer in diminishing length scales has been very generous until very recently. Most notably, the Defense Advanced Research Projects Agency (DARPA) invested about $30 M to support two major Intrachip/Interchip Enhanced Cooling (ICECool) initiatives to address the significant thermal management challenge in gallium nitride amplifiers. The Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) invested about $100 M to support research and development efforts in building cooling equipment and air conditioners (BEETIT), thermal storage (HEATS), and dry power plant cooling technologies (ARID). The Thermal Program from the Office of Naval Research and the Thermal Transport Processes Program from the National Science Foundation have been strong supporters of phase change heat transfer for a long time; their support is expected to continue. The significant federal support, in addition to industry support, has led to an increased number of publications in the area.
In this special issue, we have four unique contributions. The first paper by Kabov et al. focuses on understanding microdroplet trajectories as it experiences a region of intense evaporation near the contact line. Not only is the work fundamentally interesting, but also it provides an experimental method to probe the flow patterns in moist air near the contact line. The second paper by Park et al. develops an approach using nanoscale plasmonic structures with ultrafast pump-probe spectroscopy to investigate the adsorbed layer of liquid evaporation and condensation. With such a technique, unique insights about the thickness of the adsorbed layer and the effective evaporation coefficient can be obtained. The third paper by Nath et al. presents a review of condensation frosting, which is a significant technological challenge in many industries. The paper provides an overview of condensation frosting, explaining its distinction from icing, and offers possible approaches to prevent frost growth. Finally, the last paper by Shahriari et al. reviews the emerging opportunity to use electric fields for boiling and condensation heat transfer enhancement. The paper discusses the developments with electrically insulating and conducting liquids, and opportunities to achieve the desired manipulation capability with electric fields for heat transfer applications.
We hope that you enjoy reading this special issue and that it will inspire even more research within our field as well as in multi-disciplinary communities. In doing so, we hope that we will be closer towards addressing unresolved fundamental questions in phase change heat transfer and realizing high performance practical devices and systems.