New experimental apparatus for investigation of condensation over plain and nano-engineered surfaces

Nano-engineered surfaces have been recently studied as a promising solution for many heat transfer applications. In particular, superhydrophobic surfaces, obtained combining low surface energy and proper surface texturing, have been proposed as a viable and efficient way to promote dropwise condensation (DWC), which leads to higher heat transfer coefficients as compared to filmwise condensation (FWC). In the open literature available information regard the fabrication and characterization of these surfaces, but very few results on the heat transfer performance are published. In the design and fabrication of an experimental apparatus for studying dropwise condensation one has to face some challenges: the heat flux must be determined indirectly, by looking at the coolant side or at the wall, and, for an accurate evaluation of the heat transfer coefficient, a precise evaluation of the surface temperature is required. In this paper, a new experimental apparatus for investigation of filmwise and dropwise condensation of pure steam, flowing at different velocities, is presented. The calibration of the technique is done using a plain surface and thus preliminary test results of condensation on an untreated aluminum surface are reported.