Investigation of transport properties of porous coatings from nanoparticles of aluminum oxide

In this work, coatings of nanoparticles of aluminum oxide are investigated. Photos were obtained using an electron and optical microscope. A method is proposed for the formation of a coating of nanoparticles with and without agglomerates. The transport properties of nanoparticles of aluminum oxide, silicon carbide, titanium oxide and diamond have been investigated. The effect of agglomerates of nanoparticles on the rise of liquid has been determined.

Intensification of heat transfer during pool boiling of nitrogen on surfaces with capillary-porous coatings produced by 3D-printing

The study of heat transfer, critical heat fluxes (CHF) and evaporation dynamics at pool boiling of nitrogen at atmospheric and low pressures in a stationary heat generation regimes was performed. The two flat cooper heaters with porous coatings of various structural parameters obtained by additive 3D-printing as well as smooth one were used as working surfaces. According to obtained results such coatings significantly effect on pool boiling increasing up to six times the heat transfer coefficients (HTC) in comparison with uncoated sample. For all investigated heaters and pressures, visualization of boiling was performed using a video camera from which data on the bubble departure diameters and estimates of the active nucleation site density were obtained.

Passive Flow Control for Drag Reduction on a Cylinder in Cross-Flow Using Leeward Partial Porous Coatings

This paper presents a numerical study on the impact of partial leeward porous coatings on the drag of circular cylinders in cross-flow. Porous coatings are receiving increasing attention for their potential in passive flow control. An unsteady Reynolds-averaged Navier–Stokes model was developed that agreed well with the numerical and experimental literature. Using the two-equation shear stress transport k−ω turbulence model, 2D flow around a circular cylinder was simulated at Re = 4.2×104 with five different angles of partial leeward porous coatings and a full porous coating. For coating angles below 130∘, the coating resulted in an increase in pressure on the leeward side of the cylinder. There was a significant reduction in the fluctuation of the pressure and aerodynamic forces and a damping effect on vortex shedding. Flow separation occurred earlier; the wake was widened; and there was a decrease in turbulence intensity at the outlet. A reduction of drag between 5 and 16% was measured, with the maximum at a 70∘ coating angle. The results differed greatly for a full porous coating and a 160∘ coating, which were found to cause an increase in drag of 42% and 43%, respectively. The results showed that leeward porous coatings have a clear drag-reducing potential, with possibilities for further research into the optimum configuration.