H. R. Salimijazi, T. Behzad, J. Mostaghimi,
Volume 31, Issue 1 (6-2012)
Abstract
Open pore metallic foams can be used for high temperature, high performance heat exchanger due to their high gas permeability and heat conductivity provided that skins properly attach to the foam’s struts on the surface. In the current study, a novel process was successfully developed to fill pores on the surface of the foam sheet in order to deposit skin on the foam specimens by thermal spraying. Nickel based superalloy (Inconel 625) skins were deposited on each side of a sheet of nickel metal foam with different pore densities of 10 and 20 pores per inch by high velocity oxy-fuel (HVOF), atmospheric plasma spraying (APS), and twin wire arc spraying to form a sandwich structure. The sandwich structure can be used in high temperature heat exchanger applications. The penetration of the coating materials into the foam struts can be controlled through the filling process before spraying. The microstructure of the skins and the adhesion at the interface between the nickel foam’s struts and skins were characterized. Results showed dense skins with good adhesion to the surfaces of the foam. The foam’s struts were imbedded into the coatings deposited by HVOF more deeply than the coatings deposited by APS and wire arc spraying. Skins deposited by HVOF and wire arc spraying showed higher bending strength than the skin deposited by APS due to lower porosity and oxide content in the coating.
M. Emami, Sh. Hayashi,
Volume 38, Issue 3 (12-2019)
Abstract
The outer surface of heat exchanger tubes that work under fluidized bed waste or biomass incineration is exposed to severe high-temperature erosion-corrosion (E-C). To evaluate the behavior and enhance the service life of the tubes, the real service conditions ought to be simulated in the laboratory. In this study a test rig with a fluidized bed of hot sand was designed and manufactured to expose nickel-based SFNi4 alloy to high-temperature E-C. In order to increase the corrosiveness of the environment, the silicon oxide sand was mixed with 0, 0.5 and 1 wt.% of a mixture of NaCl and KCl salts with 1:1 molar ratio. The erosive conditions of the environment were changed by altering air flow rate from 20 to 25 L/min and changing the sand incident angle from 45 to 90 degrees. The rate of material removal was calculated by measuring the thickness of each sample before and after the test. After each experiment, the surface and cross-section of specimens were studied using SEM and EDS analysis. Finally, the optimum E-C parameters to ensure actual industrial conditions were obtained.
