New Application Technique for Gold Deposited Mylar Film

Abstract

Gold deposited Mylar film is commonly used to establish a constant heat flux convective boundary condition for wind-tunnel test surfaces. To minimize conduction through the test plate and promote a constant flux boundary, the accepted technique for mounting Mylar film to a surface is to apply the film oriented as gold-side up. However, the accepted mounting technique causes problems if the films are used to explore convective heat transfer from surfaces with high thermal conductivity protuberances and surface roughness. If high thermal conductivity elements are attached to the side with the gold layer, the local resistance of the film is lowered and hotspots with local increases in heat generation are created. To overcome the problems with roughness-element attachment, a new technique for mounting gold-deposition Mylar film in a gold-side down orientation was developed. This new application technique allows for the roughness elements to be mounted to the plastic side of the film while ensuring that the heat generation from the gold-deposition side is not disrupted. However, with this inverted mounting orientation, conduction into the test plate and conduction through the Mylar film must be considered when determining local convection coefficients. To validate measurements of convection coefficients made using the Mylar film and the new application technique, a series of test measurements has been performed using spherical segment roughness elements applied to a heated vertical test plate in natural convection. The temperature distributions of both sides of the test plate were measured using an infrared camera. The resulting unperturbed convection coefficients and the protuberance fin efficiencies are in general agreement with classical correlations for the test situations.