The use of a mass transfer technique to infer heat transfer coefficients on film cooled turbine components

The swollen polymer technique is a method for measuring mass transfer coeff icients under steady-state: conditions. Heat transfer data can then be infe rred by analogy, as with the more familiar naphthalene sublimation techniqu e. The swollen polymer technique has two significant advantages. Firstly, it c an be used with interferometric measuring methods to give a panoramic view of the distribution of the transfer coefficient over the working surface. S econdly, the mass transfer process is reversible, allowing repeated use of the working surface. Changes in thickness of a polymer coating on the working surface, initially swollen with an ester, are measured, using holographic interferometry to y ield a fringe pattern depicting loci of equal transfer coefficient over the surface. The paper describes the basis of the method, its advantages, limitations an d future potential. Extension of the technique for the simultaneous measurement of effectivenes s and heat transfer coefficient is described and its further extension for use with curved surfaces is outlined.