Development of optical naphthalene sublimation method

The naphthalene sublimation technique is one of the most convenient mass transfer methods to determine local heat transfer coefficient by using the heat and mass transfer analogy; however, it has difficulties in molding the naphthalene and measuring the naphthalene thickness in arbitrary shapes. This study introduces a new naphthalene thickness measurement technique using an optical method to be applied to arbitrary shapes. Naphthalene coating is made on an arbitrarily-shaped glass substrate using vapor plating. Later, collimated laser light is illuminated onto it and a CCD camera detects the scattered light to measure the thickness before and after the sublimation process. The correlations between the naphthalene thickness and the signal strength of the CCD image are preliminarily found. With the correlations, four wind tunnel experiments with flat plate, wedge, plate-wedge and cylinder flow are performed. The results demonstrate the capability of accurately measuring the naphthalene thickness in a fast optical manner, which eventually enables a more universal naphthalene sublimation technique.