Development of optical naphthalene sublimation method and its application to wavy channel flows

Abstract

Optical naphthalene sublimation method to measure the heat and mass transfer characteristics on arbitrary shapes is developed. Naphthalene vapor deposition technique is employed to coat on naphthalene various and complex specimens. Optical experiment is performed to find the correlation between the naphthalene thickness and the optical signal intensity. Wind tunnel experiments on a flat plate, wedges and a cylinder are performed to validate the developed optical naphthalene sublimation method. Then, wavy channels are experimented to further demonstrate this method for industrial applications. Flow visualization using smoke generation technique is also carried out to understand the flow characteristics. Naphthalene thickness using vapor deposition is easily controlled by varying the deposition time under the vacuum condition at 150 Torr. The more time elapses, the thicker naphthalene layer is formed. Coating thickness varies from 20 to $80 \mu m$ with a very fine, uniform surface, the nonuniformity of thickness is 1.2% with a 95% confidence. Correlations between the naphthalene thickness and the signal intensity of the CCD image are experimentally found by using He-Ne laser, CCD camera, optics and image board. The light intensity detected behind the coating decreases when the incidence angle is large and when the coating is thick. The light intensity decreases mainly because of scattering when the naphthalene coating is thicker. The correlation is obtained in a polynomial. With the correlations, four wind tunnel experiments with flat plate, wedge, plate-wedge and cylinder flow are performed to verify the proposed method. The transverse-averaged experimental results are in good agreement with the numerical solution with fairly high individual scatter at an x-location. The total uncertainty of experimental precision error of the transverse- averaged data is 9.7% with a 95% confidence. Internal wavy surface flows for three different wall shapes are f...