Use of melting point surface coatings for local convection heat transfer measurements in rectangular channel flows with 90-deg turns

Centrifugal forces tend to produce secondary flows around and within channel turns that can have significant effects on the convection heat transfer distribution over the channel walls. Local Nusselt number distributions are presented for 90-deg turns of radius ratios 2 and 3 in a 3 to 1 aspect ratio rectangular cross section duct oriented with the principal walls in the direction of centrifugal force. A method employing the melting phase change of a surface coating was used to determine the local heat transfer rates, and a data analysis procedure needed for quantitative application of the method to internal flows is described.