Convection heat transfer, Mass transfer analogy, fin, color change, HTC distribution
Quantification of local air-side heat transfer coefficient (HTC) on fin-and-tube heat exchanger fins is a challenging task, especially when the fin geometry is complex. A newly developed experimental method can obtain two-dimensional HTC distribution on fin surfaces with a high resolution (8.9 μm). In this research, a thin (20 μm) yellow coating is sprayed on the surface of the fins. The coated fins were exposed in the wind tunnel which has the tracer gas (50 ppmv ammonia) well mixed in the airflow. During the experiment, the color of coated surface changes from yellow to blue. The rate of local mass transfer is correlated with the rate of local color change. Then, by applying the analogy between heat and mass transfer, local HTCs on the fin surfaces are quantified. The method accuracy has been validated on fundamental shapes such as flat plates, and cylinders. Two-dimensional HTC distributions on a four-row wavy fin and a four-row slit fin have been obtained by employing this new method. As there is no local measurement on these geometries exists, the averaged HTCs on the fin surfaces have been critically compared to the averaged HTCs from entire heat exchanger measurements from the literature. This method has provided an accurate, robust, and inexpensive tool to evaluate local air-side HTCs for real-scale heat exchangers with complex fin geometry and multiple tube rows.