The objective of this study is to investigate frost formation and growth in a spirally-coiled circular fin-tube heat exchanger. The frost thickness and growth rate were measured in the transverse and circumferential directions by varying the relative humidity (or humidity ratio), air flow rate, inlet air temperature, and fin pitch. The frost thickness was affected primarily by the relative humidity, inlet air temperature, and air flow rate. The relative humidity showed a dominant effect on the frost growth among all parameters tested. An empirical correlation for the frost thickness was developed for the spirally-coiled circular fin-tube heat exchanger as a function of the Reynolds number, Fourier number, humidity ratio, and dimensionless temperature. The mean and average deviations of the predictions using the present correlation from the measured data were 4.32% and 3.96%, respectively. (c) 2013 Elsevier Ltd. All rights reserved.