Detection of frost growth and distribution on louver and offset strip fins of a microchannel heat exchanger using capacitance sensing approach

Frost growth and distribution on a microchannel heat exchanger (MCHX) are measured using a capacitance sensing approach. Capacitive sensors using two electrode layouts are developed to detect the real-time frost growth in the direction along and perpendicular to the airflow. Frosting and defrosting experiments are conducted under different air and coolant temperatures on both louver fins and rectangular offset strip (ROS) fins. The results demonstrate that the frost thickness is measured on the actual heat exchanger surface with an estimated uncertainty of ± 0.128 mm (95% confidence). A delay of frost growth on the trailing edge is captured by the sensor for both fin structures, and a larger frost thickness is obtained under lower air and coolant temperatures. The fin shape effect on the frost distribution profile is also characterized using the sensor. Compared to that on louver fin, the frost thickness at the leading edge of ROS fin is larger, as is the frost thickness difference between the leading and trailing edges. Due to the louver effect, the frost is more uniformly distributed over the fin. Based on the capacitance data at five locations, a frost distribution map is constructed and agrees well with frost imaging. This work demonstrates the development and application of a novel method for frost distribution detection for heat exchangers, providing a powerful tool for the study of the frosting process and defrost control.