Real-time frost porosity (density) measurement using capacitive sensor.

In this work, a capacitance sensing approach has been developed to remote detect the frost porosity in real-time. An interdigital electrode was designed and fabricated to sense the capacitance changing during the frost growth based on the fringing effect. Frost growth under the same surface temperature, air temperature and relative humidity but different air velocity was observed. The averaged approach by measuring the frost mass and volume was also adopted for comparison. Result shows that the frost porosity measured by the capacitance sensing approach agrees well with the averaged measurement approach with a maximum difference of 12%. The capacitance sensing approach can measure the frost dielectric constant in good agreement with the prediction of the Maxwell-Garnett’s theory as well. This approach shows great potential for real-time precise frost detection and defrost control.