Further development and experimental testing of a resistive sensor for monitoring frost formation in refrigeration systems

This work has been supported by the project Centro-01-0145-FEDER-000017 - EMaDeS - Energy, Materials and Sustainable Development, co-financed by the Portugal 2020 Program (PT 2020), within the Regional Operational Program of the Center (CENTRO 2020) and the European Union through the European Regional Development Fund (ERDF). The authors wish to thank the opportunity and financial support that permitted to carry on this project.Refrigeration systems are widely accepted as a mean to prevent food degradation. These systems usually rely on fin-and-tube heat exchangers to lower the air temperature. Due to long operation times and surface temperatures below dew point, frost may form and accumulate on the evaporators fin surface. This frost accumulation reduces and may clog the airflow, decreasing the system efficiency. Usually, most systems use a time-controlled system (stopping the compressor with or without powering a heating resistor inserted among fins to heat) to melt the ice. This method does not measure or predict the amount of frost formed, thus it is not reliable. Ice sensors that are cheap, reliable and easy to implement in commercial systems are studied. A resistive sensor is purposed, that measures the voltage between two electrodes with the water phase change (condensation and solidification -freezing-), as these states have different resistive values. Different electrode materials, morphologies and configurations are studied in order to obtain the best design.