Real-time monitoring of frost/defrost processes using a tapered optical fiber

A tapered fiber sensor was developed to detect the presence of condensed water and frost. The rough surface of the tapered fiber efficiently scattered the light propagating through the tapered fiber. The scattering loss is selective to the medium surrounding the tapered region of the fiber. Compared to the transmission intensity in the air, liquid water on the tapered fiber causes a 40% increase in transmission, whereas the presence of frost decreases the light transmission by 15%. Frost induces roughness on the surface of the tapered fiber and as a result increases light scattering and transmission losses. In contrast, liquid water uniformly covers the tapered fiber surface and reduces the light scattering. Furthermore, the amount of frozen water on the tapered surface is related to the duration of the transmission intensity peak during the defrosting process. The proposed detection scheme based on a rough tapered fiber can be utilized in real-time remote monitoring systems of the frost formation in large refrigeration systems.