Origin of the infra-red emission peak in freezing water
Paper published May 8, 2018
When droplets of purified water (1–5 ll) were cooled from the bottom, they slowly and continuously supercooled before releasing latent heat as a transient burst of infra-red (IR) radiation. In order to determine the role of this IR emission, a thin rectangular water layer was cooled unilaterally while imaged from above by an infrared (FLIR) camera. The first noticeable event was an IR burst that rapidly (\0.1 s) moved through a 5-mm-long path of water. Final solidification of the water layer was recognized by an increase in volume, as the meniscus at the air interface changed from concave to convex. The propagation of the IR burst through the water layer preceded the first visible onset of volume increase and solidification by more than one second. The transient and early appearance of the IR burst belongs to what is called the first stage of freezing. This stage has been linked to the formation of so-called spongy ice. Both IR burst and pinnately shaped spongy ice appear at the same time and share a short transient existence. It is only this early type of ice that is associated with the IR burst. By contrast, the later-occurring solid ice formation parallels a diminishing IR emission.