Apple-like Shape of Freezing Paraffin Wax Droplets and Its Origin

Abstract

Paraffin wax stores energy in the form of latent heat at a nearly constant temperature during melting and releases this energy during solidification. This effect is used in industrial energy storage. At the same time, the possible deformation of even small volumes of material as a result of phase change is insufficiently studied. In this paper, the physical nature of such deformation, probably for the first time, is studied on the example of a droplet of paraffin wax. An unusual change in the shape of a melted droplet of paraffin wax placed on a relatively cold glass plate was observed in the laboratory experiments. As the droplet solidifies, its upper surface becomes nearly flat, and a dimple is formed in the center of this surface, making the droplet look like a fruit (pumpkins are more commonly shaped like this, but the authors prefer apples). A series of experiments, as well as physical and numerical modeling of the droplet’s thermal state, taking into account the formation of a mushy zone between liquidus and solidus, made it possible to understand the role of gravity and gradual increase in viscosity and density of paraffin wax on changing the droplet shape and, in particular, to clarify the mechanism of formation of the dimple on its upper. It was shown that the mushy zone between the liquidus and solidus of the paraffin wax is responsible for the dimple formation.

Unidirectional Freezing of Polymer Solution Droplets

“…Noteworthily, this result is valid for our experiments in a quasi-steady case, where the time scale for front motion (∼ r / v ) is much larger than the thermal diffusion time scale (∼ r 2 /κ), with r the radius between the center of the droplet and the ice–liquid–air interface, v is the ice front velocity, and κ is the ice thermal diffusivity (m 2 /s). If transient heat transfer processes could not be neglected, the latent heat of the phase change and the thermal properties in the mushy zone, located in between the frozen and liquid solution, should be taken into account …”

An effect of a snow cover on solar heating and melting of lake or sea ice

“…This can be done using an equivalent additional heat capacity in a narrow temperature interval near the melting temperature as it was done by Dombrovsky et al (2019). This simple technique is not new and was successfully used by the author in the numerical solution of other problems to account for the latent heat of phase change of the first kind, including the general case when the so-called mushy zone is formed between solidus and liquidus (Dombrovsky et al, 2015;Roy et al, 2023). It is usually difficult to choose a realistic initial profile of temperature, T init (z), for the heat transfer calculations.…”