Transient freezing of water between two parallel plates: A combined experimental and modelling study

Abstract

The transient freezing/solidification of water subjected to shear flow inside a rectangular cell is investigated under laminar flow conditions. A flow of freezing water is established inside the cell by cooling the top surface of the conductive, copper plate that forms the cell's top side by contact with boiling liquid nitrogen (−197 • C). This results in an ice layer that forms and grows gradually on the ceiling of the cell, which is subjected to shear from the flow below it inside the channel. The spatiotemporal characteristics of the ice layer are recorded with optical, laser-based measurements and are compared with predictions from a transient freezing model that is developed for this purpose. Furthermore, tracer particles are introduced into the flow to aid the tracking of the ice layer and to allow for measurements based on particle image velocimetry (PIV) of the velocity field inside the flow during the ice-layer evolution. After an initial time-lag/'buffer' period (of 5-40 s) that depends on the flow conditions, a quasi-linear growth of the ice layer is observed, but at longer times the thickness of the ice layer reaches a maximum and then decreases again. The increase in the thickness, and hence thermal resistance, of the ice layer is counter-balanced by the decrease in the temperature of the copper plate. Furthermore, it is found that the flow is associated with symmetric velocity profiles, recorded along the vertical spanwise length between the ice layer at the top of the cell and the floor of the cell, while an increase of the velocity maxima is recorded as the ice layer gradually thickens and, consequently, the flow cross-section is reduced. A constant heat flux of 19.7 × 10 3 W m −2 is measured on the top side of the channel, while the heat transfer coefficients on the top side of the channel is found to be in the range of 90-110 W m −2 K −1 , depending on the wall temperature. Finally, from comparisons against the experimental data, it is concluded that the model developed herein is able to predict the freezing of water and growth of the ice layer in these flows over a range of water inlet temperatures and Reynolds numbers.

A combined experimental and computational study of phase-change dynamics and flow inside a sessile water droplet freezing due to interfacial heat transfer

“…The uncertainty of both velocity components does not exceed 5% inside the liquid droplet and does not exceed 20% close to the ice-water interface. Similar errors on a freezing solid-liquid interface are found by Voulgaropoulos et al [59].…”

Nano-engineered pathways for advanced thermal energy storage systems

“…In a situation where the temperature of the cold wall stays below the freezing point, the thickness of the frozen layer increases with time. 83,84 In latent heat thermal energy storage (LHTES) systems using PCMs, the heat flux through the material typically reduces when the solidification process starts because convective heat transfer is suppressed. The reduction in heat transfer rate during solidification can increase the duration of energy storage and, thus, reduce the system's efficiency.…”