Heat transfer by unstable solution having the lower critical solution temperature

In this article, we present new data on the non-stationary heat transfer by partially-soluble binary liq-uids in the course of deep penetration into the region of their metastable and unstable (short-term su-perheated with respect to the diffusion spinodal) states. The object of research was an aqueous solution of polypropylene glycol-425 having the lower critical solution temperature (LCST). In the course of pulse experiments, the superheating degree reached 200 K at the heating rate of 10 5 K/s. The main heating mode was the constant power mode with a characteristic pulse length of 10 ms. The pressure, being the parameter changeable in a series of measurements, was varied from 1 to 100 MPa. Upon reaching a certain superheating degree, a significant enhancement of heat transfer (EHT) has been revealed. We associate this result with the spinodal decomposition, which is the natural relaxation mechanism in the considered part of the phase diagram. An unexpected result was the detection of the deteriorated heat transfer stage, preceding the stage of EHT. These stages reflect the characteristic features of the spinodal decomposition at the given conditions. The significant effect of EHT confirms the prospects of using the solutions with LCST as coolants. A model of heat transfer during the decay of an unstable solution has been developed. It is based on an analysis of the nucleation, growth and motion of a new phase domain in the field of temperature gradient. The simulation results are consistent with the results of experiments under conditions of powerful heat release and small temporal and spatial scales . (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This article presents new data on the non-stationary heat transfer of partially-soluble binary liquids. The study focuses on an aqueous solution of polypropylene glycol-425 with a lower critical solution temperature. The experiments show a significant enhancement of heat transfer at a certain superheating degree, which is attributed to spinodal decomposition. The study also reveals a stage of deteriorated heat transfer prior to the enhancement stage. These findings have implications for the use of solutions with a critical solution temperature as coolants.