Efficient utilization of cold energy enabled by phase change cold storage brine gels with superior thermophysical properties towards biochemical reagent cold chain

Phase change cold storage, as an emerging cold chain method of maintaining a low-temperature environment and effectively ensuring the quality of biochemical reagents, is extensively utilized because of its benefits of high energy density, low cost, energy conservation and environmentally friendly mode. However, the low thermal conductivity of working medium affects its cold charging/discharging rate and operating efficiency. Meanwhile, the high leakage characteristic in the phase change process leads to a decrease of cold storage capacity and contamination of items. This work proposes the efficient utilization of cold energy enabled by leakage-free phase change cold storage brine gels with extraordinary high thermal conductivity towards biochemical reagent cold chain. Phase change thermal storage gel is prepared by confining brine in the sodium polyacrylate‑calcium alginate network and porous adsorption of expanded graphite. The prepared materials present leak free characteristics and almost 100% mass retention rate. Expanded graphite addition enables the thermal conductivity increase from 0.542 W m−1 K−1 to an extremely high value of 2.766 W m−1 K−1 (an increase of 510%). The enthalpy value of the cold storage brine gel is as high as 144 Jg−1, stably releasing cold at around −24 °C. By regulating the distribution of cold storage working medium, the minimum temperature difference inside the apparatus can be reduced from 6.7 °C to about 1 °C. Finally, performance-enhancing phase change cold storage materials and apparatus in the cold chain of biological reagents is fruitful, effectively providing a long-lasting and uniform low-temperature environment.