Institute of Refrigeration

Developing energy-efficient and environmentally friendly refrigeration technology is highly desired to tackle climate change. Emerging caloric effect-based cooling technologies such as magneto-, electro- and ionocaloric effects are promising but suffer from large driving field strengths, low adiabatic temperature change or insufficient power density. Here we propose a sorption-driven dissolution refrigeration cycle with an extendable thermal storage function. Theoretical and experimental results show larger adiabatic temperature change compared with solid-state caloric effects by using medium- or low-grade heat (80-150 degrees C) as the cyclic driving energy. We demonstrated the viability of a practical system using such a cycle, with experimental results showing adiabatic temperature change of 37 K and a minimum cooling temperature of -25.4 degrees C. Importantly, the sorption process allows the heat storage and flexible cold and heat supply to adapt to the diverse and complex application scenarios. This work shines light on the exploitation of renewable energy for efficient cooling and heating.

Strain engineering in two-dimensional (2D) transition metal dichalcogenides (TMDCs) offers a powerful approach to modulating their optoelectronic properties, yet understanding localized strain effects at the nanoscale remains challenging. Here, we employ an atomic force microscopy-tip-enhanced photoluminescence (AFM-TEPL) system to investigate room-temperature exciton behavior in monolayer WS2 nanobubbles formed on graphene substrates. TEPL mapping reveals distinct photoluminescence (PL) distributions, with trion emission dominating at the nanobubble apex, while neutral excitons (X0) accumulate in the edge wrinkle region. Both trion and X0 peaks exhibit a red-shift from the wrinkle to the apex driven by strain-induced band modulation. Surface potential (SP) and second-order capacitance gradient (CG) measurements indicate that X0 localization in wrinkles arises from dielectric screening, doping, and funneling effects, whereas piezoelectric field screening at the apex delocalizes electron-hole pairs, reducing the PL intensity. These findings highlight the complex interplay of strain, dielectric environment, and piezoelectric effects in shaping nanoscale excitonic properties. The AFM-TEPL technique proves to be a robust tool for directly probing and visualizing carrier distributions in 2D semiconductors, offering significant potential for advancing research in straintronics, optoelectronics, and beyond, with broad implications for next-generation nanotechnology and flexible device applications.

Airflow drying of trehalose-based droplets presents a promising alternative to cryopreservation for cell storage but faces challenges like non-uniform matrices that compromise cell viability. This study clarifies how initial trehalose concentration and humidity variations govern interfacial instabilities during drying. Experiments employed sessile droplets containing polystyrene microspheres dried under controlled humidity. Microscopy and interferometry revealed that low-concentration droplets formed central depressions due to radial flow-driven crust thinning, while those with higher concentrations maintained spherical caps. These surface profiles significantly influenced both wrinkle and crack patterns. Furthermore, increased airflow humidity during drying was identified as the direct cause of wrinkle formation and crack healing. By correlating instabilities with concentration-dependent crust mechanics and humidity-modulated stress evolution, this work demonstrates that regulating initial trehalose concentration and ambient humidity can mitigate mechanical damage in dried matrices.

This chapter presents an overview of low-temperature distributed heat from its definition, features, characteristics, and potential in various regions and sectors as well as the thermodynamic fundamentals of power cycles for heat recovery and conversion. Significant inconsistencies exist in the definition of the temperature boundaries that demark low-/medium-/high-temperature heat across the literature. A broader definition for low-temperature and distributed heat is proposed and adopted here, based on a comparison to the temperatures achieved by combustion and the scale of centralized power plants, which includes not only waste heat from various processes and sectors but also heat from renewable energy sources. Estimations of the waste heat potentials in the world and major regions showed that a significant share of energy consumptions is finally dissipated as waste heat, of which the majority is below 100 °C. Thermodynamic fundamentals of power cycles for recovering waste heat are then presented, which highlights that matching the temperature changes of the heat source and the working fluid is important. Power cycles based on pressurizing, evaporating, expanding, and condensing volatile fluids, also referred to as two-phase cycles, can be superior in terms of conversion efficiency to those based on ideal or other single-phase gases that do not feature phase change thanks to their high work ratios and superior matching characteristics.