Visible-Light-Sensitive Photoliquefiable Arylazoisoxazoles for the Solar Energy Conversion, Storage and Controlled-Release of Heat at Room Temperature or Lower Temperatures.

The photoswitchable MOlecular Solar Thermal (MOST) energy storage systems that are capable of exhibiting high energy storage densities are found to suffer from the poor cyclability, the use of less abundant UV light of the solar spectrum, or reduced charging/discharging rates and poor photoconversions in solid states. Herein, we have designed and readily synthesized a novel set of para-thioalkyl substituted arylazoisoxazoles, that undergo high trans-cis and cis-trans photoconversions under visible light, and show fast charging/discharging and impressive cyclability. Remarkably, the presence of C6-or C10-thioalkyl chainin photochromes permitted reversible solid-liquid phase transition with the formation of cis-enriched charged states by 400 nm light irradiation and trans-enriched discharged states by 530 nm light at various temperatures (10-35 °C). The solid-to-liquid phase transition enabled storage of the latent heat in addition to the isomerization energy, resulting in a high net energy storage density of 189-196 J/g, which are substantially higher than that of many recently reported azobenzene-based MOST compounds (100-161 J/g). Using a high-resolution infrared camera, we further demonstrated that a brief irradiation of green light can be employed to readily release the trapped photon energy as heat. Our results suggest that the arylazoisoxazole with C6-thioalkyl chain at para-position can serve as an effective and eco-friendly photoliquefiable MOST material.

Dynamics of a single-phase natural circulation system under harmonic excitation.

A natural circulation system (NCS) has a broad application in the sector of thermal engineering, for example, in nuclear reactors due to its capability in transferring heat without any support of external power or a mechanical device. NCSs, although designed for steady operation, have been found to exhibit dynamical behavior, such as periodic oscillations, depending on the input heater power. The heater power, otherwise assumed to be steady, can be fluctuating in practice. The present study focuses on the dynamics of a single-phase square NCS, which exhibits periodic dynamics and is subjected to an external harmonic perturbation (chosen as the simplest form of fluctuation) over the steady heater power. The objective of the study is to study the dynamics of NCS under external (harmonic) disturbances using the framework of forced synchronization. Toward that, a 1D transient model of a square-shaped NCS is simulated with harmonically forced input power. The transition in the nature of synchronization between mass flux oscillations and the external forcing has been characterized by varying the frequency and amplitude of external perturbation independently. We find different nonlinear effects of the harmonic forcing, such as exhibition of quasiperiodic dynamics, frequency pulling/pushing, and frequency locking or forced synchronization. The aforementioned characterization techniques open up an avenue for detailed analysis of the more complex type of fluctuating input heat in real systems.