Poplar-based thermochromic composites that change colour at 38 °C to 46 °C

The red thermochromic dye (R-TD) is the tetradecanoic acid tetradecyl ester (C28H56O2) and methyl red (C15H15N3O2) mixture that has better permeability enabling its infiltration into wood and better thermochromic properties changing its colour at above 30 °C after about 0.5 min. Thicker poplar-based thermochromic composite specimens (R-PTC, thickness: 5.0 mm) were prepared by filling the R-TD into pre-treated poplar veneer (thickness: 5.0 mm) thus allowing better penetration after pre-treatment. After R-TD infiltration, the R-PTC samples were covered by polypropylene wax for preventing R-TD from overflowing from R-PTC under the action of phase-change temperature. This R-PTC, whose colour can change from light-red to dark-red at 38 °C to 46 °C, can recover to light-red at below 38 °C after about 14 h, and the peak of colour change is at about 42 °C. R-PTC will be suitable for materials used in thermochromic furniture that can indicate the surface temperature to potential users, thus allowing assessment of likely scalded pain when used the furniture.

Phase Change Temperature Sensor for High Radiation Environment

Performance of any sensor in a nuclear reactor involves reliable operation under a harsh environment (i.e., high temperature, neutron irradiation, and a high dose of ionizing radiation). In this environment, accurate and continuous monitoring of temperature is critical for the reactor's stability and proper functionality. Furthermore, during the development and testing stages of new materials and structural components for these systems, it is imperative to collect in-situ measurement data about the exact test conditions for real-time analysis of their performance. To meet the compelling need of such sensing devices, we propose radiation-hard temperature sensors based on the phase change phenomenon of chalcogenide glasses. The primary goal is to resolve the monitoring of the cladding temperature of light water and metallic or ceramic sodium-cooled fast reactors within a temperature range of 400°C to 600°C. This work is focused on studies of Ge-Se(S) chalcogenide glasses that have crystallization temperatures in this range. Each chalcogenide glass transforms and becomes crystalline at a specific heating rate at a definite temperature. As a result of this, both the electrical resistance and optical properties of the materials change. As this is the first time such devices have been fabricated, this work submits new data regarding materials research, various device structures, fabrication, performance, and testing under irradiation. The application of these materials in devices usually involves the formation of a thin film that works as an active layer. Traditionally, thin films are prepared by thermal evaporation, sputtering or chemical vapor deposition and they require high vacuum machinery and patterning applying photolithography. To avoid using such heavy machinery and costly fabrication processes, we investigate the formulation of nanoparticle inks of chalcogenide glasses, the formation of printed thin films using the inks, low-cost sintering and demonstrate their application in electronic and photonic sensors utilizing their phase transition effects. The printed chalcogenide glass films showed similar structural, electronic and optical properties as the thermally evaporated films. The newly developed process steps reported in this work describe chalcogenide glasses nanoparticle inks formulation, their application by inkjet printing and dip-coating methods and sintering to fabricate phase change temperature sensors. To interpret and predict the printed films' performance, Raman spectroscopy, X-ray Diffraction Spectroscopy, Energy Dispersion Spectroscopy, Atom Force Microscopy, temperature dependent Ellipsometry, and other methods are used. An essential part of materials' behavior is related to the materials' and devices' response to ion beam irradiation. Both experimental data and simulation are analyzed to study the effect of irradiation. Based on the different working principles, electrical, optical and plasmonic temperature sensors are investigated. An array of optical fiber devices fabricated with different chalcogenide glasses is shown to perform a real-time temperature reading. This work could be used as a paradigm for sensor fabrication and testing for high radiation environments and nanoparticle inks of chalcogenide glasses formulation and their application by inkjet printing and dip-coating. The most novel outcome of this work adds chalcogenide glasses to the list of inkjet printable materials, thus opening up an opportunity to achieve arbitrary structures for optical and electronic applications without photolithography.

Thermal Properties and the Prospects of Thermal Energy Storage of Mg–25%Cu–15%Zn Eutectic Alloy as Phase Change Material

This study focuses on the characterization of eutectic alloy, Mg–25%Cu–15%Zn with a phase change temperature of 452.6 °C, as a phase change material (PCM) for thermal energy storage (TES). The phase composition, microstructure, phase change temperature and enthalpy of the alloy were investigated after 100, 200, 400 and 500 thermal cycles. The results indicate that no considerable phase transformation and structural change occurred, and only a small decrease in phase transition temperature and enthalpy appeared in the alloy after 500 thermal cycles, which implied that the Mg–25%Cu–15%Zn eutectic alloy had thermal reliability with respect to repeated thermal cycling, which can provide a theoretical basis for industrial application. Thermal expansion and thermal conductivity of the alloy between room temperature and melting temperature were also determined. The thermophysical properties demonstrated that the Mg–25%Cu–15%Zn eutectic alloy can be considered a potential PCM for TES.

Modeling PCM Phase Change Temperature and Hysteresis in Ventilation Cooling and Heating Applications

Applying phase change material (PCM) for latent heat storage in sustainable building systems has gained increasing attention. However, the nonlinear thermal properties of the material and the hysteresis between the two-phase change processes make the modelling of PCM challenging. Moreover, the influences of the PCM phase transition and hysteresis on the building thermal and energy performance have not been fully understood. This paper reviews the most commonly used modelling methods for PCM from the literature and discusses their advantages and disadvantages. A case study is carried out to examine the accuracy of those models in building simulation tools, including four methods to model the melting and freezing process of a PCM heat exchanger. These results are compared to experimental data of the heat transfer process in a PCM heat exchanger. That showed that the four modelling methods are all accurate for representing the thermal behavior of the PCM heat exchanger. The model with the DSC Cp method with hysteresis performs the best at predicting the heat transfer process in PCM in this case. The impacts of PCM phase change temperature and hysteresis on the building energy-saving potential and thermal comfort are analyzed in another case study, based on one modelling method from the first case study. The building in question is a three-room apartment with PCM-enhanced ventilated windows in Denmark. The study showed that the PCM hysteresis has a larger influence on the building energy consumption than the phase change temperature for both summer night cooling applications and for winter energy storage. However, it does not have a strong impact on the yearly total energy usage. For both summer and winter transition seasons, the PCM hysteresis has a larger influence on the predicted percentage of dissatisfied (PPD) than the phase change temperature, but not a strong impact on the transition season average PPD. It is therefore advised to choose the PCM hysteresis according to whether it is for a summer night cooling or a winter solar energy storage application, as this has a significant impact on the system’s overall efficiency.

Solid-Liquid Phase Diagram of the Binary System Octadecanoic Acid and Octadecanol and the Thermal Chemical Property of the Composition at Eutectic Point

Phase diagram is a powerful tool to guide the exploitation of thermal energy materials. Heat storage technology of phase-change material (PCM) was widely used to solve major energy utilization problems on large energy consumption and low utilization efficiency. In this work, a novel solid-liquid phase diagram of the binary system octadecanoic acid (C18-acid) + octadecanol (C18-OH) was investigated using the differential scanning calorimeter (DSC). The phase-change temperature and phase-change enthalpies against the composition of C18-acid and C18-OH were determined experimentally, and then the binary phase diagram of T–X (X expresses the mass fraction of C18-OH in the two components of C18-acid and C18-OH) was established for the first time. The phase diagram belongs to a binary simple system with one eutectic point, and the content of C18-OH at eutectic point is 0.4 in mass fraction. Neither solid solution nor copolymer was formed. The thermal chemical properties on the phase-change latent heat (Q), phase-change temperature (Tp), and the thermal conductivity (λ) for the composition at the eutectic point of the binary system are 198.7 J·g−1, 44.2°C, and 0.2352 W·m−1·K−1, respectively. This result indicates that the material at eutectic point has a great potential to be used as energy storage material for supply of heat and scouring bath.