Nanopolyhybrids: Materials, Engineering Designs, and Advances in Thermal Management.

The fundamental requirements for thermal comfort along with the unbalanced growth in the energy demand and consumption worldwide have triggered the development and innovation of advanced materials for high thermal-management capabilities. However, continuous development remains a significant challenge in designing thermally robust materials for the efficient thermal management of industrial devices and manufacturing technologies. The notable achievements thus far in nanopolyhybrid design technologies include multiresponsive energy harvesting/conversion (e.g., light, magnetic, and electric), thermoregulation (including microclimate), energy saving in construction, as well as the miniaturization, integration, and intelligentization of electronic systems. These are achieved by integrating nanomaterials and polymers with desired engineering strategies. Herein, fundamental design approaches that consider diverse nanomaterials and the properties of nanopolyhybrids are introduced, and the emerging applications of hybrid composites such as personal and electronic thermal management and advanced medical applications are highlighted. Finally, current challenges and outlook for future trends and prospects are summarized to develop nanopolyhybrid materials.

Fire retardant performance, toxicity and combustion characteristics, and numerical evaluation of core materials for sandwich panels.

According to fire accident statistics, fires in buildings are increasing. The flame-retardant performance of insulation materials is considered an important factor for preventing the spread of fire and ensuring evacuation. This study evaluated the flame-retardant performance and combustion characteristics of four types of organic thermal insulation used as core materials in sandwich panels. The flame-retardant performance evaluation based on total heat release and heat release rate revealed that phenolic foam (PF) satisfied the criteria for non-combustible grade insulation. An analysis of the hazardous gases released while combustion of the four insulation materials indicated that a significant amount of CO was released-an average of 19,000 ppm or higher-in the rigid urethan foam (PIR) and spray-type polyurethane foam (SPU). The fractional effective dose (FED) value was derived from the gas analysis results according to ISO 13344. PIR and SPU had an average FED value of 2.0 or higher and were identified as very dangerous in the case of fire accidents. Moreover, the evacuation time in the case of a fire in a warehouse-type building was comprehensively analyzed considering the material, size, and height for the four types of insulation. PIR was the most vulnerable to fire, and for PF, the danger limit was not reached until the end of the simulation.

Use of biochar co-mediated chitosan mesopores to encapsulate alkane and improve thermal properties.

Phase-change materials (PCMs) plays a significant role in energy conservation and thermal management systems. However, excessive seepage and insufficient thermal conductivity of pristine PCMs are restricting its real-world applications. Herein, "anisotropic-like" biochar with favorable pore characteristics is designed by combining it with chitosan for dodecane encapsulation. The use of biochar could overcome high manufacturing costs and associated environmental issues of PCM supporting materials. Biochar co-mediated chitosan enrich the mesopore proportion (96.5%) and provide interactive synergistic architecture. The prepared composite PCM exhibited outstanding latent heat retention of 95.9% after repeated cycling, high loading ratio, enhanced thermal conductivity (0.373 W/(m·K)), leakage-free, and repeatable utilization properties above the melting point of pristine dodecane. A figure of merit of 33.94 × 106 W2 S/(m4oC) was achieved, far surpassing that measure among reported biochar-based composite PCMs. This study provides insights into next-generation sustainable energy storage development for a key global sustainability goal.

Updated results on the integration of metal-organic framework with functional materials toward n-alkane for latent heat retention and reliability.

Phase change composites are in high demand in thermal management systems. Various supporting materials, including nanocomposites, have been employed to develop shape-stable phase change materials (PCMs). As the reliability of most composite materials has mostly been studied right after the preparation with specific thermal cycling measurements, it is difficult to analyze the long-term leakage-resistance capability and energy retention capacity. Additionally, achieving multifunctional phase change composites is a significant challenge for single supporting materials. Herein, we provide a follow-up report on the thermal performance of hybrid material-supported n-alkane after a storage time of one year and 50 heating/cooling cycles. The interconnected hybrid material composed of a metal-organic framework (MOF) and graphite improved the shape/thermal stability of tetradecane (TD). The as-synthesized MOF/graphite/TD composites exhibited a high latent heat retention capacity of 84.2%, low leakage rate of 1.25%, and high PCM loading capacity, making them suitable for thermal management applications, such as industrial waste heat recovery systems. Furthermore, the intermolecular interactions and capillary forces between the hybrid materials and TD provided high stability and compatibility. Therefore, the as-prepared hybrid material fabricated in this study can be important in the development of multidirectional composite PCMs with comprehensive thermal characteristics.

Passive PM2.5 control plan of educational buildings by using airtight improvement technologies in South Korea.

Modern people spend most of their time indoors. Therefore, controlling indoor air quality is one of the most important factors for health. The indoor fine dust concentration is affected by the outdoor fine dust concentration. When the latter is high, it increases due to immersion. Therefore, improving the sealing performance of a building is an effective strategy to reduce indoor fine dust concentration during periods of severe outdoor fine dust without considering indoor fine dust generating factors. Traditional methods of improving the airtightness of a building have focused on replacing windows or doors. However, for reasons such as constructability and economic feasibility, more diverse technologies need to be considered. Due to this necessity, this study applied technologies such as sealing film, sealing lid, and padding to the educational building, and then derived the airtight performance through the blower door experiment, and measured the fine dust concentration to evaluate the effect. As a result of the experiment, it was analyzed that air leakage was reduced by up to 37% and fine dust by 22%.

Practical solutions with PCM for providing thermal stability of temporary house, school and hospital in disaster situations.

Globally, humanity is at risk from the coronavirus disease (COVID-19). To address the shortage of beds in quarantining those infected with COVID-19, hospitals have prepared temporary beds. However, for temporary hospital beds, it is difficult to maintain a comfortable temperature due to lack of insulation and heat storage. Phase change materials (PCMs) are used to provide temperature stability and control for temporary structure. Therefore, this study aimed to conduct experiments that analyze the effect of room temperature stabilization using a PCM. The method of macro packed PCM (MPPCM) was used to apply the PCM to buildings. The MPPCM installation location was selected and the effect of reducing the box temperature was analyzed, according to the strength of the heat source. As a result, a maximum reduction of 4.9 °C in the box temperature was achieved. Therefore, the application of MPPCM to buildings give to stabilize the box temperature. And the result showed the possibility of providing a comfortable indoor space for temporary hospital beds.

Evaluation of thermal/acoustic performance to confirm the possibility of coffee waste in building materials in using bio-based microencapsulated PCM.

As the demand for coffee has increased, by-product disposal has become a challenge to solve. Many studies are being conducted on how to use coffee waste as building materials to recycle it. In this study, the thermal performance and acoustic performance of a composite developed using bio-based microencapsulated phase change material (MPCM) and coffee waste were evaluated, and the composite was applied as building material. The coffee waste was successfully degreased with ethanol to produce composites, and removal of contaminants and oils was confirmed via scanning electron microscopy. In the phase change process of MPCM, an appropriate amount of thermal energy is absorbed and stored, and the temperature is maintained. MPCM was used in the mixture and the improved thermal performance was evaluated via differential scanning calorimetry analysis, revealing a latent heat of 3.8 J/g for MPCM content of 10%. Further, thermal imaging cameras revealed that an increase in the proportion of MPCM leads to a slower decrease in temperature because of the heat preserved by MPCM over time. In an acoustic performance evaluation, impedance tube test results showed different aspects depending on low, mid, and high-frequency bands. Specifically, at medium frequencies, which correspond to the range of noise generated in cafes, specimens fabricated using MPCM were confirmed to exhibit a higher sound absorption coefficient and an improved acoustic performance. Hence, the composite can be considered an eco-friendly building material with promising thermal and acoustic performance.

Analysis of biochar-mortar composite as a humidity control material to improve the building energy and hygrothermal performance.

This study suggests a new perspective of biochar as a building material that improve not only for the strength but also hygrothermal properties. Biochar has a high porosity and surface area created by pyrolysis. It can be suitably used as a porous material because porous materials are used by incorporating into building materials for improving hygrothermal performance in the construction sector. To analyze whether biochar can be used as a functional building material to improve the hygrothermal performance, two types of biochar, made from oilseed rape (OSB) and mixed softwood (SWB), were prepared. A biochar-mortar composite was prepared according to the mixing ratio of the biochar from 2 wt% to 8 wt%, and the compressive strength and hygrothermal performance of them were analyzed. The compressive strength is the highest when 4 wt% of biochar into the mortar was mixed regardless of the type of biochar. Thermal conductivity of biochar-mortar composites was decreased as the biochar addition increased, and the value of biochar-mortar composites with 8 wt% OSB decreases by maximum 57.6% compared to the conventional cement mortar. The water vapor resistance factor of biochar-mortar composites increases, and biochar-mortar composites with 8 wt% SWB increases by maximum 50.9% compared to the reference. WUFI simulation shows that the biochar-mortar composites can contribute to a humidity control and no mold growth. The biochar-mortar composites can also contribute to energy savings although the amount of savings is insignificant. As a result, this study proved that when the mortar with biochar addition was possible to improve not only strength but also hygrothermal properties of mortar. This approach will be a new perspective that biochar can apply to the building material in practice.

A comparative analysis of biochar, activated carbon, expanded graphite, and multi-walled carbon nanotubes with respect to PCM loading and energy-storage capacities.

To obtain high thermal performance composite phase change materials (PCMs), various other supporting materials have been utilized to encapsulate organic PCMs. In this study, four carbon materials (biochar, activated carbon, carbon nanotubes, and expanded graphite) were introduced to support heptadecane. The composite PCMs were designed using vacuum impregnation techniques. The structural stability, chemical compatibility, thermal stability, and thermal energy storage capacity of the as-prepared materials were systematically characterized using differential scanning calorimetry, Fourier-transform infrared spectroscopy, etc. Among the supporting materials, expanded graphite had a high PCM content of 94.5%, whereas it was low for biochar-supported PCM (25.7%). Meanwhile, the latent heat storage capacity ranged from 53.3 J/g to 195.9 J/g. It was observed that the intermolecular interactions between the PCM and supporting materials and the surface functionality of the encapsulating agents play a leading role in the thermal performance of the composite PCMs. Furthermore, pore structures such as specific surface area, total pore volume, and pore size distribution have a combined effect on the crystallinity of heptadecane in the composite PCMs. The study will provide insight into developing and designing carbon-based composite PCMs for heat-storage purposes.

Evaluation of hygrothermal performance of wood-derived biocomposite with biochar in response to climate change.

Wood is a sustainable resource and building material. It provides an excellent response to climate change and has excellent insulation performance. However, structural defects may occur due to decay from moisture, resulting in poor dimensional stability. The rich organic substances contained in wood can lead to mold when the moisture content is consistently high, adversely affecting the health of occupants. Therefore, we attempted to compensate for the disadvantages of wood in regard to water stability while maintaining the high thermal insulation performance and carbon dioxide storage capacity, using biochar from thermally decomposed spruce under oxygen limiting conditions. A wood-derived biocomposite was prepared by mixing biochar and soft wood-based chips using the hot-press method, and the thermal conductivity, specific heat, water vapor resistance factor, moisture adsorption, and moisture desorption performances were analyzed. The thermal conductivity of WB10 with 10 wt% biochar content was 0.09301 W/mK. This is a 7.98% decrease from 0.10108 W/mK, the thermal conductivity of WB0 without biochar. The water vapor resistance factor tended to increase when the biochar ratio increased. As the proportion of biochar increased, the equilibrium moisture content in high relative humidity tended to decrease, and it was found that the moisture adsorption and desorption performances were affected by the ratio of the biochar. Therefore, wood-derived biocomposites using biochar can be used in environmentally friendly materials, with improved thermal insulation performance and water stability.

Circular reutilization of coffee waste for sound absorbing panels: A perspective on material recycling.

The increase in coffee consumption has led to increased production of coffee waste. Methods to recycle coffee waste are constantly being researched. Coffee powder is a porous material that can effectively be used to absorb sound. In this study, sound-absorbing panels were developed using coffee waste combined with resin. A sound absorption characterization of the new material was performed. Then, the noise reduction potential using coffee-waste sound absorbers was investigated in cafés. A café has several noise sources, such as coffee machines, music, and the voices of people. The noise reduction effect was evaluated using the ODEON simulation software together with the improvement in both the clarity and reverberation time in a case study café. In the investigated room, the acoustic definition (D50) increased up to 0.8, while the reverberation time (RT) reduced to 0.6 s. The results of this study demonstrate that the noise generated in the café was reduced by recycling the coffee waste produced as a by-product in the same building. Finally, this study presents a new construction material manufactured through coffee waste that is in turn applied to cafés where the coffee waste itself is produced.

Field study on the improvement of indoor air quality with toluene adsorption finishing materials in an urban residential apartment.

To improve the indoor air quality of apartments in Korea, a toluene adsorptive paint was manufactured and tested for its efficiency to remove the indoor toluene released from wallpaper adhesives. The toluene adsorptive paint was prepared by blending activated carbon and inorganic binder, and the pore characteristics and chemical functional groups of the activated carbon were analyzed to determine whether the micropores and surface functionalities of activated carbon affected toluene adsorption. Toluene adsorption performance of the toluene adsorptive paint was confirmed through static and verification experiments. The average adsorption efficiency of toluene adsorptive paint in the static experiment was 98.3% and the verification experiment confirmed that about 96.3% of toluene was adsorbed from the indoor air of the apartment. As a result, the use of toluene adsorptive paint effectively removes toluene, which may occur in the adhesive, and thus can be considered to have a good effect on the improvement of indoor air quality. Furthermore, toluene adsorptive paint has been found to be an effective way to achieve consumer wall finishing preferences and maintenance convenience.

Design and analysis of phase change material based floor heating system for thermal energy storage.

Pleasant interior space is essential for modern people who spend considerably more time in the buildings than they did in the past. To achieve this, one aspect includes an ambient temperature that maintains the thermal equilibrium of the human body. The construction of wood framed buildings is becoming increasingly popular worldwide, and there have been recent trends toward constructing high-rise wooden houses. In this respect, heating methods appropriate for use in wooden buildings are being studied. Dry floor heating systems are predominantly used in wooden houses, but they provide a poor heat storage performance, which is not conducive to saving energy. In this study, the effects of thermal comfort and energy savings were analyzed after applying a phase change material (PCM) to floor heating, which can be used to reduce the peak temperature and contribute to energy savings. To enable shape stabilization, this study used Macro-Packed PCM (MPPCM), as shape stabilization is necessary when applying PCM. The heat storage performance was improved by applying MPPCM to a dry floor heating system. Paraffin-based PCMs, such as n-octadecane, n-eicosane, and n-docosane, were used to obtain a comfortable floor temperature range. Experimental temperatures ranged from 28 °C to 35 °C, with an entire temperature range of 7 °C. Experimental results showed that the heat storage performance of MPPCM reduced the amount of energy used for heating by 43%, and n-eicosane was the most effective PCM for use in floor heating with respect to obtaining a comfortable floor temperature.