Abstract
The heating and cooling energy consumption of buildings accounts for about 15% of national total energy consumption in the United States. In response to this challenge, many promising ...technologies with minimum carbon footprint have been proposed. However, most of the approaches are static and monofunctional, which can only reduce building energy consumption in certain conditions and climate zones. Here, we demonstrate a dual-mode device with electrostatically-controlled thermal contact conductance, which can achieve up to 71.6 W/m
2
of cooling power density and up to 643.4 W/m
2
of heating power density (over 93% of solar energy utilized) because of the suppression of thermal contact resistance and the engineering of surface morphology and optical property. Building energy simulation shows our dual-mode device, if widely deployed in the United States, can save 19.2% heating and cooling energy, which is 1.7 times higher than cooling-only and 2.2 times higher than heating-only approaches.
A series of novel flexible polymer composites consisted of boron nitride foam (BNF), boron nitride nanosheets (BNNS) and polydimethylsiloxane (PDMS) were designed and fabricated by vacuum-assisted ...infiltrating BNNS/PDMS mixtures into 3D BNF synthesized via chemical vapor deposition (CVD). Their microstructure, thermal, mechanical and dielectric properties were studied. Contributed to the interconnected networks of BNF and synergistic effect of BNNS with BNF, 10wt% BNNS/BNF/PDMS composite shows a high thermal conductivity of 0.56Wm−1K−1, high heat resistance index of 275.6°C, 33% increment of Young’s modulus compared to PDMS, relative permittivity of 3, dissipation factor of 0.0051, EMI shielding effectiveness of 1.5dB at X band and breakdown strength of 21.8MV/m. Due to the outstanding comprehensive properties, BNNS/BNF/PDMS composites have a promising potential application in wide electronic packaging field.
Heat management is more and more crucial challenge since the development of modern electronic devices towards miniaturization and high dense integrity. Highly thermal conductive composites based on ...graphene are ideal heat-dissipating materials for their excellent heat dissipation ability, outstanding mechanical properties as well as low coefficient of thermal expansion. Numerous efforts have been made towards the development of graphene-based polymeric composites with high performance. Furthermore, it has been demonstrated that microstructure engineering of graphene-based construction of three-dimensional networks and high orientation is extremely important to improve the properties of composites. In this review, the research progress on the latest strategies of microstructure engineering of graphene for highly thermal conductive composites is summarized. Both fabrication methods and theoretical simulations are discussed. Finally, development and perspectives of highly thermal conductive composites are presented.
Fecal indicator bacteria, such as Escherichia coli (E.coli) and Enterococcus, have been widely used to indicate the presence of pathogens. However, the suitability of fecal indicator bacteria to ...represent health risks is still being challenged, particularly in tropical aquatic environments. The objective of this study is to understand the occurrence and prevalence of indicators and pathogens in areas with contrasting land use, as well as to identify the major correlations between indicators, pathogens and environmental parameters. The spatial and temporal variation of indicators and pathogens was studied to examine the distribution patterns for areas with different land use, and the impact of seasonal changes on microbial populations. A total of 234 water samples were sampled for two years from reservoirs and their tributaries, and tested for fecal indicator bacteria, coliphages, human specific markers, pathogenic bacteria and viruses. The prevalence of indicators and pathogens in reservoirs were generally low, while relatively high concentrations were observed in tributaries to varying degrees. Of the enteric viruses, norovirus GII was among the most prevalent and had the highest concentration. Although strong correlations were found between indicators, only relatively weak correlations were found between indicators and pathogens. The results in this study showed that none of the bacteria/phage indicators were universal predictors for pathogens. Inclusion of the alternative indicators, Methanobrevibacter smithii, Bacteroides and human polyomaviruses (HPyVs) to monitoring programs could help to determine whether the fecal source was human. The microbial distribution patterns allow the classification of sampling sites to different clusters and thus, help to identify sites which have poor water quality. This approach will be useful for water quality management to pinpoint factors that influence water quality and help to prioritize sites for restoration of water quality.
Display omitted
•Norovirus GII was the most prevalent enteric viruses.•Land use classification was correlated to the distribution of pathogens/indicators.•Alternative indicators helped to improve the prediction of enteric viruses.•Cluster analysis identified sites with poor water quality.
Nowadays, the demand for more personalized healthy food recipes is increasing over time, but traditional personalized recipe recommendation systems often tend to overlook the differences that exist ...in different users’ health conditions. This paper aims to address the issue by proposing an innovative personalized health recipe recommendation framework. This framework is based on different health needs, aiming to address users with different health conditions. More explicitly, the hybrid recommendation algorithm based on facial health recognition is designed to recommend the most suitable recipes for the user by taking into account the user’s health status and preferences. In addition, the fitness factor will adjust the recommendation results to best meet the user’s taste preferences and health goals. Experimental results and user research results show that the recommendation results of this framework are more accurate compared to existing systems, and therefore, users are more satisfied.
Efficient thermal transportation in a preferred direction is highly favorable for thermal management issues. The combination of 3D printing and two-dimensional (2D) materials such as graphene, BN, ...and so on enables infinite possibilities for hierarchically aligned structure programming. In this work, we report the formation of the asymmetrically aligned structure of graphene filled thermoplastic polyurethane (TPU) composites during 3D printing process. The as-printed vertically aligned structure demonstrates a through-plane thermal conductivity (TC) up to 12 W m–1 K–1 at 45 wt % graphene content, which is ∼8 times of that of a horizontally printed structure and surpasses many of the traditional particle reinforced polymer composites. The superior TC is mainly attributed to the anisotropic structure design that benefited from the preferable degree of orientation of graphene and the multiscale dense structure realized by finely controlling the printing parameters. Finite element method (FEM) confirms the essential impact of anisotropic TC design for highly thermal conductive composites. This study provides an effective way to develop 3D printed graphene-based polymer composites for scalable thermal-related applications such as battery thermal management, electric packaging, and so on.
In the present study, high thermally conductive and electrically insulated polymer composites containing modified dense graphene foam (MGF) and modified hexagonal boron nitride (M-h-BN) via ...polydopamine (PDA) coating and 3-aminopropyltriethoxysilane (APTS) grafting were manufactured and studied. Due to the double percolated networks built by MGF and M-h-BN, the polydimethylsiloxane (PDMS) matrix composite has high thermal conductivity of 23.45Wm−1K−1 and 2.11Wm−1K−1 in in-plane and out-of-plane directions, respectively. In addition, an insulated layer of M-h-BN/PDMS can be introduced onto both sides of composite sample with the help of infiltration technique, which results in a high breakdown strength of 4.5 kV/mm. Owing to the excellent comprehensive properties, the M-h-BN/MGF/PDMS composite has a promising application in heat management field of the microelectronic industry.
With the growing challenges of modern electronics in heat dissipation, developing thermal management materials with high thermal conductivity and electrical insulation property remains an important ...issue for electronics. In this work, a novel three-dimensional network (3D) of boron nitride/reduced graphene oxide (BN/rGO) with covalent bond connections were fabricated by using the surface modification and ice-templated methods. The as-prepared boron nitride/reduced graphene oxide/nature rubber composites (BN/rGO/NR) possessed an enhanced through-plane thermal conductivity of 1.28 W m−1 K−1 and satisfactory electrical insulation at a low filler loading of 4.9 vol%. The results demonstrated that the covalent bond connections and three-dimensional networks of fillers greatly reduced the interfacial thermal resistance as well as phonon scatterings at the filler/filler and filler/matrix interface simultaneously. More importantly, this strategy provided a creative insight to the design of advanced thermal management materials and also presented a bright application prospect for next-generation electronic packing.
BN and rGO were connected by the covalent bonds through using the surface modified method. BN/rGO/NR composites were fabricated by the ice-templated and vacuum-assisted method. Display omitted
To meet the increasing demands for effective heat management of electronic devices, a graphene-based polymeric composite is considered to be one of the candidate materials owing to the ultrahigh ...thermal conductivity (TC) of graphene. However, poor graphene dispersion, low quality of exfoliated graphene, and strong phonon scattering at the graphene/matrix interface restrict the heat dissipation ability of graphene-filled composites. Here, a facile and versatile approach to bond graphene foam (GF) with polydimethylsiloxane (PDMS) is proposed, and the corresponding composite with considerable improvement in TC and insulativity is fabricated. First, three-dimensional GF was coated with polydopamine (PDA) via π–π stack and functional groups from PDA reacted with 3-aminopropyltriethoxysilane (APTS). Then, the modified GF was compressed (c-GF) to enhance density and infiltrated with PDMS to get the c-GF/PDA/APTS/PDMS composite. As a result, these processes endow the composite with high TC of in-plane 28.77 W m–1 K–1 and out-of-plane 1.62 W m–1 K–1 at 11.62 wt % GF loading. Besides, the composite manifests obvious improvement in mechanical properties, thermal stability, and insulativity compared to neat PDMS and GF/PDMS composite. An attempt to use the composite for cooling a ceramic heater is found to be successful. Above results open a way for such composites to be applied for the heat management of electronic devices.
Polyurethane (PU) based composites were fabricated by cross-linking hydroxyl-terminated polybutadiene (HTPB) chains with modified graphene oxide (MGO). The MGO worked as both the reinforcing agent ...and the cross-linker and strong interface between MGO sheets and PU matrix was formed, which provide the MGO/PU composites with well improved properties. Compared to neat PU and traditional direct-mixing GO/PU composites, the elastic modulus and tensile strength of 1 wt% MGO/PU composites increase significantly by 195.3% and 63.8%, respectively. Other properties such as thermal stability, anti-creep property and dynamic shear moduli are also much improved. All the improvements come from the enhanced interface bonding between MGO and PU, as well as dense molecular chains network in the composites. It can be expected that cross-linking method would be an effective fabrication approach and interface controlling strategy for the development of high-performance composites.
PDF
