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In situ thermal remediation can rapidly remove volatile organic pollutants, regardless of permeability or heterogeneity in the subsurface, which has received more attention in recent years. This study aims at investigating the heat transfer during thermal conduction heating (TCH), a heating method of in situ thermal remediation. The experiments were performed in a 134.5-cm tall × 107.5-cm wide × 7.5-cm thick tank containing a heating resistance to heat the aquifer and 62 thermocouples to measure temperature. The temperature of the points was recorded in real time through a multi-channel temperature patrol instrument. Then, isotherms were drawn, which were quantitatively analyzed from the aspects of temperature distribution, heated zone area, heat transfer distance, and influencing radius. The influence of groundwater velocity, aquifer medium, and heating resistance power was investigated. The results show the following: (1) The quantitative analysis proved that the higher the groundwater velocity, the faster the heated zone reaches a stable state. (2) The heated zone area in a coarse/fine sand aquifer is larger than that in a medium sand aquifer, and the stable time of the heated zone is in the order of fine sand < coarse sand < medium sand. (3) The greater the heating resistance power is, the more rapidly the heated zone reaches a stable state. (4) It has been quantitatively concluded that the V-shaped distribution of the heated zone is more obvious at a high groundwater velocity or with a high-power heating resistance. These findings are significant for the practical application of Thermal conduction heating.

Less attention was paid to the remediation of volatile organic compounds (VOCs) contaminated soil treated by thermal conduction heating (TCH) coupled with chemical oxidization. In this study, the lab-scale remediation experiments of trichloroethylene (TCE)-contaminated soil by TCH and TCH coupled with persulfate (TCH + PS) were performed to explore the influences of PS usage, temperature, reaction time, and the variation of soil properties. TCE was removed from contaminated soils using TCH with a temperature lower than boiling point, and the removal ratio of TCE reached 78.21% with a reaction time of 6h at 60 °C. In the TCH + PS treatments, the removal ratio increased to 87.60~99.50% when the PS dosage was increased from 7.0 mmol/kg to 17.5 mmol/kg at 60 °C. However, the usage efficiency of PS had no positive relationship with oxidant usage and temperature. The treatment with 14 mmol/kg PS after 3h at 50 °C had the highest PS usage ratio of 3.05. In addition, soil pH and soil organic matter (SOM) did not decrease significantly in the TCH-only treatment, while the content of SOM declined by almost 50% after the TCH + PS treatment. Overall, it was concluded that TCH + PS achieved higher removal efficiency, whereas TCH had less disturbance on soil pH and SOM. As such, the applicability of TCH-only or TCH + PS treatments is site-specific.

In this paper, an experimental study of a system for heating an air-conditioned bed during a 2 h lunch was carried out. The results show that the power consumption of heat conduction heating was only 0.34 kW·h and that the average heat dissipation was 81.3 W, while the power consumption of convection heating was 1.43 kW·h, accompanied by an average heat dissipation of 748.7 W. Regardless of the power consumption or the heat dissipation, the convection heating was significantly higher than the heat conduction heating. As a result, the room air temperature increased from 12.3 °C to 17.3 °C under convection heating, but only increased from 14.4 °C to 15.2 °C under heat conduction heating. The study results indicate that when using heat conduction heating, water temperatures in the range of 38~40 °C could meet the thermal comfort needs of the human body; however, a higher temperature range was required when using convection heating. In contrast, the grade of the hot water required for heat conduction heating was lower. It was also found that the temperature under convection heating rises faster, but it tends to lead to a dry feeling after a long time, while the conductive heating showed a slower temperature rise. There was a cool feeling for 20 min when the heating started, and then the thermal comfort improved. The air-conditioning system in this paper was investigated in a heating experiment in the winter lunch break mode and compared with convection heating. The heat conduction heating resulted in better thermal comfort and higher energy efficiency. It is suggested to adopt the heat conduction heating mode in the winter heating operation of this system.

Thermal management becomes increasingly important as we decrease device size and increase computing power. Engineering materials with high thermal conductivity, such as boron arsenide (BAs), is hard because it is essential to avoid defects and impurities during synthesis, which would stop heat flow. Three different research groups have synthesized BAs with a thermal conductivity around 1000 watts per meter-kelvin: Kang et al. , Li et al. , and Tian et al. succeeded in synthesizing high-purity BAs with conductivities half that of diamond but more than double that of conventional metals (see the Perspective by Dames). The advance validates the search for high-thermal-conductivity materials and provides a new material that may be more easily integrated into semiconducting devices. Science , this issue p. 575 , p. 579 , p. 582 ; see also p. 549 Boron arsenide has an ultrahigh thermal conductivity, making it competitive with diamond for thermal management applications. Conventional theory predicts that ultrahigh lattice thermal conductivity can only occur in crystals composed of strongly bonded light elements, and that it is limited by anharmonic three-phonon processes. We report experimental evidence that departs from these long-held criteria. We measured a local room-temperature thermal conductivity exceeding 1000 watts per meter-kelvin and an average bulk value reaching 900 watts per meter-kelvin in bulk boron arsenide (BAs) crystals, where boron and arsenic are light and heavy elements, respectively. The high values are consistent with a proposal for phonon-band engineering and can only be explained by higher-order phonon processes. These findings yield insight into the physics of heat conduction in solids and show BAs to be the only known semiconductor with ultrahigh thermal conductivity.

Additive manufacturing (AM), known as 3D printing, enables rapid fabrication of geometrically complex copper (Cu) components for electrical conduction and heat management applications. However, pure Cu or Cu alloys produced by 3D printing often suffer from either low strength or low conductivity at room and elevated temperatures. Here, we demonstrate a design strategy for 3D printing of high strength, high conductivity Cu by uniformly dispersing a minor portion of lanthanum hexaboride (LaB 6 ) nanoparticles in pure Cu through laser powder bed fusion (L-PBF). We show that trace additions of LaB 6 to pure Cu results in an improved L-PBF processability, an enhanced strength, an improved thermal stability, all whilst maintaining a high conductivity. The presented strategy could expand the applicability of 3D printed Cu components to more demanding conditions where high strength, high conductivity and thermal stability are required. Copper produced by laser additive manufacturing often faces challenges with either low strength or low conductivity. Here, the authors present a design strategy to introduce uniformly dispersed nanoprecipitates during solidification, enhancing the strength while maintaining high conductivity.

Materials with ultrahigh or low thermal conductivity are desirable for many technological applications, such as thermal management of electronic and photonic devices, heat exchangers, energy converters and thermal insulation. Recent advances in simulation tools (first principles, the atomistic Green’s function and molecular dynamics) and experimental techniques (pump–probe techniques and microfabricated platforms) have led to new insights on phonon transport and scattering in materials and the discovery of new thermal materials, and are enabling the engineering of phonons towards desired thermal properties. We review recent discoveries of both inorganic and organic materials with ultrahigh and low thermal conductivity, highlighting heat-conduction physics, strategies used to change thermal conductivity, and future directions to achieve extreme thermal conductivities in solid-state materials. This Review provides an overview of experimental and theoretical methods for the understanding of thermal transport, summarizes recent progress in materials with ultrahigh (or low) thermal conductivities, and outlines strategies for the engineering of extreme thermal conductivity materials.

Polymer dielectrics with enhanced thermal stability and electrical insulation are urgently needed for capacitive energy storage applications in electric power systems. There is a persistent challenge to break the contradictory correlation between high heat resistance and low electrical conduction in polymers. Here, we employ benzyl-induced crosslinking to rearrange short-range structural units in polyimide chains, reducing electrical conduction loss. The designed polymer exhibits an electrical conductivity more than 3 orders of magnitude lower than that of commercial heat-resistant polymers, while its glass transition temperature ( T g ) increases from 236.31 °C (for polyetherimide) to 289.72 °C. Consequently, a discharged energy densities of 6.38 J cm −3 and 3.04 J cm −3 , with charge-discharge efficiencies above 90%, are achieved at 200 °C and 250 °C, respectively, demonstrating among the best in all-organic dielectric polymers. This work presents a feasible approach to break the adverse correlation between thermal stability and electrical insulation in polyimide materials. Polymer dielectrics have potential in capacitive energy storage applications, but achieving the required thermal stability and electrical insultation is challenging. Here, the authors report a method to rearrange short-range structural units within polyimide chains to give improved properties.

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering 1 – 5 . For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically 6 , 7 nor kinetically 3 favourable compared to low-index facets 6 – 18 . Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30 × 20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation. Large-area single-crystal high-index copper and nickel foils with several types of facet are fabricated using mild pre-oxidation of the metal foil surface followed by annealing in a reducing atmosphere.

Restricted ambient temperature and slow heat replenishment in the phase transition of water molecules severely limit the performance of the evaporation-induced hydrovoltaic generators. Here we demonstrate a heat conduction effect enhanced hydrovoltaic power generator by integrating a flexible ionic thermoelectric gelatin material with a porous dual-size Al 2 O 3 hydrovoltaic generator. In the hybrid heat conduction effect enhanced hydrovoltaic power generator, the ionic thermoelectric gelatin material can effectively improve the heat conduction between hydrovoltaic generator and near environment, thus increasing the water evaporation rate to improve the output voltage. Synergistically, hydrovoltaic generator part with continuous water evaporation can induce a constant temperature difference for the thermoelectric generator. Moreover, the system can efficiently achieve solar-to-thermal conversion to raise the temperature difference, accompanied by a stable open circuit voltage of 6.4 V for the hydrovoltaic generator module, the highest value yet. The authors demonstrate enhanced hydrovoltaic power generation using heat conduction effects to break through the slow heat replenishment limit common in evaporation-induced hydrovoltaic generators.

Thermal camouflage has been successful in the conductive regime, where thermal metamaterials embedded in a conductive system can manipulate heat conduction inside the bulk. Most reported approaches are background-dependent and not applicable to radiative heat emitted from the surface of the system. A coating with engineered emissivity is one option for radiative camouflage, but only when the background has uniform temperature. Here, we propose a strategy for radiative camouflage of external objects on a given background using a structured thermal surface. The device is non-invasive and restores arbitrary background temperature distributions on its top. For many practical candidates of the background material with similar emissivity as the device, the object can thereby be radiatively concealed without a priori knowledge of the host conductivity and temperature. We expect this strategy to meet the demands of anti-detection and thermal radiation manipulation in complex unknown environments and to inspire developments in phononic and photonic thermotronics. Thermal camouflaging techniques typically use bulky structures and require a well-defined and unchanging background. Here, the authors propose a strategy for thermal camouflage using a structured thermal surface, independent of the background material for many practical situations.