Highlights•Thermal radiation of Si microcavity with thermochromic film is studied.•Emittance enhancement of the structure was confirmed by experiment and simulation.•A highly variable emittance increment was observed.•The emittance enhancement mechanism was discussed.A high thermochromic performance is required for the thermochromic film application in space radiator. The performance can be improved by material selection or structure design. Here, we constructed a two-dimensional structure composed of silicon microcavity array coated with thermochromic film. From detailed numerical simulation, we found that periodic microcavity array plays a key role in enhancing the spectral emittance. For 1.5 μm deep microcavity with a 500 nm thick thermochromic film, an emittance peak appears at the wavelength of 12.7 μm, which corresponds to the Fabry–Perot (FP) resonance mode. Another microcavity excitation was observed in the shorter wavelength region, which matches well with its resonance wavelength. Based on the simulations, the optimal structure was fabricated by etching and sputtering methods. The fabricated structure shows a high tunable emittance behavior with emittance increment reaching 0.41. Both the experiment and simulation identified that the microcavity beneath thermochromic film can improve its thermochromic performance.

The first critical step in making vertically aligned carbon nanotube (VACNT)-based thermal interface materials is to transfer the VACNTs on a large scale. Although VACNTs have been transferred by several methods, they were only transferred inadvertently in most cases. Here we report well-controlled weak-oxidation-assisted transfer of VACNTs. Specifically, after a short time of weak oxidation, we found that VACNTs could be easily detached from the native growth substrates, and thus, a freestanding VACNT film was obtained. Then the VACNTs could be assembled onto specific substrates for its real applications. More importantly, the repeated growth–transfer synthesis of VACNT arrays can be realized in one batch by introducing an additional process of weak oxidation in chemical vapor deposition, which makes the strategy more effective. Surprisingly, no degradation in the quality was observed before and after the weak oxidation according to thermogravimetric analysis and Raman spectra of VACNTs. Enhanced thermal and mechanical properties were achieved after reactive ion etching (RIE) and subsequent metallization of the surfaces of the VACNTs, and this might be due to the removal of impurities such as amorphous carbon and entangled CNTs by RIE. These findings provide an efficient approach for transferring VACNTs, which is important for the application of VACNTs in thermal management.

Carbon nanotube (CNT) arrays show great promise in developing anisotropic thermal conductive composites for efficiently dissipating heat from high-power devices along thickness direction. However, CNT arrays are always grown on some substrates and liable to be deformed and broken into pieces during transfer and solution treatment. In the present study, we intentionally synthesized well-crystallized and large-diameter (∼80 nm) multiwalled CNT (MWCNT) arrays by floating catalyst chemical vapor deposition (FCCVD) method. Such arrays provided high packing density and robust structure from collapse and crack formation during post solution treatment and therefore favored to maintain original thermal and electrical conductive paths. Under optimized condition, the CNT arrays can be transferred into flexible composite films. Furthermore, the composite film also exhibited excellent thermal conductivity at 8.2 W/(m·K) along thickness direction. Such robust, flexible, and highly thermal conductive composite film may enable some prospective applications in advanced thermal management.Keywords: carbon nanotube array; crack-free; flexible; highly thermal conductive; scalable transfer;

•Thermochromic coatings were synthesized by plasma spraying method.•The coating exhibits a metal–insulator transition.•Emissivity increment of the coating at 97–373 K is 0.33.•Large solar absorptivity of the coating is reported.Thermochromic coating has been deposited on the substrate of stainless steel by plasma spraying method. Surface morphology, solar absorptivity, and the temperature dependence of infrared spectra and emissivity are reported. The observation of surface morphology shows that the microstructure and the compactness of the coating are related to the spray distance. The investigation of thermal radiative properties indicates that the coating has a large solar absorptivity exceeding 0.8 and its tunable range of emissivity is remarkable, approaching 0.33 at 97–373 K.

•Thermochromic film was prepared by RF magnetron sputtering.•Infrared properties of thermochromic film are investigated.•Thermochromic film exhibits a tunable infrared emissivity property.•Influence factors of film emissivity are investigated.Thermochromic films are prepared on the substrate of yttria stabilized zirconia by radio frequency magnetron sputtering technique. Crystalline structure and surface morphology are characterized. Characterization result shows that the films are of perovskite structure exhibiting a dense and smooth surface morphology. Composition analysis is performed and the result indicated that the element composition of films can be adjusted to close its stoichiometric ratio by controlling the oxygen flow ratio. Temperature-dependent reflectivity and emissivity are studied. Reflectivity spectra show that the film undergoes a transition from a metallic state to a non-metallic state with increasing temperature. Emissivity of the films is large above the transition temperature and it decreases sharply below the temperature. The emissivity increment at 97–373 K can approach 0.39 by controlling sputtering pressure, working gas and film thickness.

Thermochromic material La0.7Ca0.2Sr0.1MnO3 is synthesized by solid-state reaction method. The solar absorptance, thermal emittance and reflectance are investigated. The research results indicated that the material has such a large solar absorptance value of 0.78 that it is disadvantageous for the thermal control material in space. Within the 97–373 K range, the thermal emittance of the material increases with the rise of temperature, and its variation amplitude is 0.6. To reduce the high solar absorptance and keep the variation amplitude of the emittance, solar reflection films are deposited onto the surface of the material. Experimental results show that the solar absorptance is reduced from the 0.78 of bare thermochromic material to the 0.27 of thermochromic material with solar reflection films, and the variation amplitude of the emittance is not affected by the films. In addition, irradiation suitability study of the material with solar reflection films for space application suggests that the variable emittance properties have no degradation undergoing the electrons and protons irradiation.

La0.7Ca0.2Sr0.1MnO3La0.7Ca0.2Sr0.1MnO3 is a thermochromic material which can be used as thermal control device. However, its solar absorptivity is too high for that in spacecraft application. To reduce its solar absorptivity, an optical thin film is designed in this paper by using simulated annealing genetic algorithm. This film can effectively reflect the solar radiation at the short wave and can be transparent at long wave. A designed optical thin film is deposited on the surface of thermochromic material by electron beam evaporation. Experiments show that the solar absorptivity is reduced from 0.78 to 0.28 at short wave, and the transmissivity is 0.87 at long wave. The results match pretty well with the theoretical predictions in a global view.Highlights► We present a study of the optical properties of La0.7Ca0.2Sr0.1MnO3La0.7Ca0.2Sr0.1MnO3 (LCSMO). ► An optical thin film is designed using the SAGA to reduce the solar absorptivity of LCSMO. ► The designed thin film is deposited by electron beam evaporation on the LCSMO substrate. ► The simulated solar absorptivity and spectral reflectivity match pretty well with the measured results in a global view. ► The solar absorptivity is decreased experimentally from 0.78 to 0.28.

By accounting for the external and internal force acting on the suspended magnetic nanoparticles and motion characteristics of the suspended magnetic nanoparticles in the magnetic fluids, the three-dimensional microstructure of magnetic fluids is investigated by means of the molecular dynamics simulation method. The distribution of suspended magnetic nanoparticles and microstructure of the magnetic fluid are simulated in both absence and presence of an external magnetic field. The effects of the nanoparticles volume fraction, the dipole-dipole interaction potential and the particle-field interaction potential on the microstructures of the magnetic fluids are discussed. The main results obtained here are summarized as follows. The suspended magnetic nanoparticles tend to aggregate and make the irregular distribution structure in the absence of an external magnetic field. When the magnetic fluid is exposed to a magnetic field, the magnetic nanoparticles suspended in the carrier fluid tend to remain chained-alignment in the direction of the external magnetic field. The tendency of chain-alignment morphology of the suspended magnetic nanoparticles is enhanced with the nanoparticles volume fraction, the dipole-dipole interaction potential and the particle-field interaction potential.

•Thermal radiative properties of the device based on manganese oxides were studied.•Particles irradiation experiment in simulated space environment was conducted.•The irradiation-induced degradation of the device was presented.•The degradation mechanism of thermal radiative properties was discussed.Influence of particles irradiation, 60–1000 KeV electrons and 100 KeV protons in energy, on the thermal radiative behaviors of variable emissivity devices based on manganese oxide have been investigated. To evaluate thermal radiative degradation, the solar absorptivity, temperature-dependent reflectivity, and thermal emissivity of these devices are studied before and after particles irradiation. The thermal radiative degradation behavior in device without coating solar reflection films is reported, and the degradation mechanism is discussed. In addition, it is revealed that the thermal radiative properties of the device coated solar reflection films shows an excellent stability without degradation in simulation environment.

•Four different volume fractions nanofluids are introduced into jet arrays impingement.•Nanofluids can effectively improve the heat transfer coefficients.•Dispersant SDBS is proved to weaken the heat transfer using jet arrays impingement.•An enhancement on heat transfer of 6.8% using nanofluid is achieved.In this study, nanofluids were introduced into jet arrays impingement as the working fluid. The heat transfer features of the nanofluids were experimentally investigated. Four different Cu-nanoparticle volume fractions ranged from 0.17 Vol.% to 0.64 Vol.% and two dispersant sodium dodecyl benzoic sulfate (SDBS) mass concentrations varied from 0.05 wt% to 0.1 wt% were involved. The influences of the nanoparticle volume fraction and the dispersant SDBS on the heat transfer of nanofluids were discussed. The experimental results show that the suspended nanoparticles increase the heat transfer performances of the jet arrays impingement cooling system. It had also been found that compared with the case of using nanofluids without any addition of dispersant, the nanofluid with dispersant led to a great deterioration on impingement heat transfer coefficient and even the heat transfer coefficients were smaller than that of the base liquid.