High Thermal Emittance Research Articles

Experimental Research of Diffusion Combustion and Emissions Characteristics Under Oxy-Fuel Combustion Mode

Abstract Internal combustion Rankine cycle (ICRC) concept implements oxy-fuel combustion, direct water injection (DWI), and waster heat recovery (WHR) into traditional Otto or diesel cycle to realize high thermal efficiency and low emission powertrain. In order to support ICRC realization, this paper is dedicated to investigate the feasibility of implementing oxy-fuel combustion into diffusion combustion which provides fundamental information for future compression ignition (CI)-ICRC engine. The prototype oxy-fuel diffusion combustion engine test bench is established based on a retrofitted diesel engine, and the O2/CO2 mixture intake system, high-pressure common rail fuel injection system, and high-performance electronic controller are designed and installed within engine test bench to investigate the combustion and emission characteristics under different intake oxygen fractions (OF), fuel injection durations, and fuel injection timing. The optimum intake OF and fuel injection strategies are acquired within the selected experimental conditions, a 41.1% brake thermal efficiency (BTE), and 1.2% coefficient of variation (CoV) is achieved utilizing 55% intake OF, 0.7 ms fuel injection duration and 352 °CA (after exchange top dead center (TDC)) fuel injection timing. The oxy-fuel diffusion combustion proved to be a feasible solution for simultaneously reduction in NOX and particulate emissions, and NOX emissions lower than 90 × 10−6 with particulate matters (PM) around 0.1 filter smoke number (FSN) is observed during engine bench testing. The result of this study provides fundamental information for future CI-ICRC prototype engine establishment and optimization, which also could be utilized as reference guidance for potential industrialization of internal combustion engine (ICE) with oxy-fuel combustion mode.

Reduced Graphene Oxide-Based Spectrally Selective Absorber with an Extremely Low Thermal Emittance and High Solar Absorptance.

Carbon‐based black materials exhibit strong solar absorptance (αsolar >0.90), which play key roles in transforming solar energy into available power for solar‐thermal, thermophotovoltaic, thermoelectric, and many other systems. However, because of high thermal emittance (>95%), these carbon‐based materials always cause huge energy loss that hinders the solar‐thermal conversion efficiency tremendously. In this study, a reduced graphene oxide–based spectrally selective absorber (rGO‐SSA) is demonstrated, which possesses a recorded low thermal emittance (≈4%) and high solar absorptance (αsolar ≈ 0.92) by easily regulating the reduction level of inner 2D graphene sheets. Compared to conventional carbon‐based black materials, thermal emittance of this rGO‐SSA is largely reduced by ≈95.8% and the cutoff wavelength of rGO‐SSA is broadband‐tunable that can range from 1.1 to 3.2 µm. More importantly, this simply sol‐gel coated rGO‐SSA has high temperature tolerance at 800 °C for 96 h that is hardly achieved by other cermet‐based or photonic‐based SSAs. Based on this rGO‐SSA, ultrafast solar steam escape (0.94 mg cm−2 s−1) under concentrated solar irradiance is achieved directly. The insight from this study will provide a new strategy for constructing thermally stable carbon‐based SSAs and greatly facilitate the solar‐thermal practical significance.

Synthesis of Single Crystal LiNi0.92Co0.06Mn0.01Al0.01O2 Cathode Materials with Superior Electrochemical Performance for Lithium Ion Batteries

Compared to conventional polycrystallines, single crystal layered cathode materials exhibit the excellent structural and thermal stability, storage and lifetime at high voltage and elevated temperature. However, these single crystal materials are less reported, especially for Ni ≥ 0.92 in nickel-rich cathode materials. In this paper, single crystal LiNi0.92Co0.06Mn0.01Al0.01O2 (NCMA) cathode materials are researched. The experiment demonstrates that co-doping fluxing agents in B-NCMA (NCMA with 1000ppm W and 1000 ppm Mo) sample facilitate to generate uniform and small crystal size, which delivers a high initial discharge capacity of 221.4 mAh g−1 at 0.1 C. Moreover, the superior capacity retention of 94.9% after 100th cycle at 45 °C is obtained. Furthermore, DSC analysis of cycled B-NCMA material displays high thermal release temperature and low gas emission, revealing decent thermal stability. XRD, dQ·dV−1 and EIS results suggest that co-doping fluxing agents beneficial to form less cationic mixing, more stable phase structure and less internal resistance, respectively, which are associated with excellent rate capacity, cycling and thermal stability of single crystal NCMA. In our opinion, this study will stimulate that more fluxing agents are found and applied on single crystal nickel-rich cathode materials, which will have a bright future in the high-energy lithium ion battery fields.

A visible-to-infrared broadband flexible electrochromic device based polyaniline for simultaneously variable optical and thermal management

A visible-to-infrared broadband flexible electrochromic device based on H2SO4-doped polyaniline films has been constructed for simultaneously variable optical and thermal management. Upon electrochemically manipulating, the demonstrated electrochromic device could change from a wide bandgap semiconductor to an insulator, causing the device to transform from a high thermal emitter with dark green to an optical reflector with bright yellow. High infrared emission changes of 0.4 and 0.3 for the device are observed at the wavelength ranges of 8–14 μm and 2.5–25 μm, respectively, which are higher than most reported electrochromic devices. A promising cycling stability and flexibility of the device are also observed. The thermal imaging results reveal that the device can be electrochemically and reversibly tuned to blend them with their environment. Furthermore, both the theoretical calculation and experimental results demonstrate that the device exhibits different heat transfer rates, facilitating the thermal management of the indoor object. The illustrated capabilities of the device make the electrochromic device highly promising for the optical management in visible-infrared regions and thermoregulation in indoor environment.

Mid-infrared emissivity of nylon, cotton, acrylic, and polyester fabrics as a function of moisture content

The effectiveness of material to emit energy as thermal radiation is important in determining the apparent temperature in infrared thermographic measurements. For this reason, a number of measurements of the thermal emissivity in the mid-infrared thermographic (8–12 µm) region have been reported for fabrics. However, many fabrics adsorb moisture from the air, and condensed water has a relatively high thermal emissivity. In this manuscript, we report measurements of adsorption isotherms and mid-infrared thermal emissivity for nylon, cotton, polyester, and acrylic as a function of their moisture content in weight percent at temperatures just above ambient. We find that the order of water mass percentage gain for the fabrics in high humidity conditions are polyester < acrylic < nylon < cotton. The thermal emissivity is ∼0.88 independent of moisture content for the fabrics polyester, cotton, and nylon, while acrylic shows a pronounced increase in thermal emissivity as moisture content increases, ranging from ɛ ∼ 0.81 at low humidity conditions to ɛ ∼ 0.88 under high humidity conditions. In this work, emissivity measurements are made by imaging through a novel infrared window made from household cling wrap and interpreted with equations that are independent of window transmittance and sample temperature.

Green emitting Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ phosphor with high thermal emission stability for warm WLEDs and FEDs

By hetero-valence substituting Ba2+-Si4+ for Lu3+-Al3+ pair in Lu3Al5O12: Ce3+, a new green phosphor Ba1.5Lu1.5Al3.5Si1.5O12: Ce3+ (BLAS: Ce3+) has been obtained. It crystallizes in garnet structure with space group Ia-3d (230). In the structure, Ba2+ ions are incorporated into both dodecahedral Lu3+ and octahedral Al3+ sites while Si4+ ions only occupy tetrahedral Al3+ sites. Under the blue light irradiation of 450 nm, an intense green light peaking at 520 nm was observed and the PL spectrum can be fitted in two Gaussian components, due to the crystal field splitting of Ce3+ 5d states under D2 symmetry constrains. The optical doping concentration of BLAS: Ce3+ is 6% mol, of which the IQE and EQE are 89.1% and 51.8%, respectively. Furthermore, this sample exhibits an extremely good thermal stability, i.e. the integrated emission intensity is still more than 90% of the initial intensity at 480 K. Then, a w-LED device was fabricated from this new green phosphor BLAS: Ce3+ and commercial red phosphor (Ca,Sr)AlSiN3: Eu2+, which shows a quite high color rendering (Ra = 88.2) and a relatively low color temperature 4772 K. Besides, the phosphor exhibits a stable chromaticity under different acceleration voltages. The phosphor may be promising material for the development of solid-state lighting and display systems.

Fabrication and characterization of Ni-Ce-Zr ternary disk-shaped catalyst and its application for low-temperature CO2 methanation

This study optimized a Ni-Ce-Zr catalyst and its contents for a CO2 methanation reaction by selecting a disk shape with a high mechanical strength, good durability, and thermal emission resistance. The physical and chemical properties of the obtained catalysts were determined by X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller, hydrogen temperature-programmed reduction, and temperature-programmed desorption of CO2 analyses. In addition, the activity and stability of the obtained catalysts were then evaluated and compared. It was determined that the combined Ni-Ce-Zr catalyst positively affects the conversion of CO2 to CH4. Furthermore, a CO2 methanation experiment was performed under atmospheric pressure conditions at 200–350 °C. The CO2 conversion was 82% at 300 °C, and the CH4 selectivity was 100%. A durability test revealed a difference in the conversion of approximately 6% for 1000 h, which indicates that the catalytic performance was maintained for a significant period.

An unusual transient following the short GRB 071227

ABSTRACT We present X-ray and optical observations of the short duration gamma-ray burst GRB 071227 and its host at z = 0.381, obtained using Swift, Gemini South, and the Very Large Telescope. We identify a short-lived and moderately bright optical transient, with flux significantly in excess of that expected from a simple extrapolation of the X-ray spectrum at 0.2–0.3 d after burst. We fit the SED with afterglow models allowing for high extinction and thermal emission models that approximate a kilonova to assess the excess’ origins. While some kilonova contribution is plausible, it is not favoured due to the low temperature and high luminosity required, implying superluminal expansion and a large ejecta mass of ∼0.1 M$\odot$. We find, instead, that the transient is broadly consistent with power-law spectra with additional dust extinction of E(B − V) ∼ 0.4 mag, although a possibly thermal excess remains in the z band. We investigate the host, a spiral galaxy with an edge-on orientation, resolving its spectrum along its major axis to construct the galaxy rotation curve and analyse the star formation and chemical properties. The integrated host emission shows evidence for high extinction, consistent with the afterglow findings. The metallicity and extinction are consistent with previous studies of this host and indicate the galaxy is a typical, but dusty, late-type SGRB host.

SrTiO3 as a new solar reflective pigment on the cooling property of PMMA-ceramic composites

Abstract Polymer-ceramic hybridization is an important method for preparing functional materials. Strontium titanate (SrTiO3, ST), a typical perovskite ceramic, has been widely applied in the electronics industry and photocatalytic fields. However, ST was barely reported to be utilized in cool materials. Herein, ST ceramic, as a solar reflective pigment, was introduced into a polymer matrix to prepare cool material. Specifically, the influences of both weight contents and surface grafting modification about ST on the properties of poly(methyl methacrylate) (PMMA)/ST composites were investigated, which include cooling performance, surface roughness, thermal emissivity, dispersion of particles and mechanical strength. The obtained composites containing 20 wt% unmodified ST possess excellent cooling property due to high thermal emissivity (86.8%, in 8–13 μm) and high solar reflectance (70.7%, in the whole solar band) which increased by 142% than that of pure PMMA resin. Temperature test highlighted that the composites containing 20 wt% unmodified ST was only 26.6 °C, 11.4 °C lower than that of PMMA resin and only 2 °C higher than initial temperature. Moreover, the surface grafting modification of ST by the silane coupling agent was proved to improve the dispersibility of ST in PMMA resin. Both the cooling and mechanical properties of composites containing modified ST particles were further improved. Though the solar reflectance of PMMA/ST composites was lower than that of PMMA/TiO2 composites, temperature tests showed that the PMMA/ST composites had a similar cooling performance with the PMMA/TiO2 composites when the content of the ceramic particles were 5.8 v%. This work not only prepared the polymer-ceramic hybrid materials with excellent cooling performance but also expanded the application of ST ceramic in the field of composites.

Experimental Research of High-Temperature and High-Pressure Water Jet Characteristics in ICRC Engine Relevant Conditions

The internal combustion Rankine cycle (ICRC) concept provides a potential solution for future high thermal efficiency and low emission powertrains, and direct water injection (DWI) proved to be the key parameter for ICRC optimization. This paper was dedicated to investigating the fundamental mechanisms of water spray characteristics under different water injection control parameters. In order to do so, an experimental test system was carefully designed and built based on the Bosch and Schlieren methods: the Bosch method is utilized to measure the effect of injection and ambient pressure on water injection characteristics, and the Schlieren method is utilized to investigate the impact of water injection and ambient temperature on water spray and evaporation processes. The experimental results indicate that both control parameters show important effects on water injection and spray characteristics. The water injection and ambient pressure show significant impacts on steady-state flow quantity and cyclic water injection quantity, and the water injection and ambient pressure affect the evaporation ability of water vapor within the spray which leads to a different variation trend during the initial, developing, and developed water spray stages. The results of this work can be used as fundamental supplements for ICRC, steam assistant technology (SAT), and DWI-related ICEs experimental and numerical researches, and provide extra information to understand the DWI process within engine-relevant conditions.

High-temperature tungsten-hafnia optimized selective thermal emitters for thermophotovoltaic applications

Tungsten-hafnia (W-HfO2) selective thermal emitters with high hemispherical emittance for thermophotovoltaic (TPV) applications are explored through numerical simulations. Two structures were analyzed: a planar multilayer stack and a grating. In both cases, through suitable design choices high thermal emittance with low directional sensitivity can be obtained. The designs are obtained by optimization of the structures using a genetic algorithm and a suitable cost function, along with simulations of the structures’ emittance by using rigorous coupled wave analysis. Calculations show that these optimized structures possess high hemispherical thermal emittance for the wavelength range that matches the optical response of GaSb photovoltaic cells. For each structure, both the output power from the TPV cell and the conversion efficiency are studied as a function of emitter temperature and physical understanding of the optimized structures is developed.

Optical properties of sputter deposited nanocrystalline CuO thin films

Black copper oxide thin films with high solar absorptance (α), high thermal emittance (ε), low diffused reflectance and moderate electrical conductivity are required for various light absorption applications and are conventionally prepared using processes involving carcinogen chemicals. Therefore, there is a need to develop these coatings using eco-friendly processes. In this paper, CuO thin films have been deposited on copper, glass and Si substrates using reactive direct current magnetron sputtering of Cu target. The structural, chemical and morphological characterization of the coatings was carried out using X-ray diffraction, micro-Raman spectroscopy, X-ray photoelectron spectroscopy and field emission scanning electron microscopy techniques. The results showed that both oxygen flow rate and sputtering time have a significant effect on the optical properties of the films. The optimized films were found to be of the composition CuO with α and ε of 0.955 and 0.52, respectively. The emissivity could be further increased to 0.78 after sandblasting of the substrate.

Metamaterial-Based Radiative Cooling: Towards Energy-Free All-Day Cooling

In the light of the ever increasing dangers of global warming, the efforts to reduce energy consumption by radiative cooling techniques have been designed, but are inefficient under strong sunlight during the daytime. With the advent of metamaterials and their selective control over optical properties, radiative cooling under direct sunlight is now possible. The key principles of metamaterial-based radiative cooling are: almost perfect reflection in the visible and near-infrared spectrum (0.3–3 µm) and high thermal emission in the infrared atmospheric window region (8–13 µm). Based on these two basic principles, studies have been conducted using various materials and structures to find the most efficient radiative cooling system. In this review, we analyze the materials and structures being used for radiative cooling, and suggest the future perspectives as a substitute in the current cooling industry.

Analysis of Cool Roof Passive Techniques for Residential Buildings in a Subtropical Humid Climate

The objective of this study was to provide the thermal comfort by means of passive cool solar reflective materials which have a high solar reflec­tance and high thermal emittance on the existing roof and thereby reducing the consumption of electrical energy. Experiments were performed by using locally available solar reflective materials to insulate the roofs. In this work, the thermal performance of concrete roof and asbestos sheet roof with and without insula­tion has been analyzed by performing experiments to existing buildings. The re­sults are verified by computer simulation using Computational Fluid Dynamics tools with FLUENT software. The result of using solar reflective paint with high reflective coating shows a fall of 4.8°C in peak hours and saves 303 kWh when considering an energy load with an air conditioner in the summer season, in comparison to non-insulated pitched and flat roof energy loads of residential buildings in Bhopal. An optimum solution of an insulator for both types of roofs is presented. The application is intended for low-rise or medium-rise residential buildings in a subtropical climate like Bhopal.

Effects of a Carbon Nanotube Additive on the Corrosion-Resistance and Heat-Dissipation Properties of Plasma Electrolytic Oxidation on AZ31 Magnesium Alloy.

Plasma electrolytic oxidation (PEO) coating was obtained on AZ31 Mg alloy using a direct current in a sodium silicate-based electrolyte with and without a carbon nanotube (CNT) additive. The surface morphology and phase composition of the PEO coatings were investigated through field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion-resistance properties of the PEO coatings were evaluated using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution. Furthermore, the heat-dissipation property was evaluated by a heat-flux measurement setup using a modified steady-state method and Fourier transform infrared spectroscopy (FT-IR). The results demonstrate that, by increasing the concentration of CNT additive in the electrolyte, the micropores and cracks of the PEO coatings are greatly decreased. In addition, the anticorrosion performance of the PEO coatings that incorporated CNT for the protection of the Mg substrate was improved. Finally, the coating’s heat-dissipation property was improved by the incorporation of CNT with high thermal conductivity and high thermal emissivity.

Highly colloidal luminescent porous Tb-doped gadolinium oxide nanoparticles: Photophysical and luminescent properties

Highly colloidal luminescent Gd2O3:Tb nanoparticles(NPs) were prepared by urea-based homogeneous co-precipitation process. X-ray diffraction pattern (XRD), transmission electron microscopy(TEM), energy dispersive x-ray analysis(EDX), thermogravimetric analysis(TGA), zeta potential, Fourier transform infrared(FTIR), FT-Raman, UV/Visible and photoluminescence spectroscopy to examine the crystallographic, phase purity, shape & size, thermal stability, surface chemistry, optical and photoluminescence properties. XRD results exhibited the single phase, highly pure cubic phase Gd2O3:Tb nanocrystals with an average grain size of 10–20 nm. The Gd2O3:Tb NPs exhibits attractive thermal, optical and luminescent properties for their use in long-term biological studies because of high thermal, photo-stability and strong emission sensitivities in the visible region. Optical features of Gd2O3:Tb NPs were examined in aqueous media and estimated energy band gap on the basis of absorption spectra. An observed strong peak located at 359 cm−1 is assigned to the Fg Raman active mode of cubic phase of nanocrystalline Gd2O3. The luminescence spectra show well dominant green emission transition in between 535–560 nm (5D4→7F5) under monitoring UV light (325 nm). Optically active, aqueous sensitivities, porous surface and strong luminescent NPs as revealed from TEM micrographs could be a promising candidate for future fluorescent biomedical applications.

Largely Lowered Transition Temperature of a VO2/Carbon Hybrid Phase Change Material with High Thermal Emissivity Switching Ability and Near Infrared Regulations

AbstractVanadium oxide (VO2) as a phase changing material possesses abrupt infrared (IR) transmission and thermal emissivity changing during the metal–insulator transition across transition temperature (τc) of 68 °C. However, the high τc, moderate IR transmission and emissivity regulating ability limits its applications in various fields. A VO2/carbon hybrid phase change material fabricated via homemade plasma enhanced chemical vapor deposition is reported. The material shows a best reported thermal emissivity contrast (0.44) among the experimental values, a largely lowered τc (45 °C), promising a near IR‐regulation ability with enhanced photothermal effect in smart windows applications. The theoretical calculation results proved that the improvement of emissivity contrast is due to the hybridization of carbon. This work provides a new approach to synthesize VO2 hybrid materials, which have wide applications in camouflage, sensing, and smart windows.

ALMA Thermal Observations of Europa

Abstract We present four daytime thermal images of Europa taken with the Atacama Large Millimeter Array. Together, these images comprise the first spatially resolved thermal data set with complete coverage of Europa’s surface. The resulting brightness temperatures correspond to a frequency of 233 GHz (1.3 mm) and a typical linear resolution of roughly 200 km. At this resolution, the images capture spatially localized thermal variations on the scale of geologic and compositional units. We use a global thermal model of Europa to simulate the ALMA observations in order to investigate the thermal structure visible in the data. Comparisons between the data and model images suggest that the large-scale daytime thermal structure on Europa largely results from bolometric albedo variations across the surface. Using bolometric albedos extrapolated from Voyager measurements, a homogenous model reproduces these patterns well, but localized discrepancies exist. These discrepancies can be largely explained by spatial inhomogeneity of the surface thermal properties. Thus, we use the four ALMA images to create maps of the surface thermal inertia and emissivity at our ALMA wavelength. From these maps, we identify a region of either particularly high thermal inertia or low emissivity near 90° west and 23° north, which appears anomalously cold in two of our images.

A REVIEW OF MATERIAL COVER FEATURES FOR MITIGATING URBAN HEAT ISLAND

AbstractUrban Heat Island (UHI) is related to the increase of urban compared to rural temperature as the result of global phenomenon. The increase of temperature is predicted to be intensified along with the extend of urban activity in the near future. Therefore, the discussion on UHI becomes significance. This paper discusses the result of literature studies on thermal characteristics of materials that potentially used to reduce Urban Heat Island, especially in utilizing pavement and roof cover. The result of the study concludes that the reduction of UHI is determined by: 1) the high-level albedo (the ratio between the reflected heat and the absorbed heat) of material that is influenced by the color and texture of its surface; 2) The high level thermal emittance of material; 3) The lower capacity of material to store the heat. 4) The capability thermal conductivity of material surface. Recommended pavements to reduce UHI are cool pavement, reflective pavement, porous pavers, permeable pavers, pervious pavement, water retaining pavement. Roof cover materials that reduce Urban Heat Island are Cool Roof and Green Roof. The design and toughness of materials should be considered to reduce UHI. Keywords: Urban Heat Island, material feature, thermal performance.

Electrodeposition of a Selective Coating Based on Black Cobalt on Stainless Steel (AISI 304) and Inconel 600 Substrates for Solar-to-Thermal Energy Conversion

Conversion of solar to thermal energy in solar collectors is achieved through selective coatings on metal substrates. The main characteristics of the selective coatings are a high solar absorptance and low thermal emittance, metallic substrates resistant to high operating temperatures and atmospheric corrosion. In this work, selective black cobalt solar coatings electrochemically deposited onto stainless steel (AISI 304) and Inconel 600 substrates, with an intermediate layer of bright nickel as an infrared reflector, are characterized. The transformation capacity of solar-to-thermal energy depends on the thickness of the films, which depends on the galvanostatic deposition time. Hence, by controlling the charge applied in the electrochemical deposition process, the optical properties can be optimized. The black cobalt coating used in this work has the characteristic of high absorption in the solar spectrum and low emission in the infrared, even after a thermal treatment of up to 500 °C on stainless steel substrates (AISI 304). The thermal stability of the selective coatings was studied by means of a thermal treatment in the range of 300 and 750 °C in air, observing the change in the optical properties due to the influence on the solar absorptance and the thermal emittance. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Vis – IR reflectance were evaluated before and after the heat treatment using an integrating sphere (2 μm to 15 μm). The black cobalt coatings presented homogeneity, stability, good adhesion and solar absorptance of 96% and thermal emittance of 7% (calculated at 100 °C). Results suggest that the electrochemically deposited black cobalt coating (UV-Vis absorber/IR reflector/metallic substrate) can be scaled-up and applied at medium to high temperatures for the conversion of solar radiation into heat.