Search Results (43)

The Co-CuCoMnO_x coatings with varying proportions were prepared and investigated to develop a novel metal–ceramic solar selective absorption coating employed at high temperature. The CuCoMnO_x powders were synthesized using the solid-phase reaction method. Subsequently, Co-CuCoMnO_x coatings were deposited on the surface of 316L steels utilizing the atmospheric plasma spraying (APS) technique. The results showed that the synthesized CuCoMnO_x powders were mainly composed of two phases, which were Cu_1.5Mn_1.5O₄ and MnCo₂O₄. The CuCoMnO_x powders had a solar absorptance of 0.929 and an infrared emittance of 0.862, which was considered a good solar absorbent. The synthesized Co-CuCoMnO_x coating had a typical thermal spray layered stacking structure. The chemical phases of the coatings were mainly Co, CoO, and CoCuMnO_x. Due to the addition of CuCoMnO_x inhibiting the oxidation of Co during the thermal spraying process, the 95Co-5CuCoMnO_x (wt%) coating exhibited the optimal quality factor (α/ε) of 2.184, with a solar absorptance α of 0.808 and an infrared emittance ε of 0.370, respectively. Moreover, this specific coating demonstrated a good thermal stability for up to 3 h when exposed to an atmospheric environment at 450 °C. The results indicate its significant potential for high-temperature solar selective absorption coating. Full article

The present work aims to develop the current CubeSats architecture. Starting from the framework of project ARAMIS (an Italian acronym for a highly modular architecture for satellite infrastructures), a new concept of smart tiles has been developed, employing multifunctional structures and lightweight, composite materials. This enables increased CubeSat mass efficiency and payload volume. An embedded battery tile has been designed, built, and tested from a vibration point of view. In the present work, the LiPo batteries selected for the prototype have been tested with the HPPC testing procedure, to extract their equivalent Randles circuit parameters. Thus, the thermal power dissipation from the batteries can be estimated. With these data, Thermal Desktop simulations of a representative ARAMIS CubeSat are performed, considering LEO orbit and hot/cold cases. Firstly, a parametric analysis was conducted to evaluate the thermal behaviors of various design alternatives. A suitable configuration for the CubeSat was then found, enabling the validation of the embedded battery tile from a thermal point of view. The final configuration includes heaters for the LiPo batteries, a commercial CubeSat skeleton made in aluminum alloy, and a top coating for smart tiles with proper solar absorptivity. Full article

This paper continues the mathematical research of the novel glass tube collectors for water heating. The subject of this research is a vacuum solar collector composed of a glass tube and a selective (using the SnAl₂O₃ coating) flat absorber plate. Water heating is performed using gravitational driving force and single-stage direct flow. The thermal performance with the geometric optimization (absorber width and glass tube thickness) of the presented solar collector type was determined using the specially designed iterative calculation algorithm (phase 1) and the double multi-criteria analysis (phase 2). Different operational (absorber temperature, ambient temperature and wind speed), geometric (mass, surface occupation, total surface occupation and volume occupation), economic (manufacturing costs and exploitation costs) and ecological (embodied energy and greenhouse gas emission) indicators were taken into account. The results showed that the useful heat power has an increasing trend if the flat absorber plate width increases, while the thermal efficiency has a decreasing trend. It was also determined that the glass tube thickness and the thermal performance of the solar collector are oppositely dependent. The main conclusion of this paper is that the optimal performance of such non-conventional solar systems is achieved when the absorber plate width is between 85 and 90 mm. Full article

Solar collectors represent an attractive green technology for water heating, where sunlight is efficiently absorbed by a selective coating and the generated heat is transferred to water. In this work, the improvement and scale-up of an electrodeposited black nickel selective coating with a modified silica (MS) film deposited by spray pyrolysis are reported. The MS material was prepared by the sol–gel method using tetraethyl orthosilicate with the addition of n-propyl triethoxysilane to obtain a porous film with an adequate refractive index and enhanced flexibility. The reflectance of electrodeposited selective coatings was characterized with and without the MS film and compared to a commercially available coating of black paint. The MS film increased the solar absorptance from 89% to 93% while maintaining a much lower thermal emittance than the painted coating. The reflectance of the MS film remained unchanged after prolonged thermal treatment at 200 °C (200 h). The fabrication process was scaled up to 193 cm × 12 cm copper fins, which were incorporated in commercial-size flat-plate solar collectors. Three complete collectors of an area of 1.7 m² were fabricated and their performance was evaluated under outdoor conditions. The results show that the electrodeposited selective coating with the MS film outperformed both the commercial black paint system and the system without the modified silica film. Full article

In recent years, third-generation solar cells have experienced a remarkable growth in efficiency, making them a highly promising alternative energy solution. Currently, high-efficiency solar cells often use top electrodes fabricated by thermal evaporation, which rely on high-cost and high energy-consumption vacuum equipment, raising significant concerns for mass production. This study develops a method for fabricating silver electrodes using the screen-printing process, aiming to achieve solar cell production through an all-solution coating process. By selecting appropriate blocking-layer materials and optimizing the process, we have achieved device efficiencies for organic photovoltaics (OPVs) with screen-printed silver electrodes comparable to those with silver electrodes fabricated by thermal evaporation. Furthermore, we developed a method to cure the silver ink using near-infrared (NIR) annealing, significantly reducing the curing time from 30 min with hot air annealing to just 5 s. Additionally, by employing sheet-to-sheet (S2S) slot-die coating, we scaled up the device area and completed module development, successfully verifying stability in ambient air. We have also extended the application of screen-printed silver electrodes to perovskite solar cells (PSCs). Full article

Solar thermal selective coatings (STSCs) are crucial for enhancing the thermal efficiency of receivers in solar power applications. Enhancing the photothermal conversion performance of STSCs is crucial for improving the thermo-economic efficiency of these sustainable high-temperature applications. Wherefore, in this study, we comprehensively review the ongoing technologies and enhanced strategies of solar thermal selective coatings, highlighting their advantages, drawbacks, technological advancements, and mechanisms. This review comprehensively examines the latest advancements in material synthesis, coating structure designs, and induced aging mechanisms of STSCs. It critically discusses the various types of STSCs, and the research techniques employed to assess photothermal performance and enhance thermal stability. Lastly, the limitations and future expectations of STSCs are also highlighted. This paper serves as a detailed guide for planning and implementing various types of STSCs in diverse solar power applications. Full article

Due to climate change, population increase, and the urban heat island effect (UHI), the demand for cooling energy, especially in urban areas, has increased and will further increase in the future. Technologies such as radiative cooling offer a sustainable and energy-free solution by using the wavelength ranges of the atmosphere that are transparent to electromagnetic radiation, the so-called atmospheric window (8–13 µm), to emit thermal radiation into the colder (3 K) outer space. Previous publications in the field of textile building cooling have focused on specific fiber structures and textile substrate materials as well as complex multi-layer constructions, which restrict the use for highly scaled outdoor applications. This paper describes the development of a novel substrate-independent coating with spectrally selective radiative properties. By adapting the coating parameters and combining low-emitting and solar-reflective particles, along with a matrix material emitting strongly in the mid-infrared range (MIR), substrate-independent cooling below ambient temperature is achieved. Moreover, the coating is designed to be easily applicable, with a low thickness, to ensure high flexibility and scalability, making it suitable for various applications such as membrane architecture, textile roofs, or tent construction. The results show a median daytime temperature reduction (7 a.m.–7 p.m.) of 2 °C below ambient temperature on a hot summer day. Full article

In its simplest terms, a closed-cavity façade (CCF) is a sealed, unventilated enclosure equipped with motorized shading devices, internal double or triple glazing, and external single glazing. This technology effectively controls solar energy and daylight entry into buildings. This research aims to enhance the thermal efficiency of CCFs in tropical climates using Venetian blinds (VB) and advanced glass coatings. EnergyPlus and DesignBuilder were employed to assess various CCF designs and compare them to a single glazing unit (SGU) with grey coatings. This was inspired by a residential case study on Penang Island, Malaysia. The findings indicate that CCFs surpass SGUs in thermal performance and occupant comfort, particularly in Malaysia’s humid tropical climate. CCFs reduced operating temperatures by a monthly percentage ranging from 33.5% to 68.75% in all operations. On an annual basis, temperature reductions ranged from 27.5% to 80.25%, with maximum decreases between 2 °C and 4 °C and minimum decreases between 0.5 °C and 1 °C compared to SGU units. The results show that CCFs outperform SGUs in thermal performance and comfort, reducing operating temperatures by 33.5% to 68.75% monthly and 27.5% to 80.25% annually. Temperature reductions ranged between 2 °C and 4 °C at maximum and 0.5 °C and 1 °C at minimum compared to SGU. Notably, Venetian blinds with nano-coatings (83/58) and low-E coatings (83/23) (T_vis/T_sol) were the most effective. This study highlights the importance of selecting appropriate coatings for CCFs, and demonstrates their potential in enhancing interior temperatures and comfort in Malaysia’s climate. The findings emphasize the significant impact of innovative glazing technologies on improving operational temperatures and occupant comfort using closed-cavity façades in the tropics. Full article

Asphalt pavements absorb more than 90% of the incident solar radiation, which induces not only high-temperature degradation but also the urban heat island (UHI) effect. In this study, a novel nanoscale non-stoichiometric compound containing tungsten (M_xWO₃) was used for the first time to prepare thermal shielding coatings to reduce the temperature of pavements and mitigate the UHI effect. Coatings with good shielding characteristics were selected for outdoor thermal insulation tests to evaluate their properties. M_xWO₃ (M = K, Na, Cs) exhibited significant thermal shielding, especially Cs_xWO₃. Outdoor thermal insulation tests were performed for the Cs_xWO₃ coatings, and it was found that the greater the doping, the more significant the thermal shielding effect. Compared with untreated pavements, the surface-coated pavement exhibited significant cooling at 5 cm and 15 cm depth-wise, which reduced the overall pavement temperature by 1–2 °C, and the coating thickness affected the cooling effect. Full article

Flat plate collectors (FPCs) are the leading solar thermal technology for low-medium range temperature applications. However, their expansion in developing countries is still lacking because of their poor thermal performance. Improving the thermal performance of flat plate collectors (FPCs) is a crucial concern addressed in this review This study comprehensively discussed the performance improvement methods of FPCs, such as design modification, reflectors, working fluid, and energy storage materials, by covering current issues and future recommendations. Design factors such as coating and glass cover thickness, thickness of absorber plate and material, air gap between the glass cover and absorber plate, and riser spacing, along with insulation materials, are examined for their impact on FPC performance. Absorber design changes with selective coatings for improving the heat transmission rate between the working fluid and absorber are critical for enhancing collectors’ thermal output. The nanofluids utilization improved FPC’s thermal performance in terms of energetic and exergetic outcomes in the 20–30% range. Moreover, adding a heat storage unit extends the operating hours and thermal output fluctuations of FPCs. Research suggests that employing turbulators and nanofluids as heat transfer fluids are particularly effective for enhancing heat transfer in FPCs. This comprehensive review serves as a critical tool for evaluating and comparing various heat transfer augmentation techniques, aiding in the selection of the most suitable option. Full article

Solar thermal collectors represent a practical option to capture energy from the sun, providing low-cost domestic and industrial heating and decreasing the dependency on fossil fuels. Spinel-type metal oxides show interesting physicochemical properties and so can be used as active materials for converting solar energy to electrical, chemical, and heat energy. We report the synthesis and characterization of nickel–cobalt mixed metal oxides used as an active phase in selective paints for solar absorber coatings applied to a domestic flat collector. The nickel–cobalt mixed oxides crystallized in the cubic phase related to the spinel structure, exhibiting good thermal stability and reproducibility. These mixed oxides presented oxidation states (2+ and 3+) for both nickel and cobalt. The coatings fabricated from the selective paints based on nickel–cobalt mixed oxides showed a solar absorptance value of 94%, while for the commercial paint Solkote^®, the value was 93%. A representative coating based on the NiCo₂O₄ composition was evaluated for the first time in a domestic-type flat solar collector for water heating under real operating conditions, achieving an outstanding performance that competes with that of commercial collectors. The potential application of nickel–cobalt mixed oxides in solar collectors opens up new opportunities for future innovations and developments in functional absorber coatings. Full article

The energy efficiency of a small-scale solar concentrating thermal device is investigated, based on Monte-Carlo Ray-Tracing (MCRT) and Computational Fluid Dynamics (CFD) modeling. The device consists of a Fresnel lens collector—engraved on a 1 m rectangular plate—and a 10 cm sized plate receiver, with drilled cylindrical channels with a diameter of 10 mm. Inlet velocities and heat transfer fluid (HTF) temperatures lie within the range of 0.25–1 m/s and 100–200 °C, respectively. The configurations examined involve the utilization of a selective coating on the absorbing surface of the receiver, increasing the channel diameter to 15 mm and the receiver size to 20 cm, and insertion of a glass envelope in front of the absorbing surface. Energy efficiency increases with increasing fluid velocity up to 80%, a level beyond which no further improvement is observed. The coating contributes to a reduction in heat losses; it brings substantial benefits for the lower velocities examined. The increase in channels diameter also contributes to an increase in the energy efficiency, while the increase in receiver dimensions leads to the opposite effect. The glass cover does not improve the performance of the collector, due to substantial optical losses. Full article

The stainless steel chemical coloration demonstrates excellent repeatability of process when adopted to fabricate solar selective absorber coatings (SSACs) on TTS445J1 stainless steel base material. The optical performance, morphology, and composition of coatings are characterized by UV-3600, IR-Affinity-1, SEM, EDS, etc. The experimental results suggest that the Cr-Fe composite oxides with coatings in a spinel structure obtained by chemical coloration on a stainless steel surface exhibit outstanding spectral selectivity, with α/ε = 0.9334/0.1326. The coatings were generated by the direct reaction between the stainless steel substrate composition and the coloring solution, which changes the traditional way of combining the coating with the substrate by physical methods. Comparing the SEM images of the coatings before and after aging at 500 °C in air, we noticed no significant changes at the interface between the coatings and the substrate, indicating excellent coating adhesion. At the same time, the substrate grains did not change much after the chemical reaction of the stainless steel substrate, indicating that the oxidation resistance of the stainless steel substrate was not weakened. Finally, the Cr-Fe composite oxide exhibited excellent thermal stability in air. Based upon a microstructure analysis, the Performance Creation (PC) is 0.01 after aging at 500 °C for 200 h in high-temperature air, primarily because of the loss of H₂O molecules from the hydrates in the coatings. After aging for 800 h, PC = 0.0458. After the aging hours are extended to 1000 h, PC = 0.0762. During the aging process at high temperature, the coatings of the Cr-Fe composite oxides maintained stable composition and phase structures. The decay in optical performance is due mainly to the reconstruction of the surface morphology of the coatings as a result of the largening of grains. Full article

Proper selections of microwave-transmitting thermal control materials play key roles in the orbit operations of aerospace microwave detectors. Currently, white paint and germanium-coated polyimide film are common choices for microwave-transmitting thermal control, which have been extensively studied from the perspective of material compositions, ignoring the influence of the micro-nano structure on the surface of the material. Inspired by Saharan silver ants relying on micro-nano structures of hairs for heat protection and dissipation, in this paper, based on finite element simulation, spectral characteristics (e.g., solar absorptance and infrared emissivity) of three types of biomimetic micro-nano structures (e.g., including pyramid, tetrahedron, and triangular prism) were studied and compared. Simulation results revealed that spectral characteristics of these biomimetic micro-nano structures were mainly regulated by the tip height and the air gap; the decrease of the tip height led to the decrease in the solar absorptance and the infrared emissivity; the solar absorptance was decreased, and the infrared emissivity was increased with the increase of the air gap. When these biomimetic structures were compared with flat surfaces without micro-nano topographies, a decrease of the solar absorptance to block the incidence of heat flow from the sun and an increase of the infrared emissivity to dissipate its own heat to the space were located, which may give suggestions on the adjustment of spectral characteristics of aerospace microwave-transmitting thermal control materials. Full article

In this study, nitrogen-doped nickel graphene core cells (N-NiGR) are synthesized using the thermal chemical vapor deposition method. The structural, morphological, and chemical composition properties of N-NiGR are investigated using X-ray diffractometry (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. N-NiGR has shown potential as a material that can assist charge carrier transportation in the photoactive a layer of planar hybrid solar cell (PHSC) owing to its high charge carrier mobility and stability with the solution process. Here, we investigated for the first time an enhancement of the solar cell efficiency (by up to a 2% increase) in PHSCs by incorporating the charge selective N-NiGR into the device’s photoactive layer. Synthesized N-NiGR with different concentrations are incorporated into the active layer of the devices as charge transport material. The device structure of an ITO-coated glass/Hole transport layer/(PBT7+N-NiGR+SnS)/Electron transport layer/Cathode is fabricated and the maximum power conversion efficiency of the device was observed to be about 4.35%. Full article