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A study of the effects of ullage during the burning of horizontal PMMA and MMA surfaces
摘要： Experimental and numerical investigations of burning of horizontal surfaces of poly methyl methacrylate and methyl methacrylate are presented. A burner used in this study allows for the fuel surface to be oriented horizontally at a given distance from the burner rim. One of the aims of this study is to understand the effects of ullage (distance between burner rim and fuel surface) on the burning rate of the fuel and the flame structure. In the case of poly methyl methacrylate, the surface at an initial ullage regresses during its burning, and in the case of methyl methacrylate, the pool level is maintained at the given ullage by supplying the fuel at the rate of its burning. Careful repeatable measurements of temperature and species fields are carried out. These reveal the structure of a small‐scale pool flame established over a polymeric fluid such as methyl methacrylate, and such data are scarce in literature. In order to complement the experimental results, fire dynamics simulator is employed to simulate the experimental cases. Flame structure and flow field in the gas phase have been presented and discussed. As the ullage increases, the burning rate decreases. This trend is explained using surface convective heat flux results.
关键词： fire dynamics simulator (FDS),convective heat flux,burning rate,poly methyl methacrylate (PMMA),flame structure,ullage
更新于2025-09-23 15:23:52
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Direct utilization of solar linear Fresnel reflector on multi-effect eccentric horizontal tubular still with falling film
摘要： The paper presents a multi-eccentric tubular desalination system heated directly by a linear Fresnel reflector (LFR) field to enhance the productivity. In this novel system, the solar radiation is sent directly into desalination unit. The configuration and working processes of the proposed design are described in details. The tube inner wall with absorbing coating were used as a receiver by placing in the cylindrical cavity to absorb concentrated solar energy and transfer it to a falling water film. To verify the performance of the system in different effects, an indoor experimental eccentric tubular still was fabricated and tested under different heating conditions from 400 to 1600 W respectively. The experimental results showed that the maximum accumulated yield of the 1st and 2nd effect are about 28.27 kg and 21.37 kg, respectively. The outdoor experimental results show that the cumulative output of the unit is about 11.35 kg, the maximum performance ratio (PR) is about 2.88 with an evacuated tube solar collector. A two-effect tubular desalination system for linear Fresnel reflector with a capacity of 63.68 kg/d was proposed according to the presented theoretical and experimental work. By taking solar linear Fresnel reflector heating mode, the cost of water production reaching about $6.16/ton.
关键词： Falling water film,Heat and mass transfer,Solar distillation,Horizontal tubular still,Multi-eccentric
更新于2025-09-23 15:23:52
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An unstructured Monte Carlo ray-tracing method for solving radiative heat transfer in 3D gray semitransparent medium
摘要： Monte Carlo ray-tracing method (MCRTM) is widely used for solving the Radiative Transfer equation (RTE) due to its high accuracy and flexibility. In this paper, a MCRTM is developed for solving the radiative heat transfer in gray semitransparent media with complex geometries which are discretized by 3D unstructured grids. A novel algorithm associated to unstructured four-node tetrahedron element is proposed for generating random emitting positions of rays, and the ray tracing process is performed based on Beer's law. Meanwhile, radiation distribution factors are used for calculating radiative source terms which are loaded to the grid. The present method is first validated by comparing the predictive results with those from previous studies on a cubic enclosure, a 3D L-shaped enclosure, and a 3D elliptical enclosure, respectively. Furthermore, a radiation-conduction heat transfer problem is examined in a cylindrical enclosure. All the comparisons show that the present method is in good agreement with these previous cases. This method can be well adapted to various complex geometries. In addition, since the source term is calculated by the radiation distribution factor, which can be reused for different conditions as long as the volumetric radiative properties remain unchanged, this will bring great advantage when coupled with other heat transfer models such as conduction, convection, combustion, etc.
关键词： Monte Carlo ray-tracing method,Radiative heat transfer,Semitransparent medium,Radiation distribution factor,Unstructured grids
更新于2025-09-23 15:23:52
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Real-time estimation of time-dependent imposed heat flux in graded index media by KF-RLSE algorithm
摘要： Due to the large computational time caused by complex computational process of the existing inversion algorithm, real-time reconstruction of high-magnitude time-dependent heat flux in graded index media is quite challenging. In this study, based on hybrid technology of the Kalman filter and recursive least-square estimator (KF-RLSE), the real time reconstructed high-magnitude time-varying heat flux on graded index media surface, and the measurement information comes from the opposite side of the media. The ideal participating media, which is assumed to be isotropic scattering, constant thermophysical properties, and opaque and diffuse gray boundary, is employed to verify the reliability and validity of the proposed. All the reconstruction results show that the KF-RLSE algorithm can effectively reconstruct the boundary heat flux regardless of the positive or negative gradient of the refractive index. When the refractive index of each position increases or reduces, the transient heat flux on the surface can still be predicted effectively and acceptably. Furthermore, effects of different parameters on the accuracy and stability of the estimated results are also investigated. The reconstructed results show that the time-dependent heat flux can still be effectively reconstructed even when the measurement noise does not match its covariance. Meanwhile, the accuracy of the reconstruction results improves with the decrease of measurement noise covariance when the measurement noise distribution is fixed in a curtain range.
关键词： Recursive least squares estimator,Inverse radiation-conduction problem,Time-dependent heat flux,Graded index media,Kalman filter
更新于2025-09-23 15:23:52
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Transparent wood bearing a shielding effect to infrared heat and ultraviolet via incorporation of modified antimony-doped tin oxide nanoparticles
摘要： Optically transparent wood (TW) is an emerging candidate for applications in energy efficient buildings. In this study, anti-ultraviolet and infrared heat shielding TW was prepared based on the delignification of the wood's substrate. This was followed by infiltration of pre-polymerized methyl methacrylate (PMMA) with modified antimony-doped tin oxide (ATO) nanoparticles. The ATO addition enhanced the interfacial bonding among the compounds, which improved the fracture strength, leading to a high fracture strength of 96.4 MPa and modulus of 4.27 GPa with addition of 0.3% ATO. Furthermore, the obtained ATO/TW exhibited high transparency, excellent near infrared (NIR) heat shielding performance, and ultraviolet (UV) shielding properties according to the ultraviolet–visible spectrophotometer measurement, the infrared heat shielding simulation test, and the UV-shielding test. The TW treated with 0.3% ATO still maintained a very low thermal conductivity of around 0.2 W m?1 K?1. After addition of 0.7% ATO, the obtained TW had a quite low UV transmittance of ＜20%. The Aspergillus niger maintained high viability after UV irradiation treatment when shielded with TW treated with 0.7% ATO. The findings indicate that the multifunctional and durable ATO/TW has a potential to be used as energy-saving building material.
关键词： A. Nano composites,A. Wood,B. Ultraviolet shielding,B. Infrared heat shielding
更新于2025-09-23 15:23:52
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Performance of a modified solar chimney power plant for power generation and vegetation
摘要： This paper develops a mathematical model to investigate the performance of a modified solar chimney power plant (MSCPP) for purposes of both power generation and vegetation. It then estimates the net added benefit. Results show that with the vegetation area enlarging, the MFR of the vapor increases, and more heat is used as the latent heat for water evaporation, leading to considerable reduction of the power. Condensation from the saturated air occurs only for very large vegetation area. On a cooler day, the plant produces less power and the condensation occurs for smaller vegetation area. Higher relative humidity of ambient air results in clear reduction of the MFR of the vapor evaporating from the vegetation area, and accordingly the great enhancement of the power. The benefit from agricultural products is larger than the benefit loss caused by the electricity loss, and the benefit of fresh water condensed from the saturated air is negligible. This leads to net added benefit for the MSCPP compared to the conventional plant. The net added benefit becomes greater with larger vegetation area. When the chimney is heightened from 1000 m to 1500 m, the power is enhanced greatly; however, the net added benefit becomes smaller.
关键词： Vegetation,Solar collector,Latent heat,Fresh water,Solar chimney,Power generation
更新于2025-09-23 15:23:52
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A study of methods to enhance infrared emissivity of Molybdenum surfaces
摘要： Single crystal Molybdenum is one of the most promising materials for the First Mirror (FM) of ITER optical diagnostics due to its high resistance to erosion under neutral atom bombardment. Other advantages are: low CTE, high thermal conductivity, and advantageous mechanical properties at elevated temperatures. The FMs are normally located in the front-end of ITER port plugs, being subject to volumetric heat loads up to ～1 W/cm3 and higher. Active cooling of Mo mirrors by water or gas flow has limited applicability due to remote handling, integration and risk requirements. An athermal design with radiative cooling was developed for the H-alpha FM unit (FMU) with an all-Mo/TZM structure comprising a TZM housing, two Mo mirrors and the TZM cleaning electrodes. The main idea is to minimize mirror angular displacements and to keep the alignment at temperatures up to ～350 °C. That requires a balance between thermal contact and radiative heat sinks. The most uniform temperature profile is obtained by weak thermal contact between FMU and support structure, but that leads to the highest FM temperature, since the normal as-milled Mo surface has a very low effective emissivity (ε < 0.1 at 200…400 °C). Well-known tools for surface blackening are: enhanced roughness, oxidation, V-grooving, and coatings, which should be analyzed for outgassing rate, thermal radiation and long-term stability in Hydrogen environment. In this study, a number of techniques to enhance Mo surface effective emissivity were tested: V-grooving, detonation spray coating, drilling and surface electro-erosion. Spectral emissivity of the test samples was measured by Bruker Vertex-70 infrared Fourier spectrometer and the effective values were derived for subsequent thermal analyses. Alumina coatings were found to be the most effective tool with ε ≈ 0.8…0.9. However, V-grooving and drilling also provide acceptable results (εeff ≈ 0.25…0.3) and do not require qualification for applicability to ITER. The trade-off between different techniques is discussed in detail.
关键词： Emissivity,ITER,Heat load,Molybdenum,Mirror
更新于2025-09-23 15:23:52
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Radiative thermal conduction of molten tin sulfide estimated from its optical emission spectrum
摘要： Molten semi-conductors have potential utility in thermoelectrics or heat-management at high temperature (900 °C and above), though their development requires further analysis of their thermal conduction mechanisms, in particular radiative heat-transfer. Using a container-less method based on the floating zone furnace, the optical emission properties of a pendant droplet of molten tin sulfide (SnS) are investigated in the UV–visible (200–850 nm) and near IR (900–2050 nm) ranges. The emissivity results suggest a low emissivity for molten SnS at the peak of radiation for the temperature range of 890–950 °C. Corresponding estimates of radiative thermal conductivity suggest its minor contribution to the overall thermal conduction of molten SnS.
关键词： Container-less,Radiation,Melts,Emissivity,Radiative heat-transfer,Molten semi-conductor
更新于2025-09-23 15:23:52
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Graphene electrode diagnostic with IR imaging of Joule heat emission
摘要： Conductive graphene electrode of large area is required for some applications like for example photovoltaics or touch screens. Such large area graphene membrane needs specific test methods to assess defects which may obstacle its performance. In this work the infrared imaging of Joule heated graphene was proposed to estimate its uniformity and mechanical continuity. Thermal signatures of the typical mechanical defects like scratches and local resistivity inhomogeneity were identified. Distribution of the heat emission around such defects were simulated using finite elements method and then experimentally verified by recording of thermal landscape around the corresponding real graphene defects. Proposed method gives micrometric resolution and ability to inspection of large area electrodes depending on applied optics. Presented results give suggestions how graphene imperfections generate observed hot points related to graphene layer defects.
关键词： Finite elements,Joule heat,Defect,Graphene,Infrared
更新于2025-09-23 15:23:52
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Evolution of the infrared emissivity of Ni during thermal oxidation until oxide layer opacity
摘要： The mid-infrared (3–22 μm) emissivity of high-purity Ni has been studied in its pure state, during an isothermal oxidation in air at 730 °C and in the fully oxidized state. Measurements in pure Ni were performed in Ar between 200 and 800 °C and a change of slope in the temperature dependence of the total normal emissivity around its Curie temperature (354 °C) was observed. An oxidation process was carried out at 730 °C for 33 days, when the emissivity stopped evolving and the results were representative of NiO. During the ?rst stages, the emissivity evolved forming the usual interference patterns of semi-transparent ?lms. A mixture of oscillatory and monotonic behaviours of the emissivity as a function of wavelength and oxide layer thickness was found, which manifests as a non-trivial evolution of the total normal emissivity, di?erent than that reported in previous studies. Finally, the emissivity of NiO was measured from below its Néel temperature (252 °C) to 850 °C. It showed the typical shape of a ceramic material with an extra vibrational mode due to two-phonon processes and an additional absorption band around 5 μm in the antiferromagnetic phase produced by magnons. The temperature dependence of its total normal emissivity di?ers signi?cantly from that of a lightly oxidized nickel sample from the literature. Overall, the in?uence of the surface characteristics on the thermal radiative properties of oxidized Ni is thoroughly discussed and highlights the importance of accounting for all possible sources of infrared emissivity evolution in order to make accurate radiative heat transfer calculations.
关键词： Nickel oxide,Infrared emissivity,Radiometry,Radiative heat transfer,Magnetic phase transition,Nickel,Oxidation
更新于2025-09-23 15:23:52