Thermal transients during processing of materials by very high power ultrasonic additive manufacturing

Dynamic recrystallisation at interfaces has been suggested as the bonding mechanism in the joining of metallic tapes, during very high power ultrasonic additive manufacturing. To understand the reasons for such occurrence of dynamic recrystallization, thermal transients from the interface regions were recorded during processing of aluminum alloy (3003 and 6061 series) and 11 000 copper tapes under similar conditions. Measurements in 3003 Al were also carried out for different processing parameters. Measured peak temperatures were seen to increase with increase in shear strength of the material and ultrasonic vibration amplitude. The observations have been rationalized based on interfacial heating at asperities due to adiabatic plastic deformation.     

Interfacial thermal resistance measurement between metallic wire and polymer in polymer matrix composites

The addition of thermally conductive particles is an effective way to increase thermal conductivity of polymers. For highly filled composites and therefore for a high effective thermal conductivity, the heat transfer at the matrix/particle interface becomes a key point to obtain further improvement. However the interfacial thermal resistance R_i between particles and matrix is difficult to measure because of the low sensitivity of temperature to R_i and because of the small size of the particles. A setup has been developed to measure R_i between nickel wires (fiber-like particles) of a few tens micrometer diameter and a polymer matrix. The temperature measurement of the heating wire associated with a thermal model allowed to estimate values of R_i between 0.3 × 10⁻⁵ and 1.6 × 10⁻⁵ m² K W⁻¹ and for various wire diameters and sample temperatures. Some R_i measurements have been validated using a thermo-elastic model.     

Morphological,thermal and dynamic mechanical properties of Cathay poplar/organoclay composites prepared by in situ process

In order to improve the thermal stability and dynamic mechanical properties of Cathay poplar (Populus cathayana Rehd.) wood, a kind of organoclay, that is, organo-montmorillonite (OMMT), was introduced into its structure via an in situ process by sequentially impregnating poplar wood with sodium-montmorillonite (Na-MMT, in concentrations of 1.0%, 2.0%, and 4.0%) and didecyldimethylammonium chloride (DDAC, in a concentration of 2.0%). Consequently, the wood/organoclay composites were prepared. The X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersed X-ray analysis (SEM-EDXA) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the morphological and chemical alterations of the composites. Also the effects of clay type and concentrations on the thermal stability and dynamic mechanical properties of the composites were studied. The results showed that didecyldimethylammonium ions were intercalated into the galleries of Na-MMT through cation exchange, partially separating the silicate layers. Thereafter, the inorganic Na-MMT transformed to OMMT during the in situ synthesis process, and the latter was successfully intercalated into the wood cell wall. The thermal degradation was alleviated in the wood/clay composites, among which the wood/OMMT composites exhibited the best thermal stability. According to dynamic mechanical analysis (DMA) results, the wood/OMMT composites showed an enhancement in energy storage and a diminution in energy dissipation compared to other groups. The improvements in the thermal stability and dynamic mechanical properties of the composites became more significant with the increasing clay content.     

矿物质对焦炭热性能影响的研究及应用

分析矿物质在炼焦煤中存在形式及对焦炭热性能的影响,通过对焦炭溶损反应机理研究,结合国内外研究成果,运用煤中矿物组成理论指导配煤和采购,优化煤种结构以改善焦炭热性能。     

Could sperm quality be affected by a building environment? A literature review

The human body responds psychologically and physiologically to the thermal environment to which it is exposed. Fanger's PMV model has been adopted for the design of built environments and building maintenance from the end of the 1960s. The sperm quality of humans has been decreasing since the 1970s. The thermal environment is one of the most important factors of the Sick Building Syndrome (SBS). It is well known that spermatogenesis is very sensitive to heat exposure. Mild thermal exposure increases tissue microcirculation and consequently produces an appropriate supply of nutrients and oxygen to tissue cells; thus, it can modulate the proliferation of Sertoli cells in which the spermatogonia stem cells develop into adult spermatozoa. Excessive exposure to heat is harmful to spermatogenesis, and excessive testicular cooling can cause the cessation of spermatogenesis.     

Impact of adaptive thermal comfort on climatic suitability of natural ventilation in office buildings

In earlier work [1], NIST developed a climate suitability analysis method to evaluate the potential of a given location for direct ventilative cooling and nighttime ventilative cooling. The direct ventilative cooling may be provided by either a natural ventilation system or a fan-powered economizer system. The climate suitability analysis is based on a general single-zone thermal model of a building configured to make optimal use of direct and/or nighttime ventilative cooling. This paper describes a new tool implementing this climate suitability methodology and its capability to consider an adaptive thermal comfort option and presents results from its application to analyze a variety of U.S. climates. The adaptive thermal comfort option has the potential to substantially increase the effectiveness of natural ventilation cooling for many U.S. cities. However, this impact is very dependent on the acceptable humidity range. If a dewpoint limit is used, the increase is significant for a dry climate such as Phoenix but much smaller for humid climates such as Miami. While ASHRAE Standard 55 does not impose a limit on humidity when using the adaptive thermal comfort option, the necessity of limiting humidity for other reasons needs to be considered.     

Thermodynamic analysis of hydrogen-rich syngas production with a mixture of aqueous urea and biodiesel

An auxiliary power unit based on a solid oxidation fuel cell for heavy-duty vehicles has been receiving attention for high efficiency, low emissions, and more comfort and safety in vehicles. This study explores hydrogen-rich syngas production via reforming of a mixture of aqueous urea and biodiesel by thermodynamics analysis. The aqueous urea is available from Adblue used in a selective catalyst reduction providing efficient control of nitrogen oxides from heavy-duty vehicles to minimize particulate mass and optimize fuel consumption. The results show that at a reaction temperature of 700 °C, urea/biodiesel ratio = 3, and oxygen/biodiesel ratio = 9, the highest reforming efficiency is 83.78%, H₂ production 30.43 mol, and CO production 12.68 mol. This study verified that aqueous urea could successfully replace the steam in autothermal reforming, which provides heat and increases syngas production, and reforming aqueous urea mixed with biodiesel has ultra-low sulfur, low carbon and little modifying the fuel system.     

Thermal comfort of people in the hot and humid area of China—impacts of season,climate, and thermal history

We conducted a climate chamber study on the thermal comfort of people in the hot and humid area of China. Sixty subjects from naturally ventilated buildings and buildings with split air conditioners participated in the study, and identical experiments were conducted in a climate chamber in both summer and winter. Psychological and physiological responses were observed over a wide range of conditions, and the impacts of season, climate, and thermal history on human thermal comfort were analyzed. Seasonal and climatic heat acclimatization was confirmed, but they were found to have no significant impacts on human thermal sensation and comfort. The outdoor thermal history was much less important than the indoor thermal history in regard to human thermal sensation, and the indoor thermal history in all seasons of a year played a key role in shaping the subjects' sensations in a wide range of thermal conditions. A warmer indoor thermal history in warm seasons produced a higher neutral temperature, a lower thermal sensitivity, and lower thermal sensations in warm conditions. The comfort and acceptable conditions were identified for people in the hot and humid area of China.     

High porous yttria-stabilized zirconia with aligned pore channels: Morphology directionality influence on heat transfer

High porous yttria stabilized zirconia with unidirectionally aligned channels is used in engineering applications with extremely low thermal conductivity. This property is strongly influenced by microstructure features such as pore volume fraction, pore size distribution, random porous microstructure and pore morphology directionality. Although several models are reported in the available literature, but their analytical formulas are formalised for homogeneous structures or they are based on proportion between solid and fluid phases. These differences from real microstructures cause significant computational errors especially when thermal conductivity changes as the function of the measurement direction (parallel or perpendicular). In this context, the application of an intermingled fractal unit's procedure capable of reproducing porous microstructure as well as predicting thermal conductivity has been proposed. The results are in agreement with experimental ones measured for parallel and perpendicular directions and suggest improving the formalisation of fractal modelling in order to obtain an instrument of microstructure design.     

Visibly transparent conjugated polymers based on non-alternant cyclopenta-fused emeraldicene for polymer solar cells

In this study, we synthesized two emeraldicene (EMD)-based conjugated polymers, PBTEMD and PFEMD, through polymerization of 4,7-di(thien-2-yl)benzo[c][1,2,5]thiadiazole and 9,9-bis(2-ethylhexyl)-9H-fluorene, respectively. We then blended these EMD-derived polymers (as electron-donating materials) with [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) in the active layers of polymer solar cells (PSCs) and investigate their optoelectronic properties and related photovoltaic performance. To best of our knowledge, this study is the first to use EMD derivatives for PSC applications. We compared the molecular structures, absorption behavior, energy levels, thermal properties, and thermal stability of these two polymers to determine their suitability for use in PSCs. The main absorption of PFEMD was in the near-IR spectrum (600–800 nm). We observed a transparency of greater than 80% for the blend film of PFEMD having a thickness of 95 nm; the constructed device exhibited a power conversion efficiency (PCE) of 2.5% and the transparent PFEMD:PC₆₁BM-derived device exhibited a PCE of 1.2% under AM 1.5 G irradiation (100 mW cm⁻²). We observed a significant improvement in thermal stability for the device incorporating the additive crosslinker TBT-N₃; it retained approximately 60% of its initial PCE after accelerated heating (150 °C) for 18 h. In contrast, the PCE of the corresponding normal device decayed to 0.01% of its initial value.