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.     

A non-lumped dynamic simulation method of sorption compressor for sorption cryocooler

A dynamic analysis of sorption compressor is motivated by the design of a practical sorption compressor. In this paper a non-lumped dynamic simulation method based on a non-isothermal parameter has been developed. An algorithm for simulating the dynamic behaviors of sorption compressor involving mass and energy transport is described and is calculated using Computational Fluid Dynamics (CFD). The calculated time-dependent pressure and temperature across the sorption compressor are obtained and verified by experiments. Then, the effects of thermal gradient and non-equilibrium adsorption–desorption on the net gas outflow from the sorption compressor are also investigated. It is shown that thermal gradient and non-equilibrium adsorption–desorption can significantly affect the net gas outflow with the same total heat input.     

Failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting. Part I: Material and fractographic characterization

The failure analysis of a martensitic stainless steel (CA-15M) roll manufactured by centrifugal casting and used in cast glass rolling was carried out by means of traditional characterization techniques (optical metallography, SEM, EDX microanalysis, tensile testing and XRD). The roll was in the as-cast condition and its microstructure featured large proportion of δ ferrite (between 20% and 27%) in a martensitic (α′) matrix, with the δ/α′ interfaces presenting an intergranular network of M₂₃C₆ carbides. The crack propagation began in the internal surface of the roll, with δ/α′ intergranular and transgranular cleavage in the “equiaxed region” of the casting, progressing to δ/α′ intergranular ductile fracture in the “columnar” and “chilled regions”. Tensile thermal stresses in the internal surface of the roll associated with microstructural embrittlement (network of interfacial carbide and microporosities) are thought to be the main causes for the premature failure of the roll. Finally, materials selection was performed to replace the CA-15M stainless steel with another class of stainless steel for centrifugal casting.     

Microstructural changes and mechanical behaviour of a near lamellar γ-TiAl alloy during long-term exposure at 700 °C

Ti-44Al-5Nb-1W-1B with a near lamellar microstructure was exposed at 700 °C for up to 10000 h in air. The changes in microstructure were investigated using scanning and transmission electron microscopy. It has been found that the combined addition of Nb and W can restrict parallel decomposition of α₂ lamellae into ultrafine γ lamellae, but causes prevalent precipitation of fine β(B2+ω) particles from α₂ lamellae and precipitation/growth of ω particles from β(B2) grains. However, although 3/4 of α₂ lamellae dissolved and majority of them transformed to β(B2+ω), tensile ductility is reduced only by 30% while the strengths remain essentially unchanged for the thermally exposed alloy. This is attributed to the widespread distribution of β(B2+ω) particles. On the other hand, fatigue limit was found to decrease during the first 5000-h exposure but finally increased by 11% after 10000-h exposure. The reasons for the decrease and increase of fatigue strength at different exposure stages are discussed by considering two contradictory effects on the exposed alloy: 1) exposure-induced embrittlement due to microstructural changes (harmful); 2) annealing of fatigue samples in a warm air environment for prolonged time (beneficial).     

Laser cutting of triangular blanks from thick aluminum foam plate: Thermal stress analysis and morphology

Laser cutting of triangle blank from aluminum foam is carried out. Thermal stress field in the cutting section is predicted using ABAQUS finite element code in line with the experimental conditions. Laser cutting experiments are carried out prior to the model study to determine the optimum cutting parameters for the quality cuts. Temperature predictions are compared with thermocouple data obtained from the experiment. Morphological and metallurgical changes in the cut section are examined using optical and scanning microscopes, energy dispersive spectroscopy, and X-ray diffraction. It is found that von Mises attains high values along the circumference of the cut edges at the onset of cooling cycle initiation. Laser cut edges are free from defects and asperities; however, locally distributed few dross attachments take place at the kerf exit.     

Analysis of multi-layered filament-wound composite pipes under combined internal pressure and thermomechanical loading with thermal variations

The composite pipes manufactured by filament winding technology have anisotropic behavior owing to different reinforced ply angles. Composite pipes can be exposed to the thermomechanical loading due to hot fluid that flows into them. In this paper, based on the three-dimensional anisotropic elasticity, an exact elastic solution for thermal stresses and deformations of the pipes under internal pressure and a temperature gradient has been studied. Giving heat convection conditions the variation of temperature field within the pipe is obtained by solving the conduction equation at the wall. The influence of temperature field in the governing equations of thermoelasticity has been considered via a constitutive law. The shear extension coupling is also considered because of lay-up angles. Stress, strain and deformation distributions for different angle-ply pipe designs are investigated using the present theory.     

Internal short circuit in Li-ion cells

Effects of internal short circuit (ISCr) on thermal stability of Li-ion cells of various sizes (130-1100 mAh) are investigated using a combination of experimental methods and thermal modeling. Three experimental methods were evaluated: small nail penetration, small indentation, and cell pinch test. The small nail penetration and indentation tests created significant heat sinking to the cell-can or to the nail. Only the cell pinch test provided a reasonable approximation of a high risk ISCr event. ISCr location plays a critical role in the consequences of an ISCr event. ISCr at the edge of the electrode is the worst case because of its limited heat conduction to the cell-can. The effects of cell capacity and state of charge on ISCr are also evaluated through tests and thermal modeling.     

Vertical Stiffness and Deformation Analysis Models of Rubber Isolators in Compression and Compression-Shear States

The vertical stiffness and deformation theories of rubber isolators in compression and compression-shear states are systemically researched in the paper, a series of basic concepts, such as origin compression stiffness, origin compression longitudinal elastic modulus, offset vertical stiffness, etc. are suggested with corresponding theoretical formula and experimental estimation method. Based on the basic concepts and newly suggested calculating theories, the deformation calculating theory related to pure compression state and compression-shear state of isolating bearing is established. The vertical stiffness, offset vertical stiffness and deformation tests are performed with nature rubber bearings and lead plug rubber bearings total 16 original specimens to verify the new concepts and computation model of rubber isolators. All test results show that the theories established in the paper are suitable for analyzing the vertical stiffness and deformation of rubber isolators.