Transverse Thermoelectricity in Fibrous Composite Materials

Transverse thermoelectric elements have the potential to decouple the electric current and the heat flow, which could lead to new designs of thermoelectric devices. While many theoretical and experimental studies of transverse thermoelectricity have focused on layered structures, this work examines composite materials with aligned fibrous inclusions. A simplified mathematical model was derived based on the Kirchhoff Circuit Laws (KCL), which were used to calculate the equivalent transport properties of the composite structures. These equivalent properties, including Seebeck coefficient, electrical conductivity, and thermal conductivity, compared well with finite element analysis (FEA) results. Peltier cooling performance was also examined using FEA, which exhibited good agreement to KCL model predictions. In addition, a survey was conducted on selected combinations of thermoelectric materials and metals to rank their transverse thermoelectricity with respect to the dimensionless figure of merit

Enhanced Thermoelectric Cooling through Introduction of Material Anisotropy in Transverse Thermoelectric Composites

Transverse thermoelectric materials can achieve appreciable cooling power with minimal space requirement. Among all types of material candidates for transverse thermoelectric applications, composite materials have the best cooling performance. In this study, anisotropic material properties were applied to the component phase of transverse thermoelectric composites. A mathematical model was established for predicting the performance of fibrous transverse thermoelectric composites with anisotropic components. The mathematical model was then validated by finite element analysis. The thermoelectric performance of three types of composites are presented, each with the same set of component materials. For each type of component, both anisotropic single-crystal and isotropic polycrystal material properties were applied. The results showed that the cooling capacity of the system was improved by introducing material anisotropy in the component phase of composite. The results also indicated that the orientation of the anisotropic component’s property axis, the anisotropic characteristic of a material, will significantly influence the thermoelectric performance of the composite. For a composite material consisting of Copper fiber and Bi2Te3 matrix, the maximum cooling capacity can vary as much as 50% at 300 K depending on the property axis alignment of Bi2Te3 in the composite. The composite with Copper and anisotropic SnSe single crystal had a 51% improvement in the maximum cooling capacity compared to the composite made of Copper and isotropic SnSe polycrystals

Numerical and Experimental Study on Ventilation Panel Models in a Subway Passenger Compartment

The internal flow field study of car compartments is an important step in railroad vehicle design and optimization. The flow field profile has a significant impact on the temperature distribution and passenger comfort level. Experimental studies on flow field can yield accurate results but carry a high time and computational cost. In contrast, the numerical simulation method can yield an internal flow field profile in less time than an experimental study. This study aims to improve the computational efficiency of numerical simulation by adapting two simplified models—the porous media model and the porous jump face model—to study the internal flow field of a railroad car compartment. The results provided by both simplified models are compared with the original numerical simulation model and with experimental data. Based on the results, the porous media model has a better agreement with the original model and with the experimental results. The flow field parameters (temperature and velocity) of the porous media model have relatively small numerical errors, with a maximum numerical error of 4.7%. The difference between the numerical results of the original model and those of the porous media model is less than 1%. By replacing the original numerical simulation model with the porous media model, the flow field of subway car compartments can be calculated with a reduction of about 25% in computing resources, while maintaining good accuracy. Keywords: Numerical simulation, Experiment, Ventilation panel model, Subwa

Investigation on the fluid-solid coupling effect in high-speed train’s windshield structure

The high-speed train’s windshield structure is vital to the boundary layer development and drag reduction design. Up to date, windshield structures are assumed as rigid body in most train aerodynamic numerical simulations. This research investigates the fluid-solid coupling effect of high-speed train’s windshield structure based on an 8-car formation model. The influence of speed level and windshield installation location on the flow field parameter and windshield deformation profile are systematically analysed. The results indicate that, with the development the boundary layer, the time-averaged pressure coefficient, lateral force coefficient and windshield’s displacement all gradually decrease from 1st windshield to 4th windshield along the stream direction. In the connecting region between the windshield and vestibule, a pair of negative pressure zone are formed and gradually intensify along the downstream direction, such that the time-averaged deformation, as well as the vibration amplitude of windshields experience a slight increase. According to the power spectral density analysis, the vibration frequency of all windshields’ displacement varies between 10.25 Hz and 12.5 Hz. Meanwhile, the pantograph structure will lead to the generation of vortex group, these vortices will lead to additional small low frequency peaks for windshields installed on the downstream direction of pantograph

Characterization of Dextran Biosynthesized by Glucansucrase from <i>Leuconostoc pseudomesenteroides</i> and Their Potential Biotechnological Applications

Glucansucrase was purified from Leuconostoc pseudomesenteroides. The glucansucrase exhibited maximum activity at pH 5.5 and 30 °C. Ca2+ significantly promoted enzyme activity. An exopolysaccharide (EPS) was synthesized by this glucansucrase in vitro and purified. The molecular weight of the EPS was 3.083 × 106 Da. Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy showed that the main structure of glucan was 97.3% α-(1→6)-linked D-glucopyranose units, and α-(1→3) branched chain accounted for 2.7%. Scanning electron microscopy (SEM) observation of dextran showed that its surface was smooth and flaky. Atomic force microscopy (AFM) of dextran revealed a chain-like microstructure with many irregular protuberances in aqueous solution. The results showed that dextran had good thermal stability, water holding capacity, water solubility and emulsifying ability (EA), as well as good antioxidant activity; thus it has broad prospects for development in the fields of food, biomedicine, and medicine