Structure and performance of electroblown PVDF-based nanofibrous electret filters

Poly(vinylidene fluoride) (PVDF)-based nanofibrous mats were produced via electrically assisted solution blowing (electroblowing). Morphology and filtration properties of the nanofibrous mats were investigated as a function of polymer concentration and applied voltage. The average fiber diameter was reduced from 727 ± 366 nm to 408 ± 143 nm and from 424 ± 233 nm to 328 ± 105 nm, using 16 wt% and 12 wt% concentrations, respectively, with an increase of electric voltage from 0 to 30 kV. In addition, the pore size of the mats produced from 12 wt% concentration decreases with the increase of electric voltage. Results showed that electroblown mats possess high filtration properties and performance. Enhancement of mechanical capturing efficiency is attributed to the reduction in fiber diameter and pore size. The enhancement of electrostatic capturing efficiency is thought to be from the improved electret property of the mats, which eliminates the need for a second step to polarize nanofibrous mats. As a result, both mechanical and electrostatic capture efficiency of the mats is enhanced compared to solution blown PVDF mats. The emerging electret property might be due to the accumulation of the electrostatic charges at high voltage and the enhanced polarized β phase, which is the result of the high drawing ratio applied to the polymer jet during the spinning process.     

Combined heat and power generation via hybrid data center cooling-polymer electrolyte membrane fuel cell system

Although there has been a lot of waste heat utilization studies for the air-cooled data center (DC) systems, the waste heat utilization has not been studied for the liquid-cooled DC systems, which have been rapidly gaining importance for the high-performance Information and Communication Technology facilities such as cloud computing and big data storage. Compared to the air-cooled systems, higher heat removal capacity of the liquid-cooled DC systems provides better heat transfer performance; and therefore, the waste heat of the liquid-cooled DC systems can be more efficiently utilized in the low-temperature and low-carbon energy systems such as electricity generation via polymer electrolyte membrane (PEM) fuel cells. For this purpose, the current study proposes a novel hybrid system that consists of the PEM fuel cell and the two-phase liquid-immersion DC cooling system. The two-phase liquid immersion DC cooling system is one of the most recent and advanced DC cooling methods and has not been considered in the DC waste heat utilization studies before. The PEM fuel cell unit is operated with the hydrogen and compressed air flows that are pre-heated in the DC cooling unit. Due to its original design, the hybrid system brings its own original design criteria and limitations, which are taken into account in the energetic and exergetic assessments. The power density of the PEM fuel cell reaches up to 0.99 kW/m² with the water production rate of 0.0157 kg/s. In the electricity generation case, the highest energetic efficiency is found as 15.8% whereas the efficiency increases up to 96.16% when different multigeneration cases are considered. The hybrid design deduces that the highest exergetic efficiency and sustainability index are 43.3% and 1.76 and they are 9.4% and 6.6% higher than exergetic and sustainability performances of the stand-alone PEM fuel cell operation, respectively.     

Messmodelle im Ingenieurbauwesen. Eine Bilanz

Measurement models in civil engineering. A review The research project “‘Last Witnesses’ Measurement Models in Civil Engineering – Scientific Significance and Preservation” was funded as part of the priority program 2255 “Construction as Cultural Heritage” of the German Research Foundation (DFG) and consists of three sub-projects divided between the University of Innsbruck, the Karlsruhe University of Applied Sciences and the Technical University of Munich. The project aimed to locate the last surviving measurement models in German-speaking countries, document them, classify them in terms of construction history, digitise them and evaluate their state of conservation. This report is intended to provide an overview of the initial situation, the approaches, the difficulties and the results and findings achieved in the project.     

Bearing strength of pin‐connected polymer composites subjected to dynamic loading

In this study, static load bearing strength of pin‐connected carbon fiber‐reinforced polyphenylenesulphide (PPS) composites that have [(0°/90°)]_3s stacking sequence was investigated. Firstly, the samples were loaded dynamically, and then the same samples were loaded statically. The results obtained from this sequential experiment were compared with the results obtained from samples that were loaded only statically. In addition, the fatigue life and failure mechanisms were investigated with respect to the selection of the geometrical parameters. Dynamic and static loading experiments were performed according to the ASTM STP 749 and ASTM D953 standards, respectively. To obtain optimum load bearing values, the ratio of distance between the edge and hole center to hole diameter (E/D) and ratio of sample width to hole diameter (W/D) has been systematically changed. According to the experimental results, maximum load bearing values have been obtained when E/D ratio was equal to 2. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Experimental evaluation of the influence of macro circumferential residual stress on the wear resistance of some metals

To investigate the effect of residual stress on the wear resistance of metals, macro circumferential residual stresses σ^I were modelled as externally applied stress, below the yield stress of the material because residual stress cannot exceed yield stress, with a special apparatus. In order to compare the effect of residual stress on wear resistance, three different stress levels were applied to each specimen, 0 R_e, 0.5 R_e, and 0.8 R_e. A full programme of testing under all combinations of factors would be very expensive and time consuming, so, in the present case, all the other factors were fixed at constant values, while the chosen factor was varied in a controlled way in a series of tests. There has been no universally accepted theory or law on the effect of residual stress on wear resistance. In this study, the wear results for dry wear tests in terms of residual stress applied mechanically to specimens were very difficult to interpret.