Spiral ring cavity to improve the stability of a centrifugal compressor

Journal of Mechanical Science and Technology - In this study, a spiral ring cavity (SRC) is proposed to improve the operational stability of a centrifugal compressor. Aerodynamic performance of the...     

Effect of opening area on the suppression of self-ignition of high-pressure hydrogen gas leaking in the air by an extension tube

The most influential factor for self-ignition of high-pressure hydrogen is known to be the strength of the shock. Thus, the self-ignition can be suppressed by weakening the shock strength, which is possible by reducing the area where the hydrogen is ejected in this study. To confirm the possibility of this method, experiments were done by controlling the burst pressure of up to 302 bar and the ratio of the opening area. The experimental results showed that the minimum burst pressure of self-ignition is increased exponentially as the opening area is reduced. This confirmed that reducing the opening area under the same burst pressure conditions has an effect on the suppression of self-ignition. However, it was also found that the minimum shock speed that causes self-ignition gradually decreases as the opening area becomes smaller, which results from an increasing in mixing. The CFD simulation results showed that the volume of the flammable region in the tube was increased and the hydrogen-air mixing efficiency also increased when the opening area became smaller. The results suggest that reduction of the opening area can suppress a self-ignition by weakening the shock strength, but it should be noted that an increase in mixing effect also occurs.     

Thermal destruction of HFC-134a in pilot-, and full-scale gasification systems

There is much interest in reducing hydrofluorocarbon (HFC) emissions due to their high global-warming potential. Many treatment technologies have been developed, including the plasma, catalytic, and thermal destruction of waste HFCs. From an economic perspective, existing facilities should be capable of ensuring their destruction, without the addition of more energy or after-treatment systems. Here, a high-temperature thermal destruction method for HFC-134a from end-of-life vehicles (ELVs) is presented at the pilot and full operating scales. The method involves reductive conditions in a laboratory-scale reactor and a gasification melting system. The destruction removal efficiency (DRE) increased as the reaction temperature and the normal stoichiometric ratio (NSR) increased in a laboratory-scale reactor. HFC-134a was completely destroyed at 950 °C, a residence time of 4 s, and NSR of 1.0–2.0. The optimum NSR was found to be 1.5 for this system. Based on FT-IR and GC-MS analysis, a removal efficiency of more than 99.99% was obtained in pilot and full-scale systems. HFC-134a was completely destroyed at the feed rates of 0.15, 0.375, 0.75, and 1.5 kg/h in a pilot-scale system. The atmospheric emissions, including dioxin, were shown to satisfy regulatory levels for the pilot and full-scale systems. This suggests that gasification-melting system can be useful tools for decomposition of HFCs and has the potential to be a practical process for the treatment of wastes from ELVs including not only the automobile shredder residue and but also refrigerants.     

Available human feeder cells for the maintenance of human embryonic stem cells

Mouse embryonic fibroblasts (MEFs) have been previously used as feeder cells to support the growth of human embryonic stem cells (hESCs). In this study, human adult uterine endometrial cells (hUECs), human adult breast parenchymal cells (hBPCs) and embryonic fibroblasts (hEFs) were tested as feeder cells for supporting the growth of hESCs to prevent the possibility of contamination from animal feeder cells. Cultured hUECs, hBPCs and hEFs were mitotically inactivated and then plated. hESCs (Miz-hES1, NIH registered) initially established on mouse feeder layers were transferred onto each human feeder layer and split every 5 days. The morphology, expression of specific markers and differentiation capacity of hESCs adapted on each human feeder layer were examined. On hUEC, hBPC and hEF feeder layers, hESCs proliferated for more than 90, 50 and 80 passages respectively. Human feeder-based hESCs were positive for stage-specific embryonic antigen (SSEA)-3 and -4, and Apase; they also showed similar differentiation capacity to MEF-based hESCs, as assessed by the formation of teratomas and expression of tissue-specific markers. However, hESCs cultured on hUEC and hEF feeders were slightly thinner and flatter than MEF- or hBPC-based hESCs. Our results suggest that, like MEF feeder layers, human feeder layers can support the proliferation of hESCs without differentiation. Human feeder cells have the advantage of supporting more passages than when MEFs are used as feeder cells, because hESCs can be uniformly maintained in the undifferentiated stage until they pass through senescence. hESCs established and/or maintained under stable xeno-free culture conditions will be helpful to cell-based therapy.     

Economic analysis of heating and cooling systems from the various perspectives: Application to EHP and GHP in Korea

Energy flow from the primary energy to the final energy use varies depending on which device is used for the heating and cooling energy service. This paper presents economic analyses of medium capacity space heating and cooling systems from three perspectives – primary energy, final consumer, and social cost perspective. From the analysis results of primary energy and final consumer perspective, electric heat pump (EHP) system is found to be superior to the gas engine driven heat pump (GHP) system for the energy consumption and cost-effectiveness due to its higher system efficiency. However, the result of social cost perspective shows the GHP system is superior to the EHP system considering incurred incremental electricity generation capacity construction cost and avoided gas storage tank construction cost due to a new installation of each system. And this paper suggests three analysis methodologies – the primary energy, final consumer, and social cost perspective – can be used for developing various measures and policies for integrated demand side management.     

A new antimicrobial substance produced by Staphylococcus pasteuri isolated from vegetables

Staphylococcus aureus is important food-borne pathogen in agricultural products consumed in a fresh state. The antimicrobial activities of staphylococci isolated from vegetables in Korea against S. aureus were investigated. Coagulase-negative staphylococci (CNS) isolates (12) with antimicrobial activities against S. aureus were identified as S. xylosus, pasteuri, and epidermidis. CNS isolates exhibited antimicrobial activities against Gram-positive bacteria. Inactivation of S. pasteuri antimicrobial activity by proteases suggested that the substances evaluated were antimicrobial peptides or bacteriocins. None of the S. pasteuri isolates possessed homologous DNA fragments known to be bacteriocin genes, except for nukacin. The nukM gene that encodes a post-translational modification enzyme in the nukacin gene cluster was not detected in S. pasteuri isolates. S. pasteuri probably produces one or more new antimicrobial substances.     

Effects of inlet relative humidity (RH) on the performance of a high temperature-proton exchange membrane fuel cell (HT-PEMFC)

A high temperature-proton exchange membrane fuel cells (HT-PEMFC) based on phosphoric acid (PA)-doped polybenzimidazole (PBI) membrane is able to operate at elevated temperature ranging from 100 to 200 °C. Therefore, it is evident that the relative humidity (RH) of gases within a HT-PEMFC must be minimal owing to its high operating temperature range. However, it has been continuously reported in the literature that a HT-PEMFC performs better under higher inlet RH conditions. In this study, inlet RH dependence on the performance of a HT-PEMFC is precisely studied by numerical HT-PEMFC simulations. Assuming phase equilibrium between membrane and gas phases, we newly develop a membrane water transport model for HT-PEMFCs and incorporate it into a three-dimensional (3-D) HT-PEMFC model developed in our previous study. The water diffusion coefficient in the membrane is considered as an adjustable parameter to fit the experimental water transport data. In addition, the expression of proton conductivity for PA-doped PBI membranes given in the literature is modified to be suitable for commercial PBI membranes with high PA doping levels such as those used in Celtec^® MEAs. Although the comparison between simulations and experiments shows a lack of agreement quantitatively, the model successfully captures the experimental trends, showing quantitative influence of inlet RH on membrane water flux, ohmic resistance, and cell performance during various HT-PEMFC operations.     

Block and Random Living,Ring‐Opening Metathesis Copolymerization of Functionally Differentiated Carbazole‐Containing Norbornene Monomers

The synthesis of novel diblock polymers containing both a potential charge transport and a non‐linear optic block has been accomplished. The synthesis exploits the living, ring‐opening metathesis block copolymerization of two norbornene type monomers, one of which contains an unsubstituted N‐carbazolyl ring while the other has a bromo substituent at the 3‐position of the carbazole ring. Conversion of the bromo functionality to a 2,2‐dicyanovinyl group introduces the non‐linear optic property. The first monomer was prepared by the previously reported efficient cation radical Diels–Alder cycloaddition of N‐trans‐1‐propenylcarbazole to 1,3‐cyclopentadiene, while the second was obtained by N‐bromosuccinimide bromination of the first monomer. For purposes of comparison, the corresponding random copolymer was also synthesized.