Temperature Dependence of on-Line DGA Results for Transformers through Membrane Extraction

Concentration detection of gases dissolved in transformer insulation oil is an effective method to diagnose incipient fault in electrical equipment. The permeation process of gases dissolved in transformer oil through extraction membrane is studied. Temperature dependence with accuracy of on-line DGA results through gases extraction with polymer membrane is analysed. An algorithm which includes temperature coefficient which can improve the accuracy of DGA results is proposed. An on-line DGA system with Teflon membrane and electrochemical gas sensors is constructed; while the results are adjust by temperature coefficient. Compared with GC results in the laboratory, the accuracy of the on-line DGA results has been improved.

Exploring the MEMS Enabled Water Preservation in Micro-Scale Direct Methanol Fuel Cells

To ensure the Direct Methanol Fuel Cells (DMFC) achieve a high power density, it is necessary to use high concentration methanol in the storage. However, it is still necessary to supply the needed water in the PEM process. Thus, it becomes necessary to preserve the water from losing at the cathode side. In this exploration, hydrophobic Teflon membrane, with micro-size pores, is applied at the outside of the cathode to prevent water exits to the air stream but still allowing the oxygen to diffuse through. Gold film is sputtered at the inner face of the Teflon membrane to provide electric conductivity. Water tests indicate that this membrane is able to hold significant pressure and allowing the water to be pushed back through PEM to the anode. This modified cathode has been assembled into a micro fuel cell. Electrochemical tests indicated that this fuel cell operates well at various temperatures. Compare with a same fuel cell but using carbon paper instead, it appears that the sputtered gold film has the potential to provide sufficient conductivity. Although the water preservation capability has not been fully validated due to the present micro-scale measurement limitation, this exploration has indicated a promising method to improve the energy density of micro-DMFC.

DEVELOPMENT OF FLOW INJECTION METHOD FOR ONLINE DETERMINATION OF THIOCYANATE BASED ON OXIDATION BY PERMANGANATE

The importance of developing method for thiocyanate becomes obvious, because thiocyanate can inhibit iodine uptake of thyroid gland leading to mumps disease. In this work, thiocyanate is oxidized by permanganate in the acid donor stream to cyanide, which is directly converted to hydrogen cyanide. Then, hydrogen cyanide diffuses through a Teflon membrane into acceptor stream containing nickel(II) in ammoniacal buffer to form tetracyanonickelate(II) which is detected spectrophotometrically at 267 nm. Analytical figures of merit were linear up to 50 mg L-1 for thiocyanate, with RSD of 1.34%, and detection limit of 0.07 mg L-1, respectively. Interfering anions were eliminated under stoichiometric amount of permanganate and sample throughput was 20 h-1. The method was validated for determining thiocyanate samples from synthetic and gold process waters with satisfactory results. Keywords: Thiocyanate, flow injection, permanganate, spectrophotometry

Crankcase Emission Contributions to PM for Two Tier 2 Line-Haul Locomotives

This paper documents the quantification and characterization of particulate matter (PM) emitted from two Tier 2 diesel locomotives, and the impact of crankcase ventilation (CCV) on PM emissions. Emission testing was performed on one General Electric (GE) model ES44DC locomotive, and one Electro-Motive Diesel (EMD) model SD70ACe. A semi-continuous organic carbon/elemental carbon (OC/EC) analytical procedure was used to collect and determine the OC and EC of PM. PM was also measured gravimetrically using Teflon membrane filters. Testing was performed for the locomotives in an unmodified configuration “with CCV”, and then again without the CCV included in the emissions measurements. Without CCV, the two-stroke SD70ACe brake specific filter-based PM and OC/EC PM, over the Line-haul Locomotive Duty Cycle (LHLDC), were reduced by approximately 15% to 16%, respectively, compared to testing with CCV. The 4-stroke ES44DC showed a reduction of 11% for the OC/EC PM which was mainly due to a reduction in OC PM. When crankcase emissions were not included, OC PM was reduced for nearly all throttle notches, and especially under high load conditions, although the differences were not always significant at a 95% confidence interval. With CCV, the relative OC portion of the Line-haul composite PM value for both locomotives was approximately 42–47%. Without CCV, the absolute brake-specific OC PM over the LHLDC was reduced by 30%, thereby reducing the relative OC portion to approximately 34–38%. This work showed that the OC PM fraction is significant for the locomotives tested, and controlling OC can lead to more than 40 percent reduction in PM. Furthermore, almost one-third of the OC PM was contributed by CCV, therefore better control of blow-by PM from both locomotive types can lead to a significant reduction in OC PM.

Evaluation of flow injection analysis for determination of urea in sheep's and cow's milk

Difficulties in measuring the urea content in sheep's milk often occur with spectral photometry due to the high protein and fat concentrations of the milk. In this study an enzymatic flow procedure (QuickChem 8000 Ion Analyser, Lachat Instruments, Milwaukee, USA) to determine the urea content in ovine and bovine milk was evaluated. Urea content is determined by the Berthelot reaction after splitting it enzymatically with urease. The free ammonia diffuses through a teflon membrane into a stream of reagent solutions. Detection takes place by means of a reaction between the ammonium ions with hypochlorite and salicylate producing a green colour, which is measured spectrometrically in a flow meter at 660 nm. By using a diffusion cell chemical deproteinisation of milk is not necessary and capacity is high. The assessed procedure exhibited high accuracy and precision and reached a sample capacity of 55 samples an hour. Storage of the milk samples for several days as well as chemical preservation with bronopol had no effect on the measurement procedure. Due to the complexity of the apparatus and the costs associated therewith, the device proves less suitable for routine diagnostics but rather serves as a reference method for the measurement of urea concentration in milk.