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Investigations into Performance of Dry EDM Using Slotted Electrodes
Govindan Puthumana,Suhas S. Joshi 한국정밀공학회 2011 International Journal of Precision Engineering and Vol. No.
Dry EDM is an emerging EDM technology, which uses gas as dielectric fluid. Due to low density of gaseous dielectric, the process experiences i) unconstrained plasma expansion thereby reducing the effective material removal rate (MRR) and ii)inefficient disposal of debris. This work proposes use of electrodes with peripheral slots to provide more space for the flow of dielectric for effective debris disposal and consequently improve MRR. In this regard, a comprehensive experimentation using Taguchi L16 orthogonal array has been planned initially to optimize the number of peripheral slots on the electrodes,and then to understand the effect of the slots on material removal, tool wear, oversize and depth achieved as a function of processing conditions. It is observed that the optimum number of peripheral slots on electrode for effective debris evacuation is four for the electrode configuration used in this work. The statistical analysis shows that in dry EDM,discharge current (I), gap voltage (V), rotational speed (N) and pulse off-time (Toff) control MRR. Also, use of slotted electrodes significantly reduces the electrode wear rate, and attachment of debris particles on the electrodes.
Govindan, Muthuraman,Chung, Sang-Joon,Moon, Il-Shik American Chemical Society 2012 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.51 No.6
<P>The sustainable applicability of Ag(II)/Ag(I) redox mediator was studied in a semipilot-scale system for treatment of model artificial flue gases containing NO and SO<SUB>2</SUB>. Various discontinuous current supplies were tested for their effect on sustainable use of the electrogenerated mediator. Current density, cell volume, number of flow-through cell, and feed flow rates were varied in electrochemical thin layer cells to improve the applicability of the proposed current supply method. Discontinuing current flow every (5/5) min on–off (<I>i</I><SUB>DC5</SUB>) resulted in improved regeneration capacity of Ag(II) after 15 h. After extended operation (24 h), removal efficiencies of 62% NO and 100% SO<SUB>2</SUB> were achieved by mediated electrochemical oxidation both individually and simultaneously using the proposed discontinuous current supply, demonstrating the sustainable use of the mediator. This study will be taken as a pretest for long-term sustainability testing of the mediator, Ag(II), during industrial scaling up.</P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ie2015813'>ACS Electronic Supporting Info</A></P>
Govindan, M.,Karunakaran, K.,Nallasamy, P.,Moon, I.S. Pergamon Press ; Elsevier Science Ltd 2015 Talanta Vol.132 No.-
This work describes the quantitative analysis of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> and NH<SUB>4</SUB>HCO<SUB>3</SUB> using a simple solution phase titration method. Back titration results at various (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>-NH<SUB>4</SUB>HCO<SUB>3</SUB> ratios demonstrated that 6:4 ratio caused a 3% error in their differentiation, but very high errors were found at other ratios. A similar trend was observed for the double indicator method, especially when strong acid HCl was used as a titrant, where still less errors (2.5%) at a middle ratio of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>-NH<SUB>4</SUB>HCO<SUB>3</SUB> was found. Remaining ratios with low (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> (2:8, 4:6) show high +ve error (found concentration is less) and high (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> (7:3, 8:2, and 9:1) show high -ve error (found concentration is higher) and vice versa for NH<SUB>4</SUB>HCO<SUB>3</SUB>. In replacement titration using Na<SUB>2</SUB>SO<SUB>4</SUB>, at both higher end ratios of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>-NH<SUB>4</SUB>HCO<SUB>3</SUB> (2:8 and 9:1), both -ve and +ve errors were minimized to 75% by partial equilibrium arrest between (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> and NH<SUB>2</SUB>COONH<SUB>4</SUB>, instead of more than 100% observed in back titration and only double indicator methods. In the presence of (NH<SUB>4</SUB>)<SUB>2</SUB>SO<SUB>4</SUB> both -ve and +ve error% are completely reduced to 3+/-1 at ratios 2:8, 4:6, and 6:4 of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>-NH<SUB>4</SUB>HCO<SUB>3</SUB>, which demonstrates that the equilibrium transformation between NH<SUB>2</SUB>COONH<SUB>4</SUB> and (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> is completely controlled. The titration conducted at lower temperature (5<SUP>o</SUP>C) in the presence of (NH<SUB>4</SUB>)<SUB>2</SUB>SO<SUB>4</SUB> at higher ratios of (NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB>-NH<SUB>4</SUB>HCO<SUB>3</SUB> (7:3, 8:2,and 9:1) shows complete minimization of both -ve and +ve errors to 2+/-1%, which explains the complete arresting of equilibrium transformation. Finally, the developed method shows 2+/-1% error in differentiation of CO<SUB>3</SUB><SUP>2-</SUP> and HCO<SUB>3</SUB><SUP>-</SUP> in the regeneration process of NaHCO<SUB>3</SUB> from crude desulfurized sample. The developed method is more promising to differentiate CO<SUB>3</SUB><SUP>2-</SUP> and HCO<SUB>3</SUB><SUP>-</SUP> in industrial applications.
Govindan Raghunathan,Sriram Sokalingam,Nagasundarapandian Soundrarajan,Ganapathiraman Munussami,Bharat Madan,이선구 한국생물공학회 2013 Biotechnology and Bioprocess Engineering Vol.18 No.2
Green fluorescent protein (GFP) has been used as a reporter marker in a wide range of biological and bioengineering studies. The expanded use of GFP in the field of biosensors, biochips and bio-conjugations requires the stability of GFP in organic co-solvent systems. This prompted us to examine the kinetic stability of two different GFP sequences, n-GFP and s-GFP, showing different folding robustness and thermodynamic stability, under a range of organic co-solvent systems. n-GFP and s-GFP are variants whose biophysical properties are comparable to wild type and super folder GFPs, respectively. The stability of n-GFP and s-GFP in 50% water-miscible organic solvents showed that s-GFP with higher thermodynamic stability exhibited much higher stability against organic solvents than n-GFP, which has lower thermodynamic stability. s-GFP was quite stable even in 90% organic solvents. Circular dichroism analysis confirmed that s-GFP maintained its native structure in organic co-solvent systems, whereas n-GFP showed structural variations under these conditions. Four highly fluctuating loop regions were identified from molecular dynamic simulations under the organic cosolvent conditions. A structural comparison of n-GFP and s-GFP suggested that the improved kinetic stability of s-GFP was due to its larger number of hydrogen bonds and salt-bridges that were present in four loop regions. This study suggests that thermodynamically stable s-GFP can be a good choice for use under harsh organic co-solvent conditions.