Effect of channel and plenum aspect ratios on the performance of microchannel heat sink under different flow arrangements

S. S. Sehgal,Krishnan Murugesan,S. K. Mohapatra 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.9

Microchannels based heat sinks are considered as potential thermal management solution for electronic devices. The overall thermal performance of a microchannel heat sink depends on the flow characteristics within microchannels as well as within the inlet and outlet plenum and these flow phenomena are influenced by channel aspect ratio, plenum aspect ratio and flow arrangements at the inlet and outlet plenums. In the present research work an experimental investigation has been carried out to understand how the heat transfer and pressure drop attributes vary with different plenum aspect ratio and channel aspect ratio under different flow arrangements. For this purpose microchannel test pieces with two channel aspect ratios, 4.72 and 7.57 and three plenum aspect ratios, 2.5, 3.0 and 3.75 have been tested under three flow arrangements, namely U-, S- and P-types. Test runs were performed by maintaining three constant heat inputs,125 W, 225 W and 375 W in the range 224.3 ≤ Re ≤ 1121.7. Reduction in channel width (increase in aspect ratio, defined as depth to width of channel) in the present case has shown about 126 to 165% increase in Nusselt number, whereas increase in plenum length (reduction in plenum aspect ratio defined as width to length of plenum) has resulted in 18 to 26% increase in Nusselt number.

고분자 전해질 연료전지용 Sulfonated Poly(ether sulfone)의 합성 및 특성 평가

김형준(Krishnan, N.N.),조은애(Kim, H.-J.),오인환(Prasanna, M.),홍성안(Cho, E.-A.),임태훈(Oh, I.-H.),Hong, S.-A.,Lim, T.-H. 한국신재생에너지학회 2005 한국신재생에너지학회 학술대회논문집 Vol.2005 No.06

Sulfonated poly(ether sulfone) copolymers (PESs) were synthesized using hydroquinone 2-potassium sulfonate (HPS) with other monomers (bisphenol A and 4-fluorophenyl sulfone). PESs with different mole% of hydrophilic group were prepared by changing the mole ratio of HPS in the polymerization reaction. The chemical structure and the thermal stability of these polymers were characterized by using ¹H-NMR, FT-IR and TGA techniques. The PES 60 membrane, which has 60 mole% of HPS unit in the polymer backbone, has a proton conductivity of 0.091 S/cm and good insolubility in boiling water. The TGA showed that PES 60 was stable up to 272?C with a char yield of about 29%;at;900?C;under;N₂ atmosphere. To investigate the single cell performance, the catalyst coated PES 60 membrane was used and a single cell test was carried out using H₂/O₂ gases as fuel and oxidant at various temperatures. We observed that the cell performance was enhanced by increasing the cell temperature. A current density of 1400 mA/cm² at 0.60 V was obtained at 70?C.

The in-vitro and in-vivo radio labeling unfolds the vitellogenin protein expression site of Bombyx mori L as the ventral perivisceral fat body

Mohiadeen Batcha M.,Sajith Ahamed A.,Ur Rahman M. Ashiq,Janarthanan S.,Krishnan M. 한국응용곤충학회 2023 Journal of Asia-Pacific Entomology Vol.26 No.2

The present study aims to focus on the site of fat bodies involved in the differential expression of vitellogenin protein in Bombyx mori L which is not yet fully understood. Culturing fat bodies and analyzing in in vitro and in vivo approaches made it useful to study this pattern. In Bombyx mori, L. The vitellogenin protein is 200–205 kDa and resolves at two molecular weight regions that are at 180 kDa and 42 kDa. We subject dorsal perivisceral (DPV) and ventral perivisceral fat body (VPV), haemolymph for this radio labeling cell culture and incorporation experiment. Based on our in vitro and in vivo experiments of S 35 methionine fluorography, Scanning densito metric, Western blot analysis and RT-PCR expression studies had strongly proven that the ventral perivisceral fat body is the significant and exclusive site of differential vitellogenin expression in silkworm, Bombyx mori but not in dorsal peripheral fat body tissues, haemolymph by radiolabeling studies. The present paper describes an experimental set-up based on the incubation of ventral perivisceral and dorsal perivisceral fat bodies and the measurement of vitellogenin with S 35 protein labeling incorporation method. These findings from our lab were the first report proved by in vitro and in vivo labeling experiments.

Some reliability properties of extropy for residual and past lifetime random variables

Krishnan Aswathy S.,Sunoj S. M.,Unnikrishnan Nair N. 한국통계학회 2020 Journal of the Korean Statistical Society Vol.49 No.2

In the present paper, we study the residual extropy using distribution function and quantile function approaches. We also investigate extropy in past lifetime in both approaches. Some characterizations and ageing properties of these extropy measures are proposed. Different stochastic orders based on the residual and past lifetime extropy are also presented.

Sulfonated poly(ether sulfone)-based silica nanocomposite membranes for high temperature polymer electrolyte fuel cell applications

Krishnan, N.N.,Henkensmeier, D.,Jang, J.H.,Kim, H.J.,Rebbin, V.,Oh, I.H.,Hong, S.A.,Nam, S.W.,Lim, T.H. Pergamon Press ; Elsevier Science Ltd 2011 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.36 No.12

Fuel Cell operation at high temperature (e.g. 120 <SUP>o</SUP>C) and low relative humidity (e.g. 50%) remains challenging due to creep (in the case of Nafion<SUP>(</SUP>R)) and membrane dehydration. We approached this problem by filling PES 70, a sulfonated poly(ether sulfone) with a T<SUB>g</SUB> of 235 +/- 5 <SUP>o</SUP>C and a theoretical IEC of 1.68 mmol g<SUP>-1</SUP>, with 5-20% silica nano particles of 7 nm diameter and 390 +/- 40 m<SUP>2</SUP> g<SUP>-1</SUP> surface area. While simple stirring of particles and polymer solutions led to hazy, strongly anisotropic (air/glass side) and sometimes irregular shaped membranes, good membranes were obtained by ball milling. SEM analysis showed reduced anisotropy and TEM analysis proved that the nanoparticles are well embedded in the polymer matrix. The separation length between the ion-rich domains was determined by SAXS to be 2.8, 2.9 and 3.0 nm for PES 70, PES 70-S05 and Nafion<SUP>(</SUP>R) NRE 212, respectively. Tensile strength and Young's modulus increase with the amount of silica. Ex-situ in-plane proton conductivity showed a maximum for PES 70-S05 (2 mS cm<SUP>-1</SUP>). In the fuel cell (H<SUB>2</SUB>/air, 120 <SUP>o</SUP>C, <50%), it showed a current density of 173 mA cm<SUP>-2</SUP> at 0.7 V, which is 3.4 times higher than for PES 70.

Recent analytical approaches to detect exhaled breath ammonia with special reference to renal patients

Krishnan, S. T.,Devadhasan, J. P.,Kim, S. Springer 2017 Analytical and Bioanalytical Chemistry Vol.409 No.1

<P>The ammonia odor from the exhaled breath of renal patients is associated with high levels of blood urea nitrogen. Typically, in the liver, ammonia and ammonium ions are converted into urea through the urea cycle. In the case of renal dysfunction, urea is unable to be removed and that causes a buildup of excessive ammonia. As small molecules, ammonia and ammonium ions can be forced into the blood-lung barrier and occur in exhaled breath. Therefore, people with renal failure have an ammonia (fishy) odor in their exhaled breath. Thus, exhaled breath ammonia can be a potential biomarker for monitoring renal diseases during hemodialyis. In this review, we have summarized the source of ammonia in the breath of end-stage renal disease patient, cause of renal disorders, exhaled breath condensate, and breath sampling. Further, various biosensor approaches to detect exhaled ammonia from renal patients and other ammonia systems are also discussed. We conclude with future perspectives, namely colorimetric-based real-time breathing diagnosis of renal failure, which might be useful for prospective studies.</P>

Theoretical probe on modified organic dyes for high-performance dye-sensitised solar cell

S. Krishnan,K.Senthilkumar 한국물리학회 2018 Current Applied Physics Vol.18 No.9

We have proposed newly designed organic sensitizers, which could potentially be the best performing organic dyes for Dye Sensitised Solar Cell applications (DSSC). The designed sensitizers are derivatives of “Triphenylamine (TPA) - Tetrathienoacene (TTA) - Thiophene (T) - cyanoacrylic acid (A)” (TPA-TTAR-T-A) sensitizer. Our conclusions were based on calculations performed using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) methods, on various theoretical parameters of sensitizers that are pertinent to the Power Conversion Efficiency (PCE) of the solar cell. We strategically incorporated substitutions on the spacer located between the π- bridge and the anchoring group, where the thiophene was inserted in previous study. We found that strengthening the electron withdrawing ability around thiophene spacer by fluorination and cyano substitution, and replacement of thiophene spacer with fluorinated and cyano substituted benzodithiophene complexes results in improved opto-electronic properties of the sensitizers. Thereby, we identified six new derivatives and for each derivative we have studied the parameters concerning short circuit current (Jsc), such as molecular geometry, absorption spectrum, frontier molecular orbital patterns, electronic energy levels and excited state life time. Also, we have analysed the intramolecular charge transport characteristics of the designed dyes. By considering the overall computed parameters we were able to sort out two new sensitizers TPA-TTAR-2FT-A and TPA-TTAR-2F2CNBDT-A that delivered the needed characteristics and thereby brings in confidence that these sensitizers could challenge TPA-TTA-T-A as the best performing organic sensitizer.

Alkyl chain modified sulfonated poly(ether sulfone) for fuel cell applications

Krishnan, N.N.,Henkensmeier, D.,Jang, J.H.,Kim, H.J.,Ha, H.Y.,Nam, S.W. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.6

A new alkyl chain modified sulfonated poly(ether sulfone) (mPES) was synthesized and formed into membranes. The MEAs were tested in the PEMFC and evaluated systematically in the DMFC by varying the methanol concentration from 0.5 to 5.0 M at 60 <SUP>o</SUP>C and 70 <SUP>o</SUP>C. The synthesized mPES copolymer has been characterized by nuclear magnetic resonance spectroscopy, fourier transform infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. The proton conductivity of the resulting membrane is higher than the threshold value of 10<SUP>-2</SUP> S cm<SUP>-1</SUP> at room temperature for practical PEM fuel cells. The membrane is insoluble in boiling water, thermally stable until 250 <SUP>o</SUP>C and shows low methanol permeability. In the H<SUB>2</SUB>/air PEMFC at 70 <SUP>o</SUP>C, a current density of 600 mA cm<SUP>-2</SUP> leads to a potential of 637 mV and 658 mV for 50 μm thick mPES 60 and Nafion NRE 212, respectively. In the DMFC, mPES 60's methanol crossover current density is 4 times lower than that for Nafion NRE 212, leading to higher OCV values and peak power densities. Among all investigated conditions and materials, the highest peak power density of 120 mW cm<SUP>-2</SUP> was obtained with an mPES 60 based MEA at 70 <SUP>o</SUP>C and a methanol feed of 2 M.

Cigarette smoke and related risk factors in neurological disorders: An update

G, S.B.A.,Choi, S.,Krishnan, J.,K, R. Masson Pub. USA, Inc 2017 Biomedicine & pharmacotherapy Vol.85 No.-

<P>Cigarette smoking is known to be harmful to health, and is considered the main cause of death worldwide, especially in India. Among the well-distinguished diseases related to smoking are, chronic obstructive pulmonary disease, oral and peripheral cancers, and cardiovascular complications. However, the impact of cigarette smoking on neurocognitive and neuropathological effects, including anxiety, Alzheimer's disease, Parkinson's disease, ischemic stroke, and blood-brain barrier dysfunction, still remains unclear. Cigarette smoke consists of more than 4500 toxic chemicals that combine to form free radicals, which lead to oxidative stress-associated neurological disorders. Herein, we discuss the role of antioxidant agents in delaying or attenuating disease complications. In addition, in this review, we discuss the neuropathological effect of cigarette smoke and its interference in neurodegeneration. (C) 2016 Elsevier Masson SAS. All rights reserved.</P>

NONLINEAR OPTICAL TRANSMISSION OF SURFACE-MODIFIED NICKEL SULPHIDE NANOPARTICLES: SATURATION OF ABSORPTION AND OPTICAL LIMITING

V. S. MUTHUKUMAR,J. K. KIRAN,JASON REPPERT,R. SATYAJIT,VAMSI KRISHNA,G. NAGESHWAR RAO,S. SIVA RAMA KRISHNAN,S. SIVA SANKARA SAI,K. VENKATARAMANIAH,A. M. RAO 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.3

Saturable absorbers and optical limiters have contrary optical transmission properties. We report observations of simultaneous occurrence of both these effects in a nickel sulphide nanoparticle (average dia. ~5 nm) solution and a simultaneous quantitative measurement of both. Intensity dependent nonlinear transmission studies carried out using a 7 ns Nd:YAG laser at 532 nm by the Z-scan method, revealed efficient optical limiting in nickel sulphide nanoparticle suspensions. Induced nonlinear optical scattering was identified to be the mechanism of optical limiting, and absorption at 532 nm was found to saturate. A modification of the conventional Z-scan implementation led to the retrieval of the saturation intensity which is otherwise overshadowed by very strong nonlinear scattering.