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광범위한 전단률에서 적용가능한 수정된 POWER LAW 유체에 대한 GRAETZ문제 해법
T.F. irvine, Jr 한국유변학회 1995 Korea-Australia rheology journal Vol.7 No.1
층류 열전달에서 작은 Reynolds number에서의 원통내의 흐름에대한 Power law 유 체의 해법이 사용될 수가 없는 것을 낮은 전단률(Shear Rate)에서 Power Law 법칙이 적용 되지 않기 때문이다. 본 연구에서는 이문제를 새로운 구성방정식을 이용하여 높은 전단률에 서는 Power Law 법칙이 낮은 전단률에서는 Newtonian 법칙이 그 중간에서는 천이과정을 모두 포함하는 전범위의 전단률에 대해 해결하였다. 이러한 구성방정식의 기본개졈은 실험 결과와도 잘 일치하였따. 이 구성방정식을 이용하여 Graetz 문제를 해결하였고 경계조건은 일정온도와 일정열속이다. 이용하기 쉬운 전단률변수는 적용범위가 Newtonian인지 Power law 인지 아니면 중간 천이과정인지를 나타내준다.
Irvine, John T.S.,Bae, Joongmyeon,Park, Jun-Young,Choi, Won Seok,Kim, Jung Hyun Elsevier 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.2
<P><B>Abstract</B></P> <P>The electrochemical properties and long-term performance of an in-situ composite cathode comprised of SmBa<SUB>0.5</SUB>Sr<SUB>0.5</SUB>Co<SUB>2</SUB>O<SUB>5+δ</SUB> (SBSCO) and Ce<SUB>0.9</SUB>Gd<SUB>0.1</SUB>O<SUB>2−δ</SUB> (CGO91) are investigated for metal supported solid oxide fuel cell (MS-SOFC) application.</P> <P>The Area Specific Resistance (ASR) of an in-situ composite cathode comprised of 50 wt% of SBSCO and 50 wt% of CGO91 (SBSCO:50) is 0.031 Ω cm<SUP>2</SUP> in the first stage of measurement at 700 °C; this value of ASR increases to 0.138 Ω cm<SUP>2</SUP> after 1000 h. The ASR of SBSCO:50 (in-situ sample at 750 °C) is 0.014 Ω cm<SUP>2</SUP> at the initial stage of measurement; the increase of ASR after 1000 h at 750 °C is only 0.067 Ω cm<SUP>2</SUP>. These results suggest that the optimum temperature for in-situ firing of an SBSCO:50 cathode sample of MS-SOFC is higher than 700 °C, ideally around 750 °C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Electrochemical properties of the in-situ SBSCO:50 cathode were investigated. </LI> <LI> The ASR values of in-situ cathode were 0.031 and 0.014 Ω cm<SUP>2</SUP> at 700 and 750 °C. </LI> <LI> The increase of ASR after 1000 h at 750 °C was found to be only 0.067 Ω cm<SUP>2</SUP>. </LI> </UL> </P>
Baek, Seung-Wook,Azad, Abul K.,Irvine, John T.S.,Choi, Won Seok,Kang, Hyunil,Kim, Jung Hyun Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.432 No.2
<P><B>Abstract</B></P> <P>SmBaCo<SUB>2</SUB>O<SUB>5+d</SUB> (SBCO) showed the lowest observed Area Specific Resistance (ASR) value in the LnBaCo<SUB>2</SUB>O<SUB>5+d</SUB> (Ln: Pr, Nd, Sm, and Gd) oxide system for the overall temperature ranges tested. The ASR of a composite cathode (mixture of SBCO and Ce<SUB>0.9</SUB>Gd<SUB>0.1</SUB>O<SUB>2−d</SUB>) on a Ce<SUB>0.9</SUB>Gd<SUB>0.1</SUB>O<SUB>2−d</SUB> (CGO91) electrolyte decreased with respect to the CGO91 content; the percolation limit was also achieved for a 50wt% SBCO and 50wt% CGO91 (SBCO50) composite cathode.</P> <P>The ASRs of SBCO50 on the dense CGO91 electrolyte in the overall temperature range of 500–750°C were relatively lower than those of SBCO50 on the CGO91 coated dense 8mol% yttria-stabilized zirconia (8YSZ) electrolyte for the same temperature range. From 750°C and for all higher temperatures tested, however, the ASRs of SBCO50 on the CGO91 coated dense 8YSZ electrolyte were lower than those of the CGO91 electrolyte.</P> <P>The maximum power densities of SBCO50 on the Ni-8YSZ/8YSZ/CGO91 buffer layer were 1.034Wcm<SUP>−2</SUP> and 0.611Wcm<SUP>−2</SUP> at 800°C and 700°C.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The ASR properties using two types of electrolytes are investigated. </LI> <LI> SBCO50 showed the lowest ASR values in the overall temperature range. </LI> <LI> The percolation limit was also achieved for a SBCO50 composite cathode. </LI> <LI> SBCO50 on CGO91 has to be adopted at 750°C or in a lower temperature range. </LI> <LI> SBCO50 on CGO91 coated 8YSZ has to be used as a temperature of 750°C of above. </LI> </UL> </P>
Lee, Daehee,Myung, Jaeha,Tan, Jeiwan,Hyun, Sang-Hoon,Irvine, John T.S.,Kim, Joosun,Moon, Jooho Elsevier Sequoia 2017 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>Solid oxide fuel cells (SOFCs) can oxidize diverse fuels by harnessing oxygen ions. Benefited by this feature, direct utilization of hydrocarbon fuels without external reformers allows for cost-effective realization of SOFC systems. Superior hydrocarbon reforming catalysts such as nickel are required for this application. However, carbon coking on nickel-based anodes and the low efficiency associated with hydrocarbon fueling relegate these systems to immature technologies. Herein, we present methane-fueled SOFCs operated under conditions of catalytic partial oxidation (CPOX). Utilizing CPOX eliminates carbon coking on Ni and facilitates the oxidation of methane. Ni-gadolinium-doped ceria (GDC) anode-based cells exhibit exceptional power densities of 1.35 W cm<SUP>−2</SUP> at 650 °C and 0.74 W cm<SUP>−2</SUP> at 550 °C, with stable operation over 500 h, while the similarly prepared Ni-yttria stabilized zirconia anode-based cells exhibit a power density of 0.27 W cm<SUP>−2</SUP> at 650 °C, showing gradual degradation. Chemical analyses suggest that combining GDC with the Ni anode prevents the oxidation of Ni due to the oxygen exchange ability of GDC. In addition, CPOX operation allows the usage of stainless steel current collectors. Our results demonstrate that high-performance SOFCs utilizing methane CPOX can be realized without deterioration of Ni-based anodes using cost-effective current collectors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Direct CH<SUB>4</SUB> fueled SOFCs operated via catalytic partial oxidation are demonstrated. </LI> <LI> A high performance of 0.74 W cm<SUP>−2</SUP> at 550 °C is achieved. </LI> <LI> Enhanced CH<SUB>4</SUB> conversion suggests a promising internal reforming by CPOX. </LI> <LI> Adsorption dynamics on Ni catalysts is elucidated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>