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Kshetrimayum, Krishnadash S.,Jung, Ikhwan,Na, Jonggeol,Park, Seongho,Lee, Yongkyu,Park, Seongeon,Lee, Chul-Jin,Han, Chonghun American Chemical Society 2016 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.55 No.3
<P>Computational fluid dynamic (CFD) simulation of heat transfer in a microchannel reactor block for low temperature Fischer-Tropsch (FT) synthesis was considered. Heat generation profiles for different operating conditions (GHSV 5000 h(-1); catalyst loading 60%-120%, where 100% loading equals 1060 kg/m(3) of cobalt based catalyst from Oxford Catalyst Ltd.) were obtained from a single channel model. Simulations on a reactor block quantified the effects of three coolant types: cooling oil (Merlotherm SH), subcooled water and saturated water, on reactor temperature, and also evaluated the effect of wall boiling conditions. At process conditions of GHSV 5000 h(-1) and catalyst loading of 120%, predicted temperature gradients along channel length were 32, 17 and 12 K for cooling oil, subcooled water and saturated water, respectively. A modified reactor block showed improved thermal performance as well as heat transfer enhancement due to wall boiling conditions.</P>
마이크로채널 반응기를 이용한 강화된 저온 피셔-트롭쉬 합성반응의 전산유체역학적 해석
Krishnadash S. Kshetrimayum,나종걸(Jonggeol Na),박성호(Seongho Park),정익환(Ikhwan Jung),이용규(Yongkyu Lee),한종훈(Chonghun Han) 한국가스학회 2017 한국가스학회지 Vol.21 No.4
피셔-트롭쉬 합성반응은 CO와 H2의 혼합가스로 이루어진 합성가스를 부가가치가 높은 탄화수소 제품으로 변환시킨다. 본 논문에서는 저온 피셔-트롭쉬 합성반응과 단일, 다중 마이크로채널 반응기에 패킹시킨 촉매를 기반으로 강화된 반응조건의 열전달을 고려하여 전산유체역학 기반의 시뮬레이션을 진행하고 분석하였다. 단일채널모델을 통하여 CO 전환률이 ~65% 이상, C<SUB>5+</SUB> 선택도가 ~74% 이상을 달성하면서도 Co 기반의 super-active 촉매를 통해 GHSV를 30000 hr<SUP>-1</SUP>을 달성할 수 있음을 보였다. 다중 마이크로채널 반응기모델에서는 열전달 시뮬레이션을 동시에 해석하여, 3가지의 다른 반응기구조에 대해서, 직교류 wall boiling 냉매를 사용시 △T<SUB>max </SUB>가 23 K였으며 평행유동 subcooled 냉매와 평행유동 wall boiling 냉매의 경우 각각 15 K와 13 K의 △T <SUB>max</SUB> 를 보였다. 반응기 전체적으로 498 - 521 K에서 온도제어가 가능했으며 계산된 사슬성장 가능성은 저온 피셔-트롭쉬 합성에 적합한 것으로 보인다. Fischer-Tropsch synthesis reaction converts syngas (mixture of CO and H2) to valuable hydrocarbon products. Simulation of low temperature Fischer -Tropsch Synthesis reaction and heat transfer at intensified process condition using catalyst filled single and multichannel microchannel reactor is considered. Single channel model simulation indicated potential for process intensification (higher GHSV of 30000 hr<SUP>-1</SUP> in presence of theoretical Cobalt based super-active catalyst) while still achieving CO conversion greater than ~65% and C<SUB>5+</SUB> selectivity greater than ~74%. Conjugate heat transfer simulation with multichannel reactor block models considering three different combinations of reactor configuration and coolant type predicted ΔTmax equal to 23 K for cross-flow configuration with wall boiling coolant, 15 K for co-current flow configuration with subcooled coolant, and 13 K for co-current flow configuration with wall boiling coolant. In the range of temperature maintained (498 - 521 K), chain growth probability calculated is desirable for low-temperature Fisher-Tropsch Synthesis.
Na, Jonggeol,Kshetrimayum, Krishnadash S.,Jung, Ikhwan,Park, Seongho,Lee, Yongkyu,Kwon, Okbae,Mo, Yonggi,Chung, Jongtae,Yi, Jongyeol,Lee, Ung,Han, Chonghun Elsevier 2018 CHEMICAL ENGINEERING AND PROCESSING Vol.128 No.-
<P><B>Abstract</B></P> <P>Design and operation of pilot-scale (1.0 BDP) compact GTL process comprising of reforming section, CO<SUB>2</SUB> separating section, and Fischer-Tropsch (FT) synthesis section is presented. Detailed systematic computer-aided design procedure adopted to design a modular 0.5 BPD pilot-scale microchannel reactor used in the pilot plant operation is also presented. The modular microchannel FT reactor block design consists of 528 process channels and numerous coolant channels arranged in cross-cocurrent-cross configuration for adequate heat removal. On average 98.27% CH<SUB>4</SUB> conversion to syngas in reforming section comprising of a pre-reformer unit and a tri-reformer unit, and CO<SUB>2</SUB> separation rate of 36.75% along with CO/H<SUB>2</SUB> reduction from 2.67 to 2.08 in CO<SUB>2</SUB> membrane separation section were achieved from the entire pilot plant operation duration of 450 h. Parallel operation of FT microchannel reactor and multitubular fixed-bed type FT reactor for comparison showed that multitubular fixed-bed type reactor undergoes reaction runaway for the applied process conditions, while microchannel reactor showed adequate temperature control. Overall CO conversion of 83% and adequate temperature control at three different applied operating temperatures of 220 °C, 230 °C, and 240 °C subsequently during the 139 h FT reactor operation demonstrated the appreciable performance of the present microchannel FT reactor designed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Design and operation of pilot scale (1.0 BDP) compact GTL process. </LI> <LI> Systematic computer-aided design procedure is formulated. </LI> <LI> Reactor modeling and optimization using CFD and cell-coupling methods. </LI> <LI> Parallel operation FT microchannel reactor and multitubular fixed bed reactor. </LI> <LI> The designed reactor gives satisfactory temperature control. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
L^r LINEQUALITIES OF GENERALIZED TURÁN-TYPE INEQUALITIES OF POLYNOMIALS
Thangjam Birkramjit Singh,Kshetrimayum Krishnadas,Barchand Chanam 경남대학교 기초과학연구소 2021 Nonlinear Functional Analysis and Applications Vol.26 No.4
If $p(z)$ is a polynomial of degree $n$ having all its zeros in $|z|\leq k$, $k\leq 1$, then for $\rho R\geq k^2$ and $\rho\leq R$, Aziz and Zargar [4] proved that\max\limits_{|z|=1}|p'(z)|\geq n\dfrac{(R+k)^{n-1}}{(\rho+k)^n}\left\{\max\limits_{|z|=1}|p(z)|+\min\limits_{|z|=k}|p(z)|\right\}. We prove a generalized $L^r$ extension of the above result for a more general class of polynomials $p(z)=a_nz^n+\sum\limits_{\nu=\mu}^{n}a_{n-\nu}z^{n-\nu}$, $1\leq \mu\leq n$. We also obtain another $L^r$ analogue of a result for the above general class of polynomials proved by Chanam and Dewan [6].
Park, S.,Jung, I.,Lee, Y.,Kshetrimayum, K.S.,Na, J.,Park, S.,Shin, S.,Ha, D.,Lee, Y.,Chung, J.,Lee, C.J.,Han, C. Pergamon Press 2016 Chemical engineering science Vol.143 No.-
The objective of this study is to design a microchannel Fischer-Tropsch reactor with the evaluation of several flow configurations and distribution effect. A cell coupling computation was carried out for the microchannel reactor of five different flow configurations. In the cell coupling method, all the process and cooling channels are decomposed into a number of unit cells, and then coupled to solve the material and energy balances. The realistic flow distribution effect was incorporated into the model by using results obtained from computational fluid dynamics (CFD). The kinetic model was validated with experimental data, and the results of the reactor model was compared with data taken from the literature and the results were found to be in good agreement. Several case studies were conducted to see the effect of flow configurations, flow distribution, and catalyst loading zones. It was observed that the geometry of cross-co-cross current was found to give the best performance among the designs considered. The study also reveals that flow distribution and catalyst loading zone need to be carefully controlled for the safe, robust, and reliable reactor design and operation.
ON AN INEQUALITY OF S. BERNSTEIN
Barchand Chanam,Khangembam Babina Devi,Kshetrimayum Krishnadas,Maisnam Triveni Devi,Reingachan Ngamchui,Thangjam Birkramjit Singh 경남대학교 기초과학연구소 2021 Nonlinear Functional Analysis and Applications Vol.26 No.2
If $p(z)=\sum\limits_{\nu=0}^na_{\nu}z^{\nu}$ is a polynomial of degree $n$ having all its zeros on $|z|=k$, $k\leq 1$, then Govil [3]proved that\begin{align*}\max\limits_{|z|=1}|p'(z)|\leq \dfrac{n}{k^n+k^{n-1}}\max\limits_{|z|=1}|p(z)|. \end{align*} In this paper, by involving certain coefficients of $p(z)$, we not only improve the above inequality but also improve a result provedby Dewan and Mir [2].