전기전도도 측정을 통한 반류수 MLE공정에서 공기공급 제어기술 개발

장신요(Shinyo Chang),신풍식(Pung Shik Shin),정연구(Yeon-Koo Jeong),최영준(Young June Choi) 대한환경공학회 2020 대한환경공학회지 Vol.42 No.3

목적 : 반류수를 대상으로 무산소조에서 전기전도도 측정을 통해 호기조의 공기공급량을 제어할 수 있는 기술을 개발하여 공정성능 향상 및 에너지 사용량 절감을 달성하고자 하였다. 방법 : 전기전도도가 생물학적처리의 운전지표로 활용될 수 있는지를 검증하기 위해 각 공정별 수질인자와 전기전도도의 상관성 분석을 여름철(메탄올 투입), 겨울철, 가을철 시기로 나누어 실험하였다. 기존에 제시된 필요공기량 수식을 간단히 정리하여 경험식을 제시하고, 이를 활용해 전기전도도 범위에 공기공급량을 순차적으로 넣어 조견표를 작성하였다. 성능평가는 암모니아성질소와 총무기질소의 제거효율, SNR과 SDNR, 공기공급량의 변화, 유입수 변화에 대한 공정의 안정성 등을 기준으로 판단하였다. 결과 및 토의 : 계절별로 전기전도도와 각 수질항목의 상관계수가 0.5267 ~ 0.9115 범위로 암모니아성질소, 총무기질소, DOC, 인산염인 순서로 높게 산출되었다. 상관계수 0.5 이상으로 생물학적 처리공정의 운전지표로 전기전도도 가 활용될 수 있음을 알 수 있었다. 전기전도도와 암모니아성질소의 회귀식은 계절별로 재현성이 확보되어 전기전도도를 통해 암모니아성질소를 추정하는 것이 가능할 것으로 판단된다. 호기조 말단 DO가 3.4 mg/L 정도에서 겨울철 질소처리효율이 가장 양호하였다. 호기조 DO는 공기공급량으로 제어할 수 있으며 질소와 상관성이 높은 전기전도도를 직접 측정하여 공기공급량을 제어하고 질소처리효율을 향상시키는 것이 가능함을 알 수 있었다. 전기전도도와 유입유량을 통해 필요공기량을 산정할 수 있는 경험식을 제시하였고, 식 계수를 구한 결과 A", (B" + X") 는 각각 0.0589 (m³-air/h)/(m³/h)/(μS/cm), -77.562 (m³-air/h)/(m³/h)로 나타낼 수 있었다. 겨울철기간 무산소조의 전기전도도 측정값에 따라서 공기공급량을 자동 제어한 결과는 총무기질소 제거효율과 SDNR이 실플랜트 조건보다 각각 8.3%, 0.007 g-N/g-MLSS/d 높게 나타났다. 자동제어한 기간 동안에 공기공급량/유입유량 평균비가 36(m³-air/h)/(m³/h)로 실플랜트 조건보다 공기공급량을 21.7% 감소시킬 수 있었다. 결론 : 전기전도도 기반 MLE공정의 공기공급 제어기술은 질소제거 효율 향상 및 에너지 사용량 절감을 동시에 달성할 수 있을 것으로 판단된다. Objectives : This study aimed to achieve improved process performance and energy saving by developing a technology to control the air supply of an aerobic basin by measuring the conductivity in the anoxic basin. Methods : To verify whether conductivity can be used as an operation indicator of biological treatment, the correlation analysis between water quality factor and conductivity of each process was conducted by dividing into summer (methanol input), winter and autumn periods. An empirical formula was presented by briefly arranging the required air quantity formula, and a quick reference was prepared by putting air supply in the conductivity range sequentially. The performance evaluation was judged based on the removal efficiency of ammonia nitrogen and total inorganic nitrogen, SNR and SDNR, the change of air supply, the stability of the process against inflow change. Results and Discussion : The seasonal correlation coefficients of conductivity and water quality items were calculated in the order of ammonia nitrogen, total inorganic nitrogen, DOC, and phosphate in the range of 0.5267 ~ 0.9115. It was found that the conductivity could be used as an operation indicator of the biological treatment process with a correlation coefficient of 0.5 or more. The regression equations for the conductivity and ammonia nitrogen are secured by season, so it is possible to estimate the ammonia nitrogen through the conductivity. At the end of the aerobic basin DO was 3.4 mg/L, the nitrogen treatment efficiency in winter was the best. The aerobic basin DO can be controlled by the air supply, and it can be seen that it is possible to control the air supply and improve the nitrogen treatment efficiency by directly measuring the conductivity having a high correlation with nitrogen. An empirical formula for estimating the required air volume through conductivity and inflow is presented. A" and (B" + X") are 0.0589 (m³-air/h)/(m³/h)/(μS/cm) and -77.562 (m³-air/h)/(m³/h). The result of automatic control of air supply according to the measured conductivity of anoxic tank during winter season showed that total inorganic nitrogen removal efficiency and SDNR were 8.3% and 0.007 g-N/g-MLSS/d higher than the actual plant conditions, respectively. During the automatic control period, the air supply/inflow average ratio was 36 (m³-air/h)/(m³/h), which could reduce the air supply by 21.7% compared to the actual plant conditions. Conclusions : The air supply can be estimated from the flow rate and conductivity. The air supply control technology of the conductivity-based MLE process will be able to simultaneously improve nitrogen removal efficiency and reduce energy consumption.

Quantitative Conductivity Estimation Error due to Statistical Noise in Complex B1 + Map

신재욱,이준성,김민오,최나래,서진근,김동현 대한자기공명의과학회 2014 Investigative Magnetic Resonance Imaging Vol.18 No.4

In-vivo conductivity reconstruction using transmit field (B1+) information of MRI was proposed. We assessed theaccuracy of conductivity reconstruction in the presence of statistical noise in complex B1+ map and provided a parametricmodel of the conductivity-to-noise ratio value. Materials and Methods: The B1+ distribution was simulated for a cylindrical phantom model. By adding complex Gaussiannoise to the simulated B1+ map, quantitative conductivity estimation error was evaluated. The quantitative evaluationprocess was repeated over several different parameters such as Larmor frequency, object radius and SNR of B1+ map. Aparametric model for the conductivity-to-noise ratio was developed according to these various parameters. Results: According to the simulation results, conductivity estimation is more sensitive to statistical noise in B1+ phase thanto noise in B1+ magnitude. The conductivity estimate of the object of interest does not depend on the external object surroundingit. The conductivity-to-noise ratio is proportional to the signal-to-noise ratio of the B1+ map, Larmor frequency,the conductivity value itself and the number of averaged pixels. To estimate accurate conductivity value of the targetedtissue, SNR of B1+ map and adequate filtering size have to be taken into account for conductivity reconstruction process. In addition, the simulation result was verified at 3T conventional MRI scanner. Conclusion: Through all these relationships, quantitative conductivity estimation error due to statistical noise in B1+ map ismodeled. By using this model, further issues regarding filtering and reconstruction algorithms can be investigated for MREPT.

Correlation between Hydraulic Conductivity and Electrical Conductivity for Porous Media

Tae Min Oh,Kyu Won Kim,Gye Chun Cho 한국지반공학회 2013 international journal of geo-engineering Vol.5 No.2

Hydraulic conductivity (permeability) is a very important physical property in geotechnical engineering. Monitoring of the hydraulic conductivity is useful for evaluating the ground condition by nondestructive methods. An electrical conductivity measurement technique can be applied to infer hydraulic conductivity. The goal of this study is theoretically to correlate the hydraulic conductivity and electrical conductivity for porous materials and to verify the developed correlation. The verification process is carried out through experimental tests involving glass beads and Joomunjin standard sand. The test variables are the electrical conductivity of the pore fluid, the porosity, and the particle size. The test results show that the estimated hydraulic conductivity realized by the developed correlation is in good agreement with the measured hydraulic conductivity results. Therefore, this preliminary study provides evidence of the strong possibility of the electrical conductivity being feasible for use to monitor the hydraulic conductivity of porous materials.

Temperature dependence and cation effects in the thermal conductivity of glassy and molten alkali borates

Kim, Youngjae,Morita, Kazuki Elsevier 2017 Journal of non-crystalline solids Vol.471 No.-

<P><B>Abstract</B></P> <P>The thermal conductivity of Li<SUB>2</SUB>O-B<SUB>2</SUB>O<SUB>3</SUB>, Na<SUB>2</SUB>O-B<SUB>2</SUB>O<SUB>3</SUB> and K<SUB>2</SUB>O-B<SUB>2</SUB>O<SUB>3</SUB> glass systems was measured as a function of the temperature. As the temperature increases, the thermal conductivity of the glass phase initially increases and then reaches a plateau. Afterwards, in the liquid phases, a further increase in the temperature leads to a decrease in the thermal conductivity. The thermal conduction phenomenon can be better described by considering the glass and molten oxide systems as a one-dimensional continuum. It was found that the temperature corresponding to the highest thermal conductivity lies close to the one-dimensional Debye temperature (<I>Θ</I> <SUB> <I>D</I>1</SUB>). According to phonon gas model, the variables affecting the thermal conductivity were evaluated. Below <I>Θ</I> <SUB> <I>D</I>1</SUB>, the increase in heat capacity with the temperature leads to a corresponding increase in the thermal conductivity. The heat capacity then becomes constant above <I>Θ</I> <SUB> <I>D</I>1</SUB> leading to the observed plateau in the thermal conductivity of the glass phase. After melting the glass, the decrease in thermal conductivity with increasing temperature is due to changes in sound velocity and mean free path. The relative content of 3- and 4-coordinated boron was analyzed by <SUP>11</SUP>B MAS-NMR. The cation effect on the thermal conductivity of alkali borate glasses was evaluated through their ionization potentials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> By phonon gas model, variables determining thermal conductivity in the glassy and molten oxide system were evaluated. </LI> <LI> The glassy and molten oxide system was treated as a conducting medium of one-dimensional continuum. </LI> <LI> In the non-crystalline oxide system, maximum thermal conductivity could be found near one-dimensional Debye temperature. </LI> <LI> Effect of cation on thermal conductivity in the alkali borate system was evaluated through the ionization potential. </LI> </UL> </P>

반도체 재료의 격자열전도도 분석

임종찬,양희선,김현식,Lim, Jong-Chan,Yang, Heesun,Kim, Hyun-Sik 한국마이크로전자및패키징학회 2020 마이크로전자 및 패키징학회지 Vol.27 No.4

열전소재의 격자열전도도 저감은 열전성능 증대를 위해 가장 빈번하게 사용되는 방법이다. 하지만 전체 열전도도에서 다른 열전도도 기여분을 제외하는 방법으로만 격자열전도도를 구할 수 있기 때문에 격자열전도도를 정확하게 분석하는 것을 간단한 작업이 아니다. 본 연구에서는 먼저 전자/홀에 의한 열전도도 기여분 (모든 소재 적용)과 쌍극 전도에 의한 기여분 (작은 밴드 갭 소재 적용)을 정확하게 계산해야만 격자열전도도를 정확하게 분석할 수 있음을 설명한다. 전자/홀에 의한 기여분을 계산하기 위해 필수적인 로렌츠 숫자 계산법 (싱글 파라볼릭 모델링 및 간단한 식 이용)과 쌍극 전도에 의한 기여분 계산법 (투 밴드 모델링) 또한 소개한다. 격자열전도도의 정확한 분석은 격자열전도도 저감을 위한 여러 결함 제어 전략의 효과를 객관적으로 평가할 수 있는 강력한 분석 도구로 사용될 수 있다. Suppressing lattice thermal conductivity of thermoelectric materials is one of the most popular approach to improve their thermoelectric performance. However, accurate characterization of suppressed lattice thermal conductivity is challenging as it can only be acquired by subtracting other contributions to thermal conductivity from the total thermal conductivity. Here we explain that electronic thermal conductivity (for all materials) and bipolar thermal conductivity (for narrow band gap materials) need to be determined accurately first to characterize the lattice thermal conductivity accurately. Methods to calculate Lorenz number for electronic thermal conductivity (via single parabolic model and using a simple equation) and bipolar thermal conductivity (via two-band model) are introduced. Accurate characterization of the lattice thermal conductivity provides a powerful tool to accurately evaluate effect of different defect engineering strategies.

토양 칼럼의 경계흐름과 계면활성제가 수리전도도에 미치는 영향연구

정승우,주병규 유기성자원학회 2009 유기물자원화 Vol.17 No.1

수리전도도는 다공성매체 시스템의 중요한 특성인자이다. 수리전도도를 측정하는 방법은 실외측정방법과 실내측정방법이 있다. 수리전도도의 실내측정은 일반적으로 투수측정기를 이용한다. 기존의 투수측정방식으로 산정한 수리전도도는 경계흐름의 영향을 고려하지 않고 모든 유체가 수직으로 이동한다는 가정으로 결정되었다. 하지만 실제 토양에서 유체는 수직, 좌우 방향으로 이동할 수 있다. 본 연구에서는 경계흐름을 배제한 투수계를 이용하여 경계흐름이 수리전도도에 미치는 영향을 평가하였다. 실험결과 기존방식으로 산정한 수리전도도에 비해 경계흐름을 배제한 수리전도도가 약 1/3에 해당하였다. 투수측정기를 이용한 수리전도도 측정에 있어 경계흐름에 대한 영향을 고려한 수리전도도 결정이 필요하다. 또한 토양 입경과 계면활성제가 수리전도도에 미치는 영향을 파악하였다. 토양입경과 수리전도도는 비례하는 것으로 나타났으며 계면활성제는 수리전도도를 감소시키는 것으로 확인되었다. 계면활성제 농도가 증가할수록 수리전도도는 보다 많이 감소하였다. 수리전도도를 결정하는 물리적 특성을 평가한 결과 유체의 점도가 가장 큰 영향을 미치는 것으로 나타났다. The hydraulic conductivity of porous media is the most important property in soil characteristics. The hydraulic conductivity is determined by outdoor and indoor methods. Indoor methods normally use soil columns for flow test. Assumption of the column test is that fluid one-dimensionally flows through the column. However, fluids may flow toward the wall of the column, resulting in "boundary flow". This study investigated the effect of boundary flow on the hydraulic conductivity by using a permeameter excluding boundary flow. The results showed that the hydraulic conductivity excluding boundary flow was much smaller than the hydraulic conductivity employing the conventional determination method. This study also investigated the effects of particle size and surfactant on the hydraulic conductivity. As the particle size increased, the hydraulic conductivity was increased. The hydraulic conductivity was reduced by increasing surfactant concentration. The result showed that the viscosity of fluid significantly affected the determination of hydraulic conductivity.

Effective hydraulic conductivity of discrete fracture network with aperture-length correlation

Jianting Zhu 한국지질과학협의회 2020 Geosciences Journal Vol.24 No.3

Determining effective hydraulic conductivity is critical to understand groundwater flow behavior in fractured rock masses and is required for large-scale numerical simulations. A new approach is developed to estimate the effective hydraulic conductivity of a discrete fracture network with aperture and trace length being stochastic and correlated. The aperture and length are assumed to follow a joint lognormal distribution. The average flowrate through the network is determined by integrating flowrate in the fracture ensemble with the laminar flow and non-linear flow being separately considered based on the Reynolds number. The effective hydraulic conductivity of the discrete fracture network is then determined from the idea that Darcy’s law still applies to the overall flow behavior through the network. For comparison, the simple average hydraulic conductivity is also developed based on the assumption that flow in all fractures is laminar and aperture and trace length are uncorrelated. Based on the developed approach, the effects of aperture and trace length uncertainty, their correlation degree, and non-linear flow characteristics on the ratio of effective hydraulic conductivity over simple average hydraulic conductivity are examined. The results demonstrate that the effective hydraulic conductivity can be either larger than or smaller than the simple average hydraulic conductivity depending on correlation level between aperture and trace length and the degree of non-linear effect in the network. Non-linear flow reduces the effective hydraulic conductivity of the fracture network. Correlation between aperture and trace length increases the effective hydraulic conductivity. Aperture uncertainty tends to reduce the effective hydraulic conductivity.

Opto-thermal technique for measuring thermal conductivity of polyacrylonitrile based carbon fibers

Jang, Dawon,Lee, Dong Su,Lee, Aram,Joh, Han-Ik,Lee, Sungho Elsevier 2019 Journal of industrial and engineering chemistry Vol.78 No.-

<P><B>Abstract</B></P> <P>Thermal conductivity of carbon fibers (CFs) is an important property because CFs are used as heat dissipation fillers in composites for aerospace and electronics applications. However, evaluating thermal conductivity of a single filament of CFs is an arduous task due to dimensional issue of specimens and limitations of conventional measurement system. Therefore, we suggest an opto-thermal technique using Raman spectroscopy to measure thermal conductivity of commercial polyacrylonitrile based CFs (T300, T700SC and T800H). The opto-thermal technique used that G band from Raman spectroscopy of carbon materials is shifted depending on temperature. For verifying an accuracy of the technique, the laser absorbance of CFs were estimated, and the thermal conductivity was measured depending on the length of CF. The measured data were reflected in the thermal conductivity calculation formula. It was demonstrated that the method provides more reasonable thermal conductivity values compare to a conventional Angstrom method. In addition, this simple technique confirmed that graphitic structure of CFs played a critical role in their thermal conductivity.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An opto-thermal technique was demonstrated to measure thermal conductivity of commercial polyacrylonitrile based CFs. </LI> <LI> The G band shift depending on temperature in Raman spectra was used for obtaining thermal conductivity of CFs. </LI> <LI> For an accurate measurement, a laser absorbance of CFs was estimated by UV–vis-NIR spectrometer and simulation. </LI> <LI> The thermal conductivity of T300, T700SC, and T800H were found to 13.8, 12.7, and 37.5W/mK, respectively. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Suppression of bipolar conduction via bandgap engineering for enhanced thermoelectric performance of p-type Bi_0.4Sb_1.6Te₃ alloys

Kim, Hyun-Sik,Lee, Kyu Hyoung,Yoo, Joonyeon,Shin, Weon Ho,Roh, Jong Wook,Hwang, Jae-Yeol,Kim, Sung Wng,Kim, Sang-il Elsevier 2018 Journal of alloys and compounds Vol.741 No.-

<P><B>Abstract</B></P> <P>Substitutional doping is known to be effective when used to enhance the thermoelectric figure of merit <I>zT</I>, and this is generally explained as resulting from a reduction in the thermal conductivity caused by an additional atomic-scale defect structure. However, a comprehensive analysis of the substitutional doping effect on the electrical and thermal properties together has not been undertaken, especially when the bipolar thermal conductivity becomes serious. A previous study by the authors also showed that the <I>zT</I> of Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB> thermoelectric alloys was enhanced by indium (In) doping due to the reduction of the total thermal conductivity. Here, we more closely analyze the electrical and thermal transport properties of a series of indium (In)-doped p-type Bi<SUB>0.4</SUB>Sb<SUB>1.6-x</SUB>In<SUB>x</SUB>Te<SUB>3</SUB> (x = 0, 0.003, 0.005, 0.01) using both the single-parabolic-band model and the Debye-Callaway model in an effort to investigate the origin of the observed thermal conductivity reduction more closely. The bipolar contribution to the total thermal conductivity was estimated exclusively based on a two-band model based on a single-parabolic-band model. Furthermore, the lattice thermal conductivity was calculated using the Debye-Callaway model while taking additional In substitutional defects into consideration. The calculations indicated that the significant suppression of bipolar thermal conductivity was achieved as a result of the increased bandgap in Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB> caused by In doping. Additional point defects from In doping also reduced the lattice thermal conductivity, but not as much as the bipolar thermal conductivity did. The study suggests that the suppression of bipolar conduction by means of a bandgap modification can be an effective approach for enhancing <I>zT</I> further via a simple In-doping process in Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Thermal conductivity reduction in In-doped Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB> is analyzed. </LI> <LI> Bandgap increase by In doping suppresses bipolar conduction significantly. </LI> <LI> Extra point defects by In doping reduces lattice thermal conductivity. </LI> <LI> The <I>zT</I> enhancement in In-doped Bi<SUB>0.4</SUB>Sb<SUB>1.6</SUB>Te<SUB>3</SUB> is mainly due to bipolar suppression. </LI> </UL> </P>

Effects of Y₂O₃ additions on the densification and thermal conductivity of spark plasma sintering AlN ceramics

Kyoung Hun Kim,Joo Seok Park,Byung Ha Lee,K. B. Shim,Jong Pil Ahn,Jae Hong Chae 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.1

Spark plasma sintering (SPS) of AlN ceramics was carried out with Y₂O₃ as a sintering additive at sintering temperatures of 1,550 to 1,700 ℃. The effects of Y₂O₃ additions on the sintering behavior and thermal conductivity of AlN ceramics were studied. Y₂O₃ added to AlN showed a noticeable higher densification rate than pure AlN, but the formation of yttrium aluminate phases by the solid-state reaction of Y₂O₃ and Al2O3 occurred on the AlN surface which could retard the densification during the sintering process. The thermal conductivity of AlN specimens was improved by the addition of Y₂O₃ up to 3 wt% in spite of the formation of a YAG secondary phase in the AlN grain boundaries because Y₂O₃ additions could reduce the oxygen content in the AlN lattice which is primary factor controlling the thermal conductivity. However, the thermal conductivity decreased at a 5 wt% addition because the extra formation of the YAG phase in grain boundaries could decrease the thermal conductivity by phonon scattering thus surpassing the helpful contributions of smaller Y₂O₃ additions. Spark plasma sintering (SPS) of AlN ceramics was carried out with Y₂O₃ as a sintering additive at sintering temperatures of 1,550 to 1,700 ℃. The effects of Y₂O₃ additions on the sintering behavior and thermal conductivity of AlN ceramics were studied. Y₂O₃ added to AlN showed a noticeable higher densification rate than pure AlN, but the formation of yttrium aluminate phases by the solid-state reaction of Y₂O₃ and Al2O3 occurred on the AlN surface which could retard the densification during the sintering process. The thermal conductivity of AlN specimens was improved by the addition of Y₂O₃ up to 3 wt% in spite of the formation of a YAG secondary phase in the AlN grain boundaries because Y₂O₃ additions could reduce the oxygen content in the AlN lattice which is primary factor controlling the thermal conductivity. However, the thermal conductivity decreased at a 5 wt% addition because the extra formation of the YAG phase in grain boundaries could decrease the thermal conductivity by phonon scattering thus surpassing the helpful contributions of smaller Y₂O₃ additions.