순환 유동층 보일러의 수력학적 특성 파악을 위한 다차원 수치해석과 상사법칙의 상호 보완적 활용에 관한 연구

양창원 과학기술연합대학원대학교 2020 국내박사

순환유동층 연소로에서 수력학적 특성 실험 및 모델링 : 유동매체량에 따른 수력학적 특성을 중심으로

김은경 연세대학교 대학원 2003 국내석사

본 연구는 순환유동층의 주요 설계 및 운전 변수의 하나인 유동물질의 유동매체량(solid mass inventory)에 따른 순환 유동층 내에서의 수력학적 특성을 파악하여 이를 바탕으로 운전 및 설계변수를 예측하는 것이 주 목적이다. 실험실 규모의 순환유동층 실험 데이터와 이를 근간으로 모델링에는 IEA-CFBC 및 상용 CFD 해석코드를 사용하여 순환유동층 내에서 수력학적 특성을 평가 및 비교하기 위한 기초 자료를 제공하는 데 그 목적이 있다. 층물질 유동매체량과 공기 주입량을 변화시켰을 때의 순환유동층 내에 유동화 형태에 미치는 영향을 이해하고자 하였다. 실험은 직경 0.05 m와 높이 3 m의 아크릴 판으로 제작된 냉간 순환유동층에서 수행되었으며 사용된 유동물질은 흑색의 샬리카 카보네이트로 입경분포는 100 ∼ 500 ㎛ 범위를 이룬다. 상승부 공탑속도는 1.39 ∼ 3.24 m/s이고, J-밸브의 유동화 속도는 0.139 ∼ 0.232 m/s로 주어졌다. 실험으로부터 순환유동층 내 축방향 고체분률과 고체순환율이 측정되었고, 실험 데이터는 IEA-CFBC와 상용 CFD 코드를 이용한 모델링을 통해 검증 비교되었다. 또한 본 연구에서는 소규모 연구실 규모의 실험장치로부터 대규모 플랜트로의 용량확대(scale-up) 기초자료 확보를 위해 IEA-CFBC와 상용 CFD 코드를 이용해 모델링이 수행되었다. This paper discusses effect of solid of mass inventory on the hydrodynamic characteristics of circulating fluidized bed(CFB). Operating parameters of solid mass inventory and air flow rates were varied to understand their effects on fludization pattern. Experimental measurements were made in a CFB of which height and diameter are 3 m and 0.05 m, respectively. Black SiC particles ranging from 100 ㎛to 500 ㎛ were employed as the bed material. Superficial gas velocity of riser and J-valve fluidizing velocity were in the ranges of 1.39 3.24 m/s and 0.139 0.232 m/s, respectively. The axial solid fraction and solid circulation rate of CFB were calculated based on the experimental data and compared with modellings through IEA-CFBC Model and commercial CFD code(FLUENT).

液體-固體 循環 流動層 反應器에서 水力學 및 熱傳達 特性

신광식 忠南大學校 2004 국내박사

A liquid-solid circulating fluidized bed can be utilized effectively as a multiphase flow reactor, bioreactor or adsorption and contacting system, especially when viscosity of the continuous liquid medium is relatively high. In addition to several unique advantages of liquid-solid fluidized beds, the liquid-solid circulating fluidized beds can minimize dead zone and increase the contacting efficiency among liquid and solid phases, in the riser by enhancing shear stress at the interfaces owing to the extremely high liquid velocity However, there has been little attention to the liquid-solid circulating fluidized bed until now, even on the fundamental hydrodynamics. In the present study, thus, the multiphase flow behavior characteristics such as, the hydrodynamic, solid holdup and pressure fluctuation the liquid dispersion have been investigated in the riser of a liquid-solid circulating fluidized bed(0.102m-ID×3.5m-heig.). In addition, the heat transfer and temperature difference fluctuations(△T) between the immersed heater and the bed proper have been investigated. Aqueous solutions of carboxymethyl cellulose(CMC:_(μL)=0.96~38mPa · 5)have been used as the solid and liquid phase, respectively. It has been found that the solid holdup decrease with increasing liquid velocity or viscosity, but it increase with increasing solid paticle size or solid circulation rate. It has been found that phase space portraits of pressure fluctuations becomes more scattered and correlation dimension(D_(c)) of pressure fluctuation tends to increase with increasing d_(p) or G_(s), elucidating that the flow behavior of fludized particles becomes more irregular or random with increasing d_(p) or G_(s). However, the increase of U_(L) results in the slight decrease in the value of D_(c) It is Interesting to note that the dependence of heat transfer coefficient (h) upon operating variable is very similar to that of pressure fluctuation upon them; the value of h increase with increasing d_(p) or G_(s), while it tends to decrease slightly with increasing U_(L). The value of h has been well correlated in terms of dimensionless groups as well as operating variables. It was found that the attractor in the phase space portraits became more scattered and complicated with increasing particle size or solid circulation rate, but it became somewhat less scattered with increasing liquid velocity The correlation dimension of temperature fluctuations increased with increasing particle size or solid circulation rate, but it did not change considerably with increasing liquid velocity. The overall heat transfer coefficient could be predicted from the correlation dimension of temperature fluctuations within this experimental conditions. The heat transfer coefficient decrease with increasing liquid viscosity but it increase with increasing particle size or solid circulation rate, however, it does not change considerablely with increasing liquid velocity. The solid holdup and heat transfer coefficient have well correlated in terms of operating variales or dimensionless groups. The infinite space model has been employed to obtain the radial dispersion coefficient from the radial concentration profiles of tracer. the pressure fluctuation have been analyzed by means of autocorrelation coefficient as well as power spectral density function. The dominant frequency which has been obtained from the autocorrelation coefficient of pressure fluctuation decreases with increasing liquid viscosity or liquid velocity The liquid radial dispersion coeffiicient decreases with increasing liquid velocity or viscosity, but it increase as the solid circulation rate or particle size increases. The liquid radial dispersion coefficient has been well correlated with operating variables as well as dimensionless groups.

液-固 傾斜斷面 流動層에서 水力學 및 壓力變動 特性

延周珉 충남대학교 2000 국내석사

Fluidization Characteristics, Pressure fluctuations and flow regime of liquid-solid flow in liquid-solid tapered fluidized beds have been investigated by using the chaotic method. Effects of liquid flow rate, particle size and initial bed height on the correlation dimension and power spectral density function has been discussed. Experiments were carried out with a conical column of 0.5 m in length with an apex angle of 12°. The column size increased from 0.05 m I.D. at bottom to 0.15 m I.D. at the top. Tap water and spherical glass beads with a density of 2.500 kg/㎥ and diameter in the range of 1-3 mm have been used as liquid and solid phase, respectively. The initial fixed bed heights of the tapered fluidized bed are 0.15, 0.20, 0.25, 0.30 m, respectively. Five flow regimes have been identified in liquid-solid tapered fluidized beds; they are the fixed-bed, partially fluidized-bed, fully fluidized-bed, transition and turbulently fluidized-bed regimes. The maximum pressure drop(△P mas), minimum partial fluidization velocity(U mpf) and minimum fluidization velocity(U mf) have been increased with increasing initial fixed bed height. The correlation dimension of pressure fluctuations has increased with increasing initial bed height and decreased with increasing particle diameter. The ranges of the five regimes are enlarged by increasing the initial fixed-b ed heitht and particle diameter. Hydrodynamic characteristics in liquid-solid tapered fluidized beds has been well predicted by means of chaotic parameters such the power spectral density function and the correlation dimension. A thesis submitted to the Committee of the Graduate School, Chungnam National University in partial fulfillment of the requirements for the degree of Master of Engineering Conferred in February, 2001.

다중벽 탄소나노튜브 유동층에서의 수력학적 거동 및 벽면 열전달 특성

이민지 한국교통대학교 일반대학원 2020 국내석사

본 연구는 열전달 측정 기구(30 mm I.D. X 50 mm length)가 부착된 유동층 cold model 장치(0.15 m I.D X 2.0 m high)에서 다중벽 탄소나노튜브 (multi-walled carbon nanotube; MWCNT)의 수력학적 거동과 벽면 열전달 현상을 파악하기 위한 연구를 수행하였다. 층물질로 MWCNT의 종류인 entangled CNT (ENCNT I: ρs = 110 kg/m3, ENCNT II: ρs = 94 kg/m3) 2 종과 vertically aligned CNT (VACNT: ρs = 31 kg/m3) 1 종을 사용하였다. MWCNT 입자는 기존 Geldart 분류 영역에서 벗어난 결과로 보아, 각 MWCNT의 입자 물성 특성(크기, 밀도, 형상)에 따라 유동 현상이 다를 것으로 예상된다. MWCNT 입자의 유동화 체제는 기체유속에 따라 고정층, 부분 유동화, 완전 유동화를 따랐다. ENCNTs의 경우, 부분 유동화 영역에서 추가적인 거동이 관측되었다. 서로 다른 형상을 가지는 ENCNTs는 층에서 네트워크 구조가 다르게 발현되어, 유동화 거동은 서로 상이한 체제 전이를 가졌다. 기체유속에 따른 벽면 평균 열전달 계수(havg)는 각 MWCNT 입자의 흐름 영역에 따라 변화하는 것을 관측하였다. ENCNTs의 경우, havg 의 변화가 고정층 단일 증가 경향을 보였으며, 부분 유동화 영역에서부터 완전 유동화 이후 havg가 기울기 변화를 가지며 증가하는 경향을 확인할 수 있었기 때문이다. 유속에 따른 havg 변화에 따라, 벽면 열전달 현상은 벽 근처 고체 흐름 뿐만 아니라 층 전체 입자의 거동에 영향을 받고 있다고 할 수 있다. 따라서, MWCNT의 벽면 열전달 현상을 설명하기 위하여 세분화된 흐름 영역을 제안하였다. 최종적으로, MWCNT의 수력학적 거동과 벽면 열전달 현상을 바탕으로 havg를 예측할 수 있는 상관 관계식을 최초로 제안하고자 하였다. 식은 MWCNT의 흐름 영역인 고정층, 부분 유동화, 완전 유동화의 개별식으로 제안하였다.

三相循環流動層에서 水力學 및 壓力變動 特性

金聖勳 충남대학교 2000 국내석사

Hydrodynamic characteristics of three-phase circulating fluidized beds have been analyzed by adopting the somewhat noble stochastic methods. More specifically, the time series of pressure fluctuations which can visualize the gas-liquid-solid flow behavior in the riser have been measured and analyzed by means of chaos analysis to obtain the values of stochastic parameters such as Lyapunov exponent, Kolmogrov entropy etc. Phase holdup characteristics have been also investigated in a gas-liquid-solid circulating fluidized bed(0.102m I.D. × 3.5m in height). Effects of velocities of dispersed gas and continuous liquid phases and solid circulation rate on the individual phase holdup, axial and radial distribution, and pressure fluctuations in the riser have been determined. Compressed air and water have been used as a dispersed gas and a continuous liquid phase, respectively. Glass beads whose diameter is 2.1㎜ have been used as a fluidized solid phase. It has been found that the gas holdup has increased with increasing dispersed gas velocity, but liquid velocity and solid circulation rate have little effect on the gas holdup. The liquid holdup has increased with increasing liquid velocity, however, it has decreased with increasing gas velocity and solid circulation rate. The solid holdup has increased with increasing solid circulation rate and gas velocity, whereas, it has decreased with increasing liquid velocity. The axial distribution of solid holdup has become uniform with increasing liquid velocity. The gas holdup and bed porosity have been well correlated in terms of operating variables such as gas and liquid velocities and solid circulation rate. The phase space portraits of pressure fluctuations have been more scattered with increasing gas velocity and solid circulation rate, which they have been less scattered with increasing liquid velocity. The largest Lyapunov exponent and Kolmogorov entropy obtained from pressure fluctuations in the riser have increased with gas velocity and solid circulation rate, but they have decreased with increasing liquid velocity, elucidating the similar results that have been expected by measuring the pressure drop and phase holdups in the riser. The chaotic hydrodynamics of three phase circulating fluidized beds have been well expressed by means of chaotic parameters quantitatively. The results of this study can be utilized to obtain the pre-requisite knowledge for the design, control and optimum operation of three-phase circulating fluidized bed.

三相循環流動層에서 水力學 및 半徑方向 混合特性

辛光湜 충남대학교 2000 국내석사

Hydrodynamic and radial mixing characteristics of liquid phase have been investigated in the riser of a three-phase circulating fluidized bed(0.102m ID × 3.5m in height). Phase holdup and radial mixing characteristics have been investigated in a gas-liquid-solid circulating fluidized bed. Effects of velocities of dispersed gas and continuous liquid phases and solid circulation rate on the individual phase holdup and radial mixing coefficient of liquid phase have been determined. Compressed air and water have been used as a dispersed gas and a continuous liquid phase, respectively, Glass beads whose diameter 2.1mm have been used as a fluiidzed solid phase. It has been found that the gas holdup has increased with increasing dispersed gas velocity, but liquid velocity and solid circulation rate have little effect on the gas holdup. The liquid holdup has increased with increasing liquid velocity, however, it has decreased with increasing gas velocity and solid circulation rate. The solid holdup has increased with increasing solid circulation rate and gas velocity, whereas, it has decreased with increasing liquid velocity. The axial distribution of solid holdup has become uniform with increasing liquid velocity. The gas holdup and bed poresity have been well correlated in terms of operating variables such as gas and liquid velocities and solid circulation rate. The radial dispersion coefficient of liquid phase was determined by using the infinite space model from the radial concentration prefiles of tracer. As a result of this study, the radial dispersion coefficient of liquid phase has increased with increasing gas velocity and solid circulation rate, however, it has decreased with increasing not only liquid velocity but also bed porosity in the riser of a three-phase circulating fluidized bed. The radial dispersion coefficient has been well correlated in terms of operating variables such as gas and liquid velocities and solid circulation rate.

逆流식 充塡塔에서 水力學的인 分析과 이산화탄소의 脫着에 關한 硏究

양선혜 東亞大學校 大學院 1995 국내석사

This study was carried out to interpret hydraulic behavior and CO_(2) gas desorption in countercurrent packing tower which packed 50 mm plastic Hiflow-ring. The results are as follows: 1. To compare with conventional packing, 50mm Hiflow-ring could save energy because of low pressure drop under high load. 2. As relative error between calculated value and investigated value was less than 6% in the loading pint arid flooding point we found that we can predict results mathematically which occurres in the packing tower. 3. The unique magnituteds of packing which was used are as follows. C_(L) = 2.1×10^(-4), n =0.787 so we can predict efficency which occurres.

高性能 充塡物을 利用한 HC1 가스 處理를 위한 水力學籍 硏究

하상안 東亞大學校 大學院 1990 국내석사

Packings are sucessfully applied in the thermal separation processes for a relatively long time, and hence exists still a growing demand, particularly in absorption processes in which pollutants but also useful substance are removed from off-gas streams and which thus contribute towards the prevention of air pollution. A report is presented on the performance of modern packings dumped for application in the field of mass separation processes. The evaluation of the results is based on extentive experimental inverstigations of rectification, absorption, liquid-liquid extraction and desorption systems. The following are indicated the efficiency in terms of the number of theoretical stages per unit height or in terms of the height of transfer unit or the pressure drop per unit height as well as per gas phase transfer unit and liquid hold up. Where by either the gas capacity factor or the liquid load was adopted as influencing parameter, and finally the maximum gas capacity factor as a function of the flow parameter. The results are pressed in diagrams, appendix and tables.

Hydrodynamic characteristics in the unstable operating range of a pump-turbine unit

서준원 Graduate School, Yonsei University 2020 국내박사

Nowadays, pumped-storage power plants require high flexibility and reliability to meet the variable grid demands. When the pump-turbine operates under different GVOs and part-load conditions, various unstable and transient phenomena are present. Unusual flow characteristics such as reverse flow, rotating stalls, flow recirculation, and stationary vortexes can induce high dynamic forces and torque variations on the entire system and create a positive slope in the discharge-head curve. Therefore, understanding the characteristic behavior of the four-quadrant characteristic curve is important, which has detail performance information through all discharge range of operation. The present study contributes to the understanding of the hydrodynamic characteristics of the unstable operating range of a Francis type pump-turbine unit. First, an overview of this thesis and its background and related to previous studies were provided. Second, a numerical analysis method for use in commercial CFD packages was introduced. Moreover, the simulation strategy was illustrated for establishing a performance prediction technique on transient behavior. Third, the hydraulic characteristics of a full-scale model at various guide vane opening conditions in turbine mode were investigated. A three-dimensional Reynolds-averaged Navier-Stokes (RANS) equation was solved to evaluate the hydraulic performance. Before conducting the study of the transition region, which is the off-design operation region, the unsteady-state analysis method for the normal operating region of the pump and turbine modes was established, and then the transition region corresponding to the off-design operation region was sequentially performed. In the case of steady-state analysis, it is judged that it is applicable to predict the operating point of runaway condition. However, when conducting accurate prediction and analysis of the internal flow of the S-shaped characteristics curve, the unsteady-state analysis should be performed. Fourth, the hydraulic characteristics of a full-scale model at various guide vane opening conditions in pump mode were investigated. This chapter was carried out to investigate the hump-region characteristics and a detailed analysis of the dynamic flow characteristics was conducted. It was confirmed that irregular flow occurs in the circumferential direction at the runner outlet. High normalized magnitudes were observed in relatively low-frequency regions under the discharge of the hump region conditions. Particularly, the vortex pattern repeatedly increased and decreased and a dominant and unsteady pressure was exhibited in the relatively lower-frequency region of 0.2 and 0.8 f/fn in the vaneless space. These phenomena in the positive slope can adversely affect the hydraulic performance and operational stability because the specific part-load condition was approximately 5 times greater than the 1st BEP at the design point. Fifth, the performance characteristics of model-scales in transition regions were investigated. S-shaped characteristics among model-scales such as full-scale, IEC60193 standard-scale, lab-scale were compared to investigate the influence of scale-effect. The results of the analysis of the unsteady-state of the full and lab-scale models were confirmed to show the identical slope curve except for the values of the specific conditions, and the values were offset at a constant level. The reliability of the computational result was validated by comparing the experimental results. The difference between Ned, Qed, and Ted values derived through experiment and numerical analysis results are compared. It was shown that the numerical analysis and the tendency of the experiment well-matched in the overall operating and transition region. As a result of comparing the values, it showed very high reliability within 4%. The internal flow characteristics and pressure pulsation characteristics at the operating point of a specific transition region were analyzed based on the comparatively verified data. At the runaway and low-discharge conditions, the frequency spectra of the pressure fluctuations are remarkable by the frequency f/fn = 0.6 (representing the rotating stall) and the frequency f/fn = 7, 14, and 21 (representing the 1st, 2nd, and 3rd BPF). These results present a rotating stall with a frequency propagation of about 60% of the runner speed. Since passages are stalled, the internal flow field is completely blocked. Therefore, the incidence angle tends to decrease and tends to recover from the existing stalled passage. The leading edge shows a positive shape, while the trailing edge shows a shape in the reverse pump. However, it showed a different form from the runaway condition because of the presence of backflow and one stall cell under low-discharge conditions. In the upstream of the stall passage, the incidence angle tends to decrease because the incoming flow rate is more than twice as high as the average value of each passage. The blade loading distribution of the leading edge shows a negative shape, and the pattern of the reverse pump at the trailing edge is almost disappeared. The results of this study were compared with the results of previous researchers who performed the rotational stall frequency through numerical and experimental studies. Furthermore, based on the formula in the international standard, efficiency change in hydraulically similar operating conditions having different Reynolds numbers was compared with the numerical analysis results. The result of comparing the difference between the result calculated through numerical analysis and the value predicted through the calculation formula was 0.54%, and it was confirmed that the result has a fairly high level of reliability. 양수발전용 펌프터빈은 관내 유수를 이용하여 작동하는 유체기계로서 국부적인 압력강하에 의한 캐비테이션 현상이 수반되며 다양한 천이현상들이 발생한다. 그러므로 성능 및 신뢰성 향상을 위한 천이영역 운전상태 파악 및 설비 문제발생시 체계적인 기술지원을 위한 대책을 수립하는 것이 중요하다. 본 연구는 양수발전용 펌프터빈의 운전영역 확장 및 신뢰성 향상을 위해 천이영역에 관한 신뢰성 높은 해석기법, 유동메커니즘에 관하여 순차적으로 연구를 수행하였다. 범용의 비속도를 갖는 양수발전용 펌프터빈을 연구대상으로 선정하였으며, 실물모델의 양수모드 및 발전모드에 대한 연구를 토대로 수치해석기법을 정립한 뒤 축소모델의 발전모드에 대한 상세한 연구를 수행하였다. 수치해석 수행 시 발생할 수 있는 격자계, 난류모델, 경계면 조건 및 경계면의 위치 등의 해석조건이 수력학적 성능에 미치는 영향을 파악하고자 실물모델의 삼차원 정상상태 RANS 해석을 수행하였다. 매개변수연구를 통해 변수조건이 수력학적 성능에 미치는 영향을 분석하고 성능검증을 통해 해석기법을 합리적으로 결정하고 일관성 있게 표준화하였다. 정상상태 해석의 경우 양수 및 발전모드의 천이영역에 대한 연구 수행 시 시간에 관한 항을 고려하지 않기 때문에 천이영역 특성곡선에 대한 대략적인 분석은 가능하나 상세한 연구를 수행하기에는 적합하지 않다. 따라서, 표준화된 정상상태 해석결과를 반영하여 비정상상태 및 천이영역에 대한 연구를 수행하였다. 실물모델을 기준으로 상사법칙을 적용하여 축소모델에 대한 축적효과를 우선적으로 분석하였다. 실물 및 축소모델의 설계운전영역의 경우 시간 항의 영향이 지배적이지 않았으나, 탈설계운전영역의 경우 완전히 다른 형태의 특성곡선을 보였다. 두 모델의 비정상 상태 해석 결과는 특정 조건의 값을 제외하고는 동일한 기울기의 곡선을 나타내었으며 값은 일정한 수준으로 오프셋 되는 경향을 보였다. 축소모델의 해석결과에 대한 신뢰성은 실험결과와 비교를 통해 검증하였다. 축소모델 실험장비는 4상한 완전특성곡선(설계 및 탈설계 운전영역)을 측정가능하도록 설계 및 제작되었다. 한국생산기술연구원에 실험실 규모의 축소모델을 설치하고 검증 테스트를 수행하였다. 성능시험방법은 국내규격(KS B6018:2015) 및 국제표준규격 (IEC60193:1999)에 기반하여 측정되었으며, 실험데이터는 한국산업기술시험원에 의해 인증되었다. 수력학적 성능특성곡선 뿐만 아니라 시간에 따른 압력 맥동 특성을 측정가능하도록 구성하였다. 실험 및 수치해석 결과는 설계 및 탈설계영역에서 전반적으로 잘 일치하는 경향을 보였으며 특성곡선 내의 무차원화 된 값을 비교한 결과 4% 이내의 높은 신뢰성을 나타냈다. 천이영역 중에서 대표적인 운전점을 선정하여 내부유동 및 압력맥동 특성을 분석 하였다. Runaway 및 low-discharge 조건에서 압력맥동 주파수 스펙트럼은 f/fn = 0.6 (회전실속)과 주파수 f/fn = 7, 14, and 21 (1st, 2nd, and 3rd 베인 통과 주파수)가 지배적으로 나타냈다. 해당 결과는 러너 회전속도의 약 60%로 전파되는 회전실속을 나타내며, 시간 이력-압력맥동 실험과 수치해석 결과가 일치함을 확인하였다. 가이드베인에서 러너로 유입되는 유량과 날개깃의 각도 차이에 의해 러너의 선단부에서 역류의 흐름이 유로폐쇄현상을 유발하였으며, 더 나아가 회전실속의 결과로 이어졌다. 회전실속에 발생한 상류와 하류에서는 입사각이 감소하거나 증가하는 경향을 나타내었으며, 날개깃 면 하중분포 가 다양한 형태를 나타내었다. 최종적으로, 해당 연구결과를 선행 연구자들의 결과와 비교분석 하였으며, 국제표준규격의 공식에 기초한 계산된 축적효과와 수치해석 및 실험을 통한 효율의 차이를 비교한 결과 0.54%로 높은 신뢰성을 가짐을 확인하였다.