Kalman D. Migler

Polymer Processing Instabilities: Control and Understanding

“공정 엔지니어를 위한 PRO/II with PROVISION 실무”는 국내의 정유사, 석유화학사와 엔지니어링사를 비롯하여 관련 연구소 및 대학에서 가장 많이 사용되고 있는 범용 모사기 중의 하나인 Simulation Science사의 PRO/II를 이용하여 단위조작 장치에 대한 모사기법에 대한 예제와 그 해결방법들을 모아 놓은 책이다. 이 책의 특징은 국내에서는 최초로 단위조 작 모듈에 대한 공정모사 예제를 실제 화학공정의 조업이나 설계 시에 발생할 수 있는 예제 들을 모아 놓았다는 점이다. 이 책의 저자인 동양대학교 생명화학공학부의 조정호 교수의 다년간의 현장 실무경험을 통하여 축적된 내용들을 예제화하였다는 점에 있어서 화학공정 을 설계하고 조업하는 현장 실무 엔지니어 뿐만 아니라 화학공학을 배우는 3, 4학년 학생 및 대학원생들에게도 좋은 지침서가 될 수 있으리라 사료된다. 이 책의 내용을 살펴보면 1장에서는 PRO/II with PROVISION의 윈도우즈 상에서의 입력 방법과 키워드를 이용한 입력방법을 비교하여 서술하였으며, 2장에서는 평형단 조작 장치의 기본이 되는 각종 플래쉬 문제를 다양하게 소개하였다. 3장에서는 각종 열교환기 관련 예제 를 다루었으며, 4장에서는 펌프, 압축기 및 밸브 등과 같이 압력 변환장치에 관련된 문제들 을 수록하였다. 특히 3장과 4장에서는 단순한 플래쉬 계산이나 압력변환장치의 단위 장치들 에 대한 모사뿐만 아니라 다른 단위조작 장치와 연결된 문제와 엔지니어링 회사에서 실제 설계 시에 부딪히기 쉬운 실제적인 문제들을 위주로 수록하였다. 5장에서는 증류탑, 흡수탑 및 추출탑에 대하여 단순한 이성분계 증류에서부터 hydrocarbon distillation, chemical distillation을 위시하여 sour water stripper, amine absorber 및 방향족 회수를 위한 추출 탑의 모사에 이르기까지 실제 석유화학공장에서 가동되고 있는 증류, 흡수 및 추출탑 위주로 예제를 만들어서 소개한 면이 색다르다. 6장에서는 반응기 형태별 모사 예제들이 수록되었 는데 PFR, CSTR 및 Kinetic Reactor에 대한 예제가 수록되어 있어서 이 책을 공부하는 것 은 단위조작과 반응공학을 동시에 학습하는 효과가 있을 것으로 생각되어진다. 마지막으로 7장에서는 공정모사기의 추가적인 기능으로서 controller, calculator, optimizer 및 case study를 이용하는 방법의 소개와 더불어서 실 예제를 통하여 공정 최적화에 대한 감각도 익 힐 수 있도록 해 놓았다. 2004년에 출간된 공정모사에 관한 지침서와 더불어 지속적으로 출간이 이루어질 공정모 사에 사용하는 열역학 모델 식에 대한 선정 지침서 및 특수증류공정설계, 환경공정설계에 관 한 책들은 화학공학 교과서와 실제 화학공정을 모사기를 통하여 정량적으로 해석하고 모형 화시키는 기법을 소개한다는 면에 있어서 주목할 만하다.

Elastic Flow Instability, Curved Streamlines, and Mixing in Microfluidic Flows

Flow instabilities are well known to occur in macroscopic flows when elastic fluids flow along curved streamlines. In this work we use flow visualization to study the mechanism underlying a purely elastic flow instability for Poiseuille flow in a micro (μ)channel having a zigzag path (curved streamlines) and quantitatively investigate its implications for fluid mixing (studied by fluorescence microscopy) in the μchannel. We find that the instability enhances mixing over the range of applied flow rates. For Newtonian streams, mixing occurs by molecular diffusion, and, as expected, mixing worsens with increasing flow rate because of decreasing residence time. However, for elastic fluid streams, we find substantial enhancement of mixing at sufficiently high throughputs, which indicates a strategy to counter the loss of diffusive mixing at high throughputs by exciting an elastic flow instability. Flow visualization is done using neutrally buoyant non-Brownian tracer particles added to the elastic fluids and a...

Infrared thermography of welding zones produced by polymer extrusion additive manufacturing

In common thermoplastic additive manufacturing (AM) processes, a solid polymer filament is melted, extruded though a rastering nozzle, welded onto neighboring layers and solidified. The temperature of the polymer at each of these stages is the key parameter governing these non-equilibrium processes, but due to its strong spatial and temporal variations, it is difficult to measure accurately. Here we utilize infrared (IR) imaging - in conjunction with necessary reflection corrections and calibration procedures - to measure these temperature profiles of a model polymer during 3D printing. From the temperature profiles of the printed layer (road) and sublayers, the temporal profile of the crucially important weld temperatures can be obtained. Under typical printing conditions, the weld temperature decreases at a rate of approximately 100 °C/s and remains above the glass transition temperature for approximately 1 s. These measurement methods are a first step in the development of strategies to control and model the printing processes and in the ability to develop models that correlate critical part strength with material and processing parameters.

Dynamic light scattering investigations of nanoparticle aggregation following a light-induced pH jump

There are many important processes where the stability of nanoparticles can change due to changes in solution environment. These processes are often difficult to study under controlled changes to the solution conditions. Dynamic light scattering was used to measure the initial kinetics of aggregation of carboxylated polystyrene nanoparticles after well-defined pH jumps using aqueous solutions of photoacid generator (PAG). With this approach, the pH of the solution was controlled by exposure to ultraviolet (UV) light without the delays from mixing or stirring. The aggregation kinetics of the nanoparticles was extremely sensitive to the solution pH. The UV exposure dose is inversely correlated with the resulting surface charge of the nanoparticles. Decreasing pH decreases the electrostatic repulsion force between particles and leads to aggregation. The reaction-limited or diffusion-limited aggregation kinetics was sensitive to the pH quench depth, relative to the acid-equilibrium constant (pK(a)) of the surface carboxylic acid groups on the nanoparticles. Since numerous PAGs are commercially available, this approach provides a flexible method to study the aggregation of a variety of solvent-dispersed nanoparticle systems.

Measurement of impedance of individual carbon nanotubes

We describe impedance measurements of individual single wall carbon nanotubes (SWNTs) in the frequency range of 40 Hz to 100 MHz. The tubes were assembled on the active channel of field effect transistor (FET) structures from aqueous suspension using dielectrophoresis. The FET channels were made by using photo-lithography. We utilized a resistance-capacitance (RC) lumped element circuit model to describe the observed impedance of the tubes and the corresponding contact resistance. At the low frequency limit the impedance is frequency independent and equivalent to the real resistance. In the high frequency range we observe a sharp conductor-insulator transition at a crossover frequency, above which the circuit response becomes capacitive. The extracted SWNT capacitance, CSWNT, of about 4 10-14 F/mum, is independent on the total real resistance, however the CSWNT value is larger than that theoretically predicted quantum capacitance of a perfect tube. Our observations also indicate that the damping frequency is lower than the theoretically predicted in SWNTs.

Impedance and Capacitance Measurement of Individual Carbon Nanotubes

We experimentally examined the impedance of individual single wall carbon nanotubes (SWNT) in the frequency range of 40 Hz to 110 MHz. The tubes were assembled as a conducting channel of field‐effect transistor (FET) structures from aqueous suspension using dielectrophoresis. At the low frequency limit the impedance is independent of the frequency and equivalent to real resistance. We observe a sharp conductor‐insulator transition at a crossover frequency of about 2.5 MHz, above which the circuit response becomes capacitive. The extracted SWNT capacitance, CSWNT, of about 4 10−14 F/μm, is independent of the total real resistance, however the CSWNT value is larger than that theoretically predicted quantum capacitance CQE. Within this formalism we estimate that the effective Fermi velocity of charge carriers, vF, for our SWNT is about 103 m/s, which is about two orders of magnitude below vF of a perfect tube. Our results agree qualitatively with the theoretical impedance characteristic of a SWNT, and furthe...