불확실성 정량화를 이용한 유기랭킨사이클의 강건한 설계에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 화학생물공학부, 2019. 2. 이원보.운전 조건의 변화에 유연한 대처가 가능하며 열역학 파라미터의 측정 오류에 강건한 유기 랭킨 사이클(ORC)을 설계하는 방법론이 개발되었다. 강건한 유기 랭킨 사이클 설계에 앞서, 액화 천연가스(LNG)로부터 최대로 냉열을 추출하기 위해, 다성분 작동 유체를 사용하여 ORC 을 설계하는 방법론이 제안되었다. 제안된 시스템은 다단계의 형태를 보이는 ORC로, 각 단계의 액화기에서 발생하는 엑서지 손실을 최소로 하기 위하여 이 성분 작동 유체를 사용하였다. 각 단계의 작동 유체로서 최적의 혼합물을 찾기 위하여 혼합물의 질량 분율과 압력을 변화시켜 가며 액화기에서 발생하는 엑서지 손질의 최소화를 진행하였다. 최적 작동 유체 혼합물을 선택한 후에 제안된 ORC의 효율 최적화를 위해 ORC 유닛들의 운전 조건들을 이용한 효율 최적화를 시행하였다. 이에 더해 사용된 열원의 온도 변화에 따른 공정 효율의 민감도 분석을 진행하였다. 이어지는 섹션에서는 운전 중 작동 유체의 조성이 변하는 상황에서도 전력을 최대한으로 생산할 수 있는 ORC 설계 방법론이 개발되었다. 제안된 방법은 ORC의 출력이 평균적으로 최대가 되는 설계를 찾는다. ORC의 안정적인 운전에 악영향을 주는 요소들(열교환기 내의 최소 설계 온도 차 위반과 팽창기 블레이드 표면에 액체방울이 형성)을 억제하기 위해, 이러한 요소들이 발생했을 때 목적 함수가 패널티를 받도록 하였다. 최적화에 필요한 통계학적 모멘트들을 구하는 데에는 두 단계가 필요하다. 우선, 노미날 운전 조건 하에서 ORC 시뮬레이션을 통해 열교환기의 면적을 얻는다. 다음으로 계산된 열교환기 면적을 고정한 상태로 조성을 노미날 값으로부터 변화시켜 다시 시뮬레이션을 진행하고, 이로부터 노미날 운전 조건으로 계산했을 때와는 다른 목적 함수의 값을 얻는다. 조성은 노미날 값을 중심으로 분포되어 있다고 가정하였으며, 이때 조성이 선택될 확률은 모든 범위에서 같다고 가정하였다. ORC 출력의 평균값과 분산값을 적은 수의 샘플들로부터 계산하기 위하여 Polynomial Chaos Expansion(PCE) with sparse grid quadrature가 사용되었다. 최적화를 진행한 결과, 조성의 작은 변화라도 ORC의 안정적인 운전에 심각한 영향을 미칠 수 있다는 사실을 알게 되었으며, 제안된 방법을 통해 조성의 불확실성에도 불구하고 유연한 운전이 가능한 ORC를 설계할 수 있었다. 마지막으로, 조성의 불확실성에 더해 열원의 온도와 열역학 파라미터에도 불확실성이 있는 경우를 위한 최적화 방법이 개발되었다. 이전 섹션에서 조성 변화에 가장 둔감한 것으로 밝혀진 작동 유체를 이용하여, 알려진 임계 온도와 임계 압력에 측정 오차가 있는 경우를 위해 다시 최적화를 진행하였다. 또한, 열원의 온도가 노미날 값에서 벗어나는 경우도 ORC 운전의 유연성을 높이기 위해 고려되었다. 총 9개의 불확실한 열역학 파라미터 혹은 디자인 변수들이 고려되었고, 이는 과도한 계산량을 필요로 하므로 이전 섹션으로 개발된 방법으로는 최적화를 수행하기에 무리가 있었다. 따라서 PCE에 기반한 대체 모델을 이용하여 최적화를 진행하는 방법이 개발되었다. 개발된 대체 모델은 평균과 분산을 분석적으로(analytically) 구할 수 있게 해주기 때문에 최적화에 걸리는 시간을 급격하게 감소시켜 주었다. 대체 모델을 이용하여 최적화를 진행한 결과 열역학 파라미터의 불확실성과 디자인 조건의 불확실성에도 불구하고 평균적으로 높은 전력을 생산할 수 있는 ORC를 설계하게 되었다.A method to design the optimal working fluid mixture of Organic Rankine Cycles (ORC), which is operationally flexible and robust against measurement error in thermodynamic parameters, has been developed. Prior to design robust ORC, an optimal design of ORC for utilizing Liquefied Natural Gas (LNG) as heat sink of which evaporation process is not isothermal is proposed to represent a design procedure to extract as much energy as possible from a multicomponent heat sink without consideration of robustness. The proposed system adopts binary working fluids for each stage to minimize the exergy destroyed in the condensers of each stage of the cycle. The best combination of working fluids was selected through minimization of the amount of destroyed exergy by varying the flow rate, composition, and pressure of the working fluid. After selecting the working fluids, process optimization was performed through a parametric study. In addition, a sensitivity analysis was performed to observe the effect of temperature variation of the heat sources in the range of 25 - 85 ℃ on the net power generation. At the following section, a systematic method to design a robust ORC using LNG and multicomponent working fluid, which yields maximum power output even when the composition of the working fluid varies from the nominal point during operation of ORC has been developed. The proposed method seeks the optimal composition giving both the maximum mean of ORC power output. To suppress the factors that adversely affect the operation of ORC (violation of minimum temperature difference in heat exchanger and formation of liquid droplet in expander), the objective function is penalized when they occur. The procedure to derive the statistical moments consists of two steps. Initially, the required heat exchanger area is obtained by simulation of ORC model with a nominal operating conditions (composition, pump discharge pressure, and expander discharge pressure). At the next step, the simulation is carried out again with the obtained area and the varying composition. The mass fraction of each substance in the working fluid is assumed to follow uniform distribution centered at the nominal point. To obtain the mean and variance with a small number of simulations, Polynomial Chaos Expansion (PCE) with sparse grid quadrature is employed. It has been shown that small changes in composition can have serious consequences for stable operation of ORC, and the design of working fluid by the proposed method allows flexible ORC operation despite the existence of uncertainty in the composition. Finally, the optimization takes into account uncertainties in thermodynamic parameters and heat source in addition to composition. Using the selected working fluid which was turned out to be the most insensitive from the uncertainty of composition, optimization is carried out again when the critical temperature and pressure of each substance composing the working fluid varies within its measurement uncertainty, which can be found in the literature. Also, the temperature of the heat source varies from the nominal design point to enhance the operational flexibility of ORC. In sum, the design of ORC was performed assuming a total of the nine parameters or design variables with uncertainty, which requires excessive amount of computation with the method suggested in the previous section. Therefore, the optimization using a surrogate model was devised to efficiently find the optimal and robust ORC design. Because the proposed surrogate model is constructed based on PCE, the statistical moments can be derived analytically, which leads to reduce the time for optimization drastically. Comparing the ORC design, which was taken with more uncertainty, to the design obtained in the previous section, the former design showed the highest output even when the parameters and design variables were changing from the nominal point.1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Thesis outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 Conventional ORC configuration . . . . . . . . . . . . . . . . . . . . 5 2 Design and optimization of cascade organic Rankine cycle for recovering cryogenic energy from liquefied natural gas using binary working fluid 10 2.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Description of the proposed cascade organic Rankine cycle . . . . . . 14 2.3 Simulation and optimization of power generation cycle . . . . . . . . 21 2.3.1 LNG cold exergy recovery part . . . . . . . . . . . . . . . . . 25 2.3.2 Recuperation part . . . . . . . . . . . . . . . . . . . . . . . . 29 2.4 Simulation and optimization results . . . . . . . . . . . . . . . . . . 31 2.4.1 Result for LNG cold exergy recovery part . . . . . . . . . . . 31 2.5 Working fluid selection and process optimization result for recuperation part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.6 Energy and exergy analyses . . . . . . . . . . . . . . . . . . . . . . . 43 2.7 Sensitivity analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 2.8 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3 Robust design of multicomponent working fluid for organic Rankine cycle - consideration on operational uncertainty 52 3.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.1.1 Evaluation of the objective function . . . . . . . . . . . . . . 62 3.1.2 Polynomial chaos expansion . . . . . . . . . . . . . . . . . . 66 3.2 Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 3.2.1 ORC with LNG heat sink using ternary working fluid . . . . . 71 3.2.2 Precision test for PCE . . . . . . . . . . . . . . . . . . . . . 77 3.2.3 Influence of penalty function . . . . . . . . . . . . . . . . . . 80 3.2.4 Results and discussion . . . . . . . . . . . . . . . . . . . . . 83 3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Docto

Effect of Retinoic Acid on the Differentiation and Lysozyme Expression in Human Airway Epithelial Cells

BACKGROUND AND OBJECTIVES: Retinoic acid (RA)-deprived cultures of normal human tracheobronchial epithelial (NHTBE) cells became squamous metaplastic, failed to produce mucin and instead secreted or released large amounts of lysozyme (LZ). The purpose of this study was to elucidate the relationship between RA-deficiency induced squamous metaplasia and increased LZ as a function of time. MATERIALS AND METHOD: The change of lysozyme protein and lysozyme mRNA was investigated over time in cultures using passage-2 normal human tracheobronchial epithelial (NHTBE) cells and passage-2 normal human keratinocytes (NHK). The amount of lysozyme and mucin was measured with dot blot, message of lysozyme with RT-PCR, and cornifin mRNA with Northern blot. RESULTS: Lysozyme message levels were consistently higher in RA-sufficient than RA-deficient cultures. Intracellular and extracellular LZ increased to a peak on the day 16 and thereafter decreased in the RA-deficient cultures. LZ gene expression in the RA-deficient cultures was barely detectable on the day 7 but was clearly expressed between days 10 and 14, but thereafter message levels decreased markedly. On day 12, large numbers of cells began to exfoliate in the RA-deficient cultures. Extracellular LZ appeared simultaneously at the apical surface, presumably released from the exfoliated cells, which contained high concentrations of LZ. Intracellular LZ levels were more than 11 fold less in NHK cells compared to NHTBE cells. CONCLUSION: This study suggests that cellular accumulation of lysozyme protein is a unique feature of metaplastic squamous differentiation. Further studies are needed to find out what mechanisms are involved.ope

Treatment of Snoring and the Change of Surgical Treatment

Although snoring is a common medical symptom, it is a cause not only of social problems but of otolaryngological illnesses such as Obstructive Sleep Apnea Syndrome (OSAS). Various treatment methods have been used to treat snoring, including Uvulopalatopharyngoplasty, which is a surgical approach to treating snoring and OSAS. Recently, the laser-assisted Uvulopalatoplasty (LAUP) is being used to treat snoring in an out-patient basis. In addition, with the advancement of medical equipments, radiofrequency volumetric tissue reduction method, implant surgery, and injection snoreplasty method were also introduced. Other surgical methods such as lateral pharyngotomy and uvulopalatal flap were also tried. Despite these new surgical methods, long term follow-up after the surgery is needed if better surgical outcomes are to be obtained.ope

Blindness Secondary to Sphenoid Fungus Ball

The close vicinity of the optic nerve to the sphenoid sinus may cause visual loss in the sphenoid fungus ball. We present a case of blindness secondary to sphenoid fungus ball without any evidence of orbital invasion in imaging studies. A 61-year-old man, suffering from uncomplicated diabetes, was referred for right visual loss that developed 1 day ago. He perceived hand motion on the right. CT and MRI revealed a fungus ball in the right sphenoid sinus. However, there was no evidence of orbital invasion. Endoscopic sphenoethmoidectomy was performed to remove the fungus ball. Systemic mega-dose steroid and amphotericin B were started because he lost the light perception 3 days after surgery. Biopsy revealed aspergillus fungus ball and no evidence of mucosal invasion. However, blindness was not reversed. Evidence of orbital invasion in imaging diagnosis is elusive in sphenoid fungus ball; therefore, systemic antifungal treatment should be initiated and early endoscopic sphenoidotomy should be performed in case of rapidly progressing visual loss, especially in diabetic or immunocompromised patients. Mega-dose steroid therapy for optic neuropathy should be selective because it may aggravate underlying systemic diseases to cause early termination of systemic antifungal treatment.ope

A Solitary Malignant Schwannoma in the Choana and Nasal Septum

Malignant schwannoma is an extremely rare tumor and the risk of malignant schwannoma increases in patients with von Recklinghausen’s disease. Recently, we encountered a case of solitary malignant schwannoma in the choana and posterior nasal septum. Malignant schwannoma has not been previously reported in these locations. A 53-year-old man, who was immunologically healthy and showed no abnormal dermatological lesions, presented with a polypoid mass in the right nasal cavity and underwent endoscopic mass excision. The mass originated from the choana and the posterior portion of the right nasal septum. This mass was confirmed as a malignant schwannoma on histological examination and immunohistochemical staining. After endoscopic excision, postoperative adjuvant radiotherapy was administered, and there was no recurrence at 1 year after treatment. This case suggests that a solitary malignant schwannoma should be considered in the differential diagnosis of a mass in the posterior nasal cavity.ope

A Case of Fibrous Dysplasia Simultaneously Involving the Sphenoid Sinus and the Clivus

Fibrous dysplasia is an uncommon benign bone disorder in which normal medullary bone is replaced by fibrotic and osseous tissue. Limited involvement of the sphenoid sinus or the clivus is extremely unusual. Here, we present a case of fibrous dysplasia in a 46-year-old female that involved the sphenoid sinus and the clivus simultaneously. Imaging modalities demonstrated an expansile lesion filling the entire left sphenoid sinus, extending to the clivus. Biopsy specimen was obtained by endoscopic sphenoid sinusotomy, and it showed extensive spindle-shaped fibroblastic cells with irregularly shaped trabeculae of woven bone which was compatible with fibrous dysplasia. After 6-month follow-up, the patient displayed no evidence of recurrenceope

Brain abscess caused by chronic invasive actinomycosis in the nasopharynx: A case report and literature review

RATIONALE: Actinomycosis is a rare anaerobic, gram-positive bacterial infection caused by Actinomyces, which is part of the normal flora in the oral cavity and respiratory and female genitourinary tracts. The cervicofacial area is the most common site of involvement, and involvement of the central nervous system is rare. PATIENT CONCERNS: We report a case involving a 51-year-old woman who developed an actinomycotic brain abscess 15 months after the treatment of noninvasive nasopharyngeal actinomycosis, which recurred as an invasive form. DIAGNOSES: Histopathological examination of the surgical specimens revealed actinomycosis. INTERVENTIONS: The patient was treated by surgical drainage of the brain abscess and long-term antibiotic treatment. OUTCOMES: Follow-up brain imaging performed 12 months after surgery showed complete resolution of the brain abscess, and there were no further signs or symptoms of infection. LESSONS: Physicians should be aware of the typical clinical presentations of cervicofacial actinomycosis. Moreover, they should know that actinomycosis may mimic the process of malignancy at various anatomical locations.ope

Cyclooxygenase Inhibitors Regulate the Expression of a TGF-β Superfamily Member That Has Proapoptotic and Antitumorigenic Activities

The antitumorigenic activity of nonsteroidal anti-inflammatory drugs (NSAIDs), cyclooxygenase (COX) inhibitors, is well established, but responsible molecular mechanisms are not fully understood. NSAIDs stimulate apoptosis by COX dependent and independent mechanisms in colorectal cells in culture. Identification of genes regulated by COX inhibitors could lead to a better understanding of their proapoptotic and anti-neoplastic activities. Using subtractive hybridization, a cDNA which was designated as NSAID activated gene (NAG-1) was identified from NSAID-treated HCT-116, human colorectal cells. NAG-1 has an identical sequence with a novel member of the TGF-beta superfamily that has 5 different names. In the HCT-116 cells, NAG-1 expression is increased and apoptosis is induced by treatment with some NSAIDs in a concentration and time-dependent manner. NAG-1 transfected cells exhibited increased basal apoptosis, increased response to NSAIDs and reduced soft agar cloning efficiency. Furthermore, transplantable tumors derived from NAG-1 transfected HCT-116 cells showed reduced tumorigenicity in athymic nude mice compared with vector-transfected HCT-116 cells. The increased NAG-1 expression by NSAIDs provides a suitable explanation for COX-independent apoptotic effects of NSAIDs in cultured cells. These data demonstrate that NAG-1 is an antitumorigenic and proapoptotic protein, and its regulation by COX inhibitors may provide new clues for explaining their proapoptotic and antitumorigenic activities.ope

The Clinical Effects of Laser Surgery in Simple Snorers on Polysomnography

Objectives：We aimed to evaluate the clinical effects of the recently developed laser surgery in patients who were diagnosed by polysomnography as simple snorers. Materials and Methods：We operated on 35 patients with apena index of below 5, using CO 2 laser, from June, 1993 through May, 1994 at Yongdong Severance Hospital. For these patients, we carried out before and after assessments of three different kind：first, a follow-up assessment of subjective symptoms, such as snoring, daytime somnolence, nocturnal arousal, and headache；second, a psychodynamic analysis done by a psychiatrist on insomnia and depression；and third, an assessment of subjective atisfaction for 24 weeks following the surgery. Results：Snoring improved in 74.2% of the patients, and daytime somnolence improved in 80.0% of the patients. Nocturnal arousal showed improvement in all the subjects whereas headache showed improvement in 66. 7% of the patients. In the psychodynamic analysis, insomnia as observed in 22.9% of the subjects, showing significant improvemnt. However, depression didn’t improve significantly. Subjecive satisfaction of the surgery was noted to be the greatest at the fouth week of the operation but it gradually decreased thereafter. The most common postoperative complication was foreign body sensation (31.4%), which disappeared spontaneously within 3 to 6-months of the operation. Conclusion：Laser snoring surgery in simple snorers is found to be an effective method to lessen snoring. However, patients should be informed beforehand that this method of surgery may not fully meet their expectations.ope