Optimization of Shell and Tube Heat Exchanger by Using Hybrid Optimization Algorithm with Genetic Algorithm and Mesh Adaptive Direct Search (GA-MADS)

Nguyen Van Hap,Geun Sik Lee,Nguyen Minh Phu 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

태양열 이용 해양온도차발전시스템의 성능 예측

Nguyen Van Hap,이근식(Geun Sik Lee) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.1

전력을 생산하기 위해 해양온도차발전을 이용하는 것은 재생에너지를 이용하고 환경을 보호하는 한 가지 방법이다. 본 연구에서는 울산지역의 기후조건이 태양열 이용 해양온도차발전(SH-OTEC)에 미치는 영향을 조사하기 위하여 시뮬레이션을 수행하였다. 태양열 에너지는 제 2 의 열원으로 사용되었다. SH-OTEC 시스템에 사용할 가장 적합한 작동유체를 선정하기 위하여 여러 작동유체를 수치모사하였다. 해석결과, R152A 가 가장 적합한 작동유체로 나타났으며, R600 와 R600A 가 각각 그 다음 순으로 나타났다. 집열판 출구온도를 20℃ 증가하였을 때 집열판의 유효면적은 월평균 태양에너지 게인(gain)의 변화로 인하여 50㎡ 에서 97㎡ 으로 요동함을 볼 수 있었다. 2-4%의 전형적인 해양온도차발전의 효율은 태양열을 이용함으로써 연평균 효율은 6.23%까지 증가하였다. The use of ocean thermal energy conversion (OTEC) to generate electricity is one of the methods proposed to utilize renewable energy and to protect the environment. In this study, simulations were performed to investigate the effect of weather conditions in the Ulsan region, Korea, on the efficiency of a solar-heating OTEC (SH-OTEC) system. This system utilizes solar thermal energy as the secondary heat source. Various working fluids were also simulated to select one that is suitable for this system. The results showed that R152A, R600, and R600A, in that order, were the most suitable working fluids. The effective area of the solar collector for a 20℃ increase in the collector outlet temperature fluctuated from 50 to 97 ㎡ owing to the change in the monthly average solar gain. The annual average efficiency of the SH-OTEC increases to 6.23%, compared to that of a typical conventional OTEC, which is 2?4%.

배플과 관군간의 적정 누설유동을 이용한 쉘-관 열교환기의 성능향상

Nguyen Van Hap,이근식(Geun Sik Lee) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.3

배플과 관군간의 누설유동이 쉘-관 열교환기 성능에 미치는 영향을 FLUENT 를 사용하여 조사하였다. 쉘측 출구온도를 최대로 하는 최적누설유동을 찾기 위해 쉘측 단면적에 대한 누설단면적 비가 0%-40% 범위의 5 가지 누설유동을 가진 쉘-관 열교환기에 대하여 CFD 모델이 개발되었다. 관 입구 및 벽면온도를 일정하게 유지하고 Reynolds 수를 4952 부터 14858 증가시키면서 유동장 및 온도장을 계산하였다. 해석결과, 출구온도, 압력강하, 열전달률은 Reynolds 수뿐만 아니라 누설유동에도 크게 영향을 받는 것으로 나타났다. 누설유동은 열전달률과 압력강하를 동시에 낮추는 결과를 제시한 기존의 결과와는 달리, 본 연구에서는 적정의 누설유동은 배플 주위의 재순환영역에 추가적인 모멘텀을 공급함으로써 최대출구온도, 작은 압력강하, 높은 열전달률을 유도하는 효과를 발휘하는 새로운 결과를 얻었다. 20%의 누설단면적이 최적의 누설단면적으로 나타났다. In this study, the effects of the leakage flow between the baffle and tube bundles on the performance of a shell and tube heat exchanger (STHE) were examined using the commercial software ANSYS FLUENT v.14. A computational fluid dynamics model was developed for a small STHE with five different cases for the ratio of the leakage cross-sectional area to the baffle cross-sectional area, ranging from 0 to 40%, in order to determine the optimum leakage flow corresponding to the maximum outlet temperature. Using fixed tube wall and inlet temperatures for the shell side of the STHE, the flow and temperature fields were calculated by increasing the Reynolds number from 4952 to 14858. The present results showed that the outlet temperature, pressure drop, and heat transfer coefficient were strongly affected by the leakage flow, as well as the Reynolds number. In contrast with a previous researcher"s finding that the leakage flow led to simultaneous decreases in the pressure drop and heat transfer rate, the present study found that the pertinent leakage flow provided momentum in the recirculation zone near the baffle plate and thus led to the maximum outlet temperature, a small pressure drop, and the highest heat transfer rate. The optimum leakage flow was shown in the case with a ratio of 20% among the five different cases.

Geometry Optimization of Exhaust System with Adjoint Method

Nguyen Van Hap,Kim MyungSoo(김명수),Hwang GyuChul(황규철),JoengJongHwa(정종화),GeunSik Lee(이근식) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.5-3

해양온도차발전용 반경류 터빈의 설계 및 해석

Nguyen Van Hap,이근식(Geun Sik Lee) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.3

해양온도차발전용 터빈의 효율과 크기를 파악하기 위해 R134a 를 작동유체로 하고 출력 5 kW 인반경류형 터빈의 설계가 수행되었다. 터빈입구온도 25oC, 출구 정압 4.9 bar, 질량유량 1.16 kg/s 로 설정하고 평균유동해석을 수행하여 터빈의 회전수와 주요 치수를 결정하였다. 이들을 바탕으로, 3 차원 터빈모델을 구축하였으며, 도출된 터빈회전수 12,820 rpm 에 대하여 전산유체역학(CFD) 소프트웨어 ANSYS CFX 를 이용하여 볼류트와 노즐을 포함하는 터빈 내부 유동장 특성과 효율이 조사되었다. 80%이상의 터빈 효율이 적정 범위 내의 노즐 안내깃 수(10-15 개)에서 제시되었으며, 가장 높은 터빈 효율은 15 개의 안내 깃에서 나타났다. The preliminary design of a radial inflow turbine using R134a as the working fluid at 5 kW of power for application to ocean thermal energy conversion (OTEC) is performed to obtain the trends for the efficiency and geometrical dimensions of the turbine. Using input conditions that included a turbine inlet temperature of 25°C, an outlet static pressure of 4.9 bar, and a mass flow rate of 1.16 kg/s, the results of a mean flow analysis show the major dimensions of the turbine, along with an angular velocity of 12,820 rpm. Based on these results, a three-dimensional turbine model is constructed for a computational fluid dynamics (CFD) analysis. The flow characteristics inside the turbine, including the volute and nozzle, are investigated using the CFD software ANSYS CFX. For a pertinent number of nozzle guide vanes, ranging from 10 to 15, the turbine efficiency was higher than 80%, with the highest efficiency shown by a nozzle with 15 guide vanes.

재순환케이싱처리 높이변화가 터보차저 압축기의 성능에 미치는 영향

Nguyen Van Hap,Zhou Tianjun,이근식(Geun Sik Lee) 대한기계학회 2015 大韓機械學會論文集B Vol.39 No.8

자동차용 터보차저 원심압축기의 재순환케이싱처리(RCT)부의 높이변화가 압축기의 성능에 미치는 영향이 조사되었다. 연구대상 RCT 부의 높이는 1.2mm, 1.5mm, 1.8mm 의 세가지이며, 회전수 범위는 90,000 - 150,000 rpm, 유량 범위는 0.015 kg/s - 0.08 kg/s 이다. 전압력비와 등엔트로피 효율 비교 결과, 본 수치계산은 실제압축기의 성능 제원과 최대오차 0.7%의 범위 내에서 잘 일치하였다. 해석결과, RCT 부 높이 1.2mm, 1.8mm, 1.5mm 순서로 균일 압력분포, 높은 압력비, 넓은 작동범위를 얻었다. 이들 세가지 경우 모두, 회전수가 증가할수록 이들의 압력비는 높아지나 운전범위는 좁아지는 전형적인 압축기 맵의 특성을 보여주었다. In this study, we investigate the performance variations of an automotive turbocharger compressor with respect to the height variation of the recirculating casing treatment (RCT). We use three RCT heights, namely 1.2 mm, 1.5 mm, and 1.8 mm. We vary the compressor speed from 90,000 to 150,000 rpm, and the flow rate from 0.015 kg/s to 0.08 kg/s. The calculation results of the total pressure ratio and isentropic efficiency showed good agreement with the performance data provided by the manufacturer within a 0.7 percent error. The results showed that the RCT heights of 1.2 mm, 1.8 mm, and 1.5 mm, in that order, exhibited a more uniform pressure distribution, higher pressure ratio, and wider operational range. As the number of revolutions per minute increased, we obtained typical characteristics of a compressor map having a narrower operational range in the region of higher pressure ratio.

Energy and exergy analyses of the Kalina system integrated with a two-phase turbine

Nguyen Van Hap,Nguyen Minh Phu 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.1

The Kalina power cycle can be integrated with a two-phase turbine as a substitute for the expansion valve to yield useful mechanical energy. An energy- and exergy-based mathematical model was formulated to analyze and evaluate the performance of the proposed cycle in this study. Independent parameters, including the base ammonia-water solution concentration, separator pressure, temperature difference in the recuperator, and vapor turbine outlet pressure, were used to analyze the sensitivity of efficiencies. The results show that the proposed cycle is efficient in terms of energy and exergy efficiencies. The two-phase turbine power is much larger than the solution pump power, and the exergy destruction of the turbine is much smaller than that of a throttle valve. The effect of the base solution concentration was dominant. At low concentrations, the energy and exergy efficiency improvements were 140 % and 160 %, respectively. At high concentrations, the substitution was not significant because the solution flow rate through the two-phase turbine was negligible. Furthermore, the efficiency enhancement was notable at a high vapor turbine outlet pressure.

Design and Analysis of a Radial Turbine for Ocean Thermal Energy Conversion

Nguyen Van Hap,Geun Sik Lee(이근식) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12

A radial inflow turbine using the working fluid of R134a at the power of 5 kW and the angular velocity of 12,820 rpm is designed and analyzed for application of ocean thermal energy conversion (OTEC). The operating inlet temperature of the turbine adopted is 25℃ and the outlet static pressure is 4.9 bar. Flow characteristics inside the turbine including the volute and the nozzle are investigated by using the CFD software of ANSYS CFX. In addition, the CFD results indicated that the 15 guide-vane nozzle showed the highest turbine efficiency for variations of number of the nozzle guide vanes of the turbine.

태양열 이용 해양온도차발전 재생사이클에 대한 열역학적 해석

Nguyen Van Hap,이근식(Geun Sik Lee) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5

관누설유동이 쉘-관 열교환기의 성능에 미치는 영향에 대한 수치해석

Nguyen Van Hap,이근식(Geun Sik Lee) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.5