Enhancement analysis of turbulent flow and heat transfer of supercritical CO2 in a static mixer with three helical blades

Huibo Meng,Yunjuan Yao,Yanfang Yu,Bowen Shi,Pengcheng Ding 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.1

Supercritical CO2 has excellent flow and heat transfer characteristics, but studies are lacking on the heat transfer characteristics of static mixers using it as a working medium. To obtain the heat transfer enhancement mechanism of supercritical CO2 within static mixers with three helical blades (TKSM), the flow and heat transfer characteristics of supercritical CO2 in horizontal and vertically upward of TKSM were determined by three-dimensional steady-state numerical simulation at Re=7,900−22,385, respectively. With other parameters fixed, lower heat flux, inlet temperature, operating pressure, or higher mass flow corresponds to higher heat transfer coefficients (h). The orthogonal test revealed that mass flow has the greatest effect on heat transfer. Besides, the results showed that the comprehensive performance evaluation criteria (PEC) of TKSM were 1.18–1.64 times and 1.25–1.47 times of Kenics static mixer (KSM) in two different states. Considering the local deterioration of the horizontal flow, the vertically upward flow was recommended with uniform temperature distributions. Compared with the horizontal flow, the heat transfer capacity of TKSM in the upward flow increases by 92.64%–119.63%, whereas the buoyancy effect decreases by 99.83%–99.97%.

Heat transfer characteristics of supercritical CO₂ in a helical coil gas cooler on the change of coil diameter

Hoo-Kyu Oh(오후규),Tae-Guen Yu(유태근),Geon-Sang Roh(노건상),Hak-Keun Ku(구학근),Jiating Yan 한국마린엔지니어링학회 2007 한국마린엔지니어링학회 학술대회 논문집 Vol.2007 No.-

The heat transfer characteristics of supercritical CO₂ during gas cooling process are investigated experimentally. The test section is a helically coiled tube with I.D. of 4.55, O.D. of 6.35 and length of 10000 [㎜]. The helical coil diameter is 41.35 and 26.75 [㎜], respectively. The apparatus consist of a receiver, a variable-speed pump, a mass flow meter, a pre-heater, a gas cooler (test section) and an isothermal tank. The range of the refrigerant mass fluxes is from 200 to 800 [㎏/㎡s] and the pressure in the gas cooler varies from 7.5 to 10.0 [㎫]. The main experimental results are summarized as follows; as the gas cooling pressure decreases gradually, the heat transfer coefficient increases greatly. The mass flux has a positive effect on heat transfer like constant property condition. The heat transfer coefficient at coil diameter 26.75 [㎜] is larger than that of coil diameter 41.35 [㎜]. The data is compared with the existing correlations, which generally under-predict the measured data. However the experimental data show a relatively good agreement with correlations by Pitla et al. except for pseudo critical temperature.

헬리컬 코일형 가스냉각기 내 CO₂의 냉각 전열 특성

전민주(Min-Ju Jeon),유태근(Tae-Guen Yu),손창효(Chang-Hyo Son),오후규(Hoo-Kyu Oh) 대한설비공학회 2006 대한설비공학회 학술발표대회논문집 Vol.2006 No.11

The cooling heat transfer coefficient of CO₂ (R-744) in helically coiled tubes was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and a gas cooler (test section). The test section consists of a helically coiled copper tube of 4.55 and 2.45 ㎜. The experiments were conducted at saturation temperature of 100 to 20℃, and mass flux of 200 to 600 ㎏/㎡s. The test results showed the variation of the heat transfer coefficient tended to decrease as cooling pressure of CO₂ increased. The heat transfer coefficient with respect to mass flux increased as mass flux increased. The experimental results were also compared with the existing correlations for the supercritical heat transfer coefficient, which generally under-predicted the measured data. However, the experimental data showed a relatively good agreement with the correlations of Pitla et al. except for the pseudo critical temperature.

초임계 이산화탄소의 수직 상향 유동에서의 관내 열전달에 관한 실험적 연구

김동억(Dong Eok Kim) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.7

초임계 CO₂의 수직상향유동에서의 난류열전달에 관한 실험적연구가 내경 4.5 mm 의 원형관에서 수행되었다. 실험범위는 유체평균온도 29 - 115 ℃, 압력 74.6 - 102.6 bar, 국부 벽면 열유속 38 - 234 kW/m² 그리고 질량유속 208 - 874 kg/m²였다. 중간정도의 벽면 열유속 및 낮은 질량유속에서 벽면온도는 확연한 최대점을 나타냈다. 열전달에 대한 부력 및 유동가속의 영향을 살펴보기 위하여 실험 및 참조상관식(Kranoshchekov and Protopopov<SUP>(12)</SUP>)에서 획득된 Nusselt 수의 비를 부력 및 유동가속을 나타내는 변수인 Bo<SUP>*</SUP> 및 q<SUP>+</SUP>를 이용하여 분석하였다. 이 분석을 통해 유동가속 변수인 q<SUP>+</SUP>는 실험에서의 열전달 현상을 적절히 표현할 수 있는 변수라는 것을 확인할 수 있었다. 마지막으로 초임계 유체의 수직상향 유동에서의 새로운 열전달 상관식이 개발되었으며, 이 상관식은 ±30 %의 오차범위에서 실험데이터를 잘 예측하였다. An experimental investigation of turbulent heat transfer during the vertical upward flow of supercritical CO₂ was conducted in a circular tube with inner diameter of 4.5 mm. The experiments were conducted at bulk fluid temperatures ranging from 29 to 115 °C, pressures from 74.6 to 102.6 bar, local wall heat fluxes from 38 to 234 kW/m², and mass fluxes from 208 to 874 kg/m²s. At moderate wall heat and low mass fluxes, the wall temperature had a noticeable peak value. For observing the buoyancy and flow acceleration effects on heat transfer, the ratios of Nusselt numbers from the experimental data and a reference correlation were compared with the Bo<SUP>*</SUP> and q<SUP>+</SUP> distributions. The flow acceleration parameter q<SUP>+</SUP> appropriately represented the heat transfer phenomena in the experiments. A new heat transfer correlation for the vertical upward flow of the supercritical pressure fluid was developed, and was found to agree with the experimental data with an error margin of ±30 %.

초임계 이산화탄소 브레이튼 사이클과 스팀 랭킨 사이클의 비교 및 특성 분석

김선진(Sun Jin Kim),이지성(Ji Sung Lee),김민수(Min Soo Kim) 대한설비공학회 2015 대한설비공학회 학술발표대회논문집 Vol.2015 No.11

Steam rankine cycle already does a role to generate electric power. but power demand increases steadily. So high efficiency power generation technology is needed to handle this problem. Supercritical carbon dioxide(S-CO2) brayton cycle becomes one of the solutions of energy problem. In this paper, results of comparative study of two cycles are presented. Power output and heat source temperature of two cycles are the same. In the same operating conditions, total thermal efficiency and overall heat transfer coefficient (UA) of two cycles are calculated and compared. Efficiency of S-CO2 cycle surpasses that of steam cycle at about 600OC of heat source temperature. UA of two cycles are decreased with increase of heat source temperature. In the same heat source temperature, the average UA of S-CO2 cycle is smaller than that of steam cycle. UA of cooler in steam cycle is very large. So power generation efficiency and cost of designing heat exchanger of the cycle are the advantages of S-CO2 cycle.

PREDICTION OF A HEAT TRANSFER TO CO₂ FLOWING IN AN UPWARD PATH AT A SUPERCRITICAL PRESSURE

Cho, Bong-Hyun,Kim, Young-In,Bae, Yoon-Yeong Korean Nuclear Society 2009 Nuclear Engineering and Technology Vol.41 No.7

This study was performed to evaluate the prediction capability of a commercial CFD code and to investigate the effects of different geometries such as a 4.4 mm tube and an 8/10 mm annular channel on the detailed flow structures. A numerical simulation was performed for the conditions, at which the experimental data was produced by the test facility SPHINX. A 2-dimensional axisymmetric steady flow was assumed for computational simplicity. The RNG $\kappa-\varepsilon$ turbulence model (RNG) with an enhanced wall treatment option, SST $\kappa-\omega$ (SST) and low Reynolds Abid turbulence model (ABD) were employed and the numerical predictions were compared with the experimental data generated from the experiment. The effects of the geometry on heat transfer were investigated. The flow and temperature fields were also examined in order to investigate the mechanism of heat transfer near the wall. The local heat transfer coefficient predicted by the RNG model is very close to the measurement result for the tube. In contrast, the local heat transfer coefficient predicted by the SST and ABD models is closer to the measurement for the annular channel.

평활관 및 마이크로핀관 내 초임계 이산화탄소의 냉각열전달 특성

이대훈(Daehun Lee),전민주(Minjoo Jeon),손창효(Changhyo Son),오후규(Hookyu Oh) 대한설비공학회 2010 대한설비공학회 학술발표대회논문집 Vol.2010 No.6

The cooling heat transfer characteristics of supercritical CO₂ in smooth and micro-fin tubes were investigated experimentally. The main components of the refrigerant loop are a receiver, a CO₂ compressor, a mass flow meter, an evaporator and a micro-fin tube as a test section. The test was conducted at mass flux from 1200 to 2000 ㎏/㎡s, inlet cooling pressure from 9 to 10 ㎫. The cooling heat transfer coefficients of the micro-fin tube are about 12~39% higher than those of the smooth tube. In comparison with test results and existing correlations, correlations failed to predict the cooling heat transfer coefficient of CO₂ in the micro-fin tube. Therefore, it is necessary to develop reliable and accurate predictions determining the cooling heat transfer coefficient of CO₂ in the micro-fin tube.

내경 4.57㎜ 관내 CO₂의 증발 열전달 특성

손창효(Son, Chang-Hyo) 한국산학기술학회 2008 한국산학기술학회논문지 Vol.9 No.3

수평관내 CO₂의 증발 열전달 계수를 실험적으로 조사하였다. 냉매 순환루프의 주요 구성품은 수액기, 변속 냉매 펌프, 질량 유량계, 예열기, 증발기(시험부)로 구성된다. 시험부는 내경 4.57㎜의 수평 평활 스텐레스관이다. 실험은 질량유속 400-900 ㎏/㎡s, 포화온도 5-20℃, 열유속 10-40 ㎾/㎡인 조건에서 수행하였다. 실험결과로부터 CO₂의 열전달은 대류비등보다는 핵비등에 더 많은 영향을 받는 것을 알 수 있었고, CO₂의 질량유속은 핵비등에 많은 영향을 미치지 않는 것으로 나타났다. 실험결과와 종래의 상관식을 비교해 본 결과, 기존의 상관식은 실험데이터를 과소예측하였지만, 정 등의 상관식은 좋은 일치를 보였다. 따라서, 수평관내 CO₂의 증발 열전달 계수를 예측할 수 있는 정확한 상관식의 개발이 필요하리라 판단된다. The evaporation heat transfer coefficient of CO₂ (R-744) in a horizontal tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth, horizontal stainless steel tube of inner diameter of 4.57㎜. The experiments were conducted at mass flux of 400 to 900 ㎏/㎡s, saturation temperature of 5 to 20℃, and heat flux of 10 to 40 ㎾/㎡. The test results showed the heat transfer of CO₂ has a greater effect on nucleate boiling more than convective boiling. Mass flux of CO₂ does not affect nucleate boiling too much. In comparison with test results and existing correlations, All of the existing correlations for the heat transfer coefficient underestimated the experimental data. However Jung et al.'s correlation showed a good agreement with the experimental data. Therefore, it is necessary to develope accurate predictions determining the evaporation heat transfer coefficient of CO₂ in horizontal tubes.

PREDICTION OF A HEAT TRANSFER TO CO₂ FLOWING IN AN UPWARD PATH AT A SUPERCRITICAL PRESSURE

BONG-HYUN CHO,YOUNG-IN KIM,YOON-YEONG BAE 한국원자력학회 2009 Nuclear Engineering and Technology Vol.41 No.7

This study was performed to evaluate the prediction capability of a commercial CFD code and to investigate the effects of different geometries such as a 4.4 mm tube and an 8/10 mm annular channel on the detailed flow structures. A numerical simulation was performed for the conditions, at which the experimental data was produced by the test facility SPHINX. A 2-dimensional axisymmetric steady flow was assumed for computational simplicity. The RNG k-ε turbulence model (RNG) with an enhanced wall treatment option, SST k-ω (SST) and low Reynolds Abid turbulence model (ABD) were employed and the numerical predictions were compared with the experimental data generated from the experiment. The effects of the geometry on heat transfer were investigated. The flow and temperature fields were also examined in order to investigate the mechanism of heat transfer near the wall. The local heat transfer coefficient predicted by the RNG model is very close to the measurement result for the tube. In contrast, the local heat transfer coefficient predicted by the SST and ABD models is closer to the measurement for the annular channel.

초임계 이산화탄소 브레이튼 사이클의 예비냉각기를 위한 직관형 PCHE의 열전달 특성

박주현(Joo Hyun Park),권진규(Jin Gyu Kwon),김무환(Moo Hwan Kim),차재은(Jae Eun Cha),조항진(HangJin Jo) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

A printed circuit heat exchanger (PCHE) take an attention as a new type of heat exchanger for a high pressure system. The PCHE is fabricated by the photochemical etching and diffusion bonding process. The PCHE has micro-channels with complex geometries due to photochemical etching that provide high heat transfer performance and can operate at high pressure and high temperature due to diffusion bonding. In order to attain these advantages, PCHE was considered as a heat exchanger of supercritical CO₂ (sCO₂) Brayton cycle. The sCO₂ Brayton cycle is operated at high pressure and high temperature in order to operating at supercritical region. In this study, the heat transfers of a straight PCHE for a sCO₂ cooling with water were measured experimentally. To verify effect of properties near the critical point of CO₂, experiments with different operating condition was conducted. It can be explained about better heat transfer performance near the critical point.