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Three-dimensional numerical simulation of pulsating heat pipes
Duy-Tan Vo,Hyoung-Tak Kim,Kwang-Hyun Bang 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.11
A three-dimensional computational fluid dynamics modeling has been developed for pulsating heat pipe (PHP) using ANSYS Fluent. The VOF model with variable density and vapor pressure relation successfully simulated the oscillating and circulating motions of PHP. The predicted wall temperatures showed the same indication of the mode of flow motion and the flow direction as observed in experiments. The predicted heat transfer rates agreed well with the experimental data within 5%. It is also found that the realizable k-ε turbulence model is appropriate to PHP simulation and the use of variable density for liquid and vapor as well as vapor pressure equation is crucial.
Key Determinants of Repurchase Intention toward Organic Cosmetics
Phuong Ngoc Duy NGUYEN,Vinh Tan NGUYEN,Nguyen Ngoc Thao VO 한국유통과학회 2019 The Journal of Asian Finance, Economics and Busine Vol.6 No.3
This paper aims to discover factors and their influences degree to repurchase organic cosmetic in Vietnam. In addition, this research also discloses the main segments that have high demand re-buying intention based on demographic groups of gender, age, income, educational level, job, type of products, and place of production. Twenty-eight scale was designed based on previous studies and adjusted to match the 5-point Likert scale to conduct measurement. By using survey method to test hypotheses and set up conceptual models to collect 295 Vietnamese consumers who have experience in consuming organic cosmetic by explain the results through Smart PLS software. The findings show that there is positive attitude of customers to the intention of acquiring organic cosmetics, green perceived and customer satisfaction. In addition, customer satisfaction, knowledge of products, safety values, and environmental protection consciousness also play important roles to form a positive attitude of customers for products. Moreover, the consciousness of green living of consumers accounts for a high proportion in creating customer satisfaction for organic products. The results show useful information for current premises to determine the factors that influence the decision to repurchase organic cosmetic product, that provide business strategies.
Robust Precoding and Postcoding for Multicell Multiuser Transmission using Imperfect CSI
Nguyen-Le, Hung,Nguyen-Duy-Nhat, Vien,Tang-Tan, Chien,Bao, Vo Nguyen Quoc The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.5
This paper studies the problem of precoding and post-coding design for multicell multiuser downlink transmissions in the absence of perfect channel state information (CSI). Using statistical information of imperfect CSI, an iterative multiuser multicell transceiver design is formulated by minimizing the mean squared error (MSE) cost function of signal and leakage interference under per-base station power constraint (PBPC). The convergence of the iterative precoding and postcoding algorithm is verified by analytical and empirical results. The proposed precoding and postcoding algorithm offers a low computational complexity and robustness against CSI imperfection.
Experiment and modeling of jet breakup in fuel-coolant interactions
Bang, Kwang-Hyun,Kim, Hyoung-Tak,Tan, Vo Duy Elsevier 2018 Annals of nuclear energy Vol.118 No.-
<P><B>Abstract</B></P> <P>In light water reactor core melt accidents, the potential risk of energetic molten fuel coolant interaction (FCI, steam explosions) in a partially-flooded reactor cavity has drawn substantial attention. However, when the cavity is completely filled with coolant and the reactor vessel lower head is submerged for the purpose of external reactor vessel cooling, the jet breakup behavior in this case could not only be quite different from the case of partially-flooded reactor cavity, but also affect the risk of fuel coolant interactions. In this study, the jet breakup in liquid-liquid system was experimentally investigated for a fully-flooded and a partially-flooded cavity, and the existing jet breakup models were evaluated against the experimental data. The jet breakup experiment, named as COLDJET, was carried out using the Woods metal whose melting point was 72 °C. The melt jet temperature was lower than the boiling point of coolant so that only the hydrodynamic aspect of jet breakup was investigated. The jet diameter was 50 mm and the coolant depth was 1 m. To investigate the effect of air space of free-falling jet, the experiment was conducted for both fully-flooded and partially-flooded cavities. In the latter case, the free-fall distance in air space was 1 m. A high-speed video camera (typically 4000 fps) was used to visualize the jet breakup and there was an obvious difference in jet breakup behavior between the fully-flooded and the partially-flooded cavities. The jet breakup lengths which were identified in the jet front falling speed were compared with existing models and found that the agreement with the Epstein and Fauske’s model was remarkable. The solidified debris were collected, dried, and sieved to obtain the debris size distribution. It was observed that the average debris size in case of the fully-flooded condition was much smaller than that of the partially-flooded condition at the same jet injection velocity. This is because the entrained air layer between the melt and water acted as like vapor film in boiling condition. The prediction of most probable debris size by the model based on Kelvin-Helmholtz instability showed a good agreement with the experimental data. The jet breakup tests were also simulated using the TRACER-II code, which is a two-dimensional, transient, four-fluid code that can calculate the mixing and propagation of energetic fuel-coolant interactions. The test results were used to improve the jet breakup models of the code as well as to validate the code.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experiment of melt jet breakup was carried out using Woods metal under non-boiling condition. </LI> <LI> Debris from melt jet breakup in fully-flooded pool is finer than that in partially-flooded pool. </LI> <LI> Simulation of jet breakup using TRACER-II code shows a good agreement with the experimental data. </LI> </UL> </P>
Robust Precoding and Postcoding for Multicell Multiuser Transmission using Imperfect CSI
Hung Nguyen-Le,Vien Nguyen-Duy-Nhat,Chien Tang-Tan,Vo Nguyen Quoc Bao 한국통신학회 2016 Journal of communications and networks Vol.18 No.5
This paper studies the problem of precoding and post-coding design for multicellmultiuser downlink transmissions in theabsence of perfect channel state information (CSI). Using statisti-cal information of imperfect CSI, an iterative multiuser multicelltransceiver design is formulated by minimizing the mean squarederror (MSE) cost function of signal and leakage interference underper-base station power constraint (PBPC). The convergence of theiterative precoding and postcoding algorithm is verified by analyt-ical and empirical results. The proposed precoding and postcodingalgorithm offers a low computational complexity and robustnessagainst CSI imperfection.
친환경 연소에 따른 가스 터빈 내 유동 및 성능 특성의 수치해석적 연구
김병욱(Byungwook Kim),마이탄담(Thanh Dam Mai),보두이딴(Duy Tan Vo),장성호(Sungho Chang),유재영(Jaiyoung Ryu) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
The need to reduce greenhouse gas emissions from gas turbines has raised in response to the international demand for greenhouse gas reduction. Eco-friendly combustion, which can be represented by hydrogen combustion and oxy-fuel combustion, have potential of enormous reduction of greenhouse gases. However, previous researches hardly considered about the effect of such combustion in the turbine part. In this study, hydrogen combustion and oxy-fuel combustion simulation were performed to analyze the characteristics of flow in combustor. Quantitative investigation of the gas turbine flow characteristics and performance by each combustion condition were performed by following gas turbine simulation. The gas turbine used for computational analysis is GE-E3 1.5 stage model, and conditions of the flow were based on combustion simulation results. The analysis shows that the output of hydrogen increased due to the fast flow velocity, but the total-to-total efficiency diminished compared to natural gas.
Tien Huynh Manh,Khanh Quoc Le Tran,Phat Tan Ho,Man Minh Vo,Thong Quang Pham,Thong Duy Vo 대한소화기학회 2023 대한소화기학회지 Vol.81 No.6
Strongyloidiasis, a chronic helminth infection caused by the parasitic nematode Strongyloides stercoralis, has various clinical manifestations. Although rare, duodenal obstructions and venous thromboembolism are possible complications of strongyloidiasis. This paper presents the case of a 47-year-old Vietnamese male with a history of right lower limb edema, anorexia, nausea, vomiting, diarrhea, and abdominal discomfort lasting for four months. Venous Doppler ultrasound detected a thrombus in the right femoral vein, while an abdominal CT scan revealed a mass lesion suggestive of a lower bile duct tumor. Esophageogastroduodenoscopy showed a friable duodenal cap mucosa with multiple ulcers and edematous mucosa of the second part of the duodenum that caused a partial lumen obstruction. The final histological examination of the biopsy specimen revealed chronic duodenitis with larvae consistent with Strongyloides stercoralis. The patient was treated with Ivermectin for two weeks and anticoagulation therapy for three months. After treatment and a six-month follow-up, the patient's gastrointestinal symptoms and leg swelling resolved completely. This is the first documented case of a patient in Vietnam with strongyloidiasis who presented with venous thromboembolism and duodenal obstruction.