초음속 노즐 내에서 수증기의 비평형 응축 효과

Santhosh Senguttuvan,이장창 한국전산유체공학회 2018 한국전산유체공학회지 Vol.23 No.4

Non-equilibrium condensation during the rapid expansion of steam in turbomachinery affects the flow performance. The latent heat released during the condensation process leads to condensation shock, which decelerates the flow. In the present paper, the numerical modeling of the non-equilibrium condensation in a supersonic nozzle is achieved by solving two transport equations based on the classical nucleation theory corrected for non-isothermal effects as well as the droplet growth law of Hill. The numerical model is successfully validated to be in good agreement with the experimental data. The effect of condensation of the steam in the nozzle is studied by comparing various flow properties of the steam flow with and without condensation. The results show that the exit Mach number of the nozzle is reduced by 13.5%, and that the total temperature at the exit and boundary layer thickness of the flow are increased by 11.5% and 28%, respectively, due to the latent heat released during the condensation process.

Numerical estimation of non-equilibrium condensation in steam ejector

Jabir Edathol,Heuy Dong Kim(김희동) 한국추진공학회 2018 한국추진공학회 학술대회논문집 Vol.2018 No.5

KEjectors are commonly used in aerospace, chemical and nuclear industries to generate low pressures and thereby passive pumping, by utilizing readily available high pressure steam. In supersonic ejectors there is a possibility of steam condensation inside the nozzle during the rapid expansion process. The formation of droplets can change the ejector performance substantially. Majority of the studies reported in literature neglect the effect of condensation because of the difficulties in modeling. To make numerical predictions of the flow and mixing inside an ejector, the condensation of steam is to be accounted using suitable condensation models reported in the literature. In a supersonic expansion inside a nozzle, because of the high velocity and expansion rate, the condensation process departs far away from the equilibrium state. This type of non-equilibrium condensation is numerically modeled using additional transport equations which are used to compute the mass fraction of condensate generated by the phase change process. In the present work a 2-equation non-equilibrium condensation model with ANSYS FLUENT is used study the flow characteristics. The methodology is validated against experimental studies reported in the literature and used to thoroughly examine steam flow in a supersonic ejector.

비평형 응축이 충격파 진동에 미치는 영향에 관한 수치 해석적 연구

전흥균(Heung Kyun Jeon),김인원(In Won Kim),권영두(Young Doo Kwon),권순범(Soon Bum Kwon) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.3

본 연구에서는 NACA0012/14/15 천음속 에어포일 유동에서 비평형 응축이 충격파 진동에 미치는 영향을 TVD 수치해석을 통하여 연구하였다. 주류 마하수 0.81-0.90에 대해, 정체점 상대습도 및 에어포일의 기하학적 형상이 유동 특성에 미치는 영향이 구명되었다. 받음각 α=0°, 정체점 온도(288K) 및 주류 마하수가 0.87인 경우, 정체점 상대습도의 증가는 Terminating Shock의 충격파 강도를 약화시킨다. 정체점 상대습도가 30%인 경우 961Hz이던 충격파의 진동수가 60%일 때는 912Hz로 약 5% 감소한다. 정체점 상대습도가 동일한 경우는 주류 마하수가 클수록 충격파의 진동수 및 이동거리는 크게 된다. 또, 진동의 한 주기에 대해 항력계수의 변화도 구명되었다. 정체점 상대습도가 높을수록 최대 항력 계수는 작고, 항력계수의 변화폭 또한 감소한다. 한편 에어포일의 최대 두께가 두꺼울수록 초음속 영역의 크기는 증가하며 충격파의 진동수 및 이동거리도 증가한다. In this study, to find the characteristics of the oscillation of a terminating shock wave in a transonic airfoil flow with non-equilibrium condensation, a NACA00-12,14,15 airfoil flow with non-equilibrium condensation is investigated through numerical analysis of TVD scheme. Transonic free stream Mach number of 0.81-0.90 with the variation of stagnation relative humidity and airfoil thickness is tested. For the free stream Mach number 0.87 and attack angle of α=0°, the increase in stagnation relative humidity attenuates the strength of the terminating shock wave and inactivates the oscillation of the terminating shock wave. For the case of M∞=0.87 and ?060%, the decreasing rate in the frequency of the shock oscillation caused by non-equilibrium condensation to that of ?0=30% amounts to 5%. Also, as the stagnation relative humidity gets larger, the maximum coefficient of drag and the difference between the maximum and minimum in CD become smaller. On the other hand, as the thickness of the airfoil gets larger, the supersonic bubble size becomes bigger and the oscillation of the shock wave becomes higher.

EFFECT OF NON-EQUILIBRIUM CONDENSATION OF WET STEAM IN THE MODIFIED SONIC NOZZLE

Balasubramanian Dhandapani,Jang-Chang Lee(이장창) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4

The non-equilibrium condensation effects of steam in the modified sonic nozzle are investigated. The modified sonic nozzle in this paper is based on the sonic nozzle of ASME where the flow velocity reaches Mach number one at the throat and where the pressure ratio of inlet/outlet(P1/P3) is operated with greater than two to achieve sonic state. As the superheated dry steam accelerates through the nozzle, the condensation of steam occurs and then the steam becomes the wet steam which is two phases mixture with saturated vapor and liquid droplets. The numerical modeling of the non-equilibrium condensation in the modified sonic nozzle is obtained by solving two transport equations based on the classical nucleation theory with the droplet growth law of Hill. The numerical results show that the Mach number reaches 1.2 immediately after throat, the droplet nucleation rate increases rapidly with increasing subcooling level(ΔT), and the liquid mass fraction increases gradually downstream of nozzle. Also the condensation effects in the modified sonic nozzle is compared internally with its different thermal choking ratio’s and with dry steam cases for better realization of the modified sonic nozzle.

증기 압축식 냉동 시스템에서 R600a 비평형 냉매가 응축에 미치는 영향

황석진(Seok Jin Hwang),정지환(Ji Hwan Jeong) 대한설비공학회 2019 대한설비공학회 학술발표대회논문집 Vol.2019 No.-

A vapor compression refrigeration system consist of a compressor, a condenser, an expansion device and an evaporator. In order to avoid mass flow reduction when vapor enters the capillary, the refrigeration system is designed so that refrigerant is in a subcooled state between condenser and capillary tube. Some previous researchers have reported that the presence of non-equilibrium two phase flow at the condenser outlet in refrigeration system using R600a. There are studies on the effect of R600a non-equilibrium on the system, but there is a lack of research on how non-equilibrium progresses inside the condenser. In this study, experiments were performed under conditions that non-equilibrium two-phase flow occurred. It is found that The temperature is maintained at the beginning of condensation and is decreased before it turns into totally liquid.

Study of divergence angle influence for sonic nozzle in non-equilibrium condensation

Balasubramanian Dhandapani,이장창 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6

The condensation happens generally in a nozzle during expansion of compressed steam from convergent to the divergent part of the nozzle. The divergence angle is the angle measured from the throat of the nozzle to the outlet. In this paper, the outlet is kept constant and the throat diameter is varied. In turn, the divergence angle of the sonic nozzle is altered. The effect of divergence angle on condensation phenomena is investigated with wet steam in a sonic nozzle. For analyzing the wet steam properties, the non-equilibrium condensation model is used. This model is the classical nucleation theory coupled with the droplet growth rate equation. The base nozzle is designed with the throat diameter of 4.5 mm and other dimensions are calculated according to ASME nozzle formulas. Furthermore, the chosen divergence angles are 3°, 4.2°, and 6° for which the throat diameters are 4.5 mm, 3 mm, and 1.5 mm, respectively. As the divergence angle is gradually increased, the position of maximum Mach number of the flow moves upstream, the static temperature of the flow near the throat reaches the lower value, and the droplet nucleation rate is increased. The condensation shock gets gradually stronger with decreasing the divergence angle.

Numerical sensitivity study on nucleation bulk tension factor of non-equilibrium condensation model

Eryun Chen,Shiyin Fu,Ailing Yang,Shuxue Peng,Gaiping Zhao 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.2

The spontaneous condensation process of steam has obvious non-equilibrium characteristics, the accurate prediction of which is challenging. In this work, the nucleation bulk tension factor (NBTF) is used to modify the droplet surface tension for improving the accuracy in the calculation of the steam condensation flow. The non-equilibrium condensation processes in two nozzles are numerically simulated using a surface tension model with NBTF. The influence of NBTF on the simulation accuracy of the steam spontaneous condensation flow is analyzed. The correlation among the optimal value of NBTF, steam expansion rate and inlet parameters is emphatically studied. The obtained results show that the optimum value of NBTF is not sensitive to the change in the steam expansion rate under the same working conditions. It has no significant correlation with the total inlet temperature, but has a significant positive correlation with the total inlet pressure. Based on the numerical results, a cubic polynomial regression model between the optimal NBTF and total inlet pressure is obtained, the reliability of which is further verified by numerical calculation of a wet steam two-phase flow in the Bakhtar plane cascade. These results can provide a reference for determination of the optimum NBTF in wet steam condensation nucleation models.

Effect of non-equilibrium condensation on lift divergence Mach number at transonic speeds

전흥균,최승민,권영두,권순범 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.7

In the present paper, the effects of non-equilibrium condensation on the lift divergence Mach number with the angle of attack in a transonic2-D moist air flow of NACA0012 are investigated using a numerical analysis with a total variation diminishing scheme. In the caseof T0 = 298 K and α = 3°, the lift divergence Mach number Mld decreases with increasing Φ0 up to 40%, whereas beyond Φ0 = 40%, thelift divergence Mach number is nearly constant at Mld = 0.75. On the other hand, for the case of α = 6°, Mld increases with increasing Φ0up to 47%, and then Mld begins to decrease with an increase in Φ0. Because of the attenuating effect of non-equilibrium condensation onthe shock stall, for the case of α = 3°, CL generally decreases with an increase in Φ0, whereas for M∞ = 0.85, which is appreciably largerthan the lift divergence Mach number, CL increases with an increase in Φ0. In the case of M∞ = 0.85, regardless of Φ0, it is shown that thelocation of the maximum Mach number at the upper wall side is nearly constant at x/c = 0.4. It is found that the Mach number for theminimum CL decreases with an increase in Φ0.

The effect of non-equilibrium condensation on the coefficients of force with the angle of attack in the transonic airfoil flow of NACA0012

S. M. Choi,J. S. Kim,권영두,S. B. Kwon 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.6

A transonic flow with a non-equilibrium condensation past NACA0012 profile whose aspect ratio AR is 1.0 with the angle of attack was analyzed by numerical analysis using a TVD scheme, and investigated using an intermittent indraft type supersonic wind tunnel. Transonic flows of 0.70-0.90 in free stream Mach number with variations of Φ0 and α were tested. For the same M∞ and α, the increase in stagnation relative humidity Φ0 caused a decrease in the drag coefficient of profile (that is total) which is composed of the components of form, viscous, wave and condensation; however, the lift coefficient up to Φ0 = 50% increased in the opposite direction. As an example, in the case of M∞ = 0.83, Φ0 = 50%, α = 3o and T0 = 298K, the decreasing rate of the coefficient of profile drag and the increasing rate of the lift coefficient compared to the case of Φ0 = 0% caused by non-equilibrium condensation amounted to 65% and 52%, respectively. In addition, for the same Φ0 and α, as the free stream Mach number M∞ increased, at first, the lift coefficient increased slightly, and then suddenly severely dropped, and finally remained nearly constant. The suddenly dropped free stream Mach number in CL became larger with an increase of Φ0. It turned out that the drag coefficients of form and viscous were almost independent of Φ0. The contribution of wave drag to the coefficient of profile drag for M∞ = 0.83, Φ0 = 30%, α = 3o and T0 = 298K amounted to approximately 79%, and in the case of Φ0 = 60%, the contribution of the non-equilibrium condensation to the reduction in the coefficient of the profile drag compared to the case without condensation amounted to 75%. Especially, for the case of Φ0 = 0% and α = 0o, there was an oscillatory flow region around M∞ = 0.87.

초음속 습공기 유동에서 비정상 공동유동의 진동

신춘식(Choonsik Shin),이종성(Jongsung Lee),김희동(Heuydong Kim),Toshiaki Setoguchi 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.11

Numerical simulations have been carried out for a supersonic two-dimensional flow over open, rectangular cavities (length-to-depth ratios are L/D = 1.0) in order to investigate the effect of non-equilibrium condensation of moist air on supersonic flows around the cavity for the flow Mach number 1.83 at the cavity entrance. In the present computational investigation, a condensing flow was produced by an expansion of moist air in a Laval nozzle. The results obtained showed that in the case with non-equilibrium condensation for L/D = 1.0, amplitudes of oscillation in the cavity became smaller than those without the non-equilibrium condensation. Furthermore, the occurrence of the non-equilibrium condensation reduced the peaks of power spectrum density and the frequency of the flow field oscillation increased in comparison with the case of S0 = 0.