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Hongbing Ding - One of the best experts on this subject based on the ideXlab platform.

  • performance of supersonic Steam ejectors considering the nonequilibrium Condensation phenomenon for efficient energy utilisation
    Applied Energy, 2019
    Co-Authors: Yan Yang, Hongbing Ding
    Abstract:

    Abstract Supersonic ejectors are of great interest for various industries as they can improve the quality of the low-grade heat source in an eco-friendly and sustainable way. However, the impact of Steam Condensation on the supersonic ejector performances is not fully understood and is usually neglected by using the dry gas assumption. The non-equilibrium Condensation occurs during the expansion and mixing process and is tightly coupled with the high turbulence, oblique and expansion waves in supersonic flows. In this paper, we develop a wet Steam model based on the computational fluid dynamics to understand the intricate feature of the Steam Condensation in the supersonic ejector. The numerical results show that the dry gas model exaggerates the expansion characteristics of the primary nozzle by 21.95%, which predicts a Mach number of 2.00 at the nozzle exit compared to 1.64 for the wet Steam model. The dry gas model computes the static temperature lower to 196 K, whereas the wet Steam model predicts the static temperature above the triple point due to the phase change process. The liquid fraction can reach 7.2% of the total mass based on the prediction of the wet Steam model. The performance analysis indicates that the dry gas model over-estimates a higher entrainment ratio by 11.71% than the wet Steam model for the Steam ejector.

  • boundary layer of non equilibrium condensing Steam flow in a supersonic nozzle
    Applied Thermal Engineering, 2018
    Co-Authors: Chao Wang, Xiaotong Wang, Hongbing Ding
    Abstract:

    Abstract The occurrence of non-equilibrium process of Steam Condensation has a significant effect on the efficiency of low pressure part Steam turbine. To investigate the phenomenon of non-equilibrium Condensation of supersonic nozzle including several self-excited oscillating modes, a full Navier-Stokes viscous laminar model for non-equilibrium condensing Steam flow was established and validated by experiments and theory. The flow characteristics of pressure oscillation and velocity phase diagrams of different self-excited oscillating modes were analyzed. Finally, the distinct distributions of mass fluxes for both core flow field and viscous boundary layer of the condensing Steam flow were discussed further. The results showed the relative variation of the displacement thickness of throat boundary layer is up to 55.73% which is significant.

Yousef N Dabwan - One of the best experts on this subject based on the ideXlab platform.

  • design of Steam Condensation temperature for an innovative solar thermal power generation system using cascade rankine cycle and two stage accumulators
    Energy Conversion and Management, 2019
    Co-Authors: Guangtao Gao, Jingyu Cao, Gang Pei, Yousef N Dabwan
    Abstract:

    Abstract An innovative solar thermal power generation system using cascade Steam-organic Rankine cycle (SORC) and two-stage accumulators has recently been proposed. This system offers a significantly higher heat storage capacity than conventional direct Steam generation (DSG) solar power plants. The Steam Condensation temperature ( T 2 ) in the proposed system is a crucial parameter because it affects the SORC efficiency ( η SORC ) in normal operations and the power conversion of the bottoming organic Rankine cycle (ORC) in the unique heat discharge process. The present study develops a methodology for the design of T 2 with respect to a new indicator, that is, the equivalent heat-to-power efficiency ( η eq ). η eq is a compromise between the efficiencies in different operation modes. The effects of main Steam temperature ( T 1 ), Baumann factor (a), mass of storage water ( M w ), and ORC working fluid on T 2 are investigated. Results show that η eq is a better indicator than η SORC . The optimum Steam Condensation temperature ( T 2 , o p t ) that corresponds to the maximum η eq ( η eq , m a x ) is generally higher than that based on the maximum η SORC . T 2 , o p t reduces as T 1 , a, and M w decrease. η eq , m a x rises with the increment of T 1 and the decrement of a and M w . Pentane is a more preferable ORC fluid than benzene and R245fa. The T 2 , o p t and η eq , m a x of pentane are, respectively, 139–190 °C and 20.93%-24.24%, provided that T 1 ranges between 250 °C and 270 °C, a varies from 0.5 to 1.5, and M w changes from 500 ton to 1500 ton.

Moo Hwan Kim - One of the best experts on this subject based on the ideXlab platform.

  • pure Steam Condensation model with laminar film in a vertical tube
    International Journal of Multiphase Flow, 2011
    Co-Authors: Dong Eok Kim, Ki Hoon Yang, Kyung Won Hwang, Moo Hwan Kim
    Abstract:

    Abstract A new physical model for calculating the liquid film thickness and Condensation heat transfer coefficient in a vertical condenser tube is proposed by considering the effects of gravity, liquid viscosity, and vapor flow in the core region of the flow. To estimate the velocity profile in the liquid film, the liquid film was assumed to be in Couette flow forced by the interfacial velocity at the liquid–vapor interface. For simplifying the calculation procedures, the interfacial velocity was estimated by introducing an empirical power-law velocity profile. The resulting film thickness and heat transfer coefficient from the model were compared with the experimental data and the results obtained from the other Condensation models. The results demonstrated that the proposed model described the liquid film thinning effect by the vapor shear flow and predicted the Condensation heat transfer coefficient from experiments reasonably well.

  • Effect of an interfacial shear stress on Steam Condensation in the presence of a noncondensable gas in a vertical tube
    International Journal of Heat and Mass Transfer, 2008
    Co-Authors: Kwon-yeong Lee, Moo Hwan Kim
    Abstract:

    Experimental and analytical studies were performed to examine local Condensation heat transfer coefficients in the presence of a noncondensable gas inside a vertical tube. The experimental data for pure Steam and Steam/nitrogen mixture bypass modes were compared to study the effects of noncondensable nitrogen gas on annular film Condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm. The experimental results demonstrated that the local heat transfer coefficients increased as the inlet Steam flow rate increased and the inlet nitrogen mass fraction decreased. The results obtained using Steam/nitrogen mixtures with a low inlet nitrogen mass fraction were similar to those obtained using pure Steam. Therefore, the effects of noncondensable gas on Steam Condensation were weak in the small-diameter condenser tube because of interfacial shear stress. A new correlation based on dimensionless shear stress and noncondensable gas mass fraction variables was developed to evaluate the Condensation heat transfer coefficient inside a vertical tube with noncondensable gas, irrespective of the condenser tube diameter. A theoretical model using a heat and mass transfer analogy and simple models using four empirical correlations were developed and compared with the experimental data obtained under various experimental conditions. The predictions of the theoretical model and the simple model based on a new correlation were in good agreement with the experimental results.

  • experimental and empirical study of Steam Condensation heat transfer with a noncondensable gas in a small diameter vertical tube
    Nuclear Engineering and Design, 2008
    Co-Authors: Kwon-yeong Lee, Moo Hwan Kim
    Abstract:

    Abstract An experimental study was performed to investigate local Condensation heat transfer coefficients in the presence of a noncondensable gas inside a vertical tube. The data obtained from pure Steam and Steam/nitrogen mixture Condensation experiments were compared to study the effects of noncondensable nitrogen gas on the annular film Condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm (about 1/2-in.). The experimental results demonstrated that the local heat transfer coefficients increased as the inlet Steam flow rate increased and the inlet nitrogen gas mass fraction decreased. The results obtained using pure Steam and a Steam/nitrogen mixture with a low inlet nitrogen gas mass fraction were similar. Therefore, the effects of noncondensable gas on Steam Condensation were weak in small-diameter condenser tubes. A new correlation was developed to evaluate the Condensation heat transfer coefficient inside a vertical tube with noncondensable gas, irrespective of the condenser tube diameter. The new correlation proposed herein is capable of predicting heat transfer rates for tube diameters between 1/2- and 2-in. because of the unique approach of accounting for the heat transfer enhancement via an interfacial shear stress factor.

Predrag Stojan Hrnjak - One of the best experts on this subject based on the ideXlab platform.

  • numerical study of Steam Condensation inside a long inclined flattened channel
    International Journal of Heat and Mass Transfer, 2019
    Co-Authors: S Noori Rahim M A Abadi, William A Davies, Predrag Stojan Hrnjak, Josua P Meyer
    Abstract:

    This paper was a colloborative project between the University of Pretoria and the University of Illinois at Urbana-Champaign.

  • thermo hydraulic model for Steam Condensation in a large inclined flattened tube air cooled condenser
    Applied Thermal Engineering, 2019
    Co-Authors: William A Davies, Predrag Stojan Hrnjak
    Abstract:

    Abstract A thermo-hydraulic model for calculating capacity, heat transfer coefficient and void fraction of an inclined air-cooled Steam condenser is presented. The condenser tube has an elongated-slot cross-section, with inner dimensions of 214 × 16 mm. The model was developed for a 10.7 m-long tube, and validated by comparison with experiments in a 5.7 m-long tube. The model is for downward inclination angles from 0 to 90°, with co-current vapor and condensate flow. The cooling air is in cross flow. This model is developed based on existing models for inclined, stratified-flow Condensation. These have been adapted to the flattened-tube air-cooled condenser geometry and conditions. The model couples both air- and Steam-side behavior in order to accurately resolve the variations in heat transfer coefficients, temperatures, and heat flux. On the Steam side, the model is for stratified flow, and separates the flow into two sections: a falling film along the wall, and an axially-flowing condensate river along the tube bottom. The axially-flowing condensate river is modeled using open-channel-flow theory. On the air side, heat transfer coefficient is determined from a combination of empirical correlation and CFD. The model and experimental results show agreement within 5% for capacity and 20% for void fraction for all tube inclinations.

Koji Okamoto - One of the best experts on this subject based on the ideXlab platform.

  • Richardson number criteria for direct-contact-Condensation-induced thermal stratification using visualization
    Progress in Nuclear Energy, 2020
    Co-Authors: Nejdet Erkan, Koji Okamoto
    Abstract:

    Abstract This study aims to suggest a dimensionless number to determine the formation and disappearance of thermal stratification induced by direct contact Condensation in a 1/20 scaled-down suppression pool of the Fukushima Daiichi nuclear power plant. The modified Richardson number, which represents the ratio of buoyancy force to inertia of Steam, was employed to explain the thermal stratification in the suppression pool. Steam Condensation experiments were performed at both sub-atmospheric and atmospheric pressures. A blow-down pipe with an inner diameter of 12.7 mm was used to inject and condense Steam in the suppression pool. The effects of Steam mass on the thermal stratification behaviors were examined by varying the Steam mass flow rate (mass flux) from 0.50 kg/hr (1.10 kg/m2·s) to 2.50 kg/hr (5.48 kg/m2·s). The Steam Condensation was visualized using a high-speed camera. In the results, thermal stratification was successfully reproduced in this study, and it was observed that the behaviors of thermal stratification (vertical temperature profile) was affected by the Steam mass flow rate and the subcooling temperature. The Richardson number was evaluated by measuring the size and frequency of Steam bubbles. The time evolution of the Richardson number was analyzed with vertical temperature profiles of water in the suppression pool. The critical Richardson number, which determines the formation and disappearance of thermal stratification, was suggested to be of the order of 1.

  • experimental investigation into thermal stratification by direct Condensation in a scaled suppression pool of fukushima daiichi nuclear power plant
    2014 22nd International Conference on Nuclear Engineering, 2014
    Co-Authors: Shinji Takahashi, Nejde Erka, Daehu Song, Wataru Sagawa, Koji Okamoto
    Abstract:

    Experimental and numerical studies into thermal stratification by direct Steam Condensation in a torus type suppression pool were carried out to investigate the reactor core isolation cooling in the accidents of Fukushima Daiichi nuclear power plants. The suppression pool was manufactured to be a 1/22 scaled model of a Fukushima Daiichi nuclear power plant. Two different types of spargers were employed to simulate different units of the plants. In a sparger, 132 holes were uniformly drilled on the side of a pipe. However, the other sparger injected Steam to the bottom. Flow rate was varied in a wide range to examine the effect on thermal stratification in the suppression pool. The experimental results showed that the sparger type influenced formation of thermal stratification. Moreover, Steam flow rate strongly affected the onset time of thermal stratification, and the disappearance of the thermal stratification was affected by subcooling temperature. Computer simulation using a commercial software was conducted and the results show similar temperature profiles to the experimental results. Steam Condensation was visualized in a vicinity of the spargers using high speed camera.Copyright © 2014 by ASME