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Min Zeng - One of the best experts on this subject based on the ideXlab platform.
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effect of non Condensable Gas on laminar film condensation of steam in horizontal minichannels with different cross sectional shapes
International Communications in Heat and Mass Transfer, 2016Co-Authors: Yining Wu, Qiuwang Wang, Min ZengAbstract:Abstract In the present study, a 3-D numerical simulation of laminar film condensation of steam in the presence of non-Condensable Gas is performed in horizontal minichannels with six cross-sectional shapes based on the volume of fluid (VOF) method. Mixture of steam and oxygen enters the channel with uniform temperature, while the inlet volume fraction of oxygen increases from 0% to 3%. It is shown that the existence of non-Condensable Gas results in significant reduction in the mass transfer rate from vapor to liquid along the interface in the axial direction. And then the heat transfer coefficient of condensation with oxygen is demonstrated to decline sharply compared with that of the pure vapor condensation.
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numerical simulation of laminar film condensation in a horizontal minitube with and without non Condensable Gas by the vof method
Numerical Heat Transfer Part A-applications, 2015Co-Authors: Bengt Sunden, Qiuwang Wang, Min ZengAbstract:Based on the volume of fluid (VOF) method, a steady three-dimensional numerical simulation of laminar film condensation of water vapor in a horizontal minitube, with and without non-Condensable Gas, has been conducted. A user-defined function defining the phase change is interpreted and the interface temperature is correspondingly assumed to be the saturation temperature. An annular flow pattern is to be expected according to a generally accepted flow regime map. The heat-transfer coefficient increases with higher saturation temperature and a smaller temperature difference between the saturation and wall temperatures, but varies little with different mass flux and degree of superheat. The existence of a non-Condensable Gas will lead to the generation of a Gas layer between vapor and liquid, resulting in a lower mass-transfer rate near the interface and higher vapor quality at the outlet. In consequence, the heat-transfer coefficient of condensation with a non-Condensable Gas drops sharply compared with th...
Xiaobin Shen - One of the best experts on this subject based on the ideXlab platform.
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effect of evaporator tilt on a loop heat pipe with non Condensable Gas
International Journal of Heat and Mass Transfer, 2019Co-Authors: Huanfa Wang, Xiaobin ShenAbstract:Abstract The coupling effect of non-Condensable Gas (NCG) and evaporator tilts on the steady state operation of a loop heat pipe (LHP) was investigated both experimentally and theoretically in this work. Nitrogen was injected quantitatively into an ammonia-stainless steel LHP to simulate NCG, and the steady state characteristics of the LHP were studied under three typical evaporator tilts. According to the experimental results, the main conclusions below can be drawn. (1) The temperature is the highest under adverse tilt and the lowest under favorable tilt no matter whether there is NCG in LHP. (2) The existence of NCG could cause the increase of temperature under all three typical evaporator tilts, but the temperature increment caused by NCG seems to be relatively small under adverse tilt. (3) The increments of the temperature caused by NCG display different patterns under different tilts. Theoretical analysis was conducted to explain the results: the temperature under the coupling effect of NCG and evaporator tilt was determined by the energy balance between the heat leak from evaporator to compensation chamber and the cooling capacity of returning subcooled liquid. With the increase of heat load, the augmentation of heat leak caused by NCG and the enhancement of subcooled liquid cooling effect were incongruent. The coupling effect of NCG and evaporator tilts should be considered in the terrestrial application of LHP.
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Effect of evaporator tilt on the startup performance of loop heat pipe with non-Condensable Gas
CSAA IET International Conference on Aircraft Utility Systems (AUS 2018), 2018Co-Authors: Huanfa Wang, Xiaobin Shen, Rui YangAbstract:This work investigated the startup performance of a loop heat pipe (LHP) with non-Condensable Gas (NCG) under different evaporator tilt angles from −15° to 90°. The working fluid of the tested LHP was ammonia and nitrogen was injected into the LHP to simulate NCG. The main conclusions are summarized as follows: (1) When the tilt angle of evaporator was relatively small, the LHP could operate normally unless there was a large amount of NCG. The reverse flow usual occurred in the case without NCG and could be inhibited in the case with a small amount of NCG; (2) When the tilt angle was relatively large, the LHP could startup successfully with a small amount of NCG but not without NCG. (3) The LHP could not startup when the NCG inventory was large enough at all evaporator tilts.
Xiaoping Yang - One of the best experts on this subject based on the ideXlab platform.
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experimental study on the effect of non Condensable Gas dissolved in sub cooled water on steam jet condensation in a rectangular channel
International Journal of Heat and Mass Transfer, 2019Co-Authors: Pengfei Fu, Yao Zhou, Xiaoping YangAbstract:Abstract An experimental study was performed to investigate the effect of non-Condensable Gas dissolved in sub-cooled water on steam-water direct contact condensation (DCC). Non-Condensable Gas dissolved in the sub-cooled water was removed mostly by a deGassing membrane device, and the mass fraction of dissolved oxygen was reduced from 7.6 mg/L to 4.6 mg/L and 1.1 mg/L respectively by deGassing. Before and after deGassing, the flow patterns, thickness of the mixture layer, temperature and pressure distributions, as well as average volumetric heat transfer coefficient were discussed respectively. The visualization results proved that the mixture layer between the water region and steam region mainly consisted of steam, hot water and a small amount of non-Condensable Gas dissolved out from water at saturated state. Furthermore, the formation mechanism of the mixture layer was qualitatively discussed. Besides, the temperature and pressure distributions on upper and bottom wall were hardly affected by the non-Condensable Gas dissolved in sub-cooled water. Moreover, the average volumetric heat transfer coefficient was investigated before and after deGassing, and it was concluded that the dissolved non-Condensable Gas had a slight effect on the heat and mass transfer characteristic of DCC process.
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interface dynamics and pressure oscillation of stable steam jet condensation in water flow in a confined channel with the presence of non Condensable Gas
International Journal of Heat and Mass Transfer, 2017Co-Authors: Xiaoping Yang, Nana ChenAbstract:Abstract Though direct contact condensation (DCC) has been widely used in many industrial fields, the noise and vibration caused by pressure oscillation becomes an unignorable problem during the operating of related equipments. So there is an urgent need to find methods to reduce noise and vibration. In the present work, experimental study was conducted on the dynamic of steam-air mixture condensation in water flow in a confined channel, expecting to reduce the pressure oscillation intensity by means of adding a proper amount of air into steam. The experiments were tested in stable flow pattern region with steam mass flux, water Reynolds number, water temperature and air mass fraction in the range of 350–600 kg/m 2 s, 78,000–164,000, 30 °C and 0–5%, respectively. The observation and image processing of interface behavior and flow pattern transitions provides insight into the pressure oscillation mechanism with non-Condensable Gas involved. Dynamic pressures on the wall of channel were obtained. The results showed that the DCC of steam-air mixture was determined by two important factors, e.g. Gas velocity at nozzle outlet and air content. When Gas had a higher velocity, the air layer around the interface would be destroyed so that the effect of air on condensation would be weakened, but the interface was relatively stable. With air content increased to a critical value, stable flow patterns would transform into unstable due to the increase of air quantity. Moreover, the flow pattern transitions could be reflected also by the variation of pressure oscillation intensity. When air content was lower than the critical value, the gathering of air around the interface decreased the fluctuation of interface penetration length, which resulted in the dramatic decrease of pressure oscillation intensity. However, with air content increased to be higher than the critical value, stable jet would transform into unstable, leading to a rapid increase of pressure oscillation intensity. In addition, the results of various test conditions showed that the critical air mass fraction increased with the increase of steam mass flux but decreased with the increase of water Reynolds number. Furthermore, an optimal air mass fraction which could minimize the pressure oscillation intensity under various test conditions was suggested.
Ali Alshehri - One of the best experts on this subject based on the ideXlab platform.
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numerical modeling of vapor condensation over a wide range of non Condensable Gas concentrations
International Journal of Heat and Mass Transfer, 2020Co-Authors: Ali Alshehri, Sahar Andalib, Pirouz H KavehpourAbstract:Abstract This paper presents a numerical model to study the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of Non-Condensable Gases (NCG). State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed a striking agreement between the two solutions at different NCG mass fractions (0.5%–10%) and subcooling degrees (5∘F–40∘F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient.
Ping Cheng - One of the best experts on this subject based on the ideXlab platform.
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3d lattice boltzmann investigation of nucleation sites and dropwise to filmwise transition in the presence of a non Condensable Gas on a biomimetic surface
International Journal of Heat and Mass Transfer, 2019Co-Authors: Ping ChengAbstract:Abstract Condensation in the presence of non-Condensable Gas on a biomimetic pillared subcooled surface with hybrid wettability (with hydrophilic top and hydrophobic side and bottom) is investigated using a newly developed 3D multi-component multiphase lattice Boltzmann model. Three preferred nucleation sites with different surface wettability contrasts are found: (i) at the corner of side and bottom hydrophobic surface; (ii) at the center of the bottom hydrophobic surface, and (iii) on the top hydrophilic surface of the pillar. Influencing factors, such as pillar geometrical parameters, subcooling degree and non-Condensable Gas concentration, on dropwise-to-filmwise condensation transition are examined. For dropwise condensation on a top hydrophilic pillar surface, the droplet undergoes a two-stage growth pattern from “changing contact line” to “constant contact line”. Non-Condensable Gas is found to aggregate near the condensing interface in the vapor phase and at corners of pillar side surface and bottom surface. Increasing pillar width or pillar height (with other geometric parameters remained unchanged), as well as decreasing degree of wall subcooling or non-Condensable Gas concentration, can delay transition from dropwise to filmwise condensation.
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lattice boltzmann simulation of forced condensation flow on a horizontal cold surface in the presence of a non Condensable Gas
International Journal of Heat and Mass Transfer, 2017Co-Authors: Chaoyang Zhang, Ping Cheng, W J MinkowyczAbstract:Abstract A multi-component/multi-phase (MCMP) lattice Boltzmann method (LBM) with vapor/liquid phase change is proposed in this paper. Two equations of state (EOS) including Peng-Robinson (PR) EOS for water and ideal Gas EOS for the non-Condensable Gas (NCG) are applied in the thermal equation. Based on this newly developed MCMP phase-change LB model, the problem of forced condensing flow on a horizontal cold plate at constant wall temperature in the presence of NCG is simulated. Effects of the NCG inlet fraction and plate subcooled temperature on forced film condensation under the same inlet velocity are simulated. Condensate film thickness, distributions of velocity/temperature/NCG fraction in the entire flow field, as well as condensation heat transfer on the cold plate are obtained numerically. The effect of an interfacial parameter (containing inlet NCG fraction and wall temperature) on film thickness is shown in good agreement with an existing analytical model, which validates the correctness and accuracy of this newly developed MCMP phase-change LB model. Since this novel model does not involve any approximations/assumptions nor the use of empirical correlations for interfacial mass transfer, the results can be considered as the first attempt in the direct numerical simulation of laminar forced condensation heat transfer on a horizontal cold plate in the presence of a NCG.