• Journal of Mechanical Science and Technology
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• v.16 no.11
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• pp.1511-1521
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• 2002

High-speed moist air or steam flow has long been of important subject in engineering and industrial applications. Of many complicated gas dynamics problems involved in moist air flows, the most challenging task is to understand the nonequilibrium condensation phenomenon when the moist air rapidly expands through a flow device. Many theoretical and experimental studies using supersonic wind tunnels have devoted to the understanding of the nonequilibrium condensation flow physics so far. However, the nonequilibrium condensation can be also generated in the subsonic flows induced by the unsteady expansion waves in shock tube. The major flow physics of the nonequilibrium condensation in this application may be different from those obtained in the supersonic wind tunnels. In the current study, the nonequilibrium condensation phenomenon caused by the unsteady expansion waves in a shock tube is analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which are fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme is applied to solve the governing equation systems. The computational results are compared with the previous experimental data. The time-dependent behavior of nonequilibrium condensation of moist air in shock tube is investigated in details. The results show that the major characteristics of the nonequilibrium condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.3980-3990
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• 1996

When a moist air is rapidly expanded in a supersonic nozzle, nonequilibrium condensation occurs at a supersaturation state. Condensation shock wave appears in the nozzle flow if the releasing latent heat due to condensation goes beyond a critical value. It has been known that self-excited oscillations of the condensation shock wave generate in an air or a steam nozzle flow with a large humidity. In the present study, the passive control technique using porous wall with a cavity underneath was applied to the condensation shock wave. The effects of the passive control on the steady and self-excited condensation shock waves were experimentally investigated by Schlieren visualization and static pressure measurements. The result shows that the present passive control is a useful technique to suppress the self-excited oscillations of condensation shock wave.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.7
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• pp.951-958
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• 2002

Rapid expansion of a moist air or a stream through a supersonic nozzle often leads to non-equilibrium condensation shock wave, causing a considerable energy loss in flow field. Depending on amount of latent heat released due to non-equilibrium condensation, the flow is highly unstable or a periodical oscillation accompanying the condensation shock wave in the nozzle. The unsteadiness of the condensation shock wave is always associated with several kinds of instabilities as well as noise and vibration of flow devices. In the current study, a passive control technique using a porous wall with a plenum cavity underneath is applied for the purpose of alleviation of the condensation shock oscillations in a transonic nozzle. A droplet growth equation is coupled with two-dimensional Navier-Stokes equation system. Computations are carried out using a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. An experiment using an indraft wind tunnel is made to validate the present computational results. The results show that the oscillations of the condensation shock wave are completely suppressed by the current passive control method.

• Nuclear Engineering and Technology
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• v.47 no.5
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• pp.567-578
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• 2015

In a nuclear reactor containment, wall condensation forms with noncondensable gases and their accumulation near the condensate film leads to a significant reduction in heat transfer. In the framework of nuclear reactor safety, the film condensation in the presence of noncondensable gases is of high relevance with regards to safety concerns as it is closely associated with peak pressure predictions for containment integrity and the performance of components installed for containment cooling in accident conditions. In the present study, CUPID code, which has been developed by KAERI for the analysis of transient two-phase flows in nuclear reactor components, is improved for simulating film condensation in the presence of noncondensable gases. In order to evaluate the condensate heat transfer accurately in a large system using the two-fluid model, a mass diffusion model, a liquid film model, and a wall film condensation model were implemented into CUPID. For the condensation simulation, a wall function approach with a heat/mass transfer analogy was applied in order to save computational time without considerable refinement for the boundary layer. This paper presents the implemented wall film condensation model, and then introduces the simulation result using the improved CUPID for a conceptual condensation problem in a large system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.2
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• pp.82-88
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• 2017

There are main issues of defect type that condensation, concrete crack and noise in apartment buildings. Especially, according to the Apartment Defect Dispute Mediation Committee in Korea (ADDMC) at Ministry of Land Infrastructure and Transport in Korea (MLIT), condensation defects are great importance (14 percent) on whole number of reported cases of faults from 2015 in Korea. Most condensation defects have many different causes that take a toll on the resident's life and space. So it is very important to early detection and repair. For preventing the condensation in apartment buildings, there are building codes in Korea such as 'Standard of Method and Judgment for Apartment defect of investigation, Repair cost Estimate'. This research aims to study on the improvement of preventing the condensation aforementioned korea standard. Types and characteristics (opaque wall, windows, doors) of cause of occurrence and existing state condensation defect is analyzed from evaluation of real application 100 case in 2015 ADDMC data.

• Nuclear Engineering and Technology
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• v.55 no.2
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• pp.780-791
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• 2023

To study oscillation characteristic of steam and non-condensable gas direct contact condensation through multi-hole sparger at low mass flux, a series of experiments of pure steam and mixture gas condensation have been carried out under the conditions of steam mass flux of 20-120kg/m²s, water temperature of 20-95 ℃ and mass fraction of non-condensable gas of 0-5%. The regime map of pure steam condensation through multi-hole sparger is divided into steam chugging, separated bubble, aggregated bubble and escaping aggregated bubble. The bubbles behavior of synchronization in the same hole columns and desynchronized excitation between different hole columns can be found. The coalescence effect of mixture bubbles increases with water temperature and non-condensable gas content increasing. Pressure oscillation intensity of pure steam condensation first increases and then decreases with water temperature increasing, and increases with steam mass flux increasing. Pressure oscillation intensity of mixture gas condensation decreases with water temperature and non-condensable gas content increasing, which is significantly weaker than that of pure steam condensation. The oscillation dominant frequency decreases with the rise of water temperature and non-condensable gas content. The correlations for oscillation intensity and dominant frequency respectively are developed in pure steam and mixture gas condensation at low mass flux.

• Journal of IKEEE
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• v.22 no.3
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• pp.645-650
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• 2018

IT-based automatic controller that control the temperature and humidity to prevent dew condensation of distributing board was designed and implemented in this paper. The dew condensation temperature was deduced from room temperature and humidity of distributing board. Based on the comparisons between the deduced dew condensation temperature and the temperature of surface condensation, the facilities that can prevent the condensation was implemented to be operated in due order. Also, the remote monitoring module to monitor operation status of controller was implemented using LoRa technique. The performances for controller operation and data transmission were validated from the transmission and operation test for dew condensation prevention. The controller can be put to good use at the facilities that requires the condensation prevention.

• Journal of Adhesion and Interface
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• v.6 no.1
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• pp.7-10
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• 2005

Condensation control of nano-particles has become important in order to fabricate minute condensed structures. In this study, we focus our attention on condensation mechanism of polymer aggregates in a resist film. The polymer aggregate is structural component of a resist material which is used in lithography process. The condensation nature of polymer aggregates in the resist film surface is observed by using atomic force microscope (AFM). By using the AFM, the condensation of polymer aggregates can be observed clearly. The condensation of polymer aggregate strongly affects to precise fabrication of resist pattern below 100nm size. The interaction force among polymer aggregates can be analyzed based on Derjaguin approximation. We also discuss about condensation nature of polymer aggregates in the resist film surface with the help of micro sphere model.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.9 no.4
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• pp.15-24
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• 2013

On this Thesis, We conduct a research of curtain wall high-rise apartment located in Songdo for preparing a simple method to check possibility of condensation on each part of curtain wall using only indoor temperature, humidity and outdoor temperature. According to CFD analysis result, condensation occurred if indoor environment did not ventilated. On the other hand, in case of ventilation on indoor environment, condensation did not appear; so I could find ventilation prevent surface condensation on inside surface of curtain wall. Moreover, when temperature of the floor is higher, condensation is decrease more than lower floor temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.12
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• pp.621-627
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• 2017

Nitrogen ion with various levels of dose and irradiation energy was irradiated on aluminum surfaces. Contact angle of surface was increased and surface color was changed by nitrogen ion implantation. During steam condensation experiment using nitrogen ion implanted specimen, dropwise condensation initially occurred on specimens. However, condensation mode eventually changed into filmwise condensation. The color of the surface was also changed from yellow-brown to silver-white. This change of surface color and condensation mode were results of hydrolysis reaction between condensate and nitrogen ion implanted on aluminum surfaces.