Condensation mode transition and condensation heat transfer performance variations of nitrogen ion-implanted aluminum surfaces

Kim, Kiwook,Jeong, Ji Hwan Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.125 No.-

<P><B>Abstract</B></P> <P>Aluminum substrate specimens are irradiated with nitrogen ions at various ion dose and ion energy levels in order to realize dropwise condensation on the specimen surfaces. Dropwise steam condensation initially occurs on these specimens, but the condensation mode changes into filmwise condensation. When the condensation mode changes to filmwise condensation, the heat transfer coefficient is measured to be approximately 40% lower than that predicted using the Nusselt theory; in addition, the color of the surface changes from yellow-brown to silver-white. This surface color change is the result of the hydrolysis reaction between the condensate and the nitrogen ion-implanted aluminum surface. Non-condensable gas is generated by the hydrolysis reaction, and this non-condensable gas diminishes the heat transfer coefficient. In addition, the material composition of the specimen’s surface changes and causes the transition of the condensation mode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nitrogen ions are irradiated on aluminum substrates. </LI> <LI> Dropwise condensation initially occurs but change into film condensation soon. </LI> <LI> Hydrolysis reaction produces non-condensable ammonia gas. </LI> </UL> </P>

Condensation oscillation characteristic of steam with non-condensable gas through multi-hole sparger at low mass flux

Zhang Dandi,Tong Lili,Cao Xuewu 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.2

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 20e120kg/m2s, water temperature of 20e95 C and mass fraction of non-condensable gas of 0e5%. 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.

Steam Condensation Enhancement by Applying Self-Assembled Monolayer (Chlorosilane) on Titanium Corrugated Tubes

NAE-HYUN KIM,한호승 대한설비공학회 2019 International Journal of Air-Conditioning and Refr Vol.27 No.1

It is well known that dropwise condensation enhances the condensation heat transfer coefficient significantly compared with film condensation. In the present study, dropwise condensation heat transfer characteristics on titanium corrugated tubes were investigated. Two corrugated tubes with different corrugation pitch and depth were tested at the steam pressures of 5 and 10 kPa. To promote dropwise condensation, silane-based SAM was coated. For bare corrugated tubes, significant enhancement of condensation heat transfer was noted, especially for the 2.1/0.2 (corrugation pitch/corrugation depth in mm) tube. For SAM-coated tubes, the heat transfer enhancement was significant (2.61 at 5 kPa and 2.45 at 10 kPa) for the smooth tube. For the corrugated tubes, however, the enhancement decreased to 1.78 and 2.22 for 8.7/0.4 tube and to 1.26 and 1.52 for 2.1/0.2 tube. The present results suggest that corrugations may not be as an effective heat transfer method for dropwise condensation as it is for film condensation. This result was supported by the photos taken by mist spray, which suggested that surface tension drained condensation by corrugations is not a major heat transfer mechanism for dropwise condensation on corrugated tubes.

실내수영장 공조관리 요인이 시설물 결로원인과 예방에 미치는 영향

성하동 대한안전경영과학회 2018 대한안전경영과학회지 Vol.20 No.2

This study is empirically intended to look into the effects of HVAC management on condensation cause and prevention in indoor swimming pools. The findings are summarized as follows. First, the experience of condensation in indoor swimming pools showed that 132 out of 142 people in total experienced the condensation in indoor swimming pools, which they had a high experience rate of 92.3%. For the location of condensation, the wall joints were 46.8% and the windows were 34.5%, which a total of 72.3% occurred in the wall joints and windows. Second, the effect of construction design, HVAC management and building construction on the cause of condensation in indoor swimming pools showed that building construction had an effect on the cause and location of condensation depending on the seasonal time, partially adopting hypothesis 1. Third, the effect of condensation-causing factors on condensation-preventing factors in indoor swimming pools showed that condensation had a close relationship with air and temperature conditions depending on the time and location of condensation, adopting hypothesis 2. As for the above-stated findings, the HVAC management in indoor swimming pools is an important concern factor that continues to cause condensation despite the development of advanced construction materials. Especially, building construction is a main factor that has a direct effect on condensation in the HVAC management of facilities. This implies that the window management is important in maintaining the wall joints - which can suppress the selective use and defect occurrence of construction materials - or confined spaces for a long time.

Experimental study on the condensation of sonic steam in the underwater environment

Zhaoming Meng,Wei Zhang,Jiazhi Liu,Ruihao Yan,Geyu Shen 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.4

Steam jet condensation is of great importance to pressure suppression containment and automaticdepressurization system in nuclear power plant. In this paper, the condensation processes of sonic steamjet in a quiescent subcooled pool are recorded and analyzed, more precise understanding are got in directcontact condensation. Experiments are conducted at atmospheric pressure, and the steam is injected intothe subcooled water pool through a vertical nozzle with the inner diameter of 10 mm, water temperaturein the range of 25e60 C and mass velocity in the range of 320e1080 kg/m2s. Richardson number iscalculated based on the conservation of momentum for single water jet and its values are in the range of0.16e2.67. There is no thermal stratification observed in the water pool. Four condensation regimes areobserved, including condensation oscillation, contraction, expansion-contraction and double expansioncontractionshapes. A condensation regime map is present based on steam mass velocity and watertemperature. The dimensionless steam plume length increase with the increase of steam mass velocityand water temperature, and its values are in the range of 1.4e9.0. Condensation heat transfer coefficientdecreases with the increase of steam mass velocity and water temperature, and its values are in the rangeof 1.44e3.65 MW/m2 C. New more accurate semi-empirical correlations for prediction of the dimensionlesssteam plume length and condensation heat transfer coefficient are proposed respectively. Thediscrepancy of predicted plume length is within ± 10% for present experimental results and ± 25% forprevious researchers. The discrepancy of predicted condensation heat transfer coefficient is with ± 12%.

내부결로 평가방법에 따른 총 함습량 비교

김경수(Kim, Kyung-Soo),장향인(Jang, Hyang-In),박창영(Park, Chang-Young),유동철(Yoo, Dong-Chul),최창호(Choi, Chang-Ho) 한국건축친환경설비학회 2017 한국건축친환경설비학회 논문집 Vol.11 No.6

Although the domestic condensation standards are set forth in the “Standards for Preventing Condensation in Multi-Residential Houses” stipulated by the Ministry of Land, Infrastructure and Transport, they are interpretation on surface condensation acquired by using the method evaluating the dew point temperature, and cannot be applied to the interpretation of interstitial condensation. As such, this study aims to contemplate foreign interstitial condensation evaluation methods and conducts comparative analysis according to the interstitial condensation evaluation factors. After the interpretation model is set, the comparison through the performance evaluation following the evaluation standards are conducted based on the interpretation factors contemplated in the previous stage. Thus, this study intends to contribute to the improvement of the standards for the domestic interstitial condensation evaluation. The study results are as follows. (1) Even though ISO 13788 and EN 15026 predict the condensation based on the humidity transfer, ISO 13788 cannot respond to complex external environments. Hence, EN 15026 of the condensation calculation method is more precise than the ISO 13788. (2) Results of the performance evaluation suggested that in the case (Interstitial Surface 1) of Solid Brick Masonry and Interior Plaster, the risk of condensation of ISO 13788 and EN 15026 are 40.2% and 24.0%, respectively, and it is analyzed that complex climate factors and water transfer (capillary phenomenon) are reasons for such difference. (3) Results of the performance evaluation indicated that in the case (Interstitial Surface 2) of EPS and Interior Plaster, the risk of condensation of ISO 13788 and EN 15026 are 20.8% and 0%. Accordingly, it is viewed that the evaluation method considering water transfer (capillary phenomenon) and complex climate factors should be added to the domestic condensation standards.

고밀도 데이터센터의 층간 슬래브 결로발생 평가사례에 대한 연구

조진균(Cho Jin-Kyun),박상현(Park Sang-Hyun) 대한건축학회 2011 대한건축학회논문집 Vol.27 No.9

Recently, the condensation of floor slab often occurring in data centers is an important problem because IT equipments are particularly sensitive to high humidity levels. This work aims to study the indoor environment conditions favourable for surface condensation of high-density data centers. The risk for occurrence of surface condensation depends mainly on the surface energy balance and on the moisture content of the ambient air. This paper describes an evaluation tool for assessing condensation risk and the effect of remedial measures, and presents a method to solve these problems by using IES4D VE energy model. This measure of condensation risk is calculated for two zones (between IT server rooms and office areas) from air temperatures, moisture generation and ventilation rates. Because of different environment conditions and air conditioning period of time, the risk of surface condensation between two zones will be high. We analyzed insulation factors and cooling conditions of IT server room, and predicted the change of indoor temperature to find the cause of the condensation state. The results show that the application of floor slab insulation can substantially increase the lowest inside surface temperature, temperature difference ratio and inside air humidity for preventing surface condensation.

전열교환 환기장치의 급배기 풍량비에 따른 결로방지 방안의 제안

김동석,김종원,이정재 대한건축학회지회연합회 2017 대한건축학회연합논문집 Vol.19 No.6

The element core which is really conduct heat exchange is a important component of the heat recovery ventilation system. When it is polluted and destroyed by condensation, polluted air is flowing into indoor and heat exchange rate is decrease. But the element core was not included in condensation detected range. This study was conducted to examine the applicability of condensation prevention according to the supply & exhaust air flow ratio control without additory equipment configuration. Experiments was conducted to the supply & exhaust air flow ratio 1.0:1.0 to 1.0:2.5 in winter outside temperature(-6.0℃ to -15.0℃) and condensation of the element core was judged with the hydrochromic detection sheet. The hydrochromic detection sheet was made by the hydrochromic ink which is changed the color when it contact water, the hydrochromic detection sheet could detect condensation in the element core which could be not detect by naked eyes. As a result, as the supply & exhaust air flow ratio increased, the condensation decreased. The lower outside temperature, the larger the supply & exhaust air flow ratio which was required to prevent condensation. In order to raise applicability of the supply & exhaust air flow ratio control, the study configured exhaust air temperature(the minimum exhaust air temperature 2.5℃ when condensation was not occured) as control criterion and established a control algorithm. Because heat exchange rate and condensation occur condition are changed according to the material and form of element core, In order to generalization of this algorithm, It is necessary to classify element core by property and conduct various experiments.

Boundary layer measurements for validating CFD condensation model and analysis based on heat and mass transfer analogy in laminar flow condition

Soma Shu,Ishigaki Masahiro,Abe Satoshi,Sibamoto Yasuteru 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.7

When analyzing containment thermal-hydraulics, computational fluid dynamics (CFD) is a powerful tool because multi-dimensional and local analysis is required for some accident scenarios. According to the previous study, neglecting steam bulk condensation in the CFD analysis leads to a significant error in boundary layer profiles. Validating the condensation model requires the experimental data near the condensing surface, however, available boundary layer data is quite limited. It is also important to confirm whether the heat and mass transfer analogy (HMTA) is still valid in the presence of bulk condensation. In this study, the boundary layer measurements on the vertical condensing surface in the presence of air were performed with the rectangular channel facility WINCS, which was designed to measure the velocity, temperature, and concentration boundary layers. We set the laminar flow condition and varied the Richardson number (1.0–23) and the steam volume fraction (0.35–0.57). The experimental results were used to validate CFD analysis and HMTA models. For the former, we implemented a bulk condensation model assuming local thermal equilibrium into the CFD code and confirmed its validity. For the latter, we validated the HMTA-based correlations, confirming that the mixed convection correlation reasonably predicted the sum of wall and bulk condensation rates.

동절기 발코니 창호 표면의 결로 발생 예측을 위한 가상센서 가능성 검토

김승빈(Kim, Seung-Bin),손유라(Son, Yu-Ra),양정훈(Yang, Jeong-Hoon) 대한건축학회 2024 대한건축학회논문집 Vol.40 No.3

Persistent condensation in residential spaces can lead to structural damage and mold growth, posing health risks to occupants. While existing studies focus on reducing condensation, theres a gap in research on condensation prediction. This study aims to explore the feasibility of a virtual sensor for condensation prediction using machine learning and data from prior studies. A high-accuracy virtual sensor model was developed and verified using condensation measurement data. Data preprocessing and Pearson correlation analysis were conducted, and input variables were selected through ReliefF evaluation. Indoor and outdoor temperature and humidity were chosen as final input variables. A prediction model was crafted using classification learning algorithms: Decision Tree(DT), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP). Validation of the prediction model was performed using Confusion matrix, Accuracy, and F-1 score. The accuracy of the virtual sensor model was 97.1% for Decision Tree, 98.5% for SVM, and 98.6% for MLP. The developed model is expected to effectively prevent condensation in residential spaces susceptible to surface condensation. Future work will focus on integrating virtual sensors into existing ventilation and air conditioning systems for practical application in residential spaces.