• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.5
• /
• pp.27-34
• /
• 2018

Recently, liquid desiccant systems have received attention for the dehumidification of air. LiCl and LiBr are widely used in liquid desiccant systems due to their excellent thermo-physical properties. In this study, dehumidification tests were conducted with Celdek elements using LiCl and LiBr. During the tests, the dry and wet-bulb air temperatures were maintained at $35^{\circ}C$ and $28^{\circ}C$, respectively. The solution temperature was $20^{\circ}C$, the solution concentration was 50%, the solution circulation rate was 50 kg/h, and the frontal air velocity was varied from 2.0 to 4.0 m/s. The results show that the amount of dehumidification increased as the frontal velocity increased. On average, LiCl showed 27% higher dehumidification performance than LiBr, which was probably due to the lower saturation of the absolute humidity of LiCl compared with that of LiBr. On the other hand, LiBr yielded 12% larger pressure drop than LiCl. In general, the Sherwood numbers of LiCl and LiBr were approximately the same, showing that the effect of the desiccant on the Sherwood number was insignificant. Existing correlations highly overpredicted the present Sherwood numbers.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.18 no.1
• /
• pp.702-708
• /
• 2017

The heat generation rate in a telecommunications cabinet keeps increasing due to the increased usage of mobile devices. Insufficient removal of the heat increases the cabinet temperature, which results in the malfunction of the electronic devices. In this study, tests were conducted on aluminum and plastic heat exchangers for cooling a telecommunications cabinet, and the results were compared with theoretical predictions. The aluminum heat exchanger comprised counter flow parallel channels with 4.5-mm pitch, and the plastic heat exchangers comprised cross or cross-counter flow triangular channels with 2.0-mm pitch. The volume of the cross flow heat exchanger was the same as that of the aluminum heat exchanger, and the volume of the cross-counter heat exchanger was 33% larger than that of the aluminum heat exchanger. The results show that the heat transfer rate is the highest for the cross-counter heat exchanger and lowest for the aluminum one. The temperature efficiency of the cross-counter heat exchanger was 56% higher than that of the aluminum one and 20% higher than that of the cross flow heat exchanger. The pressure drop of the cross-counter heat exchanger was approximately the same as that of the aluminum one. The heat exchange efficiency was the highest for the cross-counter heat exchanger and lowest for the cross flow heat exchanger. The theoretical analysis somewhat overestimated or underestimated the data.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.7
• /
• pp.734-739
• /
• 2016

The globe valve is a linear motion valve that is designed primarily to stop, start, and regulate flow. The disk of a globe valve can be removed totally from the flow path or it can completely close the flow path. In this study, numerical analysis using ANSYS-CFX was initially performed to predict the flow coefficient and build a prototype model of a globe valve. The flow coefficient is the volume of water at $15.6^{\circ}C$ that will flow per minute through a valve with a pressure drop of 1 psi across the valve. In other words, it is an important factor for determining the size of the valve. From the analysis results, the fluid flux of water and flow coefficient of the valve were extracted. From the numerical results, a prototype of ultra-fine precision control valve, which can regulate the fluid flow of range 0 ~ 0.1 gal per min, was developed. The experimental results were compared with the numerical results using the flow coefficient ($C_v$) graph. From the comparative results, the flow coefficient ($C_v$) error percentage between the numerical and experimental results was very low, which is acceptable, proving that the proposed prototype model is convincing. In addition, it is possible to predict the flow coefficient using only numerical analysis.

• Journal of Welding and Joining
• /
• v.15 no.1
• /
• pp.92-100
• /
• 1997

Weld repair of ASTM A-470 class 8 high pressure (HP) steam turbine rotor steel has been performed to extend the service life of older fossil units. Microhardness measurements were conducted across the weldment from unaffected base metal (BM) to weld metal (WM). The hardness of the BM was VHN 253, however it dropped up to VHN 227 at the heat affected zone (HAZ) close to unaffected BM for multipass SAW. This area of hardness drop is called "siftening zone" and has a width of 0.5-0.6mm. During creep rupture test, failure occurred around the softening zone and rupture time was 772.4hr at 19Ksi (132 Mpa) and 593.deg. C. Multipass MIG and TIG welding have been employed to reduce the softening zone width. The softening zone width for MIG was 0.3-0.4mm and for TIG was zero-0.4mm depending on heat inputs. However creep rupture time was decreased as softening zone width reduced. Creep rupture time also showed a close relationship with heat inputs in TIG process. The higher heat input, the longer rupture time. Most failure occurred at intercritical HAZ (ICHAZ), however rupture location was shifted to coarse grained HAZ (CGHAZ) as heat input decreased. The rupture surface showed tearing and dimple which indicated transgranular fracture. fracture.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.6
• /
• pp.757-764
• /
• 2019

Depressurization occurs around underwater objects moving at high speeds. This causes cavitation nuclei to expand, resulting in cavitation. Cavitation is accompanied by an increase in noise and vibration at the site, particularly in the case of thrusters, and this has a detrimental ef ect on propulsion performance. Therefore, predicting cavitation is necessary. In this study, an analytical method for cavitation noise is developed and applied to an elliptic wing. First, computational fluid dynamics are performed to obtain information about the flow fields around the wing. Then, through the cavitation nuclei density function, number of cavitation nuclei is calculated using the initial radius of the nuclei and nuclei are randomly placed in the upstream with large pressure drop around the wing tip. Bubble dynamics are then applied to each nucleus using a Lagrangian approach for noise analysis and to determine cavitation behavior. Cavitation noise is identified as having the characteristics of broadband noise. Verification of analytical method is performed by comparing experimental results derived from the large cavitation tunnel at the Korea Research Institute of Ships & Ocean Engineering.

• Nuclear Engineering and Technology
• /
• v.52 no.7
• /
• pp.1386-1395
• /
• 2020

High fidelity nuclear reactor fuel assembly simulation using CFD method is an effective way for the structure design and optimization. The validated models and user practice guidelines play critical roles in achieving reliable results in CFD simulations. In this paper, the international benchmark MATiS-H is studied carefully and the best user practice guideline is achieved for the rod bundles simulation. Then a 5 × 5 rod bundles model in the advanced pressurized water reactor (PWR) is established and the detailed three-dimensional thermal-hydraulic characteristics are investigated. The influence of spacer grids and mixing vanes on the flow and hear transfer in rod bundles is revealed. As the coolant flows through the spacer grids and mixing vanes in the rod bundles, the drastic lateral flow would be induced and the pressure drop increases significantly. In addition, the heat transfer is enhanced remarkably due to the strong mixing effects. The calculation results could provide meaningful guidelines for the design of advanced PWR fuel assembly.

• Korean Chemical Engineering Research
• /
• v.43 no.4
• /
• pp.452-457
• /
• 2005

Foam-type MFI zeolite catalyst was prepared by dispersing fine ($-0.2{\mu}m$) particles of MFI zeolite on silicalite foam. Catalytic cracking of n-octane was investigated over the foam-type catalyst and Delplot method was employed to interpret product compositions for deducing reaction mechanism. The Si/Al molar ratio of dispersed MFI zeolite was estimated 25 and its dispersed amount of silicalite foam was 25 wt％. Since the apparent density of the foam type catalyst was very low $0.11g{\cdot}cm^{-3}$, the catalyst loading amount could be varied from 0.02 g to 0.5 g without concerning pressure drop, providing a wide variance in the residence time of the reactants and products. The conversion and olefin yield in the catalytic cracking of n-octane increased with the catalyst loading. The product composition was very simple and could be explained by applying the protolytic cracking mechanism when the catalyst loading was small. Higher loading of the catalyst brought about further reactions of cracked products, accumulating lower olefin and paraffin with low reactivity in product stream and resulting in complex product composition.

• KSBB Journal
• /
• v.16 no.6
• /
• pp.603-608
• /
• 2001

In this study, we studied on the remeval of toluene vapors in a lab-scale biofilter. Biofiltration was performed in a column fed downflow with contaminated air at ambient conditions. The column was packed with mixture of Peat and Calstene(5:3 vol. Ratio), Synthesized media, Bark and Wood chip, which were inoculated with microbial population of selected stains(Pseudomonas. putida, KCCM 11343, ATCC 12633). The microorganisms were immobilized on the bed medium and then biofilm were formed. The biofilter was operated under the conditions of various inlet toluene concentrations for 180 days and treated up to the elimination capacity of maximum 40 g/㎥hr at the inlet load of 30 g/㎥ hr with percentage removals of 20∼90% and gas retention times between 1 and 2 min. The pressure drop was very negligible through the biofilter columps because its value of 0.054 cmH$_2$O/m was much less than others. The effect of operating conditions such as flow rate, inlet toluene concentration and moisture contents on the performance of the biofilter was sequentially investigated in this study.

• Applied Chemistry for Engineering
• /
• v.24 no.4
• /
• pp.433-437
• /
• 2013

Electrical discharge plasma created in a multi-channel porous ceramic membrane-supported catalyst was applied to the decomposition of a volatile organic compound (VOC). For the purpose of improving the oxidation capability, the ceramic membrane used as a low-pressure drop catalyst support was loaded with zinc oxide photocatalyst by the incipient wetness impregnation method. Alternating current-driven discharge plasma was created inside the porous ceramic membrane to produce reactive species such as radicals, ozone, ions and excited molecules available for the decomposition of VOC. As the voltage supplied to the reactor increased, the plasma discharge gradually propagated in the radial direction, creating an uniform plasma in the entire ceramic membrane above a certain voltage. Ethylene was used as a model VOC. The ethylene decomposition efficiency was examined with experimental variables such as the specific energy density, inlet ethylene concentration and zinc oxide loading. When compared at the identical energy density, the decomposition efficiency obtained with the zinc oxide-loaded ceramic membrane was substantially higher than that of the bare membrane case. Both nitrogen and oxygen played an important role in initiating the decomposition of ethylene. The rate of the decomposition is governed by the quantity of reactive species generated by the plasma, and a strong dependence of the decomposition efficiency on the initial concentration was observed.

• Applied Chemistry for Engineering
• /
• v.29 no.4
• /
• pp.382-387
• /
• 2018

In this study, the reaction characteristics of combined steam and carbon dioxide reforming of methane (CSCRM) reaction using Pd-Ni-YSZ catalyst were investigated according to types of catalysts and gas compositions. Catalysts were prepared in the form of powder and porous disk. The injected gases were supplied at different ratios of $CH_4/CO_2/H_2O$. As a result, the conversion of $CH_4$ and $CO_2$ was improved as a result of using the porous disc type catalyst as compared with that of the powder type catalyst. When the $CH_4/CO_2/H_2O$ ratio of the feed gas was 1 : 0.5 : 0.5, the $H_2/CO$ ratio was adjusted close to 2. However, after 6 hours of the reaction, $CH_4$ conversion was partially reduced by the carbon deposition and the pressure drop increased from 0.1 to 0.8. This issue was then solved by optimizing the water content. As a result, it was confirmed that the durability was secured by preventing the carbon deposition when the gas was supplied at a $CH_4/CO_2/H_2O$ ratio of 1 : 0.5 : 1, and the conversion rate was maintained at a relatively high level.