• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.6
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• pp.635-642
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• 2010

Experimental investigations have been carried out to examine the evaporative heat transfer characteristics of R-134a with the channel-bending angle (CBA) in microchannel heat exchangers. In this study, we examined the effects of evaporation temperature and Reynolds number of R-134a on the evaporative heat transfer characteristics of R-134a in microchannel heat exchangers with CBAs of $120^{\circ}$, $150^{\circ}$, and $180^{\circ}$ under counterflow conditions. Experimental results show that the evaporative heat transfer rate and evaporative heat transfer coefficient increased with an increase in the Reynolds number of R-134a. Further, the evaporative heat transfer rate corresponding to CBAs of $120^{\circ}$ and $150^{\circ}$ increased to values greater than the evaporative heat transfer rate corresponding to $180^{\circ}$ by approximately 17.1% and 13.3%, respectively, for evaporating temperatures in the range $4.9-14.9^{\circ}C$. The evaporative heat transfer coefficient was affected by the channel angle with increasing evaporative heat transfer coefficient at small channel bending angle.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.2
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• pp.76-83
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• 2022

Since the 3D printing mortar is exposed to the atmosphere immediately after printing, moisture is largely evaporated from the surface of the layer. The evaporation of moisture on the surface of the layer greatly causes drying shrinkage and increases the risk of cracking and damage to the structure due to drying shrinkage. This study experimentally evaluated the shrinkage behavior of the initial age using the mortar used for 3D printing. The change in shrinkage was evaluated by comparing the shrinkage of the specimen cured by the sealing method and the atmospheric exposure method. In addition, compared with the case where type 1 cement was used 100%, the shrinkage amount was evaluated when 20% of fly ash was replaced and 10% of silica fume was used. In particular, the effect of three chemical admixtures applied using 3D printing on shrinkage was evaluated experimentally. When fly ash and silica fume were used, the shrinkage amount increased by 60 - 110% compared to the case when type 1 cement was used. The application of viscosity modifiers and shrinkage reducers reduced the shrinkage by at least 18% and at most 70% depending on the curing conditions. The temperature of the specimen temporarily decreased to 15 ℃ at the beginning of curing, and the correlation between the internal temperature of the specimen and the shrinkage behavior was observed.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.23 no.4
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• pp.393-399
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• 2005

Since vegetations are near the wavelength range in 700nm and have absorbent as well as reflective wavelength ranges, there is a much difference in terms of its reflection rate. There are currently many researches on vegetation index being conducted in order to apply the remote-sensing technology to vegetations rising their characteristics of absorbent and reflective wavelength ranges. Normalized Difference Vegetation Index (NDVI) and Perpendicular Vegetation Index (PVI) have been most commonly used. It is usually the evaporation, carbon-dioxide consumption, and chlorophyll density that represent the activity of vegetation, but chlorophyll density is the most commonly used among them. Since the red wavelength range used to obtain the NDVI and PVI has a strong extinction of chlorophyll, it is also useful to test chlorophyll density. The NDVI, in particular, is used to identify the vegetation conditions summarily, and thus, is suitable for initiative researches. Nevertheless, since these vegetation index produce mixed information of the Vegetation vigor and vegetation cover, it is essential to monitor a wavelength range that is independent from redundancy of the Vegetation vigor and vegetation cover. Although many vegetation indices have evaluated both the vegetation vigor and Vegetation cover simultaneously, this research intends to emphasize the utility of separable evaluations of the Vegetation vigor and Vegetation Cover rate through an experiment with grasses. As a result of evaluating vegetation index using spectral reflectance, a separable evaluation of the vegetation vigor and cover has been found more useful.

• International Journal of Automotive Technology
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• v.5 no.4
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• pp.221-238
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• 2004

Wall interactions of direct injection spray were investigated using laser-sheet imaging, shadowgraphy, wetted footprint and phase Doppler interferometry techniques. A narrow-cone high-pressure swirl injector is used to inject iso-octane fuel onto a plate, which has three different impact angles inside a pressurized chamber. Heated air and plate conditions were compared with unheated cases. Injection interval was also varied in the heated case to compare dry- and wet- wall impingement behaviors. High-speed macroscopic Mie-scattering images showed that presence of wall and air temperature has only minor effect on the bulk spray structure and penetration speed for the narrow-cone injector tested. The overall bulk motions of the spray plume and its spatial position at a given time are basically unaffected until a few millimeters before impacting the wall. The surface properties of the impact surface, such as the temperature, the presence of a preexisting liquid film also have a small effect on the amount of wetting or the wetted footprint; however, they have strong influence on what occurs just after impact or after a film is formed. The shadowgraph in particular shows that the plate temperature has a significant effect on vapor phase propagation. Generally, 10-20% faster horizontal vapor phase propagation is observed along the wall at elevated temperature condition. For impingement onto a preexisting film, more splash and evaporation were also observed. Contrary to some preconceptions, there is no significant splashing and droplet rebounding from surfaces that are interposed in the path of the DI gasoline spray, especially for the oblique impact angle cases. There also appears to be a dense spray front consists of large sac spray droplets in the oblique impact angle cases. The bulk of the spray is not impacted on the surface, but rather is deflected by it The microscopic details as depicted by phase Doppler measurements show that the outcome of the droplet impaction events can be significantly influenced. Only droplets at the spray front have high enough Weber numbers for wall impact to wet, splash or rebound. Using the sign of vertical velocity, the time-resolved downward droplets and upward droplets are compared. The Weber number of upward moving droplets, which seldom exceeds unity, also decreases as the impact angle decreases, as the droplets tend to impact less and move along the wall in the deflected spray plume.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.5
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• pp.491-498
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• 2010

Humidification of PEM fuel cells is necessary for enhancing their performance and lifetime. In this study, a humidification system was designed and tested; the system includes an air-supply tube (inner diameter: 75 mm) through which a nozzle can be directly inserted and a cyclonic separator for the removal of water droplets. Three types of nozzles were employed to study the influence of injection pressure, air flow rate, and spray direction on the humidification performance. To evaluate the humidification performance, the concept of humidification efficiency was defined. In the absence of an external heat source, latent heat for evaporation will be supplied by the own enthalpies of water and air. Thus, the amount of water sprayed from the nozzle is the most critical factor affecting the humidification efficiency. Water droplets were efficiently removed by a cyclonic separator, but re-entrainment occurred at high air flow rates. The absolute humidity and humidification efficiency were $21.29\;kJ/kg_{da}$ and 86.57%, respectively, under the following conditions: nozzle type PJ24; spray direction angle $90^{\circ}$; injection pressure 1200 kPa; air flow rate 6000 Nlpm.

• Analytical Science and Technology
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• v.27 no.4
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• pp.187-195
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• 2014

It is very important to minimize the damage of latent fingerprints at enhancing the contrast. This study proves the enhancement effects of cyanoacrylate-fumed latent fingerprints using p-dimethylaminobenzealdehyde (DMAB) on semi-porous surfaces and the influence factors. The latent fingerprints in experiment were developed for cyanoacrylate treatment in a vacuum chamber and used after drying at room temperature for 24 hours. For fluorescence staining, the cyanoacrylate-developed marks using DMAB were sublimated during 48 hours under the different conditions of surface area, temperature, atmospheric pressure. First experiment showed how surface area effects on the sublimation rate and fluorescence intensity by DMAB of particle size and container size. In addition, the fluorescence staining using DMAB with solvent-free contact method had the greatest fluorescence intensity after 36 hours and a low fluorescence intensity over a certain size of surface area. Second experiment showed that the evaporation of DMAB solid crystals got a satisfying result in a temperature of $20^{\circ}C$ and reduced time to get the greatest fluorescence intensity. It took a long time to get a optimum level of fluorescence intensity at $30^{\circ}C$ or more and it was less effective in fluorescence intensity. Third experiment on the pressure indicated that the fluorescence intensity of vacuum was weaker than nonvacuum but it was inapplicable to very high variations in pressure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.4
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• pp.263-273
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• 2016

The effect of recirculated exhaust gas on performance and exhaust emissions with FGR rate are investigated by using a natural circulation, pressurized draft and water tube boiler with FGR system operating at several boiler loads and over fire air damper openings. The purpose of this study is to apply the FGR system to a power plant boiler for reducing $NO_x$ emissions. To activate the combustion, the OFA with 0 to 20% is supplied into the flame. When the suction damper of two stage combustion system installed in the upper side of wind box is opened by handling the lever between $0^{\circ}$ and $90^{\circ}$, also, the combustion air supplied to burner is changed. It is found that the fuel consumption rate per evaporation rate did not show an obvious tendency to increase or decrease with rising the FGR rate, and $NO_x$ emissions at the same OFA damper opening are decreased, as FGR rates are elevated and boiler loads are dropped. While a trace amount of soot is emitted without regard to the operation conditions of boiler load, OFA damper opening and FGR rate, because soot emissions are eliminated by the electrostatic precipitator with a collecting efficiency of 86.7%.

• Journal of Wetlands Research
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• v.22 no.4
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• pp.312-320
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• 2020

Various LIDs with natural water circulation function are applied to reduce urban environmental problems and environmental impact of development projects. However, excessive Infiltration and evaporation of LID facilities dry the LID internal soil, thus reducing plant and microbial activity and reducing environmental re duction ability. The purpose of this study was to develop a real-time measurement system with complex sensors to derive the management plan of LID facilities. The test of measurable sensors and Internet of Things (IoT) application was conducted in artificial wetlands shaped in acrylic boxes. The applied sensors were intended to be built at a low cost considering the distributed LID and were based on Arduino and Raspberry Pi, which are relatively inexpensive and commercialized. In addition, the goal was to develop complex sensor measurements to analyze the current state o f LID facilities and the effects of maintenance and abnormal weather conditions. Sensors are required to measure wind direction, wind speed, rainfall, carbon dioxide, Micro-dust, temperature and humidity, acidity, and location information in real time. Data collection devices, storage server programs, and operation programs for PC and mobile devices were developed to collect, transmit and check the results of measured data from applied sensors. The measurements obtained through each sensor are passed through the Wifi module to the management server and stored on the database server in real time. Analysis of the four-month measurement result values conducted in this study confirmed the stability and applicability of ICT technology application to LID facilities. Real-time measured values are found to be able to utilize big data to evaluate the functions of LID facilities and derive maintenance measures.

• Korean Journal of Agricultural and Forest Meteorology
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• v.11 no.4
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• pp.233-246
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• 2009

The partitioning of evapotranspiration (ET) into evaporation (E) and transpiration (T) is critical in understanding the water cycle and the couplings between the cycles of energy, water, and carbon. In forests, the total ET measured above the canopy consists of T from both overstory and understory vegetation, and E from soil and the intercepted precipitation. To quantify their relative contributions, we have measured ET from the floors of deciduous and coniferous forests in Gwangneung using eddy covariance technique from 1 June 2008 to 31 May 2009. Due to smaller eddies that contribute to turbulent transfer near the ground, we performed a spectrum analysis and found that the errors associated with sensor separation were <10%. The annual sum of the understory ET was 59 mm (16% of total ET) in the deciduous forest and 43 mm (~7%) in the coniferous forest. Overall, the understory ET was not negligible except during the summer season when the plant area index was near its maximum. In both forest canopies, the decoupling factor ($\Omega$) was about ~0.15, indicating that the understory ET was controlled mainly by vapor pressure deficit and soil moisture content. The differences in the understory ET between the two forest canopies were due to different environmental conditions within the canopies, particularly the contrasting air humidity and soil water content. The non-negligible understory ET in the Gwangneung forests suggests that the dual source or multi-level models are required for the interpretation and modeling of surface exchange of mass and energy in these forests.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.331-336
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• 2019

In this study, required properties and optimized procedure conditions for the pitch based soft carbon anode of lithium ion battery was investigated for improving the initial efficiency and rate performance. Each petroleum residue was thermally treated at 360, 370, and $410^{\circ}C$ for 3 hours to synthesis a pitch and the corresponding pitch shows the softening point of 86, 98, and $152^{\circ}C$, respectively. The elemental analysis and thermal characteristics of the pitch were investigated by EA analysis and TGA. It was noted that the low H/C and improved thermal stability were obtained with the high softening point. The obtained pitch was carbonized at $1,200^{\circ}C$ for 1 hour to produce a soft carbon based anode. As a result of investigating the crystal structure by XRD analysis, it was found that the crystallinity of soft carbon increased with increasing the softening point. It was considered that relatively higher boiling components and decreases in the evaporation component resulted the components participation for cyclization during the heat treatment process. The soft carbon based anode with an improved crystallinity shows the enhanced initial efficiency and rate performance. The mechanism of both improvements was also discusssed based on the developed crystal structure of soft carbon based anode materials.