• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.2
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• pp.149-155
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• 2007

The row-by-row heat transfer characteristics of fin-and-tube heat exchangers were experimentally investigated. Three wavy fin samples having different rows (one, two and three) and one plain fin sample (three row) were tested for $600{\leq}Re_{D}{\leq}4,000$. The heat transfer data were obtained for individual rows, and the corresponding heat transfer coefficients were reduced from the data. Results showed that the heat transfer coefficients were strongly dependent on the tube row. The heat transfer coefficient decreased as the tube row increased. However, the row effect was different depending on the fin shape. For the wavy fin, the row effect significantly decreased as the Reynolds number increased, yielding approximately the same heat transfer coefficients at $Re_{D}{\approx}2,500$. For the plain fin, however, the row effect lasted for the whole Reynolds number range. The increased mixing of bulk flow by wavy channels appears to induce high heat transfer coefficient (accordingly diminishing row effect) at downstream rows. The heat transfer coefficients of individual rows were higher for heat exchangers having larger tube rows.

• Journal of Environmental Science International
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• v.7 no.6
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• pp.745-751
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• 1998

The well-mixed room model has been traditionally used to predict the concentrations of contaminants in indoor environments. However, this is inappropriate because the flow fields in many indoor environments distribute contaminants non-uniformly, due to imperfect air mixing. Thus, some means used to describe an imperfectly mixed room are needed. The simplest model that accounts for imperfect air mixing is a two-zone model. Therefore, this study on development of computer program far the two-zone model is carried out to propose techniques of estimating the concentration of contaminants in the room. To do this, an important consideration is to divide a room into two-zone, i.e. the lower and upper zone assuming that the air and contaminants are well mixed within each zone. And between the zones the air recirculation is characterized through the air exchange parameter. By this basic assumption, the equations for the conservation of mass are derived for each zone. These equations are solved by using the computational technique. The language used to develope the program is a VISUAL BASIC. The value of air exchange coefficient($f_12$) is the most difficult to forecast when the concentrations of contaminants in an imperfectly mixed room are estimated by the two-zone model. But, as the value of $f_12$ increases, the air exchange between each zone increases. When the value of $f_12$ is approximately 15, the concentrations in both zone approach each other, and the entire room may be approximately treated as a single well-mixed room. Therefore, this study is available for designing of the ventilation to improve the air quality of indoor environments. Also, the two-zone model produces the theoretical base which may be extended to the theory for the multi-zone model, that will be contributed to estimate the air pollution in large enclosures, such as shopping malls, atria buildings, atria terminals, and covered sports stadia.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.2
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• pp.141-150
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• 2000

In order to genralize the vertical dispersion of plume at long distances on mesoscale over complex terrain dispersion coefficients data have been obtained systematically according to lapsed time after release by using a composite turbulence water tank that simulates convective boundary layer. Dispersion experiments have been carried out for various combined conditions of thermal turbulence intensity mechanical turbulence intensity and plume release height at slightly to moderately unstable conditions. Results of tracer dispersion experiments conducted using water tank camera and image processing system have been converted into atmospheric dispersion data through the application of similarity law. The equation $\sigma$z/Zi=aX/(b+c X2)0.5 where $\sigma$2; vertical dispersion coefficient zi : mixing height X : dimen-sionaless downwind distance was confirmed to be an appropriate and general equation for expressing $\sigma$2 variation with turbulence intensity and plume release height, The value of "a" was found to be principally affected by mechanical turbulence intensity and that of "b" by mechanical turbulence intensity and release height. It was confirmed that the magnitude of "c" varies with release height. Results of water tank experiments on the relationship of $\sigma$2 vs downwind distance x have been compared with actual atmospheric dispersion data such as CONDORS data and Bowne's nomogram Operating conditions of a composite turbulence water tank for simulating the field turbulence situations of CONDORS experiments and Bowne's $\sigma$2(x) nomogram for suburban area have also been investigated in terms of water temperature difference between convection water tank and bottom plate heating tank grid plate stroke mixing water depth length scale and velocity scale. Moreover the effect of mechanical turbulence intensity on vertical dispersion has been discussed in the light of release height and downwind distance. height and downwind distance.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.6
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• pp.63-71
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• 1998

In this paper, we experiment the characteristics of coupling coefficient, gain, diffraction efficiency and dependence of time determined by TWM(Two-Wave Mixing), using Fe-LiNbO$_3$ crystal(doped with 0.015Wt.%). From these results, we proposed to apply for optical memory application. The highest coupling angle of 14。 and maximum coupling coefficient of 6.9$cm^{-1}$ / are obtained at 514.5nm wavelength. Also, maximum diffraction efficiency is 54.13% when intensity ratio and writing beam incident angle are 0.1 and 14o, respectively. After fixing process, diffraction efficiency is 21.4%. As an example, we demonstrated the writing and reconstruct optical data using spatial light modualtor and angular multiplexing in most optimal condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.2
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• pp.219-229
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• 2016

This study presents the analysis of flood and bed deformation caused by reservoir failure. The CCHE1D is used to simulate 1D non-uniform, non-equilibrium sediment transport and bed deformation. The CCHE1D deals with the adaptation length for non-equilibrium sediment, classified sediment particle for non-uniform sediment and mixing layer for the exchange with the sediment moving with the flow. The model is applied to Ha!Ha! river basin where was experienced reservoir failure in 1996 to analyze non-uniform and non-equilibrium sediment transport. The calculations are compared with morphological bed changes of pre- and post-flood. In addition, model sensitivity to main parameters involving adaptation length ($L_{s,b}$), non-equilibrium coefficient (${\alpha}_s$), mixing layer thickness (${\delta}_m$) and porosity (p') is analyzed. The results indicates that thalweg change is the most sensitive to non-equilibrium coefficient (${\alpha}_s$) among those parameters in the study area.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.901-904
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• 2008

Immense quantities of coal combustion by-products are produced every year, and only a small fraction of them are currently utilized. Therefore, this study investigated and analyzed the applications of porous concrete for the efficient utilization of bottom ash. This study examines on application of polymer to improve strength properties of porous concrete using coal-ash. As the results, when the mixing ratio of bottom ash increases, void ratio and coefficient of permeability of porous concrete increases, but its strength decreases. Also, as the mixing ratio of polymer increases, its void ratio and coefficient of permeability decreases. When specific amount of polymer is mixed, we can find its strength properties are improved.

• Journal of the Korea Organic Resources Recycling Association
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• v.28 no.4
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• pp.35-41
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• 2020

The immobilization of the hydroxylamine-oxidoreductase on the water channel surface was performed to investigate the efficacy of ammonia removal in turbulent flow. The reaction by this enzyme proceeds rapidly by converting hydroxylamine into nitrous acid. For the analysis of the effect, a dimensionless mass transfer governing equation was established with the physical properties based on room temperature. The ammonia diffusion coefficient in water and the kinematic viscosity coefficient of water were 2.45×10-9 ㎡/s and 1×10-6 ㎡/s, respectively. The distribution of ammonia concentration in the water was calculated with respect to the distance from the point at which exposure to ammonia began. The quantitative distribution with respect to the mixing depth was also found. Such a quantitative analysis can provide insight into whether the enzyme immobilized on the water channel surface can be effectively used for ammonia removal.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.27 no.3
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• pp.203-210
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• 2021

With the development of package printing technology, the package has expanded from the basic function of protecting products to the marketing function through package design. Color, the visual element that composes the package design, is delivered to the consumer most quickly and effectively. As color marketing of these package designs expands, accurate color reproduction that the product wants to express is becoming more important. The color of an object is transmitted by absorption and scattering of light. Spectral reflectance refers to the intensity of light reflected by an object at different wavelengths by the spectral effect. As a result, the color of the object is expressed in various colors. Packaged printing inks have their own absorption and scattering coefficients, and the Kubelka-Munk model for color reproduction and prediction defines the relationship between these correlation coefficients through reflectance. In the Kubelka-Munk model for color reproduction and prediction, the relationship between the absorption and scattering coefficients (K/S) of printed material is predicted as the sum of the K/S values according to the mixing ratio of all color ink used. In this study, the reflectance of the measured print is reversely calculated at the mixing ratio of print ink using the Kubelka-Munk model. Through this, the relationship value of the ink-specific absorption/scattering coefficient constituting the final printed material is predicted. Delta E is derived through the predicted reflectance, and the similarity between the measured value and the predicted value is confirmed.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.10
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• pp.51-59
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• 1998

($Na_{1/2}Ln_{1/2}$)$TiO_3$ceramics have a high relative dielectric constant and a positive temperature coefficient of resonant frequency ($\tau_f$)(where Ln represents a lanthanide: $La^{+3}$, $Pr^{+3}$, $Nd^{+3}$ and $Sm^{+3}$). On the other hand, $MgTiO_3$ ceramic has a high Qf value and a negative temperature coefficient. So We have investigated the microwave dielectric properties of $xMgTiO_3$-(1-x) ($Na_{1/2}Ln_{1/2}$)$TiO_3$. In these systems, there are no clues on solid-solution and secondary phase. There are mixed phases with $MgTiO_3$and ($Na_{1/2}Ln_{1/2}$)$TiO_3$ phases. Its dielectric characteristics (Qf, temperature coefficient and dielectric constant) are intermediate between ($Na_{1/2}Ln_{1/2}$)$TiO_3$ and $MgTiO_3$ and are predictable by the logarithmic mixing rule. The dielectric ceramic compositions temperature coefficient each approximates to zero at Ln=La, x=0.9, Ln=Pr, x=0.87, and Ln=Nd, x=0.84. At this time, there are Qf values in the range of 55,000 to 28,00GHz and relative dielectric constants in the range of 22 to 25.

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.507-515
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• 1994

Fly ash and betonite samples were selected and characteristics of them were investigated. Fly ash was found to be similar to bentonite in particle size distribution but quite different in microstructure. The most special aspect of fly ash was high alkalinity of its solution. Distribution coefficients of Cs and Co on the samples were measured to survey the effects of mixing. Fly ash showed higher distribution coefficient of Co than that of Cs. Through various experiments, factors affecting the distribution coefficients of Co and Cs on mixture of bentonite and fly ash were identified. Comparison of the distribution coefficients of Cs on fly ash and bentonite mixture with those on sand and bentonite mixture suggests that fly ash would be useful as an efficient additive of backfill material if pertinent mixing ratio was chosen.