• 대한기계학회논문집
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• 제17권9호
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• pp.2339-2358
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• 1993

Since the rate and completeness of combustion in direct injection engines were controlled by the characteristics of gas flow fields and sprays, an understanding of those was essential to the design of the direct injection engines. In this study the numerical simulations of injection pressure effects on the characteristics of gas flow fields and sprays were preformed using the spray model that could predict the interactions between gas fields and spray droplets. The governing equations were discretized by the finite volume method and the modified k-.epsilon. model which included the compressibility effects due to the compression/expansion of piston was used. The results of the numerical calculation of the spray characteristics in the quiescent environment were compared with the experimental data. There were good agreements between the results of calculation and the experimental data, except in the early stages of the spray. In the motoring condition, the results showed that a substantial air entrainment into the spray volume was emerged and hence the squish motion was relatively unimportant during the fuel injection periods. It was found that as the injection pressure increased, the evaporation rate of droplets was decreased due to the narrow width of spray and the increased number of droplets impinged on the bottom of the piston bowl.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.827-838
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• 2013

Interaction layer growth between U-Mo alloy fuel particles and Al in a dispersion fuel is a concern due to the volume expansion and other unfavorable irradiation behavior of the interaction product. To reduce interaction layer (IL) growth, a small amount of Si is added to the Al. As a result, IL growth is affected by the Si content in the Al matrix. In order to predict IL growth during fabrication and irradiation, empirical models were developed. For IL growth prediction during fabrication and any follow-on heating process before irradiation, out-of-pile heating test data were used to develop kinetic correlations. Two out-of-pile correlations, one for the pure Al matrix and the other for the Al matrix with Si addition, respectively, were developed, which are Arrhenius equations that include temperature and time. For IL growth predictions during irradiation, the out-of-pile correlations were modified to include a fission-rate term to consider fission enhanced diffusion, and multiplication factors to incorporate the Si addition effect and the effect of the Mo content. The in-pile correlation is applicable for a pure Al matrix and an Al matrix with the Si content up to 8 wt%, for fuel temperatures up to $200^{\circ}C$, and for Mo content in the range of 6 - 10wt%. In order to cover these ranges, in-pile data were included in modeling from various tests, such as the US RERTR-4, -5, -6, -7 and -9 tests and Korea's KOMO-4 test, that were designed to systematically examine the effects of the fission rate, temperature, Si content in Al matrix, and Mo content in U-Mo particles. A model converting the IL thickness to the IL volume fraction in the meat was also developed.

• 한국안전학회지
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• 제10권3호
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• pp.120-129
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• 1995

직접분사엔진에서 기상과 분무액적간의 유동특성 및 분무특성에 미치는 선회비의 영향에 대하여 수치해석 하였다. 정적인 환경에서는 분무초기를 제외하고는 계산과 실험결과가 잘 일치하였다. 운전상태에서는 연료분사 기간동안 속도장의 영향이 증가하여 스쿼시유동의 중요성이 상대적으로 감소하였다. 선회비가 증가할수록 높은 난류에너지가 연소실내에 분포되며 분무액적이 확산되고 기상과의 상호작용이 강해져서 증발률이 증가하였다.

• 한국전산유체공학회지
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• 제9권4호
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• pp.55-63
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• 2004

The three-dimensional Stokes flow within a staggered screw channel is obtained by using a finite volume method. The geometry is intended to mimic the single screw extruder having staggered arrangement of flights. The flow solution is then subjected to the analysis of the stirring performance. In the analysis of the stirring performance, the stretching-mapping method developed by the author is employed for calculating the materials' stretching exponents, which are to be used in quantification of the mixing effect. The numerical results Indicate that the staggered geometry gives indeed far much better stirring-performance than the standard (nonstaggered) flight geometry. It was also shown that care must be given to the selection of the basis planes for evaluating the local stretching rate, and it turns out that the best method (H-method) has its basis plane just on the half way between the past and future evolution of fluid particles subjected to the defromation. In evaluating the stretching exponent, the expansion ratio must be considered which is one of the characteristic differences of the actual three-dimensional flows from the two-dimensionmal counterparts. The larger axial pressure-difference causes in general the smaller stirring performance while the flow rate is increased. The smaller channel length also increases the stirring performance.

• Biomolecules & Therapeutics
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• 제8권2호
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• pp.132-139
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• 2000

This study was performed far investigation of influence on renal function of idazoxan, $\alpha_{2}$-adrenergic antagonist, using the dog. Idazoxan, when giver. into vein, produced the decrease of urine volume(vol) accompanied with the reduction of free water clearance($C_{H2O}$), amounts of sodium excreted in urine($E_{Na}$), with the increase of potassium excreted in urine($E_{K}$), and so ratios of potassium against sodium($K^{+}/Na^{+}$) were elevated, at this time, greatened reabsorption rate of sodium and diministered that of potassium in renal tubules were appeared. Idazoxan administered into a renal artery elicited the augmentation of vol, glomerular filtration rate(GFR), renal plasma flow(RPF) and no change of filtration fraction(FF) in only ipsilateral kidney, whereas $E_{Na},\;E_{K}\;and\;K^{+}/Na^{+}$ were increased and $C_{H2O}$ was decreased in both control and experimental kidney. Idazoxan given into carotid artery showed partial increased vol, remarkable expanded RPF and unchanged GFR, and so filtration fraction(FF) was markedly reduced. Above results suggest that anti- diuretic action of idazoxan given into vein is mediated by reduction of $C_{H2O}\;and\;E_{Na}$, diuretic action only in the ipsilateral kidney by idazoxan given into a renal artery is caused by hemodynamic improvement through expansion of vas afferens in glomeruli.

• International Journal of Air-Conditioning and Refrigeration
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• 제6권
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• pp.36-44
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• 1998

R-410a and R-407c which have the best potential among R-22 alternatives were tested as drop-in refrigerants against a set of R-22 baseline tests. The performance evaluations were carried out in a psychometric calorimeter test facility using the residential spilt type air conditioner under the ARI rating conditions. Except the lubricant and hand-operated expansion valve, the other parts of the air conditioner were the same with the commercial system. Performance characteristics were measured; compressor power, capacity, VCR, mass flow rate and COP. The tests showed that R-407c can be directly charged into the current refrigeration system because its vapor pressure and other thermochemical properties are similar to those of R-22. However, it is required to change the volume flow rate of compressor in order to achieve the volumetric capacity of R-22. This results from its relatively small VCR and capacity. Meanwhile, R-410a has vapor pressure values too high to be substituted for the current system and this resulted relatively low COP of R-410a compared to that of R-22.

• 설비공학논문집
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• 제9권1호
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• pp.82-91
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• 1997

R-410a and R-407c witch have the best potential among the substances being considered as R-22 alternatives were tested as "drop in" refrigerants against a set R-22 baseline tests for comparison. The performance evaluations were carried out in a psychrometric calorimeter test facility using the residential split-type air conditioner under the ARI rating conditions. Other than the use of different lubricant and a hand-operated expansion valve, one of the commercial systems was selected for the experiment. Performance characteristics were measured; compressor power, capacity, VCR, mass flow rate and COP. The tests showed that R-407c can be directly applied to the existing refrigeration system because of its similar vapor pressure and other thermopysical properties with those of R-22. However, it required change to the volume flow rate of compressor in order to achieve the similar performance with R-22 because of its relatively small VCR and capacity. Meanwhile, R-410a has too high a vapor pressure to be applied to the existing system and this feature results in relatively low COP of the system compared to that of R-22. But this could be improved by changing compressor design considering R-410a's relatively high VCR and capacity compared to those of R-22.

• Journal of the Korean Wood Science and Technology
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• 제22권2호
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• pp.61-70
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• 1994

This study was executed to find the applicability of press drying of tree disk by investigating the shrinkage and drying defect and to form appropriate model by comparing the actual moisture content(MC) and internal temperature in respect of drying time with calculated values based computer simulation to which was applied finite difference method. In press drying disk, heating period, constant drying rate period maintained plateau temperature at 100$^{\circ}C$ and falling drying rate period were significantly distinguished. Actual MC and internal temperature were analogous to those calculated at comparing points. Heat transfer model formed by Fourier's law using specific heat of moist wood and conduction coefficient considering fractional volume of each element of wood cell wall, bound water, free water and air showed applicability as basic data to developing heat expansion, shrinkage and drying stress during press drying. Also mass transfer model formed by Fick's diffusion law using water vapor diffusion coefficient showed applicability. Longitudinal shrinkage was developed by pressure of hot press and tangential shrinkage was restrained by hygrothermal recovery. The heart check, surface check and ring failure were occurred differently in species, but V-shaped crack didn't develop.

• 한국농공학회지
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• 제34권3호
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• pp.33-42
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• 1992

The shear strength of cohesionless Soils results from particle-to-particle friction and structural resistance by interlocking. And, the shear strength of soils is subjected to vary depending on the internal states and external condtions. If the volume change occurring in the soils and stress-strain relationships under the internal and external changes can accrurately he described, it is possible to predict the behaviors of soils. To accomplish these objectives a series of drained triaxial compression tests and isotropic compression test was performed on the Banwol sand at different relative densities ranging from 20% to 80% and different confining pressures ranging from 0.4kgf/cm$^2$ to l2kgf/cm$^2$. The results and main conclusions of the study are summarized as follows; 1.When the relative density or the confining pressure is increased, the maximum deviator stress is increased. The ratio of the maximum deviator stress and the confining pressure is linearly proportional to the relative density. 2.It is observed that the dilatancy depends not only upon its relative density but also the confining stress, and that the maximum deviator stress is obtained after the diatancy occurs. 3.The volume of sands undergoes initial contraction prior to the dilatancy occurred by strain softening. The dilatancy rate eventually approaches the critical state or a constant volume. 4.At lower strains, Poisson's ratio approaches a certain minimum value regadless of the state of materials. At larger strains, however, the ratio is increased as the relative density is increased. 5.It is observed that the modulus of elasticity is linearly proportional to the relative density and the pressure. 6.When the relative density is increased, the friction angle of sands is linearly increased. 7.When the relative density is increased, the expansion index and the compression index are linearly decreased, and the ratio of the two is about 1/3.

• 한국지역사회생활과학회지
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• 제12권1호
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• pp.69-85
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• 2001

The purpose of this study was to replace the highly imported wheat consumption with rice in order to improve the rate of food self-sufficiency. Also, the study focused on the possibility of compounded bread making with rice flour, its taste for the Korean who have westernized eating styles, and the development of rice flour compounded bread as an alternative for wheat allergic people. Therefore, the researcher produced the soaked-rice flour, toasted-rice flour, and Extrusion-Expansion of Rice (E-ER) flour by different processing methods to bake rice wheat bread with the 10～50% mixing proportion. The volume and structure of bread were observed with Scanning Electron Microscope (SEM), and the sensory quality and the baking property were analyzed with a seven-point Likert type scale of Quantitative Descriptive Analysis (QDA). The sensory quality consisted of seven qualities such as color, size and distribution of air cell, flavor, softness, chewing, and overall quality that were evaluated as higher rating showed the better quality. The results of this study are: 1. The volume of the three types of rice wheat bread was almost same or bigger than wheat bread with the 20% of mixed proportion. 2. The size and distribution of air cell of E-ER wheat bread observed by SEM were more evenly distributed that toasted-rice wheat bread. The E-ER wheat bread had soft structure and was relatively similar to wheat flour bread. However, the structure of soaked-rice wheat bread was significantly different to other types of rice wheat bread. The structure of 10% mixed all three types of rice wheat bread was similar and evenly distributed to wheat bread but was bigger and coarser as higher mixing proportion of rice flour. 3. The dark brown color of rice wheat bread showed low sensory quality. 4. Both soaking-rice flour and E-ER flour were able to be mixed with wheat flour up to the 50%, and the seven sensory quality of these wheat bread were better than those of wheat bread. Among the three types of rice flour, toasted-rice wheat bread showed low bread property and sensory quality compared to soaked-rice or E-ER wheat bread. Consequently, this study showed that rice wheat bread that contains 20～30% of rice flour was better than wheat bread in the appropriate volume, seven sensory qualities and bread property.