• Solar Energy
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• v.19 no.3
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• pp.29-41
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• 1999

Three-dimensional natural convective heat transfer in a vertical channel with a protruding single module was investigated experimentally. The particular interest was in the removal of thermal energy from the module by convective heat transfer. Hence radiative and conductive heat losses were estimated by using thermocouples and heat flux sensor respectively. The flow fields in the channel were visualized by means of a smoke-method. Also, local temperatures were measured by thermocouples inside the channel, along the vertical wall and module surface. It is found that convective heat transfer was promoted at the lower comer of the module and was decreased at the upper comer due to a recirculation zone. A general correlation of the critical channel ratios was found as a function of Rayleigh number. For the range of $8.28{\times}10^3<Ra^*_c<3.48{\times}10^6$, a useful correlation for the mean Nusselt number was proposed as a function of modified channel Rayleigh number.

• Horticultural Science & Technology
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• v.31 no.4
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• pp.429-436
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• 2013

Kimchi cabbage 'Choongwang' cultivar is mainly cultivated during summer in Gangneung area. 'Choongwang' cultivar was harvested in late July, applied with predrying, room cooling, and forced air cooling, and then packaged with/without 0.02 mm HDPE film to estimate the effect of postharvest treatment on quality characteristics (weight loss, trimming loss, firmness, SSC, color index, sensory evaluation) during 8 week storage at $2^{\circ}C$. Kimchi cabbage without 0.02 mm HDPE film showed high weight loss up to 13-20% while those of with liner were significantly lower. Also forced air cooling among the postharvest treatments was effective to reduce both weight loss and trimming loss. Appearance and freshness in sensory evaluation were the important factors in estimating good quality during storage. Liner treatment with forced air cooling showed highly significant for maintaining appearance and freshness ($P{\leq}0.01$). Color index was no differences between with/without 0.02 mm HDPE film and postharvest treatments. After 6 weeks storage in without 0.02 mm HDPE film with room cooling or control appearance was severely damaged and also internal browning was found. While in with 0.02 mm HDPE film internal browning was found after 8 weeks storage, just in room cooling or predrying treatment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.689-695
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• 2012

The friction factor in a rod bundle and the loss coefficient at a spacer grid were examined. As a test section, 25 smooth rods, 9.5 mm in diameter and 2000 mm in length, were prepared and installed in a $5{\times}5$ square array in a square channel. In this case, the P/D (Pitch-to-Diameter ratio) was 1.35. In this work, plain (i.e., no mixing vanes), split-vane, and hybrid-vane spacer grids were tested. In a bare rod bundle (i.e., no spacer grid), the measured friction factors were in good agreement with the previous correlations. Among the spacer grids tested, the hybrid-vane spacer grid presented the largest friction factor in the rod bundle and loss coefficient. This may be because of the flow pattern change induced by large relative plugging of the flow cross section and mixing vane geometry. At Re=$5{\times}10^5$, the predicted loss coefficients of plain, splitvane, and hybrid-vane spacer grids were approximately 0.79, 0.80, and 0.88, respectively.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.47 no.4
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• pp.97-104
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• 2010

In this paper, we provide an embedded type non-contact bio-radar heart and respiration rate monitoring system. We implemented the rate finding algorithm into the embedded system. The high-speed and reliable real-time signal processor is then tested. To avoid null-point data loss problem, we applied quadrature demodulation. Among several other combining techniques, we suggest arctangent demodulation for quadrature channel combining and DSP is used for real-time signal processing. We also suggest DC-offset compensation technique to preserve the wanted DC components of the IQ signals for accurate demodulation while keeping the dynamic range of the ADC lower. Using Texas Instrument C6711 series DSP and external 12Bit ADC, we implemented proper elliptic digital filter and autocorrelation detection algorithm for robust commercial hand held device.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.18-25
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• 2016

Enhanced tubes are used widely in the evaporators of large tonnage compression-type refrigerators. The evaporators consist of tube bundles, and the refrigerant properties are dependent on the locations in the tube bundles. In particular, the saturation temperatures of low pressure refrigerants (R-11, R-123) are strongly dependent on the locations due to the saturation temperature-pressure curve characteristics. Therefore, for the proper design of evaporators, local property predictions of the refrigerants are necessary. In this study, a computer program that simulates the flooded refrigerant evaporators was developed. The program incorporated theoretical models to predict the refrigerant shell-side boiling heat transfer coefficients and pressure drops across the tube bundle. The program adopted an incremental iterative procedure to perform row-by-row calculations over the specified incremental tube lengths for each water-side pass. The program was used to simulate the flooded refrigerant evaporator of the "T" company operating with R-123, which yielded satisfactory results. The program was extended to predict the performance of the flooded refrigerant evaporator operating with R-11, R-123, and R-134a. The effects of bundle aspect ratio are investigated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3D
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• pp.363-369
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• 2008

Change is inevitable and is a reality of construction projects. Change adjustment includes the cost associated with materials, labor, etc. However, the actions of a contractor can cause a loss of productivity and furthermore can result in disruption of the whole project because of a cumulative or ripple effect. Because of its complicated nature, it becomes a complex issue to determine the cumulative impact (ripple effect) caused by single or multiple change orders. Furthermore, owners and contractors do not always agree on the adjusted contract price for the cumulative impact of the changes. What is needed is a reliable method to identify and quantify the loss of productivity caused by cumulative impact of change orders. This study survey the change orders data in domestic area for public construction and analyze to quantify change order impact. This study developed concepts of "%CO", "%Delta", "%T" to capture change order effect on project and search the relationships between them. Finally, this study find strong relationship between change order and loss.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.989-1002
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• 2018

Grouting for the rock joint is to strengthen the rock strata by infiltrating cement grout materials into the rock joints. Grouting is one of a field of study which is difficult to develop deterministic and quantitative design approach because of multiphase behaviors of grout materials and 3 dimensional features of rock joints. Therefore, GIN (Grouting Intensity Number) can be a good index with appropriate monitoring of pressure and volume of grout. In this paper, we investigate the effects of joint roughness (JRC) and rheology of cement material during the infiltration of cement grout material into rock joint through CFD (computational fluid dynamics) analyses. With rough joint surface and increase of WC ratio, the frictional resistance during the grouting increases. The results have been summarized with polynomial correlations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.38-46
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• 2006

The characteristics about the pressure drop in microtubes have been investigated. The test tubes are the circular, seamless, stainless steel tubes with an inner diameter of 0.244, 0.430, and 0.792 mm, respectively. R-l34a was used as a test fluid. Early flow transition which has been reported in some previous studies is not found in single-phase flow pressure drop tests. The conventional theory between friction factor and Reynolds number predicted the experimental friction factors within an absolute average deviation of $8.9\%$. The two-phase flow pressure drop increases for higher quality and mass flux, and for reduced inner diameter. The existing correlations fail to predict the experimental data. A new correlation to predict the two-phase flow pressure drop is developed in the form of the Lockhart-Martinelli correlation. The effects of the tube diameter and the surface tension were considered, and the correlation predicted the experimental data within an average absolute deviation of $8.1\%$.

• The Korean Journal of Food And Nutrition
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• v.11 no.1
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• pp.87-98
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• 1998

This study was conducted to investigate Osteoporosis on the effect of dietary factors and past young age period's dairy products consumption on BMD in 170 postmenopausal Korean women without diagnosed disease. Bone mineral density(BMD) of lumbar spine was investigated by dual energy X-ray absorptiometry. Dietary assesment of the subjects were measured by Cognitive Food Frequency Recall method. The measurements of group average were 57.9kg of body weight, 36.73 of BMI(Body Mass Index), 2103.3㎉ of energy, 638.7mg of dietary calcium, 70.3g of protein, and 10.58mg of iron. Nutrient intake levels were similar to or more than the level of Korean Recommended Dietary Allowances. Bone Mineral Density(BMD) of Lumbar spine(L2-L4) of group average was 0.912g/$\textrm{cm}^2$, and under 50 yr's 1,02g/$\textrm{cm}^2$, 50~54 yr's 0.92g/$\textrm{cm}^2$, 55~59 yr's 0.85g/$\textrm{cm}^2$, over 60 yr's 0.85g/$\textrm{cm}^2$, had been getting low degree on aging. BMD of the Lumbar spine was positively correlated with calorie, body weight, dietary calcium, protein, phosphorus and serum albumin. Past dairy products consumption experiment was highly significant on BMD in teenage period(R square = 26, p-value 0.0031). Particularly in over 60 yr group, the correlations between BMD and past dairy products consumption in teenage period had shown highly significance(r=0.48, p<0.02). 55~59 yr age group had also positive correlation(R squae = 0.29, p<0.05). This results confirm that the most effective way of preventing osteoporosis and the fractures is to maximize peak bone mass in early life and to minimize bone loss through the balanced intake of Ca and other nutrients and regular physical activity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.9
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• pp.761-772
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• 2015

Microfin tubes having an outside diameter (O.D.) of 7.0 mm are widely used in residential air conditioning systems and heat pumps. It is known that the mass fluxes for air conditioners and heat pumps under partial load conditions are several tens of $kg/m^2s$. However, literature surveys reveal that previous investigations were limited to mass flux over $100kg/m^2s$. In this study, we conduct R-410A evaporation heat-transfer tests at low mass fluxes ($50-250kg/m^2s$) using a 7.0 mm O.D. microfin tube. During the test, the saturation temperature was maintained at $8^{\circ}C$, and the heat flux was maintained at $4.0kW/m^2$. For comparison purposes, we also test a smooth tube with a 7.0 mm O.D. The results showed that the heat-transfer enhancement factor of the microfin tube increased as the mass flux decreased up to $150kg/m^2s$, which decreased as the mass flux further decreased. The reason for this was attributed to the change of the flow pattern from an annular flow to a stratified flow. Within the test range, the frictional pressure drops of the microfin tube were approximately the same as those of the smooth tube. We then compare experimental data obtained with the predictions obtained for the existing correlations.