• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.6 no.4
• /
• pp.255-261
• /
• 1977

This study was concerned with the performance of solar air heater using parallel channels. Heat transmission model was developed and fabricated to increase the economic feasibility for solar heating system by using the cheap zinc plate. The prformance was discussed as a function of mass flow rate, and plate, inlet and outlet temperatures. Experimental results show that heat transmission model is sufficient for the analysis of thermal characteristics of air heater and collection efficiency is better than the domestic water heater, as the range 32-49 percent. Collection efficiency in the 2 layers of glass cover is better than that in 1 layer, so it is considered better to use the 2 layers of glass cover during the cold winter season in Korea.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1997.05a
• /
• pp.273-278
• /
• 1997

Critical two-phase flow rates of subcooled water through very short tube (L=20 mm) with small diameters (D=1.0 mm) has been measured for wide ranges of subcooling(0~186$^{\circ}C$) and pressure (0.5~2.0 MPa). Experimental results show that subcooled critical two-phase flow rates can be expressed in terms of two scaling parameters for geometries and initial conditions. They are discharge coefficient of cold water, ( $C_{d}$ )$_{ref}$, and dimensionless subcooling, $\Delta$ $T^{*}$$_{sub}$, respectively. A new empirical correlation expressed in terms of ( $C_{d}$ )$_{ref}$ and $\Delta$ $T^{*}$$_{sub}$ is obtained for subcooled two-phase flow rates through very short length tube. Comparisons between the mass fluxes calculated by Present correlation and a number of experimental data show that the agreement is very good.ood.ood.ood.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.30 no.6
• /
• pp.1044-1055
• /
• 1997

To find out generating mechanism of eddies in the polar frontal zone of the East Sea, we carried out a series of numerical experiments using the nonlinear $1^{1/2}-layer$ model allowing the effect of the polar front. We assumed the polar front at about $39^{\circ}N$ in zonal direction with the cold water region in the northern part and the warm water region in the southern part of the model ocean. To examine the effect of the frontal motion without the influence of the Tsushima Current from the beginning of the geostrophic adjustment, the initial state of the model ocean was assumed motionless. Eastward current was caused by the geostrophic adjustment process in the polar frontal zone that induced a steady northward coastal current along the Korean coast to satisfy the mass continuity. The overshooting of this coastal current acted as an initial disturbance of the zonal flow field which caused meanders and eddies. The spatial scales of eddies were in good agreement with the baroclinic instability theory.

• 한국신재생에너지학회:학술대회논문집
• /
• 2005.06a
• /
• pp.339-344
• /
• 2005

A PEMFC system model for FCEV was constructed and simulated numerically to examine the heat/water flow of the system and air/fuel humidification process for various operation conditions (ambient pressure /temperature/humidity, operating temperature, power load). We modeled PEMFC stack which can generate maximum electricity of about 80 kW. This stack consists of 400 unit cells and each unit cell has $250cm^2$ reacting area. Uniform current density and uniform operating voltage per each cell was assumed. The results show the flow characteristics of heat and water at each component of PEMFC system in macro-scale. The capacity shortage of the radiator occurred when the ambient was hot $(over\;40^{\circ}C)$ and power level was high (over 50 kW). In spite of some heat release by evaporation of water in stack, heat unbalance reached to 20kW approximately in such a severe operating condition. This heat unbalance could be recovered by auxiliary radiators or high speed cooling fan with additional cost. In cold environment, the capacity of radiator exceeded the net heat generation to be released, which may cause a problem to drop the operating temperature of stack. We dealt with this problem by regulating mass flow rate of coolant and radiator fan speed. Finally, water balance was not easily broken when we retrieved condensed and/or unused water.

• Journal of the Korean Solar Energy Society
• /
• v.36 no.5
• /
• pp.73-89
• /
• 2016

To assure maximum economic benefits and the energy performance of solar water heating systems, the proper sizing of components and operating conditions need to be optimized. In recent years, a number of studies to design optimally solar water heating systems have been tried. This paper presents a design method for optimizing the various capacity-related and installation-related design variables based on life cycle cost using a genetic algorithm. The design variables considered in this study included the types and numbers of solar collector and auxiliary heaters; the types of storage tanks and heat exchangers; the solar collector slope; mass flow rates of the fluid on the hot and cold sides. The suggested method was applied for optimizing a solar water heating system for an elementary school in Seoul, South Korea. In addition, the effectiveness of the proposed optimization method was assessed by analyzing the obtained optimal solutions of six case studies, each of which was simulated with different solar fractions. It is observed that a trade-off between the equipment cost and the energy cost results in an optimal design that yields the lowest life cycle cost. Therefore, it could be helpful to apply the optimal solar water heating system by comparing the various design solutions obtained by using the optimization method instead of the engineer's experience and intuition.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.25 no.2
• /
• pp.151-163
• /
• 1992

Seasonal variations of water mass distributions in the Yellow Sea, the East China Sea, and the adjecent seas of Cehju Island, are investigated. A common seasonal variation over these whole areas is shown. Warm and saline waters are extended northwestward into the Yellow Sea in winter and retreated back southeastward to the East China Sea in summer. Barotropic numerical model results suggest that monsoon winds could drive such seasonal variations. Upwind flows play an important role in the processes. In the numerical model results, upwind flows are shifted to China. It is due to energy dissipations by complicated coast lines and shallow bottom topographies in the northern part of the Yellow Sea. The shifted routes of upwind flows agrees well with that of the southward extensions of the Yellow sea Bottom Cold Waters in summer.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1999.05a
• /
• pp.185-191
• /
• 1999

An air-conditioning system based on the chemical heat storage principle was considered. $H_2O$ was chosen as the reaction gas and the working fluid as well. Na$_2$S, CaCl$_2$, MnCl$_2$, BaCl$_2$, MgCl$_2$, Fe$_2$(SO$_4$)$_3$ and MnSO$_4$ were tested as the solid reactants by using Cahn pressure balance. Na$_2$S was superior to other salts in respect of high capability of absorption of water gas, 5 moles of $H_2O$ per unit mole of Na$_2$S, and adequate temperature of adsorption, $65^{\circ}C$ at 7torr, and of desorption, 13$0^{\circ}C$ at 76torr. Clausius-Clapeyron diagram of Na$_2$S was obtained via adsorption experiments at several vapor pressures of water gas. To enhance heat and mass transfer characteristics, usually below 1W/m K, of the reactor bed of general adsorption systems, expanded graphite block was adapted as the support of Na$_2$S salt. Expanded graphite blocks had thermal conductivity values of 20~80W/mK with respect to 100~400kg/㎥ of block bulk density. Permeability values of expanded graphite blocks were 10$^{-13}$ ~ 10$^{-14}$ $m^2$ with respect to 100~300kg/㎥ of block bulk density showing highly decreasing values of permeability, below 10$^{-l4}$$m^2$, in the range of above 150kg/㎥ of block bulk density.y.

• Journal of Food Hygiene and Safety
• /
• v.32 no.5
• /
• pp.389-395
• /
• 2017

A simultaneous determination of 5 phenolic acids (gallic acid, chlorogenic acid, caffeic acid, pcoumaric acid, trans ferulic acid) and 9 flavonoids (procyanidin b1, aspalathin, rutin, vitexin, hyperoside, isoquercitrin, luteolin, quercetin, chrysoeriol) in rooibos tea has been carried out by ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS). A validated analysis method in this study was applied to rooibos aqueous infusions. Rooibos tea is an antioxidant-rich tea which has anti-cancer, anti-aging, anti-inflammatory, anti-diabetic effect. Extraction yield of phenolics depends on steeping time and temperature of water. Tea infusions were prepared by placing 1 g of tea leaves or 1 tea bag in 100 mL of boiled water, and then at 3, 6 and 30 minutes intervals the infused teas were taken to carry out the analysis of phenolic contents. Another tea infusion was conducted with cold water ($25-30^{\circ}C$) for 30 minuntes. As a result, the total amount of phenolics was highest in rooibos tea steeped with hot water for 30 minutes, followed by 6 minutes, 3 minutes and cold water 30minutes and the result has statistical significance.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.7
• /
• pp.545-554
• /
• 2007

Flow condensation heat transfer coefficients(HTCs) of R22, propylene, propane, DME and isobutane are measured on a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed refrigerant saturation temperature of $40{\pm}0.2^{\circ}C$ with mass fluxes of 100, 200, $300kg/m^2s$ and heat flux of $7.3\sim7.7kW/m^2$. The data are obtained in the vapor Quality range of $10\sim90%$. Test results show that at same mass flux the flow condensation HTCs of propylene, propane, DME and isobutane are higher than those of R22 by up to 46.8%, 53.3%, 93.5% and 61.6% respectively. Also well-known correlations developed based upon conventional fluorocarbon refrigerants predict the present data within a mean deviation of 30%. Finally, the pressure drop increase as the mass flux and Quality increase and isobutane shows the highest pressure drop due to its lowest vapor pressure among the fluids tested.

• 한국해양학회지
• /
• v.20 no.3
• /
• pp.37-54
• /
• 1985

A description of the "phytohydrography" in the southwestern waters of the East Sea is given from concurrent measurement of temperature, chlorophyll-a, nutrients, and phytoplankton and also from the calculated primary production during the two cruises in May and October, 1984. Past history of water mass is relatively well reflected in the distribution of phytoplankton species, but such a reflection is rarely shown in the distribution of physical and chemical parameters in general. Upper layer of the waters around Ul-gi and Gampo is typically characterized by the high chlorophyll-a, high primary production, and low nanofraction ratio due to the continuing supply of nutrients from the nutrient-rich cold water underneath. Water of Tsushima current shows poor standing crop in terms of cell numbers and chlorophyll-a concentrations, extremely high nanofraction ratio, and very low primary production. The overwhelming importance of the nanofraction is confirmed in phytoplankton cell numbers, chlorophyll-a concentration, and possibly enough in primary production. This emphasizes the exceptionally strong inflow of warm water into the study area from south among all the waters around the whole Korean peninsula.