• KIEAE Journal
• /
• v.2 no.3
• /
• pp.33-38
• /
• 2002

The intermediate range of temperatures($100{\sim}300^{\circ}C$) which can be achieved with CPCs(Compound Parabolic Concentrators) without tracking device provides both economic and thermal advantages for solar collector design. The present paper summarizes critical design considerations for CPC with cylindrical absorber and its optical performance using ray tracing program. Concentration ratios vary as acceptance half angle, ratio of reflector height to aperture width and ratio of reflector area to aperture area. This effects showed that the concentration ratio was increased as acceptance angle but optimum ratio of reflector height to aperture width existed at critical value. As a result of ray tracing, solar ray losses was maximized at acceptance half angle and this problem was solved by increasing absorber tube diameter. The concentrating flux distribution on the absorber surface was uniform but peak flux existed.

• Journal of the Korean institute of surface engineering
• /
• v.23 no.3
• /
• pp.150-159
• /
• 1990

The magnetic properties of electrodeposited iron and cobalt films on porous aluminum oxide film were examined. There exists perpendicular magnetic anisotropy due to the shape anisotropy. The coercivity and squareness ratio of films were strongly dependent on deposited particle diameter. The effect of packing fraction on squareness ratio was also apprecible. Unlike the iron-deposited films, the magnetic properties of cobalt films were changed by preferred orientation because of it's large crystal ansotropy constant.(about 10 times of Fe) The Fe deposited films were found to be more suitable for perpendicular magenetic recording media bacause perpendicular coercivity, squareness ratio and the ratio of perpendicular coercivity to horizontal ones of iron films are greater than those of cobalt films.

• Food Science and Preservation
• /
• v.1 no.1
• /
• pp.9-14
• /
• 1994

Soluble solids($^{\circ}$Brix), acid content and edible part ratio of Citrus unshiu collected at sorting Places in south Cheju area wee more lowered, and peel thickness was more thickened with increasing fruit size. Compared to early variety of Citurs unshiu(C. unshiu Miyakawa Mar), peel thickness of medium variety of Citurs unshiu(C. unshiu Hayashi Mar) was more thickened, and edible part ratio was more lowered with increasing fruit size. Soluble solids of medium variety of Citurs unshiu were lowered, and acid contents were increased compared to early variety. Processing properties for pressing concentrated juice was good for early variety of Citurs unshiu, especially on fruit diameter of 50-65mm. Soluble solids, acid contents and juice ratio were decreased with increasing peel thickness. The quality properties for fresh fruit with peel thickness had a good correlation on early variety of Citurs unshiu, and these data are supposed to be applied to the quality evaluation of Citurs unshiu produced in Cheju.

• Steel and Composite Structures
• /
• v.47 no.1
• /
• pp.121-134
• /
• 2023

This paper tested 11 concrete-encased concrete-filled steel tube (CFST) composite columns and one reinforced concrete column under combined axial compression and lateral loads. The primary parameters, including the loading system, axial compression ratio, volume stirrup ratio, diameter-to-thickness ratio of the steel tube, and stirrup form, were varied. The influence of the parameters on the failure mode, strength, ductility, energy dissipation, strength degradation, and damage evolution of the composite columns were revealed. Moreover, a two-parameter nonlinear seismic damage model for composite columns was established, which can reflect the degree and development process of the seismic damage. In addition, the relationships among the inter-story drift ratio, damage index and seismic performance level of composite columns were established to provide a theoretical basis for seismic performance design and damage assessments.

• Journal of the Korean Society of Safety
• /
• v.19 no.2
• /
• pp.104-111
• /
• 2004

The aim of this study was to investigate the influence of inorganic pigments on the physical properties of cement mortar. For this purpose, the compressive strength and absorption test were carried out on cement mortar imxed with inorganic pigments by changing the proportion of cement mortar, water-cement ratio, and ratio of pigment. The result of this study can be summarized as follows: the compressive strength of colored mortar rapidely increased in red and yellow mortar, as the mix ratio of pigment increased. In case of green and black mortar, however, the compressive strength decresed as the mix ratio incresed. In case of red and yellow mortar, the absorption of colored mortar increased as the mixing ratio increased, if the mean particle diameter of the pigment is small. In case of green and black mortar, the absorption ratio decreased as the mix ratio increased. After investigating the overall physical properties of colored mortar, it was confirmed that the proper mix ratio of pigment securing the properties of colored mortar was below 6% of the weight of the cement to be used.

• Steel and Composite Structures
• /
• v.21 no.4
• /
• pp.921-947
• /
• 2016

Concrete Filled Fibre Reinforced Polymer Tube (CFFT) for new columns construction has attracted significant research attention in recent years. The CFFT acts as a formwork for new columns and a barrier to corrosion accelerating agents. It significantly increases both the strength capacity (Strength enhancement ratio) and the ductility (Strain enhancement ratio) of reinforced concrete columns. In this study, based on predefined selection criteria, experimental investigation results of 134 circular CFFT columns under axial compression have been compiled and analysed from 599 CFFT specimens available in the literature. It has been observed that actual confinement ratio (expressed as a function of material properties of fibres, diameter of CFFT and compressive strength of concrete) has significant influence on the strength and ductility of circular CFFT columns. Design oriented models have been proposed to compute the strength and strain enhancement ratios of circular CFFT columns. The proposed strength and strain enhancement ratio models have significantly reduced Average Absolute Error (AAE), Mean Square Error (MSE), Relative Standard Error of Estimate (RSEE) and Standard Deviation (SD) as compared to other available strength and strain enhancement ratios of circular CFFT column models. The predictions of the proposed strength and strain enhancement ratio models match well with the experimental strength and strain enhancement ratios investigation results in the compiled database.

• Solar Energy
• /
• v.10 no.3
• /
• pp.3-12
• /
• 1990

This paper deals with experimental research to increase thermal storage efficiency of hot water stored in an actual storage tank for solar application. The effect of increased energy input rate due to stratification has been discussed and illustrated through experimental data, which was taken by changing dynamic and geometric parameters. Ranges of the parameters were defined for flow rate, the ratio of diameter to height of the tank and inlet-exit water temperature difference. During the heat storage, when the flow was lower, the temperature difference was larger and the ratio of diameter to height of the tank was higher, the momentum exchange decreased. As for this experiment, when the flow rate was 8 liter/min, the temperature difference was $30^{\circ}C$ and the ratio of diameter to height of the tank was 3, the momentum exchange was minimized resulting in a good thermocline and a stable stratification. In the case of using inlet ports, if the modified Richardson number was less than 0.004, full mixing occured and so unstable stratification occured, which mean that this could not be recommended as storage through thermal stratification. Using a distributor was better than using inlet ports to form a sharp thermocline and to enhance the stratification. It was possible to get storage efficiency of 95% by using the distributor, which was higher than a storage efficiency of 85% obtained by using inlet ports in same operation condition. Furthermore, if the distributor was manufactured so that the mainpipe decreases in diameter toward the dead end to maintain constant static pressure, it might be predicted that further stable stratification and higher storage efficiency are obtainable(ie:more than 95%).

• Applied Chemistry for Engineering
• /
• v.9 no.6
• /
• pp.901-906
• /
• 1998

Gas and liquid flow characteristics were investigated in an internal circulation airlift reactor using a single nozzle for a gas distributor. In three reactors with different diameters of the downcomer and heights of the riser, the gas holdup in the individual flow zone and the impulseresponse curve of tracer for an air-water system were measured for various gas velocities and reactor heights. Experimental results showed that the flow behavior of bubbles in the riser was the slug flow due to strong coalescences of bubbles and that the bubble flow pattern in the downcomer was the transition bubble flow for the smaller diameter of the downcomer, however, it was the homogeneous bubble flow for the larger one. And mean gas holdups in the individual flow zone and the reactor were greatly increased with decreasing the diameter of the downcomer for the equal ratio of height of the top section to that of the riser. Also, the mixing time was much effected by the height of the top section of reactor and for the equal ratio of height of top section to that of the riser, it was increased with increasing the diameter of the downcomer and the height of the riser. Flow characteristics of liquid were mainly varied with the bubble flow pattern in the downcomer and the size of the top section of reactor. And circulation velocities of liquid in the riser were increased with increasing gas velocities and the size of the top section of reactor, and for the equal ratio of height of top section to that of the riser, they were increased with increasing the diameter of the downcomer and the height of the riser.

• The Journal of Korean Society for Radiation Therapy
• /
• v.14 no.1
• /
• pp.79-84
• /
• 2002

The main cause factor for effective the output, especially in small & irregular shaped field of electron beam therapy, are collimation system, insert block diameter and energy. In the absorption deose of treatment fields, we should consider the lateral build-up ratio (LBR), which the ratio of dose at a point at depth for a given circular field to the dose at the same point for a 'broad-field', for the same incident fluence and profile. The LBR data for a small circular field are used to extract radial spread of the pencil beam, ${\sigma}$, as a function of depth and energy. It's based on elementary pencil beam. We consider availability of the factor, ${\sigma}$, in the small & irregular fields electron beam treatment.

• Journal of the Korean Society of Safety
• /
• v.33 no.1
• /
• pp.7-15
• /
• 2018

The friction factors according to the flow regimes in helical coil tubes depend on the coil diameter, the tube diameter, and the coil pitch. In previous studies, correlations for the laminar flow regime in helical coil tubes have been proposed. However, studies on the transition flow regime and the turbulent flow regime are insufficient and further researches are necessary. In this study, characteristics of the friction factors for the laminar, transition and turbulent flow regimes in helical coil tubes were experimentally investigated. The helical coil tubes used in the experiments were made of copper. The curvature ratios of the helical coil tubes, which means the ratio of helical coil diameter to inner diameter of the helical coil tube are 24.5 and 90.9. Experiments were carried out in the range of $529{\leq}Re{\leq}39,406$ to observe the flows from the laminar to the turbulent regime. The friction factors were obtained by measuring the differential pressures according to the flow rates in the helical coil tubes while varying the curvature ratios of the helical coil tubes. Experimental data show that the friction factors for the helical coil tube with 24.5 in the curvature ratio of the helical coil tube were larger than those in the straight tube in all flow regimes. As the curvature ratio of the helical coil tube increases, the friction factor in turbulent flow regime tends to be equal to that of the straight tube. In addition, it was confirmed that the transition flow regimes in the helical coil tubes were much wider than those in the straight tube, also the critical Reynolds numbers were larger than those in the straight tube. The results obtained in this experimental study can be used as basic data for studies on the water hammer phenomenon in helical coil tubes.