• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.74-80
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• 2014

This paper describes the development of the dual-thrust flight motor for enhancing the hit probability of unguided rockets. We designed dual-thrust flight motor by shape modification of the double base propellant with high burning rate, and confirmed the dual-thrust performance by static firing tests. The test results showed the thrust ratio of about 1:7.6 between sustaining phase and boosting phase, and had a quietly normal dual-thrust characteristics. And the results showed that there was not the fire extinction phenomenon of propellant due to the pressure drop.

• Solar Energy
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• v.14 no.2
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• pp.39-50
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• 1994

Experiments have been conducted to measure the heat transfer coefficient and pressure drop in fluidized bed double pope heat exchangers with smooth tube and longitudinal finned tube. The effect of particle size(alumina beads; do=0.41, 0.54, 0.65, 0.77 mm) and static bed height on the heat transfer coefficient has been evaluated in terms of pumping power. The heat transfer coefficient for the smooth tube and finned tube heat exchangers has been compared with single phase double pipe heat exchanger. Results show that the heat transfer coefficients for the finned tube in $2.96{\sim}3.45$ times higher than the smooth tube. The heat transfer coefficients for the fluidized bed heat exchanger is higher than the single phase heat exchanger for the most of pumping power range tested. The maximum increase in the heat transfer coefficient for fluidized bed is 91.3% for the smooth tube and 127.1% for the finned tube.

• Korean Chemical Engineering Research
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• v.54 no.5
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• pp.678-686
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• 2016

The effect of internal and shroud nozzle distributor to bubbling fluidized beds which has the size of $0.3m-ID{\times}2.4m-high$ column was modeled by CPFD (Computational Particle-Fluid Dynamics). Metal-grade silicon particles (MG-Si) were used as bed materials which have $d_p=149{\mu}m$, ${\rho}_p=2,325kg/m^3$ and $U_{mf}=0.02m/s$. Total bed inventory and static bed height were 75 kg and 0.8 m, respectively. Effect of vertical internal on the bubble rising velocity was investigated. Bubbles were split by internal when the axial position of the internal from the distributor, z = 0.45 m. Bed pressure drop and axial solid holdup were not affected by internal. However, in the case that axial distance of internal from distributor was too close to jet penetration length, bubbles were not separated and bypassed internal, and faster than without internal or z = 0.45 m.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.790-797
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• 2011

Hydrodynamic similarity was analyzed by employing scaling factor in three phase fluidized beds. The scaling factor was defined based on the holdups of gas, liquid and solid particles and effectivity volumetric flux of fluids between the two kinds of fluidized beds with different column diameter. The column diameter of one was 0.102 m and that of the other was 0.152 m. Filtered compressed air, tap water and glass bead of which density was 2,500 kg/$m^3$ were used as gas, liquid and solid phases, respectively. The individual phase holdups in three phase fluidized beds were determined by means of static pressure drop method. Effects of gas and liquid velocities and particle size on the scaling factors based on the holdups of each phase and effective volumetric flux of fluids were examined. The deviation of gas holdup between the two kinds of three phase fluidized beds decreased with increasing gas or liquid velocity but increased with increasing fluidized particle size. The deviation of liquid holdup between the two fluidized beds decreased with increasing gas or liquid velocity or size of fluidized solid particles. The deviation of solid holdup between the two fluidized beds increased with increasing gas velocity or particle size, however, decreased with increasing liquid velocity. The deviation of effective volumetric flux of fluids between the two fluidized beds decreased with increasing gas velocity or particle size, but increased with increasing liquid velocity. The scaling factor, which was defined in this study, could be effectively used to analyze the hydrodynamic similarity in three phase fluidized processes.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.293-303
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• 2012

Recently, as construction technology improved, concrete structures not only became larger, taller and longer but were able to perform various functions. However, if extreme loads such as impact, blast, and fire are applied to those structures, it would cause severe property damages and human casualties. Especially, the structural responses from extreme loading are totally different than that from quasi-static loading, because large pressure is applied to structures from mass acceleration effect of impact and blast loads. Therefore, the strain rate effect and damage levels should be considered when concrete structure is designed. In this study, the low velocity impact loading test of steel fiber reinforced concrete (SFRC) slabs including 0%~1.5% (by volume) of steel fibers, and strengthened with two types of FRP sheets was performed to develop an impact resistant structural member. From the test results, the maximum impact load, dissipated energy and the number of drop to failure increased, whereas the maximum displacement and support rotation were reduced by strengthening SFRC slab with FRP sheets in tensile zone. The test results showed that the impact resistance of concrete slab can be substantially improved by externally strengthening using FRP sheets. This result can be used in designing of primary facilities exposed to such extreme loads. The dynamic responses of SFRC slab strengthened with FRP sheets under low velocity impact load were also analyzed using LS-DYNA, a finite element analysis program with an explicit time integration scheme. The comparison of test and analytical results showed that they were within 5% of error with respect to maximum displacements.