• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.10
• /
• pp.1318-1326
• /
• 2001

The evaporation heat transfer coefficient and pressure drop for refrigerant R-22 flowing in the plate and shell heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were farmed in the exchanger by three plates of commercial geometry with a corrugated trapezoid shape of a chevron angel of 45 ° Upflow boiling of refrigerant R-22 in one channel receives heat from the hot downf1ow of water in the other channel. The effects of the mean vapor quality, mass flux, heat flux and pressure of R-22 on the evaporation heat transfer and pressure drop were explored. The quality change of R-22 between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.05. The present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux, the evaporation heat transfer coefficient and pressure drop are higher for the entire range of the vapor quality Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower.

• Journal of Pharmaceutical Investigation
• /
• v.32 no.1
• /
• pp.41-45
• /
• 2002

The purpose of this study is to microencapsulate a highly hygroscopic drug, pyridostigmine bromide (PB), with a waterproof wall material, in order to increase the flowability of the drug particles. Polyvinylacetaldiethylaminoacetate (AEA), Eugragit E and Eugragit RS were examined as the wall materials. Microcapsules containing PB were prepared by the evaporation technique in an acetone/liquid paraffin system using aluminum tristearate as a core material, and evaluated for drug encapsulation efficiency, surface morphology, particle size and drug dissolution. The encapsulation of PB in the wall material was almost complete. Among the wall materials examined, AEA exhibited the most excellency in shape, surface texture, flowability, size distribution of microcapsules. Above results suggest that AEA would be a potential wall material for microcapsulation of highly hygroscopic drugs, such as PB. Through microencapsulation with AEA, inconvenience of handling of PB powders encountered in the process of weighing and packing the powders to tableting die or capsule body could be greatly improved.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.12 s.243
• /
• pp.1360-1368
• /
• 2005

This study investigates the characteristics of spray, such as evaporation rate and spray trajectory, for a 4-hole injector which is applied to a 4-valve motorcycle gasoline engine. Three dimensional, unsteady, compressible flow and spray within the intake-port and cylinder have been simulated using the VECTIS code. Spray characteristics were investigated at 6000 rpm engine speed. Furthermore, we visualized fuel behavior in the intake-port using a CCD camera synchronized with a stroboscope in order to compare with the analytical results. Boundary and intial conditions were employed by complete 1-D simulation of the engine using the WAVE code. Fuel was injected into the intake-port at two time intervals relative to the position of the intake valves so that the spray arrived when the valves were closed and fully open. The results showed that the trajectory of the spray was directed towards the lower wall of the port with injection against the closed valves. With open valve injection, a large portion of the fuel was lifted by the co-flowing air towards the upper half of the port and this was confirmed by simulation and visualization.

• Journal of Adhesion and Interface
• /
• v.9 no.2
• /
• pp.1-7
• /
• 2008

Using biodegradable polycaprolactone, the microcapsules were prepared by solvent evaporation method. Retinol was selected as a core material, which was used as an important ingredient material in cosmetic fields. Poly(vinyl alcohol) was used as a stabilizer. The shape and property of the microcapsules were characterized by scanning electron microscope and differential scanning calorimeter, and the release rate of the microcapsule was measured by UV spectrophotometer. The microcapsules were prepared, changing the concentration of wall material, the stirring rate, and the concentration of stabilizer. Under the optimum condition, the microcapsules were formed, which showd 5~6 um in diameter and got the homogeneous sphere shape.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.4
• /
• pp.290-299
• /
• 2008

Evaporation heat transfer characteristics of $CO_2$/propane mixtures in horizontal smooth and micro-fin tubes have been investigated by experiment. The experiments were carried out for several test conditions of mass fluxes, heat fluxes, compositions of $CO_2$/propane refrigerant mixtures and tube geometries. Direct heating method was used for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. Heat transfer coefficient data during evaporation process of $CO_2$/propane mixtures were measured for 5 m long smooth and micro-fin tubes with outer diameters of 5 mm, respectively. The tests were conducted at mass fluxes of 318 to 997 $kg/m^2s$, heat fluxes of 6 to 20 $kW/m^2$ and for several mixture compositions (100/0, 75/25, 50/50, 25/75, 100/0 by wt% of $CO_2$/propane). The differences of heat transfer characteristics between smooth and micro-fin tubes for various compositions of $CO_2$/propane refrigerant mixtures and the effect of mass flux, and heat flux on enhancement factor (EF) and penalty factor (PF) were presented.

• Journal of ILASS-Korea
• /
• v.14 no.3
• /
• pp.109-116
• /
• 2009

The purpose of this study is the experimental and numerical investigation on the DME spray characteristics in the combustion chamber according to the injection timing in a common-rail injection system. The visualization system consisted of the high speed camera with metal halide lamp was used for analyzing the spray characteristics such as spray development processes and the spray tip penetration in the free and in-cylinder spray under various ambient pressure. In order to observe the spray characteristics as a function of injection timing, the piston head shape of re-entrant type was created and the fuel injected into the chamber according to various distance between nozzle tip and piston wall in consideration of injection timing. Also, the spray and evaporation characteristics in the cylinder was calculated by using KlVA-3V code for simulating spray development process and spray tip penetration under real engine conditions. It was revealed that the high ambient pressure of 3 MPa was led to delay the spray development and evaporation of DME spray. In addition, injected sprays after BTDC 20 degrees entered the bowl region and the spray at the BTDC 30 degrees was divided into two regions. In the calculated results, the liquefied spray tip penetration and fuel evaporation were shorter and more increased as the injection timing was retarded, respectively.

• Food Science and Biotechnology
• /
• v.18 no.1
• /
• pp.157-161
• /
• 2009

Resveratrol-loaded poly($\varepsilon$-caprolactone) (PCL) nanoparticles were prepared by oil in water (O/W) emulsion solvent evaporation method. The morphology of the nanoparticles was evaluated using atomic force microscope (AFM), in which well-shaped and rigid nanoparticles were prepared. The mean particle size of nanoparticles prepared using only dichloromethane (DCM) ($523.5{\pm}36.7\;nm$) was larger than that prepared with a mixture of DCM and either ethanol (EtOH) ($494.5{\pm}29.2\;nm$) or acetone ($493.5{\pm}6.9\;nm$). The encapsulation efficiency of nanoparticles prepared only with DCM as dispersed phase ($78.3{\pm}7.7%$) was the highest of those prepared with solvent mixtures. An increase in the molecular weight of PCL led to an increase in encapsulation efficiency (from $78.3{\pm}7.7$ to $91.4{\pm}3.2%$). Pluronic F-127 produced the smallest mean size ($523.5{\pm}36.7\;nm$) with the narrowest particle size distribution. These results show that dispersed phase, molecular weight of wall materials, emulsion stabilizer could be important factors to affect the properties of nanoparticles.

• Journal of computational fluids engineering
• /
• v.14 no.2
• /
• pp.9-18
• /
• 2009

The cargo containment system (CCS) for ships carrying cryogenic fluid consists of at least two levels of barriers and insulation layers. It is because, even though there is a small amount of leak through the primary barrier, the liquid tight secondary barrier blocks further leakage of the cryogenic fluid. However, once the secondary barrier is damaged, it is highly possible that the leaked cryogenic fluid flows through the flat joint made of glass wool and reaches the inner hull of the ship. The primary objective of the present study is to investigate the influence of the damage extent in the secondary barrier on the amount of leaked cryogenic fluid reaching the inner hull and the temperature distribution there. Simulation results using a computational fluid dynamics tool were compared with the experimental data for the leaked cryogenic fluid flow and evaporation in the secondary insulation layer. The experimental and computational results suggest that, unless there is a massive leak, the cryogenic fluid mostly evaporates in the insulation layer and does not reach the inner hull in the state of liquid.

• Transactions of the Korean hydrogen and new energy society
• /
• v.16 no.3
• /
• pp.284-289
• /
• 2005

Thermal analysis of cryogenic-capable vessels with insulations have been carried out to store liquid hydrogen($LH_2$). The combined insulations of MLI(Multi-Layer Insulation) and VCS(Vapor-Cooled Shield) under high vacuum are considered in the analysis for various volumes of vessels. Vapor-Cooled Shields(VCS) are installed at cylinder wall as well as disc side of the $LH_2$ vessels. The results indicate that optimal distribution of boiloff vapor from $LH_2$ vessel into two sides of VCS exists based on the evaporation loss. As the volume of $LH_2$ vessel is increased, mass flow rate of boiloff is increased while the evaporation loss per unit volume is decreased.

• Proceedings of the KSME Conference
• /
• 2007.05b
• /
• pp.2113-2118
• /
• 2007

In this study, a mathematical model for a thermal analysis of a flat heat pipe with a grooved wick structure is presented. The effects of the liquid-vapor interfacial shear stress, the contact angle, and the amount of liquid charge have been included in the proposed model. In particular, the axial variations of the wall temperature and the evaporation/condensation rates are considered by solving the one-dimensional conduction and the augmented Young-Laplace equations, respectively. In order to verify the model, the results obtained from the model are compared to existing experimental data.