• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1207-1217
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• 1997

The present work experimentally investigated the effects of mass flux, heat flux, inlet quality on the heat transfer performance inside the U-bend of smooth and microfin tube using R-22 and R-407C refrigerants. The parameters were 200 and 400 kg/m$^{2}$ s for mass flux, 6 and 12 kw/m$^{2}$ for heat flux, 0.1 and 0.2 for inlet quality under the pressure of 0.65 MPa. The apparatus consisted of the test section of four straight sections and three U-bends, preheater, condenser, refrigerant pump, mass flow meter etc. The average heat transfer coefficient at the downstream straight section after U-bend was affected by U-bend due to the centrifugal force and mixing of two-phase flow in the U-bend. The average heat transfer coefficient at the U-bend was 4 ~ 33 % higher than that at the straight section. The average heat transfer coefficients were affected in the order of mass flux, heat flux and inlet quality. The average heat transfer coefficients in the microfin tube were lager by 19 ~ 49% and 33 ~ 69% than that in the smooth tube at the straight section and at the U-bend separately. The average heat transfer coefficients for R-407C were larger by 33 ~ 41% and 17 ~ 29% than that for R-22 in the smooth tube and the microfin tube separately.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.411-422
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• 1998

In this study, experiments were carried out to provide nucleate pool boiling heat transfer data for a plain tube and 4 different low fin tubes employing 2 refrigerant mixtures of R410A, R407C, and 12 pure fluids. Low fin tubes were machined on a 19.05mm nominal outside diameter copper block according to the manufacturer's low fin tube specifications. Cartridge heaters were used to generate uniform heat flux on the tubes. For all refrigerants, heat flux varied from 10㎾/$\m^2$ to 80㎾/$\m^2$. It is found that heat transfer coefficients(HTCs) of high vapor pressure refrigerants are usually higher than those of low pressure fluids. On the other hand, the fin effect was more prominent with low pressure refrigerants than with high pressure ones. Optimum fin density as well as the increase in heat transfer coefficient with the increase in fin density were found to be strongly fluid dependent. HTCs of Rl23, a low pressure alternative refrigerant, were similar to those of Rll while HTCs of R134a, an intermediate pressure alternative refrigerant, were roughly 20% higher than those of Rl2. Finally, HTCs of R32, R125, R143a, and R410A were all higher than those of R22 by 30~50%.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.83-89
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• 2000

This paper presents a pressure drop correlation for evaporation and condensation of alternative refrigerant with oil in micro-fin tubes. The correlation was developed from a data base consisting of oil-free pure and mixed refrigerants in micro-fin tube; Rl25 R134a. R32 R410a(R32/R125 50/50% mass), R22, R407c(R32/R125/R134a, 23/25/52% mass) and R32/R134a(25/75% mass). The micro-fin tube used in this paper had 60 0.2mm high fins with a 18 helix angle. The cross sectional flow area $(A_c)$ was $60.8 mm^2$ giving an equivalent smooth diameter$(D_e)$ of 8.8mm. The hydraulic diameter $(D_h)$ was estimated to the 5.45mm. The new correlation was obtained by replacing the friction factor and the tube-diameter in Bo Pierre correlation by a friction factor derived from pressure drop data for a micro-fin tube and the hydraulic diameter, respectively. This correlation was also used to predict some pressure data with a lubricant after using a mixing viscosity rule of lubricants and refrigerants. As a result, the new correlation was also well predicted to the measured data within a mean deviation of 19.0%.

• Journal of Pharmaceutical Investigation
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• v.34 no.5
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• pp.407-411
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• 2004

New formulations of amlodipine maleate tablet have been investigated to enhance the stability of the drug against light and humidity. Three kinds of amlodipine maleate tablets were prepared. One is prepared by previously known formulation (formulation C), the others were by new formulations using hydrophilic polymer $(Opadry^{\circledR})$ coated granules (formulations A and B). Amlodipine maleate powder was coated with $Opadry^{\circledR}$ to produce the coated granules and it was mixed with other excipients to produce the tabletting mass of new formulations A and B. Dissolution rate of newly formulated tablets was over 80% within 10 minutes in 0.01 M HCl medium, and its dissolution pattern was similar to that of $Norvasc^{\circledR}$ tablet. After 6 months storage under accelerated conditions, residual drug contents of tested formulations (A and B) were not significantly different from formulation C, ranging from 96.2 to 100.4%. Meanwhile, dissolution amount of formulation C was significantly reduced compared to that of formulation A (p<0.05), showing formulation A was more stable than unprotected formulation C at the accelerated conditions. Results of appearance, hardness and disintegration remained unchanged during stability study. In conclusion, it showed that the new formulations had enhanced the stability characteristics and hydrophilic coating technique was an alternative and promising method to improve the stability of amlodipine maleate tablet.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.315-324
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• 2000

R-410A, R-407C, and four refrigerant mixtures composed of R-32, R-l34a, R-l43a, R-l52a, R-600(butane), and R-600a(isobutane) were tested in an attempt to replace R-22 used in most of the residential air conditioners. The performance evaluation was carried out in a psychrometric calorimeter test facility using a residential spilt type air conditioner under the KS rating conditions. Except for the lubricant and hand-operated expansion valve, the other parts of the air conditioner were the same with the commercial system. Performance characteristics were measured; COP, capacity, compressor power, and VCR. R-410A was shown to have 5.5% higher COP and 3.5% lower capacity than R-22. R-32/134a/600a (42.8/ 46.0/11.2 wt%) mixture have the best performance among the four refrigerant mixtures composed of hydrofluorocarbon and hydrocarbon. This inixture have 3.0% lower COP and 1.6% lower capacity than R-22.

• Korean Journal of Plant Resources
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• v.27 no.2
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• pp.111-118
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• 2014

Contents of phenolics, flavonoids, and catechins, and antioxidant activity were investigated in the ethanol extracts of three different flower species, Magnolia denudata, Prunus mume, Carthamus tinctorius. Total phenolics were more present in M. denudata than P. mume or C. tinctorius, ranging from 72.6 to 118.0 mg/kg (p < 0.05). Total flavonoids level had same tendency to total phenolics content, showing highest amount (25.1 mg/kg) in M. denudata. The antioxidant activity of the methanol extracts from all the flowers dose-dependently increased. DPPH free radical scavenging activity at 250 mg/kgwas higher in M. denudata and P. mume by 93.0 and 92.6%, respectively, than C. tinctorius by 23.0% (p < 0.05). Total catechins content including 6 compounds was higher in M. denudate (9,425.5 mg/kg) than that in P. mume or C. tinctorius (3,407.8 or 190.6 mg/kg). However, P. mume extracts showed highest amount in caffeine as well as vitamine C. DPPH radical scavenging activity in three different flowers was highly correlated with contents of total phenolics ($r^2=0.7994$), total flavonoids ($r^2=0.9131$), and total catechins ($r^2=0.5929$), and their content and activities were different depending on species.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.435-449
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• 1995

In this paper, pressure drop through a capillary tube is modeled to determine the length of a capillary tube for a given set of conditions. HCFC-22 and its alternatives, HFC-134a, R407B, and R410A are used as working fluids. The conditions on which the model is tested are as follows : condensing temperature; 40.0, 45.0, 50.0, $55.0^{\circ}C$, degree of subcooling;0.0, 2.5, $5.0^{\circ}C$, capillary tube exit condition;choked flow, capillary tube diameter;1.2~2.4mm, mass flow rate;5.0~50.0g/sec. The results justify the use of Stoecker's model which yields the results very close to the values in ASHRAE handbook. While McAdams' method yields much better results than Duckler's in calculating the viscosity of the fluid in 2-phase, the friction factor suggested by Stoecker seems to be the best for capillary tubes of large diameter used in residential air conditioners. For each refrigerant, 372 data with various variables are calculated by the model. The results show that capillary tube length varies very uniformly with changes in condensing temperature and degree of subcooling. Based on this fact, regression analysis is performed to determine the dependence of mass flow rate on the length and diameter of a capillary tube, condensing temperature, and degree of subcooling. Thus determined correlation yields a mean deviation of 2.36% for 1,488 data, showing an excellent agreement.