• Journal of Power System Engineering
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• v.18 no.6
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• pp.126-132
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• 2014

The P-T characteristics of mixed refrigerant in thermostatic expansion valve sensing bulb were studied using R-134a and R-410A refrigerant. The characteristics of mixed refrigerant were investigated according to pressure variation and the variation of composition ratio of R-134A and R-410A in the temperature range of $-15^{\circ}C{\sim}15^{\circ}C$. The Thermodynamic characteristic values of the mixed refrigerants were identified using the characteristic value analysis program of mixed refrigerant(Refrop v9.0, NIST). The P-T characteristics in the case of the mixing ratio of 90:10 for R-410A and R-134A were the same result as R-22. And the physical properties showed similar results with R-22. The Maximum operating pressure(MOP) of mixed refrigerant showed a tendency to decrease with decreasing the mixing ratio of additive gases($N_2$ or He) gases. The characteristics in the case of the mixing ratio of 80:1 for mixed refrigerant and additive gases were the similar result as Reference refrigerant.(R-22 MOP, Sporlan company) In addition $N_2$ and He, both showed the same results. It was able to confirm that a MOP on the thermostatic expansion valve sensing bulb can be maintained by adjusting the mixing ratio of mixed refrigerant gases and additive gases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1245-1252
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• 2001

The condensation pressure drop for pure refrigerants R-22, R-134a, and a binary refrigerant mixture R-410A flowing in a small diameter tube was investigated. The test section is a counterflow heat exchanger with refrigerant flowing in the inner tube and coolant flowing in the annulus. The test section consists of 1220 [mm] length with horizontal copper tube of 3.38 [mm] outer diameter and 1.77 [mm] inner diameter. The refrigerant mass fluxes ranged from 450 to 1050 [kg/(㎡$.$s)] and the average inlet and outlet qualities were 0.05 and 0.95, respectively. The main experimental results were summarized as follows : In the case of single-phase flow, the pressure drop of R-134a is much higher than that of R-22 and R-410A for the same Reynolds number. The friction factors for small diameter tubes are higher than those predicted by Blasius equation. In the case of two-phase flow, the pressure drop increases with increasing mass flux and decreasing quality. The pressure drop of R-134a is much higher than that of R-22 and R-410A for the same mass flux. Most of correlations proposed in the large diameter tube showed enormous deviations with experimental data. However, the correlation predicted by Honda et al showed relatively good agreement with experimental data for R-134.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.981-989
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• 2005

In this study, external condensation heat transfer coefficients (HTCs) are measured on a low fin tube and Turbo-C tubes at the saturated vapor temperature of $30^{\circ}C$, $39^{\circ}C$, and $50^{\circ}C$ for R22, R410A, R407C and R134a with the wall subcooled at $3{\~}8^{\circ}C$. The HTCs of all refrigerants decreased as increasing the saturation temperature from $30^{\circ}C$ to $50^{\circ}C$. This trend is due to better thermodynamic properties of the liquid phase at low temperature Beatty and Katz's prediction yielded a $20.0\%$ deviation for the low fin tube data. The heat transfer enhancement factors for the 26 fpi low fin tube and Turbo-C tubes are 4.0${\~}$5.5 and 3.0${\~}$8.1 respectively for the refrigerants tested. Finally the performance of Turbo-C tube is better than that of the low fin tube.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1980-1985
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• 2007

The purpose of this study is to investigate the performance of an autocascade refrigeration system using the refrigerant mixtures of R-134a(64${\sim}$72wt%), R-23(20${\sim}$25wt%) and R-14(8${\sim}$12wt%) as working fluids by experiment. The experimental apparatus consisted of a autocascade system with a compressor, condenser, evaporator, gas-liquid separator and cascade condenser, etc. Two main causes to this failure were considered as follows. First, the pressure ratio in the compressor was extremely increased at the beginning of the experiment. Second, the outlet temperature in compressor was higher than its limited temperature. For a stable operation of the compressor, a portion of the mixed refrigerant was by-passed at the inlet of the heat exchanger and transferred directly to the suction of the compressor in the modified system. The experimental parameters were changed weight of R-134a(1800g, 2800g), R-23(700, 800, 900g) and R-14(300, 400, 500g). The results showed that the best performance in case of R-134a of 2800g, R-23 of 900g and R-14 of 500g.

• Proceedings of the SAREK Conference
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• 2003.07a
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• pp.126-126
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• 2003

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.704-710
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• 2017

Although the desalination technique using gas hydrate formation is at a development stage compared to the commercially well-established reverse osmosis (RO), it still draws attention because of its simplicity and moderate operational conditions especially when using refrigerants for guest gases. In this study, DFT (density functional theory)-based molecular modeling was employed to explain the energetics of the gas hydrate formation using HFC (hydrofluorocarbon) and HCFC (hydrochlorofluorocarbon) refrigerants. For guest gases, R-134a, R-227ea, R-236fa, and R-141b were selected and three cavity structures ($5^{12}$, $5^{12}6^2$, and $5^{12}6^4$) composed of water molecules were constructed. The geometries of guest gas, cavity, and cavity encapsulating guest gas were optimized by molecular modeling respectively and their located energies were then used for the calculation of binding energy between the guest gas and cavity. Finally, the comparison of binding energies was used to propose which refrigerant is more favorable for the gas hydrate formation energetically. In conclusion, R-236fa was the best choice in terms of thermodynamic spontaneity, less toxicity, and low solubility in water.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2284-2293
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• 2004

The evaporation heat transfer coefficient h$\_$r/ and frictional pressure drop Δp$\_$f/ of refrigerant R-134a flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the oblong shell and plate heat exchanger by four plates of geometry with a corrugated sinusoid shape of a 45 chevron angle. Upflow of refrigerant R-134a boils in two channels receiving heat from downflow of hot water in other channels. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature and vapor quality of R-134a were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. The results indicate that the evaporation heat transfer coefficient h$\_$r/ and pressure drop Δp$\_$f/ increase with the vapor quality. A rise in the refrigerant mass flux causes an increase in the h$\_$r/ and Δp$\_$f/. But the effect of the average heat flux does not show significant effect on the h$\_$r/ and Δp$\_$f/. Finally, at a higher saturation temperature, both the h$\_$r/ and Δp$\_$f/ are found to be lower. The empirical correlations are also provided for the measured heat transfer coefficient and pressure drop in terms of the Nusselt number and friction factor.

• Journal of Ginseng Research
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• v.46 no.3
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• pp.376-386
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• 2022

Background: Brain-derived neurotrophic factor (BDNF)-tropomyosin-related kinase B (TrkB) plays a critical role in the pathogenesis of depression by modulating synaptic structural remodeling and functional transmission. Previously, we have demonstrated that the ginsenoside Rb1 (Rb1) presents a novel antidepressant-like effect via BDNF-TrkB signaling in the hippocampus of chronic unpredictable mild stress (CUMS)-exposed mice. However, the underlying mechanism through which Rb1 counteracts stress-induced aberrant hippocampal synaptic plasticity via BDNF-TrkB signaling remains elusive. Methods: We focused on hippocampal microRNAs (miRNAs) that could directly bind to BDNF and are regulated by Rb1 to explore the possible synaptic plasticity-dependent mechanism of Rb1, which affords protection against CUMS-induced depression-like effects. Results: Herein, we observed that brain-specific miRNA-134 (miR-134) could directly bind to BDNF 30 UTR and was markedly downregulated by Rb1 in the hippocampus of CUMS-exposed mice. Furthermore, the hippocampus-targeted miR-134 overexpression substantially blocked the antidepressant-like effects of Rb1 during behavioral tests, attenuating the effects on neuronal nuclei-immunoreactive neurons, the density of dendritic spines, synaptic ultrastructure, long-term potentiation, and expression of synapse-associated proteins and BDNF-TrkB signaling proteins in the hippocampus of CUMS-exposed mice. Conclusion: These data provide strong evidence that Rb1 rescued CUMS-induced depression-like effects by modulating hippocampal synaptic plasticity via the miR-134-mediated BDNF signaling pathway.

• Proceedings of the SAREK Conference
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• 2007.06a
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• pp.25-25
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• 2007

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.319-320
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• 2013