• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.102-111
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• 2000

A numerical model which simulates the simultaneous heat and mass transfer within a vertical tube GAX absorber was developed. The ammonia vapor and the solution liquid are in counter-current flow, and the hydronic fluid flows counter to the solution liquid. The film thickness and the velocity distribution of the liquid film were obtained by matching the shear stress at the liquid-vapor interface. Two-dimensional diffusion and energy equations were solved in the liquid film to give the temperature and concentration, and a modified Colburn-Drew analysis was used for the vapor phase to determine the heat and mass fluxes at the liquid-vapor interface. The model was applied to a GAX absorber to investigate the absorption rates, temperature and concentration profiles, and mass flow rates of liquid and vapor phases. It was shown that the mass flux of water was negligible compared with that of ammonia except the region near the liquid inlet. Ammonia absorption rate increases rapidly near the liquid inlet and decrease slowly. Both the absorption rate of ammonia vapor and the desorption rate of water near the liquid inlet increase as the vapor mass flow rate increases, but the mass fluxes of the ammonia and the water near the liquid outlet decrease as the mass flow rate of the vapor increases.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.8
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• pp.1085-1096
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• 2000

An experimental study was performed to examine the heat and mass transfer characteristics of $LiBr-H_2O$ solution flowing over a single horizontal tube with the water vapor absorption. Effects of the flow rate and the temperature of the solution at the top of the tube, the absorber pressure and the drainage pattern were considered. The absorption rate depends highly on the absorber pressure at the low flow rate condition while on the solution inlet temperature at the high flow rate condition. Also, when the flow rate is low, the absorption performance with the sheet flow drainage appeared to be higher than that with the dripping/jet drainage. However, at the high flow rate condition, the case became reversed. The liquid film became wavy with the higher absorption rate. The waves were more probable to form with the lower flow rate and temperature of the solution, and with the higher absorber pressure.

• KIEAE Journal
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• v.11 no.3
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• pp.69-73
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• 2011

In general, there are two types of PVT module depending on the existence of the glass in front of PV module: glazed and unglazed. On the other hand, the water-type PVT modules can be classified into two types, according to absorber type: the sheet-and-tube absorber PVT module and the fully wetted absorber PVT module. The aim of this study is to analyze the electrical and thermal performance of a water-type PVT module with fully wetted absorber. For this study, a prototype of unglazed PVT module with fully wetted absorber was designed and built, and both the thermal and electrical performances of the prototype module were measured in outdoor conditions. A conventional mono-crystalline Si PV module was tested alongside the PVT module for their electrical performance comparison. The results showed that the thermal efficiency of the PVT module was average 51% and its electrical efficiency was average 14.3% in mean fluid temperature $10-40^{\circ}C$, whereas the electrical efficiency of the conventional PV module was average 12.6%. It is found that the electrical efficiency of the PVT module was improved by approximately 14% compared to that of the PV module. The temperature of PVT module becomes lower due to the cooling effect by the fluid of the absorber. The results proved that the electrical efficiency was higher when the mean fluid temperature was lower.

• Applied Chemistry for Engineering
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• v.21 no.1
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• pp.71-75
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• 2010

The efficient performance of absorber is of great importance for the absorption heat pump cycle. The experimental study of absorber with spiral tube of tangential feeding of liquid phase has been investigated using methanol-glycerine as a working fluid. The effect of change in absorber operating conditions was analyzed to improve the performance. The increase in solution flow rate and cooling flow rate positively affects the absorber performance while an increse in the solution concentration negatively affects the absorber performance. The results showed that mass absorption flux was in the range of $0.2{\sim}0.6kgm^{-2}sec^{-1}$, the solution heat transfer coefficient between 1.6 and $4.2kwm^{-2}K^{-1}$, the absorber thermal load from 0.9 to 1.5kw and the mass transfer coefficient from 0.9 to 1.7 m/sec.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.121-126
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• 2011

The heat from PV modules should be removed for better electrical performance, and can be converted into useful thermal energy. A photovoltaic-thermal(PVT) module is a combination of PV module with a solar thermal collector which forms one device that converts solar radiation into electricity and heat simultaneously. In general, there are two different types of PVT module: glazed PVT module and unglazed PVT module. On the other hand, two types of the PVT module can be distinguished according to absorber on PV module rear side: the sheet-and-tube absorber PVT module and the fully wetted absorber PVT module. In this paper, the experimental performance of water type unglazed PVT with fully wetted absorber was analyzed. The electrical and thermal performance of the unglazed PVT were measured in outdoor conditions, and the results were analyzed. The experimental results showed that the thermal efficiency of the PVT module was 42% average, and its electrical efficiencies were 15.2% and 14.2% average, respectively, for the mean fluid temperature of $10-20^{\circ}C$ and $21-30^{\circ}C$. Thermal efficiency depends on solar radiation, mean fluid temperature and ambient temperature. The PVT module temperature is related to the cooling effect of the PV module by the fluid of the absorber. The results proved that the electrical efficiency was higher when the mean fluid temperature was lower.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.328-334
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• 2000

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube, hydrophilic tube. The additive concentration was about $0.05{\sim}5.5mass%$. The heat transfer coefficient was measured as a function of solution flow rate in the range of $0.01{\sim}0.034 kg/ms$. The experimental result were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect which was generated by addition of the surfactant is observed in each test tube.

• Journal of Power System Engineering
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• v.15 no.4
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• pp.11-18
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• 2011

A Shock absorber is one of the most important components in vehicle suspension systems. In general, many repeated analyses are required for the design of a shock absorber to satisfy the suspension characteristics of a specific automobile, like fluid flow analysis and mechanical analysis. The purpose of this study is to develop a fast design tool for shock absorber designers. One of the efficient solutions for this can be an empirical design method considering phenomenological effects from the shock absorber design variables. In order to extract the shock absorber's experimental characteristics, we used Taguchi method. This method showed that which design variables have major effects for the shock absorber's damping characteristics. This empirical design method also showed the direction of the design changes to satisfy the designer's intension.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.12
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• pp.1214-1222
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• 2001

The present study investigated the effect of diameter and length on the absorption performance of a vertical falling film type absorber using $LiBr-H_2$O solution of 60 wt%. The parameters were diameter of absorber (17.2, 23.4, 31.1 mm), length of absorber (771, 1150, 1528 mm), and film Reynolds numbers (50, 70, 90, 110, 130, 150). As the diameter of the absorber was increased, the absorption mass flux, Sherwood number, heat flux, and heat transfer coefficient were increased, in which Sherwood number and heat transfer coefficient were increased up to 13% and 30% respectively. As the length of the absorber was increased, the total absorption rate and heat transfer coefficient were increased by 37% and 35% respectively, while the absorption mass flux was decreased.

• Korean Chemical Engineering Research
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• v.52 no.3
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• pp.314-320
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• 2014

Regarding the design of the gas sweetening absorber, the gas distribution analysis for the increase of the sour gas removal and reduction of the tower height is very important research topics. Recently, regarding the $CO_2$ capture technology which is a promising option for the reduction of the greenhouse gas (GHG), the need for the gas distribution improvement is increased as the gas treating capacity increases. In this paper, we have investigated the sour gas distribution in the absorber using CFD (Computational Fluid Dynamics) based on 10 MW post-combustion $CO_2$ capture plant installed in Boryeong power station, Korea Midland Power company. For this purpose, we suggested the three possible technology options (splash plate, spiral gas line and U-tube) for the gas distribution enhancement and compared the effect of the each cases. The result showed that the U-tube installed in the absorber increase the gas distribution about 30% compared to the base case, while the delta P increasement was about 10%. From these results, it was found that the U-tube installation is an effective technology option for the gas distribution enhancement in the gas sweetening absorber.

• Advances in Energy Research
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• v.4 no.4
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• pp.299-323
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• 2016

Cylindrical parabolic solar concentrators of small concentration ratio are attractive options for working temperatures around $120^{\circ}C$. The heat gained can be utilized in many applications such as air conditioning, space heating, heating water and many others. These collectors can be easily manufactured and do not need to track the sun continuously. Using a heat pipe as a solar absorber makes the system more compact and easy to install. This study is devoted to modeling a system of cylindrical parabolic solar concentrators of small concentration ratio (around 5) fitted with a heat pipe absorber with a porous wick. The heat pipe is surrounded by evacuated glass tube to reduce thermal losses from the heat pipe. The liquid and vapor flow equations, energy equation, the internal and external boundary conditions were taken into consideration. The system of equations was solved and the numerical results were validated against available experimental and numerical results. The validated heat pipe model was inserted in an evacuated transparent glass tube as the absorber of the cylindrical parabolic collector. A calculation procedure was developed for the system, a computer program was developed and tested and numerical simulations were realized for the whole system. An experimental solar collector of small concentration, fitted with evacuated tube heat pipe absorber was constructed and instrumented. Experiments were realized with the concentrator axis along the E-W direction. Results of the instantaneous efficiency and heat gain were compared with numerical simulations realized under the same conditions and reasonably good agreement was found.