• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.82-86
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• 2011

Lightweight aggregate which is composed of sintered polycrystalline materials usually has a certain portion of pores inside of it. Because of such a structural characteristics, it tends to that movement of water in aggregate shows an abnormal behavior against the change of outside environment. In general, water movement behavior is controlled by porosity, distribution of pore size; however, dense surface layer will also affect water movement behavior in case of artificially sintered aggregates. Factors affecting water movement behavior in the aggregate are pore distribution, pore shape, pre-wetting method, etc. In this study, absorption characteristics of aggregate under the pressure and absorption rate according to water dipping time are analyzed for the basis of pressure pumping of lightweight concrete. Two kinds of aggregates were used for the test: one is made by 'L' company in Germany and the other is of our own made at the pilot plant in Kyonggi University. Absorption rate of aggregate is measured according to water dipping time, vacuum pressure, and quenching condition. Absorption rate of aggregate with $300^{\circ}C$ quenching is higher than that of aggregate with 24 hr water dipping. Generally the more vacuum the higher water absorption rate. Water absorption rate of 'L' aggregate under -300 mmHg is 54 % higher than that of aggregate with 24 hr water dipping; however, only 2 % increase in water absorption was measured for the K622 and K73 which were of our own.

• Advances in concrete construction
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• v.11 no.4
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• pp.323-333
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• 2021

The main objective of this study is to characterize and evaluate the hydrophobic performance of polymer-based water-repellent coatings on cementitious mortar surfaces. Different concentrations of poly(vinyl acetate) (PVAc) and poly(1,4-butylene adipate) (PBA) were prepared in the laboratory and their applicability and performance was tested experimentally by water absorption test and analysis of surface contact angles of cementitious mortar specimens. According to the results of this study, it can be stated that incorporation of nano polymer particles on the surface of cementitious mortar specimens can enhance contact angles and reduce water absorption by increasing hydrophobicity. However, a dosage limit exists for polymer materials in coating, and observed hydrophobic improvements decreases when polymer dosage reached beyond the limit. Additionally, it is observed that water absorption of polymer coated cementitious mortars is closely related with the results of surface contact angle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.175-181
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• 1994

This paper deals with the correlation of absorption rate in absorber and evaporation rate in evaporator. The evaporator consists of a copper tube of 10mm dia, and 600mm long and chilled water flowing through the tube is fed by the chilled water circulator. The flowrate of LiBr-water solution in the absorber plays a significant role in determining the magnitude of the heat transfer rate from chilled water to refrigerant There exists a flowrate of solution which has a maximum value of heat transfer. It is interesting to note that the absorption rate of absorber increases with increasing the heat transfer rate of the evaporator. Also, absorption rate increases with evaportation rate, and the ratio(the former/the other) depends on the inlet temperature of LiBr-water solution in the absorber. The heating capacity in the absorber is higher than the refrigerating capacity in the evaporator.

• Journal of Electrical Engineering and Technology
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• v.7 no.2
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• pp.230-235
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• 2012

Cases of insulation breakdown damage of water-cooled generator stator windings occur frequently due to coolant leakage and water absorption worldwide. Such serious accidents may cause not only enormous economic loss but also very serious grid accidents in terms of stable supply of electric power. More than 50 % of domestic generators have been operated for more than 15 years, and leak and water absorption problem of windings are often found during the planned preventive maintenance period. Since 2005, leak and water absorption tests have been performed for total watercooled stator windings after fully drying the inside of the windings. The results are then comprehensively analyzed. The result of the test performed by GE, a foreign manufacturer, for 141 generators showed failures in 80 of them (failure rate: 57 %), whereas in the tests carried out in Korean domestic power plants, only 14 out of 50 generators showed failures (failure rate: 28 %).

• Journal of the Korean Wood Science and Technology
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• v.34 no.2
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• pp.10-21
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• 2006

Recycled polypropylene (RPP) - Wood Saw Dust (WSD) composites with and without acetylation of filler were produced at different filler loading (15%, 25%, 35% and 45% w/w) and filler size (300, 212 and $100{\mu}m$). The RPP-WSD was compounded using a Haake Rheodrive 500 twin screw compounder at $190^{\circ}C$ at 8 MPa for 30 minutes. The mechanical properties and water absorption properties of modified and unmodified WSD-PP composites were investigated. Acetylation of WSD improved the mechanical and water absorption characteristic of composites. The decrease of filler size (300 to $100{\mu}m$) of the unmodified and acetylated WSD showed increase of tensile strength and impact properties. The composites exhibited higher tensile modulus properties as the filler loading increased (15% to 45%). However tensile strength, elongation at break and impact strength showed the opposite phenomenon. Water absorption increased as the mesh number and filler loading increased. With acetylation, lower moisture absorption was observed as compared to unmodified WSD. The failure mechanism from impact fracture of the filler-matrix interface with and without acetylation was analyzed using Scanning Electron Microscope (SEM).

• Composites Research
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• v.21 no.2
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• pp.8-14
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• 2008

Decrease of strength in composite material is generally caused by water absorption. It makes fracture of material, and loss of money or human lives. The objective of this study is to investigate the causes of decrease in strength by water absorption. Mechanism of water absorption was supposed as three steps. This mechanism is consisted of absorption into resin, absorption between resin and surface treatment agent, and delamination between fiber and resin. Conditions of test were supplied differently; kinds of fiber and resin, immersion time etc. Both of reversible reaction and irreversible reaction occurred simultaneously. Most of decrease in strength was finished at 2.5% water absorption, and the strength was recovered. At 4% water absorption, most of decrease was caused by irreversible reaction, therefore, there was a tendency not to be recovered in strength.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.9
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• pp.669-675
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• 2008

The objectives of this paper are to examine the effect of nano-particles on the pool type absorption heat transfer enhancement and to find the optimal conditions to design a highly effective compact absorber for ammonia/water absorption system. The effect of $Al_2O_3$ nano-particles and carbon nanotube(CNT) on the absorption performance is studied experimentally. The experimental ranges of the key parameters are 20% of ammonia concentration, $0{\sim}0.08\;vol%$ (volume fraction) of CNT particles, and $0{\sim}0.06 \;vol%$ of $Al_2O_3$ nano-particles. For the ammonia/water nanofluids, the heat transfer rate and absorption rate with 0.02 vol% $Al_2O_3$ nano-particles were found to be 29% and 18% higher than those without nano-particles, respectively. It is recommended that the concentration of 0.02 vol% of $Al_2O_3$ nano-particles be the best candidate for ammonia/water absorption performance enhancement.

• Journal of the Korean Solar Energy Society
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• v.27 no.4
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• pp.19-26
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• 2007

This paper concerns the study of absorption refrigeration and heat pump cycle to use sewage. Simulation analysis on the double-effect absorption refrigeration cycle with parallel and two-stage heat pump cycle has been performed. The working fluid is Lithium Bromide and water solution. The absorption refrigeration cycle use sewage as a cooling water for the absorber and condenser, and absorption refrigeration cycle does that as a chilled water for the evaporator of the first stage cycle. And the two-stage cycle consists of coupling double-effect with parallel and single effect cycle so that the first stage absorber and condenser produces heating water to evaporate refrigerant in the evaporator of the second stage. The effects of operating variables such as a absorber temperature on the coefficient of performance have been studied for absorption refrigeration and heat pump cycle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.9
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• pp.860-867
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• 2001

Absorption of water vapor into LiBr-$H_2O$ O solution flowing over a finned inclined surface is numerically investigated. The momentum, energy, and diffusion equation are numerically solved using a finite difference method. The four different shapes of the wall surfaces are considered to find the best surface for absorption assuming that the wall temperature and the surface tension are constant. The effects of the fin interval and Reynolds number are investigated. Based on the numerical results, it is known that the parabolic surface shows better absorption performance than the other surfaces, and that water vapor absorption increases gradually with decreasing the fin interval.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.1
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• pp.26-33
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• 2004

In general, an absorption chiller or heat pump is operated under the constant cooling water flow rate condition even though the system works with a partial load. The objective of this paper is to study the effect of the cooling water flow rates and the temperature of cooling water on the system performance to find the energy saving methode for the partial load operation of the double effect $H_2O$/LiBr absorption chiller. It is found that the performance of the system is sensitive to the temperature of cooling water than the cooling water flow rate, so the decrease of the performance due to reducing the cooling water flow rate can be overcome with the reduction of the cooling water temperature by 1$^{\circ}C$. The flow rate of the cooling water flow rate ranges from 50％ to 100％ of the flow rate at normal conditions with a partial load. It is also found that the operation cost of the cooling water pump and the cooling tower can be reduced by 23％.