• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.12
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• pp.695-702
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• 2009

Dynamic behavior of Libr-water absorption system using low-temperature hot water was investigated numerically. Thermal-hydraulic model of single-effect/double-lift 100 RT chiller was developed by applying transient conservation equations of total mass, Libr mass, energy and momentum to each component. Transient variations of system properties and transport variables were analysed during start-up operation. Numerical analysis were performed to quantify the effects of bulk concentration and part-load operation on the system performance in terms of cooling capacity, coefficient of performance, and time constant of system. For an absorption chiller considered in the present study, optimum bulk concentration was found to exist, which resulted in the minimum time constant with stable cooling capacity. COP and time constant increased as the load decreased down to 40%, below which the time constant increased abruptly and COP decreased as the load decreased further.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.10
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• pp.990-998
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• 2004

Dynamic behavior of an ammonia-water absorption system was investigated numerically. Thermal-hydraulic model for a single-effect 3 RT chiller was developed by applying transient conservation equations of total mass, $NH_3$ mass, energy and momentum to each component. Transient variations of system properties and transport variables were analysed during start-up operation. Numerical analyses were performed to quantify the effects of bulk concentration and charging ratio on the system performance in terms of cooling capacity, coefficient of performance, and time constant of system. For an absorption chiller considered in the present study, optimum charging ratio and bulk concentration were to found to exist, which resulted in the maximum cooling capacity and COP. The time constant increased as the charging ratio increased, but decreased with the increase of bulk concentration.

• Bulletin of the Korean Chemical Society
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• v.28 no.9
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• pp.1493-1498
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• 2007

In this work, alkyl methacrylate-based microgels were synthesized by an experimental design method, and their sebum absorption characteristics were investigated. The results of fractional factorial experimentation indicated that the cross-linking agent content, solvent content, and stirring speed were the main parameters in the synthesis of the microgels. The suitable synthesis conditions were determined by the response surface design method. Through a study of the monomer and solvent effects, it was confirmed that the microgel shows the highest sebum absorption ratio when t-butyl methacrylate is used as a monomer or when acetone is used as a solvent. The optimal microgel synthesis conditions for cosmetic application were determined, and the resulting microgel had a mean particle size of 4.7 μm and a sebum absorption ratio of 435%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.4
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• pp.453-462
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• 1994

An unsteady quasi one-dimensional model of momentum, heat and mass transfer in a falling film of a vertical plate absorber which is cooled by air was developed using the integral method. Energy conservation of the absorber wall is considered in the model. The model can predict absorption rate, film thickness and mean velocity as well as concentration and temperature profiles. Predictions of steady state temperature and concentration profiles for LiBr/water system for constant wall temperature condition are in good agreement with the two-dimensional finite difference method solutions. Effects of operating conditions, such as convective heat transfer coefficient between the cooling air and the absorber wall, cooling air temperature and film thickness at inlet, on absorption rate of water vapor into LiBr/water solution were shown.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.2
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• pp.670-679
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• 1996

A numerical study for vapor absorption into LiBr-H$_{2}$O solution film flowing over horizontal circular tubes has been carried out. The momentum, energy and diffusion equations, which are parabolized by the boundary- layer approximation, are solved simultaneously for various mass-flow rates and inlet conditions. The results for the velocity, temperature and concentration fields, as well as the heat and mass flux at the free surface are presented. The effects of inlet conditions, i.e., flow rate, temperature and concentration, on the absorption process are also examined and discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.04a
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• pp.31-34
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• 1997

A reversible scalar phenomena in amorphous As$_{40}$ Ge$_{10}$ Se$_{15}$ S$_{35}$ have been investigated by blue-pass-filtered Hg lamp and He-Ne laser. Annealing causes the shift of the absorption edge to shelter wavelengths approximately 0.17ev, also illumination moves it to longer wavelengths about 0.05 ~ 0.07eV and it increases the refractive index maximum 0.3. Therefore the thermalbleaching(TB) and photodarkening(PD) effects have been understood by the results related to optical absorption characteristics. TB could be estimated as increasing the stabilization of amorphous chalcogenide films since absorption slope of extended regions(U) was not changed by annealing. On the other hand, PD could be understood as due to the enhancement of disorder since the slope of Urbach’s tail(1/F) around an absorption edge were decreased by illumination.ion.n.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.443-446
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• 1997

This paper raises issues in testing the absorption coefficients of sound-absorptive samples in the standing wave tube according to the Korean standard of KS F 2814. The code does not consider any effect of air-damping during test. This limitation has been shown to yield much variation of sound absorption coefficients for recent sample tests whose coefficients are less than 10 %. An improved method of calculating the sound absorption coefficients is proposed in this work and its effectiveness in real test is also illustrated. Finally, the guide line for the modification of our national standard code KS F 2814 is suggested for the future.

• KSBB Journal
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• v.6 no.1
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• pp.99-103
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• 1991

The optimum conditions and rates of absorption of isobutylene in aqueous para-toluene sulfonic acid(PTSA) were studied experimentally in a stirred reactor. The effects of acid concentration(30-70 wt%), acid loading (0.3-5), mixing intensity(400-1000 rpm), and temperature ($20-80^{\circ}C$) on the absorption conditions were examined. The absorption rate of isobutylene was first order in isobutylene and variable order in PTSA concentrations. The apparent energy of activation was found to be 13 Kcal/mole.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.439-443
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• 2011

Using the projection operator technique, a reduced density matrix theory for linear absorption spectrum of energy transfer systems is developed for the theoretical absorption line shape of the systems with non-Condon transitions. As an application, we considered a model system of OH vibrations of water. In the present model calculation, the OH vibration modes are coupled to each other via intra-molecular coupling mechanism while their intermolecular couplings are turned off. The time-correlation functions appearing in the formulation are calculated from a mixed quantum/classical mechanics method. The present theory is successful in reproducing the exact absorption line shape. Also the present theory was improved from an existing approximate theory, time-averaged approximation approach.

• Current Optics and Photonics
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• v.6 no.6
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• pp.583-589
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• 2022

Vanadium dioxide (VO₂) is a well-known material that undergoes insulator-to-metal phase transition near room temperature. Since the conductivity of VO₂ changes several orders of magnitude in the terahertz (THz) spectral range during the phase transition, VO₂-based active metamaterials have been extensively studied. Experimentally, it is reported that the metal nanostructures on the VO₂ thin film lowers the critical temperature significantly compared to the bare film. Here, we theoretically studied such early transition phenomena by developing an analytical model. Unlike experimental work that only measures transmission, we calculate the reflection and absorption and demonstrate that the role of absorption is quite different for bare and patterned samples; the absorption gradually increases for bare film during the phase transition, while an absorption peak is observed at the critical temperature for the metamaterials. In addition, we also discuss the gap width and VO₂ thickness effects on the transition temperatures.