• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.122-133
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• 1997

Numerical analysis using finite volume method has been carried out to examine the effect of degree of superheat of LiBr aqueous solution on heat and mass transfer occurred in absorption process. According to the result of this study, it was found that refrigerant vaper was generated at the entrance region of absorber when LiBr aqueous soltion was superheated. As the degree of superheat increases, heat transfer rate increases and vapor absorption rate decreases. The increase in averaged Nusselt and Sherwood numbers could be found as film Reynolds number increases. The larger the degree of superheat, the greater the averaged Nusselt and Sherwood numbers.

• Journal of Sericultural and Entomological Science
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• v.37 no.1
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• pp.33-38
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• 1995

The mechanical properties and structure of degummed silk fiber stretched after being treated with 8M LiBr aqueous solution were investigated. The mechanical properties of degummed silk fiber were depended upon the treatment temperature of 8M LiBr aqueous solution. That is, the strength and elongation had a tendancy to increase with the temperature, whereas the Young's modulus tended to decrease. The X-ray diffraction pattern showed that the crystalline orientation was disordered by 8$0^{\circ}C$ treatment neverthless destruction of the crystallites did not occur. rho silk fiber could be successfully stretched up 160% under the condition of 8M LiBr aqueous solution at 80 * after immersed for 1hr. For the highly stretched sample(160%), the tensile strength and Young's modulus were significantly improved in spite of lower elongation at break. According to the examination of X-ray diffraction pattern and SEM, the orientation tends to be occured more and more with stretching ratio. From the DSC thermograms, it shows that the thermal decomposition behavior was different between untreated and treated specimen with 8M LiBr aqueous solution. The maximun endothermic peak of thermal decomposition tends to increase to high temperature with the increase of stretching ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1267-1276
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• 1998

Falling-film evaporation experiments with aqueous lithium bromide (LiBr) solution were performed to investigate the heat transfer characteristics of enhanced copper tubes. Enhanced tubes (a knurled tube, a spirally grooved tube, and a tube coated with $20{\mu}m$ aluminum particles) and a bare tube were selected as test specimens. Averaged evaporation fluxes of water were obtained from horizontal tubes with various film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. The enhanced performance of steam generation was compared between tubes with varying parameters. The knurled tube geometry showed the most excellent performance among the tubes tested. The specified enhanced tubes were more useful for generating steam on a low grade heat source such as waste heat.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.294-302
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• 1997

Falling-film evaporation experiments for aqueous solution of lithium bromide (LiBr) were performed on a horizontal smooth 19.05-mm-dia copper tube. Average heat transfer coefficients were obtained with varied film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. Heat transfer coefficients increase with increasing system pressure and decreasing concentration. For degrees of wall superheat, the heat transfer coefficient did not't show the distinct trend. For this experimental ranges, heat transfer coefficients showed maximum values at an optimal film Reynolds number. The results of this work were compared with pool boiling data reported previously, and it was shown that the heat transfer performance is superior to the pool boiling.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.250-255
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• 1991

Performance analysis of double-effect absorption heat pump system has been done to find improved working pairs (or mixture) by computer simulation. Based on the thermodynamic analysis, the coefficient of performance and mass flow ratio are investigated to compare three aqueous solutions [LiCl-water, LiSCN-LiBr-water, LiCl-$CaCl_2$-$Zn(NO_3)_2$-water] which was developed for only cooling, with conventional LiBr-water solution. It is found that the performances of the new aqueous solutions are better than that of LiBr-water solution not only in cooling systems, but also in heating systems. Theoretical thermodynamic performance data can be used in heat recovery systems by basic design data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3293-3303
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• 1996

Numerical analyses have been performed to estimate the absorption heat and mass transfer coefficients in absorption process of the LiBr aqueous solution and the total heat and mass transfer rates in a vertical tube absorber which is coolING ed by air. Axisymmetric cylindrical coordinate system was adopted to model the circular tube and the transport equations were solved by the finite volume method. Absorption behaviors of heat and mass transfer were analyzed through falling film of the LiBr aqueous solution contacted by water vapor in tube. Effects of film Reynolds number on heat and mass transfer coefficients have been also investigated. Especially, effects of tube diameter have been considered to observe the total heat and mass transfer rates through falling film along the tube. Based on the analysis it has been found that the total mass transfer rate increases rapidly in a region with low film Reynolds number(10 ~ 40) as the film Reynolds number increases, while decreases beyond that region. The total heat and mass transfer rates increase with increasing the tube diameter.

• International Journal of Industrial Entomology and Biomaterials
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• v.20 no.2
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• pp.99-105
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• 2010

In this paper, the regenerated silk fibroins were dissolved in LiBr aqueous solution with different dissolution temperature and time, and the effects of the dissolution condition on the regeneration yield, molecular weight, wet spinnability, and electrospinnability of regenerated silk fibroin were investigated. The regeneration yield, molecular weight distribution, and wet spinnability of regenerated silk fibroin were nearly affected by the dissolution temperature and time. However, the electrospinning performance of silk fibroin was influenced by the dissolution condition implying the electrospinning of silk fibroin is more sensitive process than the wet spinning in the range tested in this study. While $25^{\circ}C$ of dissolution temperature resulted in a good electrospinnability of regenerated silk fibroin, the electrospinnability was slightly deteriorated when silk fibroin was dissolved at $60^{\circ}C$ for 6 hours. Also, though the fiber diameters of electrospun silk fibroin produced by the dissolution at $25^{\circ}C$ for 6 hours and 24 hours were 443 and 451 nm, respectively, that at $60^{\circ}C$ for 5 min was reduced to 411 nm. The fiber diameter was more decreased to 393 nm when the dissolution time increased up to 6 hours at $60^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.2
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• pp.144-152
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• 1997

Film absorption involves simultaneous heat and mass transfer in the vapor-liquid system. In the present work, the absorption process of water vapor by an aqueous soluton of LiBr flowing inside of the vertical tube was investigated. The continuity, momentum, energy and diffusion equations for the solution film and vapor were formulated in integral forms and solved numerically. The model could predict the film thickness, the pressure gradient, and the heat and mass transfer rate. Particularly the effects of vapor flow conditions on the absorption process were investigated in terms of the vapor Reynolds number. As the vapor Reynolds number increased, the shear stress at the vapor-solution interface also increased. Consequently solution film became thinner at higher vapor flowrate under the co-currentflow condition. Thinner film was capable of higher heat transfer to the wall and leaded to higher absorption rate of the water vapor into the solution film.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.3
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• pp.219-227
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• 1989

Performance analysis of an absorption heat pump system for solar energy recovery has been done by computer simulation to find improved working pairs. Based on the thermodynamic analysis, the coefficient of performance and mass flow ratio have been calculated to compare two aqueous solutions [LiCl-water, $LiCi-CaCl_2-Zn(NO_3)_2$-water] which were developed for cooling by others, with the conventional LiBr-water solution. As a result of this analysis, the performances of the new aqueous solutions were found to be better than that of LiBr-water solution not only in cooling systems, but also in heating and in heat transformer systems. Their theoretical thermodynamic performance data were given here with.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.19-27
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• 2001

In the present study, the effects of film Reynolds number (60∼200) and volumetric content of non-absorbable gases (0∼10%) in water vapor on the absorption process of aqueous LiBr solution were investigated experimentally. The formation of solution film on the horizontal tubes of six rows was observed to be complete for Re>100. Transition film Reynolds number was found to exist above which the Nusselt number and Schmidt number diminishes with solution flow rate. As the concentration of non-absorbable gases increased, mass transfer rate decreased more seriously than heat transfer rate did. the degradation effects of non-absorbable gases seemed to be significant especially when small amount of non-absorbable gases was introduced to the pure water vapor.