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This research consists of a proposal of three methods that analyze the contribution of each operational variable in the prediction of the coefficient of performance of three different absorption systems aimed at reducing the independent variables for a faster and more efficient prediction. Methods considered in this study are correlation analysis, principal component analysis combined with correlation analysis, and Garson’s method. The experimental information includes (i) an absorption heat transformer with duplex components, (ii) an absorption single-state heat transformer, and (iii) a double-absorption heat transformer. For each case, the three methods were applied, the results were discussed in order to find the coincidences and discrepancies. [ABSTRACT FROM AUTHOR] more...

LiBr/H2O falling-film absorption is a common heat-and mass-transfer process in an absorption air-conditioning system. By analyzing the coupled heat and mass transfer of the falling-film absorption process, two-dimensional physical and mathematical models of the falling-film absorption along a vertical wall were established. The model was solved using the Fluent computational-fluid-dynamics software. The interfacial temperature, the concentration profile across the falling film, and the average heat-and mass-transfer fluxes and coefficients were obtained. The effect of the Reynolds number on the heat and mass transfer of the falling film was investigated. The results show that, when the film Reynolds number is less than 150, the average interfacial temperature increases with the increasing Reynolds number; however, the rising trend of the average interfacial temperature is more and more gentle. The average mass-transfer coefficient increases with the increasing Reynolds number, while the average heat-transfer coefficient decreases. Simultaneously, with the increasing Reynolds number, the average heat-and mass-transfer fluxes first increase and then decrease. An optimal Reynolds number exists that leads to the maximum heat- and mass-transfer fluxes. The average heat-and mass-transfer fluxes reach their maximums, 7.2 kW/m2 and 2.9×10-3 kg/(m2?s), respectively, when the Reynolds number is 50. more...

It is well known that application of solar powered absorption refrigeration (SPAR) systems will save energy, especially for air conditioning during the summer. This paper presents a SPAR system where evacuated tubes act as both solar collector and solution generator simultaneously while aqueous lithium bromide (H 2 O/LiBr) is used as the working fluid. In order to investigate the heat absorbing and vapor generating characteristics of lithium bromide solution in the evacuated tube, a test system was built and tested outdoors in Guangzhou in October 2015. The test results showed that lithium bromide solution in an evacuated tube can be heated up rapidly and generate vapor continuously. The vaporization rate, the solution concentration, the equivalent refrigerating capacity, the total energy absorbed by the solution, the thermal collecting efficiency and the solar coefficient of performance in theory were analyzed according to the test data. The work provides a reference for the design and simulation of SPAR systems where evacuated tubes are used as both solar collector and lithium bromide solution generator. [ABSTRACT FROM AUTHOR] more...

• A single-bubble absorption model for LiBr solution under vacuum condition is established. • A visible experimental platform is established to validate the accuracy of the model. • The effects of structure and operation parameters on heat and mass transfer are analyzed. • The heat and mass transfer mechanisms are revealed to improve the performance of absorber. Bubble absorption has an efficient performance in absorption units, and lithium bromide (LiBr)-H 2 O is the most popular working medium in absorption system due to its safety and environmental protection. Limited to the vacuum operation, the researches of bubble absorption for LiBr solution are less reported and the bubble absorption characteristic for LiBr solution is still not clear. In this study, a single-bubble heat and mass transfer model is established to investigate the heat and mass transfer coefficients of bubble absorption for LiBr solution under vacuum condition. A visible experimental platform is established to validate the feasibility of vacuum operation and the model accuracy. The experimental results showed the relative deviation is less than 11.9%. Base on the current model, the effects of structure and operation parameters are comprehensively analyzed to explore the appropriate configuration. The results indicate that the heat and mass transfer coefficients increase significantly with the increase of the orifice diameter and the bubble velocity, while they reduce with the increase of solution concentration. It can be explained that large orifice diameter expands the contact area, and high velocity strengthens the convection, which promote the absorption. Dilute solution concentration reduces the viscous force and surface tension, thereby enhancing the heat transfer. It is expected to provide guidance for the heat and mass transfer mechanisms and contribute to advance the structure and configuration of absorption system. [ABSTRACT FROM AUTHOR] more...

Absorption refrigeration systems gained considerable attention recently for their environmental friendly behavior and for activation using thermal energy sources. In LiBr-H 2 O absorption chillers, solution crystallization represents a severe problem. The crystallization of the solution blocks the chiller internal piping and stop the chiller operation. In this paper a crystallization detection function is developed and embedded into a dynamic simulation model to detect solution crystallization due to abnormal operation. The crystallization detection function is developed by introducing critical concentration equation that was generated from linearization of the crystallization line in Equilibrium chart for aqueous lithium bromide solutions. The model successfully depicted the solution concentration when the solution concentration is approaching the crystallization line. [ABSTRACT FROM AUTHOR] more...

Abstract: An experimental investigation of vertical in-tube falling film heat transfer with different heat fluxes and concentrations of lithium bromide solution were conducted. The experiments show that the heat transfer coefficient increases with the decrease of inlet concentration and significantly increase with heat flux increase. An experimental correlation of falling film heat transfer coefficient is obtained: The comparison of falling film generator with immersed tube generator shows that the heat transfer coefficient is 4.37 times higher than that of immersed tube generator, which can significantly reduce the volume of the falling film generator. The volume of falling film generator is only 52.1% of the volume of immersed tube generator. [Copyright &y& Elsevier] more...

To further explore the influence law of nanoparticles on the surface tension of stable nano-Lithium Bromide solution (LiBr), the effects of temperature, solution concentration, dispersant and nanoparticles on the surface tension were investigated by Wilhelmy plate method under atmospheric pressure. The results demonstrate that the surface tension ascends with the augmentation of solution concentration and the amount of nanoparticles, decreases with increasing temperature and the amount of dispersant. The surface tension of the solution decreases obviously after adding dispersant. However, there is an optimal value for the amount of dispersant, and the surface tension of solution tends to be gentle increased after exceeding the optimal value of the dispersant, which is 2 wt%. Continue to add nanoparticles, the solution surface tension increases slightly, however, it is still less than pure LiBr. For instance, when the solution temperature is 30 °C and the solution concentration is 50 wt%, the surface tension of nano-LiBr added with 0.01 wt% nanoparticles decreases by 26.20%. The surface tension of nano-LiBr is impacted by coupling of the dispersant and nanoparticles at the same temperature and solution concentration. A surface tension calculation model of nano-LiBr was fitted using experimental data, and the maximum error was 2.78%. • The surface tension of nano-LiBr was measured by Wilhelmy plate method under steady-state conditions. • The effects of temperature, solution concentration, dispersant and nanoparticles on surface tension are clarified. • Based on the experimental data, a semi empirical model of the surface tension of stable nano-LiBr was obtained. [ABSTRACT FROM AUTHOR] more...

The purposes of this study are to measure the saturated vapor pressure and the mass transfer rate of lithium bromide (LiBr) aqueous solution in the presence of 40 nm CuO nano-particles with the concentrations of 0.0, 0.01, 0.05, 0.1 and 0.12 wt%, and to research the effects of nano-particles, solution concentration and temperature on the saturated vapor pressure and the water vapor absorption rate. Experimental results demonstrate that nano-particle is the main factor affecting the saturated vapor pressure and the mass transfer rate. The saturated vapor pressure decreases with nano-particle mass fraction up to an optimum concentration (0.1 wt% in CuO nanofluids) while increases by increasing the concentration of nano-particle further, and the effective change ratio of saturated vapor pressure increases first and then decreases as mass fraction of nano-particle increases. The mass transfer rate is also initially increased with increasing nano-particle concentration and then emerges a slowly rising tendency. The effective absorption ratio is enhanced when the nano-particle concentration increases, and the value of maximum effective absorption ratio is obtained when the nano-particle concentration is 0.1%. The effective absorption ratio has the maximum values of 2.20 and 2.85 in 58% LiBr solution with nano-particle concentration of 0.05% and 0.1%, respectively. • The saturated vapor pressure and mass transfer characteristics of the nano-LiBr solution are measured by balanced kettles. • Various factors affecting the saturated vapor pressure and mass transfer rate of the LiBr solution are clarified. • The maximum effective absorption ratio is 2.20 and 2.85 in 58% LiBr solution added 0.05% and 0.1% nanoparticles. [ABSTRACT FROM AUTHOR] more...