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Transient processes are experimentally investigated at the initial stage of heat and mass transfer with steam absorption on the surface of 57.8 % water solution of lithium bromide in a bath with a diameter of 70 mm. The experiments were carried out both with a pure solution and with a solution where n-octanol surfactant was added. It is shown that with a sharp steam pressure increase in the volume above the surface of an absorbing solution, local temperature inhomogeneities are generated on the solution surface. The growth rate of these inhomogeneities is proportional to the growth rate of the steam pressure. It was found that, in contrast to the solution without surfactant, where convective flow is observed only during a short time interval after steam supply to the absorber, in a fixed layer of water-LiBr solution with surfactant addition, there is stable thermocapillary convection in the near-surface layer of solution during absorption. It is shown that for variable bottom topography, there can be space-localized zones, where the temperature on the solution surface is determined by the shape of bottom topography. [ABSTRACT FROM AUTHOR]

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]

• A low-cost turbine-type flow meter was design, constructed and tested for Li/Br mix. • All aspects of operation, equationing and analysis of the flowmeter were described. • Flowmeter proposed present advantages to measure flow of fluids in sorption systems. • Difference between data collect from the Medyflow and ultrasonic meter was less of 4%. The objective of this work is the design, construction and testing of a conventional turbine-type flow meter for liquids, especially for low-cost lithium bromide (LiBr) saline solution. This meter is directly coupled to the piping, through flanged connections where the fluid flows by driving a turbine that rotates freely in the casing mounted axially inside the meter. The turbine speed is proportional to the speed of flow of the fluid in the process. A Hall effect sensor W1305347 coupled to the meter has its magnetic field changed each time one of the turbine blades passes through it, thus generating an electric pulse. The amplification is applied to the pulses that are then treated as frequency and/or current by a microcontroller that interprets the signal and provides the visualization of the instantaneous flow in the digital indicator, as well as its total in time. The proposed meter, aims to overcome difficulties encountered in measuring flow of fluids in absorption systems since the working fluid is a crystalline salt that can present formation of solid phase crystallizing at moderate values of concentration, as well as low values of working pressure and high values of viscosity of the solution. This study describes all aspects of design, construction, operation, equationing and analysis of the characteristics of the volumetric flowmeter (MedyFlow). The validation of the meter (MedyFlow) proved to be effective since the results were very close to those obtained by the ultrasonic meter with errors of less than 4% statistically proven by F-TEST. [ABSTRACT FROM AUTHOR]

A set of mathematical models is developed based on energy and mass conservation to predict the mass transfer characteristics of falling film absorption of lithium bromide (LiBr) aqueous solution added with nanoparticles. Experimental measurements are conducted to validate the mathematical models, and good agreement is acquired. Simulations are performed to investigate the mass transfer of LiBr aqueous solution added with nanoparticles. Results showed that nanoparticles could significantly improve the water vapor absorption rate of nanofluid in the process of falling film absorption. Moreover, the water vapor absorption rate increased with the number of nanoparticle additives. With the same number of nanoparticles, the water vapor absorption rate of LiBr solution increased with the solution flow and with the change of solution flow trend for logarithmic curve. The mass transfer enhancement factor also increased with the number of nanoparticles. In addition, the mass transfer coefficient of absorber increased with the number of nanoparticle additives. When the flow rate of nanofluid with 0.05% and 0.1% added nanoparticles was 1.0 L min −1 , the mass transfer coefficient increased by 1.28 and 1.41 times, respectively. These results are beneficial in improving the mass transfer of the working medium used for an absorption refrigeration cycle and enhancing the performance of an absorption chiller. [ABSTRACT FROM AUTHOR]

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.

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]

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This study presents a novel hybrid methodology to estimate the coefficient of performance in an absorption intermittent cooling system; the system is for ice production and operates with an ammonia/lithium nitrate mixture. The hybrid model integrates a polynomial fitting method and an artificial neural network model to improve the network performance and the estimation of the COPs. The improvement uses fewer hidden neurons without sacrificing accuracy in the prediction. The proposed hybrid model has two neurons in the input and two in the hidden layers and shows better results than those obtained through polynomial fitting or artificial neural networks separately. The developed model presents an excellent agreement between experimental and simulated values of the coefficient of performance with a determination coefficient R 2 > 0.9978 . [ABSTRACT FROM AUTHOR]

• 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]

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]

A new high temperature double effect lithium bromide Solution absorption heat transformer (HDAHT) system is presented, which consists of a second effect generator between the generator and condenser of the high temperature single effect absorption heat transformer system (HSAHT). The HDAHT has the unique capability of raising the temperature of high temperature waste heat sources to more useful levels. The influence of the various operating parameters on the system's coefficient of performance (COP) for the HDAHT is simulated. It is found that the COP increases when the evaporator temperature, low pressure generator (LPG) temperature and the intermediate concentration of lithium bromide increase and decreases with increments of the absorption temperature, high pressure generator (HPG) temperature and the weak concentration of lithium bromide. In certain operating conditions, the COP of HDAHT system can be 20% more than that of the HSAHT, reaching to 0. 61. The obtained results can be helpful to improving the HDAHT system performance and making the design of the system optimum. [ABSTRACT FROM AUTHOR]

For utilization of the residual heat of flue gas to drive the absorption chillers, a lithium-bromide falling film in vertical tube type generator is presented. A mathematical model was developed to simulate the heat and mass coupled problem of laminar falling film evaporation in vertical tube. In the model, the factor of mass transfer was taken into account in heat transfer performance calculation. The temperature and concentration fields were calculated. Some tests were conducted for the factors such as Re number, heating flux, the inlet concentration and operating pressure which can affect the heat and mass transfer performance in laminar falling film evaporation. The heat transfer performance is enhanced with the increasing of heat flux. An increasing inlet concentration can weaken the heat transfer performance. The operating pressure hardly affects on heat and mass transfer. The bigger inlet Re number means weaker heat transfer effects and stronger mass transfer. The mass transfer obviously restrains the heat transfer in the falling film solution. The relation between dimensionless heat transfer coefficient and the inlet Re number is obtained. [ABSTRACT FROM AUTHOR]

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]

Falling film generation process in lithium bromide absorption refrigeration generation system is researched in this paper. To describe the coupled heat and mass transfer of laminar falling film in vertical generation tube, a mathematical model is developed, in which the effect of mass transfer on heat transfer is carefully evaluated. Moreover, an equation related Re number with solution volume flow was also obtained in given conditions. We carried out the experiments with the mass fraction of the inlet solution LiBr being 49.5% and obtained an empirical correlation of heat transfer with the film Re number and heat flux in different volume flow. Specifically, when 5kW/m2 2 and Re<500 the heat transfer correlation is given as: h=14009.87qw0.0764Re−0.5391. [ABSTRACT FROM AUTHOR]

Abstract: A solar-driven 10-ton LiBr/H2O single-effect absorption cooling system has been designed and installed at the School of Renewable Energy Technology (SERT), Phitsanulok, Thailand. Construction took place in 2005, after which this system became fully operational and has been supplying cooling for our main testing building''s air-conditioning. Data on the system''s operation were collected during 2006 and analyzed to find the extent to which solar energy replaced conventional energy sources. Here, we present these data and show that the 72m2 evacuated tube solar collector delivered a yearly average solar fraction of 81%, while the remaining 19% of thermal energy required by the chiller was supplied by a LPG-fired backup heating unit. We also show that the economics of this cooling system are dominated by the initial cost of the solar collector array and the absorption chiller, which are significantly higher than that of a similar-size conventional VCC system. [Copyright &y& Elsevier]

This paper was focused on the dynamic characteristics of a gas fired double-effect lithium bromide absorption chiller when it is disturbed by the changes of some running parameters, such as the mass flow rates or temperatures of entering cooling or chilled water, and the gas consumption rate. The dynamic models of each component, as well as the system model, were established with lumped parameters. A simulation software was also developed with FORTRAN and VB languages. Several dynamic responses of the chiller were investigated with this simulation software. The simulation results were verified by experimental data when the entering temperature of cooling water is varying, and the both are consistent with each other. The relationships between the gas consumption rate and the temperatures of entering cooling or chilled water when a stable leaving chilled water temperature is needed were also presented. [ABSTRACT FROM AUTHOR]

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]

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]

• Propose novel thermally-driven hybrid absorption cycle for producing steam and refrigeration effect simultaneously. • Build the pilot-scale facility of the proposed hybrid absorption cycle and propose the theoretical model validation. • Introduce the solution distribution ratio to flexibly control the heating or cooling capacity. • Analyze the operating characteristics under various working conditions. • Provide comprehensive and valid data for full-scale hybrid absorption system. For flexible use of a thermally driven absorption system for heating and cooling effects, a hybrid absorption cycle, which contains a sub-heat pump and a sub-refrigeration cycle, is proposed. Each sub-cycle shares a generator and a condenser, and the flow rate of the solution and the refrigerant entering each sub-cycle is adjusted by the general operating conditions, such as the heating source temperature and flow rate of the working fluid. The proposed hybrid absorption cycle introduced the solution distribution ratio to easily adjust the amount of the solution flow rate entering each sub-cycle, and as a result, the flexible control of the desired heating and cooling capacities was simultaneously achieved. We first proposed the experimental investigation using the pilot-scale hybrid absorption system for simultaneously producing 120 °C steam of approximately 110 kg/h and 8 °C cooling effect. The experimental analysis validified the steady-state theoretical model, and the theoretical simulation characterized the operating characteristics, such as the variations in three pressure levels, the circulation ratios, and the system performance in terms of the practical operating conditions and the defined solution distribution ratio. It was noted that the decrease in the solution distribution ratio, i.e., more amount of the solution entering the sub-refrigeration cycle than entering the sub-heat pump cycle, contributed the decrease in the COP of the sub-refrigeration cycle from 0.74 to 0.72, but brought about the increase in total COP from 0.53 to 0.60. It was concluded that all the parameters considered greatly influenced the heat transfer characteristics of the hybrid absorption cycle, and the heating and cooling effects could be flexibly controlled by the solution distribution ratio. The present study provides comprehensive and valid data for the further experimental investigations to determine main parameters that affect the performance characteristics of the proposed hybrid absorption cycle. [ABSTRACT FROM AUTHOR]