Study On Absorption Properties Of Lithium Bromide Solution In Horizontal Tubes And Mesh Inserts Alternating Structure

Absorption refrigeration can make full use of various low-grade heat sources, such as solar energy, geothermal energy, and industrial waste heat, the whole process does not produce any additional pollution, to meet the requirements of low-carbon environment. Absorption refrigeration system has the advantage of low noise operation due to free of the compressor. In absorption refrigeration field, lithium bromide absorption refrigeration with its high coefficient of performance is the first choice. The absorber is the core part in a lithium bromide absorption chiller, and its heat and mass transfer characteristics has significant impact on the overall performance. The in depth study of the horizontal tubular structure of lithium bromide falling film absorber and make improvements to enhance the absorption heat and mass transfer, can lay the theoretical foundation for the design and development of more efficient absorption chillers, and has broad application prospects.In this paper, investigation was performed around a novel absorption scheme with alternating heat and mass transfer proposed by our research group, which inserting longitudinally corrugated mesh packing into the gaps of traditional absorber tube rows, and experimental study were carried out on both absorption performance and visualization of flow pattern of the film of this new absorber.Numerical simulation model is established on the bare horizontal tubes bundle falling film absorber, in which the absorption process is divided into falling film zone, drop formation zone and drop fall zone. With this model, the local distributions of film and heat and mass transfer coefficients on a single column horizontal tube surfaces were investigated. The theoretical results of heat and mass transfer in the horizontal tube absorption body were obtained, and also minutiae chracteristics of heat and mass transfer for absorption were provided that could not be available with the experimental data. The trends of temperature, concentration fields and transfering heat and local heat transfer coefficient in the absorber were analysed and discussed.For experimental research, a test rig of single pressure absorption and desorption closed system was built, with combination of the multifunction of falling film absorption, parameter control, data measurement and acquisition. Relying on the experimental system, a large number of experiments were carried out. The heat and mass transfer experimental data were obtained under different spray desity on both bare horizontal tubes absorber and alternating structure absorber by the experimental study. Under the same working conditions, as compared with bare horizontal tube absorber, the maximum absorption rate and average cooling load of alternating structure absorber were strengthened 17.2% and 6.23% respectively, a number of other heat and mass transfer data indicator were also strengthened by different magnitudes. The comparison and analysis were also carried out on experimental results of bare horizontal tube absorber with numerical model results, to verify the correctness of the calculation model.In addition, a visualization experimental test rig with open loops was built to observe the liquid film flow pattern on tube and mesh screen alternating structure, and experiment was conduct with this test rig. By comparing the difference of fluid flow patterns and film distribution between bare horizontal tube absorber and alternating structure absorber, the mechanism of heat and mass transfer enhancement with alternating structure in absorption process was revealed. The tube and mesh alternating structure can change the fluid flow patterns in the gaps between tubes, which resulting in a more uniform distribution of the solution in the absorption body, reduce the solution spatter rate and collect splash solution, improve the absorbent usage efficiency, reduce dry spots area ratio and raise the wetting ratio of the tube surface thus increase the effictiveness of the heat transfer area.The results from Lithium bromide absorption performance and flow visualization experiments of alternating structure absorber show that the absorption properties of the absorber can be enhanced by alternating structure of tube bundle with mesh inserts.