Study Of High Efficiency Libr/Water Absorption Cooling Cycles And Heat And Mass Transfer In Absorber

The LiBr/water solution absorption chiller which is driven by thermal energy plays an important role in electric load balance, energy structure improvement and waste heat recovery. To promote the absorption technology, the multi-stage cycles with high energy efficiency should be developed. On the other hand, the attention is necessary to be concerned on the falling film transfer process in components, especially for the absorber to decrease the cost and volume of the machine.The series, reverse-series and parallel LiBr/water triple-effect absorption cooling cycles are discussed using computer programs. The newly developed correlations of LiBr/water solution properties at high temperature are added into the program. The governing equations set, the solving method and calculation results are presented for each cycle. The energy efficiency of these triple-effect cycles are investigated on an equivalent basis of the same solution developing difference and the maximum working temperature, pressure and crystallization limit in all cycles are compared by selecting COP (Coefficient of Performance) as the common condition. The results show that parallel triple-effect cycle is more desirable.Due to the high temperature exhaust rejected from gas-fired triple-effect cycles, an exhaust heat recovery loop is suggested to be integrated with the conventional cycles to increase the cooling efficiency. Based on the parallel configuration, the annual gas savings are calculated and compared with the cost of the additional generator to design the size of the recovery generator. The results show that the optimum vapor production ratio in heat recovery generator is 2.8%, which present considerable economic effects.The droplet formation of the LiBr/water solution between horizontal tubes is investigated using high speed camera. The droplet initial shape, detachment, falling and the waviness of the film outside the tube which are often neglected in the absorption model are discussed. The variation of droplet surface area and volume to the time is studied using image edge detection, curve fitting algorithm and curve revolving integral methods. The 3D simulation of droplet formation on horizontal tubes is carried out based on Fluent software. The simulation results are compared with the real images.Based on the analysis of the droplet flow process, the prediction of the droplet evolution at different solution amount is proposed to replace the ideal sphere droplet mode between horizontal tubes in the falling film absorption model. The variation of solution temperature and concentration during the absorption are analyzed. The change of vapor absorption amount and solution temperature in the tube bundles are discussed at different solution spray density.The experiment of falling film absorption on horizontal tubes is carried out. The plain tube, floral tube and floral tube with low fins are assembled in the system. 1-octanol and 2-ethyl-l-hexanol are added into the solution at different concentration as surfactants. The effects of high efficiency tubes and surfactant to the heat and mass transfer are discussed at different solution spray density. The results indicate that the floral tube shows better overall performance. The effects of surfactant to the enhancement of heat and mass transfer are much over the structured tube surface. The 2-ethyl-l-hexanol is considered better than 1-octanol both in heat and mass transfer. There is an optimum surfactant concentration in the solution and higher surfactant concentration is required for larger solution flowrate.