Improved Simulation Model for Air-Liquid Contactors in Open Absorption Air Conditioning Systems

摘要

Air conditioning (A/C) is one of the primary consumers of electricity in many sectors of the economy. Increasing energy efficiency in the A/C industry is a primary goal. While the use of the vapor compression cycle in HVAC applications is still dominant and will remain so for many years, a promising approach is represented by the use of an open cycle Liquid Desiccant System (LDS) designated to deal with the latent heat load. The LDS utilizes as its source of power low-grade waste or solar heat, of the type obtainable from low-cost flat plate collectors, and has the potential to provide dehumidification as required by the load. The LDS inherent storage capability is an attractive feature in such a solar- driven system. The possibility of using low grade heat as a power source for A/C goes a long way toward the elimination of pollution and utilizing renewable and environmentally-safe energy sources. Generally, the LDS employs an aqueous solution of hygroscopic salt, such as lithium chloride, in direct contact with the air. The absorber and desorber are of counter-flow design. Three system heat transfer configurations of interest should be considered: (1) Adiabatic absorber/desorber units; (2) Internally cooled/heated absorber/desorber with counter-current flow arrangement between the cooling/heating water and the LiCl solution; (3) Internally cooled/heated absorber/desorber with co-current flow arrangement between the cooling/heating water and the LiCl solution. Usually, an adiabatic mode of operation has been employed (in preference to one with heat exchange simultaneous with absorption and desorption) for the following advantages: (1) Simpler design and maintenance; (2) More compact heat exchangers; (3) Less severe corrosion problems; (4) Elimination of inadequate wetting of the heat transfer surfaces. To select the preferred LDS configuration, a system analysis and computer simulations are needed. Attention should be given to the characteristic performance of individual key components and their influence on the overall system performance. This paper describes an analysis of an improved simulation model for air-liquid contactors adopted for use in computer simulation. The computer simulation code ABSIM was modified, and employed to improve the simulation capabilities of certain units forming part of the LDS system. The paper describes the effect of various operating parameters on the performance of the several LDS configurations described above.