Study of multi-stage multi-effect regenerator for liquid desiccant air-conditioning system
Date of Issue2017-06-30
Interdisciplinary Graduate School (IGS)
Energy Research Institute @ NTU (ERI@N)
Nanyang Technologial University
With increasing importance placed on energy efficiency and indoor-air-quality, the advanced energy efficient liquid desiccant assisted air-conditioning (LDAC) systems have attracted attention in the recent years. The thesis aims to develop a vacuum graded LDAC system with multi-stage-effect dehumidification and regeneration systems employing membrane technology namely VMEMD for improving the efficiency of the conventional LDAC system. The proposed multi-effect regeneration test-bed maximizes not only the heat transfer between the heating fluids and salt solution but also mass transfer of water vapour across the hydrophobic membrane. Subsequent findings are obtained through the experimental investigations of multi-effect membrane based LDAC system employing various control parameters of the test facility. We found that the conventional VMEMD is not suitable for the regeneration of LiCl solution for dehumidification purposes. Therefore, the VMEMD system has been modified with one steam three solution (1S-3L) passes system through modelling and simulation. Finally, an experimental investigation is conducted to prove the test-of-concept. The use of 1S-3L is the main findings of this work. The thermal efficiency of the proposed 1S-3L VMEMD system is calculated in terms of performance ratio (PR) and change in feed concentration between the inlet and outlet of the regenerator for various solution flow rates and regeneration temperatures. The proposed system is driven at the lowest temperature of 55°C. The PR value is found ~2 for VMEMD system, which can be considered a new finding. In this thesis, a comprehensive testing is conducted for the thermal performance of the conventional VMEMD regenerator of the LDAC test bed under various configurations. The desiccant heating load is handled by both the solar thermal and auxiliary heat pump systems. It is found that the PR is mainly influenced by the initial feed concentration and flow rate delivered from the absorber module. The thermodynamic frameworks of the proposed 1S-3L VMEMD system is developed employing the heat and mass balances for all the stages of VMEMD system, which simulates the working principles of the regeneration process for various driving heat source temperatures. The simulation result proves the validity of changing VMEMD configuration for handling higher inlet feed concentration. The present study shows a test-of-concept to utilize the modified VMEMD for dehumidification purposes in tropical climate.