| A refrigeration dehumidification system with membrane-based total heat recovery is an efficient way to cool and dehumidify fresh air. It is also helpful for the control of epidemic respiratory disease. In addition, this system can improve indoor air quality. It can decrease energy consumptions as well. The technology provides a solution for air dehumidification with reduced energy use. However, previous efforts were only concentrated on its feasibility studies. A practical system is scarce, because no mathematical tools are available for system design and optimization. In the present work, the mathmeatical model for thermodynamics and heat mass transfer of the whole system is set up. System optimization is conducted. Following this step, a prototype is built for practical real scale applications. Field tests show that the system performs well. The main works are summarized as following:(1) A test rig for a refrigeration dehumidification system with membrane-based total heat recovery is set up. The performances of the system under summer weather conditions are tested.(2) A mathematical model for a multi-channel parallel-plate membrane-based total heat exchanger is developed. The test data are used to validate the present model. Heat and moisture transfer in the total heat exchanger is studied. The effects of plate materials and their properties on heat and moisture transfer are studied. The results show that the plate material and their properties have tremendous impacts on the latent effectiveness. However, they have little impacts on the sensible effectiveness. Sorption curves and contact angles of the materials are measure to reflect their hydrophilicity. The effects of the varying operating conditions like air flow rates, temperature, and humidity on the sensible and latent effectiveness are evaluated. Both the numerical and experimental results indicate that the moisture resistance through plates is co-determined by thickness, sorption slope, and sorption potential. The paper exchanger has a latent effectiveness of 0.4, while the membranes have latent effectiveness of greater than 0.7.(3) A mathematical model for a refrigeration dehumidification system with membrane-based total heat recovery is developed. The test data are used to validate the model. The results indicate that the model can predict the system accurately. Simulations studies are conducted. The results indicate the system has more robustness than the conventional refrigeration system under hot and humid harsh weather conditions. The higher the fresh air temperature and humidity are, the more effective the membrane-based total heat exchanger is. This compensates the performances of the compression sub-system which deteriorates seriously under hot and humid harsh conditions. The effects of varying operating conditions and the ratios of refrigerant mass flow rates on the system performances are evaluated. The system has a COP of 6.8 and air dehumidification rates of 3.57 kg/h under nominal operating conditions. Comparing with a conventional refrigeration dehumidification system, the air dehumidification rate of this system is 4 times higher, and the COP is 2.2 times higher.(4) Optimization is conducted for system design. Based on the results, a prototype is designed and built for practical uses. Field tests are done with standard enthalpy difference experiments. The results indicate that the performance of the parallel-plate membrane-based total heat recovery is high. The perfomace is as well as expected. The two key issues are solved: 1) The membrane-based total heat recovery is realized in a pratical application; 2) The problem of performance deterioration of the compression sub-system under hot and humid harsh conditions is solved. The sensible effectiveness and the latent recovery effectiveness are 79%, 62%, respectively. The air dehumidification rates, cooling power and COP are 2.7 kg/h, 2.9kW, 4.6, respectively. The higher the air temperature and humidity are, the higher the performance are.
|
PDF Full Text Request