Study On The Performance And Evaluation Of The Ultrasonic Atomization Liquid Desiccant Dehumidification System

Liquid desiccant dehumidification systems have drawn a great deal of attention in the HVAC industry due to its great energy saving potentials and benefits for improving the indoor air quality.Within the systems,the dehumidifier and regenerator are the core parts that can produce decisive effects on the overall system performance.However,serious disadvantages were observed in the conventional packed-bed systems,such as the dramatic pressure drop of airstream,the high consumption rate of desiccant solution for wetting the packings and the specific area formed by the packings is just moderate.All of these disadvantages have hindered and restrained the further development of the liquid desiccant dehumidification systems.Therefore,it is essential to solve the aforementioned issues and enhance the mass transfer capacity of the dehumidifier and the regenerator.Power ultrasound has been proved able to facilitate the heat and mass transfer process.As to the liquid,owing to the cavitation effects of the ultrasonic system,the desiccant solution can be atomized into the tiny micro-sized droplets.Thus,the liquid-gas contact area is expanded dramatically and consequently,the dehumidification process can be promoted significantly.However,focus has only been devoted to the field of food dehydration and regeneration of solid adsorption materials,while there is little research on applying the ultrasonic atomization technology to the liquid desiccant dehumidification process.To fill this gap,this work tried to study the basic design principles and the performance characteristics of the ultrasonic atomization liquid desiccant dehumidification system(i.e.UADS),theoretically and experimentally.Additionally,efforts were also made to develop a novel concept named dehumidification perfectness for realizing the impartial evaluation of the inherent mass transfer capability of dehumidifiers,getting rid of the influence from the airstream and desiccant solution.Furthermore,method for adjusting the stability and sensitivity of the system performance was clarified.The main contents include the following aspects:Beforehand,a novel concept named as“droplets suspension rate”was proposed as the basis for developing the fundamental design principles and optimization mathematical model of the dehumidifier and the regenerator.A novel ultrasonic atomization liquid desiccant dehumidification system was set up and experiments were carried out to validate the model.It was found that the performance of the optimized UADS was improved significantly while it was able to utilize the lower-grade desiccant solution and the desiccant consumption rate decreased as well.After this,thorough experiments were carried out within the UADS to investigate its dehumidification and regeneration performance under various operating conditions.Ideal conditions were assumed and an easy-to-use model for predicting the dehumidification/regeneration performance,namely the IDM/IRM model,was developed based on the mass and energy conversion laws.The model was validated with the experimental results.Compared with the traditional packed-bed systems,much less desiccant solution was required by the UADS with the reduction amplitude reached up to 73.94%.Besides,the UADS is able to utilize lower-grade energy for desiccant regeneration with the necessary regeneration temperature lowered by 4.4 ~oC.Moreover,when integrating the UADS regenerator with the UADS dehumidifier,great energy savings during the system running process were realized(up to 60.4%)as compared with the packed-bed system.Then,a novel concept named dehumidification perfectness was proposed for realizing the impartial evaluation of the inherent mass transfer capability of various dehumidifiers/regenerators,getting rid of the influence of the properties of airstream and desiccant solutions.Experimental data from the open literatures was employed to validate the concept and its affecting factors were discussed.It was found that better dehumidification perfectness was obtained with bigger/longer effective liquid-gas contact area/time provided by the dehumidifier or the regenerator.The concept demonstrated promising potentials for comparing,predicting and improving the performance of various dehumidifiers/regenerators.After that,on the basis of the Taguchi method,full-factorial tests were carried out within a L18×L8 cross-product orthogonal array to investigate the significance of operating conditions in promoting the system performance(i.e.sensitivity analysis)and stability(i.e.stability analysis).It was found that although all of the operating conditions can exert direct influence on the system performance,their significance differed markedly.According to their significance during the ANOVA analysis,the operating conditions were classified into four types.Moreover,the optimal conditions for the UADS were figured out and validated.At the end,the economic performance of the UADS as well as a typical packed-bed system was analysed and compared via the case study.It was found that the DCOP of the UADS is better than that of the packed-bed system while its SEC is much lower.In general,less electricity was required by the UADS since the electricity saved by the fans and solution pumps was more than the consumption brought by the ultrasonic atomizers.In addition,the theoretical payback period of the UADS was about 3.63-4.23 years in present case,owing to its great energy savings during the running process.