| Obtaining fresh water from seawater by using desalination technology has become an effective measure to relieve the pressure on fresh water supply,such as multi-stage flash(MSF),low-temperature multi-effect distillation(LT-MED)and reverse osmosis(RO)et al.,which are all suitable for large/medium-size scale desalination.However,in many cases,the actual water consuming point is relatively distributed,and the water consumption is also very small.In this context,there will be a more urgent need for efficient and stable desalination technology in small-scale.Solar assisted humidification dehumidification(HDH)can play an important role in small-scale fresh water supply depending on its outstanding advantages of low energy consumption,high fresh water productivity and simple structure.However,the problems,such as the mutual restriction between humidificaition process and dehumidification process,strong dependence on stable heat sources and low heat recovery efficiency,largely limit its development and application.Based on the above background,a solar assisted heat pump,and a weak moist air compression humidification dehumidification processes were developed,and improved the fresh water productivity significantly.The main research works in this paper are summarized as follows:Firstly,according to the characteristics of solar HDH desalination system,the single-stage and two-stage solar assisted heat pump(SAHP)HDH desalination systems were proposed,respectively.The mechanisms of the performance enhancement on HDH process by improving the heat recovery were extensively investigated.The modes of energy conversion in the independent treatment for humidification process and dehumidification process were also studied in-depth.Consequently,the problems of mutual restriction between humidifier and dehumidifier in conventional HDH process were solved successfully,improving the heat recovery efficiency and system performance.Meanwhile,in order to solve the problem of low-heat recovery caused by the introduction of cooling seawater in conventional HDH process,an enhanced HDH(E-HDH)solar desalination system with weakly compressed moist air was further developed in this paper.This E-HDH cycle successfully reduces the dependence on the stable heat sources,realizes the complete heat recovery process,which makes it possible for significant increasement in fresh water productivity.Secondly,the SAHP HDH desalination experimental setup was then designed and constructed.The operation characteristics of the system was also obtained by the single factor sensitivity test and thermal performance analysis under typical working conditions.The mathematical model was established based on the proposed two-stage SAHP HDH desalination system.The optimization analysis of humidification process and dehumidification process was carried out using the two-factor sensitivity analysis method.The results showed that compared with the conventional HDH desalination system,the maximum SEC(Specific electrical consumption)of the SAHP HDH desalination system which has realized the completely independent treatment between humidification process and dehumidification process increases by nearly 60% to 16.8 kg/k Wh.Finally,an enhanced HDH(E-HDH)solar desalination system with weakly compressed moist air was developed.The experimental setup was designed and constructed.A new performance index GORe(Gained-output-ratio equivalent)was proposed,which can comprehensively evaluate the system performance from the electrical and thermal aspects.Based on the theoretical analysis and experimental tests,the operation characteristics and rules of the novel desalination system were mastered.The influence mechanisms of variable working pressure difference on fresh water productivity in the weak compression process were intensively studied.It was found that the spraying seawater temperature and the working pressure difference are the two most important factors affecting the fresh water productivity.And the optimization analysis of the humidification process,the pressure difference distribution control process and the seawater heated process was achieved.Compared with conventional HDH desalination system(GOR<3.5),the GOR of E-HDH system is about 6.49,which is an increase of nearly 85%.Additionally,the system GORe can also reach 2.60,which is one of the best records in the similar research.The solar assisted heat pump HDH desalination system and the enhanced HDH solar desalination system with weakly compressed moist air proposed in this paper enrich the technologies in the solar assisted HDH desalination system and also significantly improve the system performance,which has important theoretical significance and practical value in the promotion of the scale application for solar desalination technology. |
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