Modelling and Experimental Investigation of Humidification- Dehumidification Desalination Using a Carbon-Filled-Plastic Shell-Tube Column

The modelling and experimental investigation of a thermally coupled humidification-dehumidification desalination process using a carbon-filled-polypropylene shell-tube column are presented. A heat/mass transfer model is established to study the correlation among productivity, thermal efficiency, physicochemical parameters （gas/liquid phase temperature, heat/mass transfer coefficient, Reynolds number etc.）, and operating conditions （the temperature of feed water, the flow rates of external steam, feed water, and carrier air）; at the same time, the effects of operating conditions on the productivity and thermal eficiency of the column are investigated both theoretically and experimentally, which indicate that the optimum flow rates of external steam, feed water, and carder gas are 0.18, 60, and 10kg.h^-l, respectively, and the higher the feed water temperature （≤95℃） is, the greater the productivity and the thermal efficiency will be. Furthermore, performance comparison with the previous study shows that the condensate productivity of this carbon-filled-plastic column is not lower than that of the copper column, which demonstrates the practicability and feasibility of applying such a plastic column to the humidification-dehumidification desalination process.

Enhancement of freshwater production of the seawater greenhouse condenser

Seawater greenhouse(SWGH)is a technology established to overcome issues related to open field cultivation in arid areas,such as the high ambient temperature and the shortage of freshwater.It adopts the humidification-dehumidification concept where evaporated moisture from a saline water source is condensed to produce freshwater within the greenhouse body.Various condenser designs are adopted to increase freshwater production in order to meet the irrigation demand.The aim of this study was to experimentally investigate the practicality of using the packed-type direct contact condenser in the SWGH to produce more freshwater at low costs,simple design and high efficiency,and to explore the impact of the manipulating six operational variables(inlet air temperature of the humidifier,air mass flowrate of the humidifier,inlet water temperature of the humidifier,water mass flowrate of the humidifier,inlet water temperature of the dehumidifier and water mass flowrate of the dehumidifier)on freshwater condensation rate.For this purpose,a direct contact condenser was designed and manufactured.Sixty-four full factorial experiments were conducted to study the effect of the six operational variables.Each variable was operated at two levels(high and low flowrate),and each experiment lasted for 10 min and followed by a 30-min waiting time.Results showed that freshwater production varied between 0.257 and 2.590 L for every 10 min.When using Minitab statistical software to investigate the significant variables that contributed to the maximum freshwater production,it was found that the inlet air temperature of the humidifier had the greatest influence,followed by the inlet water temperature of the humidifier;the former had a negative impact while the latter had a positive impact on freshwater production.The response optimizer tool revealed that the optimal combination of variables contributed to maximize freshwater production when all variables were in the high mode and the inlet air temperature of the humidifier was in the low mode.The comparison between the old plastic condenser and the new proposed direct contact condenser showed that the latter can produce 75.9 times more freshwater at the same condenser volume.

Dynamic Simulation of a Novel Solar Polygeneration System for Heat, Power and Fresh Water Production based on Solar Thermal Power Tower Plant

A novel solar polygeneration system for heat, power and fresh water production with absorption heat pump(AHP) and humidification-dehumidification(HDH) desalination system was proposed for high-efficiency utilization of solar energy. A case study of the proposed system was investigated based on 1 MW solar thermal power(STP) tower plant located in Beijing. Depending on mathematical modeling of the proposed system, corresponding modules were developed in TRNSYS. Meanwhile, control and operation strategies were fully studied with principal of solar energy cascade utilization. The thermodynamic performance of the proposed system was dynamically simulated at one minute intervals in a typical day. It was found that solar energy utilization level was improved with the help of solar thermal storage system and continuous heating in different operation modes met well with flexible heating loads from 93.76 kW to 169.49 kW. During AHP operation period, its Coefficient of Performance(COP) varied from 1.39 to 1.73 due to recoverable condensate heat restricted by heating demand. Meanwhile, fresh water production of HDH increased from 352.05 kg/h to 416.62 kg/h with Gained Output Ratio(GOR) increase from 2.48 to 2.67. Compared with original STP tower plant, maximum power generation efficiency was increased from 18.66% to 19.22% with power from 1169.69 kW to 1204.44 kW.