University of Twente Student Theses


Continue Capacitieve Ontzouting

Bogt, R.W. ter (2015) Continue Capacitieve Ontzouting.

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Abstract:Introduction Large regions of the world are threatened by a shortage of fresh water. A solution for this problem is the desalination of sea water and brackish water. One way to desalt this water is by using capacitive deionization. In this study the ability to desalt droplets that way, is investigated. In addition to the desalination research, the process of making droplets is also a part of the study. Together these two separate studies form a basis for a desalination chip, in which salt water can be alternating desalinated. The complete study consists of three parts. Electrode manufacturing, electrode testing and droplet generation. Method First of all, a set of two capacitive deionization electrodes is manufactured. The electrode consists of a sputtered silver layer on which Nafion is spun, Nafion is semipermeable for positive ions. The second side consists of bare silver, at this side silver chloride will be formed. By connecting the electrode to a potentiostat, the impedance is measured as well as a voltage is put across the droplet in order to desalinate it. A decrease of salt concentration of the droplet results in an increase in the measured impedance. To prove that theory, a series of experiments has been done with a 1 mM and a 3 mM sodium chloride solution. After a set of three baseline measurements, a potential of 0.5 V was set over the droplet and finally again a set of three baseline measurements. During the time that there was a voltage across the droplet, a set of five impedance measurements where done. These measurements form a basis for the final determination whether there is desalination or not, and finally shown in graphs. The droplets are generated with a Y-junction with two feeding channels and one outlet. The feed consists of deionized water and nitrogen gas. The water supply is controlled by a syringe pump and the gas supply by a gas flow meter/controller. The results are analyzed through the use of photos. Results After ten seconds of measuring the impedance a 2 μl droplet of 1 mM sodium chloride is desalinated by an average of 12.9%. A drop of 3 mM is desalted for 14.2% in the same amount of time. After thirty seconds an average result of 18.4% desalination for the 1 mM droplet and 28.5% for the 3 mM droplet is measured. The results show that the generation of droplets is possible starting with an inlet flow of 2 μl/min water and 0.77 ml/min gas, but the stability is very low. The droplets generated at this low supply of water are of an inconsistent volume. Starting from a supply rate of 5 μl/min water, the droplet generation is stable with an average volume of 0.19 ± 0.02 μl. Conclusion The results show that it is possible to use an electrode configuration consisting of silver and silver with a layer of Nafion, for the deionization of droplets. The experimental results have shown that a drop of 1 mM sodium chloride can be deionized for 12.9% in ten seconds, at a voltage of 0.5 V. For a droplet of 3 mM sodium chloride was found that it can be deionized for 14.2% in ten seconds, at a voltage of 0.5 V. The experimental results with the droplet generation setup show that it is possible to generate droplets of water in nitrogen, with a stable volume, by using a Y-junction. This is possible with a flow of 5 μl/min of deionized water and 0.77 ml/min nitrogen gas, with the used setup. The results achieved in this study show that it is possible to develop an alternating deionization chip in a follow-up study.
Item Type:Essay (Master)
Faculty:BMS: Behavioural, Management and Social Sciences
Subject:33 physics, 81 education, teaching
Programme:Science Education and Communication MSc (60708)
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