1. University of Nairobi Institute of Nuclear Science and Technology
Design and Characterisation of an Electrohydrodynamic Multinozzle Atomizer for Thermal Desalination Processes
Presented by:
Mwaura Anselim Mwangi
S56/61782/2013
Supervisors:
Prof. Michael J. Gatari
Prof. Jan C. M. Marijnissen
Dr. Luewton L. F. Agostinho

2. Outlook Introduction Problem Statement Objectives Literature Review
Methodology
Results and Discussion
Conclusions
Recommendations
Acknowledgements
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3. Introduction
Water is considered as the most important chemical substance in the world.
(El-Dessouky & Ettouney, 2002)
Figure 1.1: Graphic display of the amount of fresh and saltwater on earth
Only about 0.5%, is what supports life on Earth and unfortunately, it is not distributed evenly on the planet.
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4. Introduction 57% - access to safe water (KIHBS 2005/2006).
60% - urban settings
20% - urban poor settlements.
KIHBS 2005/2006
Figure 1.2: Water Crisis in the Urban Poor Settlements
Jingwei et al. (2010) proved that a careful selection of the atomization method in thermal desalination can produce recovery rates as high as 90%.
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5. Problem Statement
Thus, there is need to improve the efficiency of Single Effect Distillation by out scaling the development work initiated by Agostinho (2013) and Brouwer (2011).
Agostinho (2013)
Figure 1.3: 5 Nozzle Atomizer
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6. To develop computational models to check the process parameters.
Main Objective
To design, develop and study the characteristics of an electrohydrodynamic multinozzle atomizer for thermal desalination processes.
Specific Objectives
To develop computational models to check the process parameters.
To assemble and test the multinozzle atomizer.
To study and characterise the multinozzle atomizer.
To design the optimal multinozzle atomizer configuration
To analyse the electrosprayed liquid using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Total reflection X-ray Fluorescence (TXRF).
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7. Literature Review
Desalination process involves the separation of nearly salt-free fresh water from sea or brackish water (Ettouney and Wilf, 2009).
Desalination processes can be classified based on (El-Dessouky and Ettouney, 2002):
Thermal processes
Membrane separation methods
Figure 2.1: Definition of Desalination Process
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8. Literature Review
These technologies currently in use in the market work well but still fall short of the expectation of producing potable water using techniques that have low energy requirement and limited pre-treatment of the feed water.
There is therefore a gap left to be filled and this is where the electrospray thermal desalination technique comes in.
Not only will it provide low energy consumption designs but also ensure that there is limited pre-treatment of the feed water.
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9. Atomization
Atomization is the disintegration of a liquid into small droplets (Ashgriz & Yarin, 2011).
Ultrasonic
Pneumatic
Rotary
Figure 2.2: Atomization
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10. Electrohydrodynamic Atomization
Electrohydrodynamic atomization (EHDA)/ electrospray refers to the breakup of a liquid due to electric stresses created by applying an electric potential difference between the Nozzle and the Counter Electrode. (Hartman, 1998).
(Agostinho et al., 2013)
Figure 2.3: Electrospray
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11. Modes (Agostinho, 2013) Figure 2.4: Different Electrospray Modes
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12. Multinozzle Reviews
Arnanthigo et al. (2011) designed and studied a multinozzle system with 8 nozzles in cone-jet mode.
Agostinho et al. (2013) designed and studied a 5 nozzle electrospray device. It was operated in the simple-jet mode and it had an insulative layer.
Yurteri, Hartman and Marijnissen (2010) reviewed the multinozzle devices reported and concluded that electrical interferences between the neighbouring sprays and liquid flow rate variation to all nozzles are problems that needs be overcome while designing a multinozzle device.
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13. Methodology
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14. Figure 3.1: Flow chart of the Development Process
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15. Results and Discussion
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16. Multinozzle Atomizer It has 22 nozzles
A 20 mm outer diameter and 15 mm inner diameter counter electrode (rings) were used.
A nozzle and ring-up electrospray configuration
It has a packing density of 2.2 * 103 nozzles/m2
Figure 4.1: Engineering drawing of the atomizer (a), Schematic Diagram of the Atomizer (b) and Atomizer during Experiments (c)
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17. Particle Tracing Modelling
Figure 4.2: A beam of particles diverges due to electric forces (6kV)
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18. Droplet Dispersion - 360 mL/h
0 kV
5 kV
6 kV
7 kV
8 kV
9 kV
Figure 4.3 : Superimposed images of the droplets at 360 mL.h-1 for 0 kV (a), 5 kV (b), 6 kV (c), 7 kV (d), 8 kV (e) and 9 kV (f) (spray envelope).
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19. Droplets Sizes
Table 4.1: Summarised values of Mean Diameters at different flow rates and different potentials
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20. Prototype Improvementa) b)
Figure 4.4: Proposed Multinozzle Configuration (a) and Contour plot 2D Plot of the Electric Field Strength (V/m) at 6kV (b)
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21. Prototype Improvement
Figure 4.5: Particle Tracing Model Side view (a) and Bottom view (b) at 6kV
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22. Liquid Analysis
Table 4.2: Concentration Levels of Calcium in ICP-MS (a) and TXRF (b) analytical technique
Deionised Water a) b)
ICP-MS TXRF
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23. Liquid Analysis
Table 4.3: Elemental Concentration Levels in ICP-MS (a) and TXRF (b) analytical technique
Sea Water a) b)
ICP-MS TXRF
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24. Liquid Analysis
Student t distribution method of testing two means was used to compare the two analytical methods (IAEA, 2003).
The testing was done at 95% confidence level.
For all cases, tcalc < ttab hence there was no significant difference between the two means and thus the two means are related.
Therefore, the analytical techniques could be used interchangeably.
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25. Conclusions
The packing density of this multinozzle atomizer was approximately doubled (1.2*103 to 2.2*103 nozzles/m2) that was used by Agostinho (2013).
The liquid output per unit time increased by almost five times (2.2 L/h to 11L/h).
Computational models to check the process parameters were simulated.
Application of an electric field caused wider displacement of the droplets of the outermost nozzles have compared to the inner nozzles.
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26. Conclusions
There was reduction in droplet diameter with increase in voltage.
The particle trajectories and electric field modelling matched the bench scale results.
Due to the limitations experienced by the first prototype, a second design was proposed and studied.
There was presence of electrochemical reactions when high voltage was applied.
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27. Recommendations
More research needs to be done to confirm the optimal smallest nozzle to nozzle distance.
More research needs to be done to test this device with the evaporator.
Further research needs to be conducted to determine the best droplet size and shape to be used on the evaporator.
The next phase of this research is the design and development of the evaporator system.
Solar powering the complete device may serve as an alternative source of energy.
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28. Acknowledgements Centre of Expertise Water Technology (CEW)
High Voltage Water (HVW)
Water Application Centre (WAC)
International Science Programme (ISP)
Prof. Gatari, Prof. Jan and Dr. Luewton (Supervisors)
Institute of Nuclear Science and Technology (INST)
Kenya Nuclear Electricity Board (KNEB)
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29. 15 June 2018