Scaling up nanoscale water driven energy conversion into evaporation driven engines and generators.

1. RENEWABLE ENERGY FROM EVAPORATING WATER
(Scaling up nanoscale water driven energy conversion into
evaporation driven engines and generators)
JYOTHI ENGINEERING COLLEGE, CHERUTHURUTHY
Department of Mechanical Engineering
February 2017
Seminar Guide, Submitted by,
Mr. SREEJITH A ALBERT V X
Asst. Professor S8-ME-A
Dept. of Mechanical Engineering 2013 – 17 Batch
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2. Vision:
“To provide quality education of international standards in Mechanical
Engineering and promote professionalism with ethical values, to work in a
team and to face global challenges.”
Mission:
• To provide an education that builds a solid foundation in Mechanical
Engineering.
• To prepare graduates for employment, higher education and enable a
lifelong growth in their profession.
• To develop good communication, leadership and entrepreneurship skills to
enable good knowledge transfer.
• To inculcate world class research program in Mechanical Engineering.
Department Of Mechanical
Engineering
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3. CONTENTS
1. Introduction
2. Bacterial spores
3. Challenges
4. HYDRAs
5. Evaporation driven engines
a) Oscillatory engine
b) Rotary engine
6. Advantages and Limitations
7. Future scope
8. Conclusion
9. Reference
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4. INTRODUCTION
 Evaporation is a natural phenomenon in the earth’s climate.
 Evaporation is nothing but a thermal separation process.
 Theoretically, evaporation means vaporization of a liquid
below its boiling point.
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5.  Thus, no boiling occurs and the rate of vaporization depends
on the diffusion of vapours through the boundary layers above
the liquid.
 Essential requirements in the process are:
1. The source of energy to vaporize the liquid water (solar or
wind)
2. The presence of concentration gradient between the
evaporating surface and the surrounding air.
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Fig.1: Mechanism of Evaporation

6. FACTORS AFFECTING
EVAPORATION
1. Temperature
• As the temperature of air is increased, its capacity to hold
moisture also increases.
• Any increase in air temperature raises the temperature of
water at the evaporation source which means that more
energy is available to the water molecules for escaping from
liquid to a gaseous state.
• Warmer the evaporating surface, higher the rate of
evaporation.
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7. 2. Humidity
• Drier air evaporates more water than
moist air.
• In other words, higher the vapour
pressure, lower the rate of
evaporation.
• It is a common experience that
evaporation is greater in summer and
at mid-day than in winter and at night.
3. Surface area
• The rate of evaporation is determined
by the area of the exposed surface of
water.
• Larger areas of evaporating surface
increase the rate of evaporation.
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8. 4. Wind speed
• When the winds are light, layer of air just above the liquid
surface gets nearly saturated.
• When the wind velocity is high, turbulence is set up in the
air. Moisture evaporated from the ground is mixed upward.
• Higher the wind speed, greater will the rate of evaporation.
 Wherever there is a combination of high temperature, very low
relative humidity and strong wind, the rate of evaporation is
exceptionally high.
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9. BACTERIAL SPORES
 Bacterial spores are highly resistant,
dormant structures (i.e. no metabolic
activity) produced by bacteria in
response to adverse environmental
conditions.
 Resistant to temperature, heat,
chemicals and radiation etc.
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Fig. 2: Bacterial spores [2]
 Sporulation occurs when nutrients, such as sources of carbon
and nitrogen are depleted.
 Most bacterial spores are non toxic and do not cause any
harm, but some bacteria that produce spores can be
pathogenic.

10. BACTERIAL SPORES (Contd.)
 Most spore-forming bacteria are contained in the bacillus and
clostridium species.
 We are using Bacillus subtilis spores.
 Hygroscopic in nature.
 It exhibit high hydration driven actuation.
 Bacterial spores shrink and swell with changing humidity, they
can push and pull other objects forcefully.
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11. BACTERIAL SPORES (Contd.)
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 Hygroscopic materials provides a means to convert energy
from evaporation by generating mechanical force in response
to changing relative humidity.
 Nanoscale confinement of water induces large pressure.
Fig. 3 : Water molecules in nanocavities [2]

12. CHALLENGES
 Evaporation carries a significant amount of energy.
 It involves a slow rate of water transfer that limits the relative
expansion and contraction of hygroscopic materials.
 Because the relative volume of the absorbed and released
water is small, the pressure change generated during this
process has to be large for efficient energy conversion.
 Time scale of wetting and drying depend on the square of
travel distance of water [1].
 Slow rate of change of relative humidity in environment limits
power output.
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13. HYDRAs
 Hygroscopic - driven artificial muscles.
 Bacterial spores deposited on thin plastic films.
 Films change curvature as a function of relative humidity.
 The overall movement can be made linear by coating
alternating sides of longer tapes with spores.
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Fig. 4: Schematic view of HYDRA strip

14. HYDRAs (Contd.)
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Fig. 5: Preparation process of HYDRAs

15. HYDRAs (Contd.)
 Assembling several tapes as a stack, with air gaps between the
layer facilitates rapid moisture transport to and from the spores.
 The layered architecture maximizes the surface area for
evaporation and condensation.
 The small thickness of the spore layer (3 µm) reduces the travel
distance of water within the HYDRAs.
 Scaling up the size of the material in two dimensions will
proportionally increase the surface area for evaporation, while
keeping the thickness of the spore layer constant.
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16.  Spores assemble into a relatively dense layer upon initial
drying of the spore glue mixture.
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Fig. 6: SEM image of the top of a HYDRA sample [2]
HYDRAs (Contd.)

17. HYDRAs (Contd.)
 The actuation behavior of HYDRA strips is observed by
placing them inside transparent plastic tubes and flowing air
with changing relative humidity.
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Fig. 7: Elongation as a function of relative humidity [1]

18. HYDRAs (Contd.)
 HYDRAs can quadruple their length as the relative humidity
changes from 30% to 80%.
 The amount of moisture absorbed by the HYDRAs in this
process is 5% by weight.
 The average curvature of individual arcs vary from 0.7mm to
2.8 mm.
 The response curve exhibits an ‘S’-like shape.
 At high RH, the radius of curvature of each arc increases.
 Tests of the stability of actuation performance showed that the
extension of strips reduces only slightly even after 1 million
cycles.
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19. 19
Fig. 8: The stability of the actuation performance of HYDRAs [1]
HYDRAs (Contd.)

20. HYDRAs (Contd.)
 The graph shows normalized length of a
HYDRA strip in dry and humid
conditions as a function of load weights.
 When loaded with increasing weight, the
range of motion reduces.
 But remains significant even at load
weights that are 50 times more than the
strips (0.31 g versus 6 mg).
 It is estimated that half a kilogram of
spore have the capacity to lift a car from
ground to a level of one meter [1].
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21. EVAPORATION – DRIVEN ENGINES
1. The oscillatory engine
2. The rotary engine
 They start and run autonomously when placed at air-water
interfaces.
 They can operate as long as air is not saturated
 Both are driven by hygroscopic - driven artificial muscles
or HYDRAs.
 These engines are able to power an electricity generator to
light up LEDs and drive a miniature car.
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22. THE OSCILLATORY ENGINE
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23. THE OSCILLATORY ENGINE
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 Using HYDRAs, Oscillatory engine were made that allow
and block evaporation in a cyclical fashion.
 So that energy can be continuously extracted from
evaporation.
 Evaporation rate controlled by shutter mechanism.
 Coupling the expansion and contraction of the HYDRA to
the shutters results in a self-starting oscillatory movement
with net power output.

24. WORKING
24
Fig. 10: Shutter mechanism
 HYDRAs are placed horizontally above the water surface and
coupled them to a beam that is compressed beyond the
buckling limit (bistable element).

25. WORKING (Contd.)
25
Fig. 11: Stages of oscillatory motion

26. WORKING (Contd.)
1) Stage I: When the shutters are closed, the relative humidity
of the chamber increases, causing HYDRAs to expand.
2) Stage II: As HYDRAs expand towards the right, they force
the buckled beam to switch its position.
3) Stage III: Shutters open and let the relative humidity of the
chamber recede, causing HYDRAs to contract.
4) Stage IV: Contracting HYDRAs pull the buckled beam and
force it to switch its position which then closes the shutters
and brings the system back to stage I.
 The rapid piston like motion of the rod allows it to act as an
engine, supplying power to external systems.
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27. 27
 The data show that the increasing of water surface temperature
shortened the period of oscillation
 The device exhibited oscillations even with a water surface
temperature well below the air temperature (16 ºC versus 25
ºC).
 The most rapid oscillations, observed at 31 ºC, had a period of
3 s.

28. EXPERIMENTAL SET-UP FOR
ELECTRICITY GENERATION
• Oscillatory engine is coupled to a generator.
• Depending on the direction of the oscillatory motion, two
oppositely connected LEDs gave light repeatedly and in
alternating order as water evaporates.
• Power developed ≈ 60µW.
• But still significant , when small area of water covered by
HYDRAs (9.6cm × 7.6cm) is considered.
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29. Fig. 12: Voltage and power versus Time
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30. THE ROTARY ENGINE
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31. THE ROTARY ENGINE
 Moisture mill
 Driven by water evaporating from wet paper.
 HYDRAs are assembled around two concentric rings.
 Four or five such structures are connected in parallel via a
central axis.
 The entire structure rotates freely around ball bearings.
 The structure was inserted half way into an enclosure such that
the hydra face walls lined with wet paper.
 Wet paper provides the humidity gradient.
 Induces different degrees of curvature in spore-coated films.
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32. THE ROTARY ENGINE
 Horizontal shift in the centre of mass of the entire structure
creates torque that causes the rotational motion.
 Blue plastic blocks attached to HYDRAs increase positional
shift of centre of mass thereby the torque.
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33.  Rotation speed depends on the relative humidity outside
the chamber and the speed of airflow near the device.
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34. DEMONSTRATION
 EVA- World’s first evaporation driven car.
 Miniature car of 0.1 kg.
 Engine is placed above a frame attached to two pairs of wheels.
 The rotary engine can drive a vehicle forward if its rotation is
coupled to the wheels with a rubber belt.
 As the water evaporates from wet paper, the car moves forward.
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Fig. 13: EVA

35. ADVANTAGES & LIMITATIONS
 Advantages
• Renewable source of energy.
• Low cost of materials used.
• Bacterial spores are resistant to temperature, stress etc.
• No external power requirement.
• It produces little or no waste products such as carbon
dioxide or other chemical pollutants.
 Limitations
• Engine stops beyond certain relative humidity.
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36. FUTURE SCOPE
 Soft robotic system
 Bio-hybrid cell based
actuators
 Artificial muscles
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 Power generation
system
 Energy storage

37. FUTURE SCOPE IN POWER
GENERATION
 Electricity from giant floating power generators that
sit on reservoirs .
 Electricity from huge rotating machines similar to
wind turbines placed above water bodies.
 Engines without fuel and battery, that use the
mechanical energy stored in spores to propel a full-
sized vehicle.
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38. CONCLUSION
 A new source of renewable energy.
 Nanoscale energy conversion mechanism is scaled up to create
macroscopic devices.
 Evaporation-driven car and the powering of LEDs highlight
the energy from evaporation.
 The engines presented here may find applications as energy
sources for a wide range of off-the-grid systems that function
in the environment.
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39. REFERENCE
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[1] Chen, Xi, et al. "Scaling up nanoscale water-driven energy
conversion into evaporation-driven engines and
generators." Nature communications 6 (2015).
[2] Chen, Xi, et al. "Bacillus spores as building blocks for
stimuli-responsive materials and nanogenerators" Nature
nanotechnology (2014): 137-141.
[3] Kumar, Navneet, and Jaywant H. Arakeri. "Natural
Convection Driven Evaporation from a water
surface" Procedia IUTAM 15 (2015): 108-115.
[4] Agnarsson, I., Dhinojwala, A., Sahni, V., & Blackledge, T. A.
(2009). Spider silk as a novel high performance biomimetic
muscle driven by humidity. Journal of Experimental
Biology, 212(13), 1990-1994.

40. REFERENCE
[5] Ronzino, Amos, and Vincenzo Corrado. "Measuring the
hygroscopic properties of porous media in transient regime.
From the material level to the whole building HAM
simulation of a coated room." Energy Procedia 78 (2015):
1501-1506.
[6] Zhdanova, Alena, Olga Vysokomornaya, and Pavel Strizhak.
"Evaporation Features of Water Droplets with Typical Subsoil
Impurities During the Motion Through High-Temperature
Gas Environment: Research Experience at Tomsk Polytechnic
University." Procedia-Social and Behavioral Sciences 206
(2015): 327-332.
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Any Questions