Comparative study of innovative solar still modifications ......Solar powered generator. Water pump....
Transcript of Comparative study of innovative solar still modifications ......Solar powered generator. Water pump....
Convective cover: Will prevent the heat from
radiating away from the system.
Copper sheet: Coated with a spectrally
selective absorber: Will optimize the solar
energy absorbed (Cao et al., 2014).
Insulating polystyrene foam: Will serve as a
floating material to prevent water-copper sheet
contact thus sustaining copper sheet
temperature.
The key aspect of this technology is
heat loss prevention, which is achieved
by the convective
cover and the
bottom
insulating
material via
thermal
concentration
and heat
localization
Comparative study of innovative solar still modifications: A step
towards water crises mitigation and a sustainable campus
Abstract
References(1) Manikandan, V., K. Shanmugasundaram, S. Shanmugan, B. Janarthanan, and J. Chandrasekaran. (2) Ni, G., Li, G., Boriskina,
S., Li, H., Yand, W., Zhang, T., & Chen, G. (2016). Steam generation under one sun enabled by a floating structure with thermal.
Nature Energy, 7. (3) Kaviti, Ajay Kumar, Akhilesh Yadav, and Amit Shukla. “Inclined Solar Still Designs: A Review.” Renewable
and Sustainable `Energy Reviews 54 (2016): 429–451
Catalina Island entered stage 3 water rationing (50% water
reduction) as of September 6, 2016, placing strain on the USC
Wrigley Marine Science Center’s (WMSC) ability to host tens of
thousands of annual visitors (23,481 in 2015). Despite implementation of water conservation efforts and recent rain events,
freshwater remains a chronically scarce natural resource, especially
during summer months. In May 2016, the WMSC launched a pilot
study to consider solar distillation for passive generation of
freshwater using seawater. Here, we present investigations on
design improvements to enhance freshwater generation in a
conventional solar still: (1), a hybrid design containing a stepped
landscape, internal and external reflectors to direct solar irradiation
and minimize the distance water vapor needs to travel; (2), a multi-
effect basin and wicking material hybrid with external reflectors to
concentrate solar radiation, reuse the latent heat and increase
surface area. (3), One-sun Ambient Steam generator (OAS)
application to concentrate and localize heat, at the same time
prevent heat loss using a convective cover placed on top of a metal
plate and bottom insulating/floating material. The 3 design concepts
were constructed and set up at the WMSC on Mar 17, 2017.
Freshwater generation, irradiation, and temperature will be
monitored for at least 10 days. Results from this study will be used toimplement the most efficient, simple and cost-effective technological
application for passive freshwater generation on Catalina Island.
Results
*Abuyen, K.1, *Holahan, K.2, *White, M.1, Kim, D.1 Close, A.1 and Heidelberg, J.11 University of Southern California, Environmental Studies 2 University of Southern California, Viterbi, School of Engineering
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1 Solar irradiation
2 Water evaporation
3 Condensation
Solar powered generatorWater pump
Salt Water Reservoir
Field set up
Seawater
Fresh
water
vessel
Methods
Figure 6: Solar still field set up. Flow through system was applied to the MEB and
Stepped system to reduce brine formation inside the solar still. The reservoir is a
black barrel which aids in preheating the water that enters the solar still basin. The
pump is powered by a Goal Zero solar generator.
pH of the water collected are measured overtime using YSI 85 salinity probe, and
volume of water collected is being measured using a graduated cyclinder. The
temperature of the copper sheet for OAS system and inside the solar still for all the
system, are being measured via Etekcity laser grip 1080 non-contact digital laser
infrared thermometer along with HOBO logger which measures light intensity and
temperature inside the systems. Extech RF20, portable salinity refractometer is
being used to measure the salinity of the reservoir.
Convective cover
Metal plate
Hydrophilic cloth
Floating material
Wicking material
Solar
irradiation
Water
evaporation
Capillary
action
Figure 3: One-sun Ambient
Steam Generator (OAS)
Seawater
Solar still modifications
Figure 5: Multi-effect basin with
wicking material and reflective
mirrors (MEB)
Multi-effect: Increases the thermal efficiency.
Available energy in the form of latent heat, (the
energy required to turn the liquid water into
vapor) is captured from the lower chamber and
reused to heat up water in the upper chamber.
Reflectors: Increased temperature yields higher
evaporation rates; therefore reflecting mirrors are
placed on the top (north side) and bottom (south
side) of the still to direct solar radiation into the
basin.
Wicking material: Instead of a flat plate, a
material with fabric made of cylindrical polyester
will increase the surface area of the water,
allowing more to be absorbed in the base and
susceptible to evaporation to be evaporated.
OAS
SIER
MEB
Reflectors
Top chamber
Bottom
chamber
Wicking
material
Stepped: Decreases the distance the water
vapor travels before being collected via the
collection glass, thus producing more
condensate at a faster rate.
Internal and External Reflectors: Aims to
increase the amount of sun rays exposed to
the system to heat the water effectively and
efficiently. The addition of this feature is said
to increase freshwater yields by 100 to 120%
per square meter, which would, under ideal
conditions, increase the freshwater collected
to approximately 9 liters per day3.
Flow Through System: Contributes more
work to the water, creating more heat. A
black, external reservoir holds the water,
allowing for optimal UV radiation to heat the
seawater accordingly.
Figure 4: Stepped with Internal and
External Reflectors (SIER)
Rainmaker 550 Solar
Water Distiller
SIER Discussion
A primary goal of the stepped and reflector
design was to obtain optimal heating, which
would contribute to a higher freshwater yield.
While data collection is still in process, some
preliminary conclusions could be made.
Primarily, insulation of the interior is of optimal
importance for the function of the system.
Ensuring that the correct materials and
waterproof lining are used, has large effects on
the heating of the system and containing the
water in the system. Additionally, obtaining the
correct flow rate for the system is important, as
the amount of flow contributes to the amount
evaporated – a flow of about 15 gallons per
hour is suspected to produce optimal yeild1. It
was also observed that starting the flow
through system would be best after the black
reservoir has the opportunity to heat up. This
gives the water in subjected to the reflectors
and large surface area the opportunity to
evaporate while the reservoir is heating up as
well. Therefore, the water pump should not be
used until a certain water temperature is
obtained.
MEB Discussion
Volume (mL)Average Still
Temperature (◦C)
Average Cu sheet
Temperature (◦C)Salinity
3/20/2017 - 4/1/2017 2350 NA NA 0.94
4/2/2017 - 4/5/2017 2730 30.9 33.85 ~0
4/6/2017 (overcast) 840 24.7 31.45 ~0
4/7/2017 460 23.3 36.9 ~0
Time (day) 1 2 3 4 5 6 7
H2O Volume collected
(L)20 2.95 2.25 3.2 3.28 3.53 3.23
pH 8.02 7.03 5.67 6.24 6.11 6.54 6.89
EC (ppm) 32 0 0.1 0 0 0.2 0.2
Table 1: Experimental data gathered by McBryan et al using SolAqua Rainmaker 550.
Table 2: Experimental data generated from OAS-solar still system.
The multi-effect basin is meant to increase the
thermal efficiency in the solar still. Available energy
in the form of latent heat, (latent heat being the
energy required to turn liquid water into vapor) is
captured from the lower chamber; thus reusing the
latent heat in the lower chamber to heat up water in
the upper chamber.
I decided to use reflectors to direct solar radiation
into the still because increased temperature yields
higher evaporation rates. Ideally the reflecting mirror
would be as long as the base on the basin is to
maximize the surface area for reflecting potential,
but due to complications, I could only hinge the 1’ x
3’ onto the still.
The wicking material is placed inside the still
because instead of using the flat base of the still to
hold the seawater, the fabric made of cylindrical
polyester will increase the surface area that will be
able to absorb the seawater, increasing susceptibility
to evaporation.
practice. In an effort to
respond to the water
crisis on Catalina
Island, by studying and
applying 3 feasible and
cost-effective hybrid
modifications, this
study aims to increase
the water production of
a solar still, a solar
USC Wrigley Marine Science
Center’s (WMSC)
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Lab/Housing Combined Water Use
25% Reduction50% ReductionFY 15/16FY 16/17
As the most plentiful
water source near the
island is, without a
doubt, the Pacific
Ocean, desalination is
an attractive option to
mitigate the water
crisis at the WMSC.
Desalination is most
commonly considered
to be an energy
intensive and
expensive procedure,
which deters most
from investing in the
driven distillation unit that produces fresh water upon salt water
evaporation and condensation. In this passive system, seawater in
a wedged shaped basin with glass placed on top to seal, is
evaporated. Water vapor is then captured by the glass cover. As the
water vapor condensates onto the glass, via gravity the water
captured drips down the slope into a freshwater collection trough,
then to a collection vessel. Again, here we aim to increase the
water production of a conventional solar still by applying simple
and feasible technological improvements.
Figure 1 (Wrigley Institute Water Bill): The orange
and blue lines indicate the water mandates while the
purple and yellow represent the amount of water
used by the Wrigley Institute in 2016 and 2017.
Introduction
Engineering aspects for the MEB solar still and SIER are still being
modified and improved, therefore, the data is currently underway.
OAS Discussion
One of the important aspects of OAS is the
capillary system which is determined by the water
interactions that occurs between the phases at
which the water is traveling: the basin, through
the wicking material, absorbed by the hydrophilic
cloth then evaporated via convection by the
copper plate. Salt buildup was observed in the
OAS. Increase in salt concentration increases the
surface tension of the water thus reducing the
evaporation rate. This is due to the fact that
surface tension corresponds to intermolecular
forces, which leads to an inverse relationship
between surface tension and evaporation.
Second rusting was observed on the copper
plate. Rusting is basically the degradation of a
metallic material. Upon degradation this reduces
the surface area for kinetic energy. In addition to
that, rust can also act as an insulator which
prevents optimal heat transfer from the copper
sheet onto the hydrophilic cloth which then
reduces evaporation. A theoretical yield of 6
L/day during the summer months is expected
using the SolAqua Rainmaker 550. However, the
experimental set up and data gathering for this
study was conducted during Spring with
precipitation. This occurrence then added to the
reduced fresh water production since the system
was not running at optimal conditions.
AcknowledgementsThis research was supported in part by the Wrigley Institute for Environmental Studies. Thank you
to the USC Wrigley Marine Science Center’s (WMSC) staff: Kellie Spafford, Chris Rodgers, Josh
Jensen, and Randy Phelps for their assistance during the field set up of the solar stills. . Special
thanks to Bryan Tufts Ralph Bolam and Maurice Roper for constructing the solar stills. Lastly, thank
you to the alternative Spring break participants.
** presented a the 2017 USC Undergraduate Research Symposium and City of LA Spring Green EXPO