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Large Scale Dew Collection as a Source of Fresh Water Supply

  • Nimbkar agricultural research institute

Abstract and Figures

A scheme for large scale dew collection as a source of freshwater supply is outlined in the present paper. The scheme envisages bringing cold seawater (5°C) from about 500 meters depth and about 5 km from the shore, in 4, 1.22 m diameter plastic pipes. It then passes through a heat exchanger field with an area of 1.29 × 105 m2 (1.39 × 106 ft2) where it condenses 643m3 of dew over the 24 hour period. The pumping of seawater from the sea and through the field is accomplished by three 200 kW wind machines. Technical and economical feasibility of the scheme is analysed and the possibility of marine culture as a source of food is explored. The present scheme is economically not feasible as compared to a reverse osmosis facility of equivalent capacity.
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©NARI. August 2018
Published in Desalination, Vol. 36, No. 3, March 1981, pp. 299-306
Large Scale Dew Collection as a Source of Fresh Water Supply
(For other water related R&D done at NARI please visit this site)
Anil K. Rajvanshi
Director, Nimbkar Agricultural Research Institute (NARI)
Phaltan, Maharashtra, INDIA
A scheme for large-scale dew collection as a source of fresh water supply is outlined in the present
paper. The scheme envisages bringing cold seawater (50C) from about 500 meters depth and about 5 km
from the shore, in four, 1.22 m diameter plastic pipes. It then passes through an onshore heat exchanger
field with an area of 1.29 X 105 m2 (1.39 X 106 ft2) where it condenses 643 m3 of dew over the 24 hour
period. The pumping of sea water from the sea and through the field is accomplished by three 200 kW
wind machines. Technical and economical feasibility of the scheme is analyzed and the possibility of
marine culture as a source of food is explored. The present scheme is economically not feasible as
compared to a RO (reverse osmosis) facility of equivalent capacity.
With increasing industrialization and population, the world’s water supplies are being taxed to
their capacity. There is already an acute shortage of potable water in developing countries. This shortage
has necessitated the use of desalination as a means of providing fresh water for drinking purposes. All of
the existing desalination plants in the world use scarce and costly fossil to fire them. Consequently, the
majority of these plants are located in Mid East countries [1]. However, the majority of the developing
countries cannot get the costly fuel to run the desalination plants, thus pointing out the need of using
alternative desalination technology.
One of the simplest desalination technologies that have received hardly any serious attention is the
large-scale dew collection. Yet this is one of the major sources of water for plants and some animals in the
coastal and inland deserts [2]. In the desert environment the dew collection takes place because of night
sky radiation cooling. However, for production of large quantities of water the night sky radiation is not
sufficient [3, 4]. An alternative method, which is proposed in the present paper, is to pass the deep sea
cold water through suitable heat exchangers for dew condensation. Obvious advantages of the scheme over
the existing desalination processes are a) no energy is expended in evaporating the sea water the air-sea
This paper was written when the author was at Solar Energy and Energy Conversion Laboratory, Department of
Mechanical Engineering, University of Florida, Gainesville, Florida 32611, U.S.A.
©NARI. August 2018
interaction takes care of that, and b) because of assurance of constant temperature source of cold water, the
dew collection can take place continuously day and night for the whole year.
This paper discusses the technical feasibility of such a scheme and the thrust is given to presenting
an overall objective rather than detailed design calculations.
The scheme envisages bringing cold sea water at 4.50C (400F) from about 500 m (1600 ft) depth in
four, 1.22 m (4 ft) diameter plastic pipes to the shore. It then passes through a heat exchanger field (area of
1.29 X 105 m2), where it condenses about 643 m3 (170,000 gallons) of dew over the period of 24 hours.
The pumping of sea water from the sea and through the heat exchanger is accomplished by three, 200 kW
wind machines. After passing through the heat exchanger, the sea water goes through a series of ponds
where algae and fish are grown. It then returns to the ocean.
Figure 1 shows the schematic of the scheme and Figure 2 is an artist sketch of the scheme. Below
are detailed the different components of the system.
To sea
From Sea
Fresh water out
Fig. 1. Schematic of the scheme
Marine culture
Field of 695 heat exchangers
(Dew collectors)
Wind machine
powered pumps
©NARI. August 2018
Fig. 2. Artist sketch of the scheme
Heat Exchanger
The condensation of dew takes place when the cold seawater passes through the heat exchanger.
Thus the choice of heat exchanger is dictated by the following considerations; a) it should not be corroded
by sea water, b) it should effectively exchange heat with environment and c) it should be inexpensive.
Based on these points the heat exchanger chosen for the present scheme is an EPDM extruded collector
[5]. These collector mats are used for medium temperature hot water heating. In this scheme the EPDM
mat (without the glazing and the back insulation) sits on the shore inclined at an angle (about 60 to 700)
such that the dew condensation takes place on both sides of the mat.
The heat exchanger area for collecting the dew is calculated from the knowledge of condensation
heat transfer coefficient. This coefficient has been obtained experimentally [4]. It should be noted that
dew condensation will take place anytime when the heat exchanger plate temperature is less than the dew
point of the ambient air. Thus even during daytime considerable condensation occurs. The heat exchanger
area Ah is therefore given as:
During night :
2hc+r Ah (Ta Th) + 2hcond Ah (Ta Th) = mw Cp (Tout Tin) (1)
2hcond Ah (Ta Th)tn = mdew hfg (2)
©NARI. August 2018
During day :
qs Ah + 2hcond Ah (Ta Th) + 2hc+r Ah (Ta Th) = mw Cp (Tout Tin) (3)
Tout + Tin
Th = ------------ (4)
2hcond Ah (Ta Th) td = mdew hfg (5)
The values of variables used in the above equations are shown in Table 1. For the night
calculations it is assumed that the temperature of the sea water entering the heat exchanger module will be
100C (500F) and that at the exit will be 15.50C (600F). Therefore the average temperature of the heat
exchanger plate will be 12.70C (550F). Since this plant will be on shore hence an average ambient
temperature and relative humidity at night is assumed to be 23.80C (750F) and 100% respectively. The
duration of dew condensation at night is assumed to be 10 hours.
For the daytime calculations average solar radiation and ambient temperature have been assumed.
Thus over a period of 14 hours the solar radiation is assumed to have a value of about 252 W/m2 (80
BTU/ft2 hr) and ambient temperature of 26.60C (800F). These are reasonable assumptions for sea shore
©NARI. August 2018
conditions [6]. From equation (1) the mass flow rate of sea water flowing through the heat exchangers is
calculated and is 8.31 X 106 kg/hr (18.3 X 106 lbs/hr). This value is held constant during the daytime also.
Each collector module is assumed to be 18.6 m2 (50 ft X 4 ft) in area. This choice of area has
been dictated by the ease of maintenance and installation. Thus the total number of collectors is 6950. It
should be pointed out that the value of hc+r in equations (1) and (3) is that for still air. Near the sea shore
the conditions are far different from still air. However, the collectors are arranged such that they are
normal to the direction of the wind (coming from the sea) and thus act as wind breakers, thereby justifying
the assumption of hc+r .
Sea Water Intake Pipes
The choice of sea water intake pipe is governed by the following considerations; a) it should be
noncorrosive with sea water b) it should withstand the tides and the wave motions, c) it should provide
excellent insulation for the cold water during its passage to the shore and d) it should be easily assembled.
Based on these criteria the pipe chosen for the present scheme is a 1.22 m (4 ft) diameter plastic pipe with
wall thickness of 3.7 cm (1.45 inches) [7]. Four such pipes will bring the required water to the shore.
The cold sea water of 4.50C (400F) is mostly located at a depth of about 500 m (1600 ft) [8].
Moreover, the present scheme has been designed for locations where about 500 m deep waters are
available at about 5 km or less distance from shores [9]. Heat transfer calculations for a 5 km plastic pipe
show that the temperature rise of cold water of 4.50C (400F) will be less than 0.270C (0.50F) in reaching
the shore. Thus the plastic pipe provides adequate insulation. These calculations have been performed
assuming a sea water temperature profile [8] and the flow rate of water of 2.1 X 106 kg/hr (4.6 X 106
Pumping Requirements
Table 2 shows the pressure drop in various sections of the scheme and the pumping requirements.
The total pressure drop is about 176 kPa (60 ft of water). Near the sea shore there is a constant wind and
thus it is appropriate that the wind machines be used to operate the pumps. Three 200 kW wind machines
will adequately perform the pumping of sea water through collectors. Since the wind is constant near the
shore no attempt has been made to store the water in the overhead tanks. This storage would have been
necessary to overcome the pumping loss during wind-lean periods. It is also interesting to note that any
energy input in the present scheme is that from the wind machines which make this scheme consume 57
kW hr/1000 gallons. This energy requirement compares very favorably with that used in RO units (65 kW
hr/1000 gallons), and MSF (315 kW hr/1000 gallons) [10]. This is to be expected since no energy is
expended in evaporating the water.
©NARI. August 2018
Mariculture ponds
The deep sea water is an excellent feed producer for mariculture crops [9]. After passing through
the heat exchanger it can easily be run into deep ponds ( 6 m deep) to produce algae, which is a rich
protein source. These algae then can be a source of food for growing fish and clams [9]. Thus besides
providing the much needed water for the locality this scheme will also provide a source of protein and
food. Based on the results of the pioneering work done in the St. Croix island by Roels and his group [9],
the present scheme will produce about 870 tons/year (wet weight) of shellfish. It should be noted that in
the existing desalination plants such a scheme (of mariculture) cannot be implemented because of lack of
deep sea water.
Finally for the sake of completeness of the study a preliminary economic analysis of the scheme
has been done. Assuming the cost of wind machines at $ 600/kw [11], the cost of heat exchangers at $
30/m2 ( $ 3/ft2) [5] and the cost of 1.22 m (4 ft) diameter plastic pipe at $ 262/m ($ 80/ft), the capital cost
of the scheme comes out to be $ 11 million. The price of this scheme should be compared with the
existing desalination plant of an equivalent capacity. For comparison we have assumed a reverse osmosis
(RO) scheme [12]. Even taking the escalating fuel prices (at 15% annual increase) into account it has been
found that RO plant will be cheaper than the existing scheme by a factor of 2.5. However, if the fuel prices
suddenly double or triple then the present scheme (dew collection) will become economically viable. It
should be pointed out that the whole purpose behind presenting the idea of dew collection is to create
awareness of the technical merits of this scheme. Nevertheless, it is felt that with better technology and
©NARI. August 2018
materials of various components the scheme has capability of becoming economically viable. For example
the two main components with the highest price tags are the heat exchanger field ($ 4.2 million) and sea
water intake pipes ($ 5.3 million) respectively. If the field can be made of tubular heat exchangers rather
than the flat plate (as the present scheme) considerable savings in the cost can be achieved. In the absence
of any experimental data on dew collection on tubular heat exchangers we have chosen the flat plate (for
which the data exists [4]). Similarly cheaper pipes for sea water intake will reduce the cost of the scheme.
It can also be conjectured that in the future the OTEC (Ocean Thermal Energy Conversion)
schemes may very well become floating desalination plants with the cold water from the bottom used for
dew condensation. The production of fresh water may make OTEC economically viable since the
generated commodity (in this case fresh water) can be easily transported to shore in huge plastic tankers.
Right now no viable scheme of getting the generated power from OTEC plants to the shore exists [9].
The following conclusions can be drawn based on the present study.
1. Large scale dew collection near the seashore for production of fresh water is technically feasible.
2. A heat exchanger field of area 1.29 X 105 m2 (1.39 X 106 ft2) can condense 643 m3 (170,000 gallons)
of dew over a period of 24 hours.
3. The cold water for dew condensation is obtained from a depth of about 600 m. The pumping of 8.32
X 106 kg/hr (18.3 X 106 lbs/hr) of this cold water is achieved by 3, 200 kW wind machines.
4. This present scheme is economically not feasible as compared to a RO facility of equivalent capacity.
Acknowledgements : The author wishes to thank Richard Dixon, Kris Kirtikara and Rolando S. Guerra at
UF in helping in the dew condensation experimental set up and data collection. And to Rahul Pisharody of
NARI for making the artist sketch of the scheme.
1. P. M. Morris, “Desalination of Sea Water”, Chemistry & Industry, August 6 (1977).
2. Uwe George, In the Deserts of this Earth, Harcourt Brace Jovanovich Inc., New York (1979).
3. J. L. Monteith, “Dew”, Quarterly Journal, Royal Meteorological Society, Vol. 83, pp. 322-341
©NARI. August 2018
4. A. K. Rajvanshi, “Heat and Mass Transfer in Dew Collection”, in preparation.
5. Bio Energy Systems, Inc., Personal Communication.
6. B. Y. Liu and R. C. Jordan, “Availability of Solar Energy for Flat Plate Solar Heat Collectors”, in
Applications of Solar Energy for Heating and Cooling of Buildings (Eds. B. Y. Liu and R. C. Jordan),
ASHRAE GRP 170 (1977).
7. Steve Campbell, Personal Communication.
8. F. Kreith and J. F. Kreider, Principles of Solar Engineering, McGraw Hill Book Company, New
York (1978).
9. O. A. Roels, “Food, Energy and Fresh Water”, Mechanical Engineering, June (1980).
10. R. S. Silver and W. S. McCartney, Desalination, in The Marine Environment (Eds., Lenihan and
Fletcher), Vol. 5, Academic Press, New York (1977).
11. Anonymous, Wind Product Supplement, Solar Age, February (1980).
12. CH2M Hill, The U.S.A.I.D. Desalination Manual, Office of Engineering, U.S.A.I.D. Washington,
D.C., Contract AID/OTR-C-1618 (1980).
13. B. Gebhart, Heat Transfer, McGraw Hill Book Company, New York (1961).
Tin , Tout
Greek letters
heat exchanger area, m2
specific heat, kJ/kg 0C
enthalpy of vaporization, kJ/kg
combined convection and radiation heat transfer coefficient, W/m2 0C
condensation heat transfer coefficient, W/m2 0C
amount of dew condensed, kg
rate of sea water flow, kg/hr
incident solar radiation, W/m2
duration of dew condensation during day, hrs.
duration of dew condensation during night, hrs.
ambient temperature, 0C
temperature of heat exchanger place, 0C
temperature of sea water entering and leaving the heat exchanger respectively, 0C
solar absorptivity of the EPDM mat
heat exchanger efficiency
A short history of water related R&D at NARI is here.
©NARI. 2018
... Dew occurs when a surface temperature is cooled (by losing heat to the sky via radiation) below the dew point temperature of the surrounding air; and thus, water condenses and accumulates on the surface [6]; usually, it occurs overnight. Under natural conditions, dew is a precious source of water for plants and animals in arid and semi-arid environments, where other sources of water such as rain and groundwater are very scarce [1,7,8]. In general, dew occurs infrequently and the harvested amounts are sometimes very small, but in some regions dew occurs frequently with significant amounts that can be utilized for human use [9][10][11][12][13]. ...
... With increasing population growth rate and industrialization activities, the world's water supplies are being taxed to their capacity [1]. There has been a severe lack of fresh water in the world; especially in developing countries. ...
Full-text available
Since water shortage has been a serious challenge in Iran, long-term investigations of alternative water resources are vital. In this study, we performed long-term (1979–2018) model simulation at seven locations (costal, desert, mountain, and urban conditions) in Iran to investigate temporal and spatial variation of dew formation. The model was developed to simulate the dew formation (water and ice) based on the heat and mass balance equation with ECMWF-ERA-Interim (European Centre for Medium-Range Weather Forecasts–Re-Analysis) meteorological data as input. According to the model simulation, the maximum mean yearly cumulative dew yield (~65 L/m2) was observed in the mountain region in the north part of Iran with a yearly mean cumulative dew yield was ~36 L/m2. The dew yield showed a clear seasonal variation at all selected locations with maximum yields in winter (mean monthly cumulative 3–8 L/m2 depending on the location). Here we showed that dew formation is frequent in northern Iran. In other areas, where there was suffering from water-stress (southern and central parts of Iran), dew can be a utilized as an alternative source of water. The dew yield during 2001–2014 was lower than the overall mean during the past 40 years a result of climate change in Iran.
... The system's technical and economic feasibility was examined. It was determined that the current concept is not economically viable compared to a reverse osmosis facility of comparable capacity [32]. Dew is formed when moisture in the air condenses and is utilized for drinking and irrigation. ...
Full-text available
Water is essential for food security, industrial output, ecological sustainability, and a country’s socioeconomic progress. Water scarcity and environmental concerns have increased globally in recent years as a result of the ever-increasing population, rapid industrialization and urbanization, and poor water resource management. Even though there are sufficient water resources, their uneven circulation leads to shortages and the requirement for portable fresh water. More than two billion people live in water-stressed areas. Hence, the present study covers all of the research based on water extraction from atmospheric air, including theoretical and practical (different experimental methods) research. A comparison between different results is made. The calculated efficiency of the systems used to extract water from atmospheric air by simulating the governing equations is discussed. The effects of different limitations, which affect and enhance the collectors’ efficiency, are studied. This research article will be very useful to society and will support further research on the extraction of water in arid zones.
... Therefore, there is a need to look for alternative resources of water usable for beneficial applications (e.g., potable, agriculture, etc.). Actual extraction of atmospheric moisture (i.e., fog and dew), as an alternative source of water by means of planner dew condensers, has been implemented in many places worldwide [7][8][9][10][11][12][13][14][15][16][17][18][19]. ...
Full-text available
Model evaluation against experimental data is an important step towards accurate model predictions and simulations. Here, we evaluated an energy-balance model to predict dew formation occurrence and estimate its amount for East-African arid-climate conditions against 13 months of experimental dew harvesting data in Maktau, Kenya. The model was capable of predicting the dew formation occurrence effectively. However, it overestimated the harvestable dew amount by about a ratio of 1.7. As such, a factor of 0.6 was applied for a long-term period (1979–2018) to investigate the spatial and temporal variation of the dew formation in Kenya. The annual average of dew occurrence in Kenya was ~130 days with dew yield > 0.1 L/m2/day. The dew formation showed a seasonal cycle with the maximum yield in winter and minimum in summer. Three major dew formation zones were identified after cluster analysis: arid and semi-arid regions; mountain regions; and coastal regions. The average daily and yearly maximum dew yield were 0.05 and 18; 0.9 and 25; and 0.15 and 40 L/m2/day; respectively. A precise prediction of dew occurrence and dew yield is very challenging due to inherent limitations in numerical models and meteorological input parameters.
... Alternatively, cloud seeding by injecting cloud condensation nuclei (CCN) or ice nuclei (IN) in the atmosphere may also help in improving rain patterns in some semi-arid and arid areas. Recently, dew and fog water harvesting has been introduced in semi-arid areas as a source of water [3][4][5][6][7][8][9][10][11]. Table 1 for locations characteristics. ...
Full-text available
In this study, we performed model simulations to investigate the spatial, seasonal, and annual dew yield during 40 years (1979-2018) at ten locations reflecting the variation of climate and environmental conditions in Jordan. In accordance with the climate zones in Jordan, the dew formation had distinguished characteristics features with respect to the yield, seasonal variation, and spatial variation. The highest water dew yield (an overall annual mean cumulative dew yield as high as 88 mm) was obtained for the Mountains Heights Plateau, which has a Mediterranean climate. The least dew yield (as low as 19 mm) was obtained in Badia, which has an arid climate. The dew yield had a decreasing trend in the past 40 years due to climate change impacts such as increased desertification and the potential of sand and dust storms in the region. In addition, increased anthropogenic air pollution slows down the conversion of vapor to liquid phase change, which also impacts the potential of dew formation. The dew yield showed three distinguished seasonal patterns reflecting the three climates in Jordan. The Mountains Heights Plateau (Mediterranean climate) has the highest potential for dew harvesting (especially during the summer) than Badia (semi-arid climate).
... Ancient artisans were thus taking advantage of the low contact angle hysteresis of water droplets on plant leaves even without noticing it. Nevertheless, how to understand and increase dew collection efficiency remained an unsolved issue until almost 1000 years later 1,6,7,17 . The previous story from ancient China is only one case where human beings took advantage of wetting for their well-being without noticing. ...
In this thesis, we aim at obtaining a better understanding of the statics and dynamics of the wetting of liquids on soft gels, otherwise known as elastowetting. First, we develop a quantitative Schlieren optics to measure the surface deformation of a transparent gel film with a high precision over large areas in real time. The long-range surface deformation of soft PDMS films is found to be dependent on the sessile droplet size, and the thickness and elasticity of the soft films. We build a model based on linear elasticity theory with the integration of the surface tension of soft materials that predicts the long-range surface deformation in excellent agreement with the data. We also bring the experimental proof and theoretical analysis of the importance of contact angle hysteresis in the description of the deformation of the surface of the gel. We demonstrate that the tangential component of the liquid-vapor surface tension at the contact line, whose contribution are often neglected, significantly affects the surface deformation. Wetting dynamics is investigated by deflating droplets on PDMS films with well-controlled thickness. It is shown that energy dissipation in the soft gel depends on the thickness when the latter is smaller than 100 μm. The viscoelastic braking effect and the thickness effect are both well rationalized with a model based on the theory of linear viscoelasticity and a simple scaling law accounting for the thickness effect captures very well our experiments. Finally, we demonstrate that we are able to guide moving droplets with coatings having a gradient of their thickness.
... Rajvanshi et al. [6] proposed a scheme for large-scale dew collection as a supply source of fresh water. The schematic requires cold seawater to be pumped from the neritic zone to a heat exchanger field. ...
Full-text available
Dew collection, and devices for such, may play an important role in regions of our planet that are arid and lack clean water. Usually, dew collection devices are represented as an inclined plane, which is a trivial topology. In this work, we first propose the concept a dew collection device with a helicoidal structure in order to increase its surface area, and we suggest taking into account Frenkel’s mathematical model of sliding drops on an inclined surface as the fundamental idea in designing dew collection devices. We also believe that in the future this mathematical model can be used to investigate the possibility of condensing liquid drops within other planets’ atmospheres that contain hydrogen and oxygen. Finally, we represent our concept as a three-dimensional Rhino model.
... While, MED consumes less thermal energy between 40 and 60 kWh/m 3 and electrical energy consumption around 2.5 kWh/m 3 [3]. RO, on the other hand, requires electrical energy consumption around 3.7 to 8 kWh/m 3 [1,[5][6][7][8][9][10]. The reliance on fossil fuel, which is not renewable, also causes environmental problems such as greenhouse gas emission. ...
The shortage of fresh water resources is becoming more and more serious with the acceleration of modernization and industrialization, especially in some dry welding and underdeveloped areas. Scientists are bent on alleviating the issue of fresh water shortage. Concurrently, many biological species have developed elegant schemes for water-harvesting for their survival. Combining their mechanisms and design strategies is crucial to fabricate interfacial materials with efficient water collection. This paper extracts the water-collecting principles and characteristics of Namib Desert beetles, cactus and spider silk, and reviews the synthesis strategies of various bionic water collecting materials under the guidance of these typical creatures. We put an extreme emphasis on the liquid-solid interfacial interaction between the accumulative nuclear dew and functional materials' surfaces. The key factor for reliable water collection materials is the design of robust hierarchical configuration. However, these constructed microstructures are vulnerable and many practical applications are limited. Therefore, the design of architectures with durability has become a serious topic and we highlight the development, current research status on the durability and self-repair of directional water collection materials. Finally, a holistic view and future prospects of bionic directional water collection materials, including mechanisms, characterization, design strategies and fabrication techniques, are provided. We envision that these well-chosen facts and opinions will be useful in fluid handling and transportation, self-cleaning and water collection fields.
Dew water plays crucial role in agriculture in arid regions of various parts of the world and during winter in Indian northern and north-western regions, particularly. Dew is considered to be wet deposition which augments the supply of water during dry periods. It is also a source of moisture as well as nutrients helping in growth of fruits, vegetables and crops like wheat and gram to grow during winter especially at reproductive stage. Dew reduces transpirational loss of water and aids in foliar absorption which helps in survival of natural vegetation in extreme climates. However, dew increases humidity in crop canopy which is favourable for pest growth and spread of diseases in plants that negatively impact yield of crops. Emerging contaminants such as pesticides, biocides and pharmaceutical products dissolved in dew act as input in agricultural field which ultimately affect geochemistry of soil.
Full-text available
Seawater desalination plays a critical role in addressing the global water shortage challenge. Directional Solvent Extraction (DSE) is an emerging non-membrane desalination technology that features the ability to utilize very low temperature waste heat (as low as 40 °C). This is enabled by the subtly balanced solubility properties of directional solvents, which do not dissolve in water but can dissolve water and reject salt ions. However, the low water yield of the state-of-the-art directional solvent (decanoic acid) significantly limits its throughput and energy efficiency. In this paper, we demonstrate that by using ionic liquid as a new directional solvent, saline water can be desalinated with much higher production rate and thus significantly lower the energy and exergy consumptions. The ionic liquid identified suitable for DSE is [emim][Tf2N], which has a much (~10×) higher water yield than the currently used decanoic acid. Using molecular dynamics simulations with Gibbs free energy calculations, we reveal that water dissolving in [emim][Tf2N] is energetically favorable, but it takes significant energy for [emim][Tf2N] ions to dissolve in water. Our findings may significantly advance the DSE technology as a solution to the challenges in the global water-energy nexus. Directional Solvent Extraction is an emerging non-membrane desalination technology for sea water desalination but is limited by throughput and energy efficiency. Here, the authors demonstrate that the production rate and energy efficiency can be increased by using ionic liquids as directional solvent.
The tropical oceans are the world's largest collector and storage system of solar energy. This heat can be utilized to generate mechanical energy and fresh water by using the cold deep water, only about 1000 m below this vast heat reservoir, as the heat sink. After its use in the condenser of the power-generating or desalination plant, the deep water can be used in a mariculture system to produce plant and animal protein. In a small shore-based pilot plant on the north shore of St. Croix, U. S. Virgin Islands, the technical feasibility of artificial upwelling mariculture has been demonstrated and its economic potential is now under evaluation. The plant protein yield per unit surface area achieved in St. Croix is 8. 1 t/ha/yr. At current market prices, the gross sales volume of deep seawater pumped to the surface is considerably greater than that of the energy OTEC (Ocean Thermal Energy Conversion) power systems presently under consideration in the U. S. could generate from the same volume of deep water.
With reference to the letter by Professor D A Bell on page 245 of the April issue of Physics Bulletin, I would comment as follows. He asks whether anyone thought in terms of reducing irreversibility in desalination processes before the Atomic Energy Authority embarked on its desalination program.
Dew formation on short grass has been studied with a balance, recording weight of condensation, and with filter papers to absorb moisture. Three regimes are distinguished: in the first, daytime evaporation continues and the grass remains dry; in the second, the surface continues to lose weight but the grass becomes wet owing to the partial condensation of water vapour evaporating from the soil; in the third, this loss of weight ceases or there is an increase in weight attributed to condensation of atmospheric water vapour. A distinction is therefore made between ‘distillation’ of water vapour from soil to grass (1–2 mg cm−2hr−1) occurring on very calm nights through a laminar layer with a transfer coefficient approaching the molecular value; and ‘dewfall,’ the turbulent transfer of water vapour from the atmosphere, negligible when the wind at 2 m falls below 0.5 m/sec but reaching 3–4 mg cm−2hr−1 with stronger winds. This distinction is supported by analysis of the surface heat-budget. On windless nights, since heat flux from the soil and net radiative loss were almost equal, the transfers of sensible and latent heat from the atmosphere were negligible and distillation was of much greater importance than dewfall. Implications for taller crops and warmer climates are briefly considered.
The aim of the book is to present all the information necessary for the design and analysis of solar energy conversion systems. A combination of basic technical understanding and an appreciation of the economic aspects of using nonrenewable energy sources is developed. The divisions of the subject matter are as follows: introduction to solar energy and its conversion, fundamentals of solar radiation, fundamentals of fluid mechanics and heat transfer, methods of solar collection and thermal conversion, system analysis and economics of solar systems, solar heating systems, solar cooling and dehumidification, solar electric power and process heat, and a brief look at natural solar conversion systems such as wind energy, thermal ocean thermal gradient and wave power, and biomass conversion systems.
Desalination of Sea Water
  • Morris
P. M. Morris, "Desalination of Sea Water", Chemistry & Industry, August 6 (1977).
Heat and Mass Transfer in Dew Collection
  • A K Rajvanshi
A. K. Rajvanshi, "Heat and Mass Transfer in Dew Collection", in preparation.
Availability of Solar Energy for Flat-Plate Solar Heat Collectors
  • Liu
B. Y. Liu and R. C. Jordan, "Availability of Solar Energy for Flat -Plate Solar Heat Collectors", in Applications of Solar Energy for Heating and Cooling of Buildings (Eds. B. Y. Liu and R. C. Jordan), ASHRAE GRP 170 (1977).
Personal Communication
  • Steve Campbell
Steve Campbell, Personal Communication.
  • R S Silver
  • W S Mccartney
R. S. Silver and W. S. McCartney, Desalination, in The Marine Environment (Eds., Lenihan and Fletcher), Vol. 5, Academic Press, New York (1977).
Wind Product Supplement, Solar Age
  • Anonymous
Anonymous, Wind Product Supplement, Solar Age, February (1980).