GB2511075A

GB2511075A - Desalination Apparatus

Info

Publication number: GB2511075A
Application number: GB1303142.2A
Authority: GB
Inventors: Donald Earl Spence; Cody Jason Spence
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-02-22
Filing date: 2013-02-22
Publication date: 2014-08-27
Also published as: WO2014128543A1; GB201303142D0

Abstract

Desalination apparatus 10 is provided for removing impurities from an impure liquid, and comprises a vacuum chamber 14 and a solar heater 12 for raising the temperature of the impure liquid. The vacuum chamber includes a vaporization compartment (70, Fig. 2) and a condensation compartment (72, Fig. 2). The condensation compartment includes a cooling element (78, Fig. 2) for causing condensation of vapour, whilst the solar heater includes a solar collector 26 for absorbing solar radiation and a heat exchanger 28 for transferring heat absorbed by the solar collector to the impure liquid. The solar collector and the heat exchanger are fluidly interconnected in a heating circuit containing a heating fluid which includes a suspension of nanoparticles in a fluid, i.e. a nanofluid. Preferably, a nozzle (74, Fig. 2) discharges impure liquid into the vacuum chamber, the nozzle positioned to discharge in a downward direction. A desalination system and a method of desalinating seawater are also claimed.

Description

Desalination Apparatus The present invention relates to desalination apparatus, and more particularly but not necessarily exclusivdy to desalination apparatus for removing salt from sea water or brackish water.

Desalination provides a fresh water supply in areas where fresh water is otherwise unavailable, but where a plentiful supply of salt or brackish water may be found. For example, desalination is used in areas of the world with low rainfall, and onboard ocean-going ships which are at sea for long periods.

Desalination is typically an energy-intensive means of producing fresh water. The most common desalination technique is reverse osmosis, which involves the use of pumps to force water through a membrane. The pumps are typically powered by electricity, which is primarily derived from burning fossil fuels.

An alternative desalination technique works by distillation. That is, salt water is made to evaporate, and the vapour is then condensed. The condensate is desalinated water.

Distillation is generally more energy intensive than reverse osmosis. However, distillation is able to make use of waste heat at thw temperatures which cannot be used to generate electricity efficiently. In particular, solar energy may be used to heat saline water for distillation.

Solar water heating is advantageous due to the low environmental impact of the energy source. However, to heat water to a useful temperature at a reasonable rate requires very large solar panels. A reduction in panel size results in either a lower temperature of water, requiring more energy input from polluting sources, or a lower rate of flow through the panel, reducing the output of a solar desalination plant.

It is an object of this invention to provide solar distillation, and more particularly desalination, apparatus which reduces the above mentioned problems.

According to a first aspect of the present invention, there is provided desalination apparatus for removing impurities from an impure liquid comprising: a vacuum chamber including a vaporization compartment and a condensation compartment having a cooling element for condensing vapour; a solar collector for absorbing solar radiation; and a heat exchanger for transferring heat energy absorbed by the solar collector to the impure liquid, so as to raise a temperature of the impure liquid, the solar collector and the heat exchanger being fluidly interconnected in a heating circuit having a heating fluid which is or includes a heat energy absorbent nanofluid.

The impure liquid may be salt water or brackish water, with the product of the desalination apparatus preferably being fresh water.

In use, the impure liquid is heated by the solar heater, typically to 38°C or to around 38°C. The vaporization compartment of the vacuum chamber is at low pressure, typically around I 37mbar. At this temperature and pressure. water boils.

The vacuum chamber may be maintained at a low pressure by means of a vacuum pump, which is typically powered by electricity. It is therefore advantageous to heat the liquid to as high a temperature as is possible, in order to increase the vapour pressure of the liquid, consequently reducing the energy consumed by the vacuum pump.

Suspensions of nanoparticles in a liquid, or nanofluids, absorb solar radiation with very high efficiency. By using a nanofluid as the heating fluid in the solar heater, the impure liquid is raised to a greater temperature than with the use of conventional heating fluids.

This reduces the amount of non-solar energy required to operate the apparatus.

The heat exchanger may include a heated liquid outlet fluidly connected with a heated liquid inlet to the vacuum chamber, for transferring heated liquid from the heat exchanger into the vacuum chamber. In other words, the liquid may be heated in the heat exchanger before being vaporized in the vacuum chamber. The heated liquid will flash vaporize as it passes into the low-pressure vacuum chamber.

The heat exchanger may be provided integrally with the solar collector, or may be a separate unit.

Alternatively, the heat exchanger may be provided inside the vacuum chamber. In other words, the liquid may pass into the vacuum chamber before being heated.

The solar collector may be in the form of a panel, and may include a base, at least one side, a heat absorption surface and at least one baffle disposed within the panel substantially parallel with the heat absorption surface. The baffle may include an aperture near to a side of the panel, creating a tortuous flow path for the heating fluid from a side of the panel, across substantially the entire area of the collector beneath the baffle, and across substantially the entire area of the collector above the baffle.

Alternatively, the baffle may be substantially perpendicular to the heat absorption surface, creating a tortuous flow path for the heating fluid, the heating fluid passing into the solar collector to one side of the baffle, through the aperture, to the other side of the baffle, and then out of the solar collector.

Preferably, the aperture may be in the form of a slot.

The solar collector may be rectangular. circular, or any other shape. Where the solar collector is rectangular, a baffle parallel with the heat absorption surface may adjoin three of the four sides of the panel, the space between the baffle and the fourth side of the solar collector defining a slot Liquid may therefore flow across a length of the solar collector below the baffle, then up through the slot and back across the same length of the solar collector, above the baffle. Alternatively, the liquid may flow above the baffle before flowing below the baffle.

Where the solar collector is circu'ar. the slot may be in the shape of a segment or a crescent. Again, the aperture may be provided between the baffle and the side of the solar collector.

Providing a baffle parallel with the heat absorption surface increases the efficiency of the solar collector, because it allows solar radiation which is not absorbed by the heating fluid running across the top of the baffle to be absorbed by heating fluid underneath the baffle. Where fluid runs underneath the baffle and then above the baffle, the effect is that the fluid is pre-heated underneath the baffle before the main heating stage above the baffle. This increases the temperature of the heating fluid after it has passed through the panel, whilst maintaining a high flow rate through the panel. Providing baffles to separate layers of heating fluid ensures that substantially all of the available solar radiation is absorbed, and is preferable to simply increasing the thickness of the layer of heating fluid passing through the solar collector. With a thick layer of heating fluid in the panel, warmed heating fluid would convect to the top of the layer, cooler fluid at the bottom of the layer not being exposed to the sun and therefore remaining cool. Using baffles to separate the flow ensures that the entire volume of liquid flowing out of the solar coflector is heated to substantially the same temperature.

The heat absorption surface may be, for example, a glass panel. It may alternatively be a surface of the heating fluid which is directly exposed to the sun, although some form of bather is preferred as contamination of the heating fluid is thus avoided.

A plunlity of baffles may be provided, the baffles being disposed substantia'ly parallel with each other and adjacent baffles having apertures near to opposing sides of the absorption panel. Where the solar collector is circular or elliptic and therefore has only one side, apertures near to opposing sides should be taken to mean apertures which oppose each other across the circular solar collector.

Providing multiple baffles further reduces the above described problem of uneven IS heating. whilst ensuring that all of the solar radiation avaflable is utilised to the maximum possible effect.

The baffles may be made from glass. Glass allows solar radiation to pass through for absorption by the heating fluid, but prevents heat from leaving the panel by convection.

The vaporization compartment and the condensation compartment of the vacuum chamber may be divided by a wall, the height of the wall being less than the height of the vacuum chamber. Vapour may therefore pass over the top of the wail, from the vaporization compartment to the condensation compartment.

A nozzle may be provided for discharging impure liquid into the vacuum chamber, the nozzle being positioned to discharge in a downward direction at a point within the vaporization compartment below the level of the top of the dividing wall. Where the liquid is heated before it enters the vacuum chamber, it is flash vaporized on entry to the vacuum chamber. Solid particles of impurities -for example, salt -will therefore be discharged from the nozzle. By placing the nozzle so as to discharge in a downward direction below the level of the dividing wall, the possibility of impurities being introduced into the condensation compartment is eliminated.

The condensation compartment may be divided into a condensing unit and a condensate storage aiea by a gas-tight seal. For example, a trap may be provided to allow passage of condensate from the condensing unit to the condensate storage area, but to prevent vapour from entering the condensate storage area.

It is possible that small solid particles of impurity may be carried by the vapour. It is therefore advantageous to reduce as far as possible the surface area of condensate which is exposed directly to the vapour, to reduce re-contamination and improve the purity of the output from the apparatus.

A holding cistern may be provided for storing a supply of impure liquid. The impure liquid may flow from the cistern under gravity. The cistern therefore allows the desalination apparatus to operate for a period of time when an inlet pump, for example, pumping salt water from the sea, is not operating. This ensures that a purified liquid IS supply can be maintained in the event of pump faflure. Tn addition, it allows the inlet pump to be operated only at certain times of day when cheap electncity is available, for example during off-peak hours or when the weather conditions are such that output from wind turbines and photovoltaic cells is high.

The holding cistern may include a pre-heater for raising the temperature of the impure liquid prior to it entering the solar heater. The pre-heater may itself be a solar heater, and may be a glass panel on top of the cistern for admitting solar radiation into the cistern. It is also envisaged that water in the cistern may be pre-heated by waste heat from, for example, air conditioning systems.

A bleed outlet may be provided between the heated liquid outlet of the solar heater and the heated liquid inlet of the vacuum chamber for diverting liquid out of the apparatus, bypassing the vacuum chamber. This allows inadequately heated water to be flushed from the system, for example in the early morning when the so'ar heater is not yet heating the water to a useful temperature.

A liquid waste outlet may be provided in the vaporization compartment of the vacuum chamber, for disposing of excess liquid.

Where the liquid is being heated before being passed into the vaporization compartment, there should not be much liquid present in the vaporization compartment when the system is operating normally. If, however, the vacuum chamber is not at a low enough pressure or the liquid is not at a high enough temperature, then liquid may build up in the vaporization compartment and will need to be removed. Even at the correct operating temperature and pressure, some liquid vapour may condense against the walls of the vaporization compartment. A level sensor may be provided which activates a waste disposal valve andior pump in the event that the liquid level in the vacuum chamber rises above a certain point.

A punfied liquid outlet may be provided in the vacuum chamber for discharging condensate from the condensate section. Where the condensation compartment is divided into a condensing area and a condensate storage area, the purified liquid outlet may be provided as an outlet from the condensate storage area.

The cooling element may include a cooling pipe containing a cooling fluid. The cooling fluid may be circulated through the cooling pipe for absorbing heat from vapour in the vacuum chamber, and may be circulated through a cooling pool for removing heat from the cooling fluid. The cooling fluid may be continually circulated between the cooling element and the cooling pool in a closed circuit. Alternatively, cooling fluid may be pumped from, for example, the sea, and heated coolant returned to the sea.

The vacuum chamber may be substantially cylindrical and the vaporization compartment may be substantia'ly cylindricaL the vaporization compartment having a diameter less than the diameter of the vacuum chamber and being disposed within the vacuum chamber, the condensation compartment being provided between the outside of the cylindrical vaporization chamber and the outside of the cylindrical vacuum chamber. The vaporization compartment may be disposed substantially at the centre of the vacuum chamber, the condensation compartment being in the shape of a cylindrical shell, the two compartments thus being concentnc with each other. Providing a vaponzafion compartment in the centre of the vacuum chamber and a condensation compartment around the periphery of the vacuum chamber is a convenient arrangement, as the condensation compartment completely surrounds the vaporization compartment.

This helps to ensure that a large proportion of the vapour is condensed in the condensation compartment, the amount of vapour which loses heat and condenses in the vaporisation section being kept small. It is advantageous to the efficiency of the system to reduce the amount of condensation which occurs in the vaporisation section, since the heat in this liquid is wasted, especially where the liquid is heated prior to its entiy into the vacuum chamber and there is no heating element in the vacuum chamber.

Where the condensation compartment sulTounds the vaporization compartment as described above, the cooling pipe may be in a loop, multiple concentric loops, or a spiral around the outside of the cylindncal vacuum chamber, at or adjacent to the top of the condensation compartment.

An auger may conveniently be provided for removing solid waste from the vaporization compartment of the vacuum chamber. The auger is preferably provided on or adjacent to the base of the vaporization compartment of the vacuum chamber.

According to a second aspect of the invention, there is provided an impure water desalination system comprising desalination apparatus in accordance with the first aspect of the invention, and a source of sail or brackish water.

According to a third aspect of the invention, there is provided a method of desalinating seawater using desalination apparatus in accordance with the first aspect of the invention, the method comprising the steps of: exposing a heat-absorbent nanofluid to solar radiation; pre-heating salt water or brackish water by transferring heat energy of the heat-absorbent nanofluid thereto; reducing the pressure of the pre-heated salt water or brackish water, so that it vaporises wherein the salt separates; and condensing the remaining vapour to form fresh water condensate.

According to a fourth aspect of the invention, there is provided desalination apparatus for removing impurities from an impure liquid, the apparatus comprising a solar heater for pre-heating an impure liquid to be distilled, a vacuum chamber for receiving the pre- heated impure liquid, and pressure reducing means for reducing a pressure of the pre-heated impure liquid at the vacuum chamber, the solar heater including a solar-energy collector having a heat transfer liquid which comprises a suspension of nanoparticles for heat absorption, and a heat exchanger in liquid communication with the solar-energy collector for receiving the impure liquid for pre-heating, and the vacuum chamber including a vaporisation compartment for receiving the pressure reduced pre-heated impure liquid as a vapour, and a condensation compartment which is spaced from the vaporisation compartment for condensing the vapour.

For a better understanding of the present invention, and to show more clearly how it may be camed into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 shows a schematic of a desalination apparatus according to the invention; and Figure 2 shows an efflarged schematic side view of a vacuum chamber forming part of the desalination apparatus of Figure 1.

Referring firstly to Figure 1, a desalination apparatus is shown generally at 10. This embodiment is designed for removing salt from sea water on an industrial scale, although it will be appreciated that the invention may be used for removing other impurities from other Uquids. The desalination apparatus comprises a solar heater outlined by box 12, a vacuum chamber 14, a storage cistern 16 and a cooling reservoir 18.

In use, seawater is pumped from sea 100 into storage cistern 16 by seawater pump 50.

Seawater pump 50 does not need to operate continuously, as long as storage cistern 16 is kept topped up with seawater. Seawater pump 50 may therefore be activated when energy is available from intermittent renewable sources, such as wind turbines or photovoltaic cells, or at times of the day when electricity is cheaper.

Seawater is pumped from the storage cistern 16 into the solar heater 12 by seawater pump 52. When the cistern 16 is full enough to provide adequate pressure at the base of the cistern 16, the water will be able to flow under gravity and pump 52 may be bypassed, reducing the energy required to operate the system.

After the water is heated by the solar heater 12, it flows into the vacuum chamber 14 via pressure-reducing valve 21. The vacuum chamber 14 is kept at a low pressure by means of a vacuum pump 54. In this embodiment, the pressure is typically at or around l37mbar, but may be increased or reduced depending on the amount of solar energy available from the sun. The solar-heated water vaporises upon entry to the vacuum chamber 14, and is then condensed within the vacuum chamber 14. The condensate is fresh water, which may be removed from the vacuum chamber 14 via a fresh water outlet 20. If necessary, the fresh water may be pumped by a fresh water pump 56.

A bleed valve 22 is preferably provided in the flow path between the solar heater 12 and the vacuum chamber 14. The bleed valve 22 may be opened to remove inadequately heated water from the system. The inadequately heated water is fed into a bleed tank 24, from where it may be reintroduced into the desalination apparatus 10 or simply dumped back into the sea 100.

A cooling fluid is circulated between a condenser 78 within the vacuum chamber 14 and a cooling pool 18. The cooling fluid is circulated by cooling pump 58. In the embodiment shown, the cooling fluid is circulated in a closed circuit between the cooling pool 18 and the vacuum chamber 14. The volume of the cooling pool 18 is approximately equal to the volume of fresh water to be produced daily by the apparatus 10.

The s6lar heater 12 includes a solar panel 26, a heat exchanger 28, and a heating fluid pump 60. The solar panel 26, heat exchanger 28 and heating fluid pump 60 are connected in a closed heating circuit, and the heating fluid pump 60 circulates a heating fluid in that closed circuit. The heating fluid comprises a nanofluid. which is a suspension of nanopartides in a liquid.

The solar panel 26 is preferably cuboidal, having four sides, two of which 44, 46 are shown in Figure 1, a base 30 and a roof 32. Five glass baffles 34, 36, 38, 40, 42 are provided within the panel 26, parallel with the base 30 and the roof 32. Three of the &ass baffles 34, 38, 42 abut the same three sides of the solar panel 26, being disconnected from the fourth side 44 of the panel 26. The other two glass baffles 36, 40 are disconnected from the side 46 of the panel which opposes side 44. In this way, a tortuous flow path is created through the panel 26 which passes over the base 30 of the panel 26 and over each baffle 34, 36. 38. 40, 42. The heating fluid circulating in the heating circuit therefore passes across the panel six times in its journey from an inlet at or adjacent to the base 30 to an outlet at or adjacent to the roof 32.

The roof 32 of the panel 26 is preferably made from glass or other radiation-transmissible material.

Referring now to Figure 2, a detailed side view of the vacuum chamber 14 is shown.

The vacuum chamber 14 lii this embodiment is cylindrical, and is divided into a vaporization compartment 70 and a condensation compartment 72 by cylindrical wall 76. Wall 76 has a height which is less than the height of the vacuum chamber 14, so that vapour may pass over the top of the wall 76, between the vaporization 70 section and the condensation compartment 72.

At the top of the condensation compartment 72, a cooling element 78 is provided. The cooling element 78 preferably comprises a coil of copper or aluminium pipe 80, supported by a shell 80 extending from outer wall 81 of the vacuum chamber 14. The shelf 80 slopes downwardly from the outer wall 81 towards the vaporization IS compartment 7ft The shelf 80 has aflp 82 which depends from a radially inner edge 83 of the shelf 80. A further shelf 84 extends from the wall 76, at a level just below the lowermost extent of lip 82. The further shelf 84 has a lip 86 extending upwardly from or adjacent to its radially outermost edge. almost meeting the shelf 80.

In use, salt water is introduced into the vaporization compartment 70 via nozzle 74, having passed through the pressure-reducing valve 21. As the salt water enters the vacuum chamber 14 via nozzle 74 and shown by arrows A, it flash vaponzes. Salt 92 falls and collects at the bottom of the vaporization compartment 70, and the vapour rises, as shown by arrows B. The vapour condenses when it reaches the vicinity of and contacts the cooling element 78, at which point it flows along shelf 80 down the fall of the shelf, towards the centre of the vacuum chamber 14, until it runs off the edge and onto the further shelf 84. The condensate 94 accumulates in a trough 96 defined by wall 76, shelf 84 and lip 86 until it flows over the lip 86. The overflowing condensate 94 thus drains into a condensate storage area 90, which is radially outward of the vaporization compartment 70 and which extends around the outer side of the dividing wall 76. The shelves 80, 84 and the lips 82, 86 form a gas-tight seal between the condensate storage area 90 and the vaporization compartment 70.

Referring back to Figure 1, a waste outlet 48 is preferably provided for removing waste liquid from the vaporization compartment 70 of the vacuum chamber 14. In this case, a waste pump 62 is provided for pumping out the waste, and may be activated by a level sensor so that waste liquid is pumped only when it reaches a particular level in the vaporization compartment 70. The waste liquid is conveniently pumped back into the sea 100.

Beneficially, a salt auger 49 is provided at the base of the vaporization compartment 70 of the vacuum chamber 14, for removing waste salt from the vaporization compartment 70. However, other options for salt removal may be provided, for example. an access hatch for access by a labourer for manual removal, maintenance and cleaning.

The desalination apparatus maybe used for providing a supply of fresh water on a arge scale, where only salt water or brackish water is naturally available. The apparatus makes efficient use of solar energy to heat the water for desalination, reducing the amount of external energy which needs to be supplied to the system. The apparatus is also able to reduce its energy consumption at times of the day when electricity is expensive, making up the shortfall when electricity is cheap.

The embodiments described above are provided by way of example only, and various changes and modifications will be apparent to persons skilled in the art without departing from the scope of the present invention as defined by the appended claims.

I

Claims

Claims 1. Desalination apparatus for removing impurities from an impure liquid comprising: a vacuum chamber including a vaporization compartment and a condensation compartment having a cooling element for condensing vapour; a s&ar collector for absorbing solar radiation; and a heat exchanger for transferring heat energy absorbed by the solar collector to the impure liquid, so as to raise a temperature of the impure liquid, the solar collector and the heat exchanger being fluidly interconnected th a heating circuit having a heating fluid which is or includes a heat energy absorbent nanofluid.
2. Desalination apparatus as claimed in claim 1, in which the heat exchanger thcludes a heated liquid outlet in fluid communication with a heated liquid inlet of the vacuum chamber, for transferring heated liquid from the heat exchanger into the vacuum chamber.
3. Desalination apparatus as claimed in claim 1, in which the heat exchanger heats impure liquid inside the vaporization compartment of the vacuum chamber.
4. Desalination apparatus as claimed in claim 1, in which the solar collector includes a base, at least one side, a heat absorption surface and at least one baffle disposed within the panel.
5. Desalination apparatus as claimed in claim 4, in which the baffle is substantially parallel with the heat absorption surface.
6. Desalination apparatus as claimed in claim 5, in which the baffle includes an aperture near to a side of the solar collector, creating a flow path for the heating fluid from a side of the pae1, across substafflially the entire area of the collector beneath the baffle, and across substantially the entire area of the collector above the baffle.
7. Desalination apparatus as claimed in any of claims 4 to 6, in which a plurality of baffles are included, the baffles being disposed substantially parallel with each other and adjacent baffles having apertures near to opposing sides of the solar collector.
8. Desalination apparatus as claimed in any of claims 4 to 7, in which the baffle or baffles are made from glass.
9. Desalination apparatus as claimed in any preceding claim, in which the vaporization compartment and the condensation compartment are divided by a wall, the wall having an aperture near the top of the vacuum chamber.
10. Desalination apparatus as claimed in claim 9, in which the vaporization compartment and the condensation compartment of the vacuum chamber are divided by a wall, the height of the wall being less than the height of the vacuum chamber.
11. Desalination apparatus as claimed in claim 9 or claim 10, in which a nozzle is provided for discharging impure liquid into the vacuum chamber, the nozzle being positioned to discharge in a downward direction at a point within the vaporization compartment below the level of aperture in the dividing wall.
12. Desalination apparatus as claimed in any of the preceding claims, in which the condensation compartment is partitioned into a condensing unit and a condensate storage area by a gas-tight seal.
13. Desalination apparatus as claimed in any of the preceding claims, in which a holding cistern is provided for storing a supply of impure liquid.
14. Desalination apparatus as claimed in claim 13, in which the holding cistern includes a pre-heater.
15. Desalination apparatus as claimed in daim 14, in which the pre-heater is a solar heater.
16. Desalination apparatus as claimed in claim 2, in which a bleed outlet is provided between the heated liquid outlet of the solar heater and the heated liquid inlet of the vacuum chamber for diverting liquid out of the apparatus, bypassing the vacuum chamber,
17. Desalination apparatus as claimed in any of the preceding claims, in which a liquid waste outlet is provided in the vaporization compartment of the vacuum chamber, for disposing of excess liquid.
18. Desalination apparatus as claimed in any of the preceding claims, in which a purified Uquid outlet is provided in the vacuum chamber for discharging condensate from the condensing section,
19. Desalination apparatus as claimed in any of the preceding daims, in which the cooling element includes a cooling pipe for containing a cooling fluid.
20. Desalination apparatus as claimed in claim 17, in which circulation means are provided for circulating the cooling fluid through the cooling pipe for absorbing heat from vapour in the vacuum chamber, and for circulating the cooling fluid through a coofing pool for removing heat from the coofing fluid,
21. Desalination apparatus as claimed in any of the preceding claims, in which the vacuum chamber is substantially cylindrical and the vaporization compartment is substantially cylindrical, the vaporization compartment having a diameter less than the diameter of the vacuum chamber and being disposed within the vacuum chamber, the condensation compartment being provided between the outside of the cylindrical vaporization chamber and the outside of the cylindrical vacuum chamber.
22. Desalination apparatus as claimed in claim 19, in which the vaporization compartment is disposed substantially at the centre of the vacuum chamber, the condensation compartment being in the shape of a cylindrical shell.
23. Desalination apparatus as claimed in any of the preceding claims, in which an auger is provided for removing solid waste from the vaponzation compartment of the vacuum chamber,
24. Desalination apparatus substantially as described herein, with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.
25. An impure water desalination system comprising desalination apparatus as claimed in any one of the preceding claims, and a source of sail or brackish water.
26. A method of desalinating seawater utilising desalination apparatus as claimed in any one of claims 1 to 24, the method comprising the steps of: a. exposing a heat-absorbent nanofluid to solar radiation; b. pre-heating salt water or brackish water by transfening heat energy of the heat-absorbent nanofluid thereto; c. reducing the pressure of the pre-heated salt water or brackish water, so that it vaporises wherein the salt separates; and d. condensing the remaining vapour to form fresh water condensate.
27. Desalination apparatus for removing impurities from an impure liquid, the apparatus comprising a solar heater for pre-heating an impure liquid to be distilled, a vacuum chamber for receiving the pre-heated impure liquid, and pressure reducing means for reducing a pressure of the pre-heated impure liquid at the vacuum chamber, the solar heater including a solar-energy collector having a heat transfer liquid which comprises a suspension of nanoparticles for heat absorption, and a heat exchanger in liquid communication with the solar-energy collector for receiving the impure liquid for pit-heating, and the vacuum chamber including a vaporisation compartment for receiving the pressure reduced pre-heated impure liquid as a vapour, and a condensation compartment which is spaced from the vaporisation compartment for condensing the vapour.