Title: Heat exchanger in a solar water treatment system Cross-reference to related applications

[0001] This application claims priority of UK patent application No. 1402153.9, filed 7 February 2014. The entire disclosure of UK patent application No. 1402153.9 is hereby incorporated herein by reference.

Field of invention

[0002] The field of the present invention relates to a solar water treatment system comprising at least one heat exchanger for water purification and a use of a solar water treatment system for water purification in a solar water treatment plant.

Background of the invention

[0003] Heat exchangers for water purification are used in solar water treatment systems or solar water purification systems for transforming salt water and brackish water into high quality drinkable water. For example, Flores Solar Water GmbH, Munich, Germany, produces a solar water purification system having heat exchanger for water purification. Solar water purification systems including their desalination process do not require the use of electricity or chemicals to carry out the purification. The purification systems are made of several modules, which can be combined together and are thus scalable. This scalability enables a higher production of water. The design of the current solar water purification system of Flores Solar Water GmbH operates in a similar manner to the natural water cycle. Within the modules, salt water or otherwise contaminated water is heated by the sun and then evaporates (solar humidification), while salts, toxins, and harmful substances are held back and removed. The water vapor is collected for consumption. The current system enables up to 10 liters of high quality drinking water to be created from 100 liters of salt water and brackish water per day. The water produced by the solar water purification system of Flores Solar Water GmbH meets international drinking water standards. A solar water treatment system is known from the applicant's own German utility model application DE 21 2011 100 129 Ul . [0004] A heat exchanger is known in the art, for example, from the German patent application DE 10 2007 008 536 Al . The German patent application DE 10 2007 008 536 Al discloses a heat exchanger, for example in the form of a liquid cooler. The heat exchanger has a two-part collecting tank, which is composed entirely of plastic. One collecting part has openings for receiving the ends of tubes, with the tube ends being adhesively bonded therein. The two collecting parts are welded to one another at a weld seam, which runs around a periphery of their walls.

[0005] The German patent application DE 10 2006 002 627 Al and DE 10 2006 002 789 Al also disclose conventional heat exchangers having two-part collecting tanks which are bonded together by means of a welding process forming a welded connection. The patent application publications '627 and '789 do not disclose any further detail as to how the collecting tanks parts must be configured for the welded connection and how the welded connection and the production of the heat exchanger can be carried out in a cost-effective manner. The U.S. Patent Application US 5,388,567 Al and U.S. Patent Application 2006/0021745 Al disclose heat exchangers having a serpentine flow passages. These heat exchangers, however, are not described for the purpose of a solar water purification system.

[0006] It would be desirable to construct an improved heat exchanger for a solar water purification system having only a few components, and which is capable of condenses condense water vapor on its surface.

Summary of the invention [0007] The present disclosure teaches a solar water treatment system for water purification comprising a housing and at least one heat exchanger. The at least one heat exchanger is arranged in the housing. The at least one heat exchanger comprises at least two superposed plates having at least one inlet port and at least one outlet port. The at least two superposed plates are made of polymer. At least one of the two superposed plates has at least two serpentine-shaped channels. Water flows through the at least two serpentine- shaped channels. The at least two superposed plates are welded to one another by means of at least one weld seam.

[0008] The solar water treatment system with at least one heat exchanger having at least two superposed plates, wherein at least one of the two superposed plates has at least two serpentine-shaped channels enables a large condensing surface with a compact construction. This results in a good surface-area-to-volume ratio of the heat exchanger in the solar water treatment system and the water flowing in the serpentine-shaped channels. The sandwich construction with the at least two superposed plates of the heat exchanger in the solar water treatment system means that the heat exchanger has only a few components, which results in cost savings in the production and reduces the weight of the heat exchanger and thereby the solar water treatment system.

[0009] The solar water treatment system further comprising at least one water-flow plate arranged above the at least one heat exchanger and at least one heat converter arranged above the at least one water-flow plate. [0010] The at least one weld seam has at least one intermediate-weld seam, which is arranged between the at least two serpentine-shaped channels. The at least one intermediate-weld seam enables that the pressure on the weld seam can be spread out from the more critical portions, such as the serpentine-shaped channels, to more pressure- absorbing portions of the at least two superposed plates. The heat exchanger in the solar water treatment system is more pressure resistant.

[0011] The at least one weld seam has at least one circumferential- weld seam arranged around the periphery of the at least two superposed plates. The at least one circumferential- weld seam enables that the pressure on the weld seam can be spread out from the more critical portions, such as the serpentine-shaped channels, to more pressure-absorbing portions of the at least two superposed plates. The heat exchanger in the solar water treatment system is more pressure resistant. [0012] The at least one weld seam is formed as a continuous weld seam. This results in a higher pressure resistance of the heat exchanger in the solar water treatment system.

[0013] The at least one weld seam comprises at least of one of a longitudinal weld seam and a spot-weld seam. This results in a higher pressure resistance of the heat exchanger in the solar water treatment system.

[0014] The at least two superposed plates form together a module.

[0015] The module has at least one fastener for connecting the module to other neighboring ones of the modules. The at least one fastener is formed as a bayonet fastener to enable secure attachment of the modules. This results cost savings in the production as two modules are identical in construction.

[0016] The at least two superposed plates are made of polypropylene in one aspect of the invention, and can have a filler material to improve the strength of the material of the superposed plates.

[0017] Other objects, features, aspects and advantages of the disclosed heat exchanger, solar water treatment system and use of a heat exchanger in a solar water treatment system will become apparent for those skilled in the art from the following detailed description, which taken in conjunction with the annexed drawings, discloses preferred embodiments of the heat exchanger.

Brief description of the drawings

[0018] Referring now to the attached drawings, which form a part of this original disclosure:

[0019] Figure 1 is a top view of at least one heat exchanger in the solar water treatment system according to the first aspect of the present invention;

[0020] Figure 2 is an enlarged side view of the heat exchanger illustrated in figure 1 having at least two superposed plates; [0021] Fig 3 is a top view of two modules connected to each other; and

[0022] Fig 4 shows a side view of the solar water treatment system comprising the at least one heat exchanger according to the first aspect of the present invention.

[0023] Fig 4a shows a side view of a water flow plate according to an aspect of the present invention. [0024] Fig. 5 shows an example of a solar water treatment plant encompassing the solar water treatment system.

Detailed description of the invention [0025] The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protection scope of the claims in any way. The invention is defined by the claims and there equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

[0026] While various embodiments of the present invention have been described above, it should be understood that they have been presented by a way of example, and not limitation. It will be apparent to a person skilled in the relevant art that various changes in form in detail can be made therein without departing from the scope of the invention.

[0027] Figure 1 shows a top view of the heat exchanger 10a/ 10b for water purification for a solar water treatment system according to a first aspect of the present disclosure. The heat exchanger lOa/lOb comprises two superposed plates 1, which are made of polymer. The polymer of the superposed plates 1 is polypropylene, but this is not limiting of the invention. The two superposed plates 1 have one inlet port 4 and one outlet port 9, which is arranged on the rear side of the heat exchanger 10. A first one of the superposed plates la has a plurality of serpentine-shaped channels 2, which wind over the surface of the first superposed plate la in a symmetrical manner, but this is not limiting of the invention. A second one of the superposed plates lb (see Fig. 2) is formed as a planar-shaped plate, but this is not limiting of the invention. In another aspect, both the first superposed plate la and the second superposed plate lb can be provided with a plurality of serpentine-shaped channels 2. Water flows through the serpentine-shaped channels 2. The superposed plates la and lb are welded to one another by means of weld seams 7 and 8 in form of vibration welding, but this is not limiting of the invention. An intermediate-weld seam 7 is arranged between adjacent ones of the serpentine-shaped channels 2. A circumferential-weld seam 8 is arranged around the periphery of the first superposed plate la and the second superposed plate lb. The intermediate-weld seam 7 and the circumferential-weld seam 8 are formed as a continuous weld seam, but this is not limiting of the invention. The continuous weld seams 7 and 8 consist of a longitudinal weld seam and/or a spot-weld seam. Two welded superposed plates la and lb form together a module 10a or 10b. One module 10a is connected to another module 10b by means of a bayonet fastener 6 and a first connection element 13, which can be formed as flexible hose, as can be seen in figure 3.

[0028] Figure 2 shows an enlarged side view of the heat exchanger 10 for the solar water treatment system according to the first aspect of the present disclosure. The fastener 6 is disposed in the inlet port 4. The fastener 6 can be formed as a bayonet fastener 12. The first superposed plate la and the second superposed plate lb are made of polypropylene and have a filler material, so that the polymer is harder and pressure-resistant. The first superposed plate la and the second superposed plate lb are made of a polypropylene homopolymer (PPH), but this is not limiting of the invention. The polypropylene homopolymer has a rigid and high strength, is thermoformable and weldable, and is chemical resistant and corrosion resistant. The filler material cannot be welded and thus the quantity of the filler material used in the polymer has to be balanced to compromise between hardness and tightness (or pressure resistance) of the weld seam 7 and 8. The welded seams 7 and 8 have to pass a pressure test. The welded seams 7 and 8 have to sustain an overpressure of about 0,4 to about 0,6 bar. The pressure in the heat exchanger 10 should not decrease less than 10 % after a certain period of time. The first superposed plate la and the second superposed plate lb are about 1.5 mm (± 5%) thick.

[0029] Figure 3 shows a top view of two of the connected modules 10a and 10b, which together form the heat exchanger 10 for the solar water treatment system. A first module 10a and a second module 10b are connected to each other by means of the fastener 6 and the first connection element 13. The fastener 6 and the first connection element 13 are disposed at the rear side of the two connected modules 10a and 10b.

[0030] Figure 4 shows the solar water treatment system 20 according to the first aspect of the present invention comprising at least one heat exchanger 10. The solar water treatment system 20 further comprises a housing 21, which is arranged on a surface, such as the ground or on a rooftop, by means of mounting elements 22. The housing 21 is inclined with respect to the surface. The heat exchanger 10 comprising the first module 10a and the second module 10b is arranged in the housing 21 and has substantially the same orientation as the housing 21. A water- flow plate 23 is arranged above the heat exchanger 10. The water-flow plate 23 is made of plastic. The water-flow plate 23 is arranged in the housing 21 such that the water- flow plate 23 has a top portion 23a and a low portion 23b. In another aspect, the water-flow plate 23 can be formed in a staircase- like manner (as shown in Fig. 4a). The solar water treatment system 20 comprises a heat converter 30, which is arranged in parallel above the top portion 23a of the water- flow plate 23. The heat converter 30 comprises two superposed sheets (not shown), wherein at least one of the sheets has a plurality of serpentine-shaped channels (not shown), which wind over the surface of the sheet in a symmetrical manner, but this is not limiting of the invention. The housing 21 further comprises two openings, a first opening 24a and a second opening 24b, which are separated from each other, and a cover 25. The cover 25 is translucent, and is made for example from glass or a plastic.

[0031] Figure 4 shows that the housing 21 including the heat exchanger 10, the water- flow plate 23 and the heat converter 30 is aligned such that the heat converter 30 and the water- flow plate 23 is exposed to solar radiation. The heat converter 30 and the water- flow plate 23 are heated by the solar radiation 26. The salt water and/or the brackish water is pumped to the solar water treatment system 20 using, for example photovoltaic or wind- driven pump (not shown). The salt water and/or the brackish water is pumped to the inlet port 4 of the heat exchanger 10a. The inlet port 4 of the heat exchanger 10a is arranged at the low portion of the housing 21. [0032] The salt water and/or the brackish water has the following flow path: The pumped salt water and/or the brackish water flows from the inlet port 4 of the first module 10a through the plurality of serpentine-shaped channels 2 of the first module 10a to the outlet port of the first module 10a. The salt water and/or the brackish water flows from the outlet port of the first module 10a through the first connection element 13 to the inlet port of the second module 10b. The salt water and/or brackish water flows from the inlet port of the second module 10b through the plurality of serpentine-shaped channels 2 of the second module 10b to the outlet port of the second module 10b. The salt water and/or the brackish water flows from outlet port of the second module 10b through a second connection element (not shown), which is connected to an inlet port (not shown) at the top portion of the heat converter 30. The salt water and/or the brackish water flows from the inlet port of the heat converter 30 through the plurality of serpentine-shaped channels of the heat converter 30 to an outlet port (not shown) at the low portion of the heat converter 30. The outlet port of the heat converter 30 is arranged above the top portion 23a of the water-flow plate 23. The salt water and/or the brackish water flows from the outlet port of the heat converter 30 on the water- flow plate 23. The salt water and/or the brackish water coming out of the outlet port of the heat converter 30 flows from the top portion 23a of the heated water-flow plate 23 to the lower portion 23b of the heated water-flow plate 23 along a flow path 27. The salt water and/or the brackish water is heated by the solar radiation and evaporates on the flow path 27 from the top portion 23a of the heated water-flow plate 23 to the low portion 23b of the heated water- flow plate 23.

[0033] The length of the flow path 27 is increased if the water-flow plate 23 has "steps" over which the water flows, as shown in figure 4a. The salt water and/or brackish water has more time to evaporate. A longer flow path 27 of the salt water and/or brackish water on the water-flow plate 23 results in a higher efficiency of the evaporation process. As is known, the solar radiation causes the water molecules in the salt water and/or brackish water to evaporate, while leaving the salt and other impurities behind. The resulting water vapor 28 passes upwards along the inside of the cover 25 to the heat converter 30. The water vapor 28 releases a part of its energy and heats the salt water and/or brackish water flowing through the plurality of serpentine-shaped channels of the heat converter 30. As a result, the outlet port temperature T _out con of the salt water and/or brackish water at the outlet port of the heat converter 30 is higher than the inlet port temperature T i _n c _on of the salt water and/or brackish water at the inlet port of the heat converter 30. The salt water and/or brackish water having the outlet port temperature T _out iet con flows from the outlet port of the heat converter 30 on the top portion 23a of the heated water-flow plate 23 and is heated by the solar radiation 26 during the time of passing down the flow path 27. As a result, the low portion temperature T i _{ow p} i _at e of the salt water and/or brackish water at the low portion 23b of the water- flow plate 23 is higher than the top portion temperature T _top plate of the salt water and/or brackish water at the top portion 23a of the water- flow plate 23. [0034] The resulting water vapor 28 releases a part of its energy to the heat converter 30, the water vapor 28 prior to passing from the heat converter 30 downwards along the inside of the housing 21 to the rear side of the heat exchanger 10. The water vapor 28 again releases a part of its energy to the top portion of the heat exchanger 10 and heats the salt water and/or brackish water flowing through the plurality of serpentine-shaped channels of the two modules 10a and 10b of the heat exchanger 10. As a result, the outlet port temperature T _{out sec} mod of the salt water and/or brackish water at the outlet port of the second module 10b of the heat exchanger 10 is higher than the inlet port temperature T i _n fust mod of the salt water and/or brackish water at the inlet port 4 of the first module 10a of the heat exchanger 10. The water vapor 28 passes from the top portion of the heat exchanger 10b downwards along the heat exchanger 10 to the lower portion of the heat exchanger 10a, after the water vapor 28 releases a part of its energy to top portion of the heat exchanger 10. The water vapor 28 condenses on the surface of the heat exchanger 10, which is cooler than the water vapor 28. The condensed water 29 formed on the surface of the heat exchanger 10 drips off. The dripped off, condensed water 29 is guided to the first opening 24a and is collected as drinking water. The salt water and brackish water which is not evaporated during the flow path 27 but still liquid is guided to the second opening 24b and can be reused for the water purification process.

[0035] The temperature of the salt water and/or the brackish water has different temperature levels during the process in the solar water treatment system 20, but this is not limiting of the invention. The inlet port temperature T Met first module of the salt water and/or brackish water at the inlet port 4 of the first module 10a of the heat exchanger 10 has surrounding temperature. The outlet port temperature T _{out sec} . mod of the salt water and/or brackish water at the outlet port of the first module 10a of the heat exchanger 10 has a temperature of about surrounding temperature to about 40° Celsius. The outlet port temperature T _{out sec} . mod of the salt water and/or brackish water at the outlet port of the second module 10b of the heat exchanger 10 is about the same as the inlet port temperature T iniet con of the salt water and/or brackish water at the inlet port of the heat converter 30, which can be about 40° - 60° Celsius. The outlet port temperature T _ou t con of the salt water and/or brackish water at the outlet port of the heat converter 30 has a temperature about 60° - 80° Celsius. The top portion temperature T _top plate of the salt water and/or brackish water at the top portion 23 a of the plate 23 is about the same as the outlet port temperature T out con of the salt water and/or brackish water at the outlet port of the heat converter 30. The low portion temperature T _{low plate} of the salt water and/or brackish water at the low portion 23b of the plate 23 has a temperature about 80° - 100° Celsius. [0036] The solar water treatment system 20 can be used as individual units or a plurality of units can be combined together to form a solar water treatment plant 40, as shown in outline in Fig. 5. Fig. 5 shows three solar water treatment systems 20, but this is not limiting of the invention. The number chosen is dependent on the required throughput of the salt water and/or brackish water. The inputs and the outputs of the solar water treatment system 20 can be connected together.

[0037] List of reference numbers

1 superposed plates

la first superposed plate lb second superposed plate

2 serpentine-shaped channel 4 inlet port

6 fastener

7 intermediate- we Id seam

8 circumferential- weld seam

9 outlet port

10 heat exchanger

10b first module

10a second module

12 bayonet fastener

13 first connection element

20 solar water treatment system

21 housing

22 mounting elements

23 water-flow plate

23a top portion

23b lower portion

24a first opening

24b second opening

25 cover

26 solar radiation

27 flow path

28 water vapor

29 condensed water

30 heat converter

40 solar water treatment plant