This invention relates to a heat exchanger, which is intended especial- ly for use at the cooling of water in connection with the recovery of fresh water by distillation of sea water .

An apparatus for such recovery is disclosed in SE-PS 387 927, which a. o. shows an evaporation chamber comprising a plurality of flow elements, which substantially are of plane parallel and vertical rela- tionship. According to the process disclosed in said patent specifica¬ tion, cooled fresh water is to be fed into the evaporation chamber . One object of the present invention is to bring about a heat exchanger with flow elements adapted for use at the cooling of fresh water prior to its feed into the evaporation chamber. A further object of the invention is to render it pos sible to recover desalted sea water at such a price that such recovery really is econo¬ mic for being applied to normal agricultural irrigation in areas having no fresh water resources of their own. The invention is based on the idea of being able with very low overpres sures to utilize the immense low temperature resources, which are available in sea water and easily can be transferred by pumping to places of demand. The small temperature gradients here involved and to be utilized require large surfaces . This requirement is not met by conventional heat ex¬ changer s . Conventional heat exchangers are made of metallic material in order to utilize the good heat transfer coefficient of these materials. Due to the aforesaid requirement of large surfaces at fresh water production, these heat exchanger s are unreasonably expensive . Another restric¬ ting factor is the requirement of corrosion resistance of the material used in the heat exchanger s in view of the sea water effect.

The aforesaid difficulties and disadvantages are eliminated by heat exchanger designed according to the present invention. The charac¬ terizing features of such a heat exchanger become apparent from the attached claims . The invention is described in greater detail in the following, with reference to the accompanying Figures, in which schematically shown

Fig. 1 is a front view of a flow element comprised in a heat exchang according to the invention, Fig. 2 is a lateral view of the flow element,

Fig. 3 is a front view of a clamping element comprised in the flow element,

Fig. 4 is ^' a lateral view of said clamping element,

Fig. 5 shows an inlet (or outlet) in the flow element with laid-in clamping element, Fig. 6 is a lateral view of the heat exchanger, and Fig. 7 is a view from above of the heat exchanger .

The flow element according to Figs . 1 -2 consists of two thin foils 10 and 20, which in longitudinal direction of the flow element are so jointed by intermittent welding in several places in transver se direct ion, that the flow element is formed with a plurality of longitudinal gaps for water transport. In Fig. 1 three such gaps are indicated to the left and one to the right by the reference numerals 1 1 , 12 , 13, 14. The term intermittent welding is to be understood so that the joints welded are discontinuous . A welding joint is designated by 15, and a distance between two j oints is designated by 16. It is pos sible in principle to weld continuous joints, but with discontinuous joints a certain turbulence of the water flow is obtained. The flow element is connected at its upper end to two inlets 17, and at its lower end to tw outlets 18. Between said inlets 17 a clamping element 21 -22 is pro¬ vided, in such a manner, that the ends of the clamping element are secured in the inlets 17, and the foils 10, 20 are so laid about the clamping element, that the clamping element is located between the foils . The clamping element appears more clearly from Figs . 3 -4. It has the configuration of a T with an arc- shaped roof 21 and a straight remaining portion 22. The way how the clamping element is secured in an inlet 17 and, respectively, outlet 18 is more clearly apparent from Fig. 5, which shows an inlet 17 from the side -with two projections 171 and, respectively, 172 on the inside of the inlet. The end of the remaining straight portion 22 is fitted in between said pro¬ jections 171 and 172. At its lower end the flow element is connected in the same manner to the two outlets 18 , and the foils 10, 20 are laid about a clamping ele¬ ment identical with said element 21 -22. The width and length of the

flow element may be about 4 m and, respectively, 10 m, the distance between a weld joint and the neare st adjacent joint may be 3 to 4 cm, and the diameter of a flow gap at a system filled with water may be 2 to 3 cm. A great number of flow elements of the kind des cribed above are com¬ prised in the heat exchanger according to Figs . 6-7. In a container or basin 60 two main conduits 61 are provided, with four feed conduits 62, 63 , 64, 65 connected thereto. Between each two of thes e feed con¬ duits flow elements are connected, of which only a few are shown in the drawing, viz. the elements 66, 67, 68. The lower ends of the flow elements are connected to r eturn conduits 72, 73 , 74, 75 , which in their turn are connected to main conduits 71 , one of which appear s from Fig. 6. The heat exchanger further comprises inlets 76, 77 , 78 located below the flow elements, and outlets 86, 87, 88 located above the flow elements . The main conduits 61 are intended for relatively warm water fro an evaporation chamber, the main conduits 71 are intended for cooled water to the evaporat ion chamber, the inlets 76- 78 are intended for relatively cold sea water, and the outlets 86-88 ar e in-, tended for the dis char ge of heated sea water . At operating heat exchanger, the relatively warm fresh water (temper¬ ature on the inlet side, for example, x + 12 C) flowing downward will meet relatively cold sea water (temperature on the inlet side x C) flowing upward. The downwa d and, r e spectively, upward flows are facilitated thereby that the fre sh water is cooled and, respectively, the sea water is heated. The sea wate r temperature on the outlet side may be about x + 10 C, while the temperature of the cooled fresh water may be about x + 3 C . The pr es sures on both side s of the thin (0, 3 mm) plastic foils in the f low elements are almost equal and pure¬ ly static. The fre sh distillate water is given a low static over - pres sur e just sufficient to hold the channels of the elements stretched out against the ambient outer pres sure .

The container or basin indicated in Fig. 6-7 may be designed station¬ ary in earth as a basin sunk into a shore strip, or as a floating steel or concrete container or as a container of plastic cloth anchored in the sea.

In the above des cription and the attached claims the flow elements ar e

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said to consist of two foils, which is to be understood so that the two defining walls of the flow elements consist of foils . Nothing in principle obstructs each foil wall to consist of several foils .

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