PRESSURE VESSEL

Abstract: The invention relates to a pressure vessel with a number of external walls, which pressure vessel comprises: a number of pressure vessel elements grouped under pressure contact which each comprise an inlet opening and an outlet opening; and tensioning means for holding the elements together; wherein at least one surface of at least one pressure vessel element which forms part of one of the external walls of the pressure vessel comprises strengthening means.

Description: PRESSURE VESSEL The invention relates to a pressure vessel with a number of external walls and a combination of a heat exchanger and a pressure vessel . Pressure vessels are used in many different applications. Pressure vessels are thus used in central heating boilers, gas tanks for storing gases, solar boilers and so on. Known pressure vessels are usually cylindrical as this, given the dimensions and the pressure which occurs, gives the most favourable stress distribution in the wall of a pressure vessel. The drawback- however is that at large volumes the vessel takes up a disproportionately large amount of space as a consequence of its round cross-section. It moreover has a relatively great wall thickness, whereby the weight and cost are high. If such known pressure vessels are used for a heat exchanger, a heat-exchanging element is then arranged in the pressure vessel . This has the drawback that deposits form on this element which possibly contaminate the medium in the pressure vessel. In addition, extra material must be used to form the heat- exchanging element . It is an object of the invention to obviate the above stated drawbacks . This object is achieved with a pressure vessel according to the invention, which pressure vessel comprises : - a number of pressure- vessel elements grouped under pressure contact which each comprise an inlet opening and an outlet opening; and - tensioning means for holding the elements together; wherein at least one surface of a pressure vessel element which forms part of one of the external walls of the pressure vessel comprises strengthening means . Because the pressure vessel according to the invention is constructed from separate elements, any desired form can be assembled from these elements. It is advantageous herein that the elements can take a relatively non-rigid form. The walls which lie against each other under pressure contact largely neutralize each other's stresses. Only the walls forming part of one of the external walls of the pressure vessel have to be strengthened. Because use is made of a number of smaller elements, the wall thickness of each of the elements can be relatively small, so that the total weight and cost are favourable . In a preferred embodiment the strengthening means comprise indentations arranged in the walls of the pressure vessel elements. These indentations ensure that the walls acquire a greater bending stiffness and therefore bulge out less to form cylindrical wall parts under high pressure. It is herein preferred to embody the indentations in terrace form or in pyramid form. Each transition in the terrace provides strengthening of the wall in which the indentation is arranged. The indentations can be rectangular. In a further favourable embodiment wall parts of the pressure vessels can take a double-walled form, wherein these wall parts are mutually connected at regular mutual distances . In yet another preferred embodiment according to the invention the strengthening means comprise pins, which pins extend between two walls of an element and are arranged thereon. If for instance two mutually opposite wall parts form part of the external walls of the pressure surface, a strength can be obtained by mutually connecting these two walls such that the wall parts practically do not deform. In these two latter discussed preferred embodiments a pre-deformation can be applied in suitable manner. That is, an overpressure is produced between the mutually connected wall parts, whereby these wall parts are deformed by being inflated. The deformed wall parts can be seen as consisting of three-dimensionally curved surfaces which give the pressure vessel a very good pressure-resistance and rigidity. The pressure vessel elements are preferably substantially prismatic. The pressure vessel elements can hereby be grouped in simple manner to form a pressure vessel of desired shape. It is further preferred that the pressure vessel elements are manufactured from optionally stainless, thin sheet steel. Thin sheet steel is a relatively inexpensive construction material and provides sufficient strength for the manufacture of pressure vessels therewith. A further embodiment of the pressure vessel according to the invention comprises an inlet header for feeding a medium to the pressure vessel elements and an outlet header for discharging the medium, which outlet header is connected to the outlet pipes. Since an assembly of pressure vessel elements is required to manufacture a pressure vessel of large volume, all inlets and outlets of the pressure vessel elements must be mutually connected. This can be realized in simple manner by applying an inlet and outlet header. The invention further comprises a heat exchanger which comprises : - a first compartment for a first medium; and - a second compartment for a second medium in heat-exchanging contact with the first compartment; wherein at least the first compartment comprises a pressure vessel according to the invention. In a preferred embodiment of the heat exchanger according to the invention the second compartment is arranged between the pressure vessel elements. Owing to the high pressure which can prevail in a pressure vessel the pressure between two walls which are in mutual pressure contact will likewise be high. By now arranging the second compartment therebetween, and because the walls are relatively flexible and deformable, a good contact between the first and second compartment is ensured, thereby enabling a good heat transfer. The wall parts which are in mutual contact become in large measure spatially congruent owing to the pressure. Due to the rectangular form of the pressure vessel elements with flat walls there results a large internal heat-exchanging surface area. In another embodiment of a heat exchanger according to the invention the first compartment is arranged inside the second compartment. A housing can thus be arranged around the pressure vessel so that a medium flows along the pressure vessel and this medium exchanges heat or cold, optionally with two-phase evaporation, with the medium flowing in the pressure vessel . In another preferred embodiment of the heat exchanger according to the invention the second compartment is formed between two adjacent pressure vessel elements by a weld contour connecting these pressure vessel elements. The advantage is that the first medium is separated by only a single wall from the second medium and a reduction in weight is thus obtained due to fewer welds and components. The heat transfer will hereby be optimal . Spot welds connecting the two adjacent pressure vessel elements are preferably arranged within the area bounded by the weld contour. If the second compartment is brought under pressure, these spot welds prevent the material of the walls being deformed too strongly, whereby cracking could occur. The spot welds create a cushion-like surface. Yet another embodiment of a heat exchanger according to the invention comprises at least three pressure vessel elements which are mutually adjacent such that a central space is formed extending in length direction parallel to the pressure vessel elements, and wherein the weld contour between each pair of adjacent pressure vessel elements connects onto the central space such that the central space is in liquid contact with the second compartments . When the pressure vessel elements are placed in a star shape, it will be possible to form a channel in the heart of this star. By now arranging the weld contour which bounds the second compartment such that it debouches into this central space, it becomes possible to provide the second compartments with the second medium via this central space. An outlet line for the pressure vessel elements preferably extends through the central space. A compact construction is hereby created, wherein the outlet line for the first medium can be returned to the same side as where the first medium is supplied. Because the connections are present on the same side of the heat exchanger, the connection of such an exchanger is simplified. The outlet line can herein comprise a further number of parallel pipes, so that the surface area of the outlet line is enlarged and an additional heat-exchanging activity thus results between the inlet of the second medium and the discharge of the first medium. A very preferred embodiment of a heat exchanger according to the invention comprises an inlet line for feeding the first medium to the first compartment, wherein the inlet line branches to the different pressure vessel elements. This once again simplifies the connection of such a heat exchanger. It is further recommended that the length of each branch is substantially equal . Each inlet of each pressure vessel element hereby has the same resistance, whereby the same amounts of first medium are fed to the pressure vessel elements . In a further embodiment an insulation layer having a form-retaining housing therearound is arranged round the compartments. This "sandwich" construction creates a strong but light outer wall which at least partially absorbs pressure prevailing in the pressure vessel. The insulation can herein preferably absorb pressure and shear forces. The insulation can be adhered to the compartments by means of glue, but also mechanically. The invention further comprises a method for manufacturing a pressure vessel element according to the invention, which method comprises the steps of: - providing a sheet of metal ; - arranging indentations in the sheet; - cutting the sheet to form a blank; - bending the sheet to form a box-shaped element ; and - closing the box-shaped element by welding. These and other features of the invention will be further elucidated with reference to the annexed drawings: figures la-lg show schematically in perspective view an embodiment of the method according to the invention; figures 2a-2d show schematically in perspective view with partly cut-away parts a first embodiment of a pressure vessel according to the invention; figure 3 shows a perspective view of a second embodiment of a pressure vessel according to the invention; figure 4 shows a perspective view of a third embodiment ; figure 5 shows in perspective view a fourth embodiment of a pressure vessel according to the invention; figures 6a and 6b show a perspective view with partly cut-away parts of a fifth embodiment of a pressure vessel according to the invention; figure 7 shows a perspective view of a sixth embodiment; figure 8 shows a perspective view of a seventh embodiment of a pressure vessel; figure 9 shows in perspective view an eighth embodiment of a pressure vessel according to the invention; figure 10 shows a ninth embodiment of a pressure vessel according to the invention; figures 11a and lib show a perspective view with partly cut-away parts of an embodiment of a solar energy system according to the invention; figure 12 shows a perspective top view with partly cut-away parts of a tenth embodiment according to the invention; figure 13 shows the device of figure 12 in bottom view. Figures la-lg show schematically a method for manufacturing a pressure vessel element. A metal sheet is fed to a press 2 from a roll 1. This press arranges indentations 3 in the sheet. A part in the desired form is then cut out of sheet 1 with a laser 4 (see figure la) . The cut part 5 is then folded to form a box- shaped element . The box-shaped element (see figure lc) is then welded closed by means of a welding apparatus 6. Finally, the outer ends of the box-shaped element are folded up and closed by welding (see figures Id and If) . A finished pressure vessel element 7 is shown in figure lg. In figures 2a-2d is shown a first embodiment of a pressure vessel . Four pressure vessel elements 7 are placed in a square arrangement . Elongate channel plates 8 are arranged between these pressure vessel elements 7. These channel plates 8 have a cushion-like structure. Placing of the channel plates between pressure vessel elements 7 creates a heat exchanger. Tap water can for instance be stored in pressure vessel elements 7, while a heat transfer medium is carried through channel plates 8. Each pressure vessel element 7 has an inlet pipe 9 and an outlet pipe 10. Inlet pipes 9 are mutually connected and are provided with a medium by means of a main inlet pipe 11. Outlet pipes 10 of pressure vessel elements 7 are also mutually connected and debouch in a main outlet pipe 12. Channel plates 8 also have inlet and outlet pipes which come together in a second main inlet pipe 13 and a second main outlet pipe 14. It is important that the pipes from the separate elements to the main pipes are of equal length, so that a uniform flow rate occurs in these elements. A receiving block 15 is arranged for this purpose for the outlet pipes of channel plates 8. When pressure vessel elements 7 are brought under pressure they will bulge slightly if they are not restrained. A casing 16 is however arranged for this purpose which ensures that the pressure vessel elements remain lying against each other and a good contact with channel plates 8 is provided. Casing 16 also provides a trim exterior. Figure 3 shows a second embodiment of a pressure vessel 20. This pressure vessel 20 has pressure vessel elements 7 placed adjacently of each other with channel plates 8 therebetween. Inlet pipes 9 of pressure vessel elements 7 are mutually connected by means of a main inlet pipe 11. Outlet pipes 10 of the pressure vessel elements are also mutually connected by means of a main outlet pipe 12. Channel plates 8 have a collective outlet pipe 1 . The collective main inlet pipe 13 is not shown in this drawing. Figure 4 shows a third embodiment of a pressure vessel 22, wherein two pressure vessels 20 as according to figure 3 are mutually coupled. In figure 5 is shown a fourth embodiment of a pressure vessel 24 which is assembled from four pressure vessels 20 as according to figure 3. Owing to the housing-like structure, such a pressure vessel 24 is suitable for use in central heating boilers because of the compatibility with rectangular forms. Figures 6a and 6b show a boiler 26. This boiler 26 has a housing 27 in which a number of pressure vessel elements 7 are once again placed adjacently of each other. Electrical heating elements 28 are placed between these pressure vessel elements 7. These heating elements 28 are connected to a thermostat 29 arranged in housing 27. Water can once again be fed respectively discharged to and from pressure vessel elements 7 via a main inlet pipe 11 and a main outlet pipe 12. When the pressure vessel elements are brought to pressure by means of the tap water, they will then press against each other, wherein the electrical heating elements 28 are brought into intimate contact with two adjacent pressure vessel elements. Figure 7 shows a boiler 30 which is constructed in the same manner as boiler 26 of figure 6. Lines 11, 12 of boiler 30 can be concealed from view via a skirting board. This results in an aesthetically pleasing design of the boiler. In figure 8 is shown a pressure vessel 40 which has an I-shaped profile 41 as frame, on which sheet parts 42 are arranged. The sheet parts will deform when pressure vessel 40 is placed under pressure. Figure 9 shows an eighth embodiment of a pressure vessel 50 according to the invention. This pressure vessel 50, which is constructed in the same way as a pressure vessel element 7, likewise has impressions 51. A tear-off closure 52 is arranged on the top part of pressure vessel 50. Such a pressure vessel 50 can be used as a soft-drink container. It is also possible to use such a vessel for granular material which is for instance vacuum-packed. The tear-off closure will then take a form other than that shown, i.e. one which is suitable for passage of this granular material. Cat food can be mentioned as an example of granular material . Figure 10 shows a ninth embodiment of a pressure vessel according to the invention. This pressure vessel 60 also has an I-profile 61 which functions as frame. Arranged in this frame are sheet parts 62 which will deform slightly as a result of the pressure in the pressure vessel. The use of I-profile 61 as strengthening enables the manufacture of relatively flat pressure vessels. Such a pressure vessel 60 can for instance be used as a gas tank in a vehicle . Figure 11a shows a solar energy system 100 according to the invention in perspective view. This solar energy system 100 has a hollow collector 101 on which the solar radiation is incident and in which a heat transfer medium is arranged, partially in gas form and partially liquid. Owing to the incident solar radiation the liquid heat transfer medium in collector 101 will evaporate and rise upward in collector 101 and at the top be urged via pipes 102 through a heat exchanger, where the heat transfer medium once again condenses. The heat exchanger consists of a heat storage tank, as shown for instance in figure 3, consisting of elongate elements 103 and elongate flat channel plates 104 which are placed between these elements and through which the heat transfer medium runs . The condensed heat transfer medium flows further from the heat exchanger via pipes 105 to the underside of collector 101. Solar energy system 100 further has a housing which consists of a transparent upper side 106 formed from a sandwich panel, for instance of polycarbonate, and a tray-like underside 107 (see also figure lib) . The sandwich panel, also referred to as cavity panel, is shown here with channels in vertical direction. In order to prevent convection and realize a good rigidity in transverse direction, such a plate can be used with horizontal channels, i.e. lying in width direction. Solar energy system 100 is placed with the housing directly onto roof boarding 108. In order to ensure proper sealing between housing 106, 107 and the roof tiles 109 lying on the roof boarding, the housing further has an apron part 110, which can be adjusted to the form of the roof tiles by heating. Apron part 110 is coupled slidably to the housing, so that when the housing expands due to heating as a result of solar radiation the apron part 110 can displace relative to the housing, whereby cracking is prevented. In storage tank 103 is stored water which is heated by heat-exchange with the heat transfer medium. In order to prevent heat loss via roof boarding 108, the housing is further filled with a composite insulation structure 111. On a part of the elongate elements 103 a heating element 112 can be further arranged which, in the case of a shortage of radiant heat, contributes toward the heating of the water in elongate elements 103. Figure 12 shows a perspective view of a tenth embodiment of a pressure vessel 120 according to the invention. This pressure vessel is embodied as heat exchanger. This pressure vessel 120 is constructed from four sheets 121, 122, 123 and 124 bent into a substantially rectangular cross-section. These sheets are each welded to each other on the ends 125, 126, 127 bent toward each other. The thus formed four pressure vessel elements are placed against each other and the surfaces lying against each other are each provided with a peripheral weld contour 129, 130, 131 and 132. Bounded by this weld contour 129, 130, 131 and 132 is a space between the sheets lying against each other which is then expanded by means of a liquid so that compartments 133, 134, 135 and 136 are created. Provided in the middle of the four pressure vessel elements is a central space 137 which connects via openings 138 onto compartments 133, 134, 135 and 136. This central space 137 is closed on the top side shown in figure 12 by a closing plate 138. Protruding through this closing plate 138 are four pipes 139 with which liquid can be discharged from the four pressure vessel elements . Figure 13 shows the underside of pressure vessel 120 according to figure 12. A branched inlet line 140 connects onto the four pressure vessel elements. Tap water can for instance be fed to pressure vessel 120 with this inlet line 140. Figure 13 shows clearly that the length of inlet line 140 to outlet openings 141 is the same, so that the pipe resistance to each opening 141 is the same. Connected to compartments 133, 134, 135 and 136 are a number of lines 142 which discharge a medium such as central-heating water out of the compartments. The feed of the central-heating water takes place via the central space 137 and the water then flows out via the openings in compartments 133, 134, 135 and 136. The tap water heated in pressure vessel 120 and discharged via pipes 139 is then collected in a header (not shown) and flows out via a central line 143. The whole pressure vessel is enveloped by an insulation layer 144 which encloses the entire outer surface of pressure vessel 120. The insulation layer is preferably glued thereto. The insulation layer 144 is flat on the outside and enclosed by a metal housing 145. The lines 142 can also be replaced by a collection space. By now causing the branched inlet line 140 to run through this collection space, a heat-exchange can already result here.

Claims: CLAIMS 1. Pressure vessel with a number of external walls, which pressure vessel comprises: - a number of pressure vessel elements grouped under pressure contact which each comprise an inlet opening and an outlet opening; and - tensioning means for holding the elements together; wherein at least one surface of at least one pressure vessel element which forms part of one of the external walls of the pressure vessel comprises strengthening means . 2. Pressure vessel as claimed in claim 1, wherein the strengthening means comprise indentations arranged in the walls of the pressure vessel elements. 3. Pressure vessel as claimed in claim 2, wherein the indentations are terrace-shaped. 4. Pressure vessel as claimed in claim 2, wherein the indentations are substantially rectangular. 5. Pressure vessel as claimed in claim 1 or 2, wherein at least one wall takes a double form, and the strengthening means are formed by connections between the wall parts arranged at regular mutual distances. 6. Pressure vessel as claimed in claim 1, wherein the strengthening means comprise pins, which pins extend between two walls of an element and are arranged thereon. 7. Pressure vessel as claimed in claim 1, wherein the pressure vessel elements are substantially prismatic . 8. Pressure vessel as claimed in claim 1, wherein the pressure vessel elements are manufactured from thin sheet steel . 9. Pressure vessel as claimed in claim 1, comprising: - an inlet header for feeding a medium to the pressure vessel elements; and - an outlet header for discharging the medium. 10. Heat exchanger, comprising: - a first compartment for a first medium; and - a second compartment for a second medium in heat-exchanging contact with the first compartment; wherein at least the first compartment comprises a pressure vessel as claimed in claim 1. 11. Heat exchanger as claimed in claim 9, wherein the second compartment is arranged between the pressure vessel elements. 12. Heat exchanger as claimed in claim 9, wherein the first compartment is arranged in the second compartment . 13. Heat exchanger as claimed in claim 10, wherein the second compartment is formed between two adjacent pressure vessel elements by a weld contour connecting these pressure vessel elements. 14. Heat exchanger as claimed in claim 13, wherein spot welds connecting the two adjacent pressure vessel elements are arranged within the area bounded by the weld contour. 15. Heat exchanger as claimed in either of the foregoing claims 13 or 14, comprising at least three pressure vessel elements which are mutually adjacent such that a central space is formed extending in length direction parallel to the pressure vessel elements, and wherein the weld contour between each pair of adjacent pressure vessel elements connects onto the central space such that the central space is in liquid contact with the second compartments . 16. Heat exchanger as claimed in claim 15, wherein an outlet line for the pressure vessel elements extends through the central space. 17. Heat exchanger as claimed in claim 16, wherein the outlet line comprises a number of parallel pipes . 18. Heat exchanger as claimed in any of the foregoing claims 10-17, comprising an inlet line for feeding the first medium to the first compartment, wherein the inlet line branches to the different pressure vessel elements. 19. Heat exchanger as claimed in claim 18, wherein the length of each branch is substantially equal. 20. Heat exchanger as claimed in any of the claims 10-19, comprising an insulation layer arranged round the compartments and a form-retaining housing arranged round the insulation. 21. Heat exchanger as claimed in claim 20, wherein the insulation layer is adhered to the compartments and wherein the housing is adhered to the insulation layer. 22. Method for manufacturing a pressure vessel element as claimed in any of the foregoing claims, which method comprises the steps of: - providing a sheet of metal; - arranging indentations in the sheet; - cutting the sheet to a predetermined form; - bending the sheet to form a box-shaped element; and - closing the box-shaped element by welding. 23. Method as claimed in claim 22 for manufacturing a pressure vessel element as claimed in either of the claims 5 or 6, wherein a pressure higher than the intended pressure of use is set for a time in the space between the mutually connected walls or wall parts . 24. Solar energy system, comprising: - a housing comprising a part permeable by solar radiation on an upper side; - a collector which is arranged in the housing and which comprises an inclining space exposed to solar radiation via the permeable part, through which space can flow a heat transfer medium which flows in a first circulation and is coupled to a second medium circuit, wherein the first circulation takes place in a circulation tank which is filled partially with liquid and partially with vapour thereof and which operates as a circulation system which is driven by natural convection of separate evaporation and condensation; - a heat storage tank which is arranged in the second medium circuit and which is thermally coupled to a wall of the circulation tank, close to a part of the first circulation which is directed downward; and - insulation arranged in the housing at least between the space exposed to solar radiation and the heat storage tank, characterized in that the heat storage tank comprises a pressure vessel as claimed in any of the foregoing claims 1-8.

Inventors: BERTELS AUGUSTINUS WILHELMUS M, BERTELS, AUGUSTINUS, WILHELMUS, MARIA
Applicants: BERTELS AUGUSTINUS WILHELMUS M, INVENTUM B V, BERTELS, AUGUSTINUS, WILHELMUS, MARIA, INVENTUM B.V.
Application year: 2001
Main classification: F24H1
IPC codes: F24H1, F24J2, F28D20