Patent Application
20080196873
The present invention relates to a gasket assembly of a plate heat exchanger, comprising at least one gasket and a package of heat exchanger plates which are provided with inlet and outlet ports which constitute channels through the package and between the heat exchanger plates, whereby the heat exchanger plates are permanently joined in pairs to constitute cassettes, the gasket is disposed between the cassettes in a groove in the heat exchanger plates and delimits in combination with the cassettes, in every second space between plates, a first flow passage for a first fluid, and the cassettes delimit a second flow passage for a second fluid. The invention also relates to a plate heat exchanger comprising the gasket assembly, a heat exchanger plate and a gasket according to the invention.
Food manufacture is typically characterised by the need to process and treat highly viscous products, e.g. concentrates for carbonated beverages, juices, soups, dairy products and other products of fluid consistency. For natural reasons, the hygiene aspirations and expectations in this context are extremely high to enable the requirements of various authorities to be met.
Plate heat exchangers are used in the food industry for a number of different purposes. Problems with regard to so-called dead zones, the accumulation of fibres and other solid material which may be contained in products, and the possibility of flexible and effective cleaning, are extremely important factors in this context. The design of heat exchangers therefore plays a crucial part in making it possible for effective heat transfer and hygiene to be achieved while at the same time preventing so-called dead zones in which products may be caught and hence become fertile ground for bacteria growth.
In this context it is advantageous to use so-called semiwelded plate heat exchangers, i.e. heat exchangers comprising a number of cassettes formed by welding heat exchanger plates together in pairs. The weld seam normally runs along the side edges of the cassettes and around the portholes. A gasket is disposed between the respective cassettes and is normally made of a rubber material and situated in a groove of the heat exchanger plate. One fluid flows inside the cassettes, and another fluid between the cassettes. Semiwelded plate heat exchangers tolerate relatively high pressures and make it possible to open the plate package and clean the spaces between pairs of welded heat exchanger plates. The welds which replace the gaskets in every second space between plates round the heat exchange surface of the heat exchanger plates reduce the need for gasket replacement and enhance safety.
The material and configuration of the heat exchanger plates, the design of the heat transfer surfaces with regard to pattern and press depth, etc., are important factors in hygienic applications. A critical region of heat exchangers and particularly of heat exchanger plates with regard to dead zones is at the portholes, which are normally provided with a number of so-called nibs, i.e. alternating ridges and valleys, evenly distributed about the porthole in the form of a wave pattern. These nibs constitute contact points and have the important function of absorbing forces and supporting the structure against the high pressures which occur in the heat exchanger. When two or more heat exchanger plates are placed adjacent to one another, however, the nibs result in the formation of spaces in the actual flow passage, i.e. dead zones in which flowing liquid may become stationary and solid material contained in the liquid may be trapped and accumulate.
The gaskets currently used with heat exchanger plates of this type joined together to constitute cassettes take the form of, for example, so-called “clip-on” gaskets, i.e. gaskets locked firmly at the periphery of the heat exchanger plates and around the portholes by protruding locking means disposed in the gasket which are clamped firmly around the edge of the heat exchanger plate. These protruding locking means may also make it more likely that fibres etc. are caught, especially at the portholes.
GB 809 886 describes a plate heat exchanger for two heat-exchanging fluids whereby the portholes are made circular and plain in order to avoid the problem of fibres and particles being caught. That solution is achieved by the edge of the porthole being pressed outwards to form a flange or collar. The flanges of opposite portholes are so disposed as to abut against one another, thereby forming a smooth channel through the plate package. That solution does however involve manufacturing difficulties.
The object of the invention is to eliminate or at least reduce the problems indicated above and to provide an improved solution for a porthole of a heat exchanger plate. What is in particular aimed at is a new and better gasket assembly specially intended for the portholes of a cassette comprising two heat exchanger plates.
This object is achieved according to the invention by the gasket assembly indicated in the introduction, which is characterised in that said gasket in the area around the ports comprises, along its side facing the porthole, a circumferential protruding bead.
The configuration of the gasket assembly results in great reduction of the so-called dead zones at the portholes. It provides instead a plain surface in the passage through the port channel and substantially avoids the risk of highly viscous liquids which may possibly contain particles or fibrelike products being caught. Should material nevertheless be caught, the plain surface of the gasket in combination with the configuration of the porthole helps to create conditions in which the material will be swept away. The gasket assembly according to the invention thus also reduces the risk of bacteria growth, which is a major and important advantage, particularly in areas of application in which the hygiene requirements are extra high.
According to an alternative embodiment of the invention, the gasket assembly is so configured that the gasket in the area around the ports comprises, along its side turned towards the porthole, opposite recesses on the upper and lower sides of the gasket. Such a design of the gasket makes it possible for the dead zones to be largely eliminated altogether. This is a major advantage in such areas as the food and drug industry, in which the hygiene requirements are very strict.
According to a further embodiment of the invention, the heat exchanger plate has about the port a circumferential ridge disposed on the outside of the cassette between the porthole and the gasket groove. According to an advantageous embodiment of the gasket assembly according to the invention, the ridge and the gasket cooperate in that the bead of the gasket abuts against the circumferential ridge about the porthole, thereby ensuring that the gasket is not dislodged from its position by the high pressures which occur during operation.
According to an advantageous embodiment of the gasket assembly according to the invention, the bead is so configured that the cassettes in combination with the gasket at the ports provide a substantially smooth channel through the plate package. In this embodiment, the plain surface of the gasket in cooperation with the configuration of the porthole helps to reduce the risk of material being caught. According to further advantageous embodiments of the gasket assembly according to the invention, the heat exchanger plates are permanently joined together in pairs by welding or brazing.
The object of the invention is also achieved by a plate heat exchanger comprising at least one gasket assembly according to any one of claims 1-7.
The object of the invention is also achieved with a heat exchanger plate comprising the features indicated in claim 9.
The object of the invention is also achieved with a gasket which comprises the features indicated in claim 10. An advantageous embodiment of the gasket is indicated in dependent claim 11.
The invention is explained in more detail below by describing various embodiments cited by way of examples with reference to the attached drawings, in which
Configuring the heat exchanger plates 2 in such a way that as few contact points as possible occur between two mutually adjacent cassettes prevents fibres and solid materials which may be contained in the fluid being caught in the space between the cassettes. According to the invention, the plates are also so designed that contact points for necessary mechanical support occur largely only on the inside, between two plates which are to be joined together to form a cassette, by opposite ridges abutting against one another. In contrast, at portholes 4 and 5 the plates abut completely against one another and are joined together permanently so as to form a seal against the fluid which is intended to flow through the portholes. Portholes 6 and 7, which constitute the inlet and outlet to the cassettes, are provided instead with nibs 11 which are necessary for providing necessary mechanical support at the porthole.
The gasket 3, which is preferably made of an elastic material, e.g. rubber material, is disposed in a groove 12 which extends along the periphery of the constituent plates of the cassette and around ports 4 and 5. There is a ring gasket 13 round ports 6 and 7. The purpose of the gasket 3 is to seal the space between two cassettes, and it has in the area around ports 4 and 5, along its side facing the porthole, a circumferential protruding bead 14 which may have a cross-sectional configuration such as represented, for example, by the gaskets according to B and C in
To ensure that the gasket 3 is firmly disposed at the porthole and is not pressed or does not slip out of the groove 12 at high pressures and temperatures, a circumferential ridge 15 is formed in the plate about the port on the outside of the cassette between porthole 4 or 5 and the gasket groove 12. The height of the ridge 15 is such that there is a gap between two opposite ridges when two cassettes are disposed adjacent to one another. In the case of the gasket assembly according to the invention, the gasket 3 is thus situated in the groove 12 in such a way that the bead 14 abuts against the ridge 15 of the constituent plates of the cassettes at portholes 4 and 5. This arrangement results in the gasket being held securely in position while at the same time a tight, plain and smooth surface is formed in porthole 4 or 5 and in the port channel, as clearly indicated in
In contrast, if the cross-sectional configuration of the gasket is in accordance with the invention according to B, i.e. so that the gasket in the area around the ports comprises along its side facing the porthole a circumferential protruding bead 14, the volume of the dead zone will be greatly reduced. The fact that the bead 14 abuts against the ridge 15 also results in a smoother surface in the port channel. In another embodiment of the invention, the gasket has a cross-sectional configuration according to C, whereby the bead 14 is so configured that the gasket 3 in the area around the ports comprises, along its side facing the porthole, opposite recesses 16 on the upper and lower sides of the gasket. In this case the whole space at the portholes between two cassettes is largely filled by the gasket, the dead zone is eliminated and a plain smooth surface is formed in the port channel.
A gasket assembly configured according to the invention whereby a ridge around the porthole in a heat exchanger plate cooperates with a bead of the gasket results in a port channel with maximum possible smoothness of surface, with greatly reduced or no dead zones. This is of great significance, particularly in plate heat exchanger applications where there are strict hygiene requirements, but also in other applications where obstruction and so-called fouling are normally a problem. The gasket assembly and the heat exchanger comprising the gasket assembly according to the invention make it possible to achieve a plate heat exchanger which meets high hygiene requirements and is easy to clean.
It should be noted that other embodiments not here cited of the invention are also possible without departing from the scope of the invention which is indicated in the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0500216-7 | Jan 2005 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2006/000049 | 1/13/2006 | WO | 00 | 4/11/2008 |
