BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the device and the method according to the invention are described below with reference to the attached schematic drawings, which depict only the components which are necessary for understanding the invention.
FIG. 1 depicts schematically a heat exchanger system comprising a heat exchanger with various pipe connections and a component which by its function is the last component which can influence the characteristic of the incoming fluid, i.e. the pressure of the fluid.
FIG. 2 depicts part of a heat exchanger according to the invention, with a frame plate and a pressure plate and, between these, a number of heat transfer plates and gaskets. To facilitate comprehension, the heat transfer surfaces of the first three plates are turned towards the reader.
FIG. 3 depicts a transverse cutaway view of a plate and a gasket with a sensor situated between the plate and the gasket.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION
FIG. 1 depicts a heat exchanger system (1) with inter alia a heat exchanger (2). The heat exchanger (2) comprises a frame plate (3) comprising inlet and outlet ports, see FIG. 2, and a pressure plate (4). A number of heat transfer plates (5a, 5b, 5c and so on) with gaskets (6) are situated between said frame plate (3) and pressure plate (4). In the ensuing text, the heat transfer plates (5a, 5b, 5c and so on) will only be referred to as plates (5a, 5b, 5c and so on). FIG. 2 makes it clear how the gaskets (6) of the heat exchanger (2) are arranged by showing three of the plates (5a- 5c) turned 90 degrees about a vertical centreline (14) so that the heat transfer surfaces (10) of the plates (5) are turned towards the observer. In addition, the fluid flow is indicated schematically in the diagram by arrows (7).
In the preferred embodiment of the invention, each plate (5) has four ports (11a, 11b, 11c and 11d) located in such a way that each corner portion of a plate (5) comprises a port. Each plate (5) further comprises a heat transfer surface (10) and two longitudinal edges, viz. a left edge (8) and a right edge (9), a top edge (12) and a bottom edge (13). The centreline (14) extends from the top edge (12) to the bottom edge (13) (between the two upper ports (11a and 11b) and between the two lower ports (11c and 11d)) and divides the plate (5c) into two halves.
The gasket (6) is situated in a gasket recess (not depicted in the drawing) in the plate (5) and extends round the heat transfer surface (10) of the plate (5) and round the latter's ports (11a, 11b, 11c and 11d).
The plates in FIG. 2 are shown numbered from the left, the first plate (5a) being situated nearest to the frame plate (3). A sensor (15a) is situated on the third plate (5c). The sensor (15a), see FIG. 3, is situated between the gasket (6) and the plate (5c) in such a way that it abuts against both the gasket (6) and the plate (5c). The sensor (15a) is positioned at the upper left region of the plate (5c), along the longitudinal left edge (8) and lower than the upper left port (11a). In this region the gasket (6) is subject to the largest of the various fatigue factors which are all contributory causes to the possibility of a gasket failing. Examples of the fatigue factors are temperature fluctuations, friction, fluid contact and oxygen contact from the outside of the heat exchanger. Oxygen contact will dry the gasket (6), thereby contributing to the gasket (6) initially beginning to crack before subsequently failing completely.
In an alternative embodiment of the invention, a sensor (15b) is installed along a gasket diagonal (16). FIG. 2 shows the gasket diagonal (16) extending from the top of the left upper port (11a) on the third plate (5c) towards the longitudinal right edge (9) at the underside of the upper right port (11b). With this positioning, it is desirable that the sensor (15b) be located on the portion of the gasket diagonal (16) which is situated to the right of the centreline (14) of the plate (5c). The fact that plates are normally equipped with suspension devices (17) situated in the region between the upper ports (11a and 11b) makes it undesirable for sensors to be located on the portion of the gasket diagonal (16) which is nearest to the suspension devices (17) and which extends to the left of the centreline (14). This undesirability is because access to the sensors would then be difficult.
A second sensor (15d), see FIG. 1, is located at any desired point along the flow path of the fluid to the heat exchanger (2) from the last component (18), as seen in the direction of flow, of the heat exchanger system (1). The last component (18) of the heat exchanger system (1) is defined as the last component (18) which has the possibility of influencing the characteristic of the fluid entering the heat exchanger (2) e.g. the pressure. As previously mentioned, this last component (18) may for example take the form of a pump which supplies the heat exchanger (2) with fluid.
In the preferred embodiment of the invention, the aforesaid second sensor (15d), see FIG. 1, is located in such a way that the hot fluid entering the heat exchanger is monitored. This is because the pressure of the hot fluid relative to the gasket pressure in the channel for the hot fluid is crucial to being able to assess whether there is risk of leakage. Where so required by applications in which it is desirable to be able to register the incoming cold fluid, a sensor is located in such a way that the incoming cold fluid is monitored. The gasket pressure in the channel for the cold fluid is then monitored in a corresponding manner.
FIG. 2 indicates a space (19) formed between the frame plate (3) and the first plate (5a). This space (19) is drained and constitutes an insulating layer whereby the fluid flowing in a first channel (20a) (between the first and second plates (5a and 5b)) only has heat transfer with the fluid flowing in a second channel (20b) formed between the second and third plates (5b and 5c).
According to the preferred embodiment of the invention, the channels alternately contain cold and hot fluid, thus the first channel (20a) contains cold fluid, the second channel (20b) contains hot fluid, and so on.
In a plate package provided with gaskets, the greatest gasket wear and the greatest probability of gaskets failing are in the channels situated closest to a frame plate or pressure plate, since the gaskets there are subject to the highest temperatures and the greatest temperature fluctuations. The different respective thermal expansion coefficients of the frame plate and the pressure plate result in friction between the various plates, the gaskets, the frame plate and the pressure plate because they move differently in response to, for example, temperature fluctuations. Thus plates situated close to the frame plate and pressure plate do not adapt as easily to such movements as do plates located in the middle of a plate package, where all the plates situated close together move in a similar way. The aforesaid movements therefore contribute to the greatest risk of gasket failure being in the channel which first receives the incoming hot fluid and is located nearest to a frame plate or pressure plate.
The foregoing reasoning makes it clear why in the preferred embodiment of the invention the sensor (15a), see FIG. 2, is located in the upper left region of the plate (5c), below the upper left port (11a). This is the region in which the highest temperature prevails and such factors as thermal expansion coefficients impart to the mutually adjacent plates (5a-5c) and the frame plate (3) the greatest mutual mobility, thereby contributing to major stresses. The gasket (6) in this region is also exposed to oxygen action from the outside of the heat exchanger (2).
During operation, the plate heat exchanger provided with gaskets according to the invention functions in the following manner.
The sensor (15a) monitors the pressure which the gasket (6) and the plate (5c) exert upon one another. As previously mentioned, hot fluid enters from the upper left port on the third plate (5c) and is distributed in the second channel (20b). The pressure of the incoming fluid is monitored before the fluid is distributed out among the plates in the manner previously mentioned, viz. at any desired point along the fluid's flow path to the heat exchanger (2) from the last component (18) of the heat exchanger system (1), see FIG. 1.
The measured values from the sensors are registered and processed in a conventional processor. The processor monitors inter alia that the pressure of the fluid does not exceed the pressure which the gasket (6) and the plate (5c) exert upon one another. If the pressure of the fluid is greater than the gasket pressure, it means that risk of leakage through or round the gaskets (6) may arise. The values obtained for the pressure of the fluid and the gasket pressure are used for calculating a ratio between them which is a so-called differential pressure value. If changes in said differential pressure value exceed permissible limit values, also called set-values, an indicator is activated. The purpose of the indicator is to attract attention so that the process can be halted and the system can be subjected to necessary servicing operations.
In another alternative embodiment of the invention, a sensor (15c) is located on a second plate (5b) instead of on the third plate (5c). The sensor is situated between the gasket (6) and the plate (5b) in the same way as previously explained. The sensor (15c) is thus located at the upper left region of the second plate (5b, see FIG. 2), under the gasket (6) along the longitudinal left edge (8), lower than the upper left port (5a), and above the gasket diagonal (16). As the sensor (15c) is connected to the second plate (5b), the sensor (15c) also reacts to pressure changes taking place on the side of the second plate (5b) which is adjacent to the third plate (5c).
In a further alternative embodiment of the invention (not depicted in the drawings) a fragment of a gasket is placed in an environment corresponding to that prevailing in the aforesaid heat exchangers. Such simulation of the heat exchanger's gasket situation makes it possible to be able to supervise and assess the risk of fluid leakage through a gasket located in the heat exchanger without any need to be in the immediate vicinity of the heat exchanger.
The invention is not limited to the embodiment referred to but may be varied and modified within the scopes of the claims set out below, as has been partly described above.
Patent Application
20080073054
