Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Reexamination Certificate
2002-10-29
2004-06-22
Leo, Leonard (Department: 3743)
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
C165S139000, C165S174000
Reexamination Certificate
active
06752202
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a plate pack for a plate heat exchanger, comprising a number of heat transfer plates, each of which has a heat transfer portion and a number of through ports, said plates interacting in such manner, that a first flow duct is formed between them in a plurality of plate interspaces and a second flow duct is formed in a plurality of other interspaces and that the ports form at least one inlet duct and at least one outlet duct for each of the flow ducts. The invention further relates to a heat transfer plate for use in a plate pack of the type described above.
BACKGROUND ART
A conventional plate heat exchanger consists of a frame, a pressure plate, a frame plate and a number of heat transfer plates clamped together in a “plate pack”. The heat transfer plates are arranged so that their large faces face adjoining heat transfer plates and so that an interspace defining a flow duct is formed between each heat transfer plate. Each of the heat transfer plates is provided with a number of through ports, which together form at least two inlet ducts and two outlet ducts extending through the plate heat exchanger. One of the inlet ducts and one of the outlet ducts communicate with each other via some of the flow ducts and the other inlet and outlet ducts communicate with each other via the other flow ducts.
The plate heat exchanger works by two different media being supplied, each via a separate inlet, to two separate flow ducts, where the warmer medium transfers part of its heat content to the other medium by means of heat transfer plates. The two media can be different liquids, vapours or combinations thereof, so-called two-phase media.
The plate heat exchanger concept will be described in more detail in connection with a plate heat exchanger intended for so-called two-phase application and described in the Alfa Laval AB brochure The plate evaporator from 1991 (IB 67068E)(see FIG.
1
).
The medium that is to be completely or partially vaporised, for example juice that is to be concentrated, is supplied to the heat exchanger through an inlet duct located in the lower portion of the plates. The inlet is defined by two openings in the frame plate. These two openings lead directly to said inlet duct, which extends through the entire plate heat exchanger. Vapour is supplied to the flow ducts through the second inlet duct. The second inlet duct is located in an upper corner of the upper portion of the plates and, since the vapour takes up a relatively large volume, the duct has a relatively large cross-sectional area.
When the plate heat exchanger is in operation the vapour flows downwards in its interspaces and is completely or partially condensed. The condensate is discharged through two outlet ducts, which are defined by ports in the two lower corners of the plates and which lead out from the plate heat exchanger via two connecting ports in the frame plate. The second medium is conveyed upwards in its interspaces and is completely or partially vaporised before being finally discharged via an outlet duct, which is located in the other upper corner of the plates and which leads out from the heat exchanger via a connecting port in the frame plate.
A problem associated with this technique is that in long plate heat exchangers, i.e. plate heat exchangers with a large number of heat transfer plates in the plate pack, the media flows tend to vary along the length of the plate heat exchanger. Therefore, the maximum capacity of the plate heat exchanger cannot be exploited. Even if one or several plate interspaces are utilised at maximum capacity, there is a fairly large number of plate interspaces whose utilisation level is considerably below the maximum capacity. This problem is accentuated in two-phase applications, since the vapour phase of each medium is considerably more volatile than the liquid phase, which means that the vapour phase and the liquid phase will behave differently in the heat exchanger and thus present different flows in different plate interspaces of the flow duct concerned. Another problem associated with most plate heat exchangers is that it is difficult, in many cases, to obtain an even distribution of the fluid flow across the whole width of the plate, i.e. across the entire heat transfer portion. One way to try to improve the distribution is to make the inlet duct rectangular, as shown in FIG.
1
. To facilitate connection to the other components it is possible to use, for instance, two connecting ports in the frame plate, which connect directly to the rectangular inlet duct. In general, it is undesirable to have such abrupt dimensional variations in a duct, as this causes turbulence in the flow.
The above-related problems arise even if the plate heat exchanger is not being used in two-phase applications. The problems have been discussed in connection with two-phase applications, since they are more pronounced in this kind of application of a conventional plate heat exchanger.
WO97/15797 discloses a plate heat exchanger, which is intended for evaporation of a liquid, for example a refrigerant. This plate heat exchanger has an inlet duct and a distribution duct, which extend through the plate heat exchanger and communicate with each other via a number of flow passages along the length of the plate heat exchanger. The purpose of the distribution duct is, inter alia, to equalize the flow between different plate interspaces by serving as an expansion or equalization chamber between the inlet duct and the plate interspaces. This design does not, however, provide a completely satisfying solution for all operational situations to which a conventional industrial plate heat exchanger may be subjected.
GB-A-2 052 723 and GB-A-2 054 124 disclose two variants of a plate heat exchanger, which are sectioned in a front and a rear section of plate interspaces. To allow the flow to the plate heat exchanger to reach the rear section, these plate heat exchangers are provided with by-pass ducts consisting of a pipe, which is concentrically arranged in the inlet duct. The purpose of the concentric pipe is to convey part of the flow to the rear section. The plate interspaces of the first section communicate directly with the front portion of the inlet duct. The plate interspaces of the second section communicate directly with the rear portion of the inlet duct.
Consequently, there are no prior art constructions, which give a satisfactory flow distribution both along the length of the plate heat exchanger and across the width of the plates. Above all, there is no prior art construction that solves these problems in two-phase applications.
SUMMARY OF THE INVENTION
The object of the invention is to provide a solution, which allows a satisfactory flow distribution along the length of the plate heat exchanger and-across the width of the plates, and by means of which it is also possible to avoid the above distribution problems in two-phase applications.
The present object is achieved by means of a plate pack of the type described by way of introduction, characterised in that the inlet duct of at least the first flow duct comprises at least two primary ducts, which are arranged to receive a fluid flow for the first flow duct, and at least one secondary duct, which communicates with the primary ducts and the first flow duct and which is arranged to receive the fluid flow from the primary ducts and to convey the fluid flow to the first flow duct.
By providing the plate pack with two primary ducts and one secondary duct, a plate pack in which the fluid flow can be advantageously distributed both along the length of the plate pack and across the width of the plates is achieved, while at the same time allowing the plate pack to be easily connected to conventional piping systems without any adverse effects on the flow and without the need for special adapter connections between the plate pack and the conventional piping system. A certain part of a fluid flow conveyed to the inlet duct of the plate pack is deflected from the primary ducts and
Holm Karl Martin
Nilsson Nils Inge Allan
Tagesson Berndt
Alfa Laval Corporate AB
Fish & Richardson P.C.
Leo Leonard
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