Heat exchange – Flow passages for two confined fluids – Interdigitated plural first and plural second fluid passages
Reexamination Certificate
2002-10-29
2004-03-09
Flanigan, Allen (Department: 3743)
Heat exchange
Flow passages for two confined fluids
Interdigitated plural first and plural second fluid passages
C165S166000
Reexamination Certificate
active
06702006
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 first plate interspaces and a second flow duct is formed in a plurality of second plate interspaces and that the ports form at least one inlet duct and at least one outlet duct for each of the flow ducts, that the inlet duct of at least the first flow duct comprises at least one primary duct, which is arranged to receive a fluid flow for the first flow duct, and at least one secondary duct, which communicates with the primary duct and the first flow duct and which is arranged to receive the fluid flow from the primary duct and to convey the fluid flow to the first flow duct.
The invention further relates to a flow distribution device for use in an inlet duct of a plate heat exchanger, and a plate heat exchanger.
BACKGROUND ART
A plate heat exchanger may comprise a “frame plate”, a “pressure plate” and a number of intermediate heat transfer plates clamped together in a “plate pack”. The heat transfer plates are arranged and designed so that flow paths for at least two heat transfer media are formed between them. Each heat transfer plate is provided with a number of through ports, which together form at least two inlet ducts and two outlet ducts extending through the plate pack. One of the inlet ducts and one of the outlet ducts communicate with each other via some of the flow paths, which form a flow duct for one heat transfer medium, and the other inlet and outlet ducts communicate with each other via the other flow paths, which form a flow duct for another heat transfer medium.
The plate heat exchanger works by two different heat exchanging media being supplied, each via a separate inlet duct, 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, gases, 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 formed by two openings in the frame plate. These two openings lead directly to a common first inlet duct, which extends through the pack of heat transfer plates. Vapour is supplied to the flow ducts formed between the heat transfer plates and intended for this purpose through a second inlet duct. This second inlet duct is formed by ports located in an upper corner portion of the plates and, since the vapour takes up a relatively large volume, it 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 formed by ports located in the other upper corner of the plates and which leads out 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 amount of flow of the two media in the plate interspaces tends 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 a medium has different characteristics than the liquid phase. This means that the vapour phase and the liquid phase will behave differently in the heat exchanger and thus present a different distribution in the plate interspaces 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 each plate, i.e. across the entire heat transfer portion. One way to try to improve the distribution is to give the plate ports intended to form the inlet duct an elongate shape, as shown in FIG.
1
. To facilitate connection of the heat exchanger to other devices it is possible to use, for instance, two connecting ports in the frame plate, which connect directly to the inlet duct having an elongated cross-section. In general, it is undesirable to have such abrupt dimensional variations in a duct. Because of the dead flow space formed immediately behind the connecting ports of the frame plate, the first interspaces do not get the desired distribution of liquid. Instead any gases present have a tendency to flow in these plate interspaces.
The above-related problems arise even if the plate heat exchanger is not being used for two-phase applications, but they are particularly pronounced in two-phase applications.
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 along the whole length of the plate heat exchanger. The purpose of the distribution duct is, inter alia, to create substantially equal flows in the different plate interspaces by serving as an expansion or equalization chamber between the inlet duct and the plate interspaces. The proposed design does not, however, provide a completely satisfying solution for all operational situations in which conventional industrial plate heat exchangers are used.
GB-A-2 052 723 and GB-A-2 054 124 disclose two variants of a plate heat exchanger having a front and a rear section of plate interspaces. To allow the flow to the plate heat exchanger to reach the rear section, the plate heat exchanger is provided with a by-pass duct 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 primary duct and the secondary duct communicate with each other through at least one flow passage portion spanning a plurality of plate interspaces, that the extension of the flow passage portion along the primary duct is substantially smaller than the extension of the primary duct, and that there is substantially no
Holm Karl Martin
Nilsson Nils Inge Allan
Tagesson Berndt
Alfa Laval Corporate AB
Fish & Richardson P.C.
Flanigan Allen
LandOfFree
Plate pack, flow distribution device and plate heat exchanger does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Plate pack, flow distribution device and plate heat exchanger, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plate pack, flow distribution device and plate heat exchanger will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3289417