Asymmetric flow in Plate Heat Exchangers

 A typical problem for Heat Transfer Specialist in Plate Heat Exchanger design occurs when flow rates of two fluids involved in the process are by far different.

PHE is symmetric by is own nature: same flow rates, same temperature difference, same pressure drop this is an easy life in the calculation...

But in some cases (swimming pool heating, condenser/evaporators, gas coolers, shell&tube HEX replacement) ratio between flow rate could be very high (1:5)

First approach is to create a by pass on one circuit (i.e. water in swimming pool) to get partial flow heated for larger Delta T and downstream PHE mixed with rest of flow.

Then different corrugations of herringbone pattern resulting in different combinations was the second approach in order to handle the asymettric flow.

But the significant solution was utilization of different pressing depth to get channels with one side standard and another one much larger.


A plate heat exchanger comprising at least two separate flow paths for primary and secondary fluids to exchange heat, the said flow paths being substantial defined by permanently interconnected heat exchanger plates provided with a herring bone pattern of ridges and depressions and offering different pressure drops at equal mass flows of the two fluids, wherein the depressions in at least some pairs of plates defining the flow path having the lower pressure drop at least partly are alternatively of two different press depths (D₁, D₂) measure from the plan define by the tops of the ridges of the herringbone patter the heat exchanger plate, the smaller (D₂) being located between two tops of the herringbone pattern and being at least 40% of the greater (D₁), and thereby that the tops of the ridges engaging the tops of a neighboring plate to define a flow channel having high pressure drop substantially contact each other along points defined by crossing lines

https://www.google.com/patents/US20080029257

In this way also pressure drop was not a crucial factor in design because two sides could have a different profile.

In case of condensers, even connections must be different in size

    Courtesy by SONDEX Italy

The plate is designed as a semi-welded cassette, with a welded channel for the condensing side. On the medium side, there is a traditional plate heat exchanger gasket. The unique plate design makes it possible to utilize almost the whole plate area as heat transmission area. This plate is designed in two different plate patterns on the welded side. For dirty and fiber products, the plate is designed with a wide gap plate pattern. For clean products, the plate pattern is on both the welded side as well as the medium side a herringbone pattern. The plate has a combination of two different plate patterns heights. This makes it optimal for keeping a low-pressure drop on the welded side and at the same time a high turbulence on the medium side. This results in a high heat transmission U value

                               

  

The DN800/32” vapour connection makes it possible to cover many duties in a single pass solution. All connections will thus be on the head of the heat exchanger, which is of big advantage during service work. The plate pattern and inlet area are also designed for CIP cleaning making the service of the PHE easy.

PFHE can be used, as mentioned, also as Rising Film Evaporator. The SEC174 Sondex plate evaporator is a specially developed unit for evaporation duties.

The plate is designed as a semi-welded cassette, with a welded channel for the medium side, and on the evaporation side there is a traditional plate heat exchanger gasket. The unique plate design ensures an even distribution of the product over the whole plate making optimal rising film evaporation. The special designed plate pattern ensures a high turbulence of the fluids on both sides, resulting in a high heat transmission co-efficient.This results in a very compact heat exchanger with a small hold-up volume.

The unique evaporator and condenser plates from Sondex are specially designed for condensing low temperatures, vapor and for multistage evaporation of highly concentrated products.
The unique asymmetric large port holes ensure an optimal exploitation of the available heat transfer area. The unique inlet design and high thermal efficiency are what makes these plates the most efficient in the market today.

 

Therefore now with advanced technologies available on Plate Heat Exchangers corrugation in terms of chevron angle and pressing depth combination Heat Transfer Specialist can consider PHE in wider range of applications than before.