GB2201238A - Plate heat transfer apparatus - Google Patents

Plate heat transfer apparatus Download PDF

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Publication number
GB2201238A
GB2201238A GB8706301A GB8706301A GB2201238A GB 2201238 A GB2201238 A GB 2201238A GB 8706301 A GB8706301 A GB 8706301A GB 8706301 A GB8706301 A GB 8706301A GB 2201238 A GB2201238 A GB 2201238A
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GB
Grant status
Application
Patent type
Prior art keywords
plate
roughened
surface
heat transfer
plates
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
GB8706301A
Other versions
GB8706301D0 (en )
Inventor
David George Royston
Jonathan Graham Shaw
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
SPX Flow Technology Crawley Ltd
Original Assignee
SPX Flow Technology Crawley Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/18Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
    • F28F13/185Heat-exchange surfaces provided with microstructures or with porous coatings
    • F28F13/187Heat-exchange surfaces provided with microstructures or with porous coatings especially adapted for evaporator surfaces or condenser surfaces, e.g. with nucleation sites
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F3/00Plate-like or laminated elements; Assemblies of plate-like or laminated elements
    • F28F3/08Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning
    • F28F3/083Elements constructed for building-up into stacks, e.g. capable of being taken apart for cleaning capable of being taken apart

Abstract

Evaporator heat transfer plates are roughened over part of their surfaces which are contacted in use by the evaporating medium to promote nucleate boiling. The roughening may be produced by grit blasting or electro-chemical etching. The plates may be corrugated. The plates may be roughened only at the end of the plates adjacent the inlet for the evaporating medium.

Description

PLATE HEAT TRANSFER APPARATUS This invention relates to plate heat transfer apparatus.

Plate heat exchangers or evaporators are well known and consist of a pack of plates arranged in spaced face-to-face relationship to define flow passages between adjacent plates. The media in adjacent flow spaces is in heat exchange relationship by conduction through the plate. The peripheral boundaries of the flow spaces are defined by gaskets normally set in recesses or grooves in the plate. The pack of plates is under compression to ensure good sealing between the gaskets and the plates.

The surfaces of the plates are usually patterned, the patterns being formed by press- forming, with a plurality of regular ridges to maximise the conduction of heat to and from the plate and to direct the flow of the media across the whole enclosed areas of the plates.

It is an object of the invention to provide improved heat transfer plates for use in evaporating duties.

According to the invention there is provided a heat transfer plate in which parts of the surfaces of the enclosed areas of the plates in contact in use with the boiling medium are significantly roughened.

The roughening stimulates neucleate boiling to improve the efficiency of the transfer plate. In some embodiments roughening is preferably applied only in the region near and at the end of the plate associated with inlet of the boiling medium.

The plates may be roughened by grit blasting. The plates may be roughened by electro-chemical etching or chemical means.

Preferably the roughening is carried out before press-formation of any patterns in the surface, and where roughening is carried out after press-formation the plates may be re-pressed.

A roughened plate may be provided separately and fixed in use or permanently to an otherwise conventional heat exhanger plate on its evaporating medium side.

Plate evaporators will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a plan view of a plate; Figure 2A and 2B shows enlarged sectional views of a small part of the surface of the plate; and Figure 3is a cross-sectional elevation of part of an evaporator.

Referring to the drawing, Figure 1 shows a typical patterned plate. Grooves 10 are provided around the inlet ports and outlet ports to receive sealing gaskets (not shown) and also around the periphery of the corrugated or patterned central area 12. The patterned surface has been roughened, although this is not shown in Figure 1, by grit blasting. Only one surface is roughened, that is, the surface in contact with the boiling medium, or in other words the surface not in use exposed to the heating medium.

Preferably, grit in the range 30/50 to 120/220 is used, formed of sharp edged Aluminium or Corundum. Care is taken when grit blasting not to damage or roughen any sealing surfaces, such as the grooves 10, by masking such gasket receiving regions of the plate. Further, it is advantageous for some applications to roughen only part of the plate surface, say only the part corresponding to a half of the plate which is nearest the boiling medium input end in use.

The roughening is normally carried out before the plate is press-formed to provide the usual pattern of ridges in the surface of the plate. In some cases however, the plate is preferably first press-formed, then roughened and then finally press-formed again.

In Figure 2A there can be seen a roughened plate surface 14. The roughening extends about 25% into the normal thickness of the plate. In Figure 2B the same surface is shown after being later press-formed. It will be seen that some of the cavities caused by roughening such as cavity 16 have become to some extent enclosed.

In Figure 3, plates 20 are conventional patterned heat exhanger plates of say around 0.6mm thickness. Plates 21 also patterned to correspond to the plates 20, are of around 0.15mm thick and attached to the plates 20 as shown. Each side of an evaporating medium cavity is lined with a plate 21. The plates 21 are roughened over chosen parts, preferably be grit blasting. The roughening can be carried out either before or after the plate has been pressed to form its patterned configuration. The plates 21 are suitably attached or sealed so that evaporating medium does not enter between the plates 20 and the plates 21.

On normal untrea.ted plate surfaces nucleate boiling occurs on naturally formed 'active sites' for bubble growth consisting of small pits or sharp edged indentations or scratches on the heat transfer surface. For any given active site, heat transfer fluid and hydrodynamic condition there will exist a unique wall/surface temperature difference at which a bubble starts to grow and eventually leaves the active site. This activation temperature difference between surface and bulk fluid is strongly influenced by the effective port or site size. It is possible that for many heat transfer duties the available temperature difference for heat transfer'is below this critical temperature difference for bubble growth leading to reduced thermal performance.Thus it is believed that by extending the 'active site' or pore size range and population density on the surface by roughening as described, nucleate boiling can be maintained over a greatly enlarged surface temperature difference range and thus the overall heat transfer coefficient increased over that of an untreated surface.

Generally speaking the surfaces of evaporator plates are conventionally smooth to prevent fouling of the surfaces.

Surprisingly when this smooth surface is partly replaced as described by a roughened area or roughened areas, selected to where boiling will or is preferably to take place in practice, a marked improvement in performance of the evaporator is achieved.

It will be noted that a roughened surface such as that produced by grit blasting or abrasive cloth wheel may be further processed to preform a simple re-entrant surface by repressing as already mentioned. The effect of repressing is one of creating pits or channels with enclosed upper regions as seen in Figure 2B in contact with the fluid possessing one or more entry points for the fluid entry or exit from the site of nucleation. During nucleate boiling the active sites form the nucleus for bubble growth and departure and are subject to varying pressure differences arising from bubble surface tension forces. These pressure fluctuations can cause fluid to be drawn into or expelled from the cavities and so greatly increase heat transfer by a form of micro-convection.

Roughening the heat transfer surface also creates an extended surface area for fluid contact which can increase the heat transfer rate through the plate. The heat transfer area is increased by roughening perpendicular to the general plate surface and heat transferred in this direction is then conducted by the extended surface back into the plate. In practice such a form of plate enhancement is most effective if the fluid thermal conductivity is low and the viscosity is not so large as to restrict the flow of fluid between the plate surface protrusions.

Generally it is required that the described surface roughening is at least relatively severe producing definite protrusions in use into the bulk fluid (e.g. a rough sand type texture is required) for good practical results.

Claims (10)

1. A heat transfer plate for an evaporator in which chosen parts of the surface of the enclosed areas of the plate in contact in use with the boiling medium are significantly roughened.
2. A plate according to claim 1 in which the chosen parts are in the region near the end of the plate associated with the inlet of the boiling medium in use.
3. A plate according to claim 1 or 2, in which the chosen parts of the plate are roughened by grit blasting.
4. A plate according to claim 1 or 2, in which the chosen parts of the plate are roughened by electro chemical etching.
5. A plate according to any one of claims 1 to 4, in which the chosen areas are roughened before the plate is press-formed with patterns, known per se, in the surface.
6. A plate according to any one of claims 1 to 5, in which the plate is press-formed with patterns, known per se, then the chosen parts are roughened, and the plate re-pressed to its patterned shape.
7. A plate according to any one of claims 1 to 3 in which the roughening is carried out using grit in the range 30/50 to 120/220.
8. A plate according to claim 7 in which the grit is formed of Alumina or Corundum.
9. A heat transfer plate according to any of claims 1 to 8, formed of thin material arranged to be secured to the evaporating medium surface of a conventional heat exchanger plate.
10. A plate evaporator substantially as herein described with reference to any one or more of Figures 1, 2A, 2B and 3.
GB8706301A 1986-12-30 1987-03-17 Plate heat transfer apparatus Pending GB8706301D0 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8631006A GB8631006D0 (en) 1986-12-30 1986-12-30 Plate heat transfer apparatus

Publications (2)

Publication Number Publication Date
GB8706301D0 GB8706301D0 (en) 1987-04-23
GB2201238A true true GB2201238A (en) 1988-08-24

Family

ID=10609658

Family Applications (2)

Application Number Title Priority Date Filing Date
GB8631006A Pending GB8631006D0 (en) 1986-12-30 1986-12-30 Plate heat transfer apparatus
GB8706301A Pending GB8706301D0 (en) 1986-12-30 1987-03-17 Plate heat transfer apparatus

Family Applications Before (1)

Application Number Title Priority Date Filing Date
GB8631006A Pending GB8631006D0 (en) 1986-12-30 1986-12-30 Plate heat transfer apparatus

Country Status (1)

Country Link
GB (2) GB8631006D0 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1394491A3 (en) * 2002-08-26 2005-08-17 ONDA S.p.A. Plate heat exchanger

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1069535A (en) * 1964-07-20 1967-05-17 Richard Line Hummel Improvements in and relating to heat transfer surfaces
GB1523855A (en) * 1976-02-23 1978-09-06 Borg Warner Heat exchangers
GB2027352A (en) * 1978-07-25 1980-02-20 Hisaka Works Ltd Plate type evaporator
US4258783A (en) * 1977-11-01 1981-03-31 Borg-Warner Corporation Boiling heat transfer surface, method of preparing same and method of boiling
EP0053452A2 (en) * 1980-12-02 1982-06-09 Marston Palmer Ltd. Heat exchanger

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1069535A (en) * 1964-07-20 1967-05-17 Richard Line Hummel Improvements in and relating to heat transfer surfaces
GB1523855A (en) * 1976-02-23 1978-09-06 Borg Warner Heat exchangers
US4258783A (en) * 1977-11-01 1981-03-31 Borg-Warner Corporation Boiling heat transfer surface, method of preparing same and method of boiling
GB2027352A (en) * 1978-07-25 1980-02-20 Hisaka Works Ltd Plate type evaporator
EP0053452A2 (en) * 1980-12-02 1982-06-09 Marston Palmer Ltd. Heat exchanger

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1394491A3 (en) * 2002-08-26 2005-08-17 ONDA S.p.A. Plate heat exchanger

Also Published As

Publication number Publication date Type
GB8631006D0 (en) 1987-02-04 grant
GB8706301D0 (en) 1987-04-23 grant

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
732 Registration of transactions, instruments or events in the register (sect. 32/1977)