WO1991014145A1

WO1991014145A1 - Laminar flow inversion device

Info

Publication number: WO1991014145A1
Application number: PCT/AU1991/000097
Authority: WO
Inventors: John Ronald Pain
Original assignee: Heat Transfer Pty. Ltd.
Priority date: 1990-03-16
Filing date: 1991-03-15
Publication date: 1991-09-19

Abstract

A flow modification device (20) for use in heat exchangers (2) for treating fluid with high viscosity. The device has an inlet conduit (32) having an oblique end (52) located within an outlet conduit (34). The arrangement is such that fluid entering the device at the core of the inlet conduit (32) is transposed so that it exits in the outlet conduit (34) adjacent to the periphery thereof.

Description

LAMINAR ΕlDrl INVERSION DEVICE

This invention relates to a flow inversion and mixing device and method.

When a fluid flows in laminar or substantially non-turbulent flow in a heat exchanger tube particularly a fluid with high viscosity, there can be a large temperature gradient between the fluid at the perimeter and the fluid at the core of the flow. This reduces the effective temperature difference between the heat transfer medium outside the tube and the fluid near the tube wall inside the tube and therefore reduces the rate of heat transfer to the fluid with high viscosity. The longer the heat exchanger tube is, the more pronounced this reduction in heat transfer becomes as the temperature of the fluid with high viscosity at the perimeter approaches the wall temperature of the heat exchanger tube.

An object of the invention is to provide a flow inversion and mixing device which can be located in a heat exchanger system so as to counter the aforementioned drawback when the liquid is in laminar flow or non-turbulent flow in the heat exchanger system.

According to the present invention there is provided a flow modification device for modifying a flow of fluid, said device comprising : an inlet conduit, an outlet conduit, and a transfer chamber the arrangement being such that, in use, when fluid flows in the first conduit in a generally non-turbulent or laminar flow having first and second portions flow near the periphery and centre respectively of the inlet conduit, and wherein the transfer chamber is operable to direct the first and second portions to flow in the outlet conduit such that relative positions of the portions are reversed. The actual flow patterns will be complex in practice owing to some mixing which inherently occurs in the device of the invention.

Mixing of the layers is also useful because it also promotes more uniform heating or cooling of the fluid.

Preferably, the device of the invention is located between successive passes in a heat exchanger. It will be appreciated that when a fluid with high viscosity is being treated by the heat exchanger the fluid in the core of one pass of the exchanger will be effectively transposed so as to lie adjacent to the periphery of the tube wall in the next successive pass of the heat exchanger. On the other hand the fluid near the tube wall will be transposed to lie near the core in the next pass. This enhances the overall performance of the heat exchanger and prevents excessive temperature gradients in the fluid with high viscosity.

An important application of the device of the invention is in the treatment of particulate fluids that is to say fluids which have solid particles suspended therein. Fluids of this type would include crushed apple, diced tomato and gravy containing lumps of meat or peas. The device of the invention can produce a significant mixing effect without having constrictions which would tend to clog if they were present.

The invention also provides a method of transferring heat to or from a liquid having high viscosity comprising the steps of passing the fluid in a generally non- turbulent flow along a first heat transfer tube, transferring the liquid to a flow modification device and thereafter passing the fluid along a second heat transfer tube, characterised in that the flow modification device passes viscous liquid from the core of the flow in the first heat transfer tube so that it enters the second heat transfer tube near the periphery thereof.

The invention will now be further described with reference to the accompanying drawings, in which: FIGURE 1 is a schematic view of a tube type heat exchanger incorporating flow inversion and mixing devices of the invention;

FIGURE 2 is a schematic cross-section through the device of the invention; and FIGURES 3A and 3B show velocity and temperature profiles of the fluid at the inlet to the device.

The heat exchanger assembly 2 illustrated in Figure 1 comprises first, second and third passes 4, 6 and 8. The first pass includes an outer jacket 10 having an inlet port 12 and an outlet port 13 for heat exchange fluid such as steam, hot water, refrigerant or chilled water or the like. The first pass includes an inner conduit 14 one end of which includes an inlet coupling 16 for coupling to a supply of fluid with high viscosity to be heated or cooled. The second and third passes 6 and 8 of the exchanger are essentially the same as the first pass 4 and need not be described in detail. The second and third passes have outer jackets 29 and 30 respectively. The outlet end of the inner tube 14 of the first pass is connected to an outlet coupling 18 which in turn is coupled to a flow inversion and mixing device 20. The device 20 transfers fluid with high viscosity from the tube 14 to the inlet coupling 21 of the inner tube 22 of the second pass. Another device 20 of the invention transfers fluid from the outlet end of the inner tube 22 of the second pass to the inner tube 24 of the third pass. The third pass has an outlet coupling 26 for coupling to a conduit (not shown) for receiving the treated fluid with high viscosity. The outer jacket 30 of the third pass 8 has an inlet port 28 which is connected to a source of hot water, steam, refrigerant or chilled fluid. The jackets of the successive passes are coupled together so that the heat transfer fluid passes through all of the jackets in the heat exchanger assembly.

Where the fluid being treated by the heat exchanger is a fluid with high viscosity, it tends to have a high temperature differential between the part of the fluid flowing near the core and that part of the fluid flowing near the perimeter of the tube.

The devices 20 of the invention tend to reverse the locations of the core and peripheral parts of the flow and reduce the temperature gradient in the fluid as a result of mixing superimposed on the inversion effect. This results in a better overall heat transfer from the heat transfer fluid in the jackets to the fluid with high viscosity being treated. A heat exchanger assembly could be made with any number of passes with the device 20 used to interconnect adjacent passes.

Figure 2 illustrates in more detail one of the devices 20 of the invention. It comprises a first conduit 32 which extends into a second conduit 34 of wider diameter. The free end of the conduit 32 which is external to the conduit 34 has a coupling 36 which in use is connected to the outlet coupling at the outlet end of the inner tubes 14 or 22. The other end 52 of the conduit 32 opens into a chamber 33 generally located between the ends of the conduits 32 and 34. A plate 37, which is inclined at an angle B to the transverse, extends between the end of the second conduit 34 and the periphery of the first conduit 32. The plate 37 and port 41 function as a transition zone 38 where the flow gradually changes from an annular flow path 48 to a generally circular flow path into the port 41. The port 41 opens into one end of a bend portion 40 which terminates in a coupling 42 which is laterally disposed relative to the coupling 36. The second tube 34 is provided with an end cap 46 which effectively closes the end of the tube. It will be appreciated that fluid flowing into the first tube 32 is forced to reverse its direction on leaving the end of the first tube and then flow in the annular path 48 between the inner and outer tubes.

Figure 2 diagrammatically illustrates this effect by schematic streamlines 50 which show a reversal of flow and also a reversal of the position of the streamlines relative to the conduit walls. More particularly, the streamlines adjacent to the inner wall of the first conduit 32 tend, after exit from the end 52 of the first tube 32, to be located adjacent to the external periphery of the tube 32. Conversely, the streamlines near the centre of the tube 32 tend, after exit from the end 52 of the first tube 32, to be located relatively close to the inner periphery of the second tube 34. The inclined plate 37 at the transition zone 38 is intended to guide the fluid through the port 41 into the bend portion 40 with relatively little disturbance of the relative positions of constituent parts of the fluid flow.

The end cap 46 of the invention is preferably held in place by means of a nut 50 which is removably mounted on threads 54 on the end of the tube 34. This enables the cap 46 to be removed for cleaning the interior of the device.

It has been found that the performance of the device 20 of the invention can be enhanced by arranging for the end 52 of the inner tube 32 to be cut at an angle in the range from 0° to 45° and typically 25° to 35°.

In accordance with a preferred form of the invention, the cap 46 could be replaced by a plug (not shown) which has an inner face which lies parallel to and spaced from the end face 52 of the inner tube 38. Where the fluid with high viscosity being treated has a shear angle, it is preferred that the angle of the angle A of the end face 52 and the corresponding face of the plug of the tube is greater than or equal to the shear angle of the fluid with high viscosity. The plug would thus prevent the accumulation of stagnant viscous product in the region indicated by the reference numeral 56.

The transition zone 38 includes an oblique face 37 which directs the fluid from the annular flow path 48 into the bend 40. It is preferred that the angle B of the oblique face is the same as the angle A.

A prototype of the invention has been made from stainless steel, the inner tube

32 being 3" outer diameter and the outer tube 34 being 5" outer diameter. The length of the outer tube 34 is about 6" from the inner end of the bend 40 to a plane containing the tip of the end face 52 of the inner tube 32. This length could be varied but if it were too long, too much pressure drop may occur. The devices of the invention can be made in a variety of sizes. It is envisaged that the difference in diameters of the outer and inner tubes would be normally in the range from .25 to 2.5 inches and preferably .5 to 2 inches.

The prototype above was tested with a heat exchanger tube several metres in length for heating purposes, that is to say heating a fluid with high viscosity 20°C at the inlet end to say 90°C at the outlet end using steam or hot water at 110°C. At the end of the first pass of the heat exchanger, the core has very little temperature rise, say as little as 5°C. At the same time, the temperature of the fluid with high viscosity adjacent to the tube wall, has a large temperature rise, say from 70° to 80°C. Figures 3A and 3B show typical velocity and temperature profiles at the inlet to the device 20. Quite clearly this is quite undesirable because of the non-uniform manner in which the fluid with high viscosity is heated. After passing through the device 20 of the invention, the temperature of the fluid with high viscosity near the inner periphery of the bend 40 is in the range of say 25° to 35°C showing that substantial inversion and or mixing has occurred. The inverted and/or mixed fluid then enters the next pass of the heat exchanger where the relatively cold fluid is adjacent to the sidewall of the heat exchanger tube which therefore enhances significant heat transfer.

It will be appreciated that the device of the invention does not have any small constrictions in order to produce the mixing. This makes the device particularly useful for high viscosity fluids such as fruit or vegetable purees or pastes, e.g. tomato paste. H e device is also particularly useful for treatment of fluids having solid particles suspended therein, such fluids including crushed apples, diced tomatoes or gravy with pieces of meat or peas entrained therein.

Many modifications will be apparent to those skilled in the art without departing from the spirit and scope of the invention. For instance, it is possible that the device 20 could be used with the direction of flow reversed but it is thought that the device used in this way would be less effective.

Claims

CLAIMS:

1. A flow modification device (20) for modifying a flow of fluid, said device comprising : an inlet conduit (32), an outlet conduit (34), and a transfer chamber (33) the arrangement being such that, in use, when fluid flows in the first conduit in a generally non-turbulent or laminar flow having first and second portions flow near the periphery and centre respectively of the inlet conduit, and wherein the transfer chamber is operable to direct the first and second portions to flow in the outlet conduit such that relative positions of the portions are reversed.

2. A device as claimed in claim 1 wherein the inlet conduit (32) is concentrically disposed in the outlet conduit (34) and wherein, in use, the first portion flows in the outlet conduit adjacent to the periphery of the inlet conduit and the second portion flows in the outlet conduit adjacent to the periphery of the outlet conduit.

3. A device as claimed in claim 2 wherein said inlet and outlet conduits are of circular cross-section.

4. A device as claimed in claim 3 wherein one end (52) of the inlet conduit is obliquely inclined to the axis of the inlet conduit (32).

5. A device as clai sd in claim 4 wherein the angle of inclination of said one end is in the range from 0° to 45°.

6. A device as claimed in claim 5 wherein said angle is in the range 25° to 35°.

7. A device as claimed in any one of claims 2 to 6 including closure means (46,50) for closing an end of the outlet conduit (34) and wherein the chamber (33) is defined by the closure means and the periphery of outlet conduit (34) from the closure means to an end of the inlet conduit (32).

8.. A device as claimed in claim 7 wherein the closure means (46,50) is removable to give access to said chamber (33).

9. A device as claimed in claim 7 or 8 including an outlet port (41) formed in the sidewall of the outlet conduit (34), said port being spaced from said chamber.

10. A device as claimed in claim 9 including an inclined plate (37) which extends from the outlet conduit (34) to the inlet conduit (32) adjacent to the port (41).

11. A device as claimed in claim 10 wherein the angle of inclination of the plate (37) is in the range 25° to 35°.

12. A device as claimed in claim 9 or 10 wherein the port opens to a bend (40).

13. A device as claimed in claim 12 wherein the inlet conduit includes an inlet coupling (36) and wherein the bend includes an outlet coupling (42) and wherein said couplings are laterally adjacent to one another.

14. A heat exchanger assembly (2) comprising at least two passes (4,6,8) each having inner heat transfer tubes (14,22,24) and outer heat transfer tubes (10,29,30) and a device (20) as claimed in any one of claims 1 to 12 coupled between said inner tubes.

15. A method of transferring heat to or from a liquid having high viscosity comprising the steps of passing the fluid in a generally non-turbulent flow along a first heat transfer tube (14), transferring the liquid to a flow modification device (20) and thereafter passing the fluid along a second heat transfer tube (22), characterised in that the flow modification device passes liquid from the core of the flow in the first heat transfer tube so that it enters the second heat transfer tube near the periphery thereof.

16. A method as claimed in claim 15 wherein said flow modification device (20) comprises a device as claimed in claim 4 and wherein the fluid with high viscosity has a shear angle and the inclination of the one end (52) is selected to be substantially equal to said shear angle.

17. A method as claimed in claim 16 wherein the device includes an inclined plage (37) the angle of inclination of which is selected to be substantially equal to said shear angle.

18. A method as claimed in claim 15 wherein the fluid comprises fruit or vegetable purees or pastes, e.g. tomato paste.

19. A method as claimed in claim 15 wherein the fluid comprises a fluid having particulate material entrained therein.

20. A method as claimed in claim 19 wherein the fluid comprises crushed apple, diced tomato or gravy having pieces of meat and/or peas therein.