WO1999020968A1

WO1999020968A1 - Heat exchanger

Info

Publication number: WO1999020968A1
Application number: PCT/NZ1998/000152
Authority: WO
Inventors: Rodney Mitchell Innes
Original assignee: Energy Savings Concepts Limited
Priority date: 1997-10-20
Filing date: 1998-10-12
Publication date: 1999-04-29
Also published as: AU9767198A

Abstract

A heat exchanger (1) has a helical tubular member (4) with a helical outer surface (16) providing contact points (23) around the periphery of the tube (4) which engages with the inner surface of an outer tube (12) so as to create a plurality of baffles (15). A fluid will therefore be constrained to flow along the path defined by the baffles (15) with a transfer of thermal energy to or from a fluid flowing through helical tube (4) in the direction of arrow (F). The use of the heat exchanger (1) in natural convection and forced convection hot liquid boilers is described.

Description

HEAT EXCHANGER

BACKGROUND OF THE INVENTION

The present invention relates to improvements in and relating to heat exchangers.

To the present time various types of heat exchangers are available operating either off a primary source of heat or making use of waste heat. Typically in such heat exchangers their design will be such as to maximise the heat transfer between the heating and the heated fluids and this requires an appropriate design of the fluid flow paths within the heat exchanger.

In conventional shell and tube heat exchangers there can be difficulty in obtaining a sufficiently high coefficient of transfer between the fluids while achieving an appropriate pressure drop characteristic. Typically in such shell and tube heat exchangers the design of the baffle system defining the fluid flow paths can be a compromise between the desired fluid flow paths and the resultant thermal efficiency and pressure drop.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a heat exchanger which will achieve a good coefficient of heat transfer and which will avoid or at least obviate problems in heat exchangers to the present time or which at least will provide the public with a useful choice.

Further objects of this invention will become apparent from the following description.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a heat exchanger including one or more tubular members the or each of which has provided therein a helical tubular member the outer surface of which contacts the tubular member forming baffles which define a helical fluid flow path for a first fluid and wherein a second fluid to r transfer heat energy to or from the first fluid can flow through the helical member.

According to a further aspect of the present invention a heat exchanger as defined in the paragraph immediately above includes a _n further tubular member extending through the helical member to define a further fluid flow path.

Suitably the helical member may include a heat exchange conduit incorporating the technology of New Zealand Patent No. 255609 of the present applicant. 5

According to a still further aspect of the present invention a heat exchanger is substantially as herein described and/or with reference to any one of the embodiments of the accompanying drawings. 0

Further aspects of this invention which should be considered in all its novel aspects will become apparent from the following description given by way of example of possible embodiments of the invention and in which reference is made to the accompanying drawings. 5

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 : shows very diagrammatically a cross-sectional view of a heat exchanger according to one possible embodiment of the invention; 0

FIGURE 2: shows diagrammatically a cross-sectional view of a heat exchanger according to a further embodiment of the present invention;

5 FIGURE 3: shows diagrammatically an enlarged cross-sectional view of part of the heat exchanger of either Figure 1 or Figure 2;

FIGURE 4: shows an end view of the heat exchanger conduit arrangement of Figure 3 with a further embodiment indicated in outline;

FIGURE 5: shows diagrammatically part of a heat exchanger according to one possible embodiment of the invention;

FIGURE 6: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention;

FIGURE 7: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention;

FIGURE 8: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention;

FIGURE 9: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention;

FIGURE 10: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention;

FIGURE 1 1 : shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention; and FIGURE 12: shows diagrammatically part of a heat exchanger according to a further possible embodiment of the invention.

5

BRIEF DESCRIPTION OF POSSIBLE EMBODIMENTS

The present invention will for simplicity be described throughout in respect of a heat exchanger where heat is being added to the heated , « fluid. The heating and heated fluid flow paths can be interchanged in many instances and the specification where it uses these terms should be construed accordingly. It will be appreciated however that equally the present invention can be used for cooling or refrigerant purposes where heat is being extracted from a fluid to cool it and the present

. -. specification should be construed accordingly.

I b

As is well understood where one of the fluids is a refrigerant it would start as a gas and condense to a liquid releasing its heat energy, whereas in an evaporator one of the fluids would be a low temperature liquid which absorbs heat in order to vaporise.

20

Referring firstly to Figure 1 a possible embodiment of the present invention is indicated generally by arrow 1 in which the fluid to be heated can enter through the left hand inlet 2 in a direction indicated by arrow A and having been heated to a required temperature will leave

25 from the outlet 3 in a direction indicated by arrow B. The path of the fluid to be heated is through the one or more tubes 4 extending longitudinally between the end plates 5 and 6. The inlet and outlet 2 and 3 are respectively provided on outer plates 7 and 8 which may as shown be held together by a suitable threaded rod assembly 9 or the like

30 with appropriate gaskets or other sealing means being provided as appropriate (not shown). Such a threaded bolt assembly 9 has the advantage in enabling the plate 8 for example to be removed by release of the nuts 10 for example for cleaning purposes or repair.

35 The heating fluid such as steam, hot gas or the like will enter the heat exchanger 1 through an inlet referenced 1 1 to then pass through one or more tubes 1 2 each of which in the embodiment shown in Figure 1 being mounted so as to surround a respective tube 4. The cooled gas or fluid, or condensate in the case of steam will then leave through the outlet 1 3 at the bottom of the heat exchanger 1 .

In achieving good thermal efficiency it is necessary to control the flow of the heating fluid in the space between the tube 4 and the respective tube 1 2.

Turning therefore to Figures 3 and 4 it is seen that each of the tubes 4 is provided with a substantially helical outer surface referenced generally by arrow 1 6 to provide contact points 23 around the periphery of the tube 4 engaging with the inner surface of the outer tube 1 2 so as to effectively create a plurality of baffles 1 5 which will constrain the heating fluid to flow in a substantially helical path around the outside of the inner tube 4.

In Figure 1 the inlet and outlets 2 and 3 of the heat exchanger 1 for the fluid to be heated are substantially at the same level. A possible problem with such an arrangement is the tendency for air to be trapped in the upper tubes 4. In Figure 2 therefore in an alternative embodiment indicated by arrow 1 ' the heat exchanger is shown with the outlet 3' at a higher level than the inlet 2' so that in travelling through the heat exchanger 1 ' the fluid to be heated needs to travel through the upper tubes 4' and in doing so will expel any residual air which may otherwise be trapped in the exchanger 1 '.

Referring to Figure 5, one possible embodiment of the invention is shown as a non-vented heat exchanger and, in this simple form as illustrated, has the heating fluid travelling in a direction indicated by arrows X with the fluid to be heated travelling in a direction indicated by arrows Y, the latter path of the travel being through an inner helical conduit 4" defining baffles 5" between its outer surface and the outer tube 1 2" . In another embodiment, illustrated very diagrammatically and in simple form in Figure 6, the heating fluid is travelling in a direction indicated by arrows X, the fluid to be heated is travelling in a direction indicated by arrows Y through a central tube indicated by reference numeral 1 9 extending through an outer helical conduit referenced by arrow 4' " the helical outer surface of which forming baffles 5' " defining the flow path of the heating fluid as it travels in the direction indicated by arrows X between the outer tube 1 2" and the helical conduit 4' ". In this embodiment venting is achievable between the inner tube 1 9 and the helical tube 4'" as indicated by the arrows N on the left hand side of the Figure.

As a further illustration of the embodiment of Figure 6, in Figure 4 the tube 1 9 is shown in outline positioned within the helical conduit 4. The use of an additional central tube 1 9 for the fluid to be heated can be of particular advantage where that fluid has strict hygiene requirements or perhaps may be volatile and may require a totally hygienic or isolated flow path which could be supplied by special and/or separate tubing 1 9 which in an overall heat exchange system could be adapted to allow cleaning in place (CIP) as required.

Referring now to Figure 7, the same reference numerals being used as in Figure 5, the present invention is shown being used in a forced convection counter flow hot liquid boiler in which a flame F is providing the heat source with exhaust indicated by arrow Y and with the cold liquid entering as indicated by arrow X at the top of Figure 7 and the hot liquid leaving as indicated by arrow X at the bottom of Figure 7.

Similarly in Figure 8, with the same references as used as in Figure 6 the flame source F is providing the heating for the forced convection counter flow hot liquid boiler and again with the cold liquid inlet flow at the top of Figure indicated by the arrow X and the hot liquid exiting at the bottom of Figure 8, again shown by arrow X. Once again venting is achievable between the inner tube 1 9 and the helical tube 4'" as indicated by the arrows N on the left hand side of Figure. Referring as to Figure 9, the same references as used in Figure 7 are repeated where appropriate.

This embodiment shows the present invention used for a natural convection contra flow hot water boiler with the cold liquid entering as indicated by arrow X at the top of Figure 9 and the hot liquid exiting as indicated by the arrow X at the bottom of Figure 9. A flame source F provides the heat energy and as indicated by the arrows C showing the current flows, when flow X is not being drawn through, the liquid recirculates by natural convection. Liquid trapped in the spirals provided by the baffles 5 ' heats and expands and rises creating a rising current until the required temperature is reached.

Similarly in Figure 10, with the same reference numerals being used as in Figure 8, the flame source F provides the heat energy and the thermal currents C are set up, as the liquid trapped in the spirals defined by the baffles 5 is heated and expands.

Referring now to Figure 1 1 , again the same reference numerals as used in Figure 7 are retained, with the invention in this embodiment being used for high pressure fluid and gases including steam. Here the flame source F provides the necessary heating and the high pressure fluid or gas entering on the left hand side as indicated by arrow X is heated and leaves on the right hand side of Figure 1 1 .

In the alternative embodiment of Figure 1 2, with the same references being used as in Figure 8, again the high pressure fluid or gas is shown entering on the left of Figure 1 2 and after heating is leaving as indicated by arrow X on the top right of Figure 1 2.

It is seen therefore that by utilising a helical conduit, such as covered by New Zealand Patent 255609 for example, as one of the heat transfer tubes in a heat exchanger the helical outer surface of the conduit can provide the baffles for the heat exchanger in a simple yet effective manner. While the helical conduit of our New Zealand patent 255609 provides one possible option it is to be understood that any other helical tube manufactured from any suitable material by any suitable technique could be utilised in the present invention.

Where in the foregoing description reference has been made to specific components or integers of the invention having known equivalents then such equivalents are herein incorporated as if individually set forth.

Although this invention has been described by way of example and with reference to possible embodiments thereof it is to be understood that modifications or improvements may be made thereto without departing from the scope or spirit of the invention as defined in the appended claims.

Claims

CLAIMS:

1 . A heat exchanger including one or more tubular members the or each of which has provided therein a helical tubular member the outer surface of which contacts the tubular member forming baffles which define a helical fluid path for a first fluid and wherein a second fluid to transfer heat to or from the first fluid can flow through the helical member.

2. A heat exchanger as claimed in Claim 1 in which a further tubular member extends through the helical member to define a further fluid flow path.

3. A heat exchanger as claimed in Claim 1 or Claim 2 in which an inlet for one of said fluids is at substantially the same level as an outlet for the fluid after heat transfer.

4. A heat exchanger as claimed in Claim 1 or Claim 2 in which an inlet for one of said fluids is at a lower level than an outlet for the fluid after heat transfer.

5. A heat exchanger as claimed in Claim 2 in which an air flow path is provided between said helical tubular member and said further tubular member to provide venting.

6. A heat exchanger as claimed in Claim 1 in which heating is provided for the second fluid in an inner tubular member extending through said helical member.

7. A heat exchanger as claimed in Claim 6 where the heating is provided by a flame source.

8. A heat exchanger as claimed in Claim 6 or Claim 7 wherein said first fluid is a high pressure fluid which travels in the same or counter direction as the second fluid heated by the said heating.

9. A forced convection hot liquid counter flow boiler including a heat exchanger as claimed in Claim 8.

10. A natural convection contra flow hot liquid boiler incorporating a heat exchanger as claimed in Claim 8.

1 1 . A heat exchanger substantially as herein described with reference to any one of the embodiments of Figures 1 to 1 2 of the accompanying drawings.