GB2444274A

GB2444274A - Thermal acoustic baffle

Info

Publication number: GB2444274A
Application number: GB0623991A
Authority: GB
Inventors: Tom Collins; Norbert Volkmann
Original assignee: BBT Thermotechnology UK Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 2006-12-01
Filing date: 2006-12-01
Publication date: 2008-06-04
Also published as: WO2008065361A1; GB0623991D0

Abstract

The thermal acoustic baffle 38, preferably for a heat exchanger 25 for a boiler, includes a body 40 for location in a flue gas flow path of the boiler. A turbulating means 50 imparts turbulence to flue gas flowing past the baffle 38. A sound absorbing means 52 absorbs sound transmitted through the flue gas flowing past the baffle. Preferably the body 40 of the baffle 38 includes a chamber 44 therein, and the sound absorbing means is provided in the chamber. The baffle may be used in a boiler with a heat exchanger or in a method of promoting turbulence in a boiler.

Description

I

THERMAL ACOUSTIC BAFFLE

This invention relates to a thermal acoustic baffle which is suitable for use with a heat exchanger of a boiler, to a heat exchanger having such a thermal acoustic baffle, and to a boiler having a heat exchanger with such a baffle.

In boilers, for example gas and oil fired boilers used for domestic or commercial central heating and hot water supply, it is preferable to maximise the heat transfer from the flue gas to water in a surrounding water gallery. However, noise generated by the burner, combustion and flow of gasses can be substantial, and it is not unusual to include a sound absorber along the flue gas flow path.

The disadvantage with the inclusion of an independent sound absorber is that space within the boiler is inevitably reduced, or has to be increased to acconmiodate the sound absorber. This has a further consequence that, inevitably, the pressure drop of the flue gas through the boiler is increased.

Additionally, the harsh environment and extreme temperatures generated internally within the boiler, typically in the range of 800 C to 1000 C prior to high-temperature heat exchange and then typically in the range of 30 C to 200 C following low-temperature heat exchange, make the manufacture and materials used of critical importance.

The present invention therefore seeks to overcome these problems.

According to a first aspect of the invention, there is provided a thermal acoustic baffle for a boiler, the baffle comprising a body for location on a flue gas flow path of the boiler, turbulating means for imparting turbulence to flue gas flowing past the baffle, and sound absorbing means for absorbing sound transmitted through the flue gas flowing past the baffle.

Preferable and/or optional features of the first aspect of the invention are set forth in claims 2 to 16, inclusive.

According to a second aspect of the invention, there is provided a heat exchanger for a boiler, the heat exchanger comprising one or more flue gas channels, and a thermal acoustic baffle in accordance with the first aspect of the invention, mounted in the or each flue gas channel.

Preferable and/or optional features of the third aspect of the invention are set forth in claim 19 and claim 20.

According to a third aspect of the invention, there is provided a boiler comprising a housing having spaced inner and outer shells which defme therebetween a liquid gallery through which a liquid to be heated can flow, an internal combustion compartment adjacent to the liquid gallery, a burner for providing combustion in the internal combustion compartment, a heat exchanger for transferring heat from flue gas exiting the internal combustion compartment to the liquid in the liquid gallery, the heat exchanger including one or more flue gas channels, a flue gas flow path along which flue gas exiting the internal compartment can flow, and a thermal acoustic baffle in accordance with the first aspect of the invention provided on the flue gas flow path.

Preferable and/or optional features of the fourth aspect of the invention are set forth in claims 23 to 26, inclusive.

According to a fourth aspect of the invention, there is provided a method of simultaneously promoting turbulence for heat transfer in flue gas in a boiler and absorbing sound transmitted through the flue gas, the method comprising the step of locating a baffle on a flue gas flow path of the boiler, the baffle having turbulating means for imparting turbulence to flue gas flowing past the baffle, and sound absorbing means for absorbing sound transmitted through the flue gas flowing past the baffle, the baffle having a major length dimension over which flue gas flows, the turbulating means imparting turbulence to the flue gas as the flue gas flows over the distance of the major length dimension, and a minor thickness dimension which optimises velocity of the flue gas flowing across the major length dimension, the sound absorbing means having dimensions corresponding to the major length dimension and the minor thickness dimension of the baffle.

Preferably and/or optional features of the fifth aspect of the invention are set forth in claims 29 to 31, inclusive.

The present invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a front elevational view of a boiler, in accordance with the fourth aspect of the invention; Figure 2 shows a cross-sectional view taken along line A-A in Figure 1; Figure 3 shows an exploded perspective view of a thermal acoustic baffle, in accordance with the present invention; and Figure 4 shows an exploded flue gas channel with the thermal acoustic baffle located therein.

Referring to the drawings, there is shown a boiler 10 having a housing 12 with inner and outer shells 14, 16 which are fixed in spaced relationship and which define therebetween a water gallery 18 which extends around all sides of the inner shell 14, except for the front. The inner shell 14 defines an internal combustion chamber 20, and a cross-firing burner 22 is provided on one side of the housing 12 to project into the internal combustion chamber 20.

The front of the internal combustion chamber 20 includes a cover 24 which matches or substantially matches the height of the internal combustion chamber 20 and which is openable, and typically fully removable, to allow unhindered access for maintenance and cleaning, for example.

The internal combustion chamber 20 is connected to a primary heat exchanger 25 via openings in its upper surface. The heat exchanger 25 defines multiple flue gas channels 26, in this case four, which are positioned in spaced parallel relationship and which extend, typically vertically, through the water gallery 18. Each flue gas channel 26 has a uniform rectangular or substantially rectangular cross-section, both in a plane parallel to the direction of flow of flue gas through the flue gas channel 26, and perpendicular thereto.

However, the flue gas channels can be of any suitable cross-section, either circular or non-circular, and can be, for example, cylindrical, square or even triangular.

The flue gas channels 26 have outlets 28 positioned in an upper surface of the outer shell 16 of the housing 12. The interior of each flue gas channel 26 is isolated from the water gallery 18.

A flue gas chamber 30 is positioned on the upper surface of the outer shell 16.

Flue gas (arrows G) is directed along a flue gas flow path 33 defined within the boiler.

The flue gas enters the flue gas chamber 30 from the heat exchanger 25, and is directed to a secondary heat exchanger 34 mounted generally above the flue gas chamber 30. A flue gas discharge passage 36 conducts flue gas exiting the secondary heat exchanger 34 to a flue pipe and thus to the environment.

The flue gas chamber 30 may have an openable and/or removable cover to enable access to the flue gas channels 26 of the heat exchanger 25 from above and, via the internal combustion chamber 20, from below. Alternatively, the flue gas chamber 30 may be permanently sealed, and therefore access to the flue gas channels 26 is only from the internal combustion chamber 20.

To promote heat exchange, a thermal acoustic baffle 38 is mountable in one or each flue gas channel 26 of the heat exchanger 25. The thermal acoustic baffle 38 has a body 40 defined by two, typically metal, plates 42 fixed together, such as by mechanical joining or welding, along adjacent edges. The metal plates are typically stell or stainless steel, and can be solid, perforated or mesh. The plates 42 are shaped to define an envelope-like chamber 44 therebetween. The chamber 44 has a major top-to-bottom length dimension and a major front-to-back depth dimension which substantially match the corresponding length and depth dimensions of the plates 42. A minor side-to-side thickness dimension of the chamber 44 is such that, with the baffle 38 located in the flue gas channel 26, the exterior surfaces 46 of the plates 42 lie in close spaced relationship with the sides or walls 48 of the flue gas channel 26.

Typical dimensions of the baffle 38, the envelope-like chamber 44, and of the flue gas channels 26 are in the range of: length: 100 millimetres (mm) to 2000 mm; width: 5 mm to 100 mm; and height: 10 mm to 300 mm. More preferably, typical dimensions of the baffle 38, the envelope-like chamber 44, and of the flue gas channels 26 are in the range of: length: 100 mm to 200 mm; width: 5 mm to 20 mm; and height mm to 300 mm.

Each plate 42 includes a plurality of integrally formed dimples 50 or ridges which project externally. The dimples 50 or ridges form turbulating means for imparting turbulence to hot flue gas flowing past the baffle 38. Sound absorbing material 52, such as mineral-fibre wool or any other material suitable for the temperatures and conditions, is encased in the envelope-like chamber 44 for absorbing, in particular low frequency, sound transmitted through the flue gas. Typically, all or a significant proportion of the entire volume of the envelope-like chamber 44 is taken up with the sound absorbing material 52.

The plates 42 of the baffle 38 are perforated with small openings or apertures 54 across all or a significant proportion of the surface in contact with the sound absorbing material 52, including the turbulating means to aid sound absorption. The apertures 54 have a typical diameter in the range of 0.5 mm to 10 mm, and can be uniformly or randomly space apart. Each aperture 54 extends fuiiy through the thickness of the respective plate 42 to enable fluid communication between the exterior of the plate 42 and the chamber 44.

Each baffle body 40 includes hooks, slots or tabs 56 to enable the baffle 38 to be fixed or, for example, suspended in position in the flue gas channel 26. There are also features in the baffle 38, such as holes 58, to aid in the removal of the baffles 38 for service and cleaning of the baffles 38 and heat exchanger flue gas channels.

In use, the turbulating means 50 of the baffle 38 imparts turbulence to the flue gas as it travels through the flue gas channel 26. This promotes heat transfer to the walls 48 of the flue gas channel 26 and thus heat transfer to the water contained in the water gallery 18.

Due to the smooth and uniform form of the turbulating means 50, and the uniform cross-section in two-dimensions transverse to the direction of flow of the flue gas through the flue gas channels 26, the pressure drop of the flue gas across the baffle 38 is low. Thus, the baffle 38 imparts low flow restriction to the flue gas.

Furthermore, excellent low frequency sound absorption occurs due to the relatively large effective depth of the acoustic material parallel to the direction of sound travel, this depth being approximately equal to the length of the baffle 38 and irrespective of the thickness of the baffle 38 and thus the thickness of the sound absorbing material 52.

For maintenance, the baffle 38 is detached from the flue gas channel 26 and removed. A wire brush or other suitable cleaning means is then used to agitate and remove deposits built up in the apertures 54 of the perforations and on the surface of the baffle 38.

The aperture size of the perforations can be altered during production, and/or the dimensions and/or type of sound absorbing material 52 can be selected, in order to tune' the baffle 38 to absorb specific sound frequencies. This is important so that the baffles can be utiised with boilers having different capacities. For example, domestic boilers extend up to at least 70kW, and commercial boilers typically extend far higher than this.

Typically, it is desirable to absorb low frequency noise. However, by utiismg two or more specific sound absorbing materials 52, a broader range of frequencies may be absorbed, such as high and low frequency noise.

Although externally projecting dimples or ridges are used as the turbulating means, any externally projecting element on an exterior surface of the body can be utilised as turbulating means. Preferably, the externally projecting element is non-planar. However, the externally projecting element or elements can be planar or substantially planar, such as being a fin or fms. The turbulating means may also be separate of the apertures of the perforations.

The turbulating means are formed integrally or unitarily with the plates, for example by pressing. However, the turbulating means could be separately attached to the plates, for example by welding, brazing, or mechanical fixing methods.

Furthermore, the turbulating means may be provided, additionally or alternatively, on the walls of the flue gas channels. I0

Although the plates of the baffle body are fixed together, the baffle body can be formed to be open or openable, thereby allowing unhindered access to the sound absorbing material therein for maintenance and/or replacement.

It is also envisaged that the baffle body itself can be entirely formed from sound absorbing material, as a single piece or in a staged construction of one or more different materials. In this case, the plates are typically dispensed with, and the sound absorbing material can be, for example, a block of heat resistant sound absorbing ceramic material.

It is also conceivable that the baffle body, formed solely from sound absorbing material, can include turbulating means integrally or unitarily formed on its major exterior surfaces, such as by moulding. Consequently, the entire baffle, having turbulating means and sound absorbing means can be a single one-piece device.

Although a cross-firing burner is suggested, any suitable burner can be utiised and mounted at any suitable position, such as a down- firing burner.

In the above described example, the baffle is plate-like. However, other shapes are envisaged. For example, the baffle can be arcuate. In this case, a cross-section of the baffle can be circular, and typically the baffle will be cylindrical. The baffle can have a body formed in the shape of a cylindrical cage with turbulating means as described above. Sound absorbing material can be provided within the chamber formed by the cylindrical body.

It is also envisaged that the baffle could be helical, or in the form of a prism, for example a triangular prism, twisted or straight.

In the case where the baffle is formed from a single unitary piece of sound absorbing material, the baffle can be formed arcuately, cylindrically or with any desired shape. The turbulating means can be integrally formed as part of the arcuate baffle, or provided separately, as described above.

Although the baffle is shown as being held vertically, it can be positioned in any orientation, including horizontally. It is, however, preferable that the baffle extends in a plane which is in parallel or substantially in parallel with the direction of the flue gas flow path.

Through research, it has been established that, especially low frequency, noise is equally well absorbed when the perforations in the plates are dispensed with. Therefore, a baffle comprising a body, which has continuous or unbroken exterior surface, for example, by using solid or substantially solid plates, in which the sound absorbing material is encased, and which has turbulating means, can be used.

The term perforations' used herein throughout is intended to include openings or apertures, and can be provided by using mesh.

Although the or each baffle is described as being provided in a flue gas channel of a heat exchanger of a boiler, one or more of the baffles can, additionally or alternatively, be provided at any point on a flue gas flue path.

The sound absorbing material is positioned parallel to the direction of sound travel. This means that its effective depth to the sound is roughly equivalent to the length of the baffle, not the thickness of the sound absorbing material. Deeper sound absorbing material absorbs low frequency noise better.

The pressure drop of the baffle is low because it induces turbulence to the flue gas without forcing sudden changes in the gas velocity. The baffle maintains a uniform cross sectional area to gas flow and therefore a smooth change in velocity of the gas.

The induced turbulence improves heat transfer, the smooth change of gas velocity maintains a low pressure drop.

The noise to be absorbed or damped is primarily generated by combustion. This noise typically has a low frequency, generally less than or equal to 250 Hz. Fan noise from the burner is typically the second most significant contributor, with noise from gas flow and/or water effect having a relatively small effect.

A minor thickness dimension of the baffle, which is typically a leading edge of the baffle relative to the direction of flow of the flue gas, defines the cross-section in two-dimensions transverse to the direction of flow of the flue gas through the flue gas channels and therefore the mean velocity of the flue gas flowing across the major length dimension. In other words, the thickness of the baffle allows optimisation of the velocity of the flue gas, as it passes the baffle, thus allowing optimised sound absorption, turbulence, heat transfer, and pressure drop.

Although the or each flue gas channel is typically vertical, it or they could be at any orientation, including horizontal.

Although the secondary heat exchanger is mounted above the primary heat exchanger, it can be positioned at any point on the flue gas flow path downstream of the primary heat exchanger.

It will be understood that the components downstream of the combustion chamber, such as the primary and secondary heat exchangers, can be positioned anywhere relative to the combustion chamber, and do not necessarily have to be positioned above.

It has been suggested that access to the flue gas channels is from above and/or below. However, it will be readily understood that, depending on orientation of the flue gas channels, access can be, additionally or alternatively, from one or more sides.

The sound absorbing means can comprise the turbulating means, and vice versa.

For example, the sound absorbing means can be externally provided on the baffle body, and, in this case, the sound absorbing means can be formed with turbulating means.

Alternatively, the turbulating means can be provided on the baffle body, and the sound absorbing means can be incorporated as part of the turbulating means.

The turbulating means may be integrally formed as part of the baffle body, or may be separate of the body.

Various other forms of turbulating means can be considered. Even the fact that the baffle body has a dimension (typically thickness) which is presented to the flowing flue gas will cause turbulation, and therefore this is to be considered turbulating means.

It is thus possible to provide a baffle for use with a heat exchanger of a boiler which not only promotes heat transfer, but also absorbs undesirable sound transmitted through the flue gas. It is also possible to provide a method of simultaneously promoting turbulence in flue gas in a boiler and absorbing sound transmitted through the flue gas. The baffle is compact, thus maximising space utiisation within the boiler.

Further sound absorbing material, spaced from the heat exchanger, is thus not necessarily required, although provision can be made for inclusion. It is also possible to provide a baffle for use with a heat exchanger of a boiler which simply absorbs undesirable sound transmitted through the flue gas. The baffle can be tuned depending on the frequency or frequencies of sound to be absorbed.

The embodiments described above are given by way of examples only, and various other modifications will be apparent to persons skilled in the art without departing from the scope of the invention, as defined by the appended claims.

Claims

1. A thermal acoustic baffle for a boiler, the baffle comprising a body for location on a flue gas flow path of the boiler turbulating means for imparting turbulence to flue gas flowing past the baffle, and sound absorbing means for absorbing sound transmitted through the flue gas flowing past the baffle.

2. A thermal acoustic baffle as claimed in claim I, wherein the body of the baffle includes a chamber therein, the sound absorbing means being provided in the chamber.

3. A thermal acoustic baffle as claimed in claim 2, wherein the body includes two plates provided in close spaced relationship, the chamber being defined between the two plates.

4. A thermal acoustic baffle as claimed in claim 2, wherein the body has an arcuate perimeter, the chamber being provided within the perimeter.

5. A thermal acoustic baffle as claimed in any one of claims 2 to 4, wherein the chamber is sealed to prevent opening.

6. A thermal acoustic baffle as claimed in any one of claims 2 to 4, wherein the chamber is open or openable for removal of the sound absorbing material.

7. A thermal acoustic baffle as claimed in any one of the claims 2 to 6, wherein the body has a continuous or substantially continuous exterior surface.

8. A thermal acoustic baffle as claimed in any one of the claims 2 to 6, wherein the body includes perforations for fluid communication between the exterior of the baffle and the chamber.

9. A thermal acoustic baffle as claimed in claim 8, wherein the perforations are in the range ofO.5 mmto 10mm.

10. A thermal acoustic baffle as claimed in claim 8 or claim 9, wherein the perforations are incorporated with the turbulating means.

11. A thermal acoustic baffle as claimed in claim 1, wherein the turbulating means is integrally formed as part of the body.

12. A thermal acoustic baffle as claimed in claim 1, wherein the body, the sound absorbing means, and the turbulating means are integrally formed together as a single unitary device.

13. A thermal acoustic baffle as claimed in any one of the preceding claims, wherein the turbulating means includes at least one externally projecting element on an exterior surface of the body of the baffle.

14. A thermal acoustic baffle as claimed in any one of the preceding claims, wherein the turbulating means includes one or more raised portions on an exterior surface of the body of the baffle.

15. A thermal acoustic baffle as claimed in claim 14, wherein the or each raised portion is a dimple.

16. A thermal acoustic baffle as claimed in claim 14, wherein the or each raised portion is a ridge.

17. A thermal acoustic baffle substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

18. A heat exchanger for a boiler, the heat exchanger comprising one or more flue gas channels, and a thermal acoustic baffle as claimed in any one of the preceding claims mounted in the, each or one said flue gas channel.

19. A heat exchanger as claimed in claim 18, wherein the baffle is removably mounted in the flue gas channel.

20. A heat exchanger as claimed in claim 18 or claim 19, wherein the baffle is a close fit in the flue gas channel.

21. A heat exchanger substantially as hereinbefore described with reference to Figures 2 and 4 of the accompanying drawings.

22. A boiler comprising a housing having spaced inner and outer shells which define therebetween a liquid gallery through which a liquid to be heated can flow, an internal combustion compartment adjacent to the liquid gallery, a burner for providing combustion in the internal combustion compartment, a heat exchanger for transferring heat from flue gas exiting the internal combustion compartment to the liquid in the liquid gallery, the heat exchanger including one or more flue gas channels, a flue gas flow path along which flue gas exiting the internal compartment can flow, and a thermal acoustic baffle as claimed in any one of claims I to 17 provided on the flue gas flow path.

23. A boiler as claimed in claim 22, wherein the flue gas flow path is between the heat exchanger and the internal combustion compartment, and the thermal acoustic baffle is provided between the heat exchanger and the internal combustion compartment.

24. A boiler as claimed in claim 22, wherein the or each flue gas channel of the heat exchanger defines a portion of the flue gas flow path, and the thermal acoustic baffle is provided within the flue gas channel.

25. A boiler as claimed in any one of claims 22 to 24, wherein the or each flue gas channel extends upwards from a top surface of the internal combustion compartment and through the liquid gallery.

26. A boiler as claimed in any one of claims 22 to 25, wherein the or each thermal acoustic baffle is mounted in close spaced relationship with walls defming the flue gas flow path.

27. A boiler substantially as hereinbefore described with reference to Figures 1, 2 and 4 of the accompanying drawings.

28. A method of simultaneously promoting turbulence for heat transfer in flue gas in a boiler and absorbing sound transmitted through the flue gas, the method comprising the step of locating a baffle on a flue gas flow path of the boiler, the baffle having turbulating means for imparting turbulence to flue gas flowing past the baffle, and sound absorbing means for absorbing sound transmitted through the flue gas flowing past the baffle, the baffle having a major length dimension over which flue gas flows, the turbulating means imparting turbulence to the flue gas as the flue gas flows over the distance of the major length dimension, and a minor thickness dimension which optimises velocity of the flue gas flowing across the major length dimension, the sound absorbing means having dimensions corresponding to the major length dimension and the minor thickness dimension of the baffle.

29. A method as claimed in claim 28, wherein the dimensions of the sound absorbing means are selectable and are based on the noise frequency to be absorbed.

30. A method as claimed in claim 28 or claim 29, wherein the baffle is located in a heat exchanger of the boiler.

31. A method as claimed in any one of claims 28 to 30, utilising the thermal acoustic baffle as claimed in any one of claims I to 17.