AU609438B2 - Flue construction - Google Patents

Description

609438 l L

AUSTRALIA

Patents Act 1952 FO'RM COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. C Application Number: Lodged: Complete Specification Lodged: Accepted: Lapsed: Published: Priori ty: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Stewart Henry WICKS and Peter John FAASE Mr A W Tilley Rheem Australia Limited Brodie Street Rydalmere NSW 2116 Complete Specification for the Invention entitled: "FLUE CONSTRUCTION" The following statement is a full description of this invention, including the best method of performing it known to me: A203F TO: The Commissioner of Patents 051007.B33 1 This invention relates to a tank for storing of heated liquid, the tank being heated by the combustion of a fuel under the tank. It further relates to a flue construction in association with the tank to maximise the effectiveness of heat transfer from of gaseous products of combustion as they flow from the combustion location past the external surface of the tank to a point of ultimate exhaust. Specifically it eoo relates to a flue construction surrounding the external o 0* vertical wall surfaces of a tank.

mo11I Io I "0 One relevant application of the invention exists in 00 o relation to serially produced gas fuelled storage hot water systems, these being very commonly mains pressure type. This o0 particular application is relevant because continual attempts have been made over a long period to improve the efficiency 0 of such heaters while providing designs amenable to efficient mass production. The use of the invention extends broadly but is described in the following specification with most 0o°° frequent referenc, to the area of gas fuelled hot water systems.

The invention particularly concerns an improved flue construction in which a flue space is defined by a flue liner surrounding the external wall of the tank. It further extends to a means of achieving a division of this flue space by a straightforward means from a mass production point of viewso as to provide a path where flue gases can exchange heat during an upward pass through part of the flue and also during a downward pass through another part of the flue so as to reach a point of outlet from the flue with a minimal i~ :i residual amount of heat energy when discharged.

1 a. f 0 0 30 *0(I *0 S01 ft 04 p* p p *r Means of improving the efficiency of gas fuelled hot water systems including boilers are documented in patent ari other literature. For example, Australian patent application number 18306/76 in the name of J E Geary and U S patent 2687747 in the name of 0 L Bock both disclose hot water heating apparatus comprising a tank having at least one flue, extending through the water space, in which heat losses from the flue gases are said to be reduced by provision of baffles in the flue space. The experience jf the present applicant is that the improvement obtained by baffles, while significant, still leaves much room to extract theoretically available heat energy from the gas consumed.

Although well known and widely used, tanks having a flue extending through the water space are, from the standpoint of a manufacturer of a range of hot water systems, a distinctly different item for production and inventory purposes than a tank for electric heating having no flue.

Thus, an effective externally flued as distinct from an internally or centrally flued tank for a gas fuelled heater would enable the use of a common tank for both gas and electric heated models. The present invention provides an advantage to a manufacturer of a range of heaters in enabling rationalisation of production by meeting an existing market need with a reduced number of sub-assembled and component parts. Furthermore, the tank construction not involving a flue through the water space is very much easier to effectively internally coat with vitreous enamel to provide

I

t 2 1 the usual corrosion resistance required of such tanks.

Australian petty patent number 517176 in the name Vulcan Australia Ltd discloses a gas fuelled liquid heater in which a flue path surrounding a storage tank is provided having an upward and downward leg, the upward leg of the flue path in this case being in contact with the the lower part of the external wall of the tank and the downward leg being 0 outwardly disposed and concentric with respect to the upward 41i4 leg and therefore not in heat transfer relationship with the 4 tank. As will be fully described below, in the present 0" invention all upward and downward portions of the flue path are in heat transfer relationship with the tank, providing 0 1 conditions for improved thermal efficiency and more simple manufacture than the liquid heater as described in petty 4 s patent 517176.

o 0 The invention conseists of a flue construction for a 0455 liqui storage tank heated by a fuel burner under the tank, said flue construction comprising a substantially vertically arranged surface of the tank and a flue linrer disposed outwardly from the surface and enclosing the vertically arranged surface of the tank thereby defining a flue space which is divided into separate flow regions by a flue space divider, said regions comprising one fully peripherally extending region for initial upward flow, one partly peripherally extending divided region for continuing upward flow and one partly peripherally extending divided region for downward flow and wherein said flue space divider has one lower joint intermediate two higher points at opposite ends S-3-i 1 thereof and wherein said partly peripherally extending divided regions intercommunicate through an opening defined between the said two higher points of the divider and the adjacent tank wall and flue liner and wherein an exhaust opening is provided in the flue liner adjacent to a point low in the downward flow region; whereby the gaseous phase combustion products are enabled to flow from below the tank 0oa0 through said flue space in an upward and downward path to :o thereby heat said tank contents before being exhausted from the flue space through said exhaust opening.

4 0 o 0 00 In a highly preferred and significant embodiment the invantion consists of a flue construction as described in the a preceding paragraph in which the entire vertically arranged surface of the tank is contained within the flue space. The 0 o significance of this form of construction is that a maximum 0 a simplicity of construction of the flue liner is combined with *o r a maximum available area for heat transfer from the flue space into the tank.

In a further preferred embodiment the invention consists of a flue construction as described in any one of the preceding two paragraphs, in which the flue space divider is formed in a generally arcuate shape such that the combustion product flow regions bounded in part by the flue space dividei- have flow paths of gradually decreasing cross-sectional area. The importance of this embodiment is i that the flow is encouraged to take place at a greater L velocity through a significant part of the flue space than would be the case if the flow path cross-sectional area did -4 1 not progressively decrease, bearing in mind the fact that the combustion products progressively cool down during their passage through the flue space and thus their specific volume reduces while the mass flow rate remains constant; it is believed that the reducing cross-section encourages minimum drag in the flow and so assists in an optimum natural aspiration of combustion products through the flue space during heating up using a main burner. This is important in assisting proper combustion of the fuel. The preferred VO gradual and smooth change in cross-sectional area of the o divided part of the flue is also thought to assist a balancing of the warm combustion products in the flue space when on standby with the main burner not alight but a small pilot flame alight. This avoids unnecessary thermosyphoning of cooling air through the flue space when the tank is holding its full thermal capacity and so standby losses are minimised. This is equivalent to sayinag that the maintenance rate of a hot water system made using the flue construction 1:11* as described is low; this means that when no hot water demand is being made on the tank a low amount of fuel Is required to maintain the set poi nt temperature agai nst heat losses from the system.

In order that the present invention may be more clearly understood a preferred embodiment of an apparatus in accordance with the invention will now be described. The ensuing description refers to a non-limiting example only, as illustrated in and described with rz~ftorence to -the accompanying drawings, wherein: i 1 Figure 1 is a side elevational view to a reduced scale of a water heater in which a flue construction according to the invention may be usefully employed.

Figure 2 is a cross-sectional plan view of the water heater of Figure 1 sectioned at the plane II-II shown on Figure 1.

4 Figure 3 is a cross-sectional elevation view of the o0 4 water heater of the preceding Figures showing aspects of the flue construction according to the invention, sectioned as indicated by the line III-III of Figure 2.

4 o. O Figure 4 is a cross-sectional plan view of the water heater of the preceding Figures showing aspects of the flue o construction according to the invention, sectioned as indicated by the line IV-IV of Figures 1 and 3.

Figure 5 is a cross-sectional elevation view of the water heater of the preceding Figures showing aspects of the flue construction according to the invention, sectioned as indicated by the line V-V of Figure 4.

Figure 6 is a cross-sectional plan view of the water heater of the preceding Figures showing aspects of the flue construction according to the invention, sectioned as indicated by the line VI-VI of Figure Figure 7 is a cross-sectional plan view of the water heater of the preceding Figures showing aspects of the flue i III I;-a -a 1 construction according to the invention, sectioned as indicated by the line VII-VII of Figure 1.

Figure 1 shows an outer jacket 10 of a water heater 11 fixed tp one vertical wall of which is a balanced flue terminal 12. The heater is illustrated as supplied for plumbing connection to a source of mains water (not shown) oo- and to a source of fuel such as gas fed via controlling o *regulator 13 (Figs 1 4) to a burner (not shown).

1* [,Q 0 o Figure 2 shows in addition to most features referenced in Fig 1 a cylindrical tank 20 surrounded by a flue liner 21 surrounded in turn by a heat insulation layer 22, all three items enclosed within the outer jacket 10. The outside 9 0* surface of the tank wall and the inside surface of the flue 1° liner define a flue space 23 which is partly occupied by 0o flue space divider 24.

"lut d Figure 3 shows in elevation view all the features shown in Figs 1 2 together with gas burner 31 set below condensate drainage plate 32 which has drainage channel 33 J and drainage hol' 34 through which liquid condensate drains down and escapei from the flue space. The flue space 23 is defined to extend from the height of the burner to a top wall 35 of the flue liner and including the annular region as described with reference to Fig 2. The flue space divider 24 is illustrated as being made of a length of flexible fibrous heat resisting cord of thickness such as to fully occupy in a tight fit the radial dimension of the annular portion of the flue space. The positioning of the flue divider as seen with 7 -m 1 reference to Figs 3 5 is such that it has two ends positioned toward the top of the flue space in the vicinity of the junction 36 between the vertical wall of the tank and the top end 37 at points on the vertical wall approximately diametrically opposite; between the two ends, the flue divider extends downwardly to a central lowest point 38 intermediate between the top and bottom of the annular oo portion of the flue space. The flue space divider defines S three distinct regions of the flue space; the first is an a 0 "1 undivided region adapted to allow upward flow of combustion products issuing from the burner. The second and third regions are respectively for upward and downward flow of combustion products in their passage through the flue space s4 as illustrated by numerous small arrows in Fias 3 and around the top of the flue space divider ends and down to the 44 S lowest point of te divider where an outlet 39 is provided to S duct the by now relatively cool combustion products out °or, through the flue liner, thence the insulation layer and outer jacket, to an upper division in the balanced flue terminal 12 from which they escape to the atmosphere. Additional provision (not shown) is made at the lowest point 38 of the third region (i e the downward flow flue space region) for additional drainage of condensate from the flue space to the exterior of the flue. A short pipe 40 is provided above the central part of th drainage plate 32 to improve combustion and aspiration of ir to displace combusted products from the flue space. Air for combustion is drawn from a corner outside the flue liner through holes 41.

Figure 4 shows flue divider 24' and outlet 39 in 8 T I tl -I, 99*4 9 *9 0* 4 446 44 9Y) 94 9 44b 9 99a 4*I 9 9 49l 44 44 4 3O r 0 4 4 t a« sectional plan view. Cold water connection 42 (external to the jacket 10) is shown.

Figure 5 shows features included in Figures 1 to 4 as well as cold water inlet 51 to the tank and hot water outlet 52 from the tank. The disposition of divider 24 is clarified with the aid of a partial cut away view of the tank and a dotted outline of the hidden portion of the divider.

Figure 6 shows an alternative view where certain features as referenced in Figs 1 to 5 are repeated.

Figure 7 shows a cross-section in which air inlet 71 from the lower portion of the balanced flue terminal) into the square cross section outer jacket enables air for coirustion to be obtained from the terminal through the jacket wall down the space 72 created in the corner by fitting cylindrical inner components (tank and flue liner) into a square cross-section outer Jacket. As best seen by reference to Fig 51 holes 41 in the flue liner provide a path for air required for combustion of the fuel from corner spare 72 into the combustion zone.

Alternative constructional details may be embodied, one being the provision of a concave bottom end of the tank instead of the convex bottom as illustrated and best seen in Figs 3 Lnd 5, The flue space divider 24 is conveniently made from a material of uniform compoition and dimension from end to end as described in the preferred embodiment but need not be restricted to such a form; it is preferred that the divi der 24 be a heat insulating material at least near the lower, central portion of it.

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Claims (4)

1. A flue construction for a liquid storage tank heated by a fuel burner under the tank, sai: flue construction comprising a substantially vertically arranged surface of the tank and a flue liner disposed outwardly from the surface and enclosing the vertically arranged surface of the tank thereby defining a flue space which is divided into separate flov regions by a flue space divider, said regions comprising one fully peripherally extending region for initial upward flow, one partly peripherally extending divided region for continuing upward flow and one partly peripherally extending divided region for downward flow and wherein said flue space divider has one lower point intermediate two higher points at opposite ends thereof and wherein said partly peripherally extending divided regions intercommunicate through an opening defined bhoween the said two higher points of the divider and the adjacent tank wall and flue liner and wherein i exhaust opening is provided in the flue liner adjacent to a point low in the downward flow region; whereby the gaseous phase combustion products are enabled to flow from b;*low the tank through said flue space in an upward and downward path to thereby heat said tank contents before being exhausted from the flue space through said exhaust opening.

2. A flue construction as claimed in claim 1 in which the entie vertically arranged surface of the tank is contained within the flue space. 11 1

3. A flue construction as claimed in any one of claims 1 and 2 in which the flue space divider is formed in an arcuate path.

4. A flue construction for a liquid storage tank heated by a fuel burner under the tank substantially as described and as illustrated with reference to the accompanying t" illustrations. Ir DATED this 7th day of December 1987 Si RHEEM AUSTRALIA LIMITED St lt 0#0i. 7 3P i A A203P 12