Patent Publication Number: US-6666173-B2

Title: Hot gas liquid heater

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application No. 60/297,531 filed Jun. 13, 2001. 
    
    
     FIELD OF INVENTION 
     This invention relates to liquid heaters in which liquid flowing therethrough is heated by hot gas also flowing therethrough. The liquid may be water, but may of course be another liquid. 
     BACKGROUND OF THE INVENTION 
     Liquid heaters of the above general kind are well known. Usually, the liquid flows through at least one heat conducting pipe over which hot gas passes to heat the liquid therein. Problems which can arise with known water heaters of this kind include thermal shock imparted to the structure of the heater by temperature differences which occur within the heaters and corrosion caused by the hot gas or the liquid being heated. 
     It is therefore an object of the invention to provide an improved water heater of this kind in which such problems are minimized. 
     SUMMARY OF THE INVENTION 
     According to the invention, a hot gas water heater has a housing containing at least a pair of concentric spaced coils through which liquid to be heated is sequentially passed. Each coil has a helical tube with adjacent turns being connected by a web member such that the tube and web member form an imperforate coil wall. Hot gas is passed sequentially between the coils such that its flow is co-current with liquid flow in one adjacent coil and counter-current with liquid flow in another adjacent coil. 
     The hot gas may flow between a pair of adjacent coils in co-current flow with the liquid flow in the inner coil and in counter-current flow to the liquid flow in the outer coil. 
     The housing may have a central hot gas inlet through which hot gas passes to a central passage in the inner coil and a gas outlet which receives gas from a passage between an outer coil and a coil adjacent thereto. 
     At lease one coil may taper towards an adjacent coil in the direction of gas flow therethrough. There may be at least three or at least four concentric coils provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, of which: 
     FIG. 1 is a somewhat diagrammatic side view of a hot gas water heater in accordance with one embodiment of the invention, 
     FIG. 2 is a side view on an enlarged scale of a portion of one of the water carrying coils of the water heater, and 
     FIG. 3 is similar to FIG. 1 but shows another embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring first to FIGS. 1 and 2 of the drawings, a hot gas water heater has a cylindrical housing  10  with a central hot gas inlet  12  at one end and a gas outlet in the form of a chimney  14  at the other end. The housing  10  contains five concentric water-carrying metal coils  16 ,  18 ,  20 ,  22 ,  23  each constructed in the manner shown in FIG.  2 . The coil shown in FIG. 2 is identified as coil  16 , but it will be understood that the other coils  18 ,  20 ,  22 ,  23  are similarly constructed. 
     As shown in FIG. 2, the coil  16  comprises a helical water-carrying tube  24  with adjacent turns of a helical tube  24  being connected by a web member  25  such that the tube  24  and web member  25  form an imperforate annular coil wall. 
     The coils  16 ,  18 ,  20 ,  22  are supported in the housing in any suitable manner (not shown), preferably by suspension loops or an appropriate bottom support structure to provide a non-rigid mounting therein. The coil  16  has the smallest diameter and has one end located adjacent the gas inlet  12 . The coil  18  surrounds the coil  16  in spaced relationship therewith, the coil  20  surrounds the coil  18  in spaced relationship therewith, the coil  22  surrounds the coil  20  in spaced relationship therewith, and the coil  23  surrounds the coil  22  in spaced relationship therewith. 
     A gas burner and blower assembly  26  located adjacent the inlet  12  is operable to blow hot gas into the adjacent end of a central passage  27  formed by the coil  16 . The hot gas passes along the central passage  27  and, at the opposite end of the coil  16 , the hot gas encounters a circular wall  28  extending across the adjacent end of coil  18  which causes the hot gas to undergo a 180° change of direction and pass along an annular passage  30  between the coil  16  and the coil  18 . 
     After passing along the annular passage  30 , hot gas encounters an end wall  32  of the housing  10  and an annular barrier  34  between the housing end wall  32  and the adjacent end of the coil  20 . The hot gas is thereby caused to undergo a 180° change of direction and pass along an annular passage  36  between the coil  18  and the coil  20 . Similarly, after passing along the annular passage  36 , the hot gas encounters a wall  38  extending across the adjacent end of coil  22  which causes the gas to undergo a further 180° turn and pass along an annular passage  40  between the coil  20  and the coil  22 . 
     After passing along the annular passage  40 , the hot gas engages the end wall  32  of the housing  10  which causes the gas to undergo a further 180° turn and pass along an annular passage  42  between the coil  22  and the coil  23 , which is secured to a horizontal annular wall  44  of the housing  10 . After passing along the passage  42 , the hot gas engages an opposite end wall  46  of the housing  10  and travels upwardly to leave the housing  10  through the chimney  14 . 
     Cool water enters one end of outermost coil  23  through an inlet  48  and travels to the other end of the coil  23  by passing through its helical tube  24 . At the other end of coil  23 , the water passes through a transfer conduit  49  into one end of coil  22  and passes through its helical tube  24 . At the other end of the coil  22 , the water passes through a transfer conduit  50  into one end of coil  20  and passes through its helical tube  24 . At the other end of coil  20 , the water passes through a transfer conduit  52  into one end of coil  18  and passes therealong. At the other end of the coil  18 , the water passes through a transfer conduit  54  to innermost conduit  16  and passes therealong. At the other end of conduit  16 , the water leaves the housing through outlet  56 . 
     Thus, in use, hot gas from the burner and the blower assembly  26  passes along passages  27 ,  30 ,  36 ,  40  and  42  and transfers its heat through the coil walls to the water flowing therein, so that relatively cool water entering the inlet  48  is substantially heated by the time it reaches the outlet  56 . Likewise, the hot gas supplied by the burner and blower assembly  26  will have substantially cooled by the time it leaves the heater through chimney  14 . 
     It will be noted that, in accordance with the invention, the flow of hot gas through an annular passage between a pair of adjacent coils, i.e. annular passage  30 ,  36 , 40  or  42 , is co-current with the flow of water in the inner coil and counter-current to the flow of water in the outer coil, as can readily be observed from the arrows indicating the direction of water and gas flow in FIG.  1 . This provides less thermal shock on the water heater than would otherwise be the case. 
     FIG. 3 is similar to FIG. 1 but shows another embodiment of the invention. For ease of explanation, the same reference numerals are used to identify the same parts. In the embodiment of FIG. 3, coils  18 A and  22 A taper towards adjacent inner coils  16  and  20  respectively in the direction of flow of the gas to compensate for the contraction of the gas as it cools. 
     Other advantages and embodiments of the invention will now be readily apparent to a person skilled in the art from the foregoing description of a preferred embodiments, the scope of the invention being defined in the appended claims.