Abstract:
A fluid heater system for a pumping system comprises a core, a heating element and a sleeve. The core comprises a body made of thermally conductive material, and a plurality of channels formed on an outer periphery of the body. The heating element is disposed within the core. The sleeve surrounds the core adjacent the plurality of channels. The sleeve is formed of a material having a higher strength than the thermally conductive material of the core. In another embodiment, the plurality of channels is chamfered to form a portion of a common outlet plenum and the core includes a temperature sensor bore located proximate the common outlet plenum.

Description:
BACKGROUND 
       [0001]    The present invention relates generally to heaters that are used in industrial applications. More particularly, the invention relates to heaters that are used to provide variable heating to viscous fluids in conjunction with being dispensed by a pumping and spray system. 
         [0002]    In spray systems used with highly viscous materials, it is desirable to provide heat to the material within the spray system to facilitate pumping of the material to a spray gun. Specifically, elevated temperatures can reduce the viscosity of the material, making it easier to pump and spray. Highly viscous materials experience a large pressure drop when pumped through conventional heaters that utilize only a single passage through which the material flows. Various heaters have been developed in an attempt to reduce the pressure drop within the heater. Specifically, U.S. Pat. No. 4,465,922 to Kolibas describes a heated core having dual passages through which the material flows. Such a heater utilizes a core and a sleeve that covers the passages that are both fabricated from a thermally conductive material to maximize heat transfer throughout the heater. This heater also uses a temperature sensor that is disposed within an interior of the core proximate a mid-span location of the flow passages. There is a continuing need to improve the performance of heaters used in spraying systems to be able to withstand higher pressures and temperatures, and to be able to more accurately manage temperature of the pumped material. 
       SUMMARY 
       [0003]    A fluid heater system for a pumping system comprises a core, a heating element and a sleeve. The core comprises a body made of thermally conductive material, and a plurality of channels formed on an outer periphery of the body. The heating element is disposed within the core. The sleeve surrounds the core adjacent the plurality of channels. The sleeve is formed of a material having a higher strength than the thermally conductive material of the core. In another embodiment, the plurality of channels is chamfered to form a portion of a common outlet plenum, and the core includes a temperature sensor bore located proximate the common outlet plenum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a schematic of a spray system showing a heater positioned between a fluid pump and a spray gun. 
           [0005]      FIG. 2A  is a perspective view of the heater of  FIG. 1  showing an enclosure connected to a sleeve positioned between an inlet housing and an outlet housing. 
           [0006]      FIG. 2B  is an exploded view of the heater of  FIG. 2A  showing a multi-channel core and heat cartridges extended from the sleeve. 
           [0007]      FIG. 3  is a partially cut-away exploded view of the enclosure of  FIGS. 2A and 2B  showing the heat cartridges and a resistance temperature detector (RTD) connected to a circuit board. 
           [0008]      FIG. 4  is section  4 - 4  of  FIG. 2A  showing the location of the RTD of  FIG. 3  relative to an outlet plenum of the core. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]      FIG. 1  is a schematic of spray system  10  having heater  11  to which embodiments of the present invention are directed. In addition to heater  11 , spray system  10  comprises fluid container  12 , air source  14 , dispenser  16  and pump  18 . Spray system  10  is provided with pressurized air from air source  14  through air distribution line  20 . Air distribution line  20  is spliced into air source line  22 , which is directly coupled to air source  14 . In one embodiment, air source  14  comprises a compressor. Air source line  22  can be coupled to multiple air distribution lines for powering multiple dispensers. Air distribution line  20  includes other components such as filters  24 , valves  26  and air regulator  28 . Air motor assembly  34  is fed pressurized air from air distribution line  20  at air inlet  30 . Pump  18  is connected to ground  32 . The pressurized air drives air motor assembly  34  within pump  18 , which drives pump assembly  36 . After driving air motor assembly  34 , the compressed air leaves pump  18  at air exhaust port  38 . 
         [0010]    In one embodiment, pump  18  comprises a linear displacement piston pump such that air motor assembly  34  drives a piston within pump assembly  36 . Operation of the piston within pump assembly  36  draws a fluid, such as paint or an industrial coating, from container  12  through fluid line  40 . Fluid line  40  may include a suction tube having a check valve positioned to be submerged within container  12  to maintain priming of pump assembly  36 . Pump  18  pressurizes the fluid and pushes it into discharge line  42 , which is coupled to heater  11  at shut-off valve  41 . Fluid line  43  allows pressurized fluid to drain back to container  12  when director valve  44  is positioned to connect fluid line  43  and fluid line  40 . 
         [0011]    Heater  11  includes a heating device that heats the pressurized fluid between pump  18  and dispenser  16 . Fluid line  45  provides a return from dispenser  16  to pump  18  when director valve  44  is positioned to connect fluid line  45  and fluid line  40 . Fluid line  46  connects heater  11  and dispenser  16 . Dispenser  16  includes a manually operated valve that, when actuated by an operator, dispenses the fluid. In one embodiment, dispenser  16  comprises a spray gun having an orifice that atomizes the pressurized fluid. Back pressure valves  47  are positioned in fluid lines  45  and  46  to prevent back flow through system  10 . System  10  additionally may include pressure relief system  48  that allows pressurized fluid between heater  11  and dispenser  16  to be drained into container  49 . System  10  may also include filter  50  with drain valve  51  for screening impurities from the pressurized fluid. 
         [0012]    It is desirable to control the viscosity of the pumped fluid in particular spraying operations. Specifically, some fluids become less viscous at higher temperatures, which makes the fluids easier to pump and spray. For example, it is desirable to control the viscosity of fluids that are applied via dispensers employing atomized spraying techniques. Atomized spraying techniques apply a more even, consistent finish when the sprayed fluid has the same viscosity throughout the spraying operation. Heater  11  controls the temperature of the pressurized fluid between pump  18  and dispenser  16  to facilitate a more consistent spraying operation. Heater  11  may be actively controlled with electronics connected to a temperature sensor and heating elements to maintain temperatures of the fluid within a desired band. 
         [0013]    In order to pass the pressurized fluid through an in-line heater, it is typically necessary to raise the pressure of the pumped fluid to overcome the pressure losses incurred within the heater. The heater described in the aforementioned U.S. Pat. No. 4,465,922 to Kolibas utilizes dual flow passages within a heater to decrease the pressure losses within the heater. However, the pressures generated by the pump within the heater are still significant and subject the heater to loading that can cause cracking or failure of the heater components, particularly the sleeve, which are fabricated for optimal heat transfer. In one embodiment, heater  11  of the present invention utilizes a heater fabricated of materials having a high heat transfer coefficient between the heating device and the fluid, but having a high strength surrounding the pressurized fluid. 
         [0014]      FIG. 2A  is a perspective view of heater  11  of  FIG. 1  showing enclosure  52  connected to sleeve  54 , which is positioned between inlet housing  56  and outlet housing  58 .  FIG. 2B  is an exploded view of heater  11  of  FIG. 2A  showing multi-channel core  60  and heat cartridges  62  extended from sleeve  54 . Heater  11  also includes fluid outlet manifold  64 , mounting bracket  66  and fluid inlet  68 .  FIGS. 2A and 2B  are discussed concurrently. 
         [0015]      FIGS. 2A and 2B  disclose an embodiment of heater  11  incorporating an internal RTD (resistive temperature detector) temperature sensor (See  FIG. 3 ). In such a configuration, outlet manifold  64  includes plug  70 , outlet fitting  72  and plug  74 . However, in other embodiments, plug  74  can be removed and a thermometer can be inserted into outlet manifold  64 . Furthermore, plug  70  and outlet fitting  72  can be switched to accommodate connection with fluid lines in different orientations, such as is shown in  FIG. 1 . 
         [0016]    Mounting bracket  66  and U-bolt  73 A and nuts  73 B are used to secure heater  11  in a desired location, such as near fluid lines for fluid inlet  68  and outlet fitting  72 . As discussed with reference to  FIG. 1 , pressurized fluid enters inlet housing  56  at fluid inlet  68 , travels within fluid passages between core  60  and sleeve  54  to outlet housing  58 . In one embodiment of the present invention, core  60  includes three parallel flow channels  78 A,  78 B and  78 C, each of which receives fluid at inlet housing  56  and discharges fluid at outlet housing  58 . Thermal energy from heat cartridges  62  travels through core  60  to flow channels  78 A- 78 C to lower the viscosity of the pressurized fluid. Simultaneously, the increased total cross-sectional area of flow channels  78 A- 78 C limits the pressure losses generated by heater  11 . Flow channels  78 A- 78 C are discussed in further detail with reference to  FIG. 4 . 
         [0017]    In one embodiment of the invention, core  60  is fabricated from a material having a higher heat transfer coefficient than sleeve  54 , while sleeve  54  is fabricated from a material having a higher strength than core  60 . For example, core  60  may be produced from aluminum or an aluminum alloy, while sleeve  54  is produced from steel, such as stainless steel. Aluminum is approximately fifteen times more thermally conductive than stainless steel, but stainless steel is approximately two times stronger than aluminum. As such, core  60  can be optimized for transferring thermal energy from heat cartridges  62  to flow channels  78 A- 78 C, while sleeve  54  can be optimized for providing strength to heater  11  to withstand the forces generated by the pressurized fluid. Specifically, sleeve  54  plays a small part in transferring heat to flow channels  78 A- 78 C relative to the role of core  60 . Additionally, the presence of three flow channels increases the surface area of core  60  that is exposed to pressurized fluid, thereby increasing the heat transfer capability. As such, it becomes acceptable to produce sleeve  54  from a material that has superior strength capabilities to the materials of core  60 . 
         [0018]    Furthermore, sleeve  54  is readily removable from core  60  so that heater  11  can be disassembled for service and repairs. In particular, sleeve  54  can be removed so that plugged material within channels  78 A- 78 C can be dislodged. Heater  11  can thereafter be reassembled for further usage. In one embodiment, core  60  is force fit into sleeve  54 , and sleeve  54  is threaded into inlet housing  56  and outlet housing  58 . Additionally, set screws or pins  81 A- 81 D can be used to secure sleeve  54  to outlet housing  58  and inlet housing  56 . 
         [0019]    With specific reference to  FIG. 2B , heat cartridges  62  are inserted into an interior of core  60  through head  82 . Heat cartridges  62  are electrically connected to electronics disposed within enclosure  52 . For example, heat cartridges  62  and indicator light  80  are connected to a circuit board and mounted to head  82 . Indicator light  80  can be used to signal when heat cartridges  62  are active. Furthermore, a thermostat switch and a temperature sensing device, such as an RTD ( FIGS. 3 and 4 ) may be located within enclosure  52 . Core  60  includes sensor bore  83  into which a probe for the temperature sensing device extends. 
         [0020]      FIG. 3  is a close-up perspective view of RTD  84  and heat cartridges  62 A and  62 B mounted to cap  86 . Enclosure  52  is shown partially broken away and exploded from cap  86 . Heat cartridges  62 A and  62 B, RTD  84  and indicator light  80  are electrically coupled to circuit board  88  within enclosure  52 . Indicator light  80  is secured to enclosure  52  using nut  89 . Fitting  90  is connected to enclosure  52  to permit power cables to connect to circuit board  88  to provide power to heat cartridges  62 A and  62 B and other components of heater  11 . 
         [0021]    Cap  86  is secured to core  60  ( FIG. 4 ) using fasteners  92 A- 92 D. Cap  86  provides a platform for mounting electrical components, such as indicator light  80 , and housing components, such as outlet housing  58  ( FIG. 4 ), to core  60 . Heat cartridges  62 A and  62 B comprise elongate heating elements that extend through bores within cap  86  and are inserted into bores within core  60 . In the disclosed embodiment, heat cartridges  62 A and  62 B are electrical resistance heaters. Typically, heat cartridges  62 A and  62 B suitable for use with core  60  are commercially available from industrial suppliers. Heat cartridges  62 A and  62 B are electrically connected to circuit board  88  to receive power from wires extending through fitting  90 . Heat cartridges  62 A and  62 B can be removed from cap  86  and core  60  and replaced should heat cartridges  62 A and  62 B fail or wear out. 
         [0022]    RTD  84  extends through a bore within cap  86  and is inserted into a bore within core  60 . Although the invention is described with reference to an RTD, other types of temperature sensors, such as thermocouples may be used. RTD  84  includes electrical connector  94  and probe sheath  96 , which extends through fitting  98  into core  60 . Specifically, as shown in  FIG. 4 , the tip of RTD  84  extends into sensor bore  83  of core  60  so as to be located in a common outlet plenum for channels  78 A- 78 C. 
         [0023]      FIG. 4  is section  4 - 4  of  FIG. 2A  showing the location of RTD  84  of  FIG. 3  relative to common outlet plenum  100  of core  60 . Core  60  additionally includes common inlet plenum  102 . Fasteners  92 A- 92 D ( FIG. 3 ) secure cap  86  to head  82  of core  60 , and core  60  is inserted through outlet housing  58 , through sleeve  54  and into inlet housing  56 . Cap  86  is wider than core  60  such that cap  86  engages outlet housing  58  to prevent core  60  from falling to the bottom of inlet housing  56 . Set screws  81 A and  81 B secure outlet housing  58  to sleeve  54 . Set screws  81 C and  81 D ( FIG. 2B ) secure inlet housing  56  to sleeve  54 . Fasteners  104 A and  104 B secure enclosure  52  to outlet housing  58 . 
         [0024]    Flow channels  78 A- 78 C extend in a spiral path around an elongate flow section of core  60  from inlet plenum  102  to outlet plenum  104 . Sleeve  54  surrounds the elongate flow section to close-off flow channels  78 A- 78 C thereby forming sealed passages between inlet plenum  102  and outlet plenum  104 . The ribs formed on core  60  resulting from channels  78 A- 78 C include chamfer  106  and chamfer  108  at outlet plenum  100  and inlet plenum  102 , respectively, to ensure that each of channels  78 A- 78 C receives and discharges fluid at a common plenum. Additionally, core  60  is sized-down between outlet plenum  100  and head  82  at neck  110  to prevent formation of blockages in channels  78 A- 78 C between core  60  and outlet manifold  64 . As discussed previously, the surface area of flow channels  78 A- 78 C and the thermal conductivity of aluminum core  60  facilitate heat transfer from heat cartridges  62 A and  62 B to fluid within channels  78 A- 78 C. 
         [0025]    Heat cartridges  62 A and  62 B extend into bores  12 A and  12 B within core  60 . Heat cartridges  62 A and  62 B are elongate so that a majority of the length of flow channels  78 A- 78 C is heated. Probe sheath  96  of RTD  84  extends through fitting  98 , which secures RTD  84  to cap  86 . Both heat cartridges  62 A and  62 B and RTD  84  are connected to circuitry within enclosure  52  that selectively turns on heat cartridges  62 A and  62 B based on temperature readings taken by RTD  84 . The tip of probe sheath  96  extends through sensor bore  83  and into common outlet plenum  100 . As such, RTD  84  is positioned to sense a temperature of the fluid within heater  11  that is more relevant to operation of system  10  ( FIG. 1 ). 
         [0026]    In prior art systems, such as that of the aforementioned U.S. Pat. No. 4,465,922 to Kolibas, a temperature sensor is positioned centrally within the core near the mid-span of the flow channels. Such a location provides only an average temperature of the material between the inlet and the outlet that is not particularly relevant to a temperature of the material that the heater should respond to. For example, it is desirable to know the actual temperature of the fluid that is being pumped to dispenser  16  ( FIG. 1 ). In particular, during intermittent operation of system  10 , it is desirable to know the temperature at outlet plenum  100  when flow starts and flow stops so that heat cartridges  62 A and  62 B can be operated to more precisely control the temperature of the fluid that is closest to dispenser  16 . In embodiments of the present invention, sensor bore  83  allows RTD  84  to sense the temperature of the fluid within outlet plenum  100 . RTD  84  is in contact with both the material of core  60  and the actual fluid being pumped so that a more accurate reading of the temperature of the fluid is obtained. 
         [0027]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.