Abstract:
Draft inducers ( 50,40 ) having hollow axis ( 73   a   ,73   b ), folding impellers ( 37   a ) or retractable propellers ( 37   b ) having limited presence in the flue path, external motor ( 47   a   , 47   b ) with sensors ( 33   a   , 33   b ), male connection ( 63   a   , 63   b ) and female connection ( 65   a   , 65   b ) ends for connecting with flue stack and other tandem modules.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from and benefit of provisional patent application Ser. No. 61/665,847 titled “Hollow Inducers (Inducer, Hollow Draft Inducers)” filed Jun. 28, 2012, which is incorporated here by reference in its entirety. 
    
    
     This application claims priority from and benefit of patent application Ser. No. 13/731,096 titled “Hollow Axial, Helical Cyclonic Channels for Maximum Heat Recovery and Environmental Smoke Condenser (Heat Reclaimer Smoke Condenser)” filed Dec. 30, 2012, which is hereby incorporated in its entirety by reference. 
     This application claims priority from and benefit of patent application Ser. No. 13/728,051 titled “Flexible Universal Flue Pipe Connector with Damper and Sweep Access” filed Dec. 27, 2012, which is hereby incorporated in its entirety by reference. 
     FEDERALLY SPONSORED RESEARCH 
     None 
     SEQUENCE LISTING 
     None 
     BACKGROUND OF INVENTION 
     This invention relates to modular hollow inducer and use to control flue draft for solid fuel combustion and heat recovery. It relates in particular to inducing, augmenting, varying flue draft rate in response to combustion need of oxygen, heat extraction, and environmental pollutant treatment. This invention further relates to a thermostatic speed controlled air intake and exhaust that gives optimum heat recovery, environmental and combustion management 
     In combustion, there are the reactants and the resulting products or byproducts. The fundamentals of sustaining combustion are in the continuous supply of essential reactants and the removal of inhibiting, undesirable byproducts. On the supply side, one reactant, oxygen has no substitute. On the product side is desirable heat energy that is intertwined in the matrix of carbon dioxide, water and all other products that are combustion quenching and hazardous to life. 
     When there is a spike in the cost of fossil fuel, particularly petroleum, other alternative energy such as wood burning, experience a spike in demand. Many of the demands result in impromptu purchase and improper installation of wood energy devices and appliances. Some of such purchases and installations are inserting stove in a fireplace without a firebox sized flue pipe. It is a violation of the National Fire Protection Association (NFPA) design code spec and Chimney Safety Institute of American (CSIA) teaching. Basically, there is a flue size for a firebox dimension to assure operational safety and function relating to draft. Many draft inducer system designs have been presented with some varying attributes. 
     PRIOR ART 
     The following are some prior art that may be relevant: 
     
       
         
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
           
               
                   
               
             
             
               
                 U.S. Patent Documents: 
               
             
          
           
               
                 1,151,611 
                 August 1915 
                 Prat 
                 . . . 
                   
               
               
                 2,407,590 
                 January 1943 
                 Vineberg 
                 . . . 
                 126/140 
               
               
                 3,280,774 
                 December 1965 
                 English 
                 . . . 
                 110/162 
               
               
                 3,431,056 
                 March 1969 
                 Winegardner 
                 . . . 
                 431/20 
               
               
                 3,782,303 
                 January 1974 
                 Pfister et al  
                 . . . 
                 110/162 
               
               
                 3,788,795 
                 January 1974 
                 Zeitlin 
                 . . . 
                 431/13 
               
               
                 4,250,868 
                 February 1981 
                 Frye 
                 . . . 
                 126/121 
               
               
                 4,649,808 
                 March 1987 
                 Ward et al 
                 . . . 
                 98/59 
               
               
                 5,609,522 
                 March 1997 
                 Szwartz 
                 . . . 
                 454/7 
               
               
                 5,868,615 
                 February 1999 
                 Page 
                 . . . 
                 454/36 
               
               
                 6,223,740 B1 
                 May 2001 
                 Kim et al 
                 . . . 
                 126/110 R 
               
               
                 6,382,203 B1 
                 May 2002 
                 Kim et al 
                 . . . 
                 126/110 R 
               
               
                 7,210,903 B2 
                 May 2007 
                 Lyons 
                 . . . 
                 415/204 
               
               
                 7,278,832 B1 
                 October 2009 
                 Platz 
                 . . . 
                 415/204 
               
               
                 7,325,541 
                 February 2008 
                 Marcakis 
                 . . . 
                 126/77 
               
               
                 7,373,937 
                 May 2008 
                 Little et al 
                 . . . 
                 126/286 
               
             
          
           
               
                 U.S. Patent Application Publications: 
               
             
          
           
               
                 2002/0014234 A1 
                 February 2002 
                 McCarren 
                 . . . 
                 126/516 
               
               
                 2005/0048427 A1 
                 March 2005 
                 Brown 
                 . . . 
                 431/116 
               
               
                 2005/0255417 A1 
                 November 2005 
                 Brown et al 
                 . . . 
                 431/18 
               
               
                 2005/0272989 A1 
                 December 2005 
                 Brown et al 
                 . . . 
                 431/147 
               
             
          
           
               
                 Foreign Patent Documents: 
               
             
          
           
               
                 EP 0737289 B1 
                 Sep. 8, 2004 
                 Gaius D. Kazen 
                 . . . 
                 F23M9/00 
               
               
                 EP 0035550 B1 
                 Nov. 21, 1985 
                 Richard C. Hill 
                 . . . 
                 F24H1/22 
               
             
          
           
               
                 Nonpatent Literature Documents: 
               
               
                   
               
             
          
         
       
     
     How Chimneys Work, http://www.woodheat.org/how-chimneys-work.html by Woodheat.org 
     IntlliDraft™—for Fireplace Safety and Energy Saving, How It Works, Chimney Fan RS 009-016 Product Information by ENERVEX—Venting Design Solutions. WWW.Chimneyfans.com. 
     Successful Chimney Sweeping, Chapter 11, Sections 11.4-11.6, Prepared by Chimney Safety Institute of America et al, Sixth Edition, January 2002. 
     NFPA 211 Standard for Chimney, Fireplaces, Vents and Solid Fuel-Burning Appliances, 2006 Edition, Chapter 9, Section 9.11 by National Fire Protection Association. 
     A General Routine for Analysis of Stack Effect (July 1991) by John H. Klote, General Service Administration, Fire Protection Engineering Branch, Washington, D.C. 20405. http://fire.nist.gov/bfrlpubs/fire91/PDF/f91013.pdf 
     English, in U.S. Pat. No. 3,289,774 presented a burner and a draft inducer to make efficient combustion by providing stoichiometric ratio of combustion reactants and avoid undesirable excessive smoke and soot byproduct. This art recognized that natural draft, inlet draft controls, damper draft controls, and the combination of any of them is not very effective if the control results in poor combustion soot. It provides a positive inducer that correlates with the flow rate of fuel. However, the inducer comes with a 90 degree angle turn in flue pipe flow direction. The change in direction of flue pipe makes it easy for solid fuel flue carrying creosote to deposit it there and create difficulty to sweep it through that bend. Therefore, it is mainly useful for non-solid fuel combustion appliances. It regulates liquid or gaseous fuel and combustion efficiency. There is need for a draft inducer that can function with solid fuel as well as liquid and gas fuel combustion. 
     Marcakis in U.S. Pat. No. 7,325,541 discloses bimetal that expands or contracts due to temperature effect on its length to controls the air opening for a wood burning appliance. There is no active air moving component to forcefully control and effect draft, making it a passive draft inducer. Zeitlin in U.S. Pat. No. 3,788,795 introduced the use of two photoelectric dictators to regulate electric motor which rotates a damper for a boiler flue draft. The relevance of this invention is the use of draft regulation to minimize flue energy loss. Szwartz in U.S. Pat. No. 5,609,522 presented a combination damper and chimney cap apparatus for draft control ability through remote sensor. The sensor and transmitter are located by the firebox. The receiver and the draft damper cap are located at the top of the chimney. Ward et al in U.S. Pat. No. 4,649,808 disclosed a fireplace damper assembly installed downstream of a fireplace at the top of the chimney having smoke or temperature activated electrically actuated damper, a draft assist fan and a wind protection hood. Little et al, U.S. Pat. No. 7,373,937 B2 disclosed a system with actuators and plates to control draft. It optimizes the combustion efficiency of an air-tight heating system. The draft control system and method in U.S. Pat. No. 7,373,937 B2 is specific to an appliance and localized to the enclosed firebox and combustion efficiency but nothing for heat recovery and environmental management. Like Marcakis, Zeitlin, Szwartz, Ward et al these draft controls are either located atop the chimney, controls an air aperture and or has no active flue movement or blower. A better draft control need not be located at the highest height and would serve better with active air moving blower. 
     Pfister et al in U.S. Pat. No. 3,782,303 describes an inducer consisting of propeller in the flue stream connected and driven by a shaft from an electric motor that is insulated from the flue gas and heat. Its intended benefit is in resolving smoky fireplace, inadequate air supply, and insufficient chimney height. The draft inducer has the advantages of insulated motor and has draft induction for multiple flues. However, to serve multiple flues, it must remain on constantly and that means a costly exhausting air from heated living space. It is installed at the top of the chimney, making hard to reach for service in the event of a breakdown. Further, the stack is not usable in the event of a breakdown since the draft inducer will become a blockage. There is need for better failure mode effect result in a draft inducer design consideration. 
     In U.S. Pat. No. 4,250,868, Frye presented the flue draft inducer that is installed at the top of the chimney with a chimney cap and designed to control heat exchange and temperature with variable speed control switch. Frye described draft as one of the most important factors affecting combustion efficiency in fireplace and solid fuel appliances. Frye&#39;s draft inducer is electrical and mounted on the top of a hot flue path. If used for solid fuel, cleaning the inducer and the chimney has a degree of difficulty due to the fixed, non-retractable inducer and heat exchanger. Like Pfister et al, the degree of difficulty is magnified by the peak height location of the inducer and blockage of natural draft in failure mode. There is need for draft inducer durability design with the motor located outside the flue stream and flue heat. 
     Emile Prat in U.S. Pat. No. 1,151,611 describes a steam powered, pressure and vacuum modulated draft inducing fan for boilers. The apparatus would provide adequate draft control with the benefit of safe conduction of combustion byproducts from living space and some improved combustion efficiency. The device had no direct environmental and energy recovery function. Failure mode effect would render the boiler inoperable. There is need for a draft inducer that could operate synergistically with an energy recovery system with better failure mode effect. 
     Using physical science format from non-patent references above, the factors considered in design of the natural chimney draft flow (F) are cross-sectional area of the stack (A), the external air temperature (To), the temperature inside the structure and chimney (Ti), the height of the chimney (H), the force of gravity (g), and the coefficient of discharge (Y). Except for (A), (g), (Y) and (H) the other factors (To) and (Ti) vary most by circumstance. Therefore, (F) depends most on (To) and (Ti). Draft through a stack (F) in a home increases as (Ti) increases over (To) and other factors remain constant. When (A) is changed, for example, by moving smaller firebox to a larger stack, or heat recovery apparatus deposits big layer of creosote in the stack walls, (F) is affected. (F) is also particularly affected when insert stove is installed inside an existing fireplace with larger stack area (A). The result can be deadly. There is need for a draft inducer to enforce draft when any of the constants like (A) has changed. There is the need for a draft inducer when Ti is decreased such as when heat is harvested from a combustion process. 
     The disadvantage with some prior arts is that they control an aperture size with passive flue movement of air. The active draft inducers in prior arts are electromechanical motors that are exposed to high temperature flue gas. The exposure of electrical equipments in a hot exhaust path has its risk of high failure rate due to heat effects on electrical conductors and appliances. Some prior art draft inducer systems are configured mostly for combustion and exhaust. Some of the prior art systems must constantly remain in operation. Many prior art draft inducer systems block cleaning access. Others draft inducers are located at the top of chimney where they are not easily removed for repair or service to the chimney. In the event of draft inducer malfunction, the inducer itself becomes an impediment to any natural draft that may exist and the combustion system suffers a total downtime. There is need for an inducer that does not take residence in the flue part, for draft inducer motor that will last longer and failure mode effect analysis will not be catastrophic or suffer total downtime. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the forgoing deficiencies can be remedied. One embodiment of the present invention, a hollow inducer comprises a hollow axis, modular connection, perimeter impeller with external motor, and sensor modulated speed control. In another embodiment, the hollow inducer comprises a central on-demand ejection propeller, hollow axis, modular connection, external motor, optical and or temperature modulated speed. Accordingly, the present invention provides a hollow inducer having multiple advantages including: a draft inducer that has its hollow axis, a motor outside the flue path saved from flue heat and short life span, means for shelving propulsion system that does not obstruct the flue path in a failure mode effect and sweep access, it can be positioned modularly in tandem with other flue treatment modules to control the rate of combustion, that pushes flue gas out and pulls fresh air into the combustion, that senses and controls the combustion, regulates heat recovery module and makes it possible to use smaller firebox in a larger stack and vice versa. These and other advantages of one or more aspects of the hollow inducer will be readily and particularly apparent in light of the following representative illustrations and ensuing description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, closely related figures have the same number but different alphabetic suffixes. 
         FIG. 1.0A  illustrates a perspective view showing one embodiment of the propeller draft inducer. 
         FIG. 1.1A  illustrates a perspective view showing another embodiment of the impeller draft inducer. 
         FIG. 1.1B  is a cross-sectional portion of  FIG. 1.1A  showing impeller draft inducer with impellers folded in dormant position in its hollow flue pipe. 
         FIG. 1.0B  is a top view of  FIG. 1.0A  showing propeller draft inducer with propellers inserted in its flue pipe. 
         FIG. 1.0C  is a cross-sectional side view of  FIG. 1.0A  showing propeller draft inducer with propellers inserted in its flue pipe. 
         FIG. 1.1C  is a top view of  FIG. 1.1A  showing draft inducer impellers spread out in operating position (Y) in its flue pipe. 
         FIG. 1.0D  is a top view of  FIG. 1.0A  showing propeller draft inducer with propellers ejected out of its flue pipe. 
         FIG. 1.1D  is a general view of the impeller draft inducer illustrating the disconnected components prior to complete assembling. 
         FIG. 2.0   a  illustrates the application of propeller draft inducer in tandem with other energy, access and circulation modules on a Standalone appliance 
         FIG. 2.1   a  shows the application of impeller draft inducer in tandem with other energy and sweep access modules with any incinerator. 
         FIG. 2.0   b  is showing the application of propeller draft inducer in tandem with other energy and sweep access modules with an insert appliance in an existing chimney. 
         FIG. 2.0   c  is a side cross-section view of  FIG. 2.0   b  showing the application of propeller draft inducer in tandem with other energy and sweep access modules on an insert appliance in an existing chimney. 
         FIG. 2.1   b  is a side cross-section view of  FIG. 2.0   b  showing the application substitution of the propeller draft inducer with the impeller draft inducer in tandem with other energy and sweep access modules on an insert appliance in an existing chimney. 
     
    
    
     DRAWINGS—REFERENCE NUMERALS 
     40 Embodiment of FIG.  1 . 0 A Draft Propeller &amp; Controller 
     
         
         
           
               19   a  hot fluid outlet 
               19   b  hot fluid outlet 
               20   b  inside stopper 
               22   a  mounting connector 
               22   b  mounting flange 
               21   b  outside stopper 
               23   a  impeller gear 
               23   b  propeller gear 
               25   a  ball bearings 
               25   b  window opener 
               27   a  shaft gear 
               27   b  shaft gear 
               28   a  flue inlet 
               28   b  flue inlet 
               29   a  drive shaft 
               29   b  drive shaft 
               31   a  beam support 
               31   b  beam support 
               32   a  sensor link 
               32   b  sensor link 
               33   a  sensors 
               33   b  sensors 
               34   a  upper casing 
               34   b  inner casing 
               35   a  impeller casing 
               35   b  propeller casing 
               36   a  lower casing 
               36   b  window 
               37   a  impeller elements 
               37   b  propellers 
               45   a  power controller 
               45   b  power controller 
               46   a  optical sensor 
               46   b  optical sensor 
               47   a  motor 
               47   b  motor 
               48   a  flue outlet 
               48   b  flue outlet 
               51   a  top bearing cover 
               51   b  propeller beam 
               53   a  lower bearing cover 
               53   b  propeller Arm 
               57   a  mounting hinges 
               57   b  Insertion actuator 
               59   a  power and fluid inlet 
               59   b  power and fluid inlet 
               61   a  wedge 
               61   b  sash recoil spring 
               61  chimney brick wall 
               63   a  male connection 
               63   b  male connection 
               63  flue pipe 
               65   a  female connection 
               65   b  female connection 
               67   a  insert Stove 
               67   b  general combustor/Incinerator 
               67   c  Standalone stove 
               40  propeller hollow inducer 
               50  impeller hollow inducer 
               69   b  semi-circular structure 
               71   b  bow limp 
               73   b  lowers bar 
               73   a  hollow axis 
               73   b  hollow axis 
               75   b  axle rod 
               77   b  ejection recoil spring 
               110  heat extractor, like the Heat Reclaimer Smoke Condenser. This reference numeral claims the benefit of provisional patent application No. 61/612,314 filed Mar. 18, 2012 by the present inventor, titled Hollow Axial, Helical Cyclonic Channels for Maximum Heat Recovery and Environmental Smoke Condenser (Heat Reclaimer Smoke Condenser). 
               380 C heat ejector 
               710  connector, like the Flexible Universal Connector (This reference numeral claims the benefit of provisional patent application No. 61/589,813 filed Jan. 23, 2012 by the present inventor, titled Flexible Universal Flue Pipe Connector with Damper and Sweep Access). 
               905 D damper hole sealer, like Ventinox® Connector seal kit 
           
         
       
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Construction 
     FIGS.  1 . 1 A,  1 . 1 B,  1 . 1 C,  1 . 1 D 
     One embodiment of an impeller hollow inducer is illustrated in  FIG. 1.1A  (side view) and  FIG. 1.1B  (crossed-section view), generally designated as  50  and  50 C respectively. The impeller hollow inducer has hollow axis and cylindrical body with flue inlet  28   a  and outlet  48   a . The flue inlet  28   a  and flue outlet  48   a  terminates in male connection  63   a  and female connection  65   a  respectively. The draft inducer body is made of refractive materials such as 0.015″ minimum thick stainless steel or 0.005″ minimum thick titanium, has an upper casing  34   a  detachably connected to a impeller casing  35   a  which is detachably connected to a lower casing  36   a . As illustrated in the  FIG. 1.1D , the upper casing  34   a  and the impeller casing  35   a  are provided with an upper bearing cover  53   a  and the lower casing  36   a  and the impeller casing  35   a  are provided with a lower bearing cover  51   a . The upper bearing covers  53   a  and lower bearing covers  51   a  enclose ball bearings  25   a  which fills the gaps that connects the three casings. The ball bearings  25   a  provide reduced friction for the rotation of the impeller casing  35   a . Slant mounted impellers  37   a  are attached with hinges  57   a  to the inside surface of the impeller casing  35   a.    
     In  FIG. 1.1C  (top view) impellers  37   a  are uniformed, having contoured shape and balanced spacing for efficient movement of air. Wedges  61   a  are attached to the mounting hinges  57   a  to determine the balanced operating position Y for the impellers  37   a . During operation or clockwise rotation of the impeller casing  35   a , the impellers  37   a  swings to Y location. The impeller  37   a  will fold to X dormant position when for example a sweep brush is inserted. In  FIG. 1.1D  (assembling view) a mounting connector  22   a  that holds the three casings together has been severed to expose the assembly. Beam supports  31   a  connect a motor  47   a  to the upper casing  34   a . A power or fluid inlet  59   a  such as electric or hydraulic pumped fluid is connected to a power controller  45   a  and is connected to the motor  47   a . At least one temperature and/or optical sensor  33   a  are connected to the power controller  45   a  via a sensor link  32   a . The sensor link  32   b  and the sensor(s)  33   b  can be positioned at any desired location for controlling information input source. A drive shaft  29   ba  with its shaft gear  27   a  projects from the motor  47   a  and connects to the impeller gear  23   a  connected to the impeller casing  35   a.    
     Alternate Embodiments 
     FIGS.  1 . 0 A,  1 . 0 B,  1 . 0 C,  1 . 0 D 
     Another embodiment of the draft inducer is illustrated in  FIG. 1.0A  (side view) and  FIG. 1.0B  (top view), generally designated as  40  and  40   b  respectively. The draft inducer body, made of refractive materials such as 0.015″ minimum thick stainless steel or 0.005″ minimum thick titanium, has an inner casing  34   b  detachably connected to a propeller casing  35   b . The inner casing  34   b  is hollow with flue inlet  28   b  and outlet  48   b . The flue inlet  28   b  and outlet  48   b  terminates in male connection  63   b  and female connection  65   b  respectively. A window  36   b  with sash recoil spring  61   b  is connected to an opening in the inner casing  34   b  leading into the propeller casing  45   b  as illustrated in  FIG. 1.0C  (cross-sectional side view). The propeller casing  45   b  encloses a propeller beam  51   b  connected to a beam support  31   b  attached to the inner casing  34   b . The propeller beam  51   b  is rotated clockwise and counterclockwise by a beam actuator  57   b  and an ejection recoil spring  77   b  connected to the propeller beam  51   b  and the inner casing  34   b . A power or fluid inlet  59   b  such as electric or hydraulic pumped fluid is connected to a power regulator  45   b  and is connected to the beam actuator  57   b . At least one temperature and/or optical sensor  33   b  are connected to the power controller  45   b  via a sensor link  32   b.    
       FIG. 1.0C  shows the sensor link  32   b  and the sensor(s)  33   b  can be positioned at any desired location for controlling information input source. A hydraulic or electric motor  47   b  is mounted on a propeller arm  53   b  attached to the propeller beam  51   b  and projects out into a semi-circular structure  69   b . The semi-circular structure  69   b  terminates in a facedown bow-like structure with bowed limp  71   b  and lowers bar  74   b . A propeller  37   b  with a propeller gear  23   b  is mounted between the bowed limp  71   b  and lowers bar  74   b  using an axle rod  75   b . A drive shaft  29   b  from the motor  47   b  connects to the propeller gear  23   b  with its shaft gear  27   b . At the opposite ends of the bow limp  71   b  are ejection stopper  20   b  and insertion stopper  21   b  hooks.  FIG. 1.0B  and  FIG. 1.0C  shows the propeller arm  53   b  and all its attachments in the flue path inner casing  34   b  with the insertion stopper  21   b  hook stopping further insertion. When power is supplied to the power or fluid inlet  59   b , it passes through the power controller  45   b  to the actuator  57   b . The actuator piston moves from h to z position causing the rotation of the propeller beam  51   b  from X to Y position. The power the reaches the motor  47   b  and exits from a return outlet  19   b.    
     Operation 
     FIGS.  2 . 0   a ,  2 . 0   b ,  2 . 0   c ,  2 . 1   a ,  2 . 1   b,    
     The manner of using the hollow draft inducer to maintain draft in a combustion flue stack is similar but relatively easier, durable and safer than using other prior art draft inducers currently in use. The hollow draft inducer could be used to replace existing draft inducers that do not have a hollow axis, support energy recovery, better failure mode analysis effect and other easy functionalities that come with the present invention. 
     The application of propeller hollow draft inducer  40  is shown in  FIG. 2.0   a  generally designated as  400 . It can be used in tandem with other systems such an access module  710 , a circulation modules  380 C, an energy recovery and environmental module  110  on a Standalone appliance  67   b . In this application, the propeller hollow draft inducer  40  of  FIG. 1.0C  is connected to an energy recovery and environmental module  110  with it male connection  63   b  and to the flue pipe with its female connection  65   b . When power is supplied to the power and fluid inlet  59   b , the power modulator  45   b  acquires the condition of operation from the sensors  33   b . This draft sensor  33   b  will mount anywhere in the path of the flue and with other flue gas treatment equipments in tandem. The temperature sensor  33   b  could be used by the power modulator  45   b  to vary the motor speed to the temperature of the flue. In this setup, when temperature is high, heat recovery capacity may have been exceeded and combustion need to slowdown for recovery module to catch-up. The optical sensor  33   b  could be set to be proportional to power increase. In this type of setup, when there is much smoke, propulsion will increase to expel the smoke and pull-in more air to make combustion robust. 
     The modulated power goes to the actuator  57   b  and to the motor  47   b . The actuator turns the propeller beam  51   b  in clockwise direction. Simultaneously, the inside stopper/opener  20   b  lift the window  36   b  against the window sash recoil spring  61   b  and inserts the propeller arm  53   b  into the inner casing  34   b  flue path through the window  36   b . As the window  36   b  closes behind the inserted propeller, the outside stopper/opener  21   b  stops the insertion process at the programmed position. The motor  47   b  rotates the drive shaft  29   b  with shaft gear  27   b . The shaft gear rotates the propeller gear  23   b  which rotates the propeller  37   b . The rotation of the propeller  37   b  provides the induced draft to expel the flue gas that lost its buoyancy thermal energy to energy recovery and environmental treatment module  110 . In  FIG. 1.0D , power fluid inlet  59   b  is terminated, the ejection recoil spring  77   b  returns the propeller arm back to the propeller casing  35   b , leaving the inner casing  34   b  hollow for unobstructed sweep maintenance or usage with natural draft.  FIG. 2.0   b  designated  40 E, shows propeller hollow draft inducer  40  in tandem with energy recovery and environmental treatment module  110  and sweep access module  710  with an insert appliance in an existing chimney.  FIG. 2.0   c  is showing a side view cross-section of  FIG. 2.0   b  designated  40 F, the propeller draft inducer  40  in tandem with energy recovery and environmental treatment module  110  and sweep access module  710  with an insert appliance in an existing chimney 
     The impeller hollow draft inducer  50  application is illustrated in  FIG. 2.1   a , generally designated as  30 D. It can be used directly in any general combustion/incinerator  67   c  process to provide better combustion by drawing oxygen rich air through the combustion while exhausting the flue gas. In another application, it is be use with an access module  710  to provide ambient air dilution of the heat from a flue gas. Such application is useful where the flue pipe material is susceptible to high temperature from the hot flue. The impeller hollow draft inducer  50  is equally functional in a tandem such as an access module  710 , a circulation module  380 C, an energy recovery and environmental module  110  on a general combustion/incinerator  67   c  process. In this application, the impeller hollow draft inducer  50  of  FIG. 1.1  and  FIG. 1.1C  designated  50   a  and  50   c  respectively, is connected to an energy recovery and environmental module  110  with its male connection  63   a  and to the flue pipe with its female connection  65   a . When power is supplied to the power and fluid inlet  59   a , the power modulator  45   a  acquires the condition of operation from the sensors  33   a . The modulated power goes to the motor  47   a . The motor  47   a  rotates the drive shaft  29   a  with shaft gear  27   a . The shaft gear rotates the impeller gear  23   a  which rotates the impeller casing  35   a  on the ball bearings between the upper casing  34   a  and the lower casing  36   a . The initial rotation of the impeller casing  35   a  causes the impellers  37   a  to pivot on the mounting hinges  57   a  from say X until stopped at the right position Y by the wedges  61   a . Continuous rotation of the impellers  37   a  provides the induced draft for the desired applications. When power fluid or electric inlet  59   b  terminates, the draft inducer  40  remains axially hollow  73   a  as in  FIG. 1.1D  for unobstructed sweep maintenance or usage with natural draft. When a sweep brush is inserted, the hollowness widens as the impellers are nudged from Y to X position.  FIG. 2.1   b  is a side view cross-section of  FIG. 2.0   b  designated  30 E showing the substitution with the impeller inducer  50  for the propeller draft inducer  40  in tandem with energy recovery and environmental treatment module  110  and sweep access module  710  with an insert appliance in an existing chimney. 
     ADVANTAGES OF THE INVENTION 
     From the description above, a number of advantages of some embodiments of the present invention become evident:
         1. Versatile: Provide a modular flue draft inducer for used on a chimney fireplace, stand alone or insert woodstove, coal or pellet stoves, gas fireplace, incinerators and the like. Provide a different kind of exhaust means that can be positioned with various stacks, fireplaces and equipment without obstructing and requiring disassembling before routine maintenance. It can portably be relocated and fits any stack and any location in the stack and can be positioned modularly in tandem with other modules.   2. Durable: The motor is located outside the flue path and never exposed to hot and corrosive flue stream. An electric or hydraulic motor is durable in this inducer since the motor is located outside the flue path and saved from flue heat and short life span   3. Safer: Creosote removal by sweeping is fundamental to chimney fire safety. Safety of any system depends on its serviceability which depends to a great extent on accessibility. Credit to the hollow axis and no obstruction, the stack can easily be swept through without disassembly of the stack systems. Disassembly and reassembly of a system is discouraging, costly and time consuming. The result is postponement which could end in catastrophe. The inducer presents this safer, see through and easy sweep through advantage.   4. Improves combustion: After combustible has been ignited, supply of oxygen and removal of carbon dioxide has to be maintained to sustain or improve the combustion. The inducer provides active draft system with temperature and sensor variable speed, making it possible for measured amounts of air to come into the combustion chamber or fire box. The result is a hotter flame that increases efficiency of combustion and pollution abatement. Therefore, it provides a draft system that smartly and actively enforces primary air and secondary air for wood stoves and fireplaces. Further, the hollow inducer provides first-in first-out flue stream in the smoke chamber and auto regulation of rate of exhaust based on temperature of the exhaust flue; that control the rate of combustion; that pushes flue gas out and pulls fresh air into the combustion. In one embodiment, the propeller auto temperature controlled speed, chokes the combustion at the initial start of fire in the firebox and modulates draft at later stage of the combustion to control heat extraction. As the temperature increases, the air intake decreases and vice-versa to optimize rate of combustion, heat recovery and environmental treatment.   5. Supports heat recovery and smoke condensing: With the invention of the connector ( 710 ) and the heat reclaimer smoke condenser ( 110 ), this inducer provides the control rate of the flue passage based on inputs from temperature sensor and/or the smoke sensor and/or the carbon monoxide sensor. In a setup, the inducer speed is directly proportional to smoke and toxic gas but inversely proportional to the temperature. When the flue gas is very hot, the inducer slows down the exhaust for the heat reclaimer to catch-up and combustion to slow down. When the flue gas is slow and produces excessive smoke or toxic gas, such as the beginning of the fire, the sensor responds by increasing speed of the inducer to increase combustion.   6. On-demand Presence: Presence of the impeller or propeller in the flue path is minimized or absent when the inducer is not in use. This implies that the stack is fully usable in its original form. This feature is particularly valuable when there is power outage or malfunction of the inducer. This inducer has better failure mode effect analysis because it is only present on-demand and not obstructive.   7. Minimize area ratio between firebox and stack: The variable and adjustable response of the hollow inducer provides draft flow that would also negate the rigid ratio relation of firebox to smoke chamber size and chimney effective diameter. The present inventions provide an advanced draft controller that broadens the line relating flue height above the roof and the nearest taller obstruction, the size of the firebox. The hollow inducer provides auto variable draft based on temperature and/or smoke which make flue pipe ratio to firebox a smaller factor in draft consideration.       

     CONCLUSION, RAMIFICATION, AND SCOPE 
     Accordingly, the reader will see that the hollow draft inducers of the various embodiments of the present invention can be used to control draft easily and conveniently; can be maintained without disassembly the of any part of the flue system setup; can easily connect in any location of the stack and with any other module in tandem; and can augment the draft of a small firebox in a bigger flue stack. In addition, by choice or when there is power outage, the flue stack can be operated in its original form since the hollow draft inducer maintains little or no permanent presence in the flue stack path. Furthermore, the hollow inducers have additional advantages in that:
         They are relatively simple and easy to manufacture; installation can be performed without construction, sweep services can be done without scaling the chimney heights and no special tools and disassembly of the system is required.   They clearly have the advanced edge in failure mode effect analysis in that the flue stack can still be used in its original form, making the hollow draft inducer available on-demand.   They provide proportional push of flue gas and pull of fresh oxygen rich air into a combustion chamber using temperature, optical or carbon monoxide sensors.   Firebox to stack area ratio is no longer a rigid rule. And tandem equipments such as woodstoves and heat recovery smoke condenser have a controlling ally in efficiency performance.       

     The embodiments illustrated in this invention are in no way restricted to changes and modification that may be made without departing from the scope of this invention. Although the drawings and detailed descriptions above contain much specificity, those should not be construed as limiting the scope of the embodiments but as merely providing illustration of some of the embodiments. For example, the substitution of electric motor with hydraulic motor and impeller with propeller has been mentioned and demonstrated. Also, the hollow inducer could be used to prime a liquid flow in line with some adoptive modifications of the present invention. The embodiments are capable of numerous modifications, rearrangements, and substitutions of parts and elements without departing from the scope of the invention. Thus the scope of the embodiment should be determined by the appended claims and the legal equivalents, rather than the examples given.