Abstract:
A closed loop steam engine that transfers its motive power to a flow of water using a steam injector. The resulting water jet then drives a turbine, is cooled in a heat exchanger to extract useful heat and then return to the steam injector water inlet. Part of the flow of water is reused as feed water to the boiler.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/252.284, filed Nov. 6, 2015. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       MICROFICHE APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    Field of the Invention 
         [0005]    The invention relates to the field of steam engines. More specifically the invention comprises a type of steam engine that minimizes the size and number of moving parts of the engine by reducing the time the working fluid (usually water, but can also be other fluids) spends in its gaseous phase. 
         [0006]    Background 
         [0007]    There are many variations of steam engines. Most of these however are rather large and complex with numerous moving parts. They are usually expensive to produce and have high maintenance requirements as well as being very large for their power output. Therefore the use of steam power has largely been limited to large scale industrial applications or small scale models. Currently there are very few if any affordable, safe, small, low maintenance steam engines. This invention seeks to provide such an engine. One of the main challenges when designing a steam engine is that the higher the temperature of the steam, the more costly the engine becomes to produce and maintain. Superheated steam of high temperature is desirable for reasons of efficiency, however this creates multiple problems. Steel softens significantly above temperatures of 500° C. and other materials are expensive. Steam turbines are precision made to very small tolerances, run at high RPMs and are expensive to maintain and repair. Piston type steam engines have sealing problems, usually need to be oiled for lubrication and therefore often suffer oil being mixed into the water. 
         [0008]    Most steam engines therefore limit the steam temperature to around 400° C. This invention circumvents all these problems by converting the energy of the steam into momentum energy of a moving flow of water. This allows low temperature and low cost materials to be used, thus making production and maintenance easier and the engine safer, whilst only limiting the steam temperature to the maximum temperature the heat exchanger can tolerate. There have been attempts to use a steam driven stream of water to drive a turbine before (see U.S. Pat. No. 54,469. May 1, 1866, F. Millward, Rotary Steam Engine or U.S. Pat. No. 554,073, Feb. 4, 1896, J. M. Miller &amp; W. L. B. Collins, Momentum Engine), however these are open systems and do not consider the whole cycle. This invention seeks to integrate all elements into a cycle, so that no water is lost or has to be added, the momentum of the water is preserved, as well as minimizing heat losses in the system and extracting useful heat (for use in combined heat and power applications) via a heat exchanger. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The present invention comprises a closed loop steam engine that transfers its motive power to a flow of water using a steam injector. The resulting water movement then drives a turbine, is then cooled in a heat exchanger to extract useful heat and returns to the steam injector water inlet. Part of the flow of water is reused as feed water to the boiler. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]      FIG. 1  illustrates a diagram of the physical layout of the main parts of the engine. 
           [0011]      FIG. 2  illustrates a cross section through the injector and adjoining pipes. 
           [0012]      FIG. 3  illustrates the added bypass from the outlet of the steam injector back to the inlet of said steam injector. 
       
    
    
       [0013]    Arrows in the drawings show the flow direction of the fluid in the system. 
       REFERENCE NUMERALS IN THE DRAWINGS 
       [0000]    
       
           10  Steam Boiler 
           11  Steam Injector 
           12  Turbine 
           13  Cooler/Radiator 
           14  Pump 
           15  Venturi diffuser 
           16  Water takeoff to boiler 
           17  Bypass 
       
     
       DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Illustrated in  FIG. 1  is a perspective view of the basic layout of the parts that make up the engine. The present invention comprises a closed loop steam engine that is made up of the following parts. A boiler/steam generator  10  to create steam, a steam injector  11  that uses the steam from the boiler to propel a flow of water that then drives a turbine  12 . A heat exchanger  13  that receives the warm water that exits the turbine in order to extract the excess heat and then feed it back into the water inlet of the steam injector. Part of the water flow is diverted from the steam injector outlet or the turbine outlet or the heat exchanger outlet to feed back into the steam boiler. 
         [0023]    The heat exchanger can be of any type that exchanges heat with a liquid, for instance liquid/gas or liquid/liquid heat exchangers such as convectors or plate heat exchangers. There can be a pump  14  and/or a control valve attached to assist the flow into the boiler if necessary. This pump can be separate or connected directly to the turbine shaft in order to minimize the number of moving parts or even another steam injector.  FIG. 2  shows a cross section of the steam injector and the pipe  16  transporting the feed water back to the boiler. The feed-water pipe can be joined to a hole in the pipe coming out of the injector or as shown in  FIG. 2  suspended in the water flow so as to have part of the water forced into it. The flow rate is dependent upon the cross section of the pipe as well as the current pressure and velocity of the water. If the pressure after the injector is lower than the back pressure of the boiler, the pressure can be further enhanced by means of a Venturi diffuser  15 . If the engine is only used in a steady state application (one operating point), the system can be designed to run without a pump  14 , although start-up may be difficult. 
         [0024]    The turbine ideally should be enclosed with no voids or pockets of air or other gasses, so that no momentum is lost. Ideally this would be a Francis, Kaplan, Tesla or even a simple fixed propeller turbine. 
         [0025]    Research has shown, that the efficiency of a steam injector increases as the difference in velocity of the steam and water decreases. Thus it is important to maximize the speed of the water entering the steam injector. In order to do this it is either necessary to not extract all the momentum from the water when flowing through the turbine, or to create a bypass  17  for part of the water coming out of the steam injector to be re-injected into the water of the inlet of said steam injector. A regulator valve can be added for more precise control over the amount of feedback of the bypass. Also additional cooling via a second heat exchanger can be provided for this bypass or the bypass can lead to the inlet of the main heat exchanger instead of the steam injector.  FIG. 3 . shows where the bypass  17  would be placed. The bypass can be connected in the same way the feed-water pipe is shown to be connected in  FIG. 2  or simply connected to a hole in the pipe coming from the injector. 
         [0026]    The boiler  10  can be of any type, however a water-tube boiler of compact design that can safely deliver high temperature superheated steam is preferred. As the water is in a closed system there should be no problems with scale and other impurities. 
         [0027]    The connections between the individual parts of the engine as well as the bypasses can be made with hoses, pipes, carved pathways or any other conceivable way to keep water enclosed and flowing from one part to the next. 
         [0028]    The engine can use not just water but also any other suitable liquid, the proper vapor thereof being used to drive the injector, the injector then being a gas-into-liquid injector compatible with that fluid. In cold climates for instance it is a good idea to use a water/ethanol mix as the working fluid in order to guard against freezing. 
         [0029]    Best Mode of Implementation 
         [0030]    In the preferred embodiment of the invention the steam boiler is of the monotube design, more specifically a flash boiler. This is mainly for safety reasons, as a monotube/flash boiler, even if failure should occur will not create a deadly explosion. The turbine is a Tesla turbine, as these are very easy and cheap to manufacture, tolerate accidentally non condensed steam quite well and have low maintenance requirements. There is a bypass from the outlet of the steam injector through a low friction heat exchanger to cool the water and then leading back into the inlet of said steam injector. A valve regulates the amount of water in the bypass so as to keep the velocity of the water going into the steam injector in the optimal range. The main heat exchanger is a liquid/liquid heat exchanger that uses the waste heat in a combined heat and power application. The water is injected back into the steam boiler via a pipe/connection that diverts part of the flow of water from the steam injector outlet. This is assisted by an electrical pump to ensure reliable start up. The pump only assists when not enough pressure is available from the steam injector flow. A valve regulates the amount of admitted water into the boiler according to the water level in the coils.