Abstract:
A micromachine including at least one bladeless rotor, said rotor being adapted to impart energy to device energy to or derive energy from a fluid. A rotor for a micromachine comprising at least a pair of closely spaced co-axially aligned discs defining opposed planar surfaces, at least one disc having at least one aperture whereby a fluid passageway is defined between the aperture, the planar surfaces and the periphery of the rotor, the rotor being formed of a single crystal material.

Description:
This is a continuation of application No. PCT/AU00/01495, filed Dec. 4, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to micromachines and an improved rotor for micromachinery. The term micromachine is used to embrace many types of very small turbines or compressors. These machines can be as small as 12 mm in diameter with rotors of 4 mm in diameter. 
     BACKGROUND 
     Micromachines such as micro-gas turbines, combustion power generators, pumps and compressors are described in U.S. Pat. No. 5,932,940 (the M.I.T. patent), the disclosure of which is incorporated herein by reference. All of these machines contain a rotor comprising a disc or discs defining either a centrifugal compressor/pump or a radial inflow turbine. The material of construction is characterised by a strength to density ratio enabling a rotor speed of at least 500,000 rotations per minute. The machines are constructed using microfabrication techniques including vapour deposition and bulk wafer etching, the material of construction being common to all the structural elements. 
     The compressor and the turbine rotors of the devices described in the M.I.T. patent utilise a plurality of radial flow vanes. It is considered that this arrangement of blades is not desirable in micromachines for the following reasons: 
     (a) because the nature of construction involves planar fabrication techniques, fillets on corners are difficult to achieve and, in the absence of adequate fillets, high stress concentration at the blade root attachment decreases the fracture strength of these microelements; 
     (b) the placement of blades around the periphery of the discs increases the mass of the structure at the place where centrifugal stresses have the greatest effect; 
     (c) the plurality of blades tends to set up undesirable turbulence and pulsations in the working fluids, and the cyclic nature of the reaction between fluids &amp; blades results in cyclic stress fluctuations (fatigue stresses) that limit the durability (fatigue life) of the rotor assembly; 
     (d) the maximum rotor speed is limited in part by the allowable mechanical and thermal stresses that may be imposed on the rotor structure by the plurality of radial flow vanes; 
     (e) the degree of rotor balance obtainable is affected by the requirement for a plurality of radial flow vanes; and 
     (f) the rotor disc employs blades only on one side and is subject to a bending moment, caused by centrifugal blade loading. 
     It is these problems that have brought about the present invention to use a bladeless or vaneless rotor in micromachines. 
     The use of bladeless rotors has been suggested in the context of “large scale” turbines. Thus, a method for driving turbines by means of viscous drag was taught by Tesla in U.S. Pat. No. 1,061,206 and for fluid propulsion in U.S. Pat. No. 1,061,142. In both disclosures the rotor comprises a stack of flat circular discs with openings in the central portions, with the discs being set slightly apart. In the turbine embodiment the rotor is set in motion by the adhesive and viscous action of the working fluid, which enters the system tangentially at the periphery and leaves it at the center. In the fluid propulsion embodiment, fluid enters the system at the center of the rotating discs and is transferred by means of viscous drag to the periphery where it is discharged tangentially. 
     For fluid propulsion applications such as pumps and compressors, the fluid is forced into vortex circulation around a central point where a pressure gradient is created. This pressure gradient is such that an increasing radial distance from the center of rotation leads to an increase in pressure, with the density of the fluid and the speed of rotation determining the rate of pressure rise. If an outwardly radial flow is superimposed on the vortex circulation an increasing pressure is imposed on the fluid as it flows outwardly. 
     To preserve the vortex circulation, an external force must act upon the fluid, and this force must accelerate the fluid in the tangential direction as the fluid moves outwardly in order to maintain its angular velocity. This function is simply a transfer of momentum from the impeller to the fluid, and with a centrifugal compressor it may be achieved in one of two ways. A first method is to confine the fluid within a fixed boundary channel and then accelerate the channel. In an impeller of the type utilized in prior art microturbomachinery, the vanes and rotor walls form such a channel, and acceleration occurs as the fluid moves outwardly towards regions of higher impeller velocity. A second method of momentum transfer is by viscous drag and this is the principle underlying the Tesla arrangement described in the two US patents referred to above. Viscous drag always acts to reduce the velocity difference, so that in the case of a compressor where the channel walls are moving relative and parallel to the fluid, the fluid will accelerate in the direction of the channel motion. Conversely, where the fluid is moving relative and parallel to the channel walls, the channel walls will accelerate in the direction of the fluid motion. 
     Known bladeless or vaneless rotors have had limited success in large scale turbines. The relatively large number of parts required for their construction and the distortion of the discs that occur under high thermal and mechanical stress conditions have restricted their adoption. 
     It is these issues that have brought about the present invention. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a micromachine including at least one bladeless rotor, said rotor being adapted to impart energy to or derive energy from a fluid. 
     For the micromachine, the rotor of the invention may have a disc of diameter no greater than 20 mm. 
     Preferably the rotor includes a shaft centrally supporting at least two closely spaced planar discs, the discs having opposed surfaces defining a fluid passageway. At least one of the discs may have one or more apertures to allow fluid to pass into or out of the fluid passageway. The apertures preferably are close to a central region of the disc. There may be two or more apertured discs, with the apertures of each disc being aligned with those of the other disc. Preferably the discs are separated by spacers. 
     The rotor of the invention may have a backing disc supporting a plurality of annular discs in a closely spaced coaxial array. In that arrangement, each annular disc may be mounted to the backing disc or an adjacent disc by an array of spacers. The backing disc preferably is mounted coaxially on a shaft. 
     The micromachine, including its rotor, preferably has a vaned stator positioned around the periphery of the bladeless rotor. 
     The micromachine preferably is made of material capable of operating at temperature greater than 1000° C. The rotor most preferably is made of a material having a tensile strength to allow the rotor to run at speeds greater than 500,000 rpm at elevated temperatures associated with combustion. The rotor may be made of a single crystal material. The rotor may, for example, be formed at least in part from a material selected from silicon, silicon carbide, silicon coated with silicon carbide, and silicon coated with silicon nitride. 
     The rotor preferably is formed by a microfabrication technique, such as photolithography or vapour deposition. 
     According to a further aspect of the present invention there is provided a rotor for a micromachine, wherein the rotor includes at least a pair of closely spaced co-axially aligned discs defining opposed planar surfaces, at least one disc having at least one aperture whereby a fluid passageway is defined between the aperture, the planar surfaces and the periphery of the rotor, and wherein the rotor is bladeless and is formed of a single crystal material. 
     In accordance with a still further aspect of the present invention there is provided a rotor for a micromachine, wherein the rotor includes at least a pair of closely spaced co-axially aligned discs defining opposed planar surfaces, at least one disc having at least one aperture whereby a fluid passageway is defined between the aperture, the planar surfaces and the periphery of the rotor, and wherein the rotor is bladeless and manufactured of a material having a tensile strength to allow the rotor to run at speeds greater than 500,000 rpm at elevated temperatures associated with combustion. 
     In accordance with a still further aspect of the present invention there is provided a rotor, wherein the rotor includes a backing disc and at least one coaxially spaced annular disc supported on the backing disc by a central hub defining at least one aperture, wherein the rotor is bladeless and the annular disc defines an unimpeded fluid passage between the aperture and the periphery of the disc. 
     The rotor of the invention most preferably is of unitary construction. The rotor preferably is formed by a microfabrication technique, such as photolithography or vapour deposition. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
     FIG. 1 is a front elevational view of a first embodiment of a bladeless rotor for use in a micromachine, 
     FIG. 2 is a side elevational view of the bladeless rotor of FIG. 1, 
     FIG. 3 is a cross sectional view taken along the lines III—III of FIG. 1, 
     FIG. 4 is a front elevational view of a second embodiment of a bladeless rotor, 
     FIG. 5 is a sectional view of the rotor, taken through the lines V—V of FIG. 4, 
     FIG. 6 is a sectional view of the rotor, taken through the lines VI—VI of FIG. 4, 
     FIG. 7 is a three dimensional view illustrating two bladeless rotors mounted coaxially on a common shaft, 
     FIG. 8 is a front elevational view of a bladeless rotor in accordance with a third embodiment, 
     FIG. 9 is a side elevational view of the rotor of FIG. 8, 
     FIG. 10 is a sectional view of the rotor taken through the lines X—X of FIG. 9, 
     FIG. 11 is a front elevational view of a test rig illustrating operation of a radial flow turbine utilising a bladeless rotor, 
     FIG. 12 is a cross sectional view taken along the lines XII—XII of FIG. 11, 
     FIG. 13 is a front elevational view of a test rig illustrating operation of a radial flow turbine utilising a rotor with blades, 
     FIG. 14 is a cross sectional view taken along the lines XIV—XIV of FIG. 13, 
     FIG. 15 is a graph of rotor speed against plenum chamber pressure utilising the test rigs of FIGS. 11 and 13, and 
     FIG. 16 is a graph of rotor speed against mass flow in grams per second. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In U.S. Pat. No. 5,932,940 (the M.I.T. patent) there is disclosure of micromachinery in the form of micro-gas turbines and associated microcomponentry. The components such as the compressor, diffusers, combustion chambers, turbine rotors and stators are all disclosed as being manufactured using microfabrication techniques in a material that is common to all the elements. Suitable materials include a range of ceramics used in the semiconductor art or in the microelectronic fields, such materials include silicon, silicon carbide and silicon nitride. Other suitable materials include refractory metals and alloys based on nickel, tantalum, iridium and rhenium. Composite materials such as molybdenum silicide are also envisaged. The materials can also vary depending on whether they are used in the hot and cold regions of the micromachines. Such techniques and materials are suitable for use with a rotor and a micromachine according to the invention. 
     Regardless of whether the engine is a turbine or compressor it includes at least one rotor usually mounted on a shaft. In one embodiment the engine could include a common shaft driving a compressor disc at one end, defining a centrifugal compressor and a turbine disc at the opposite end defining a radially inflow turbine. The componentry is very small with the whole assembly being less that 20 mm in diameter. The micromachines are designed to run at very high speeds with a rotational speed of at least 500,000 rotations per minute being typical. In a preferred embodiment the dimensions of the machine embraces compressor and turbine discs of diameters between 1 and 20 mm with a combustion chamber having a height of between 2 to 10 mm and the axial length of the combustion chamber being between 0.5 mm and 12 mm. The materials that are used to produce the componentry should preferably be able to withstand temperature of at least 1,000° C. in the case of turbines. Again, these considerations apply similarly to a rotor and a micromachine according to the present invention, as will be evident from the following. 
     The micromachine disclosed in the M.I.T. patent utilises bladed or vaned rotors. As discussed in the introduction of the present specification, it is considered that the use of a bladed or vaned rotor in micromachinery causes a series of problems, many of which can be solved by the use of bladeless or vaneless rotors. 
     In the embodiment shown in FIGS. 1 to  3 , a suggested construction of a bladeless rotor  10  is illustrated. The bladeless or vaneless rotor  10  shown in FIGS. 1 to  3  includes two substantially smooth and planar annular discs or rings  12  and  13  co-axially supported in a close parallel array by a star shaped hub  14  which is attached to a backing disc  16 . The hub  14  is provided with openings/apertures  18  that communicate with the space  20  between backing disc  16  and the ring  12  and with the space  21  between ring  12  and ring  13 . In the example shown the rotor has a diameter of about 4 mm and a width of about 0.6 mm. The rotor is constructed from material such as silicon, silicon carbide or other suitable material and is manufactured preferably as a sub assembly of prior art microturbomachinery and by means compatible with the manufacture of associated microturbomachine components. 
     The spaces  20  and  21  form fluid passageways from opening  18  to the periphery of the rings  12  and  13 . The fluid passageways are defined by four surfaces  22 ,  23 ,  24  and  25  over which the fluid flows, namely opposing surfaces  23  and  24  of the rings  12  and  13  and the opposing surfaces  22  and  25  of the ring  12  and backing disc  16 . 
     In FIGS. 4 to  6 , a second embodiment of a micromachine rotor  30  is illustrated. In rotor  30 , a backing disc  32 , supports a cross shaped hub  34  upon which are supported in close parallel array two smooth and substantially planar annular discs or rings  36  and  37 . The hub  34  is provided with openings  38  that are in fluid connection with the space  40  between backing disc  32  and ring  36  and with space  41  between ring  36  and ring  37 . The spaces  40  and  41  form fluid passageways from openings  38 , to the periphery of the rings  36  and  37 . The fluid passageways are defined by four surfaces  42 ,  43 ,  44  and  45 , namely opposing surfaces  43  and  44  of the rings  36  and  37 , and the opposing surfaces  42  and  45  of the ring  36  and the backing disc  32 . The inner diameter  46  of the spaces  40  and  41 , is smaller than the outer diameter  48  of the openings  38 . This arrangement allows an unimpeded flow of the vortex circulation of the fluid within the fluid passageways formed by the spaces  40  and  41  and within the openings  38 . In this embodiment the rotor has a diameter of about 4 mm and a width of about 0.6 mm. 
     Construction of the rotor  10  of FIGS. 1 to  3  and rotor  41  of FIGS. 4 to  6  may be accomplished by means of microfabrication techniques in common usage such as photolithography and masking layers. In the case where silicon is the material of construction, deep trench etch processes employing anistropic plasma etching steps alternating with polymerizing steps may also be employed. Such a process is described in U.S. Pat. No. 5,501,893 and is available from Surface Technology Systems Ltd. of Imperial Park, Newport U.K. However, other etching techniques can be employed, and preferably the etchant and chemistry employed are capable of producing deep trench geometries having high aspect ratios. Other manufacturing techniques may also be employed, particularly when the material of construction is silicon carbide, in which case components may be molded by vapor deposition of the selected material into a pre-etched mold formed in for instance a silicon wafer. The resulting molded components are then removed from their molds and may be bonded together with other components to produce the finished rotor. 
     The rotor  10  shown in FIGS. 1 to  3  may operate either as a compressor/pump or a turbine. In the case where the rotor is defined as the compressor/pump in a microturbomachine, the rotor is driven up to speed within a suitable housing by either electrical or mechanical means (not shown). It should be noted that the rotor  10  will operate with equal efficiency when driven in either a clock-wise or counter clockwise direction. Fluid upon entering inlet openings  18  and coming into contact with discs  12  and  13  is subjected to two forces, one acting tangentially in the direction of rotation, and the other radially outwardly. The combined effect of these tangential and radial forces is to propel the fluid with increasing velocity in a spiral path until it reaches the perimeter of the rotor where it is ejected. In the case where the rotor is operating as a turbine in a microturbomachine the operation described above is reversed. Thus, if fluid under pressure is admitted tangentially to the perimeter of the rotor disc, the rotor  10  will be set in motion by the viscous drag properties of the fluid which, travelling in a spiral path and with continuously diminishing velocity reaches the openings  18  from where it escapes. 
     Although a rotor  10  having two discs  12 ,  13  is depicted in FIGS. 1 to  3 , it is to be understood that a plurality of more than two discs suitably serving particular operating requirements may be utilized. Similarly, rotor  30  of FIGS. 4 to  6  may have at least one further disc or ring additional to rings  36 ,  37 . 
     As may be appreciated from FIGS. 1 to  3 , stresses set up by centrifugal forces are supported radially by the star shaped hub  14  thus preventing a bending moment on the backing disc  16 . Also, as illustrated in FIGS. 1 to  3 , ends  26  of the star shaped hub  14  extending into the space  20  between the backing plate  16 , and disc  12 , and the space  21  between discs  12  and  13  in order to provide lateral support to the discs  12  and  13 . 
     In contrast, in the second embodiment illustrated in FIGS. 4 to  6 , the ends of the cross shaped hub  34  terminate below the outer diameter  48  of openings  38  thereby forming inner diameter  46  of spaces  40  and  41 . The benefits with this embodiment are that disturbed fluid flow, caused by the ends  26  of the hub  14  of rotor  10  of the first embodiment, is able to be eliminated and the viscous drag flow is permitted to continue unimpeded to the openings  38 . 
     A preferred material of construction for the rotor of the invention is silicon carbide. This material possesses the properties of high strength and dimensional stability (creep-resistance) at elevated temperatures and a high strength to density ratio. In the particular case of prior art bladeless turbine rotors where the major problems have always related to internal vibration, high temperatures, high speeds and high pressures it has been impractical to construct the rotor from silicon carbide thus limiting the high performance potential of turbine rotors operating on the principles of fluid viscous drag. The use of silicon carbide in a micro-gas turbine rotor of the present invention minimizes disc distortion and allows higher speeds and therefore improved performance. In addition, because the rotor is made by microfabrication techniques, an advantage is gained from the particular batch production methods available. In the case where microturbomachine rotors may operate at lower temperatures than micro-gas turbines the preferred material of construction may be silicon. This material is already in wide usage in microelectronic componentry and the fabrication techniques are well understood. Ceramics are excellent materials for microfabrication of highly stressed components because they demonstrate high tensile strength at very high temperatures. 
     In some applications of micromachinery, a relatively low level of thermal or mechanical stress may apply in which case the means of supporting the rings  12  and  13  as shown for rotor  10  in FIGS. 1 to  3  may be modified. The same may apply to rings  36  and  37  of rotor  30  shown in FIGS. 4 to  6 . 
     FIG. 7 is a perspective view of a micro-gas turbine rotor  50  of the present invention constructed according to Brayton cycle gas turbine practice. Rotor  50  has a radial outflow compressor unit  51  and a radial inflow turbine unit  52  each of which operates on the principles of fluid viscous drag. Units  51  and  52  are mounted by their respective support discs  53  and  54  to a respective end of a connecting shaft  55 . 
     Each of the units  51  and  52  of rotor  50  of FIG. 7 has a general form similar to that of rotor  10  of FIGS. 1 to  3  and of rotor  30  of FIGS. 4 to  6 . Detailed description of units  51  and  52  therefore is not necessary. However, as shown, the respective support discs  53  and  54  face each other along shaft  55 . Thus, the rings  56  and  57  of unit  51  are adjacent to the surface of disc  53  which is remote from unit  52 , while rings  58  and  59  are adjacent to the surface of disc  54  which is remote from unit  51 . 
     In FIGS. 8 to  10  there is shown an embodiment in which a micromachine rotor  70  comprises a support disc  72  upon which is mounted an array of spacers  73 . Each of the spacers  73  is attached by a first face to support disc  72  and by the opposite face to ring  74 . On the opposite face of ring  74  is mounted a further array of spacers  75  and these spacers attach to the inner face of ring  76 . Although six spacers  73  and six spacers  75  of a particular size and shape are shown in the drawings it is to be understood that other numbers, sizes and shapes may be effective. In this particular embodiment of the invention of FIGS. 8 to  10 , the advantage of the radial support given to the rings by the star shaped hub as shown in FIGS. 1 to  3  or a cross shaped hub as shown in FIGS. 4 to  6 , respectively, is exchanged for the advantage of an unrestricted opening  78 . This embodiment of FIGS. 8 to  10 , like the first embodiment of FIGS. 1 to  3  and second embodiment of FIGS. 4 to  6 , defines fluid passageways between the opening  78  and periphery of the rings  74  and  76 . 
     The dimensions of rotor  70  as a whole, and the spacings of the disc  72  and rings  74  and  76 , for any given machine will be determined by the conditions and requirements of the particular application of the micromachine, as with rotor  10  of FIGS. 1 to  3 , rotor  30  of FIGS. 4 to  6  and rotor  50  of FIG.  7 . In general, greater disc spacing is required for larger disc diameters, longer fluid spiral path and greater fluid viscosity. For instance, when the machine is configured as a turbine the torque is directly proportional to the square of the velocity of the fluid relative to the rotor and to the effective area of the discs, and inversely, to the distance separating them. The size and shape of the disc openings will also be determined dependent on application and rotor construction. In a multiple disc rotor, the disc furthest from the backing disc may have larger openings to not only accommodate the fluid out flow through the passage adjacent that disc, but also the fluid outflow from all other discs between the backing disc and furthest disc. Further, the surface finish of the discs is sufficiently smooth to adhere at least one layer of fluid particles to the disc thereby creating a boundary layer in the fluid vortex. 
     In its preferred forms, the present invention may provide the following advantages over the prior art-use of radial flow vanes in microturbomachines: 
     (a) reduced corner stress concentration; 
     (b) reduced turbulence and pulsation in the working fluids; 
     (c) higher rotational speeds within the limits of the tensile strength and elastic modulus of the material due to plain radial loading and absence of sharp section changes; 
     (d) an improved rotor balance; 
     (e) a reduction of the bending moment caused by centrifugal blade loading; 
     and in the case of prior art use of large scale bladeless rotors: 
     (f) no requirement for a multiplicity of parts; and 
     (g) minimized disc distortion due to a preferred material of construction giving high strength and dimensional stability at high temperatures e.g. silicon carbide or silicon. 
     The reduction or elimination of cyclic stresses that arise from reaction between blades and working fluids in prior art microturbine rotors, has the effect of achieving the advantages outlined in paragraph (b) above and, effectively, extending the fatigue life, or durability of the rotor in the present bladeless configuration. 
     FIGS. 11 and 12 show a first test rig  80  for use in testing a bladeless rotor  10  as shown in FIGS. 1 to  3 . FIGS. 13 and 14 show a second test rig  80 , used in testing a bladed rotor  100  having blades  102 . The respective rigs  80  of FIGS. 11 and 12 and of FIGS. 13 and 14 are identical, and they therefore have the same reference numerals and are described with reference to either one of them. The rotor  100  shown in FIGS. 13 and 14 has a construction modelled as closely as possible on the turbine rotors described in the M.I.T. patent. 
     The respective rigs  80  were used to demonstrate the efficiency of using a bladeless or vaneless rotor in a micromachine represented by a test rig  80  as shown in FIGS. 11 and 12 and, using a bladed rotor  100 , in a test rig  80  as shown in FIGS. 13 and 14. That is, the purpose of rigs  80  was to demonstrate the performance of such machinery when used with a bladeless rotor  10  of the kind described above, as shown in FIGS. 11 and 12, compared with performance with a conventional bladed rotor  100 , having blades  102  shown in FIGS. 13 and 14. For practical reasons a decision was made to construct a turbine with 18 mm diameter rotors  10  and  100  to be driven by compressed air. The use of compressed air meant that the turbine did not require the capacity to embrace high combustion temperatures and thus did not have to be made in high temperature resistant ceramic materials. Thus, the componentry was constructed of a readily available metal that has excellent qualities of machineability. An aluminium alloy  2011  was selected due to its characteristics of machineability and its high tensile strength. The choice of an 18 mm diameter rotor was selected also for ease of manufacture and to ensure that the rig can still be classed as a micromachine. 
     The rotor design follows the embodiment of rotor  30  as illustrated in FIGS. 4 to  6  but with all dimensions scaled in the ratio of 1:4.5. The spacing between the backing disc  32 , and the disc  36 , and between the discs  36  and  37 , was 0.375 mm, whilst the thickness of the discs  36  and  37 , was 0.375 mm. The distance between the working surfaces  44  and  45  was 1.125 mm. 
     As shown in FIGS. 11 to  14 , each test rig  50  comprises a housing block  81  having a front face  82  with an annular recess  83 . A cylindrical throughway  84  extends through the center of the block  81  from the center of the annular recess  83  to the rear face  85  of the block  81 . The throughway  84  supports spaced bearings  86 . In FIGS. 11 and 12, bladeless rotor  10  is shown as mounted at one end of a shaft  87  that is supported within the throughway  84  by the bearings  86  for axial rotation. The rear end  85  of the block  81  is closed off by an end plate  88  which is secured to the block by cap head screws  89 . The annular recess  83  at the front of the block  81  supports an annular backing plate  90  that is positioned in close proximity to the rear of the bladeless rotor  10  in FIGS. 11 and 12 and the bladed rotor  100  in FIGS. 13 and 14. The bearing plate  89  supports an annular stator  91  having profiled blades  92 . The respective stator  91  is positioned outside but close to the periphery of the rotor  10  or rotor  100  to direct incoming air to the rotor periphery. A front cover  93  is secured over the front of the housing by six cap head screws  94 . Compressed air is used to drive the turbine and the air inlet  95  is positioned at the lower right hand side of the block as shown in each of FIGS. 11 and 13. The air initially fills the annular cavity around the periphery of the respective rotor  10  and  100  and then in the case of the bladeless rotor  10  flows through the fluid passageway defined by the rotor discs to impart viscous drag to rotate the rotor and then to escape via the apertures at the center of the rotor. The annular space exterior of each rotor is also coupled via a plenum chamber to a pressure sensor (not shown) via a bleed passageway  96  shown in FIGS. 11 and 13 in the top right hand corner of the block  81 . 
     The radial inflow rotor  10 ,  100  mounted on the respective shaft  87  is supported by a respective high speed (140,000 rpm) ball bearing race, of each bearing  86 , precisely located with identical preloads in both test rigs. The air is fed tangentially to the rotor by the air inlet  95 . It is also fed to the plenum chamber that includes the pressure sensor. The respective multi-vaned stator  91  directs the air onto the rotor  10 ,  100  and each stator  91  also is modelled on the stator disclosed in the M.I.T. patent. The rigs  80  have identical exhaust apertures and the shaft  87  includes a bicoloured disc that allows the rotational speed of the shaft  87  to be read using an optical tachometer. The compressed air was regulated with coarse and fine needle valves to ensure fine flow control. 
     Every care was taken to ensure that the two test rigs  80  operated on identical parameters. In one test, the revolutions per minute were measured against the plenum chamber pressure at precise change points to retrieve repeatable data. The pressure was increased slowly to ensure measurements represented stable conditions of air flow and rotor speed. Pressure was progressively increased until the ball bearing rpm specification limit for each bearing  86  was exceeded. The results of these test, namely rotor speed against supply pressure were plotted on the graph shown in FIG.  15 . 
     The test rigs  80  were then used to conduct mass flow tests where rpm were measured against exhaust air speed. The pressure was increased slowly to ensure measurements represented stable conditions of air flow and rotor speed. Pressure was progressively increased until the ball bearing rpm specification limit was exceeded. The mass flow in grams per second was then derived from volume per second of exhaust air and a graph was plotted as shown in FIG.  16 . 
     It can be seen from the graphs of FIG. 16 there is a clear performance advantage in using the bladeless rotor  10 , compared with the bladed rotor  100 . The mass flow graphs diverged from approximately 40,000 rpm showing a strong trend to proportionately lower values, for bladeless rotor  10  compared to bladed rotor  100 , at increasing rpm. The bladed rotor  100  registered a Mass Flow figure of 30% higher than the bladeless rotor  10  at 100,000 rpm. At maximum test Mass Flow, the bladeless rotor achieved approximately 35% higher rpm than the bladed rotor  100 . The plenum pressure against rpm graph showed a similar strong trend favouring the bladeless rotor  10 . From approximately 50,000 rpm the bladeless rotor  10  achieved higher speeds than the bladed rotor  100  and this divergence increased until 140,400 rpm which was just over the specification limit of the bearings. This speed was reached at only 2.75 pounds force per square inch (psi) an improvement of 18.5% over the bladed rotor  100 . Additionally, a 27% higher pressure was required in order for the bladed rotor  100  to reach 100,000 rpm. The divergent trends of both the graphs are indicative of major performance benefits that would be expected to increase proportionally at higher rpm&#39;s. 
     A further advantage that was noted in using the two test rigs  80  was that the bladeless rotor  10  was considerably quieter than the bladed rotor  100 . 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all aspects as illustrative and not restrictive.