Fans are widely used to circulate air in ventilation systems, air conditioners, air coolers and humidifiers for businesses and residences. Fans used for these purposes can be divided into centrifugal and axial flow fans. Centrifugal fans provide high air pressure, but are limited to a direction perpendicular to the rotational axis of the fan. Axial fans circulate a large volume of air. However, the air flow is limited to a direction coaxial with the rotational axis of the fan.

Both types of fans also create unwanted noise. These types of fans do not meet the needs of consumers for a fan capable of more complicated air flow patterns; as they are not able to provide air flow along any predetermined direction with respect to the rotational axis of the fan; and are noisy. Therefore, there is a need for a quiet fan able to provide an air flow at a predetermined angle to the axis of rotation.

Summary of the Invention An object of the invention is to provide a new and improved fan which can move air at a predetermined angle with respect to the axis of rotation, without excessive noise, particularly in indoor areas.

The object of the invention is achieved in a fan which can be used in applications ranging from large scale ventilation systems to miniature cooling fans.

In broad terms, the invention provides a fan comprising at least one fan blade configured such that during rotation of the fan air moves through the fan to create an air flow pattern which is inclined at an acute angle to the axis of rotation of the fan.

In one embodiment, the fan comprises a support plate to which a motor is mounted. A wheel hub with a plurality of fan blades is mounted to the shaft of the motor. A casing is mounted to the support plate coaxially with the motor and encircling the fan blades.

In other embodiments, the casing may further comprise a mask which helps direct air into the fan, or the blades may feature a shroud at their tips to control the flow of air in this region.

An advantage of the invention lies in the ability of the fan to provide an air flow direction at a predetermined angle to the axis of rotation. This inclined angle is symmetrical around the axis of rotation and creates a cone shaped air flow pattern. The design also minimizes the noise produced by the fan.

Since the present invention provides for an airflow pattern at an angle inclined from the rotational axis of the fan, it can also be properly characterized as an inclined flow air circulation system.

Preferably, the configurations of the various parts of the fan are determined using three-dimensional flow theories of turbomachinery; internal encircling control aerodynamic theory; computer generated three-dimensional flow design; and experimental results on studies of the internal flow of an impeller. Using these theories, the meridian planes and streamlines are calculated. From the meridian component velocity of the blade, the axial velocity is calculated. The component designs are optimized so that the desired air flow axial and tangential velocities are obtained. From those parameters, blade profile geometric parameters, such as, the chord length; the blade setting angle, the blade curvature radius and the blade stream surface inclined angle are obtained. Finally, the inclined angle of the wheel hub; the inclined angle of the casing; and the mounting profile of the fan blades are determined.

Particular theories which can be used in these

calculations include: (1) Lu Wencan The Theory and Expriment of Optimum Flow Distribution for Low Pressure Axial Flow Fan, The Conference of Chinese and Japanese Fluid Machinery, Xi'an, China, (October 1987); (2) Lu Wencan Analysis and Research of Spatial Flow Distribution of an Axial Flow Fan Journal of Chinese Engineering Thermophysics (Vol. 14, No. 2,1993) (3) Lu, Wencan, Analysis and Studies on Meridian Shape of Arbitrarily Inclined Stream Surface Impellers. The Fourth International Conference of Asian Fluid Machinery, Suzhou, China (October 1993); (4) Lu, Wencan, A Control Scheme and Its Experimental Studies of Fan Internal Flow. The First International Conference of Energy Conversion and Energy Sources Engineering, Wuhan, China (October 1990); (5) Lu, Wencan, Studies and Applications of Optimum Controlled Vortex of Arbitrary Inclined Flow Surface Impellers. Journal of Chinese Engineering Thermophysics (American Edition), volume 2 (1992) whose content is incorporated by reference herein and to which reference may be made as appropriate.

A feature of an inclined flow fan in accordance with the invention lies in that the spatial three- dimensional twisted blade according to the above theories can maximise the transmittal of mechanical energy to the airflow. Thus it can produce 25-400 higher flow efficiency than a conventional fan, and make lower noise. Since the air flow is inclined, the meridian acceleration increases the absolute velocity of

the air. Further, the airflow gains a high pressure head during passage through the fan. Thus, the airflow velocity at the outlet is higher and the air flow larger than for a conventional fan.

When an aerofoil type cross section is employed in the blade the energy transfer and flow efficiency of blade may be at an optimum, and the noise may be reduced. This makes reference to"Optimum Control Vortex Design of Inclined Flow Fan for Vehicle Tunnel ", written by Lu Wencan (6th International Symposium on the Aerodynamics and Ventilation of Vehicle Tunnels, Durham, UK, 27-29, September, 1988).

Another feature of the fan according to the present invention is that a shroud may be provided on the blade tip. This can effectively control the underflow and secondary flow of air around the blade tip, thereby significantly reducing the noise and improving the performance of the blades.

By virtue of the three-dimensional air flow field produced by the fan of the invention, more effective heat exchange and circulation of air in an air - conditioned room may be achieved. In comparison with similar axial or centrifugal fans, a fan of the present invention has the features of high efficiency, low noise, large flow volume and of being compact.

A fan according to the present invention is intended mainly to be used for household air circulation purposes. The head of the fan may be mounted so as to be capable of turning though 180°, so that optimum convective heat exchange can be maintained during operation. For example, it is estimated that in a typical 5m x 5m x 3m air-conditioned room, by using a fan according to the present invention, it need only take 10 to 15 minutes to lower or raise the temperature by 4 to 5 °C, and to produce an air flow speed which is comfortable for people in the room. In particular, extrapolating from data measured in a 2.88m x 3m x 2.9m

model air-conditioned room, with an air flow of 0. 5m3/s, in a room provided with a heat source the furthermost <BR> <BR> <BR> <BR> marginal average temperature may rise by 4. 310°C. With a cooling source the temperature may drop by 4.310 °C, with an airspeed of about 0.033m/s in the given time.

A fan according to the invention may be used not only in indoor air circulation for air-conditioning, but also in ventilation and air exchange on roofs, in plant buildings, mines, work sites and houses etc.

Brief Description of the Drawings Other objects and advantages of the invention will be evident to one of ordinary skill in the art from the following description and Figures in which: Figure 1 is a diagrammatic side view, partly in section, of an embodiment of a fan of the present invention; Figure 2 is a partial side view of one embodiment of the present invention showing a blade and flange attached to a partial wheel hub; Figure 3 is a sectional end view, partly in diagrammatic form, of a fan blade showing the tip and its flange according to one embodiment of the invention ; Figure 4 is a partial side view, partly in section and in diagrammatic form, of an embodiment of an inclined flow air circulator; Figure 5 is a side elevational view of the exterior of an embodiment of an inclined flow air circulator of the present invention; Figure 6 is a schematic diagram of the structural parameters of a representative test room; Figure 7 is a plan for the arrangement of thermocouples in the room of Figure 6; Figure 8 is a block diagram of the thermocouples and temperature measuring circuit used with the room of

Figure 6 in the positions shown in Figure 7; Figure 9 is a curved surface temperature distribution diagram, showing the temperature distribution along the Z = 1.44 metre vertical plane in Figure 6 after the inclined flow air circulator has run; Figure 10 is a different representation of the temperature distribution of the Figure 9; Figure 11 is an explanatory drawing showing the relationship between the axial Z, radial r, quasi- orthogonal q, and meridian B. directions; Figure lla is a perspective view of velocity vector C at a lattice site for an optimum combination of velocity Cu and Cz ; Figure 12 is a diagram showing the streamline distribution along a meridian plane of a fan blade of one embodiment of the present invention; Figure 13 is a graph of the average relative radius (r/rt) m of a fan blade versus air flow velocity for the meridional components of the fan blade inlet Qi and of the fan blade outlet Cl2 for one embodiment of the present invention ; Figure 14 is a graph of the average relative radius (r/rt) m Of a fan blade versus air flow velocity showing the optimum variation of tangential velocity CU and axial velocity Cz for one embodiment of a fan blade of the invention; Figure 15 is a graph showing the relationship between the average relative radius (r/rt) m of a fan blade and both the fan blade chord length b and fan blade curvature radius Rofor one embodiment of the present invention; Figure 16 is a graph showing the relationship between the average relative radius (r/rt) m of a fan blade and both the stream surface-inclined angle a and the blade profile setting angle ßb for one embodiment of the present invention; Figure 17 is a diagram showing a fan blade attached

to the wheel hub outer surface surrounded by the casing inner surface, along with the inclined angle of the wheel hub ah and the inclined angle of the casing at ; Figure 18 is a graph of the relative radius r/rt of a fan blade versus the fan blade relative chord length b/bh for an embodiment of the invention; Figure 19 is a diagram of-the relative radius r/rt of a fan blade versus the fan blade setting angle b for an embodiment of the present invention; Figure 20 is a graph of the relative radius r/rtof a fan blade versus the relative curvature radius Ro/Roh of a fan blade for an embodiment of the invention; Figure 21 is a diagrammatic perspective view of a fan blade and wheel hub showing the axial direction Z, the fan rotation direction, a radial direction r, a meridian plane Pm the three dimensionally twisted shape of the blades and their attachment at the. wheel hub; Figure 22 is a diagrammatic top view of a single blade on a wheel hub showing the axis of rotation Z, the relative rotation direction u, and the blade setting angles at the blade base (ßb) h and the blade tip (b) t ; Figure 23 is a diagrammatic side view of a partial wheel hub and a single blade showing the axis of rotation Z, the direction of rotation u, the radii of the blade base at the leading rlh and trailing r2hedges and the radii of the blade tip at the leading rlt and trailing r2t edges; Figure 24 is a side elevational view of one embodiment of a wheel hub, fan blade, fan shroud subassembly of the present invention, showing the inclined shape of the outer surface of the wheel hub, the twisted three-dimensional shape of the fan blades, and fan shrouds attached to the tips of the fan blades ; Figure 25 is a diagrammatic top view of a single blade showing the axis of rotation Z, the relative rotation direction u, and the blade curvature radius at the blade base Roh and the blade tip Rot ;

Fig. 26 is a cross-sectional view of a further embodiment according to the present invention, Fig 27 is an external view of a further embodiment of the invention; Fig. 28 is a streamline distribution diagram along blade meridian plane obtained for a further design of the invention ; Fig. 29 shows the variation of meridian component velocity Cç1 (inlet) , CQ2 (outlet) of blade inlet, outlet along with average relative radius rm on a design of the invention; Fig. 30 is a variation diagram of optimum (Cz) opt and (Cu) opt along with rm distribution in flow optimization computing results of one embodiment according to the present invention; Fig. 31 is an explanatory drawing of blade chord length b and blade profile curvature radius Ro along with rm of one embodiment according to the present invention; Fig. 32 is an explanatory drawing of variation of stream surface inclined angle a along with rm ; Fig. 33 is a variable range diagram of a blade relative chord length b/bh along with rm, in which bh is a chord length of the wheel hub; Fig. 34 is a variable range diagram of a blade setting angle Pb along with rm ; Fig. 35. is a variable range diagram of relative curvature radius Ro/Roh of a blade along with rm ; and Fig 36 is an explanatory drawing of the definition of half cone angle at at blade tip and inclined angle ah in blade wheel hub of a product according to the present invention.

Description of Preferred Embodiments An inclined flow air circulation system according to the present invention employs a plurality of three- dimensionally twisted fan blades which are especially designed for optimal performance for certain

applications. The three-dimensional shape of the fan blades produces air flow along directions at an acute angle to the rotational axis of the fan. This allows for effective heat exchange and air circulation. Compared with axial or centrifugal fans, the inclined flow air circulator of the present invention features higher efficiency, lower noise, greater air flow and smaller size.

The design of the present invention is the result of research and development on fan three-dimensional flow theory; internal encircling control aerodynamic theory; and three-dimensional flow theory of turbo machinery. This has allowed the design of various fans, fan impellers and fan components which are no longer restricted to air flow in only axial or radial directions. Various theories and formulae to which the present invention relates can be found in : Lu, Wencan, Analysis and Studies on Meridian Shape of Arbitrarily Inclined Stream Surface Impellers, The Fourth International Conference of Asian Fluid Machinery, Suzhou, China (October 1993); Lu, Wencan, A Control Scheme and Its Experimental Studies of Fan Internal Flow, The First International Conference of Energy Conversion and Energy Sources Engineering, Wuhan, China (October 1990); and Lu, Wencan, Studies and Applications of Optimum Controlled Vortex of Arbitrary Inclined Flow Surface Impellers. Journal of Chinese Engineering Thermophysics (American Edition), volume 2 (1992), which are incorporated by reference herein.

As an example, the design for one embodiment of an inclined flow air circulation system comprised the steps of: Calculating the optimum shape of the meridian plane Pm components for the invention, which include the fan inlet, the revolving flow channel of blade, and the spreader cone channel of the outlet. The method used can be found in the previously referenced article, Analysis

and Studies on Meridian Shape of Arbitrarily Inclined Stream Surface Impellers.

Calculating the meridian plane three-dimensional flow field of the invention. By conducting 6-8 iterations employing a streamline iteration method, a convergent solution of the required accuracy can be obtained. The computed results are the actual fan blade streamlines in the meridian plane as shown in Figure 12 and the meridional velocity distribution as shown in Figure 13.

Carrying out optimization computation of the spatial flow pattern. Using the convergent solution of the meridian plane three-dimensional flow fields, optimization computation of the flow patterns are conducted according to the previously referenced, Studies and Applications of Optimum Controlled Vortex of Arbitrary Inclined Flow Surface Impellers.. Results of an optimization are shown in Figure 14.

Carrying out optimization computation of the three- dimensional blade profile. Using the computed results of the meridional three-dimensional flow field, air flow parameters of the blade along the quasi orthogonal q direction at various cross-sections as well as other blade geometric parameters such as chord length b, setting angle b curvature radius Ro and stream surface inclined angle a are calculated. The shape of the three dimensional blade is determined by these parameters.

Multiple iterations of this computation are performed until the blade profile is optimized. Computed results of this calculation are shown in Figure 15 and Figure 16.

At this stage the fan blade of the desired inclined flow air circulation system is optimized. For the embodiment shown in Figures 12-20, the impeller has 5 blades, each of them having a three dimensionally twisted shape. The blade setting angle decreases progressively from the wheel hub to the blade tip as

shown in Figure 16, and the blade chord length increases progressively from the blade base to the blade tip, as shown in Figure 15. The elemental blade profile is a circular arc profile of constant thickness.

After the fan blade parameters are established, the boundary layer thickness, momentum thickness, underflow and secondary flow intensities passing the blade tip gap are calculated. The method used can be found in the previously referenced article A Control Scheme and Its Experimental Studies of Fan Internal Flow. The results are used to determine the optimum dimensions of the flange structure controlling blade tip encircling.

A particular method of design may comprise the steps of: Determining the optimum outlet diameter d2t of the blade, the optimum ratio d (d=d2h/d2t) and the optimum meridian shape according to overall optimum design method based on flow rate and pressure of the fan given by the user (referring to Figure 13 and the references : Lu, Wencan, Determination of the Optimum hub-tip ratio in Impeller with Inclined Stream Surface, Fluid Engineering, Vol. 21, No. 1, (1993); Lu, Wencan, The Analysis and Research of the meridian shape for the Impeller with Arbitrary Inclined Stream Surface, the 4th International Conference of Asia on Fluid Machine, Suzhou, China, (October 1993).

Calculating the velocity distribution and streamline distribution of the meridian plane of the blade from the following equations according to the given design conditions of flow rate and air pressure and the determined blade meridian shape, <BR> <BR> <BR> <BR> <BR> <BR> <BR> Cp² = Ke #p(q)dq +e #p(q)dq #e #p(q)dq T(q)dq (1) <BR> <BR> where Integral constant K meets the continuous equation.

(Where m is mass flow, p is density) wherein the relation of Cr to q is given by the law of optimum controlled vortex (referring to : Lu, Wencan, The Research and Application of Optimum Controlled Vortex in Impeller with Arbitrary Inclined Stream Surface, Journal of Chinese Engineering Thermo-Physics (American version), (October 1993)). The relation of entropy Q to q is given by the principles of optimum velocity distribution (referring to : Lu, Wencan, The Optimum Desian of Axial Fan Used in Dust Remover, the 9th International Conference of Thermal Fluid Engineering Medium Transmission, Singapore, (June 1996)). In the equations, the directions of 1, q refer to Figure 11. The relation of stagnation enthalpy í to q is determined by the law of energy equation and loss distribution, where t is time, q is quantity of heat and p is pressure (referring to : Lu, Wencan, Fan Three-Dimensional Theory and Design, Publishing House of HUST, pp 44-46, (1986)).

The law of loss distribution refers to : Lu, Wencan, Analysis of Loss Model and Meridional form in 3-D Design of Axial Fans, Journal of Engineering Thermophysics, volume 14 No. 4, (1993).

At the same time, when equation (1) is met, the optimum combination of velocity Cu and Cz is carried out such that the streamline distribution along the meridian plane of the blade and three-dimensional airflow parameters at points of lattice sites, one of which perspective view of velocity vector C on the sites is shown in Figure lla.

Determining the number of blades N according to the hub-tip ratio d, therefore determining the parameters of the blade shape of each stream surface (cross section of the blade) is as follows: i, the angle of the chord. v=90°-ßb=90°-ß1-(ß2-ß1)/2+(i-#)/2 (6) wherein Pb is a setting angle of blade, l, 2 are angles of airflow at inlet and outlet respectively, i is an incidence angle, 6 is a deviation angle, #=(ß2e-ß1-i)/(#½m-1) (7) wherein ß2e=cot~1 [u2- (r2/rl) c2u] /clwo=b/t/t=n (r1+r2) /N m=0.92 (a/b) 2+0.002 (90-ß2), a/b---relative curvature of blade shape ii, the length of chord b= [ (r22-r12sin2v) l/2-rlcosv] /sina (8) The above parameters 6, v, b, must be determined by iteration calculation iii, the radius of median arc of blade shape is determined by the following equations, R0=b/(2sin0.5#), #=ß2-ß1-i+# (9) The parameters of blade shape along cross sections of the blade (3b, b, Ro are determined from equations (6), (7), (8) and (9), and the inclined angle of the stream surface a has been obtained when calculating the streamline distribution. When the gravity center of the

blade shape (cross section of the blade) is selected as iteration integral point, the spatial three-dimensional blade shape is obtained through an iteration integral line (generally a radial line).

Estimating internal flow loss and efficiency of blade according to the determined blade shape, if non- separation criterion of the internal boundary layers and the requirements of efficiency are not satisfied, meridian shape and related parameters are modified and the above calculating steps are repeated until the requirements are satisfied (with reference to equation (5) above and reference : Lu, Wencan, Optimization Analysis of Controlled Diffusion Fan Blading, Second International Conference on Pumps and Fans, Beijing (October 17-20, 1995)).

Calculating the parameters of boundary layer at the cross section of the blade tip, the intensities of the underflow and secondary flow according to the internal encircling control aerodynamic theory (see Figure 3), so as to determine the sizes of blade shroud (with reference to : Lu, Wencan, Experimental Investigation on the Aerodynamic Noise for Low Pressure Axial Fan with Addition Guide Vanes, Fluid Machinery, Volume 22, No. 11, (1994)).

Referring to an embodiment of the invention as shown in Figure 1, the inclined flow air circulation system is generally designated as 10. The circulation system comprises a casing 60 connected to a motor supporting plate 20 to form a housing. A motor 50 is mounted to the supporting plate 20 with a fan hub 30 being mounted to a shaft 52 on the motor. The motor 50 and hub 30 are coaxial with the casing 60. Fan blades 40 are mounted to the hub external surface at a predetermined angle. The hub 30 and blades 40 may be manufactured separately and joined to form an impeller.

Alternatively the wheel hub and blades may be integrally manufactured, for instance as a single

casting of either plastic or metal.

Figure 4 is a partially schematic view of an inclined flow air circulator. In this embodiment, the fan blade 40 is mounted at its base to the hub 30. The wheel hub 30 is fastened to a driving plate 32. This combination is held to the shaft 52 of the motor 50 by a nut 54. The driving plate 32 is rotationally connected to the motor shaft 52. While not shown, other commonly known methods and structures may also be used to attach the blades 40 to the wheel hub 30, and the wheel hub to the motor shaft 52.

The blade tips are parallel to the inner surface of the casing 60 and separated from the casing by a radial gap 76, shown in Figure 4. The radial gap may range from, for example, 1.5 to 16 millimetres. In one embodiment of the invention shown in Figures 2,3 and 24, a flange or shroud 70 is included at the tip of the blade. The flange controls under flow and secondary air flow passing through the tip gap 76. This significantly reduces noise and improves the aerodynamic performance of the blade. The flange 70 may face into the direction of fan rotation or away from the direction of fan rotation. Figure 3 is a partial, sectional view showing more detail of the flange 70 and the blade tip, including the flange width 72 and thickness 74. The flange width may be in the range of, for example, 2 to 12 millimetres and the flange thickness may be in the range of, for example, 0.5 to 4.5 millimetres.

The casing 60 can optionally be provided with a mask 62, as shown in Figure 4, to help guide air into the fan blades. The mask may be integral with the casing or may be movably attached to it. In the embodiment shown in Figure 4, air is drawn from the left of the Figure, flows through the fan, and is discharged to the right.

While the Figures show the casing as having a cone shape, with a smaller diameter air inlet and a larger

diameter air outlet, the shape of the casing can be changed so that it is cylindrically shaped, or so that the inlet has a greater diameter than the outlet. The shape of the blade tip will change to parallel that of the casing.

Figure 5 shows another embodiment of the current invention. In this Figure, air is drawn in from the lower right side of the circulator, then via the guidance of the wheel hub, fan blades and casing, air is discharged from the upper left side with a predetermined pressure, speed, and direction. The air discharge direction, unlike normal fans does not have to be parallel with the motor shaft, but may be inclined at some angle to the axis of rotation. The inclined angle is symmetrical around the axis of rotation. The result is an air flow pattern that is cone shaped, increasing in diameter as it moves away from the fan. Further, since the fan assembly shown in Figure 5 can pivot, the inclined flow direction is further adjustable.

As can be seen in Figures 2,24, and 25, each blade base is mounted to the hub. The number of fan blades mounted to the wheel hub can range from three to ten or more according to air flow requirements. Each blade 40 has a leading edge 42 and leading face 43 pointing into the direction of rotation and a trailing edge 44 and trailing face 45 pointing away from the direction of rotation. For any radial position between the blade base and tip, each blade 40 has a blade curvature radius Ro, shown in Figure 25. The leading 43 and trailing 45 faces of each blade encompass this blade curvature radius, and together the faces define a curved airfoil shape schematically shown in Figures 2 and 25. Figure 21 shows a more detailed picture of the three-dimensional blade shape and the attachment of the blades to the wheel hub 30.

Figure 21 also shows the axial direction Z, which is the same as the axis of rotation, as well as a line

in a radial direction r. A meridian plane Pm is defined by the line in the axial direction and the line in the radial direction. The relationships of the axial Z, radial r and meridian Q directions are further shown in Figure 11.

Figure 12 shows a meridian plane formed by a line in the axial direction Z and a line in a radial direction r. Lines 3'and 5'represent a two-dimensional projection of a fan blade in this meridional plane. The arrowed lines, numbered 1 through 7, show selected streamlines across the fan blade. The streamlines indicate the path of air flowing over the fan blade. As can be seen, the three dimensionally twisted shape of the fan blade 40 creates a plurality of streamlines all inclined at an angle to the axis of rotation Z. The three dimensionally twisted design of the fan blade therefore allows the inclined flow air circulation system to have an outgoing air flow direction which is inclined at an angle to the axis of rotation Z. As the fan blades rotate around the axis of rotation, the inclination angle of the air flow in each meridian plane remains the same. The result is a cone shaped pattern for the outgoing air flow.

Figure 17 is a schematic view of an embodiment of the present invention showing a fan blade 40 attached at the base to the outer surface of the wheel hub 30. The blade tip parallels the inner surface of the casing 60.

The wheel hub 30 has a conical outer surface and an inclination angle ah. The wheel hub inclination angle is the included angle between a first imaginary line defined by the intersection of the meridian plane Pm (shown in Figure 21) and the wheel hub outer surface, and a second imaginary line parallel with the axis of rotation and tangent to the wheel hub outer surface at its small diameter. The inclined angle of the wheel hub ah may range from, for example, 10 to 42 degrees. Figure 17 also shows the inclined angle of the casing ah,

similarly defined by the intersection of a first imaginary line created by the intersection of the meridian plane and the casing inner surface, and a second imaginary line parallel to the axis of rotation and tangent to the casing at its small diameter. The inclined angle of the casing ah may range from, for example 4 to 18 degrees.

As shown in Figure 23, the inclined surfaces of the wheel hub and the blade tip create different radii at the fan blade leading and trailing edges, 42 and 44 respectively. The distance from the axis of rotation to the blade base at the leading edge is designated rlh while the distance from the axis of rotation to the blade base at the trailing edge is designated as r2h. The distance from the axis of rotation to the leading edge at the blade tip is designated as rltwhile the distance from the axis of rotation to the blade tip at the trailing edge is designated as r2t.

An average relative radius rm for any section of the fan blade can be calculated by the formula: rm = ( (r1+ r2) /2)/ ( (r1t+ r2t) /2) where rlis the distance from the axis of rotation to a radial position on the blade at the leading edge and r2 is the distance from the axis of rotation to a radial position on the blade at the trailing edge. For a blade section parallel to the axis of rotation, ri will equal r2. An average relative radius of the wheel hub rmh can be calculated from the above formula using rih as ri and r2has r2. Embodiments of the present invention may have an average relative radius of the wheel hub rmh ranging from, for example, 0.3 to 0.4.

Since the blade leading, and trailing radii, rlt and r2t respectively, are different, the swept area created by the rotation of the fan blades has a correspondingly inclined shape. This gives a diameter of the swept area at the fan blade leading edge d, which is different from the diameter of the fan blade swept area at the trailing

edge d2, as shown in Figure 1. In other embodiments, the fan blade may have the same radii at the leading and trailing edges or may have a greater radius at the leading edge than the trailing edge.

The blade faces are curved, with a blade curvature radius connecting the blade leading 42 and trailing 44 edges as shown in Figure 25. The blade curvature radius is variable and may be chosen to satisfy design criteria. The particular blade curvature radius chosen at the blade base is designated Roh. The blade curvature radius chosen at the blade tip is designated Rot. The blade curvature radius chosen at any position between the blade tip and blade base is designated Ro. As shown in Figure 25, the chosen blade curvature radii will vary between the blade base and blade tip.

A relative curvature radius is given by Ro/Roh.

Since both the blade curvature radius Roand blade base curvature radius Rot are design variables, the resulting relative curvature radius Ro/Roh will also be variable.

As can be seen from Figure 20, the possible range of relative curvature radii will vary with radial position along the fan blade. The radial position along a fan blade can be indicated by the relative radius r/rt. where r is a distance from a position on the fan blade to the axis of rotation and rt is a distance from the blade tip to the axis of rotation. The possible range of relative curvature radii Ro/Roh for an embodiment of the present invention is contained within the dotted lines of Figure 20.

A chord with a length b is defined by a straight line between the leading 42 and trailing 44 edges of a blade. For any radial position on the blade, the chord length will be dependent on other blade design factors such as blade width and curvature radius. Since the blade has a continuously varying shape from blade base to blade tip, the chord length will also vary from blade base to blade tip. Figure 15 shows the variation of

blade chord length b, with average relative radius (r/rt) m for one embodiment of the present invention. For this embodiment, the chord length progressively increases from the wheel hub to the blade tip.

A relative chord length is given by b/bh, where b is the chord length at a radial position along the fan blade and bh is the chord length at the wheel hub. Since both the chord length and blade base chord length are variable based on fan blade design, the resulting relative chord length will also be variable. Figure 18 shows the possible variable range of the relative chord length, shown within the dotted lines, versus the relative radius r/rt for one embodiment of the present invention.

As shown in Figure 22, a blade setting angle pub ils defined as an included angle between the blade chord and a plane perpendicular to the axial direction and tangent to the blade trailing edge 44. Since the blades have a continuously varying shape from base to tip, the blade setting angle b can also vary from the blade base (f3b)n' shown as position 40', to the blade tip (ßb) t/shown as position 40". Figure 16 shows the variation of blade setting angle b with the average relative radius (r/rt) m for one embodiment of the present invention, as well as the relationship between the stream surface inclined angle a and blade setting angle b for a given average relative radius (r/rt) m. As can be seen, the blade setting angle Pb decreases progressively from wheel hub to blade tip in this embodiment.

Figure 19 shows the range of possible variations of blade setting angle b with relative radius of the blade r/rt for some embodiments of the invention. At the blade tip, where r/rt= 1, the blade setting angle (ßb) t can range from, for example, 22 - 37 degrees. At the blade base, the blade setting angle (ßb) h can range from, for example, 40 - 58 degrees.

The three dimensionally twisted fan blades of the

inclined flow air circulation system create an outgoing airflow pattern inclined at an acute angle to the axis of rotation. The outgoing air pattern may be further refined by varying the inclination angle of the wheel hub ah ; the inclination angle of the casing ah ; the presence and shape of a mask 62; and the presence and shape of a flange 70.

The effectiveness of the inclined flow air circulation system has been tested by measurement and modeling. Figure 6 shows a schematic diagram of a test room used for such measurement.

Thermoocouples, schematically shown in Figure 8, are arranged in the test room along a Z = 1.44 meter plane, as shown in Figure 7. An inclined flow air circulation system was run for 45 minutes, at which time temperatures were taken at each thermocouple position.

The results are graphically shown in Figures 9 and 10, which are different representations of the same data.

The measured test results have been extrapolated to a larger 5m x 5m x 3m room with either a heating or cooling source. With an inclined flow air circulation system moving 0.5 cubic meters of air per second at an average air flow speed of 0.033 meters per second, it has been estimated that only 10 to 15 minutes are needed to raise or lower the room temperature 4-5 °C. The inclined flow air circulation system can therefore provide efficient and quiet equalization of temperatures within a room.

Some further embodiments of the invention will now be described with reference to Figures 26 to 36.

Figure 26 shows a further fan which may be applied to large-scale ventilation systems or miniature fans.

It comprises a motor support plate 101, a hub 103, blades 104, a motor 110 and a casing 102. Casing 102 is mounted to the motor support plate 101. The motor 110 is mounted on the motor support plate 101 and the blades 104 are mounted on the hub 103. The blades 104 and hub

103 may be manufactured separately or made integrally.

For instance the hub 103 and blades 104 may be die cast together in a plastics or metal material in a single operation. The hub 103 has a hole in its center which coupled to the motor 110 so that the hub 103 and fan blades 104 are rotated together by the motor 110.

The structures of the various fan parts are determined by using the aforementioned three-dimensional flow theory of turbomachinery, internal encircling control aerodynamic theory, computing software system of fan three-dimensional flow design and experimental results of impeller internal flow.

As in the earlier embodiments, each blade 104 has a three-dimensionally twisted shape, which is determined by computation of the meridian three-dimensional flow field, blade flow parameters on various cross sections along quasi orthogonal q direction and geometric parameters of the blade profile.

The number of blades 104 may range from 3 to 10, depending on requirements. The outer surface of hub 103 is generally cylindrical, although it may be frustroconical, and the blades are arranged on the conical surface, and connected to the hub 103 at a predetermined angle.

Fig. 27 shows a yet further embodiment of the invention. In this embodiment, air is sucked in from lower right side, and then via the guidance of conical wheel hub and rotation of fan blades, air is blown out from upper left side in the figure with a predetermined pressure, speed, flow, etc. The position of the fan head may be varied though 180°. In this embodiment, the hub of the fan is frustoconical. As in the earlier embodiment of Fig. 2, the blade optionally has a shroud at its tip. The preferred dimensions of the shroud are discussed above with reference to Figures 2 and 3.

Blades for the above embodiment can be designed using the principals referred to above. In the design,

certain parameters are utilised as defined before in Figure 11 namely a meridian direction (1), an axial direction (Z), a radial direction (r), an included angle between the meridian direction 1 and Z axis (a), a quasi-orthogonal direction (q), and the included angle between q and r, (y) . The inclined angle a of the stream surface is given as ah at the hub and at at the tip of the blade. In this embodiment, 0<a<5°.

With reference to the parameters used in Figs 32 to 35 the curvature radius Ro is the radius of the median arc of the blade which also varies from Roh at the hub to Rot at the blade tip. The ordinate in Figures 32 to 35 is the average relative radius rm = (r/rt) m where rt is the radius of blade tip, and the average blade radius at any section of the blade as described above. Thus at the wheel hub, (7m) h = Fmh (rlh+r2h)/2) (r,, +r2t)/2). In this particular embodiment, rmh=0. 2, and (rmh) min=0. 1.

Figure 28 shows the results of a computation of the meridian stream, the streamline distribution being shown along the blade meridian plane (the meridian plane is any plane passing through the rotating central axis, <BR> <BR> <BR> <BR> i. e., the plane where r-z coordinates are located) for this embodiment. Five meridian streamlines have been shown in Figure 28.

Figure 29 shows the variation of meridian component velocities Ce1, Ci2 at the inlet and outlet of the blade respectively with the average relative radius rm, i. e. the velocity distribution of airflow along the meridian plane. Ce1 is the meridian component velocity at the inlet, Cç2 is the meridian component velocity at the outlet. After obtaining the C1 value, axial velocity CZ can be calculated, then in combination with tangential velocity Cy, the blade profile parameters on a fixed conical surface can be worked out, including the setting angle b and chord length b etc..

Figure 30 shows the results of computed blade profile optimization. The optimum distributions of

axial velocity C ; ; and tangential velocity Cy are obtained whereafter the blade shape may be optimized.

Referring to Figs. 31,32 and 34, Fig. 31 shows the variation of blade chord length b and radius of curvature Ro, while Fig. 32 and 35 show the variation of stream surface inclined angle a and the blade setting angle , respectively. These are all the result of blade profile optimization computation. The entire shape of three-dimensional blade is determined from consideration of the four parameters b, Ro, Pb and a.

Figs 28 to 32 illustrate the blade design procedure. Firstly, the inclined angle a between a blade wheel hub and position of a blade tip conical surface is determined using the theories discussed above. The conical surface positions where the blade profile cross sections of the blade are located are determined by intermediate streamline. In Fig. 29, the axial velocity CZ is worked out from CQ, optimization of velocity distributing combination is obtained from C, and Cy. The optimized blade profile parameters b, b, Ro, u are finally obtained from optimized (CZ) opt, (C") oPt Fig 33, illustrates the variable range of blade relative chord length b/bh, wherein bh is the chord length of the fan hub. The region between the dotted lines illustrates a preferred range of the invention, in which bo/boh = 0.6-2. 5.

Fig. 34, illustrates the variable range of blade setting angle (3b, and the data in the region between the dotted lines is a preferred range of the invention, i. e. in which zizis from 65° at the wheel hub to 15° at the blade tip.

Fig. 35, illustrates the variable range of radius of curvature of the blade Ro. (Roh is the radius of curvature at the fan hub). The data in the region between the dotted lines represents a preferred range of the invention, in which Ro/Roh= 0. 4-4.0.

Fig. 36 shows a typical fan according to the

present invention. The blade outlet diameter may be 0.2m, 0.3m, 0.4m, 0.5m, 0.6m, 0.7m, 0.8m respectively, the inclined angle at at the blade tip is 0-30° and the inclined angle symbol ah at the blade hub is -5-40°.