TECHNICAL FIELD

[0001] The present subject matter relates in general to impellers, and in particular, to an impeller having a helical configuration.

BACKGROUND

[0002] Typically, centrifugal pumps having spiral impeller are used in transporting fluids, for example sewage, which contains solids. These solids can include organic wastes, long fibers, and the like. The solid particles present in these fluids tend to accumulate between edges of impeller and a casing comprising the impeller. This accumulation can be to an extent that rotation of the impeller may be blocked. Also, long fibres in such fluids tend to entangle themselves around impeller vanes. Therefore, the pumps used for transporting such fluids have a tendency to get blocked or clogged by the solids particles or deposits in the fluid. This leads to the physical failure of pumps. Further, retention of certain abrasive solids, for example sand, can cause wear which lowers efficiency of the pump.

BRIEF DESCRIPTION OF DRAWINGS

[0003] The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

[0004] Fig. 1(a) depicts an isometric view of an impeller, in accordance with an implementation of the present subject matter.

[0005] Fig. 1(b) depicts another isometric view of the impeller, in accordance with an implementation of the present subject matter. [0006] Fig. 2(a) depicts a top-view of the impeller, in accordance with an implementation of the present subject matter.

[0007] Fig. 2(b) depicts progression of an inlet angle at a leading edge, in accordance with an implementation of the present subject matter.

[0008] Fig. 3(a) depicts a side view of a pump comprising the impeller within a casing, in accordance with an implementation of the present subject matter.

[0009] Fig. 3(b) depicts a curved section, in accordance with an implementation of the present subject matter.

[00010] Fig. 4 depicts a plan view of the casing comprising the helical impeller, in accordance with an implementation of the present subject matter.

DETAILED DESCRIPTION

[00011] The present subject matter provides an impeller for a centrifugal pump for pumping fluids comprising solids and quasi-solids.

[00012] Centrifugal pumps have been used for pumping viscous fluids, for example sewage waste. These viscous fluids comprise quasi-solids and solids, such as organic wastes, long-fibered solids, abrasive solids, and the like. Typically, the centrifugal pumps used for such operations have a spiral impeller provided within a housing. Edges of the spiral impeller are fitted on a rotor such that the edges are close to the housing to reduce clogging. However, solid particles, especially quasi-solids, tend to accumulate within gap formed between the edges and a wall of the housing. This further prevents rotation of the impeller, thereby, preventing working of the centrifugal pump. Also, abrasive solids, such as glass and sand, tend to cause wear of the parts of the centrifugal pump. This further reduces the efficiency of the pump despite cleaning to remove any accumulation.

[00013] Additionally, centrifugal pumps for pumping viscous fluids also tend to have cavitation issues. Cavitation is the formation of bubbles or cavities in the fluid being pumped. Cavitation is typically developed in areas of relatively low pressure around an impeller. The imploding or collapsing of these bubbles trigger intense Shockwaves inside the pump, causing significant damage to the impeller and the pump housing.

[00014] The present subject matter provides an impeller which helps in reducing chances of accumulation, and thereby clogging, and cavitation. The impeller comprises a hub and a vane. The hub comprises a top end and a base. The vane is disposed on the hub in a helical configuration. A first end of the vane is disposed above the top end of the hub and the second end of the vane is disposed on the base of the hub. A surface of the vane has a convex profile.

[00015] The vane comprises an inner edge. A first portion of the inner edge between the top end of the hub and the base of the hub is attached to the hub and a second portion of the inner edge extends above the top end of the hub. An outer edge of the vane is opposite to the inner edge. A leading edge of the vane connects the inner edge and the outer edge at the first end of the vane. The inner edge curves inwards at the leading edge. A trailing edge of the vane connects the inner edge and the outer edge at the second end of the vane.

[00016] The vane has an inlet angle and an outlet angle. The inlet angle varies from a tip of the leading edge to the hub and the outlet angle varies from a tip of the trailing edge to the hub. The tip of the leading edge may be understood as the end point of the outer edge at the first end of the vane, while a tip of the trailing edge may be understood as an end point of the outer edge at the second end of the vane. Flow of the fluid is converted from an axial input to radial output by means of turns formed between the leading edge and the trailing edge of the vane.

[00017] The present subject matter also provides a centrifugal pump comprising the impeller placed in a casing. The casing can include a suction inlet. The centrifugal pump can be used for pumping fluids with solid materials, such as sewage water.

[00018] The convex profile of the vane surface provides a three-dimensional configuration to the helical vane. The convex profile, hereinafter also referred to as three-dimensional configuration, causes movement of solid impurities in the fluids, especially quasi-solid particles, towards the hub in an axial direction while rotating. Further, the three-dimensional configuration allows for streamlining flow of fluid from the suction inlet to a discharge. Streamlining flow of fluid reduces tendency of accumulation of particles and also reduces friction caused by abrasive solid particles. Additionally, the three-dimensional configuration and the suction inlet together reduce formation of vapour cavities over the vane, thereby, reducing tendency of formation of cavities and the damage caused by cavitation.

[00019] The above and other features, aspects, and advantages of the subject matter will be better explained with regard to the following description and accompanying figures. It should be noted that the description and figures merely illustrate the principles of the present subject matter along with examples described herein and, should not be construed as a limitation to the present subject matter. It is thus understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and examples thereof, are intended to encompass equivalents thereof. Further, for the sake of simplicity, and without limitation, the same numbers are used throughout the drawings to reference like features and components.

[00020] Fig. 1(a) depicts an isometric view of an impeller 100, hereinafter also referred to as helical impeller 100, in accordance with an implementation of the present subject matter. The helical impeller 100 comprises a vane 102 and a hub 104. In an example, the hub 104 is a conical hub. The hub 104 comprises a top end 104a and a base 104b. In an example, the top end 104a is a vertex of the conical hub and the base 104b includes a conical surface of the conical hub.

[00021] The vane 102 is dispersed on the hub 104 in a helical configuration. A first end 105a of the vane 102 is disposed above the top end 104a of the hub 104. A second end 105b of the vane 102 is disposed on the base 104b of the hub 104. The surface of the vane 102 has a convex profile throughout a length of the vane 102. As will be understood, convex profile means curved or rounded outward like the exterior of a sphere or circle. The convex profile causes movement of solid impurities in the fluids towards the hub 104 in an axial direction while rotating. The convex profile also helps in streamlining flow of fluid and solids which further reduces tendency of accumulation of particles and also reduces friction caused by abrasive particles in the fluid.

[00022] The vane 102 comprises a leading edge 106, a trailing edge 108, an inner edge 110, and an outer edge 112. A first portion 114 of the inner edge 110, between the top end 104a and the base 104b, is attached to the hub 104. A second portion 116 of the inner edge 110 extends above the top end 104a of the hub 104. The outer edge 112 is provided opposite the inner edge 110. The inner edge 110 and the outer edge 112 extend substantially throughout a length of the vane 102.

[00023] The leading edge 106 connects the inner edge 110 and the outer edge 112 at the first end 105a of the vane 102. The inner edge 110 curves inwards at the leading edge 106 to form a curved section 118. The curved section 118 is shown in Fig. 1(b) in greater detail. The convex profile terminates at the trailing edge 108. The trailing edge 108 connects the inner edge 110 and the outer edge 112 at the second end 105b. In an example, a width of the vane 104 increases from the leading edge 106 to the trailing edge 108. The various edges are depicted in detail in Fig. 2.

[00024] Fig. 2(a) depicts a top-view of the helical impeller 100, in accordance with an implementation of the present subject matter. The impeller 100 has an inlet angle βΐ at the leading edge 106 and an outlet angle β2 at the trailing edge 108. In an example, the inlet angle βΐ varies from a tip of the leading edge 106 to the hub and the outlet angle β2 varies from a tip of the trailing edge 108 to the hub 104. The inlet angle βΐ varies from 18° to 65°, with a progression of 11°- 12°. The progression means the inlet angle βΐ at the leading edge 106 varies from the hub 104 to the tip of the leading edge 106. To determine the progression, leading edge 106 can be divided from the hub 104 to the tip into five equal sections where intersection of each section with the leading edge 106 has an incremental angle of 11-12 degree from the previous section. This is further explained later with respect to Fig. 2(b).

[00025] The vane 102 is arranged around the hub 104 such that the inner edge 110 of the vane 102 form-fits around the hub 104 in the first portion 114 (not shown). In an example, the outlet angle β2 varies from 14° to 22°, with a progression of 2 to 3°. The progression means that the outlet angle β2 varies from the hub 104 to the tip of the trailing edge 108. As explained for inlet angle βΐ, the trailing edge 108 from the hub 104 to the tip can be divided into five equal section where intersection of each section with the trailing edge 108 has an incremental angle of 2-3 degree from the previous section.

[00026] Fig. 2(b) depicts progression at the leading edge 106, in accordance with an implementation of the present subject matter. To determine the progression of the inlet angle βΐ from the hub 104 to the outer edge, the leading edge 106 can be divided into sections 203a, 203b, 203c, 203d, collectively referred to as section 203. Tangents 204a, 204b, 204c, 204d, 204d, collectively referred to as tangents 204, may be drawn at the leading edge 106 at junctions of each section. Angle formed between each tangent 204 and a plane comprising axis of rotation of the impeller 100 varies from the hub 104 to the tip of the leading edge 106 with the progression of 11° to 12° as shown in Fig. 2(b). Similarly, progression of about 2° to 3° may also be seen at the trailing edge 108 though not shown in the figures.

[00027] In an example, the vane 102 has a constant vane thickness between leading edge 106 and the trailing edge 108. The constant vane thickness helps in withstanding the force exerted on the vane 102 and also helps in maintaining a high flow passage volume.

[00028] In an example, the vane 102 is arranged on the hub 104 to form more than one and less than two helical turns around the hub 104. For example, one complete turn formed around the central hub 104 is equivalent to 360°. The vane 102 forms a turn between 500-540° around the hub 104. Typically, having complete helical turns, such as one or more turns, causes an increase in wrapping of long fibres around the vane 102 and the hub 104. This helical arrangement of the vane 102 reduces chances of long solid particles, such as fibres from getting entangled around the vane 102. In one example, the helical vane 102 forms one and half turns around the hub 104. The vane 102 provided on the hub 104 forms the impeller 100. The impeller 100 is then placed in a casing to form the pump as shown in Fig. 3(a).

[00029] Fig. 3(a) depicts a side view of the pump 300, in accordance with an implementation of the present subject matter. The pump 300 comprises a casing 302 and the impeller 100 provided in the casing 302. Fig. 3(a) depicts the impeller 100 with the casing 302 partially sectioned. In an example, the casing 302 is a truncated cone. The casing 302 can comprise a suction inlet 304. The suction inlet 304 leads to an inlet chamber 306. The casing 302 can also include a discharge chamber 308. The impeller 100 is placed in the casing 302 such that the leading edge 106 is substantially closer to the suction inlet 304 than the discharge chamber 308.

[00030] The impeller 100 is placed in the casing 302 such that the leading edge 106 forms a semi-open structure. The semi-open structure allows larger solid particles to move towards the hub 104 without being stuck between the leading edge 106 and the casing 302. The curved section 118 also helps in causing the solid particles to move towards the hub 104 as explained previously. The curved section 118 is shown in detail in Fig. 3(b). The suction inlet 304 and the curved section 118 together help in prevention of formation of vapour cavities. Thereby, the present configuration of the helical impeller 100 within the casing 302 reduces chances of damage caused due to cavitation as well.

[00031] The impeller 100 is arranged in the casing 302 such that the outer edge 112 forms a very thin gap with a wall of the casing 302. Minimization of the gap between the outer edge 112 and the wall of the casing 302 reduces accumulation of solid particles in the gap. The casing 302 comprising the impeller 100 is then coupled to a motor for pumping. Fig. 4 depicts a plan view of the casing 302 comprising the impeller 100 showing flow of fluid pumped through the casing 302, in accordance with an implementation of the present subject matter.

[00032] In operation, the fluid to be pumped is sucked into the casing 302 through the suction inlet 304. The fluid then flows through the inlet chamber 306 of the casing 302. Rotation of the impeller 100 within the casing 302 causes the movement of the fluid to change from an axial direction to a radial direction. The fluid is then discharged through the discharge chamber 308. Output characteristics of the impeller 100 can be varied by machining an outlet of the discharge chamber 308 and the vane 102.

[00033] The present subject matter will now be illustrated with working examples, which are intended to illustrate the working of disclosure and not intended to be taken restrictively to imply any limitations on the scope of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. It is to be understood that this disclosure is not limited to the particular methods and experimental conditions described, as such methods and conditions may vary depending on the process and inputs used as will be easily understood by a person skilled in the art.

EXAMPLES

EXAMPLE 1 : COMPUTATIONAL FLUID DYNAMICS (CFD) ANALYSIS

[00034] Preliminary Computational Fluid Dynamics (CFD) analysis was conducted using the pump comprising the impeller 100 and the casing 302. Results of the CFD analysis is as shown in Table 1.

Table 1 : CFD Analysis

Flow 220 m3/hr

Total Head 8.16 m

Speed 1450 RPM

Power 6.16 kW

Hydraulic Efficiency 79.50 %

Impeller Total Head 8.89 m

Impeller Hydraulic Efficiency 86.62 %

[00035] As can be seen from Table 1, by using the helical impeller 100 of the present subject matter, a flow of 220 m ³ /hr with an impeller of hydraulic efficiency of 86.62% can be achieved. In addition, as explained previously, the single vane impeller 100 of the present subject matter reduces clogging within the pump. This is achieved by the flow passage volume available for the fluids to flow in a streamlined manner to the outlet of the impeller 100. The streamlined flow is achieved by the three-dimensional configuration of the vane 102 around the hub 104. Further, solid particles in the fluid need not travel to the full length of the vane 102 due to the inclination of the leading edge 106 and the trailing edge 108 to the hub 104. This inclination causes the solid particles to move towards the hub 104 reducing distance travelled by the solid particles. Additionally, this increases the number of revolutions to transfer the fluid to the outlet. The single vane design of the present subject matter and arrangement of the impeller 100 in the casing 302 with very low clearance or clearance with the casing 302 prevents the solid or the fibrous material from clogging, backflow, and cavitation.

[00036] Although the subject matter has been described in considerable detail with reference to certain examples and implementations thereof, other implementations are possible. As such, the scope of the present subject matter should not be limited to the description of the preferred examples and implementations contained therein.