GB2069355A - Vibratory agitating apparatus - Google Patents

Abstract

Apparatus for maintaining an oil bath (6) at a uniform temperature, incorporates an agitator (10) for promoting flow within the oil bath thereby to reduce thermal gradients. The agitator (10) comprises a resilient strip (20) that is mounted at one end (21), above the oil level, to depend vertically within the oil bath. At its other end (25) there is mounted a permanent magnet (26) that interacts with the magnetic field established by a fixed electromagnet (40) mounted beneath the oil bath (6). The electromagnet (40) is supplied with alternating current thereby producing an alternating magnetic field that causes the agitator strip (20) to vibrate and produce flow within the oil (5). <IMAGE>

Description

SPECIFICATION Agitators This invention relates to agitators for effecting movement within a body of fluid.

The invention is more particularly concerned with agitators for causing movement within a body of liquid the temperature of which is maintained stable for reference purposes. It will, however, be appreciated that the invention also finds application for other purposes such as for mixing several substances together or for maintaining a substance in a fluid state.

Temperature reference equipment is known in which a body of liquid, such as, for example, an oil bath is i heated to a predetermined temperature and used for checking or calibrating temperature sensors immersed in the liquid. In order to reduce thermal gradients within the body of liquid, previous equipment has used some form of agitator in an attempt to obtain a more uniform temperature throughout the body of liquid. The agitator usually takes the form of a paddle or disc-shape member that is immersed in the liquid and rotated about a vertical axis. In use, these previous forms of agitator effect a swirling, rotational movement of the liquid about a vertical axis.Whilst this form of agitation may be satisfactory in some applications, it does have a disadvantage when attempting to reduce a vertical temperature gradient, since the vertical flow produced is only minimal. Moreover, with agitators of the kind having a paddle at one end of a shaft that projects through the floor of the reservoir, there are also difficulties in making an effective fluid-tight seal with the shaft. Further disadvantages arise because of the need to use rotating components and the consequent problems of providing and maintaining suitable bearings. In an attempt to overcome this, some agitators comprise a magnetic paddle immersed in the liquid and an external motor that itself rotates and causes the paddle to rotate by interaction with its magnetic field.Whilst such arrangements avoid the need to make a seal through the wall of the liquid reservoir they do still require to use rotating components.

It is an object of the present invention to provide an improved form of agitator that can be used to overcome the above-mentioned disadvantages.

According to one aspect of the present invention there is provided agitator means for effecting agitation of a body of fluid, including an elongate member mounted resiliently such that at least a portion of the member is immersed within the body of fluid, and means for effecting oscillatory displacement of said portion across its length such that flow is produced within said body of liquid.

According to another aspect of the present invention there is provided temperature reference apparatus including a reservoir for containing a body of fluid; means for maintaining the body of fluid at a predetermined temperature; and agitator means for effecting agitation of said body of fluid, said agitator means including an elongate member mounted resiliently such that at least a portion of the member is immersed within the body of fluid, and means for effecting oscillatory displacement of said portion across its length such that flow is produced within said body of fluid.

A part of the elongate member may be above the level of said fluid.

The elongate member may be a strip of resilient material and may be mounted to depend substantially vertically within the body of fluid. The said means for effecting oscillatory displacement may include first magnet means mounted on said elongate member and second magnet means mounted separate from said first magnet means.

One magnet means may be a permanent magnet, and the other magnet means may be an electromagnet arranged to produce an alternating magnetic field.

Temperature reference equipment including an agitator, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the temperature reference equipment schematically in elevation; Figure 2 shows a part of the equipment of Figure 1, including the agitator, to a larger scale; Figure 3 is a perspective view showing a part of the agitator; and Figures 4 and 5 are perspective views showing a part of two alternative forms of agitator.

With reference to Figure 1 , the temperature reference equipment is contained within a housing 1 of generally rectangular section which has a transparent perspex handle 2 that extends horizontally across the top of the housing. The housing 1 has an opening 3 in its upper surface, which enables thermocouples 4, or other temperature sensors, to be immersed in a body of glycerine oil 5 contained in a reservoir 6 within the housing.

A heating element 7 is wrapped about the reservoir 6 and is controlled by an electrical unit 8 in response to the output of a temperature sensor 9 in the wall of the reservoir, such as to maintain the oil 5 at a constant temperature. An agitator, indicated generally by the numeral 10, includes a vibrating member that is arranged to stir and reduce thermal gradients within the oil 5. A mercury-in-glass thermometer 11 is used to obtain an accurate indication of the temperature of the oil 5. The thermometer 11 is bent at right angles along its length, with its bulb 12 immersed in the oil 5 and its stem 1 3 extending within the handle 2.

With reference now to Figures 2 and 3, the agitator 10 will be described in greater detail. The agitator 10 has a strip 20 of resilient spring metal that is 50 mm long and that tapers from 12 mm at one end to 10 mm wide at the other end. The strip 20 is mounted at its wider, upper end 21 to depend vertically, parallel to the wall 22 of the reservoir 6. The strip 20 is mounted on the reservoir wall 22, above the level of the oil 5 by means of a screw 23 that extends through an annular spacing member 24 such that the strip is spaced away from the wall. At its narrower, lower end 25, and immersed in the oil 5, there is mounted a permanent magnet 26 that interacts with an alternating magnetic field.The magnet 26 is of cylindrical shape being axially magnetised and is secured to project transversely of the strip 20 by means of a bolt 27, that extends through an axial bore of the magnet, and a nut 28.

The magnetic field is established by an electromagnet 40 which is located beneath the reservoir 6 and which forms a part of the agitator 10. The electromagnet 40 comprises a cylindrical coil 41 that is wound within an annular recess 42 in a soft iron block 43. The coil 41 is connected to a 50 Hz alternating electrical supply 44 (Figure 1) which causes the electromagnet 40 to produce an alternating magnetic field having lines of force extending vertically. The permanent magnet 26 is located away from the axis of the electromagnet 40 so that it is thereby attracted to or repelled from the axis according to the sense of the magnetic field by the electromagnet.

In operation, the alternating magnetic field established by the electromagnet 40 causes the lower end 25 of the strip 20 to vibrate or oscillate across its length. This rapid vibration causes random flow within the oil 5 across any thermal gradients that might otherwise be established.

Vibration of the strip 20 in the region where it emerges from the oil 5 causes the surface tension to be broken down, thereby improving flow and further reducing thermal gradients at the oil surface.

The vibrating member of the agitator 10 could take other forms, as shown, for example, in Figures 4 or 5. In the alternative arrangement shown in Figure 4, the vibrating member has a strip 50 of the same general shape as the strip 20 of Figure 3 except that, at its lower end it is bent forwardly at right angles away from the wall 22 of the reservoir 6 to form a horizontal ledge 51. A flat, rectangular permanent magnet 52 is secured beneath the ledge 51. The strip 50 is also provided with a valve arrangement 53 close to its lower end. The valve arrangement 53 comprises an aperture 54 that is normally closed by a resilient flap 55. The flap 55 is secured at its upper end 56, by means of an adhesive, to lie flat against the forward surface of the strip 50, with the lower end 57 of the flap overlying the aperture 54.In this way, the lower end 57 of the flap 55 is urged away from the strip 50 when the strip is displaced rearwardly, thereby allowing passage of oil 5 through the aperture 54. When the strip 50 is displaced forwardly, the flap 55 is urged against the forward face, closing the aperture 54. This causes a reduced flow of oil 5 in the rearward direction, towards the wall 22. In this way, it can be seen that the vibrating movement of the strip 50 causes a greater flow of oil in the forward direction than in the rearward direction. The resultant flow within the oil 5 in the reservoir 6 is of a generally circular form about a horizontal axis.

There is a substantially horizontal forward flow, away from the wall 22, close to the strip 50, at the bottom of the reservoir 6; an upward flow, with some eddying, near the wall opposite the strip; a horizontal rearward flow across the top of the reservoir; and a downward flow between the strip and the reservoir wall.

The strip 60 shown in Figure 5 is formed with two laterai wings 62, close to its narrower, lower end 61, which extend outwards from opposite edges. The wings 62 each have a cut-away portion 63 of substantially U-shape formed at their edges. A rectangular flap 64 of thin (3 thousandths of an inch, that is, about 7.6 x 10-2 mm) phosphor-bronze alloy extends horizontally across one face of the strip 60 to overlie the wings 62 and the cut away portions 63. The flap 64 is secured at its centre, to the strip 60, by screws 65 such that the flap can be readily deflected away from the strip in the region of the wings 62. The flap 64 of the strip 60 functions in a similar way to the flap 55 of strip 50, that is, to produce a preferential flow of oil in one direction.

The circulatory motion of the oil 5 about a horizontal axis produced by the strips 50 and 60 has the effect of causing the colder oil at the bottom of the reservoir 6 to be displaced upwards to mix with the hotter oil at the top. Mixing of the oil 5 in this way produces a more uniform temperature throughout the reservoir 6 and thereby reduces thermal gradients.

Instead of providing the vibrating member of the agitator with some form of valve, preferential flow of oil in one direction could be achieved by shaping the vibrating member such that resistance to displacement of the member through the oil is greater in one direction than in the other direction.

The vibrating member could, for example, have a curved or V-shape cross-section so that the flow caused by forward movement of the concave face is greater than the flow caused by forward movement of the convex face.

The separation of the strip 20, 50 or 60 from the wall 22, and the amplitude of vibration of the strip, is selected to produce the most efficient agitation for the viscosity and temperature of the oil being used. If oil should be lost from the reservoir by evaporation or leakage, the resistance to displacement of the stip is correspondingly reduced causing the amplitude of vibration to be increased. The separation of the strip 20 from the wall 22 is also selected such that, in operation, the lower end of the strip contacts the wall 22 of the reservoir 6 when the oil falls below a predetermined level, thereby causing an audible ringing to give warning that more oil should be put in the reservoir.

It is not essential that the vibrating strip be mounted to depend vertically within the reservoir 6, it could instead be inclined away from the vertical, or extend horizontally. in place of a resilient strip, other resiliently mounted elongate members could be used, such as, for example, a rigid bar mounted by means of a leaf spring.

Agitators of the kind described could be used in other applications, such as, to mix different substances together or to maintain a substance in a fluid state. The random, or circulatory flow about a horizontal axis, caused by such agitation has particular advantages when mixing several substances having different densities. In previous agitators where a rotating flow about a vertical axis is produced there can be a tendency for separation of substances of different densities because of the centrifugal effect. Agitators according to the present invention, however, overcome the tendency of the more dense substance to settle at the bottom of the reservoir by also promoting vertical movement within the body of fluid.

Claims (20)

1. Agitator means for effecting agitation of a body of fluid, including an elongate member mounted resiliently such that at least a portion of the member is immersed within the body of fluid, and means for effecting oscillatory displacement of said portion across its length such that flow is produced within said body of liquid.

2. Agitator means according to Claim 1, wherein a part of said elongate member is above the level of said fluid.

3. Agitator means according to Claim 1 or 2, wherein said elongate member is mounted at one end.

4. Agitator means according to Claim 2 and 3, wherein said one end is located above the level of said fluid.

5. Agitator means according to any one of the preceding claims, wherein said elongate member is a strip of resilient material.

6. Agitator means according to any one of the preceding claims, wherein said elongate member is mounted to extend substantially vertically.

7. Agitator means according to any one of the preceding claims, wherein said means for effecting oscillatory displacement includes first magnet means mounted on said elongate member and second magnet means mounted separate from said first magnet means.

8. Agitator means according to Claim 7, wherein said second magnet means is mounted outside said body of fluid.

9. Agitator means according to Claim 7 or 8, wherein one magnet means is a permanent magnet, and the other magnet means is an electromagnet arranged to produce an alternating magnetic field.

1 0. Agitator means according to Claim 9, wherein said electromagnet is fixedly mounted and is arranged for supply with an alternating electric current.

11. Agitator means according to any one of Claims 8 to 10, wherein said permanent magnet is of cylindrical shape, and wherein said permanent magnet is axially polarised.

1 2. Agitator means according to any one of the preceding claims, wherein said elongate member is arranged such that flow of fluid caused by displacement of said member in one direction is greater than flow caused by displacement in the opposite direction.

1 3. Agitator means according to Claim 12, wherein said elongate member is provided with valve means arranged to close, and substantially prevent passage of fluid therethrough, on displacement of said member in said one direction, and to open, thereby allowing passage of fluid, on displacement of said member in said other direction.

14. Agitator means according to Claim 13, wherein said valve means includes resilient flap means secured with one side of said elongate member, said flap means being urged towards an opening in said elongate member on deflection of said elongate member in one direction, and urged away from the opening on deflection of said elongate member in the opposite direction.

1 5. Agitator means substantially as hereinbefore described with reference to Figures 1 and 2, and any one of Figures 3 to 5.

1 6. Temperature reference apparatus including a reservoir for containing a body of fluid; means for maintaining the body of fluid at a predetermined temperature; and agitator means for effecting agitation of said body of fluid, said agitator means including an elongate member mounted resiliently such that at least a portion of the member is immersed within the body of fluid, and means for effecting oscillatory displacement of said portion across its length such that flow is produced within said body of fluid.

1 7. Temperature reference apparatus including a reservoir for containing a body of fluid; means for maintaining said body of fluid at a predetermined temperature; and agitator means according to any one of Claims 2 to 1 5 arranged for effecting agitation of said body of fluid.

1 8. Temperature reference apparatus according to Claim 16 or 17, wherein said means for maintaining the body of fluid at a predetermined temperature includes heater means.

1 9. Temperature reference apparatus according to Claim 16, 1 7 or 18 including a thermometer arranged to provide an indication of the temperature of said body of fluid, and a carrying handle, said thermometer being arranged to extend within said handle, and said handle having at least a portion thereof that is transparent and through which said thermometer can be observed.

20. Temperature reference apparatus substantially as hereinbefore described with reference to Figure 1 and 2, and any one of Figures 3 to 5.