The invention relates to a screening device for eliminating balls for cleaning the tubes of a heat exchanger, condenser or the like from a coolant line, comprising

- a screen located in the outlet area of the heat exchanger,

- able to cover the free cross-section of the coolant line for collecting the balls and - progressively restricting the free cross-section for the coolant for the collection of the balls in the cooling medium flow direction and

- a removal line,

- positioned in the flow direction of the cooling medium behind the screen in such a way that

- the balls collected by the screen are passed into the removal line and leave the coolant line via the removal line.

In known screening devices of this type, e.g. for heat ex¬ changers, for eliminating the balls from the coolant line use is made of screens mounted in rotary manner and whose screen faces are so inclined in the active position relative to the flow direction that the balls pass via the screen surface to an outlet in the coolant line, from where they are transported away by means of the removal line and a pump and are returned to the inlet area of the heat exchanger. If the screens are pivoted into an inactive position, the coo¬ lant flows in unimpeded manner through the screens, which are flushed back and consequently freed from adhering dirt.

In smaller heat exchangers the known screening devices make the plant much more expensive due to the complicated con¬ struction, the drive and the control of the movable screen parts, as well as the sealing thereof.

Thus, the problem exists of obtaining a less expensive con-

struction for the screening device.

According to the invention this problem is solved in that the screen is fixed to the coolant line wall.

The screening device according to the invention comprises a removal line and a screen, which covers the free cross-sec¬ tion of the coolant line and extends from the coolant line wall to the removal line opening. The screen of the proposed device is fixed to the coolant line wall and is consequently a permanently operated component within the closed cooling circuit .

The cleaning processes take place at least periodically for removing corrosion and/or deposits in heat exchanger tubes or accumulations of very small parts. The balls release the deposits, which in turn effortlessly pass through the scree¬ ning device, so that the screen is not impaired as regards its function by the permanent operation and the discharged particles.

Through fixing the screen in the coolant line, the technical expenditure for this device is much lower than in movable screens. Simultaneously the stability of the arrangement is considerably increased, so that supporting and holding fra¬ mes for the screen are rendered superfluous. This reduces manufacturing costs and also greatly simplifies manufacture.

The movable screens from the outset greatly restrict con- structional possibilities and lead to a compromise between the requirements for the movable mounting and the require¬ ments for a favourable collecting action.

The problem of the transfer from the screen at the outlet and removal line can be constructionally simply solved in the device according to the invention, because it also al¬ lows a fixed connection of the screen to the removal line.

Thus, all the balls contained in the cooling medium are passed through the screen into the removal line.

The entire free cross-section of the coolant line is availa- ble to the screen, which reduces the flow resistance compa¬ red with non-fixed screening devices, because in movable screens the free cross-section is limited by shields or frame-like stabilizers for the screens.

Preferably the screen passes in funnel-shaped manner from the coolant line wall to the removal line opening. As a result of the funnel shape of the screen, compared with the prior art, there is a much more intensive collecting action on the part of the device according to the invention. Thus, the screening action of the funnel-shaped screen allows the construction of the device according to the invention with a limited overall length. Thus, compared with the known devices with movable screens, the proposed screening device has a smaller overall length in addition to the simpler construction.

The screen of the screening device according to the inven¬ tion can be implemented as a straight or inclined cone-sha¬ ped shell, as a function of the arrangement of the removal line in the coolant line. However, advantageously the funnel-shaped screen is symmetrical to the coolant line axis, i.e. it is rotationally symmetrical. This ensures that in any plane perpendicular to the centre axis of the coolant line, on the surface of the screen the same conditions pre- vail at all points for the speed of the balls. In addition, in the development of the conical or cylindrical parts only straight or circular lines occur. This simplifies the cut¬ ting of the materials in manufacture and therefore reduces costs.

In the transition area between the screen and the removal line, the flow conditions for the coolant change considera-

bly as a result of the modification to the geometry. In order to minimize the thermodynamic losses, the flow rate in the removal line is generally much lower than in the coolant line. In addition, in said transition area the velocity or speed component of a ball, which is perpendicular to the screen surface, is the same or even greater than the tangen¬ tial component of the speed or velocity. The consequence thereof can be that balls can collect in the transition area between the screen and the removal line. Consequently they are no longer available for the cleaning passes and in ex¬ treme cases lead to the clogging of the screening device.

For a high efficiency of the plant it is desirable that even in the case of a small quantity of balls to be returned, no ball accumulations or blockages occur at the critical tran¬ sition point. According to a further development of the invention openings are provided in the removal line wall for this purpose. They are located in the area of the removal line which passes into the coolant line. Considered in the coolant flow direction, the openings are positioned behind the transition between the screen and the removal line in the area in which a comparatively high flow resistance acts on the volume flow flowing at a high intake speed due to the small removal line diameter.

According to the invention the speed components of the balls parallel or tangential to the screen surface are to be high on entering the suction cross-section, i.e. the removal line opening, for a reliable conveying away of the balls. This can only be attained by a comparatively high volume flow entering through the transition point into the removal line. According to the invention, the volume flow flowing rapidly into the removal line can be used, because a considerable part of this volume flow, behind the transition, can flow back through the openings from the removal line and into the coolant line, whereas the other part passes into the slower volume flow in the removal line and takes over the further

transportation of the balls. Thus, there is no flow rate reduction within the screening device and there is a reli¬ able conveying away of the cleaning balls through the tran¬ sition area between screen and removal line.

The openings are advantageously located immediately behind the transition of the funnel-shaped screen into the removal line. At this point there is a constriction of the free tube cross-section from the coolant line diameter to the much smaller diameter of the suction or removal line. However, in this area, the increased flow resistance has not yet com¬ pletely acted on the coolant. This leads to an optimum mini¬ mizing of the residual volume flow for the conveying of the balls in the removal line.

According to the invention, the balls cannot pass through the openings in the removal line and consequently remain in the latter, where they can be conveyed away by the reduced volume flow by using pumps. The openings in the removal line are preferably slot-like for this purpose and extend in the direction of the removal line axis in the tube wall. This also avoids a pronounced mechanical weakening of the removal line.

The openings can have rectangular, square or oval, as well as rounded contours and consequently make no particularly high manufacturing demands. When dimensioning the width account need only be taken of the diameter of the balls, because even in the case of maximum permitted wear and also under the influence of the flow, the balls must not pass through the openings from the removal line into the coolant line.

Thus, the openings made in the described manner in the remo- val line walls preferably have a total surface area repre¬ senting at least 20% of the crosssectional surface of the removal line.

The screening device according to the invention has a simple overall construction and a very compact size. Its construc¬ tion also makes it easily housable within a tube bend in the coolant line. As a result of the use of a high volume flow in the critical transition area between the screen and the removal line, the screening device according to the inven¬ tion is also suitable for installations having a small ball return quantity, because the cleaning balls can reliably pass this threshold at a comparatively high speed. The fol¬ lowing minimizing of the volume flow through the openings in the removal line recommends the use of this compact scree¬ ning device more particularly in plants with small cooling water flows and therefore also small thermal performance levels, because the thermodynamic losses through this device are also low due to the limited coolant transport flow for the elimination of the balls.

An embodiment of the invention is described hereinafter relative to the drawing. The drawing is a longitudinal sec- tion through a screening device 1. The screening device 1 comprises a funnel-shaped screen 2 and a removal line 3, in which are formed slot-like openings 4, which are connected to the end of the funnel-shaped screen 2.

At A the speed or velocity t? _H1 at the surface 5 of the funnel-shaped screen 2 is shown in a vectorial splitting into its normal component ι? _N (perpendicular to the surface 5 of the screen 2) and tangential component ϋ _τ (parallel to the surface 5) . It is clear that the normal component ι? _N is much smaller than the tangential component ϋ _τ of the speed, so that no balls 6 can collect at this point A. A comparable situation occurs on splitting the speed ι? _H1 into its normal component ι? _N and tangential component ϋ _τ also at a point B, immediately upstream of the transition of the funnel-shaped screen 2 into the removal line 3. The high tangential compo¬ nent ϋ _τ of the speed ϋ _H1 also prevents a collection of balls 6.

Flow lines S indicate the cooling medium flow through the screening device 1. They also indicate that through the openings 4 in the removal line 3, in the case of a speed change from the high value t? _H1 to the lower value ϋ _H2 in the removal line 3 a considerable proportion of the transport volume passes out of the line 3 through the openings 4 and back into the coolant line 7.

For stability reasons, the funnel-shaped screen 2 construc- ted symmetrically to the centre axis is fixed to the coolant line wall 7a and consequently keeps the entire screening device 1 in the coolant flow without any additional frame at the ends of the screen 2. At the connection point of the screen 2 and the wall 7a, equal tensile forces occur along the circumference of the internal diameter of the coolant line 7.

The drawing shows the compact, simple construction of a screening device with a funnel-shaped screen.