CA3027433C

CA3027433C - Centrifugal pump for heat-sensitive fluid food products and impeller for a centrifugal pump of this type

Info

Publication number: CA3027433C
Application number: CA3027433A
Authority: CA
Inventors: Helmut Buss; Jurgen Gehling; Gunter Lutkebruns; Uwe Schwenzow; Ludger Tacke; Franz Tasler
Original assignee: GEA TDS GmbH
Current assignee: GEA TDS GmbH
Priority date: 2016-06-03
Filing date: 2017-05-19
Publication date: 2021-02-16
Anticipated expiration: 2037-05-19
Also published as: AU2017274473A1; BR112018074633A2; EP3464904B1; PH12018502565A1; DK3464904T3; AU2017274473B2; WO2017207092A1; EP3464904A1; CA3027433A1

Abstract

The invention relates to a centrifugal pump (54) for conveying heat-sensitive fluid food products (P), such as whey protein concentrates, baby food, fluid baby food concentrates, nutritious drinks or cheesemaking milk, having the further characteristics of the general terms of claim 1. The object of the invention is to create a centrifugal pump, which reduces the tendency for product fouling in the conveying of heat-sensitive fluid food products, in particular in the conveying thereof out of an infuser container for directly heating the fluid food product with water vapour, and which thereby has a significantly extended service life in relation to a hydraulically optimised centrifugal pump according to the state of the art. This is achieved in that the rear and/or front impeller gap (s1, s2) is/are increased up to many times over, in relation to a respective related minimal rear and front impeller gap (s1*, s2*) that ensures the mechanical functionality of the centrifugal pump (54), via a reduction in the width of the impeller (100) in the region of the front and the rear impeller gap (s1, s2); and in that at least the housing cover (8) is provided with a coolant chamber (8.1, 10.1) through which a coolant can flow.

Description

CENTRIFUGAL PUMP FOR HEAT-SENSITIVE FLUID FOOD PRODUCTS AND
IMPELLER FOR A CENTRIFUGAL PUMP OF THIS TYPE
TECHNICAL FIELD
The invention relates to a centrifugal pump for conveying heat-sensitive fluid food products, such as whey protein concentrates, baby food, fluid baby food concentrates, nutritious drinks or cheesemaking milk, having an inlet, an outlet, a pump housing which is formed by at least a housing cover and a housing rear wall, a pump chamber which is formed in the pump housing and which is fluidically connected to the inlet and to the outlet, an impeller which is accommodated rotatably in the pump chamber and which has blades, a blade channel which is formed in each case between two adjacent blades and which is formed so as to be open toward the housing cover and closed toward the housing rear wall by an impeller rear side, a rear impeller gap which is provided between the housing rear wall and the impeller, and a front impeller gap which is provided between the housing cover and the impeller, and to an impeller for a centrifugal pump of said type.
Heat-sensitive fluid food products of the abovementioned type contain a relatively high quantity of proteins, a high quantity of dry mass, and little water, and may exhibit low, medium or high viscosity. The expression "heat-sensitive" is to be understood below to mean that these food products exhibit a tendency to become baked on at temperatures over 100 C, that is to say exhibit a tendency under these conditions to form a lining on the walls of the centrifugal pump that conveys them.
This formation of a lining is also referred to as product fouling. The product fouling reduces the service life or operating time of the centrifugal pump between two required cleaning cycles.
PRIOR ART
A particularly critical field of use for the centrifugal pump of the generic type, for which no satisfactory solution is yet known, is the arrangement thereof downstream of a infuser vessel in which the fluid food product in question undergoes direct heating by means of culinary water vapor.
In the case of heating installations with an infuser vessel, it is known for the conveyance of the directly heated fluid food product away from the infuser vessel to be performed by means of a rotating positive-displacement pump, for example a gearwheel pump, wherein the housing thereof generally exhibits a cooling arrangement and the housing directly adjoins the outlet opening of the infuser vessel (EP 0 784 706 B1). A
gearwheel pump, owing to its type of construction, exhibits a self-cleaning capability, because the gearwheels mesh closely with one another and scrape along the associated housing walls and thus prevent the formation of a continuously growing lining (product fouling).
WO 2011/101077 Al, which claims the priority of DE 10 2010 008 448 Al, discloses a UHT installation for the treatment of heat-sensitive fluid food products, in which, inter alia, a first conveying device which is in the form of a positive-displacement pump is arranged, at the downstream side of an infuser vessel, in a connecting line to a vacuum chamber. The infuser vessel, in its lower region, a base part which tapers to an outlet opening, has a cooling arrangement for cooling said base part. Here, the positive-displacement pump may be arranged with an unquantified spacing to the outlet opening from the infuser vessel, or, in the extreme case, said outlet opening opens directly into the positive-displacement pump.
In the positive-displacement pump, a rotator is preferably used, which may, as mentioned above for example be in the form of a gearwheel or else a vane-type, screw-wheel, impeller or rotary-piston pump. Positive-displacement pumps which operate in oscillating fashion may basically likewise be used if the volume flow fluctuations caused by the oscillating operation are compensated by suitable means or do not play a role in the treatment process.

2 In WO 2016/012026 Al, the installation for the thermal treatment of heat-sensitive fluid foods known from EP 0 794 706 Bl is modified such that, now, with an otherwise unchanged configuration of the individual assemblies of the installation, the cooling jacket which surrounds the base of the infuser vessel and which imparts a cooling action extends downward to the pump and, in one advantageous embodiment, into the pump housing. The pump is a positive-displacement pump, preferably a gearwheel or piston pump. However, a centrifugal pump is also claimed, without the design of said centrifugal pump being specified. It can therefore be assumed that a conventional and hydraulically optimized centrifugal pump, which in terms of its basic construction is known to a person skilled in the art, is provided here.
WO 2010/086082 Al, which claims the priority of DE 10 2009 006 248 Al, describes an infusion system for a fluid food product to be warmed, in which infusion system an infusion chamber has a lower base part with a cooling arrangement. The infusion chamber is continued in an outlet pipe which adjoins an outlet opening in the lower base part and which likewise has a cooling arrangement. It is not stated whether the outlet pipe opens directly or indirectly via a connecting line into a conveying device of arbitrary design.
A centrifugal pump for unproblematic fluid food products, such as for example water, is well-known in terms of its basic construction. It is designed and configured so as to exhibit the highest possible hydraulic efficiency, that is to say so as to achieve the greatest possible product of volume flow and delivery head with a particular amount of drive energy. In a pump housing which is generally composed of at least two housing parts, an impeller with blades is arranged on a shaft.
Within the pump housing, a guide apparatus in the form of, for example, a spiral housing or a blade-free annular chamber adjoins an annularly encircling impeller outlet cross section.
On the suction-side housing part, a housing cover, an inlet

3 formed generally as a so-called suction connector is situated coaxially with respect to the impeller axis, and, on the pressure-side housing part, an outlet generally in the form of a so-called pressure connector is formed so as to open out tangentially on the circumference. With the housing part averted from the suction side, the housing rear wall, an impeller rear side forms a so-called rear impeller side chamber, which with regard to good hydraulic efficiency of the centrifugal pump generally has a small axial extent. Said axial or gap-width extent is specifically dimensioned to be so narrow that, with reasonable manufacturing tolerances, mechanical functionality of the centrifugal pump is ensured.
In the same way, an impeller front side, in this case, in a so-called open impeller, the leading, end-side free blade edges, is adapted, with the narrowest possible gap, to the profile of the housing cover. To reduce an axial force resulting from the pressure forces acting on the impeller on both sides, multiple pressure equalization bores of relatively small diameter are generally arranged in the hub region of the impeller, and so as to be distributed over the circumference thereof, in the impeller rear side.
US 8,113,802 82 discloses a centrifugal pump for conveying heat-sensitive fluid food products, in which a rear and a front impeller gap are provided, and the impeller is formed as an impeller which is open toward the housing cover and which is closed toward the housing rear wall by an impeller rear side. The front impeller gap between the free ends of the blades of the impeller and the housing cover is dimensioned to be very narrow, preferably less than 2 mm, in order that good sealing is ensured here with low leakage losses.
AT 413 743 B describes a centrifugal pump in the form of a radial pump, in particular coolant pump for an internal combustion engine, in the case of which at least one impeller blade is formed as a temperature-sensitive and/or rotational-speed-sensitive element. In this way, the at least one

4 impeller blade is deformable as a result of changes in temperature of the coolant and/or as a result of the Coriolis forces imparted by the coolant flow at high rotational speeds.
By means of the respective deformation, it is the intention for the conveying rate to deviate upward or downward from the conveying rate of a rigid impeller blade in a desired manner.
In the case of heat-sensitive fluid food products of the type mentioned in the introduction, it is of primary importance that, during the conveyance thereof by means of a centrifugal pump, there is the least possible tendency for deposits to form on the walls of the centrifugal pump. For example, in the case of the direct heating of highly heat-sensitive fluid food products in an infuser vessel and the subsequent conveyance of the heated fluid food product out of the infuser vessel by means of a downstream centrifugal pump of conventional type construction, that is to say of hydraulically optimized type of construction, it has been found that said centrifugal pump became blocked as a result of product fouling, and thus rendered inoperative, in an extremely short time, which in this regard ranged from seconds to a few minutes. Particularly critical regions are in this case the suction region of the impeller, because undissolved gases and in particular uncondensed water vapor can intensify the product fouling here, and the rear impeller side chamber with narrow gap width.
For the physical embodiment of a centrifugal pump in an installation for the treatment of heat-sensitive fluid food products, in which the latter undergoes direct heating by means of culinary water vapor, no satisfactory solution with regard to an adequately long service life of the centrifugal pump is yet known.
It is an object of the present invention to create a centrifugal pump which, in the case of the conveyance of heat-sensitive fluid food products of the type mentioned in the introduction, in particular during the conveyance thereof out

5 of an infuser vessel for the direct heating of the fluid food product with water vapor, reduces the tendency for product fouling and thus exhibits a considerably lengthened service life in relation to a hydraulically optimized centrifugal pump according to the prior art. A further object consists in modifying a preferably commercially available centrifugal pump such that it inhibits the growth of product fouling in its critical regions, and thus the desired service life lengthening is attained.
SUMMARY OF THE INVENTION
Said object is achieved by means of a centrifugal pump having the features of claim 1. The subclaims relate to advantageous refinements of the centrifugal pump according to the invention. Claim 22 relates to an impeller for a centrifugal pump of the embodiment claimed in the claims.
The invention proceeds from a centrifugal pump known per se, having an inlet, an outlet, a pump housing which is formed by at least a housing cover and a housing rear wall, a pump chamber which is formed in the pump housing and which is fluidically connected to the inlet and to the outlet, and an impeller which is accommodated rotatably in the pump chamber and which has blades. A blade channel is formed in each case between two adjacent blades, which blade channel is formed so as to be open toward the housing cover and closed toward the housing rear wall by an impeller rear side. A rear impeller gap is provided between the housing rear wall and the impeller, and a front impeller gap is provided between the housing cover and the impeller.
The underlying concept of the invention consists in flushing the impeller itself, and its adjacent critical regions as far as the direct pump-housing-side boundary of the impeller front side and of the impeller rear side, with the fluid food product to be conveyed, and thus inhibiting product fouling there, wherein a further underlying concept of the invention consists

6 in, during the course of the flushing according to the invention, simultaneously cooling at least the pump-housing-side boundaries in the region of the housing cover.
The fluid food product thus serves, with a part of its volume flow conveyed in the impeller, for the intentional flushing of the pump housing and of the impeller itself. Here, the volume flows of the intended flushing operations exceed, by up to several times, the inevitable equalization flows in the pump housing which result from a conventional hydraulically optimized design of the central pump. As a result of the cooling, the tendency for fluid food product to bake onto the walls of the centrifugal pump is reduced. This is realized while intentionally dispensing with an optimum hydraulic efficiency. In the centrifugal pump according to the invention, in the impeller, a volume flow is conveyed which is increased relative to the volume flow drawn in via the suction connector by the sum of all, as it were, recirculating flushing volume flows. The flushing volume flows conduct volumes out of the core of the blade channels onto the cooled walls of the pump housing and from there back into the impeller, wherein the cooling intervention allows uncondensed water vapor to condense, and the tendency for product fouling is thus reduced.
The relationships presented above show that a centrifugal pump flushed in accordance with the invention with the fluid food product that it conveys has an impeller, the hydraulic conveying rate of which must, with regard to the impeller, be higher than the hydraulic conveying rate of the centrifugal pump that is actually effected as an end result at the pressure connector. If a hydraulically optimized centrifugal pump is selected to realize a flushed centrifugal pump of the type in question, then its nominal conveying rate must be selected to be correspondingly higher by the conveying rate difference mentioned above. For the same nominal conveying rate, an outer impeller diameter of the flushed centrifugal pump will

7 therefore need to be greater than that for a hydraulically optimized centrifugal pump.
The specific solution for implementing the underlying concept of the invention as mentioned above consists, according to a first embodiment of the centrifugal pump, in that the rear and/or the front impeller gap which must imperatively exist in each case between impeller and pump housing are/is enlarged up to several times in relation to a respective minimum rear and front impeller gap, which ensures the mechanical functionality of the centrifugal pump, by reduction of the width of the impeller in the region of the front and of the rear impeller gap. As a result of the enlargement of these impeller gaps, the generation of desired and necessary flushing flows is made possible for the first time. The respective width of the front and of the rear impeller gap may be dimensioned in a manner dependent on the specific characteristics of the fluid food product.
To intensify the cooling, a further embodiment provides for the housing rear wall to also be equipped with a coolant chamber through which a coolant can flow. Gapless cooling of the pump housing is ensured if, as is also proposed, in addition to the housing-cover coolant chamber and the housing-rear-wall coolant chamber, the inlet of the centrifugal pump is formed in the manner of a suction connector which projects on the housing cover and which is equipped with a suction-connector coolant chamber. Such an embodiment is not imperative with regard to the centrifugal pump according to the invention. It is, like a centrifugal pump in the case of which the formation of a suction connector is dispensed with, suitable for a direct connection between the suction connector of the centrifugal pump and infuser vessel equipped with a coolant chamber in its base part, wherein said coolant chamber extends downward to an outlet opening which opens out of the base part and which then constitutes the final end of the infuser vessel. The suction connector may then, in this

8 arrangement, perform the function of a tubular portion which adjoins the final outlet opening of the infuser vessel. An arrangement with the centrifugal pump according to the invention is also possible in which the outlet opening as the final end of the infuser vessel is arranged directly on the housing cover of the centrifugal pump, wherein the formation of a suction connector is dispensed with there.
In all embodiments, specifically in the case of a centrifugal pump according to the invention with or without a suction connector in combination with an infuser vessel in the case of which the outlet opening or a tubular portion adjoining said outlet opening constitutes the final end, an accumulation of heated fluid food product in the base part of the infuser vessel, that is to say an accumulation with a fluctuating filling level, is undesirable, because such an accumulation leads to an undesired and undefined dwell time, which should be prevented. The centrifugal pump according to the invention has the task, in conjunction with an infuser vessel, of completely discharging, without delay, heated fluid food product which accumulates therein, without becoming blocked even in the case of intermittent accumulation.
To intensify the flushing, it is furthermore proposed that each blade channel between two adjacent blades of the impeller is, in the region of its delimiting impeller rear side, fluidically connected to the rear impeller gap via at least one flushing bore which penetrates through the impeller rear side. In this way, the radial depth of engagement of the associated flushing flow can be defined. In the most general case, the flushing bore involves passage openings of any desired shape, that is to say a circular shape, which is easy to produce, is not imperative.
A preferred embodiment provides for the front impeller gap to exhibit a maximum enlargement at an outer impeller diameter of the impeller, and for said enlargement to decrease

9 continuously, as far as into the region of the inlet into the blade channels, to the minimum front impeller gap. In this regard, it is proposed that the reduction of the width of the impeller at the outer impeller diameter amounts to 40 to 55%, preferably 50 to 55%, of the width of a hydraulically optimized impeller. In the region of the front impeller gap, a second flushing flow forms, which extends from the region of the outlet of the centrifugal pump into the region of the inlet of the impeller. As a result of the enlargement of the front impeller gap, the flow that prevails around the free leading edge of the blades of the open impeller, which is present even in the case of a narrow impeller gap and is driven by the pressure difference between the pressure and suction sides of the blades, is greatly intensified, whereby a third flushing flow is intentionally generated.
With regard to the dimensioning of the rear impeller gap, it has proven to be expedient if the access to the minimum rear, preferably radially oriented impeller gap, which starts from an outer impeller diameter of the impeller and extends as far as a hub of the impeller, is widened by up to 5 mm by reduction of the outer impeller diameter. Furthermore, an advantageous enlargement according to the invention of the rear impeller gap consists in the impeller rear side exhibiting, in the region between the flushing bore and the hub of the impeller, an annular-surface-shaped turned-out portion, the axial depth of which amounts to up to 2 mm, preferably 0.5 to 1 mm.
The positioning, shaping and dimensioning of the flushing bore are features with which the associated flushing flow is defined with regard to its radial depth of engagement, its formation and its quantitative intensity. In the case of a single flushing bore being arranged in each blade channel, it is expedient with regard to flow and manufacturing if all of these flushing bores are arranged on a single hole circle with a corresponding pitch.

With regard to the positioning of the flushing bore within the blade channel, it has proven to be advantageous if the geometrical location for the respective penetration point of the flushing bore through the impeller rear side, which also defines a hole circle diameter, is determined as follows:
= approximately by the center of the blade channel in relation to the spacing of the blades at the penetration point, and = approximately by the center of a maximum flow filament length of the blade channel between the inlet and outlet thereof.
The flushing bore is either of circular design with a bore diameter, or it has a shape which deviates from the circular shape, with a hydraulic diameter definitive of said shape. The hydraulic diameter is calculated, in a manner known per se, as a quotient of four times the passage cross section of the flushing bore and the circumference of the flushing bore. It has proven to be expedient if the bore diameter or the hydraulic diameter amounts to 30 to 50%, and in this range preferably 40 to 50%, of the spacing of the blades at the penetration point.
According to a further refinement, the invention also provides more than one flushing bore in each blade channel, wherein each of the multiple flushing bores of a blade channel is arranged on an associated hole circle, and the hole circles are radially spaced apart from one another. It is expedient here if the passage cross sections of the flushing bores on the different hole circles become smaller with decreasing hole circle diameter, because the driving pressure difference at the flushing bore becomes greater with decreasing radial spacing of the flushing bore to the axis of rotation of the centrifugal pump.
To ensure cooling suited to the specific characteristics of the heated fluid food product, the invention provides the following connection configurations of the coolant chambers.
In a first proposal in this regard, the suction-connector coolant chamber, the housing-cover coolant chamber and the housing-rear-wall coolant chamber are charged with coolant separately from one another. A second proposal provides a design variant in which at least two of the abovementioned coolant chambers are connected in series with one another.
According to a third proposal, provision is made for the suction-connector coolant chamber to be an integral portion of the housing-cover coolant chamber.
To create the pre-requisites for the flushing of the rear and of the front impeller gap, the invention provides that, proceeding from a hydraulically optimized centrifugal pump, preferably a commercially available centrifugal pump, the rear and/or the front impeller gap are/is enlarged as follows:
= either by virtue of the impeller being subjected to material removing by turning on both sides, = or by means of a spacer element which acts axially in the direction of a pump shaft and which is arranged between the housing cover and the housing rear wall, wherein the impeller is o not offset, o or is correspondingly offset axially on or with the pump shaft in the pump chamber, in relation to the housing rear wall.
The selection of the hydraulically optimized centrifugal pump for this purpose is made with regard to the above-discussed difference in the nominal conveying rate between flushed and hydraulically optimized centrifugal pump.
The invention also encompasses an impeller for a centrifugal pump, wherein the impeller is accommodated rotatably in the pump chamber of the centrifugal pump, and the centrifugal pump is designed as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed depiction of the invention emerges from the following description and the appended figures of the drawing, as well as from the claims. While the invention is realized in a wide variety of embodiments, a preferred exemplary embodiment of a centrifugal pump according to the invention, which accommodates an impeller according to the invention in its pump housing, will be described below on the basis of the drawing. In the drawing:
figure 1 shows a view of the centrifugal pump in a direction perpendicular both to its axis of rotation and to the longitudinal axis of its pressure connector, wherein the axis of rotation of the centrifugal pump is oriented in the direction of gravitational force;
figure 2 shows, in a front view, the impeller of the centrifugal pump according to the invention, wherein the viewing direction is directed into the open blade channels;
figure 3 shows, in a plan view, a meridional section through the impeller as per figure 2 in accordance with a section profile denoted therein by "B-B";
figure 4 shows, in a side view, a meridional section through the impeller as per figure 2 in accordance with a section profile denoted therein by "A-A";
figure 5 shows the front view of the impeller as per figure 2 with an approximated indication of a first and of a third flushing flow Si, S3; and figure 6 shows the side view of the impeller as per figure 4 with an approximated indication of the first, of a second and of the third flushing flow Si, S2 and S3.
The arrangement situation of a centrifugal pump 54 according to the invention illustrated in figure 1, in which the axis of rotation of a pump shaft 96 is oriented in the direction of gravitational force, is suitable for enabling said centrifugal pump 54 to be connected with an inlet 76, which may be formed as a suction connector, directly to an outlet opening in a base part of an infuser vessel (not illustrated).
The centrifugal pump 54 is particularly suitable for conveying heat-sensitive fluid food products P, such as whey protein concentrates, baby food, fluid baby food concentrates, nutritious drinks or cheesemaking milk, which enter via the inlet 76 and emerge from an outlet 94 formed as a pressure connector. The centrifugal pump 54 furthermore has, in a manner known per se, a pump housing 12 which is formed by at least one housing cover 8 and by a housing rear wall 10. In the pump housing 12, there is formed a pump chamber 98 which is fluidically connected to the inlet 76 and to the outlet 94 and which accommodates an impeller 100 (in this regard, see figures 2 to 6) such that the latter is rotatable.
If the inlet 76 is formed as a suction connector, then the latter may be surrounded by a suction-connector coolant chamber 76.1, which can be flowed through by a coolant and by means of which cooling of the inlet K3 is performed. The housing cover 8 is equipped with a housing-cover coolant chamber 8.1, which preferably completely surrounds the housing cover 8, or partially borders the latter, for example in the form of cooling pockets. The housing-cover coolant chamber 8.1 can likewise be flowed through by a coolant, and by means of said housing-cover coolant chamber, cooling of the housing cover Kl is performed. The housing rear wall 10 may be equipped with a housing-rear-wall coolant chamber 10.1, which borders the housing rear wall 10 completely or partially, for example in the form of cooling pockets. The housing-rear-wall coolant chamber 10.1 can likewise be flowed through by a coolant, and by means of said housing-rear-wall coolant chamber, cooling of the housing rear wall K2 is performed. Finally, figure 1 shows, in an approximate and schematic indication, a first flushing flow Si, a second flushing flow S2 and a third flushing flow S3 according to the invention, which are discussed in more detail in figures 5 and 6.
Figures 2 to 6 show the impeller 100, which is open toward the housing cover 8 and closed toward the housing rear wall 10 by an impeller rear side 4, with blades 2 which are curved rearwardly in a plane and in relation to a direction of rotation n (see figure 5) and which are each perpendicular to the impeller rear side 4 and form a blade channel 2.1. The rearwardly curved blade arrangement is not an imperative feature of the impeller 100 for the centrifugal pump 54 according to the invention; a forwardly curved or a purely radially oriented blade arrangement in a plane or even three-dimensional curvature may be implemented without limitation with regard to the realization of a centrifugal pump flushed in accordance with the invention. A rear side RS, formed substantially by the impeller rear side 4, of the impeller 100 is spaced apart from the housing rear wall 10 by a rear impeller gap sl (figure 6). Also, a front side VS, formed substantially by the leading edges of the blades 2, of the impeller 100 is spaced apart from the housing cover 8 by a front impeller gap s2.
The rear and/or the front impeller gap sl, s2 are/is enlarged up to several times in relation to a respective minimum rear and front impeller gap sl*, s2*, which ensures the mechanical functionality of the centrifugal pump 54, by reduction of the width of the impeller 100 in the region of the front and of the rear impeller gap sl, 32.
A preferred embodiment provides for the front impeller gap s2 to exhibit a maximum enlargement at an outer impeller diameter DL of the impeller 100, which decreases continuously, as far as into the region of the inlet into the blade channels 2.1, to the minimum front impeller gap s2*. A reduction in this regard of the width of the impeller 100 at the outer impeller diameter DL preferably amounts to 40 to 50%, preferably in this case 45 to 50%, of the width of a hydraulically optimized impeller.
Each blade channel 2.1 between two adjacent blades 2 of the impeller 100 is fluidically connected, in the region of the delimiting impeller rear side 4 thereof, to the rear impeller gap sl via at least one flushing bore 6 which penetrates through the impeller rear side 4 (see in particular figure 6).
A further preferred embodiment provides for the access to the minimum rear, preferably radially oriented impeller gap sl*, which starts from the outer impeller diameter DL of the impeller 100 and extends as far as a hub of the impeller 100, to be widened by up to 5 mm by reduction of the outer impeller diameter DL, whereby the impeller 100 is, radially at the outside, set back slightly relative to the pump housing 12.
According to the invention, the enlargement of the rear impeller gap sl preferably consists in the impeller rear side 4 exhibiting, in the region between the flushing bore 6 and the hub of the impeller 100, an annular-surface-shaped turned-out portion 2.3 (see figures 4 and 6), the axial depth of which amounts to up to 2 mm, preferably 0.5 to 1 mm.
A dimensioning of the front and/or of the rear impeller gap sl, s2 in the manner described above is determined in a manner dependent on the specific characteristics of the heated fluid food product P, and preferably in field tests.
In a preferred embodiment, in the case of a single flushing bore 6 in each blade channel 2.1, all of said flushing bores 6 are arranged on a single hole circle 2.2 with a hole circle diameter d. Here, the geometrical location for the respective penetration point of the flushing bore 6 through the impeller rear side 4, which also defines the hole circle diameter d, is determined approximately by the center of the blade channel 2.1 in relation to the spacing of the blades 2 at the penetration point, and furthermore approximately by the center of a maximum flow filament length of the blade channel 2.1 between the inlet and outlet thereof.
The flushing bore 6 is either preferably of circular design with a bore diameter Db, or it alternatively has a shape which deviates from the circular shape, with a hydraulic diameter Dh definitive of said shape. It is preferably proposed here that the bore diameter Db or the hydraulic diameter Dh amounts to 30 to 50%, and in this range preferably 40 to 50%, of the spacing of the blades 2 at the penetration point.
The invention furthermore provides for more than one flushing bore 6 to be provided in each blade channel 2.1, for each of the multiple flushing bores 6 of a blade channel 2.1 to be arranged on an associated hole circle 2.2, and for the hole circles 2.2 to be radially spaced apart from one another. The flushing bores 6 on different hole circles 2.2 may be formed with equal diameters Db or hydraulic diameters Dh or with different diameters Db or hydraulic diameters Dh from one hole circle to another. Owing to the pressure difference between the rear impeller side chamber and the blade channel 2.1 which decreases from inside to outside as viewed in a radial direction, one advantageous embodiment provides for the passage cross sections of the flushing bores 6 on the different hole circles 2.2 to become smaller with decreasing hole circle diameter d. The diameters Db or Dh of the flushing bores 6 thus become progressively smaller the closer they are to the hub region of the impeller 100, if it is sought to attain a particular flushing volume flow.
At least the housing cover 8 is, according to the invention, equipped with the housing-cover coolant chamber 8.1, which can be flowed through by a coolant. An intensification of the cooling action is obtained if the housing rear wall 10 is also equipped with the housing-rear-wall coolant chamber 10.1, which can be flowed through by a coolant. In one advantageous embodiment, in addition to the coolant chamber 8.1 on the housing cover and the coolant chamber 10.1 on the housing rear wall, the inlet 76, if it is formed in the manner of a suction connector, is equipped with the coolant chamber 76.1 on the suction connector. It is proposed that the suction-connector coolant chamber 76.1, the housing-cover coolant chamber 8.1 and the housing-rear-wall coolant chamber 10.1 are charged with coolant separately from one another. Another embodiment provides for at least two coolant chambers 76.1, 8.1, 10.1 to be connected in series with one another. According to a further proposal, the suction-connector coolant chamber 76.1 is an integral portion of the housing-cover coolant chamber 8.1.
The following measures with which a centrifugal pump according to the prior art is to be modified according to the invention ensure, in combination with one another or in each case also individually, the flushing of the impeller 100 in accordance with the invention:
= widening of the rear impeller gap sl and/or of the front impeller gap s2 (see figure 6) o either by virtue of the impeller 100 being subjected to material removing by turning on both sides, o or by means of a spacer element which acts axially in the direction of the pump shaft 96 and which is arranged between the housing cover 8 and the housing rear wall 10, wherein the impeller 100 is = not offset, = or is correspondingly offset axially on or with the pump shaft 96 in the pump chamber 98, in relation to the housing rear wall 10.
= arrangement of abovementioned flushing bores 6 in the manner described above.
Figures 5 and 6 illustrate the effects of the above measures according to the invention. As a result of the widening of the rear impeller gap sl or as a result of the widened access thereto, the associated rear impeller side chamber is, over its entire radial extent region, charged in a more or less on throttled manner with the static pressure prevailing at the outlet side of the impeller 2, which there has the outer impeller diameter DL. A lower static pressure prevails at the respective flushing bore 6 in the blade channel 2.1 than in the rear impeller side chamber. This results, in the blade channel 2.1, in the first flushing flow Si directed radially from the inside to the outside, as illustrated in figure 6 and in figure 5, shown in the latter only at one blade channel 2.1 by way of example. Since the heated fluid food product P
situated in the rear impeller side chamber can be cooled at the housing rear wall 10 because the cooling of the housing rear wall K2 is possibly provided there, fluid food product P
permanently cooled by the first flushing flow Si now preferably passes into the core region of the flow in the blade channel 2.1.
By means of the described widening of the front impeller gap s2, it is possible, as shown in figure 5 in the left-hand upper quadrant of the impeller 100, for the third flushing flow S3 to form as viewed over the respective end-side free leading edge of the blade 2 and over the radial extent region thereof. The driving forces for this third flushing flow S3 result from the pressure difference at each blade 2, which arises owing to the static pressure on the blade top side, a pressure side DS, and owing to the static pressure on the blade bottom side, a suction side SS. The third flushing flow S3 ensures an additional movement relative to, and predominantly in a circumferential direction with respect to, the housing cover 8, and thus forced cooling of the fluid food product P. because the cooling arrangement of the housing cover Kl is installed in said housing cover 8 (see figure 6).
In this case, too, the third flushing flow S3 effects an exchange of the fluid food product P into and out of the core region of the flow in the associated blade channel 2.1.
Owing to the widened front impeller gap s2, the radially oriented second flushing flow S2 can form owing to the difference between the static pressure at the outlet of the impeller 100 and the static pressure in the suction-side inlet of the impeller 100 (see figure 6), said second flushing flow being superposed on the third flushing flow S3. In this case also, said second flushing flow S2 ensures an exchange of the fluid food product P into and out of the core region of the flow in the associated blade channel 2.1.
Exemplary embodiment of a centrifugal pump 54 according to the invention:
The centrifugal pump 54 is driven by a drive motor with a nominal power of 15 kW at a nominal rotational speed n = 2900 rpm. The outer impeller diameter DL has been reduced, by removal of material by turning, from an original 205 mm to 195 mm. The impeller wheel width at the outer impeller diameter DL has been reduced from originally 19 mm to 9 mm, wherein the reduction decreases continuously, as far as into the region of the inlet into the blade channels 2.1, to the minimum front impeller gap s2*. The rear impeller gap sl has been enlarged, in the region of the annular-surface-shaped turned-out portion 2.3, by 0.7 mm in relation to the minimum rear impeller gap sl*. Each flushing bore 6 in the associated blade channel 2.1 of the total of six blade channels 2.1 is of circular design and has a bore diameter Db = 10 mm.
The above-described measures according to the invention are analogously also transferable to a closed impeller, wherein then the third flushing flow S3 over the end-side leading edge of the respective blade 2 is inevitably not possible in the manner described above. As a substitute for these flushing paths, a cover disk of the impeller 100 would then have to be provided with further flushing bores, which connect the respectively associated blade channel to a front impeller side chamber, formed between the cover disk and the housing cover 8.

LIST OF ABBREVIATIONS USED
54 Centrifugal pump 76 Inlet (suction connector) 76.1 Suction-connector coolant chamber 94 Outlet (pressure connector) 96 Pump shaft 98 Pump chamber 100 Impeller 2 Blade 2.1 Blade channel 2.2 Hole circle 2.3 Annular-surface-shaped turned-out portion 4 Impeller rear side 6 Flushing bore 8 Housing cover 8.1 Housing-cover coolant chamber

10 Housing rear wall 10.1 Housing-rear-wall coolant chamber 12 Pump housing DL Outer impeller diameter Db Bore diameter Dh Hydraulic diameter DS Pressure side (of the blades) Kl Cooling of the housing cover 1(2 Cooling of the housing rear wall K3 Cooling of the inlet (of the suction connector) = Fluid food product RS Rear side SS Suction side (of the blades) Si First flushing flow S2 Second flushing flow S3 Third flushing flow VS Front side = Hole circle diameter sl Rear impeller gap sl* Minimum rear impeller gap s2 Front impeller gap s2* Minimum front impeller gap = Direction of rotation

Claims

1. A centrifugal pump for conveying heat-sensitive fluid food products (P), having an inlet, an outlet, a pump housing which is formed by at least a housing cover and a housing rear wall, a pump chamber which is formed in the pump housing and which is fluidically connected to the inlet and to the outlet, an impeller which is accommodated rotatably in the pump chamber and which has blades, a blade channel which is formed in each case between two adjacent blades and which is formed so as to be open toward the housing cover and closed toward the housing rear wall by an impeller rear side, a rear impeller gap (s1) which is provided between the housing rear wall and the impeller, and a front impeller gap (s2) which is provided between the housing cover and the impeller, .cndot. wherein the rear and/or the front impeller gap (s1,s2) are/is enlarged up to several times in relation to a respective minimum rear and front impeller gap (s1*, s2*), which ensures the mechanical functionality of the centrifugal pump, by reduction of the width of the impeller in the region of the front and of the rear impeller gap (s1, s2), in order to intentionally flush the impeller itself and its adjacent critical regions (s1, s2) as far as the direct pump-housing-side boundary of the impeller front side, the housing cover and of the impeller rear side, the housing rear wall, with the fluid food product (P) to be conveyed, and .cndot. wherein at least the housing cover is equipped with a coolant chamber through which a coolant can flow, in order to be able to simultaneously cool at least the volumes conducted by the flushing volume flows from the core of the blade channels to the cooled walls of the pump housing.

2. The centrifugal pump as claimed in claim 1, wherein the housing rear wall is equipped with a coolant chamber through which a coolant can flow.

3. The centrifugal pump as claimed in claim 1 or 2, wherein the inlet is formed in the manner of a suction connector which projects on the housing cover and which is equipped with a suction-connector coolant chamber.

4. The centrifugal pump as claimed in any one of claims 1 to 3, wherein each blade channel is, in the region of its delimiting impeller rear side, fluidically connected to the rear impeller gap (s1) via at least one flushing bore which penetrates through the impeller rear side.

5. The centrifugal pump as claimed in any one of claims 1 to 4, wherein the front impeller gap (s2) exhibits a maximum enlargement at an outer impeller diameter (DL) of the impeller, which decreases continuously, as far as into the region of the inlet into the blade channels, to the minimum front impeller gap (s2*).

6. The centrifugal pump as claimed in claim 5, wherein the reduction of the width of the impeller at the outer impeller diameter (DL) amounts to 40 to 55% of the width of a hydraulically optimized impeller.

7. The centrifugal pump as claimed in claim 5, wherein the reduction amounts to 50 to 55% of the width of a hydraulically optimized impeller.

8. The centrifugal pump as claimed in any one of claims 4 to 7, .cndot. wherein the access to the minimum rear impeller gap (s1*), which starts from an outer impeller diameter (DL) of the impeller and extends as far as a hub of the impeller, is widened by up to 5 mm by reduction of the outer impeller diameter (DL), and .cndot. wherein an enlargement of the rear impeller gap (s1) consists in the impeller rear side exhibiting, in the region between the flushing bore and the hub of the impeller, an annular-surface-shaped turned-out portion, the axial depth of which amounts to up to 2 mm.

9. The centrifugal pump as claimed in claim 8, wherein the axial depth of the turned-out portion amounts to 0.5 to 1 mm.

10. The centrifugal pump as claimed in any one of claims 4 to 9, wherein in the case of a single flushing bore in each blade channel, all of said flushing bores are arranged on a single hole circle.

11. The centrifugal pump as claimed in any one of claims 4 to 10, wherein the geometrical location for the respective penetration point of the flushing bore through the impeller rear side, which also defines a hole circle diameter, is determined .cndot. approximately by the center of the blade channel in relation to the spacing of the blades at the penetration point, and .cndot. approximately by the center of a maximum flow filament length of the blade channel between the inlet and outlet thereof.

12. The centrifugal pump as claimed in any one of claims 4 to 11, wherein the flushing bore is of circular design with a bore diameter (Db).

13. The centrifugal pump as claimed in any one of claims 4 to 11, wherein the flushing bore has a shape which deviates from the circular shape, with a hydraulic diameter (Dh) definitive of said shape.

14. The centrifugal pump as claimed in claim 12 or 13, wherein the bore diameter (Db) or the hydraulic diameter (Dh) amounts to 30% to 50% of the spacing of the blades at the penetration point.

15. The centrifugal pump as claimed in claim 12 or 13, wherein the bore diameter (Db) or the hydraulic diameter (Dh) amounts to 40 to 50% of the spacing of the blades at the penetration point.

16. The centrifugal pump as claimed in any one of claims 4 to 9, .cndot. wherein more than one flushing bore is provided in each blade channel, .cndot. wherein each of the multiple flushing bores of a blade channel is arranged on an associated hole circle, and .cndot. wherein the hole circles are radially spaced apart from one another.

17. The centrifugal pump as claimed in claim 16, wherein the passage cross sections of the flushing bores on the different hole circles become smaller with decreasing hole circle diameter (d).

18. The centrifugal pump as claimed in any one of claims 3 to 17, wherein the suction-connector coolant chamber, the housing-cover coolant chamber and the housing-rear-wall coolant chamber are charged with coolant separately from one another.

19. The centrifugal pump as claimed in any one of claims 2 to 17, wherein at least two coolant chambers are connected in series with one another.

20. The centrifugal pump as claimed in claim 3, wherein the suction-connector coolant chamber is an integral portion of the housing-cover coolant chamber.

21. The centrifugal pump as claimed in any one of claims 1 to 20, wherein proceeding from a hydraulically optimized centrifugal pump, the rear and/or the front impeller gap (s1, s2) are/is enlarged, specifically .cndot. either by virtue of the impeller being subjected to material removing by turning on both sides, .cndot. or by means of a spacer element which acts axially in the direction of a pump shaft and which is arranged between the housing cover and the housing rear wall, wherein the impeller is .cndot. not offset, .cndot. or is correspondingly offset axially on or with the pump shaft in the pump chamber, in relation to the housing rear wall.

22. The centrifugal pump as claimed in any one of claims 1 to 21, wherein the heat-sensitive fluid food products are whey protein concentrates, baby food, fluid baby food concentrates, nutritious drinks or cheesemaking milk.

23. An impeller for a centrifugal pump, wherein the impeller is accommodated rotatably in the pump chamber of the centrifugal pump, and the centrifugal pump is designed as claimed in any one of claims 1 to 22.