Technical Field

The invention is related to a device for mixing and/or homogenizing at least one liquid product, particularly in the field of food industry or dyeing industry, and to a method for mixing and/or homogenizing the liquid product by means of said device, according to the independent claims.

Background Art

Devices for mixing and/or homogenizing a liquid are used in the food industry during the production of beverages. Beverages are in most cases composed of a plurality of ingredients, that is at least a concentrate and water, for example fruit juice and water. A production step, which is particularly important in the end phase of production, is to make sure that the end product is homogenous. This step is also important in case a liq ^¬ uid ingredient, e.g. a concentrate, that has been stored for a while has to be used for producing a final beverage. During the storage the concentrate may change its homogeneity due to different viscosities and densities of the ingredients. If the final beverage is simply produced with the untreated concentrate, the result may be that each dose has a different taste, consistency, etc. Thus, the concentrate has to be made homogenous again prior to usage. This is accomplished by using said devices to remix the concentrate.

EP 0 196 575 discloses a device for mixing at least one streaming medium. This device uses two concave and concentric impellers which are both rotors. Two streams of the liquid are inserted into a space between the two impellers and accelerated by the centrifugal force which arises because of the rotating rotor. In this way the two streams are ejected sideways from said space and they mix outside the impellers.

Disclosure of the Invention

It is a general objective of the invention to provide a device and a method with an improved mixing and/or homogenizing capability.

According to one aspect of the invention a device for mixing and/or homogenizing at least one liquid product is provided. The device for mixing and/or homogenizing at least one liquid product comprises at least two counter-rotating impellers arranged coaxially with respect to a rotation axis and having inner surfaces facing one another. At least one stream of a liquid component or at least two streams of different liquid components is or are respectively, insertable in a space between the impellers. The device further comprises at least one inlet for guiding the at least one stream into the space between the impellers and at least one outlet for guiding the homogenized and/or mixed liquid product out of the device. The two impellers have each a plurality of protrusions extending into the space between them and arranged in rows which are concentric with respect to the rotation axis, wherein the concentric rows of protrusions of the two impellers alternate, and wherein channels are formed between the protrusions. The counter-rotating impellers are adapted to subject the at least one stream in the space between them to a centrifugal force and to create a shear flow for mixing and/or homogenizing the at least one stream inside the channels.

In one embodiment the impellers have a same number of protrusions.

In another embodiment the protrusions have a shape of a right prism with an n-sided polygonal base and n faces, wherein n is greater than 2 and wherein the faces are perpendicular on surfaces of the respective impeller which delimit the space between the impellers.

In yet another embodiment each impeller is supported and rotated by a corresponding hollow shaft. In one variant at least one of the hollow shafts is connected to the at least one inlet for guiding the at least one stream through the hollow shaft and the inlet into the space between the impellers. Advantageously the hollow shaft and the corresponding inlet are made in one piece .

A second aspect of the invention relates to a method for mixing and/or homogenizing a liquid product by means of the device according to the invention.

In one embodiment of the method at least two streams are inserted through the hollow shafts and the inlets into the space between the impellers from different sides. Preferably one of the streams is inserted from a side of one impeller and the other stream is inserted from a side of the other impeller. It is further preferred that the two streams are inserted at a location of the rotation axis of the impellers. This way of inserting the liquid streams into the space between the impellers allows a maximum effect with respect to mixing quality and/or homogenization quality.

The device according to the invention is preferably used for homogenizing a beverage and/or for mixing at least two components of a beverage and/or for breaking long polymer chains from a liquid, e.g. a sugar solution .

Brief Description of the Drawings

The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein: Fig. 1 shows a side view of an embodiment of a device according to the invention in an open configuration,

Fig. 2 shows a side view of the embodiment of Fig. 1 in a closed configuration, and

Fig. 3 shows an impeller of the embodiment of Fig. 1 in a perspective view.

Modes for Carrying Out the Invention

Fig. 1 shows a side view of an embodiment of a device 1 according to the invention with two impellers 2 in an open configuration. The term open configuration means that the impellers 2 are driven back in the direction of the arrows A and B. The impellers 2 have each an inner surface 8 (referenced in Fig. 3 for better view ^¬ ing), wherein the inner surfaces 8 face one another. The two impellers 2 rotate in opposite directions around a rotation or longitudinal axis z and are driven each by a hollow shaft 3 which is actuated by a motor (not shown) . It is also possible to actuate the two impellers 2 by a single motor. The inner surfaces 8 of the impellers 2 carry protrusions 4, i.e. teeth, which are best seen in Fig. 3. In this opened configuration it is possible to clean the inner surfaces and the protrusions 4. Furthermore an inspection, e.g. a visual inspection, can be carried out in order to make sure the condition of the protrusions 4 is intact.

Fig. 2 shows a side view of the embodiment of Fig. 1 in a closed configuration. To switch from the open configuration into the closed configuration the impellers 2 are driven towards each other until they reach a minimum allowable distance from one another. This may e.g. be automatised by using a proximity sensor coupled to a main control system of the device 1 (not shown) . The shifting along the rotation axis z may e.g. be performed with a servo motor or other suitable actuation means. In the closed configuration the impellers 2 are surrounded by a casing 5 which only permits a liquid to flow out of it through an outlet 6. It is understood that the casing 5 may e.g. comprise two pieces, each one attributed to one impeller 2. When the impellers are driven into the open configuration the two pieces of the casing 5 also move apart. Other attachment means of the casing 5 are readily possible and are not explained in more detail here. The device 1 is ready for operation in the closed configuration, in which liquid may be inserted into the space be ^¬ tween the two impellers 2 in the direction of the arrow C, e.g. through the hollow shafts 3.

In one embodiment the outlet 6 is coupled to a recirculation circuit (not shown) which feeds back the mixed liquid product to the at least one inlet. In this way it is possible to increase the mixing and/or homog- enization quality.

Fig. 3 shows an impeller 2 of the embodiment of Fig. 1 in a perspective view. Its description also applies for the other impeller 2. In this view the inlet 7 attributed to the impeller 2 is seen best. Preferably the inlet 7 and the corresponding hollow shaft 3 are made in one piece. It is preferred that the inlet 7 opens into the space between the impellers concentrically with respect to the rotation axis z of the impellers 2. This measure yields the best mixing and/or homogenizing effect because the way of the liquid to the outlet is longest and as a result the liquid is mixed for a longer time.

In one embodiment (not shown) the inlets 7 are formed by a plurality of nozzles opening into the space between the impellers 2. Preferably, the nozzles are arranged uniformly and protrude into the space between the impellers 2. By providing nozzles as inlet openings it is possible to produce thinner liquid streams, the mixing of which is faster.

In a preferred embodiment the liquid quantity of the at least one liquid stream entering the space be- tween the impellers 2 is adjustable. For example it is possible to adjust the quantity of the liquid of both streams to be equal. In some applications it may be desirable to have unequal streams, e.g. when two different liquid components shall be mixed and their concentration in the mixed liquid product shall not be equal.

The protrusions 4 and their arrangement on the inner surface 8 of the impeller 2 is also seen best in Fig. 3. As can be seen the protrusions 4 are arranged in such a way that channels are formed between their adjacent faces 10. Advantageously an average width of the channels between adjacent protrusions 4 is between 0.2 mm and 1 mm, preferably 0.5 mm. The width of the channels determines the suitable types of liquid to be mixed and/or homogenized. For example a more viscous liquid should not be used in the device if it has very thin channels. Therefore, in order to increase the flexibility of the device for mixing/homogenizing, it is possible to exchange at least one of the impellers 2 with another impeller having protrusions of different size (but same shape) . In this way it is possible to increase or decrease the channel width in a simple way. For example if an impeller with thinner protrusions 4 is mounted into the device the channels between adjacent protrusions 4 of the new impeller and the old impeller 2 get wider. By this measure it is possible to adjust the device for mixing/homogenizing a liquid to an optimum mix- ing/homogenization of various liquids ranging from very liquid ones to very viscous ones.

As mentioned the protrusions 4 of each impeller 2 are arranged concentrically in rows with respect to the rotation axis z. It is preferred and illustrated in Fig. 3 that the concentric rows of protrusions 4 are arranged on steps ascending from the rotation axis z towards an edge of the impellers 2, i.e. towards the vicinity of the pointer of the reference number 2. This can be appreciated by noticing the different heights of the lat- eral faces 10 of each row of protrusions 4. As can be seen, the innermost row has the highest protrusions 4 and the height of the protrusions 4 decreases gradually for each row towards the edge of the inner surface 8. By this measure the radial liquid speed is kept substantially constant. In this advantageous embodiment the steps additionally increase the shear flow of the liquid through the channels and therefore the mixing and/or homogeniza- tion quality. Thus, the inner surfaces 8 of the impellers 2 have a shape in the style of an amphitheatre. It is however also possible to design the inner surfaces 8 of the impellers 2 to be even and parallel to one another. Other shapes are also conceivable.

The maximum height of the protrusions 4, measured from the uppermost plane (e.g. uppermost step) of the inner surfaces 8, defines the distance between the two impellers 2 and thus the volume of the space between the two impellers 2. This design criterion may be taken into account when determining how much liquid shall fit in the space between the impellers 2, i.e. the maximum allowable strength and/or "thickness" of the liquid streams .

In the embodiment with the amphitheatre-like inner surfaces 8 the top surfaces 9 of the protrusions 4 are arranged on a same plane. However it is also possible to arrange the top surfaces 9 of groups of protrusions 4, wherein the groups are preferably rows, in different planes. This has been exemplarily illustrated in the lat ^¬ eral view of Fig. 1.

Preferably all protrusions 4 have a same shape, even in case their dimensions are not equal, e.g. said different height. This is preferred because it simplifies the manufacture of the protrusions 4 and ensures that the impellers 2 can rotate in different direction with their protrusions 4 being "intermeshed" without a risk that the protrusions 4 touch one another. In the context of the present invention the term "intermeshed" is understood as not implying a form fit or any other contact between the protrusions 4. Certainly, it is possible to design the protrusions 4 to have different shapes, however in this case it has to be made sure that groups having the same shape match for both impellers 2, such that any contact between them during the rotation is avoided .

The actuation of the impellers can be done in the way described in EP 0 196 575. Normally the impellers 2 are actuated with the same speed but in different directions. In embodiments it may be preferred to use different speeds for the impellers 2.

The present device for mixing or homogenizing at least one liquid product is characterized by a high shearing effect generated between the impellers 2. The axial speed of the liquid is very small and the radial acceleration of the liquid is very high towards the edges of the impellers. The mixing or homogenization effect is not only augmented by the fact that a high shearing effect is generated but also by the fact that the liquid located inside the space between the impellers has to find a way towards the edges of the impellers through a "labyrinth" of channels.

While there are shown and described presently preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto but may otherwise variously be embodied and practised within the scope of the following claims. Therefore, terms like "preferred" or "in particular" or "particularly" or "advantageously", etc. signify optional and exemplary embodiments only.