TANK FOR STORING AND COOLING MILK.
The invention concerns a tank for storing ana cooling milk.
It is a tank with generally a cylindrical form and a vertical longitudinal axis, whose base is substantially horizontal and has a circular contour, and which comprises means for cooling the milk that car. circulate a refrigerating fluid inside at least part of its wall.
Such a type of tank is to be distinguished from those which are also generally cylindrical in shape, but which have a horizontal longitudinal axis.
This type of tank is usually used to store a very large volume of milk (2,000 to 30,000 litres), whereas the tank of the invention generally has a smaller capacity (1,000 to 2,000 litres) and is especially adapted to storing and cooling a quantity of milk equal to two successive milkings of an average sized herd.
Of course, in this application, the terms "horizontal" and "vertical" are used in reference to a flat floor on which the tank is located. Furthermore, the expression "longitudinal axis" defines the axe passing through the centre of the cylinder and parallel to its generating lines.
The tanks of this type, generally called "milk tanks", have a classification that is especially characteristic of their capacity to cool the milk from the ambient temperature to a storage temperature in a determined length of time.
Consequently, a tank which meets the "2AII" performance class of the European standard NF EN 13732
means that it can store a volume of milk equal to two successive milkings, wherein the letter A means that the ambient performance temperature is 38 °C and the figure II indicates that at maximum three hours are required to cool the milk from 35°C to 4°C.
This classification means that this tank is especially suited to use in countries where the temperatures are generally high, for example countries such as Africa, Asia or South America.
A classification of "2BII" means that the ambient performance temperature is 32 °C and also that less than three hours are required to cool the milk from 35°C to 4°C.
It is common to equip the tanks for storing and cooling the milk with a generally cylindrical form and a vertical longitudinal axis with cooling means that are connected to a heat exchanger located on the base wall of said tank. However, the surface area of this base wall is relatively small, such that the cooling capacity of such an installation is not very high.
This invention aims to overcome this disadvantage by proposing a tank for storing and cooling milk, of the type mentioned above, which permits rapid cooling of the milk, thus permitting it to be used in countries that generally have high ambient temperatures.
This invention thus concerns a tank for storing and cooling milk, of a generally cylindrical form with a vertical longitudinal axis, whose base, substantially horizontal, has a circular contour, and which comprises means for cooling the milk that can circulate a refrigerating fluid inside at least part of its wall.
Such a tank is remarkable in that said part of wall is the base wall, and that it is separated diametrically into two independent sections, wherein the first is connected to first cooling means, whereas the second is connected to second cooling means.
Consequently, by using two cooling means each "working" with one section of the base of the tank, the overall capacity to cool the milk is improved to reduce the time required.
According to other advantageous and non-restrictive characteristics of the invention:
- said base wall is formed by two sheets of metal that are welded punctually, wherein the spot welds are positioned along lines parallel to the diameter, so that in each independent part, the cooling fluid circulates through the interstices separating these spot welds;
- the distance between two spot welds of a same line is constant, wherein these welds are offset from one line to the next, so as to form a staggered row pattern;
each independent section has at least two partition walls forming a chicane, which extend parallel to the weld lines, on one part of their length, and alternatively from the peripheral edge of said base;
- said partition walls forming chicanes are aligned with one of the spot weld lines;
- said partition walls forming chicanes are made of a continuous weld on the metal sheets;
- each independent part has three partition walls forming chicanes;
- the mutual distance between two partition walls
forming chicanes increases with the distance from the
centre of said base;
said distance is governed by the following relationships:
- e2 = 47.5e1/30;
- e3 = 65e1/30;
- e4 = 82e1/30;
wherein:
- e1 is the distance between the centre of the base
wall and the first partition wall;
- e2 is the distance between the first and the second partition wall;
- e3 is the distance between the second and the third wall;

- e4 is the distance between the third wall and the peripheral edge of the base wall;
- for the cooling of a nominal volume of milk Vn, from a temperature T1 to a temperature T2 in three hours at most, the total minimum refrigerating power Pmin of said first and second cooling means is provided by the following relationship:
Pmin (W) = [Vn X (T1 - T2) X 1.16] / 6
Other characteristics and advantages of this invention will become clearer upon reading the detailed description below. It is provided in reference to the appended drawings in which:
- figure 1 is a diagrammatical front view of a tank for storing and cooling milk in compliance with this invention;
- figure 2 is a bottom view of the base wall of the tank of figure 1;
- figure 3 is an analogous view to that of figure
2, designed to illustrate more specifically the path of
the refrigerating fluid inside the base wall;
The tank shown in figure 1 has a structure that is generally known.
This tank 1 has a cylindrical body 2 with an axis X-X' that is generally vertical, and whose flat base wall 21 substantially extends horizontally. By this last expression, it is meant that this wall 21 forms with the horizontal plane an angle of several degrees, wherein the corresponding slope is sufficient to empty by gravity all of the milk contained in the tank, by a stopper or pipe provided for this purpose on this wall.
In the appended figure, the tank is eguipped with legs 4 which allow it to be stood on the floor.
Of course, when speaking of the vertical orientation of the longitudinal axis X-X' of the tank and extending substantially horizontally for the base wall 21, this refers to the positioning of the tank on the surface of a horizontal floor.
The tank of figure 1 is equipped with a cover 3 which provides access to the inside of the tank. This cover rests, in its closed position, on the upper edge of the cylindrical wall 20 of the tank.
It is associated to a set of connecting rods 30 forming a deformable parallelogram that is aided by an actuator, which makes it easier to open or respectively close.
It is furthermore equipped with a stirring rod 5, whose shaft 50 passes completely through it. This stirring rod comprises a motor 51 attached to the cover
3, which rotates the shaft 50 around itself (around its
Y-Y' axis) . The free end of the shaft carries a blade 52.
In a known manner, the previously mentioned Y-Y' axis is offset with respect to the centre of the tank 1 to mix the milk effectively. The person skilled in the art will know how to determine this position, as well as the distance of the blade 52 with respect to the base of the tank.
Figure 2 is a. bottom view, showing the base wall 21 of said tank. It is equipped with an evacuation pipe 22 permitting the tank to be emptied. A temperature probe connected to a duct 8 allows the temperature of the milk stored to be measured continuously.
In compliance with the invention, this wall is diametrically separated (according to the Z-Z' axis) into two identical and independent sections 210 and 211. The first of these sections is connected to first cooling means GF1, while the second section 211 is connected to second cooling means GF2.
More precisely, the base wall 21 is formed by two parallel sheets of metal which, except for their peripheral edge 212 which is completely welded, are welded punctually on the rest of their surface by spot welds PS which are positioned according to the lines L, L' parallel to said diameter. This weld is made for example using a laser.
The French patent application 99 03726 filed by the present applicant may be referred to for more information on the methodology used to form such a wall. In summary, once the welds have been made, the assembly is inflated by injecting a pressurised fluid, so as to
make the two sheets swell up, except in the positions where the welds are situated.
It may be noted that the distance between two spot welds PS of a same line L, L' is constant, wherein these spot welds are offset from one line to another, so as to form a staggered row pattern.
In one particularly advantageous embodiment, each independent section 210 and 211 is equipped with at least two partition walls forming a chicane.
In the example shown here, there are three partition walls forming a chicane 6, 6' and 6''. They extend in parallel to the weld lines L, L4, on one part of their length, and alternatively from the peripheral edge of said base.
These partition walls forming a chicane are each aligned with a line of spot welds. They may be seen by a continuous weld on the metal sheets.
Still in reference to figure 2, shown in the form of rectangles, are the two refrigerating units GFl and GF2 which power said tank.
The GFl unit is connected to a refrigerating fluid supply duct 7 which communicates with the inside of the base wall by one end 70 that is located in an area close to the start of the chicane 6.
The GFl unit is furthermore is connected to a refrigerating fluid return duct 7' which is connected by its end 70' to the area of the base wall close to the partition wall forming a chicane 6''.
The above description of the GFl unit also applies to the GF2 unit.
The applicant has therefore observed that by separating the base wall 21 diametrically into two
independent sections, each connected to independent cooling means, good cooling performances are obtained for the milk in a very suitable length of time.
The applicant has also observed that best results are obtained when the base wall is equipped, in each of the independent sections, with three chicanes 6, 6' and 6'', wherein the distance e1, e2, e3, e4 between two partition walls forming a chicane increases with the distance from the centre of the base wall 21.
Preferably, the following mathematical relationships govern the progressive distance between the walls:
- e2 = 47.5e1/30;
- e3 = 65e1/30;
- e4 = 82e1/30; wherein:

- e1 is the distance between the centre of the base wall and the first partition wall 6;
- e2 is the distance between the first 6 and the second partition wall 6';
- e:3 is the distance between the second 6' and the third wall 6";
- e4 is the distance between the third wall 6" and the peripheral edge of the base wall 21.
Preferably, for the cooling of a nominal volume of milk Vn, from a temperature Tx to a temperature T2 in three hours at most, the minimum total refrigerating power Pmin of said first and second cooling means is provided by the following relationship:
Pmin (W) = [Vn X (T1 - T2) X 1.16] / 6
Consequently, to pass from 35 to 4°C, Pmin is equal to approximately 6Vn.
For a nominal volume of 2,000 litres, the minimum power to be supplied is around 12,000 W. Excellent cooling results are obtained when the total surface area of the two independent sections 210 and 211 is 2.45 m2, which is to say an exchanging power (W/m2) of around 4, 900 W/m2.
Taking the above into account, the use of such a tank may be envisaged in countries where temperatures are generally high..

CLAIMS
1. Tank (1) for storing and cooling milk, generally
with a cylindrical form and a vertical longitudinal axis
(X-X'), whose base (21) is substantially horizontal and has a circular contour, and which comprises means for cooling the milk that can circulate a refrigerating fluid (FF) inside at least part of its wall, characterised by the fact that said part of wall is the base wall (21), and that the latter is separated diametrically into two independent sections (210, 211), wherein the first (210) is connected to first cooling means (GF1), while the second (211) is connected to second cooling means (GF2).
2. Tank according to claim 1, characterised by the fact that said base wall (21) is formed by two sheets of metal welded punctually, wherein the spot welds (PS) are positioned along lines (L, L') that are parallel to the diameter, such that in each independent part (210, 211), the refrigerating fluid (FF) circulates through interstices separating these spot welds (PS).
3. Tank according to claim 2, characterised by the fact that the distance between two spot welds (PS) of a same line (L, L1) is constant, wherein these spot welds are offset from one line to another, so as to form a staggered row pattern.
4. Tank according to claim 3, characterised by the fact that each independent section (210, 211) is eguipped with at least two partition walls (6, 6', 6") forming a chicane, which extend parallel to the weld lines (L, L'), on one part of their length, and
alternatively from the peripheral edge of said base wall (21) .
5. Tank according to claim 4, characterised by the fact that said partition walls (6, 6', 6") forming chicanes are each aligned with a line (L, L') of spot welds (PS).
6. Tank according to claim 5, characterised by the fact that said partition walls forming chicanes (6, 6', 6") are made of a continuous weld on the metal sheets.

7. Tank according to any of claims 4 to 6, characterised by the fact that each independent pare (210, 211) has three partition walls forming chicanes (6, 6', 6").
8. Tank according to any of claims 4 to 7, characterised by the fact that the mutual distance between two partition walls (6, 6', 6") forming chicanes increases with the distance from the centre of the base wall (21).
9. Tank according to claims 7 and 8 considered together, characterised by the fact that said distance is governed by the following relationships:

- e2 = 47.5e1/30;
- e3 = 65e1/30;
- e4 = 82e1/30; wherein:

- e1 is the distance between the centre of the base wall and the first partition wall (6);
- e2 is the distance between the first (6) and the second partition wall (6');
- e3 is the distance between the second (6') and the third wall (6");
- e4 is the distance between the third wall (6") and the peripheral edge of the base wall (21).
10. Tank according to any of the previous claims, characterised by the fact that, for the cooling of a nominal volume of milk Vn, from a temperature T1 to a temperature T2 in three hours at most, the minimum total refrigerating power Pmin of said first and second cooling means (GF1, GF2) is provided by the following relationship:
Pmin (W) = [Vn X (T1 - T2) X 1.16] / 6