FR2509996A1 - APPARATUS FOR MIXING LIQUIDS AT LOW FLOW RATES, PARTICULARLY FOR DIALYSIS - Google Patents

Abstract

The device for mixing liquids at low flow velocities is characterised by a cylindrical vessel having an upper closure, a first liquid inlet which is formed in a lower part of the side wall of the vessel and is open tangentially to the side wall, a second liquid inlet which is formed in the vessel bottom and is open vertically upwards, and a mixture outlet formed in the centre of the closure for the outflow of the mixture of the first and second liquids, and by a first pump, a second pump and a control unit. This device is advantageous for diluting concentrates in order to prepare infusion fluids, disinfectant fluids, flushing fluids and the like, and replacement fluids for artificial kidneys.

Description

 The present invention relates to an apparatus intended for mixing liquids at low flow rates and more particularly relates to an apparatus intended for mixing two liquids uniformly and continuously in a precise mixing ratio when one of the liquids has a much higher flow rate weaker than the other and that the resulting mixture is continuously discharged from the device, also at a low flow rate. The device is therefore particularly useful for continuously preparing dialysates, substitution fluids for artificial kidneys: perfusion fluids , say disinfection fluids, washing fluids, etc., by a process in which a liquid concentrate supplied at a low flow rate is mixed in a predetermined mixing ratio with a diluting liquid which has a relatively high flow rate, to obtain a discharged mixture at a weak start.

 Apparatuses for continuously mixing liquids include those in which an in-line mixer is incorporated. Since the in-line mixer is designed so as to inject a liquid continuously into a direct current of another liquid in order to mix it there, it is necessary to use means capable of injecting the liquid continuously at a precise flow so that the two liquids can be mixed uniformly in a precise ratio The means for injecting a liquid in a pulsating mode are incapable of achieving a uniform mixing even if they can be implemented with high precision and these means are therefore unusable. On the contrary, the means capable of injecting a liquid continuously with high precision and which are also capable of handling a liquid at a low flow constitute very special and extremely clod means. The means comprising an in-line mixer cannot therefore be used in practice for mixing liquids uniformly in a precise ratio when one of the liquids has a low flow rate.

 The problem mentioned above will be described more precisely. The substitution fluid which must be used for a hemofiltration treatment is prepared at a specified high concentration and contained in a large number of vials (usually with a capacity of 1000 ml) and this fluid is conveyed from the vials to the body of the patient, the vials being successively replaced one after the other during the treatment.

Since the vials of substitution fluid are very inconvenient to prepare, store and replace during processing, it would be very advantageous to be able to prepare the substitution fluid by diluting a concentrate of this fluid with pure sterelized water and free of pyrogens at the desired concentration during the execution of the treatment. Consequently, if one tries to use an apparatus comprising the above-mentioned in-line mixer for dilution, one is faced with the need to '' use means allowing the concentrate to be conveyed continuously and precisely at a low flow rate, for example from about 1 to about 12 ml / min, to take account of the concentration of the concentrates of substitution fluids found in trade, as well as tolerances on the desired concentration of the substitute fluid. Unfortunately, these means are currently very special and excessively expensive means. The apparatus comprising the in-line mixer therefore requires a high cost which is added to the amount of the costs of the treatment of the artificial kidney, thereby limiting the applications of this. therapy, which is therefore a drawback.

 The present invention, which has been made in view of the situation described above, relates to an apparatus for mixing liquid, which can advantageously also be used to dilute concentrates such as concentrates for substitute fluids without requiring the expensive means mentioned above.

 More specifically, the subject of the invention is an apparatus intended for mixing liquids at low flow rates, characterized in that it comprises: a) a mixer comprising a cylindrical container provided with an upper closing element, a first liquid inlet formed in a lower part of the side wall of the container and which opens in a direction tangential to said side wall, a second liquid inlet formed in the bottom of the container and opening vertically upwards , and a mixture outlet formed in the center of the closure element and serving to discharge the mixture of a first liquid and a second liquid; b) a first liquid reservoir connected to the first liquid inlet of the mixer by a connecting pipe; c) a first pump provided on the connecting pipe between the first liquid inlet of the mixer and the first liquid tank to supply the first liquid in a pulsating mode; d) a second liquid reservoir connected to the second liquid inlet of the mixer by a connecting pipe; e) a second pump provided on the connecting pipe between the second liquid inlet of the mixer and the second liquid tank to supply the second liquid in a pulsating mode; f) a concentration detector provided in the vicinity of the mixing outlet of the mixer or on a liquid discharge pipe connected to the mixing outlet; and g) a control unit intended to control the first and second pumps so that the pulsating supplies of liquids delivered by the pumps are different by their pulsation period and also intended to control the supplies so as to adjust the concentration in response to signals from the detector.

 According to a first characteristic of the invention, while the first liquid is animated by a swirling movement in the cylindrical container of the mixer by the fact that it is made to penetrate into this container in a direction tangential to its side wall, the material is made to penetrate. second liquid in the container through the bottom of the latter, in a direction aligned with the axis of the vortex movement. It is thus mixed with the vortex current so that the resulting mixture is discharged from the container through the central part of its upper closure element. This constitutes an original characteristic in the sense that the vortex flow is used to operate this mixing. which is in a completely opposite relation to the conventional practice of using such a vortex or spiral current for separation in cyclones.

 According to another characteristic, the first and second liquids are introduced into the container in a pulsating mode by the first and second pumps.

 According to another characteristic, it is made so that the inlet flow rate of the first liquid and the inlet flow rate of the second liquid are different by the period of their pulsation.

 According to yet another characteristic, the concentration is measured by the detector and it is adjusted by the transmission of the measurement result in reaction through the control unit.

 In view of the above, the invention also relates to a method for mixing liquids which consists in making a first liquid penetrate into a cylindrical container through an inlet located in a lower part of its side wall, in a pulsating mode , in a direction tangential to the side wall, this container having an upper closing element, a second liquid is made to penetrate into the container, in a vertical direction directed upwards, through another inlet located at the center of its bottom, simultaneously with the first stream of liquid, in a pulsating mode which differs from that of the first liquid by the pulsation period, and the mixture composed of the first liquid and the second liquid is discharged through an outlet located in the center of the closing element superior.

 The expression "cylindrical container used in the present specification designates a container having a cylindrical internal surface and the expression" wall the teral "refers to the side wall of this container which forms said internal surface. Several inlets can be provided at different locations for the introduction of the first liquid.

 With the use of the mixing apparatus according to the invention, it is possible to mix liquids continuously and uniformly in a precise mixing ratio, even if these liquids are supplied at relatively low flow rates. The device is very useful.

in practice since the liquid supplies, even if they occur at low flow rates, can be regulated with precision by adjusting the numbers of the pulses, with the use of pumps which can be obtained at low cost. The apparatus according to the invention, which is suitable for mixing liquids in a closed circuit, fulfills the aseptic conditions and can be used to dilute concentrates in order to prepare fluids for infusions, disinfectant fluids, washing fluids , etc., as well as substitute fluids.

 Since the second liquid can be conveyed at a lower flow rate than that of the first liquid, the apparatus can be particularly usable for mixing a first liquid supplied at a low flow rate while precisely obtaining a uniform mixture.

 The apparatus according to the invention is suitable for providing a liquid mixture with a low output flow rate, which can reach approximately 450 ml / min, more advantageously, approximately 100 ml / min.

Other characteristics and advantages of the invention will emerge during the description which follows. In the accompanying drawings given solely by way of example
Fig. 1 is a vertical sectional view showing an embodiment of the mixer in an apparatus according to the invention;
Fig.2 is a sectional view showing the mixer of Fig. 1
Fig. # 3 is a diagram showing the shapes of the liquid streams in the mixer of Fig. 1
Fig. 4 is a diagram which shows the construction of an apparatus according to the invention, produced in the form of an installation for supplying a replacement fluid to an artificial kidney
Fig. 5 is a graph which shows the results obtained by measuring the electrical conductivity of a mixture of liquid supplied by the apparatus according to the invention
Fig.6 is a vertical sectional view showing an already known in-line mixer
Fig. 7 is a graph which shows the results obtained by measuring the electrical conductivity of a liquid mixture supplied by the online mixer of FIG. 6, and
Fig.8 is a graph which shows the results of an experiment carried out using the apparatus according to the invention at different pulsation frequency ratios between the first liquid and the second liquid, with measurement of the electrical conductivity of the resulting mixture , the graph representing the differences between the measured value and the target value.

 Fig. 1 shows a mixer 1 intended for use in an installation according to the invention.

The mixer is essentially composed of a cylindrical container 2 and a closure element 3 of this container. The cylindrical container 2 has an internal diameter D of 29 mm and a height H of 30 mm, and has a first liquid inlet 6 formed in a part of its side wall 5, at a height of 1 mm above its bottom 4 and which opens tangentially to the side wall 5. The container also has, in the center of its bottom 4, a second liquid inlet 7 which opens vertically upwards and has an internal diameter 1 of 3 mm. The first liquid inlet 6 is provided on the outside with a tube 8 which extends tangentially to the side wall 5 and which has a diameter d of 1 mm.

 The upper closure element 3 has the shape of a cone having a height h of about 2.5 mm and it has in its center a mixture outlet 9 having an inside diameter a of 6 mm.

 When a first liquid is introduced in a pulsating mode into the container 2, through the first liquid inlet 6 of the mixer at the same time as a second liquid is introduced into this mixer through the second liquid inlet 7 in a mode pulsating whose pulsation period differs from that of the first liquid, the first liquid enters the mixer tangentially to the side wall 5 of the container and, under this effect, it circulates in vortex along the side wall 5 while the second liquid enters in the form of a column aligned on the axis of the vortex flow, as seen in FIG. 3. The second liquid mixes with the first liquid under the effect of centrifugal force, since the specific weight of the second liquid is usually greater than that of the first liquid. The introduction of the first liquid and the second liquid into the container pient occurs in a pulsating mode as mentioned above, so there can be a dead time. However, in the container the stirring can be carried out continuously due to the fact that the vortex current remains or occurs continuously. In this way, a uniform mixture, perfectly brewed, leaves the container 2 through the mixture outlet 9 formed in the upper closure element 3.

 A particular embodiment of an installation will be described below in which a mixer of the invention is incorporated.

 Fig. 4 shows an installation 30 for forming a substitution fluid in which this fluid is prepared by diulating a concentrate of substitution fluid S with sterilized water W up to a specified concentration. This fluid is contained in a reservoir 20 and is brought to the body H of a patient by an infusion apparatus 23. The installation 30 comprises an assembly 10 which constitutes an apparatus according to the invention and which comprises the mixer 1 described above , a concentrate tank 11, a sterilized water tank 12, pipes 15 and 16 which connect the mixer 1 to tanks 11 and 12 respectively, pumps 13 and 14 mounted in pipes 15 and 16 respectively, a concentration detector 17 and a control unit 18.

 The concentrate S contained in the reservoir 11 is introduced into the mixer 1 through the second liquid inlet 7 of the latter, in a pulsating mode, by the pump 13 which is controlled by pulses by the control unit 18. The sterilized water W contained in the reservoir 12 is introduced into the mixer 1 through the first liquid inlet # 6 of this mixer, in a pulsating mode, by the pump 14 which is likewise controlled by pulses. The pumps 13 and 14 are controlled by the control unit 18 so as to have different pulsation periods.

 The uniform mixture prepared in the mixer 1 in the manner which has already been indicated above and which serves as a substitution fluid having a specified concentration, is delivered by the mixture outlet 9.

Concentration detector 17 is mounted
in a liquid flow line 19, in the vicinity
of the mixing outlet 9 of the mixer 1, for control
ler the concentration of the substitution fluid so
that when necessary the pumps 13 and 14
can be controlled by the control unit 18 pen
during operation to vary the concentration
substitution fluid.

The tank 20 is a container having a ca
capacity of approximately 1000 ml. Pumps 13 and 14 are com
ordered by the control unit 18 in response to if
signals issued by level 21 and 22 gauges of such
so that the tank 20 always contains a quan
tity of substitution fluid within an interval
the predetermined.

We did experiments with nappa
reil mixer according to the invention in the way that is
described in the examples below.

EXPERIMENTAL EXAMPLE 1
By means of the mixer 1 shown in Fig.l
and 2, water was treated with reverse osmosis
which will be designated below by the expression RO water) as the first liquid at a flow rate of 945 # J / impul-
sion, with a pulse period of 102.8 pulses / n.

 The pulse width is 120 ms. A substitute fluid concentrate (of the "Kindaly GF" brand, produced by the firm Fuso Yakuhin Kogyo, Ltd, Japan), having a specific gravity of 1.20, was supplied as second liquid at a flow rate of 36, 1 J / pulse, with a pulse period of 81.3 pulses / min.

 For the detection of the concentration, the electrical conductivity of the resulting mixture was measured at a point in the pipe located immediately downstream of the mixture outlet 9 of the mixer 1.

 The mixing operation was continued for 5 hours. The differences between the instantaneous values measured during the operation and the target value, namely 14 mS / cm, were in the range of + 1.5%. The difference between the average value and the target value was - 0.3%. Fig. 5 is part of a graph which shows the measured value.

 If the mixing was continued to make it more homogeneous, it was observed that it had an electrical conductivity of 13.95 mS / cm.

COMPARATIVE EXAMPLE 1
The procedure of experimental example 1 was repeated under the same conditions, except that the line mixer 1 'shown in FIG. 6 was used to replace the mixer 1. The line mixer 1' has a first liquid inlet 6 'a second liquid inlet 7' and a mixture outlet 9 '.

 The differences between the target value, 14 mS / cm and the instantaneous values obtained were within the range of + 11%. The difference between the average value and the target value was -2.5%. Fig. 7 is part of a graph showing the measured value.

 If the resulting mixture was stirred further to mix it more homogeneously, it was observed that it had an electrical conductivity of 13.65 mS / cm.

EXPERIMENTAL EXAMPLE 2
The procedure of experimental example 1 was repeated under the same conditions, except that a mixer having a capacity of approximately 20 ml and having the same construction as that shown in FIGS. 1 and 2 and that the ratio between the period of the pulsation of introduction of water RO and the period of the pulsation of introduction of the concentrate was varied over the interval going from 0.6 to 1.6.

 The results are represented in FIG. 8, on which the percentage, positive or negative ratio relating the value of the semi-difference between the maximum of the instantaneous values and the minimum of the instantaneous values to the target value has been plotted on the ordinate 14 mS / cm, plotting the frequency of the water introduction pulses RO divided by the frequency of the concentrate introduction pulses.

 Experimental example 1 and comparative example 1 show that the apparatus according to the invention is superior to the in-line mixer in the sense that it makes it possible to obtain a uniform mixture having great precision in volume and in time.

 Experimental example 2 reveals that a better uniformity can be given to the mixture by establishing a difference in the pulsation period of the introduction between the first liquid and the second liquid and this example shows that the ratio linking the pulsation period of the introduction of the first liquid to that of the second liquid is preferably of a value which can reach 0.9 or at least 1.1.

Claims (10)

- CLAIMS -  1.- Apparatus for mixing liquids at low flow rates, characterized in that it comprises (a) a mixer (1) comprising a cylindrical container (2) provided with an upper closure element (3), a first liquid inlet (6) formed in a lower part of the side wall (5) of the container and which opens in a direction tangential to said side wall, from a second liquid inlet (7) formed in the bottom (4) from the container and opening vertically upwards, and from a mixture outlet (9) formed in the center of the closure element and serving to discharge the mixture of a first liquid and a second liquid; (b) a first liquid reservoir (12) connected to the first liquid inlet (6) of the mixer by a connection line (16), (c) a first pump (14) provided on the connection line (16) between the first liquid inlet of the mixer and the first liquid reservoir to supply the first liquid in a pulsating mode; (d) a second liquid reservoir (11) connected to the second liquid inlet (7) of the mixer by a connecting pipe (15); (e) a second pump (13) provided on the connecting line (15) between the second liquid inlet of the mixer and the second liquid reservoir to supply the second liquid in a pulsating mode; (f) a concentration detector (17) provided in the vicinity of the outlet of the mixture (9) from the mixer or on a liquid discharge pipe (19) connected to the outlet of the mixture; and (g) a control unit (18) intended to control the first and second pumps (14,13) so that the pulsating supplies of liquids delivered by the pumps are different in their pulsation period, this unit being intended to control the power supplies to adjust the concentration in response to signals from the detector (17).  2.- Apparatus according to claim 1, characterized in that the ratio linking the pulsation period of the introduction of the first liquid to the pulsation period of the introduction of the second liquid is between about 0.9 and at least about 1.1.  3.- Method for mixing liquids at low flow rates, characterized in that a first liquid is penetrated into a cylindrical container through an inlet located in a lower part of its side wall with a pulsating flow and tangentially to this wall lateral, the container having an upper closure element; a second liquid is made to enter the container, vertically from bottom to top, through another inlet located in the center of its bottom, simultaneously with the introduction of the first liquid, in a pulsating mode whose pulsation period differs from that of the first liquid, and the mixture formed of the first liquid and the second liquid is discharged through an outlet located in the center of the upper closure element.  4.- Method according to claim 3, characterized in that the ratio linking the pulsation period of the introduction of the first liquid to the pulsation period of the introduction of the second liquid can reach about 0.9 or at least about 1 , 1.  5.- Apparatus according to any one of claims 1 and 2, characterized in that it is used to deliver the mixture at a flow rate of up to about 200 ml / min.  6.- Apparatus according to claim 5, characterized in that the mixing ratio between the second liquid and the first liquid can reach about 0.1.  7.- Apparatus according to claim 6, characterized in that the first liquid is sterilized strip and the second liquid is a replacement fluid for artificial kidneys.  8.- Method according to any one of claims 3 and 4, characterized in that it is used to deliver the mixture at a flow rate of up to about 200 ml / min.  9.- Method according to claim 8, characterized in that the mixing ratio between the second liquid and the first liquid can reach about 0.1.  10.- Method according to claim 9, characterized in that the first liquid is sterilized water and that the second liquid is a replacement fluid for artificial kidneys.