Patent Publication Number: US-6666035-B1

Title: Method and system for cooling and effecting a change in state of a liquid mixture

Description:
TECHNICAL FIELD 
     The present invention relates to a method of cooling and effecting a change in state of a liquid mixture, in particular a liquid mixture for food, drugs, fertilizers, detergents, cosmetics, catalysts, enzymes or parasiticides. 
     BACKGROUND ART 
     Two types of systems are normally used for cooling and effecting a change in state of a liquid mixture. 
     In a first, the liquid mixture is placed and kept inside a vessel having a cooled inner surface, until the mixture is cooled to other than the liquid state. 
     In the second, the liquid mixture is fed along a cooling tunnel having a cooled inner surface and long enough to cool and effect a change in state of the liquid mixture. 
     Since the liquid mixture has a relatively small cooling surface and cools progressively inwards from the outermost layers, the above known systems have several drawbacks, foremost of which is the relatively long time taken to cool and effect a change in state of the liquid mixture. 
     A further drawback of the above known systems lies in output being proportional to the size of the cooling vessel and tunnel, so that, to achieve a relatively high output, the systems must be fairly large, and are therefore expensive to produce as well as to run in terms of energy consumption. 
     Apparatuses for the rapid freezing of liquids which partially overcome the aforementioned drawbacks are disclosed in EP-A-0659351 and U.S. Pat. No. 1,970,437. 
     EP-A-0659351 discloses an apparatus for the rapid freezing of liquids comprising an atomizer defined by at least one nozzle and able to atomize a liquid mixture in a freezing turret. The turret is provided with a plurality of nozzles, which supply to the interior of the turret cooling means able to effect a change in state of the liquid mixture. 
     U.S. Pat. No. 1,970,437 discloses an apparatus for the rapid freezing of liquids comprising an atomizer defined by a shower bath, a Segner wheel, a pulverizer, or a sprinkler and able to atomize a liquid in a freezing turret. The turret is provided with a plurality of pipes which supply to the interior of the turret cooled air able to effect a change in state of the liquid mixture. 
     However, due to the fact that in the apparatuses disclosed in EP-A-0659351 and in U.S. Pat. No. 1,970,437 the liquid mixture is atomized under pressure, such apparatuses have to be provided with very long freezing turrets, which are cumbersome and expensive. 
     DISCLOSURE OF INVENTION 
     It is an object of the present invention to provide a method of cooling and effecting a change in state of a liquid mixture, designed to eliminate the aforementioned drawbacks. 
     According to the present invention, there is provided a method of cooling and effecting a change in state of a liquid mixture as recited in claim 1. 
     The present invention also relates to a system for cooling and effecting a change in state of a liquid mixture. 
     According to the present invention, there is provided a system for cooling and effecting a change in state of a liquid mixture as recited in claim 14. 
    
    
     A BRIEF DESCRIPTION OF THE DRAWINGS 
     A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a partly sectioned side view of a preferred embodiment of the system according to the present invention; 
     FIG. 2 shows an axial section, with parts enlarged for clarity, of a detail in FIG. 1; 
     FIG. 3 shows an exploded view in perspective of a detail in FIG. 2; 
     FIG. 4 shows a partly sectioned side view of a further embodiment of the system according to the present invention. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a system for cooling and effecting a change in state of a liquid mixture  2  for food, drugs, fertilizers, detergents, cosmetics, catalysts, enzymes or parasiticides. 
     System  1  comprises a cylindrical, substantially cup-shaped vessel  3  having a substantially vertical longitudinal axis  4  and defined at the top by a cover  5 , which is perpendicular to axis  4  and defines, together with vessel  3 , a cooling chamber  6 . 
     System  1  also comprises a known ultrasonic atomizing device  7  (FIGS.  2  and  3 ), which is fitted to cover  5 , extends through cover  5  to face the inside of chamber  6 , and in turn comprises a cylindrical member  8  vibrating, in known manner not shown, at a vibration frequency within the ultrasonic frequency spectrum and preferably ranging between 15 kHz and 150 kHz. Member  8  is substantially coaxial with axis  4 , and comprises a wide top portion  9 , a narrow bottom portion  10 , and an intermediate portion  11  connecting portions  9  and  10 . 
     Device  7  also comprises a tubular header  12  extending substantially along portions  10  and  11 . Header  12  comprises a tubular body  13  mounted to slide axially along member  8  and fitted at one end to portion  9  by a number of screws  14  equally spaced about and extending crosswise with respect to axis  4 . Header  12  also comprises a tubular body  15  coaxial with axis  4  and in turn comprising a wide top portion  16  extending about and screwed to body  13 , and a narrow bottom portion  17  projecting from body  13  and surrounding portion  10 . In this connection, it should be pointed out that, in use, portion  16  is positioned contacting a ring nut  18  screwed onto body  13  to selectively control the axial position of body  15  along body  13 . 
     Device  7  also comprises an atomizing circuit  19  in turn comprising two annular chambers  20  and  21  arranged in series along axis  4 . Chamber  20  is defined by bodies  13  and  15  and portion  10 , is defined at the top by a sealing ring  22  extending about portion  10 , and opens outwards through a hole  23  formed radially through body  15  to communicate with a conduit  24  (FIG. 1) for supplying liquid mixture  2 ; while chamber  21  is defined between portions  10  and  17 , and extends along portion  10  so as to communicate with cooling chamber  6 . 
     System  1  also comprises a cooling device  25  housed inside chamber  6  and in turn comprising two tubular rings  26  coaxial with axis  4 . Each ring  26  is connected to a known liquid nitrogen supply device (not shown), and comprises a number of known nozzles  27 , each of which has a respective longitudinal axis  28 , is adjustable about respective axis  28  and about a further two axes (not shown) perpendicular to each other and to axis  28 , and provides for atomizing and vaporizing the liquid nitrogen to produce a cooling current of substantially gaseous nitrogen. 
     Each nozzle  27  has a circular or rectangular outlet section, so that, by combining the shape of the outlet section of each nozzle  27  with the orientation of the nozzle with respect to axis  4 , it is possible to select laminar or turbulent flow of the current of gaseous nitrogen produced by device  25 . 
     Operation of system  1  will now be described with reference to FIG. 1, and as of when liquid mixture  2  is fed, by force of gravity and at substantially atmospheric pressure, along conduit  24  to atomizing device  7 , in particular to circuit  19 . Since all points of portion  10  vibrate, at circuit  19 , at constant frequency and amplitude, and since the respective radial dimensions of chambers  20  and  21  are constant along axis  4 , liquid mixture  2  is so atomized as to produce an atomized liquid mixture  29  comprising perfectly spherical drops of respective substantially uniform compositions. 
     It should also be pointed out that the diameter of each drop assumes a given value within a range of values controllable selectively by adjusting the vibration frequency and/or amplitude of member  8  and the radial dimension of chamber  21 . 
     At the output of chamber  21 , the atomized liquid mixture  29  flows by force of gravity along a path P parallel to axis  4  and through rings  26  of cooling device  25 . At device  25 , the atomized liquid mixture  29  comes into contact with said cooling current, which is emitted by nozzles  27  at a lower temperature than atomized liquid mixture  29 , so as to cool and effect a change in state of atomized liquid mixture  29  and obtain a cooled mixture  30 . 
     Finally, the cooled mixture  30  flows by force of gravity along axis  4 , and is collected in a catch basin  30   a  at the bottom of chamber  6 . 
     In connection with the above, it should be pointed out that: 
     the physical state of the atomized liquid mixture  29  at the output of device  25  may be selectively controlled by adjusting the liquid nitrogen supply and/or the temperature of cooling chamber  6  (in the example shown in FIG. 1, the cooled mixture  30  is in the form of a paste); and 
     the cooling current may also be obtained using cooled air, cooled or liquefied inert gases, or carbon dioxide. 
     The FIG. 4 variation shows a system  31  comprising an atomizing and freezing unit  32  and a freeze drying unit  33 . 
     Atomizing and freezing unit  32  differs from system  1  by chamber  6  comprising a substantially truncated-cone-shaped bottom end  34 , and a bottom outlet channel  35  coaxial with axis  4  and having a preferably rectangular or square cross section. 
     Unit  32  also comprises a device  36  for opening and closing channel  35 , and in turn comprising two oscillating walls  37 , which extend perpendicular to the FIG. 4 plane, are mounted inside channel  35 , and are oscillated—by a known actuating device (not shown), with respect to vessel  3 , and about respective parallel axes  38  perpendicular to the FIG. 4 plane—between an open position (FIG. 4) and a closed position (not shown) respectively opening and closing channel  35 . 
     Freeze drying unit  33  comprises a known freeze drying tunnel  39  extending beneath unit  32  in a direction  40  crosswise to axis  4 , and communicating with chamber  6  by means of channel  35 ; and a supply device  41  extending inside tunnel  39  and parallel to direction  40 . 
     Device  41  comprises two pulleys  42  (only one shown in FIG.  4 ), one of which is powered, and which are fitted to a fixed frame (not shown) to rotate continuously about respective parallel axes  43  parallel to axes  38 ; and a conveyor belt  44  looped about pulleys  42  and facing channel  35 . It should be pointed out that the freeze drying step in unit  33  may be performed using, in known manner not shown, the same freezing current already used in device  25 , and which, at the output of unit  32 , is substantially defined exclusively by dry gaseous nitrogen, i.e. having no humidity. 
     Operation of system  31  will now be described assuming device  25  is set to obtain a frozen mixture  45  at the output of device  25  itself, walls  37  of device  36  are set to the open position opening channel  35 , and belt  44  is moving beneath channel  35 . 
     At the output of device  25 , the frozen mixture  45  flows by force of gravity along axis  4  and channel  35  onto belt  44 , and is fed continuously along freeze drying tunnel  39 , inside which the frozen mixture  45  is freeze dried at atmospheric pressure in known manner. 
     In a variation not shown, at the output of channel  35 , the frozen mixture  45  is collected in a tank and vacuum freeze dried in known manner. 
     Systems  1  and  31  afford several advantages, foremost of which are the following: 
     ultrasonic atomizing device  7  provides for obtaining an atomized liquid mixture  29  comprising a number of drops, in each of which the components of liquid mixture  2  are distributed homogeneously, and each of which is perfectly spherical and relatively small in diameter; 
     the drops defining atomized liquid mixture  29  together form a relatively extensive exchange surface, thus ensuring relatively effective heat exchange between atomized liquid mixture  29  and said gaseous nitrogen current; and 
     the change in state of atomized liquid mixture  29  is effected immediately downstream from the output of atomizing device  7 , i.e. when the atomized liquid mixture  29  is perfectly homogenous, thus preventing any further separation of the components of atomized liquid mixture  29 . 
     System  31  also has the further advantage of the shape and diameter of the drops forming frozen mixture  45  also ensuring relatively effective heat exchange at the freeze drying step. 
     Moreover, when freeze drying at atmospheric pressure, the drops forming frozen mixture  45  can be freeze dried completely and homogeneously without being excessively overheated, and without altering and/or damaging the composition of the freeze dried drops; whereas, when vacuum freeze drying, the duration, and hence cost, of the freeze drying step may be relatively limited. 
     System  31  also has the further advantage of atomizing liquid mixture  2 , freezing atomized liquid mixture  29 , and freeze drying frozen mixture  45  substantially continuously, thus greatly reducing the duration of the overall freeze drying cycle on system  31 . 
     With reference to FIG. 4, it should be pointed out that system  31  may also comprise a unit  46  for eliminating bacteria in liquid mixture  2  and located upstream from atomizing and freezing unit  32 . In a variation not shown, system  1  may also be provided with a unit  46 . 
     Unit  46  (of known type) comprises a chamber  47  having a longitudinal axis  48  substantially parallel to axis  4 , and two ultrasonic transducers  49  housed inside chamber  47 , on opposite sides of axis  48 ; a supply conduit  50  for feeding liquid mixture  2  into chamber  47  at a pressure greater than atmospheric pressure; and a holding tank  51  located between chamber  47  and unit  32 , connected to atomizing device  7  by conduit  24 , and having a pressure regulator  52 . 
     In actual use, liquid mixture  2  is fed successively: 
     into chamber  47 , where the two transducers  49  provide for eliminating bacteria in known manner; 
     into tank  51 , where pressure regulator  52  reduces the pressure of liquid mixture  2  to atmospheric pressure; and finally 
     into unit  32 , where the freeze drying cycle is performed as described for system  31 . 
     Finally, it should be pointed out that the foregoing description also applies in the event a solid-state component is dispersed in liquid mixture  2 , which component is microencapsulated inside the atomized drops in the course of the atomizing step performed in atomizing device  7 .