US 3099520 A
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y 1963 B. H. HALLSTROM 3,099,520
METHOD AND APPARATUS FOR PREVENTING INFECTION OF HEAT EXCHANGE CHAMBERS Filed Jan. 30, 1961 2 Sheets-Sheet 1 INVEN TOR. Benyt' HMO my H01! 5 frm July 30, 1963 B. H. HALLSTRUM 3,099,520
METHOD AND APPARATUS FOR PREVENTING INFECTION OF HEAT EXCHANGE CHAMBERS Filed Jan. 50, 1961 2 Sheets-Sheet 2 Fig. 2
IN VEN TOR. 5 9/791 H/ld/ng Ha/lS/r'm ited States The present invention relates to heat exchangers and more particularly to a method of preventing infection of the heat exchange chambers of heat exchangers, and to an improved heat exchange apparatus for this purpose.
In a heat exchanger for heating or cooling liquids, the heat exchange chambers are usually sealed from the outer surroundings by means of packings of rubber, or the like. Occasionally, the heat exchanger must be disassembled for cleaning and sterilization, especially of its heat exchange chambers.
When cooling sterile milk, for example, in a heat exchanger, it has been found that the milk is often creinfected in the apparatus, even though prior to the cooling the apparatus was sterilized by flushing its heat exchange chambers with a strong sterilizing agent (chloramine solution or steam). It has been found that this re-infection may occur due to flow of the milk through at least part of the heat exchanger under subatmospheric pressure, so that outside air or bacteria-containing milk leaked from another part of the exchanger is sucked into a heat ex change chamber in which the sterilized milk is cooled. In this way, previously sterilized milk is infected again.
According to the present invention, this difficulty is avoided by evacuating and maintaining under vacuum an outer chamber surrounding those packings which seal or delimit the heat exchange chambers. The vacuum maintained in this outer chamber should be high enough so that no leaking of air or liquid into the heat exchange chambers is possible. Leakage, if any, will instead take place from the latter chambers into the outer chamber surrounding the packings, thereby preventing bacteria or the like from entering the heat exchange chambers.
As a further precautionary measure to prevent the undesired reinfection, a sterilization agent (chloramine solution or steam) may be passed through the outer chamber surrounding the packings before this chamber is placed under vacuum.
The heat exchanger of the present invention is adapted to carry out the new method and is characterized by means forming an outer chamber which surrounds the packings partly defining the heat exchange chambers, and a vacuum pump connected to this outer chamber.
In applying the invention to plate heat exchangers, it is not necessary to provide an outer chamber surrounding the entire heat exchanger. In such a case it may be sufficient to arrange, outside the ordinary packing cords of each plate, an additional packing cord which, when the plates are pressed together in the usual pack, forms with the ordinary packing cords the outer chamber to be kept under vacuum.
The present invention is described more in detail below, reference being made to the accompanying drawings, in which:
Patented July 30, 1963 the purpose of illustration that the fluid to be cooled is milk.
In FIG. 1, reference numeral 1 designates a container provided with a cover 2 and forming a closed chamber. Within the container 1-2 is a pack of heat exchange plates -3 which is held compressed between two heavy plates 4 and 5 by bolts 6 and 7. The container is adapted to be completely filled with sterilizing liquid so that the heat exchanger 35 is completely immersed in this liquid, which is drawn oif after the interior of the heat exchanger has been sterilized and before the interior of the container is placed under vacuum. Pipes 8 and 9 are permanently connected to the cover and to the bottom of the container, respectively, and are provided with valves 8a and 9a, respectively. Sterilizing liquid is supplied through the pipe 8 to a level which completely covers the heat exchanger 37, and, when required, the same liquid is drawn off through pipe 9. One of the pipes 8-9 is connected to a vacuum pump (not shown) so that by manipulation of valves including valves 8a and 9a, the container 1 can be filled with sterilizing liquid, emptied of the liquid, and placed under vacuum. Pipes 10, 11, 12 and 13 lead to the heat exchanger 3-7, the pipes 10 and 12 extending through cover 2 and the pipes 11 and 13 extending through the container bottom. Two of these pipes, such as pipes 10 and 13, lead the milk to and from the heat exchanger, while the other two pipes lead the cooling medium to and from the exchanger. The pipes 10 13 are sealed externally against leakage by means of packings .14, 15, 16 and 17, respectively, secured to the container 1-2 around these pipes. When required, these pipes can be disconnected from the heat exchanger plates 4-5 and withdrawn from the container through the respective packings 1-447. While the heat exchange plates are in horizontal position in FIG. 1, they may be arranged vertically whereby the removal of the air bubbles from the heat exchange chambers is facilitated. This is desirable because air cushions in these chambers have a disturbing effect on the sterilization.
When the apparatus of FIG. 1 is to be sterilized, the nuts 18 and 19 are loosened on bolts 6-7 (as by remov ing cover 2), so that the heat exchange plates 3 are forced apart from each other and from the usual packing cords by the expansion of spacers (not shown) of rubber or other elastic and deformable material located at the corner portions of the plates. In this way, the sterilizing liquid can reach all the necessary areas of the heat exchanger parts. With the container closed by cover 2, this liquid is introduced through pipe 8 so as to till the container and completely immerse the heat exchanger 3-7. Upon completion of the sterilization, the nuts 18-19 are tightened to deform the plate spacers and compress the plates 3 together in a pack, the sterilizing liquid is drained from the heat exchange chambers through the valved pipes 11 and 13, and the heat exchange chambers are flushed clean by means of sterile water fed through pipes 10 and -12. Before the sterilized milk is passed through the heat exchanger for cooling, valve 9a is opened to drain the sterilizing liquid from container -1, and the latter is Q evacuated as by closing valve 9a and connecting the con- FIG. 1 is a vertical sectional view of one form of the tainer through pipe 8 to the vacuum pump (not shown), which maintains the interior of the container under vacuum during cooling of the milk.
In FIG. 2, I have shown a modified heat exchange plate 20 having the usual holes 21 and 22 for receiving the plate-carrying bars of the heat exchanger frame, these bars being shown at 37-38 in FIG. 3. A packing cord 23 delimits a chamber 24 into which hot milk is assumed to enter through a hole 25 and leave through a hole 26. Cooling liquid is assumed to be led through a hole 27 to a heat exchange chamber on the back of the plate and be led off from this chamber through a hole 28. On the front side of the plate the holes 27 and 28 are sealed against the surroundings by means of packing cords 29 and 30. An additional packing cord 31 delimits, together with the cords 23, 29 and 30, a chamber 32 which is filled with sterilizing agent through a hole 33. Air present in the chamber 32 evacuates through a hole 34 when sterilizing agent is supplied. After sterilization, the sterilizing agent is drawn off from chamber 32, and during cooling of the milk the chamber 32 is maintained under vacuum. The cord 31, which is of elastic deformable material, is normally thicker than the cords 23, 29 and 3% so that when the pressure keeping the plates pressed against each other is reduced, slots are formed between the latter cords and the plate surfaces. When it is desired to sterilize the heat exchange chambers, it is necessary only to reduce the compression of the plates enough so that these slots are formed but the chambers 32, by means of the cords 31, are sealed from the outside. Sterilizing agent can then flow into the heat exchange chambers and sterilize them.
The heat exchanger shown in FIG. 3 includes a series of plates 20 (FIG. 2) arranged vertically in a pack. A frame 35 and a supporting column 36 support the horizontal carrying bars 37 and 38 for the plates 20, which are held compressed between the frame 35 and a pressure plate 39 by means of a tightening screw 41 operable by a wheel 40. For the sake of simplicity, the inlets and outlets for milk and cooling liquid are not shown. From a container 42, sterilizing liquid flows downward through a pipe 43 into the plate chambers 32 (FIG. 2), more exactly through the holes 33. The air discharging through the holes 34 passes through a pipe 44 into the container 42 and rises therein to the liquid level. After the sterilizing, valve means comprising a valve 44a in pipe 4-4 and a three-way cock valve 43a in pipe 43 are actuated to disconnect chambers 32 from container 42 and connect these chambers through pipe 45 to a vacuum pump 46, which is operated to draw off the sterilizing liquid .from chambers 32 and maintain these chambers under vacuum during cooling of the milk int he heat exchanger.
, The heat exchanger may be an integral part of a regenerative heat exchanger wherein hot sterilized milk is cooled by means of cold 'unsterilized milk.
This application is a continuation-in-part of my copending application Serial No. 30,577, filed May 20, 1960, filed jointly with Nils T. Falkenblad.
1. The method of preventing infection of a heat exchanger of the type having a plurality of packings compressed respectively between opposed pairs of a series of heat exchange plates and defining therewith adjacent heat exchange chambers for passage of a heat-emitting medium and a heat-absorbing medium, respectively, said method comprising the steps of evacuating an outer chamber surrounding each packing and heat exchange chamber,v and maintaining said outer chamber under vacuum during passage of said media through the respective heat exchange chambers.
2. The method of claim 1, comprising also the step of passing a sterilizing agent through said outer chamber before evacuating the same.
3. A heat exchanger comprising a series of heat exchange plates, packings compressed respectively between opposed pairs of said series of plates and defining therewith adjacent heat exchange chambers for passage of a heat-emitting medium and a heat-asborbing medium, respeotively, means forming an outer chamber surrounding said packings, said outer chamber being separated by the packings from the heat exchange chambers for the respective heat-emitting and heat-absorbing media, and a vacuum pump connected to said outer chamber for evacuating the same.
4. A heat exchanger according to claim 3, comprising also a source of sterilizing liquid, and valve means for alternately connecting said source and vacuum pump to the outer chamber.
5. A heat exchanger according to claim 3, in which said means forming the outer chamber include packing cords compressed between the plates around the respective packings and forming with the plates enclosed spaces surrounding the respective packings, the plates being ported to interconnect said closed spaces with each other.
References Cited in the file of this patent UNITED STATES PATENTS 2,221,937 Astle Nov. 19, 1940 2,341,549 Helmick Feb. 15, 1944 2,362,117 David Nov. 7, 1944 2,371,217 Booth Mar. 13, 1945 FOREIGN PATENTS 2,218 Great Britain Feb. 11, 1890