Prevention of microbiological proliferation in heat exchanger

Abstract

To prevent or reduce microbiological proliferation in a heat exchanger, in particular, microbiological proliferation on a partition of the heat exchanger.SOLUTION: A heat exchanger assembly (10) including a heat exchanger (12) in which one or multiple partitions (26) which are configured to separate a first fluid (22) from a second fluid (24) and electrically connected is proposed. The assembly (10) further includes: a first electric connector (14) and a second electric connector (16) which are operably connected to the partitions (26) of the heat exchanger (12); and a power source (18) operably connected to the first electric connector (14) and the second electric connector (16). The power source (18) is configured to supply electric current to the one or multiple partitions (26) of the heat exchanger (12) through the first electric connector (14) and the second electric connector (16).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The proposed technology generally relates to the field of heat exchangers. The proposed technology specifically relates to plate type heat exchangers and heat exchangers in marine applications. The technology also relates to the prevention of microbial growth on the inner surfaces of heat exchangers. [Background technology]

[0002] A heat exchanger is a system used to transfer heat between two or more fluids. Typically the fluids are separated by a solid partition to prevent them from mixing. Heat exchangers are used in both cooling and heating processes.

[0003] Microbiological growth in heat exchangers is a known problem. Such growth can adversely affect the performance of the heat exchanger, for example with respect to flow rate and thermal conductivity. Microbiological growth is particularly problematic in marine applications where the heat exchanger is supplied with seawater. Seawater can be rich in nutrients, and the temperature of the supplied seawater is often within a range suitable for microbiological growth.

[0004] Liquid foods such as beverages and liquid dairy products also have high nutritional content. Heat exchangers used in the processing of such products typically have high microbiological growth rates and require frequent cleaning to prevent deterioration of the product quality. Typically, production must be interrupted for cleaning, and chemicals are commonly used for cleaning, which contributes to reduced efficiency and increased production costs.

[0005] Microbiological growth is particularly problematic in plate-type heat exchangers which cannot be disassembled for manual cleaning. Summary of the Invention [Problem to be solved by the invention]

[0006] The proposed technology aims to prevent or reduce microbial growth in heat exchangers, in particular on the partitions of heat exchangers. It is also an object to reduce microbial growth in heat exchangers, in particular plate-type heat exchangers, used in the processing of liquid foods. [Means for solving the problem]

[0007] In a first aspect of the proposed technology, a heat exchanger assembly is provided. The assembly comprises a heat exchanger, which is configured to separate or keep a first fluid and a second fluid separate or distinct, and forms or comprises one or more partitions or walls through which heat can be transferred or conducted between the first and second fluids. The assembly further comprises a first electrical connector (in other words, an electrical connection device) and a second electrical connector operably connected to the one or more partitions or walls of the heat exchanger. Furthermore, the assembly comprises a power source operably connected to the first electrical connector and the second electrical connector and configured to supply an electric current and / or an electric potential to the one or more partitions or walls of the heat exchanger via the first electrical connector and the second electrical connector.

[0008] Here, and throughout this specification, a partition is understood to include a wall. It is understood that a first aspect of the proposed technology is directed to a heat exchanger assembly for reducing, inhibiting or preventing microbial growth in a heat exchanger forming part of the assembly. Operatively connected is understood here to specify only that there is an electrical connection capable of supplying an electric current.

[0009] The first and second electrical connectors being operably connected to one or more partitions includes the connectors being operably connected to each of the one or more partitions. The first and second electrical connectors being operably connected to one or more partitions is also understood to include the electrical connectors being directly connected to the partitions, and the electrical connector being directly connected to one of the partitions and the partition being electrically connected to the other partition, for example by being pressed together, by welding, or by brazing.

[0010] The first and second fluids may be liquids. The assembly allows for the prevention of microbial growth on one or more partitions. The power source may be configured to provide a current or potential to reduce, inhibit, or prevent microbial growth in the heat exchanger or on one or more partitions of the heat exchanger. Furthermore, the assembly allows for the reduction of biofilm development or growth on one or more partitions. Microorganisms are understood herein to include unicellular organisms, which may exist in the form of a single cell or in colonies of cells, and microscopic multicellular organisms.

[0011] Growth conditions may depend on microbial nutrients, temperature, and oxygen levels of the fluid. For example, seawater at about 40° C. provides better growth conditions than chlorinated tap water at about 10° C. It is understood that the partition or partitions are electrically conductive. The partition or partitions may be formed of a metal or a combination of metals, such as an alloy. It is also understood that one of the electrical connectors, such as the second electrical connector, may be grounded or earthed, for example by the hull of the vessel. If the power source provides alternating current, this means that the neutral and earth wires are shared and that the phase is provided by the other electrical connector.

[0012] It will be appreciated that the heat exchanger may be a shell-and-tube heat exchanger, a plate heat exchanger, a plate-and-shell heat exchanger, a plate-fin heat exchanger, or a pillow plate heat exchanger.

[0013] The first and second electrical connectors may be spaced apart at or on the heat exchanger. The one or more partitions may extend from a first end of the heat exchanger to an opposite second end of the heat exchanger, and the first and second electrical connectors may connect to the one or more partitions at each of the first and second ends of the heat exchanger.

[0014] For example, the heat exchanger may be a shell-and-tube heat exchanger comprising a tube bundle including straight tubes forming one or more partitions and a shell surrounding the tube bundle, and the first and second electrical connectors may be connected to each of the tubes at opposite ends of the tube bundle.

[0015] The one or more partitions may further contain or enclose the first and second fluids inside the heat exchanger, meaning that both the first and second fluids are surrounded by the one or more partitions as they pass through the heat exchanger, and that the flow of the first and second fluids is restricted or inhibited by the one or more partitions as they pass through the heat exchanger. The one or more partitions may form multiple partitions.

[0016] The heat exchanger may further comprise a shell configured to contain the first fluid and / or the second fluid, for example the shell may be the two outermost plates of a plate heat exchanger or the shell of a shell-and-tube heat exchanger.

[0017] The one or more partitions may form one or more first channels through which the first fluid may flow. For example, the heat exchanger may be a shell-and-tube heat exchanger comprising a tube bundle including tubes that make up the partitions that form a plurality of the first channels.

[0018] Similarly, the one or more partitions may form one or more second channels through which the second fluid can flow. For example, the heat exchanger may be a plate type heat exchanger comprising a plurality of plates forming one or more partitions and one or more first channels and one or more second channels.

[0019] In a second aspect of the proposed technology, a method is provided for mitigating, inhibiting or preventing microbiological growth in a heat exchanger of a heat exchanger assembly according to the first aspect of the proposed technology. The method includes providing an electric current and / or an electric potential to one or more partitions of the heat exchanger by a power source. The method may further include providing a flow of a first fluid and a second fluid in or through the heat exchanger. The electric current and / or electric potential may be configured to mitigate, inhibit or prevent microbial growth in the heat exchanger or on one or more partitions of the heat exchanger.

[0020] In a third aspect of the proposed technology, a system for preventing microbiological growth in a heat exchanger is provided that separates a first fluid from a second fluid and that forms one or more partitions through which heat can be transferred between the first and second fluids. The system comprises a first electrical connector and a second electrical connector adapted to operably connect to the one or more partitions of the heat exchanger. Further, the assembly comprises a power source adapted to operably connect to the first electrical connector and the second electrical connector and configured to supply an electric current and / or an electric potential to the one or more partitions of the heat exchanger via the first electrical connector and the second electrical connector.

[0021] With regard to the first aspect of the proposed technology, the power source may be configured to supply a current or potential to reduce, inhibit or prevent microbial growth in the heat exchanger or on one or more partitions of the heat exchanger.

[0022] In a fourth aspect of the proposed technology, a method is provided for reducing, inhibiting, or preventing microbiological growth in a heat exchanger that separates a first fluid and a second fluid and that forms one or more partitions through which heat can be transferred between the first and second fluids. The method includes providing a system according to the third aspect of the proposed technology, operably connecting a first electrical connector and a second electrical connector to one or more partitions of the heat exchanger, and providing an electric current and / or an electric potential to the one or more partitions of the heat exchanger by a power source. The method may further include providing a flow of the first fluid and a flow of the second fluid within the heat exchanger. The electric current and / or electric potential may be configured to reduce, inhibit, or prevent microbial growth in the heat exchanger or on one or more partitions of the heat exchanger.

[0023] In a fifth aspect of the proposed technology, a heat sterilization apparatus for the thermal treatment of a liquid food product or a liquid component of a food product is provided, the heat sterilization apparatus comprising a heat exchanger assembly according to the first aspect of the proposed technology for heating or cooling the liquid food product. The first fluid may be the liquid food product. The second fluid may be a heating fluid such as hot water or steam, or a cooling fluid such as cold water, a brine solution, or an alcohol solution such as glycol. The liquid component of the food product shall be considered here as the liquid food product.

[0024] If the above-mentioned heat exchanger assembly is for heating, the heat sterilization apparatus may further comprise an additional heat exchanger assembly according to the first aspect of the proposed technology for cooling the liquid food. The first fluid may be the liquid food. The second fluid may be a cooling liquid such as cold water, a brine solution, or an alcohol solution such as glycol. Alternatively, two heat exchanger assemblies may be operatively connected to provide regenerative heating and cooling.

[0025] Further optional features of the proposed technique are described below. The heat exchanger may have two or more partitions, or a plurality of partitions. Adjacent partitions or all partitions may be electrically connected or coupled to each other, or the partitions may be configured to be at or share the same potential, or the heat exchanger is configured with partitions at or share the same potential. This means that the partitions are not electrically insulated from each other, for example by a non-conductive spacer separating them. This also means that the voltage difference between the partitions is small or insignificant. Electrically connected partitions may be obtained by partitions that contact each other, for example by pressing the partitions together. Electrically connected partitions may also be obtained by partitions that are joined, for example by soldering, welding or brazing, or by partitions that are connected by conductive connectors or supports. This means that all partitions are practically at the same potential. This also means that the potential in the heat exchanger is minimized and that no significant electrodes are created that may induce chemical reactions that have a negative effect on the first fluid and / or the second fluid. For example, if the first and second fluids may include water, an electrical potential within the heat exchanger may produce hydrogen and oxygen by electrolysis in the fluids.

[0026] Except for the first and second electrical connectors that operably connect to one or more partitions of the heat exchanger, the heat exchanger may be electrically insulated from the environment. To achieve this, the heat exchanger assembly may include an electrically insulating support that supports the heat exchanger. For example, the electrically insulating support may be formed of an electrically non-conductive thermoplastic material. This contributes to electrically insulating the partitions of the heat exchanger from the environment, which further contributes to improved prevention of microbiological growth.

[0027] Furthermore, the heat exchanger assembly may include a plurality of conduits connected to the heat exchanger and configured to supply the first and second fluids to the heat exchanger. The plurality of conduits may be further configured to drain the first and second fluids from the heat exchanger. The plurality of conduits may be electrically insulated. For example, the conduits may be formed of an electrically non-conductive thermoplastic material. This contributes to electrically insulating the heat exchanger partition from the surroundings.

[0028] The heat exchanger assembly may further include a plurality of fittings operatively connecting the plurality of conduits of the heat exchanger, the fittings being electrically insulating, for example, the fittings may be formed of an electrically non-conductive thermoplastic material, which contributes to electrically insulating the heat exchanger partition from the surroundings.

[0029] The heat exchanger may be configured to handle seawater. The first fluid may be seawater. This means that the first fluid contains salts and also typically contains a significant amount of nutrients for microorganisms. Additionally or alternatively, the heat exchanger may be configured to handle a liquid food, or a liquid component of a food. For example, the first fluid may be a beverage, or a liquid component of a beverage. The heat exchanger may be configured to handle a beverage or a component thereof. The first fluid may be a liquid dairy product, or a liquid component of a dairy product. For example, the first fluid may be colostrum from a dairy cow. The heat exchanger may be configured to handle a liquid dairy product or a liquid dairy component.

[0030] The heat exchanger may be a plate type heat exchanger with a plurality of plates or parallel plates forming one or more partitions. For example, the heat exchanger may be composed of 20 plates, of which 2 are outer plates and 18 are inner plates forming 18 partitions separating the first and second fluids. It is understood that the plurality of plates are of an electrically conductive material. The plates may be made of a metal or a combination of metals, for example an alloy. For example, the plates may be made of stainless steel, titanium, or a titanium alloy.

[0031] The plates may be electrically connected or coupled to each other, or the plates may be configured to be at the same potential. For example, this may be achieved by the plates being structurally connected or physically connected or in contact, for example by being pressed together with metal clamps or screws, or by adjacent plates being bonded to each other by welding or brazing. This means that the plates are not electrically insulated from each other, for example by a non-conductive spacer separating the plates. This also means that the plates cannot be at different potentials, such as one plate being at a negative potential and an adjacent plate being at a positive potential.

[0032] The first electrical connector and the second electrical connector may be structurally connected to different plates of the plurality of plates. This has the effect that the power source can generate an electric potential that generally has a component transverse to the plate. This is expected to contribute to improved performance. Structurally connected to the plate is understood here to include an electrical connector that is directly connected to the plate or forms a physical connection to the plate. Alternatively, the first electrical connector and the second electrical connector may be structurally connected to the same plate of the plurality of plates.

[0033] It will be appreciated that the electrical connector may be structurally connected to two, or more than two plates simultaneously. Conditions for microbial growth may be greater or more favorable in the first fluid than in the second fluid, and the first electrical connector may be structurally connected to adjacent or juxtaposed pairs of plates of the plurality of plates. The adjacent pair of plates may encapsulate or provide a channel for the first fluid. The adjacent pair of plates may be structurally and / or electrically connected to each other or configured to be at the same electrical potential. Similarly, the second electrical connector may be structurally connected to the adjacent pair of plates. Structural connection is understood to include physical contact of two elements, for example by being pressed together or soldered. This contributes to an optimized propagation of electrical current through the plate-type heat exchanger to prevent microbiological growth.

[0034] The first and second electrical connectors may be structurally connected to the heat exchanger or to a number of plates on both sides of the heat exchanger. This has the effect that the power source can generate an electric potential that is parallel to the plates and has a component across the plates. Structurally connected to the heat exchanger is understood here to include that the electrical connector is directly connected to the heat exchanger or forms a physical connection to the heat exchanger. This is expected to contribute to an optimized propagation of electric current to prevent microbiological growth.

[0035] The plates of the heat exchanger may have the same or similar outer shapes, and the plates may be oriented in the same direction to form a stack of plates. The or each plate of the plurality of parallel plates may have four side sections and four corner sections, each corner section being disposed between two side sections, a first electrical connector structurally connected to the first corner section, a second electrical connector structurally connected to the second corner section, and the second corner section being diagonal to the first corner section. By the second corner section being diagonal to the first corner section, it is meant that said corner section is connected by a side section, a corner section, and a further side section on either side of the first corner section.

[0036] Stated another way, the or each plate of the multiple parallel plates may have an overall rectangular shape including four corners, and the first electrical connector and the second electrical connector may be structurally connected to different corners that are diagonally disposed with respect to each other or with respect to the plate.

[0037] The heat exchanger may be a shell-and-tube heat exchanger comprising a tube bundle forming one or more partitions and a shell surrounding the tube bundle. The heat exchanger may be a straight tube heat exchanger. The first electrical connector may be connected to each of the tubes, for example at a first end of the tube bundle, by a first tube support supporting the tube bundle. Further, the second electrical connector may be connected to each of the tubes, for example at a second end of the tube bundle, by a second tube support supporting the tube bundle. Each of the tubes of the tube bundle may have an inlet at the first tube support and an outlet at the second tube support. The first tube support may be a first tube sheet or a first tube plate that connects to the shell and separates the first and second fluids. Similarly, the second tube support may be a second tube sheet or a second tube plate that connects to the shell and separates the first and second fluids.

[0038] The first tube support and the shell may form a first enclosed space configured to contain a first fluid. The heat exchanger may further comprise an inlet, e.g., formed by the shell, arranged to allow the first fluid to enter the first enclosed space from outside the shell. Similarly, the second tube support and the shell may form a second enclosed space configured to contain the first fluid. The heat exchanger may further comprise an outlet, e.g., formed by the shell, arranged to allow the first fluid to exit the first enclosed space to outside the shell. The first tube support and the second tube support may be electrically insulated from the shell.

[0039] The first tube support, the second tube support, and the shell may form a third enclosed space configured to contain a second fluid and through which the tubes extend, where the heat exchanger further comprises an inlet and an outlet arranged to allow the second fluid to enter and exit the third enclosed space and to allow the second fluid to pass outside the tubes within the third enclosed space. The tubes may extend from the first enclosed space through the third enclosed space to the second enclosed space and allow the flow of the first fluid from the first enclosed space to the second enclosed space without intermixing with the second fluid.

[0040] The inlet and outlet for the second fluid may be formed by the shell. The third enclosed space may have a cylindrical outer shape, which may have a circular or rectangular cross section. Alternatively, the heat exchanger may be a U-tube heat exchanger. A first electrical connector may be connected to each of the tubes, for example at a first end of the tube bundle, with a first tube support supporting the tube bundle. Additionally, a second electrical connector may be connected to each of the tubes at a second end of the tube bundle. Each of the tubes of the tube bundle may have an inlet and an outlet at the first tube support. The first tube support may be a first tube sheet or a first tube plate that connects to the shell and separates the first and second fluids.

[0041] The first tube support and the shell may form a first enclosed space configured to contain a first fluid. The heat exchanger may further comprise an inlet, e.g., formed by the shell, arranged to allow the first fluid to enter the first enclosed space from outside the shell. Similarly, the first tube support and the shell may form a second enclosed space configured to contain the first fluid. The heat exchanger may further comprise an outlet, e.g., formed by the shell, arranged to allow the first fluid to exit the first enclosed space to outside the shell. The first tube support may be electrically insulated from the shell.

[0042] The first tube support and the shell can form a third enclosed space configured to contain a second fluid and through which the tube extends, where the heat exchanger further comprises an inlet and an outlet arranged to allow the second fluid to enter and exit the third enclosed space and to allow the second fluid to pass through the outer surface of the tube within the third enclosed space. The inlet and outlet for the second fluid can be formed by the shell. The current can be an alternating current. The alternating current can have a square wave form, meaning that the peak voltage is approximately equal to the root mean square voltage. This type of current has been found to inhibit microbiological growth.

[0043] The alternating current may be less than 10 mA, less than 1 mA, between 0.1 mA and 1 mA, or between 0.3 mA and 0.7 mA. This current has been found to be sufficient to inhibit microbiological growth. The alternating current may have a frequency of less than 100 Hz, less than 10 Hz, or less than 1 Hz. The alternating current may be supplied at a peak voltage of less than 120 V, within the range of 40 V to 100 V, or within the range of 70 to 90 V. Additionally or alternatively, the alternating current may have a duty cycle of about 50%.

[0044] The first fluid and / or the second fluid may contain or include water, and the heat exchanger assembly may be configured to avoid or prevent electrolysis of water, or the heat exchanger assembly may be configured to avoid or prevent the heat exchanger from functioning as an electrolyzer during operation. For example, this may be accomplished by bringing adjacent and all partitions and any surrounding shells to the same electrical potential.

[0045] A more complete understanding of these and other features and advantages of the proposed technology will become apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 is a schematic diagram of an embodiment of a heat exchanger assembly including a plate-type heat exchanger. [Diagram 2] FIG. 2 is a schematic diagram of an embodiment of a heat exchanger assembly having a straight tube heat exchanger. [Diagram 3] FIG. 1 is a schematic diagram of an embodiment of a heat exchanger assembly including a U-tube heat exchanger. [Figure 4] FIG. 1 is a schematic diagram of a test apparatus. [Diagram 5] 1 is a graph showing the pressure drop (ΔP) across the heat exchanger for two different test runs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] One embodiment of a heat exchanger assembly 10 is shown diagrammatically in Figure 1. The heat exchanger assembly 10 is comprised of a heat exchanger 12, a first electrical connector 14, a second electrical connector 16, and a power supply 18. The heat exchanger 12 is a plate type heat exchanger having four parallel plates 20. The plates are rectangular and made of stainless steel. This means that each plate 20 has four side sections 28 and four corner sections 3 as shown in Figure 1.

[0048] The plates 20 are joined at the edges (not shown) and form three channels through which a first fluid 22 and a second fluid 24 flow as shown by dashed lines in FIG. 1. The first fluid 22 is seawater and the second fluid 24 is freshwater. The flow of the first fluid 22 and the second fluid 24 is generated or provided by a pump (not shown). The flow direction of the first fluid 22 and the second fluid 24 is indicated by arrows in FIG. 1 indicating parallel flow. In an alternative embodiment, the flow can be countercurrent obtained by reversing the flow of the first fluid 22 or the second fluid 24.

[0049] The two central plates 20 form two partitions 26 between which the first fluid 22 flows, thus separating it from the second fluid 24. Heat can be transferred between the first fluid 22 and the second fluid 24 through the two partitions 26. In this embodiment, the first fluid 22 has a higher temperature than the second fluid 24, and heat is transferred from the former to the latter.

[0050] The first electrical connector 14 and the second electrical connector 16 are electrical wires attached to the inner plates 20 by clamps (not shown). As shown in FIG. 1, the first electrical connector 14 is connected to the lower inner plate 20 and the second electrical connector is connected to the other upper inner plate 20. This means that the first electrical connector 14 and the second electrical connector 16 are structurally connected to different inner plates 20 and are also operatively connected to the separating partition 26. The first electrical connector 14 and the second electrical connector 16 are also attached to diagonally opposed corner sections 30 of different inner plates 20 as shown in FIG. 1. This means that the first electrical connector 14 and the second electrical connector 16 are spaced apart in the heat exchanger 12, that the first electrical connector 14 and the second electrical connector 16 are structurally connected to the heat exchanger 12 on opposite sides of the heat exchanger 12, and that the first electrical connector 14 and the second electrical connector 16 are structurally connected at different corners that are diagonally arranged relative to each other.

[0051] In an alternative embodiment, the first electrical connector 14 is connected to both inner plates 20 and the second connector 16 is also connected only to both inner plates 20 . The first electrical connector 14 and the second electrical connector 16 are connected to output terminals of a power source 18. In this manner, the power source 18 can provide current and potential to the isolation partition 26 via the first electrical connector 14 and the second electrical connector 16. In an alternative embodiment, the second electrical connector 16 is electrically grounded to earth.

[0052] There are rubber packings (not shown) between the plates 20 that prevent leakage of the first fluid 22 and the second fluid 24 from the heat exchanger 12. The plates 20 are pressed together and held in place by metal screw clamps (not shown) that contact all the plates 20. This means that the plates are electrically connected and also that the separating partitions 26 are electrically connected to each other.

[0053] The power source 18 supplies an alternating current in the form of a square wave to the first electrical connector 14 and the second electrical connector 16, and further to the one or more isolation partitions 26. The alternating current has an electric peak current between 0.3 mA and 0.7 mA, a frequency of less than 1 Hz, and a duty cycle of 50%. The alternating current is supplied at a peak voltage within the range of 70 to 90 V.

[0054] Another embodiment of the heat exchanger assembly 10 is shown diagrammatically in Figure 2. Components having the same or similar nature or function as in the embodiment described in relation to Figure 1 are given the same reference numerals. The heat exchanger 12 is a shell-and-tube type heat exchanger. The heat exchanger 12 has a tube bundle of straight tubes 44 forming one or more partitions 26 and a shell 46 enclosing the tube bundle.

[0055] Each of the straight tubes 44 is supported at one end by a first tube plate 48 forming a first tube support and at the other end by a second tube plate 50 forming a second tube support. Each of the straight tubes 44 has an inlet at the first tube plate 48 and an outlet at the second tube plate 50.

[0056] The straight tube 44, the first tube plate 48, and the second tube plate 50 are made of metal and are welded together such that the components are electrically connected to each other and are at the same electrical potential.

[0057] The first electrical connector 14 and the second electrical connector 16 are comprised of a first tube plate 48 and a second tube plate 50, respectively, and are comprised of electrical wires connecting the tube plates 48 and 50 to the power source 18. In this manner, the power source 18 is configured to provide electrical current to the tubes 44 and further to the isolation partition 26.

[0058] A first tube plate 48 and a second tube plate 50 connect to the shell and separate the first fluid 22 from the second fluid 24. The tube plates 48 and 50 are electrically insulated from the shell 46 by rubber packing (not shown).

[0059] The first tube plate 48 and the shell 46 form a first enclosed space 52 that may contain a first fluid 22. The heat exchanger 12 has an inlet in the shell 46 through which the first fluid enters the first enclosed space 52. The second tube plate 50 and the shell 46 form a second enclosed space 54 that may contain the first fluid 22. The heat exchanger 12 has an outlet in the shell 46 through which the first fluid 22 may exit the second enclosed space 54. The inlet of the tubes 44 opens into the first enclosed space 52 and the outlet of the tubes 44 opens into the second enclosed space 54.

[0060] The first tube plate 48, the second tube plate 50, and the shell 46 form a third enclosed space 56 that can contain the second fluid 24. The heat exchanger 12 has an inlet and an outlet in the shell 46 through which the second fluid 24 can enter and exit the third enclosed space 56.

[0061] Each tube 44 extends from the first enclosed space 52 through the third enclosed space 56 to the second enclosed space 54, thus constituting a first channel through which the first fluid 22 can flow from the first enclosed space 52 to the second enclosed space 54 and pass the second fluid 24 without intermixing, thus allowing heat transfer between the fluids 22 and 24. The inlet and outlet to the third enclosed space 56 are positioned such that the second fluid 24 passes through the tubes 44. In this way, the third enclosed space 56 constitutes a second channel through which the second fluid 24 can flow.

[0062] Another embodiment of the heat exchanger assembly 10 is shown diagrammatically in Figure 3. Components having the same or similar nature or function as described in relation to Figures 1 and 2 are given the same reference numerals. The heat exchanger 12 is a shell-and-tube type heat exchanger. The heat exchanger 12 has a tube bundle of tubes 44 bent into a U-shape as shown in Figure 2. The tubes 44 form one or more partitions 26.

[0063] The embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 2 in that it does not have a second tube plate 50. Instead, the tubes 44 are supported only by the first tube plate 48. As shown in FIG. 3, a second sealed space 54 is formed by the first tube plate 48 and the shell 46, and a third sealed space 56 is formed by the first tube plate 48 and the shell 46. The first sealed space 52 and the second sealed space 54 are separated by an extension of the first tube plate 48. Each tube 44 extends from the first sealed space 52 into the third sealed space 56, bends, and returns to the second sealed space 54 juxtaposed to the first sealed space 52.

[0064] The first electrical connector 14 is comprised of a first tube plate 48 and comprises electrical wires connecting the first tube plate 48 to the power source 18. The second electrical connector 16 is comprised of electrical wires connecting the power source 18 to each of the tubes 44 at the other end of the tube bundle.

[0065] example The test setup used in the proof of concept is shown in Figure 4. The setup included the heat exchanger assembly 10 described in relation to Figure 1. The electrical conductivity of the stainless steel plates 20 of the heat exchanger 12 is high. Therefore, a 51 k ohm resistor (not shown) was placed in series with the heat exchanger 12 to limit the current.

[0066] The test apparatus includes a first tank 32 containing water and a heater 36 arranged to heat the water in the first tank 32. The apparatus further includes a jacket tank 38 containing brackish seawater constituting the first fluid 22. The jacket tank 38 is coupled to the first tank 32 such that heat may be received from the first tank 32. The test apparatus also includes a second tank 34 containing cooler tap water constituting the second fluid 24.

[0067] The test apparatus further has a pressure gauge 40. The various components are connected as shown in Figure 4. The apparatus has several valves and pumps (not shown) that generate and control the flows indicated by the arrows in Figure 4. The apparatus is coupled to a drain 42 so that the tap water in the second tank 34 can be emptied from the apparatus after passing through the heat exchanger 12. The apparatus also has several thermometers (not shown) for measuring the temperatures of the first fluid 22 and the second fluid 24 at the respective inlets of the heat exchanger 12.

[0068] The following temperatures were measured by a thermometer: the inlet temperature of the first fluid 22 (Th,in) and the inlet temperature of the second fluid 24 (Tc,in). The pressure drop (ΔP) of the first fluid 22 across the heat exchanger 12 was measured using a pressure gauge. The pressure drop (ΔP) of the first fluid 22 was used to characterize the performance of the heat exchanger 12.

[0069] Two tests were performed on the same apparatus, one with and one without current flow, i.e. with and without current being supplied to the heat exchanger 12 by the power supply 18. All other test parameters were the same. The apparatus was cleaned before each test run. The same first fluid 22 (seawater) was used in both test runs. Both tests were performed over a period of 18 days.

[0070] The first fluid 22 (warm sea water) input temperature (Th,in) was kept constant at approximately 40° C. and the second fluid 24 (cold tap water) input temperature (Tc,in) was kept constant at approximately 10° C. The power supply 18 was operated at a peak current of approximately 0.54 mA, a peak voltage of approximately 80 V, and a frequency of 5 Hz.

[0071] After each test run, the heat exchanger 12 was removed and biofilm samples were taken from the inner surface of the separator partition 26 of the heat exchanger 12 facing the first fluid 22 (seawater). A sterile cotton swab was used and the same wiping pattern was repeated. Each time, approximately 2 cm 2 was wiped away.

[0072] For both trials, four biofilm samples were taken at four different locations on the inner surface of the separation partition 26. Each sample was then triplicated to avoid contamination. The samples were analyzed using laser-based flow cytometry for cell count and differentiation of dead and live bacteria. The average bacterial counts are presented in Table 1.

[0073] [Table 1]

[0074] The energization of the heat exchanger 12 clearly leads to a reduction in the number of bacteria, both total and viable. The total number of bacteria was reduced by about 9%. The effect is even greater for viable bacteria, in which case the number of bacteria was reduced to less than 3%. It can be concluded that the energization greatly reduces the bacterial growth on the partitions of the heat exchanger facing the first fluid 22 (seawater).

[0075] FIG. 5 is a graph showing the pressure drop (ΔP) of the first fluid 22 across the heat exchanger 12 as a function of time. The crosses show the results of the energized device operation and the circles show the results of the non-energized device operation. It can be seen in the graph of FIG. 3 that the pressure drop (ΔP) increases with time in the non-energized trial run, but is almost constant in the charged trial run. The pressure difference after 14 days is about 25% higher without current. This change is believed to be caused by a greater microbiological growth in the non-energized trial run compared to the energized trial run, and the growth is believed to limit the flow of the first fluid 22 through the heat exchanger 12. This leads to a decrease in the dynamic pressure after the heat exchanger, which in turn leads to a greater pressure drop (ΔP). It can be concluded that the supply of electric current to the heat exchanger 12 prevents a pressure drop (ΔP) across the heat exchanger that may be caused by microbial growth. [Explanation of symbols]

[0076] 10 Heat exchanger assembly 12 Heat exchanger 14 First Electrical Connector 16 Second Electrical Connector 18 Power supply 20 Plate 22 First Fluid 24 Second Fluid 26 Separation partition 28 Side Section 30 Corner Section 32 First Tank 34 Second Tank 36 Heater 38 Jacketed tank 40 Pressure Gauge 42 Drain pipe 44 Tube 46 Shell 48 First Tube Plate 50 Second Tube Plate 52 First sealed space 54 Second Closed Space 56 The Third Closed Space

Claims

1. 1. A system for preventing microbiological growth in a heat exchanger (12), comprising: The heat exchanger (12) includes a plurality of partitions (26) that separate a first fluid (22) and a second fluid (24), and the plurality of partitions (26) are configured to allow heat to be transferred between the first fluid (22) and the second fluid (24) through the plurality of partitions (26); The plurality of partitions (26) are electrically connected to each other; The system comprises: a first electrical connector (14) and a second electrical connector (16) configured to be operatively connected to said plurality of partitions (26) of said heat exchanger (12); a power source (18) configured to be operatively connected to said first electrical connector (14) and said second electrical connector (16); Equipped with the power source (18) is configured to provide electrical current to the plurality of partitions (26) of the heat exchanger (12) via the first electrical connector (14) and the second electrical connector (16); The system, wherein the power source (18) is configured to supply electrical current to mitigate microbial growth in the plurality of partitions (26) of the heat exchanger (12).

2. 1. A method for mitigating microbiological growth in a heat exchanger (12), comprising: The heat exchanger (12) includes a plurality of partitions (26) that separate a first fluid (22) and a second fluid (24), and the plurality of partitions (26) are configured to allow heat to be transferred between the first fluid (22) and the second fluid (24) through the plurality of partitions (26); The plurality of partitions (26) are electrically connected to each other; The method comprises: - providing a system according to claim 1; - operatively connecting said first electrical connector (14) and said second electrical connector (16) to said plurality of partitions (26) of said heat exchanger (12); - supplying an electric current to said partitions (26) of said heat exchanger (12) using said power source (18); A system comprising:

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