A cooling assembly

Abstract

A cooling assembly 10 comprising a main pump 18 which pumps cooling fluid (water, a synthetic ester-based dielectric fluid, or a mixture of ethylene glycol and water) from a storage tank 16 to a compo

Description

The present invention relates to a cooling assembly, in particular to a cooling assembly including a high-power water-cooled motor drives and a heat exchanger for use on a submarine. High powered components, such as motor drives, generate heat during operation which is detrimental to the performance of those components. Accordingly, known motor drives are required to be cooled to enable the components to operate within a desired temperature range. Known cooling assemblies incorporate such high-powered components into a closed loop internal water circuit which is coupled with a plate heat exchanger. The heat exchanger is supplied with an external supply of cooling water. In operation, the high-powered component is integrated into and cooled by water in the internal water circuit. The heat from the component heats up the water in the internal water circuit which is fed to a heat exchanger where the water is cooled and circulated back to the component to cool the components and enable it to operate within the desired temperature range. One problem with known cooling assemblies is the reliance on the external water supply to the heat exchanger, which if it fails, prevents the water in the internal water circuit from being cooled in the heat exchanger, and therefore prevents the water in the internal water circuit from cooling the component. This is a particular concern for components which are part of critical systems, such as those on submarines, and are therefore required to operate for a specified period of time should the external water supply fail. An object of the present invention is to provide an improved cooling assembly which can operate for an extended period of time should the external water supply fail. Thus, according to the present invention there is provided a cooling assembly comprising a pressurised cooling circuit containing a cooling fluid, a component in fluid communication with the cooling circuit, and a heat exchanger, the cooling circuit comprising a fluid storage tank and a pump, the heat exchanger comprising an internal circuit in fluid communication with the cooling circuit and an external circuit in fluid communication with an external fluid supply, the internal circuit in thermal communication with the external circuit such that the cooling fluid in the internal cooling circuit is cooled by the external fluid supply, the pump is configured to continuously circulate the cooling fluid around the internal circuit to the component via the fluid storage tank such that the component is cooled by the cooling fluid, in which the fluid storage tank contains a reserve volume of the cooling fluid. Advantageously, the reserve volume of the cooling fluid acts as a thermal store and increases the total volume of cooling fluid in the internal cooling circuit compared to a cooling circuit without a reserve volume, and therefore increases the time required for the cooling fluid to heat up and therefore increases the time the cooling fluid can continue to cool the component in the event of a failure of the external water supply. Increasing the cooling time enables the component to run for an extended period of time within a desired operating temperature range which is important for critical systems incorporating the component. Preferably, the cooling circuit and the internal circuit are a closed circuit not in direct fluid communication with the external fluid supply. By keeping the internal circuit separated from the external circuit this also has the advantage that the internal circuit can use a different fluid from that of the external supply, for example, water could be used externally and Midel 7131 internally. Preferably, the cooling circuit is releasably fluidly connectable to the internal circuit of the heat exchanger. Preferably, the internal circuit of the heat exchanger comprises an inlet and an outlet, in which the inlet receives a heated cooling fluid from the component and the outlet supplies a cooled cooling fluid to the component. Preferably, the fluid storage tank is positioned in the cooling circuit adjacent the outlet. Preferably, the pump is positioned in the cooling circuit between the fluid storage tank and the component. Preferably, the reserve volume is configured to enable the component to run at a specified power output for a specified extended run time if the external fluid supply ceases to supply external fluid to the external circuit of the heat exchanger. Preferably, the cooling fluid is a liquid, Preferably, the cooling fluid is one of water, a synthetic ester-based dielectric fluid, or a mixture of ethylene glycol and water. Preferably, the heat exchanger is one of a shell and tube, tube-fin or plate-fin heat exchanger. Preferably, the component is one or more of a resistor, a capacitor, a power supply, a power convertor, a motor drive, or a transistor such as an IGBT. Preferably, the cooling assembly further comprising a second heat exchanger. Preferably, the second heat exchanger is an air-water heat exchanger. Preferably, the second heat exchanger is coupled to the cooling circuit. Preferably, the second heat exchanger is arranged in the cooling circuit in parallel with the component such that the cooling fluid runs through the component and the heat exchanger in parallel. Preferably, the second heat exchanger includes an internal circuit, the internal circuit is a closed circuit not in direct fluid communication with the external fluid supply. Preferably, the cooling assembly is contained with a sealed box. According to another aspect of the present invention there is provided a system including the aforementioned cooling assemblies. The invention will now be described by way of example only with reference to the accompanying drawings, in which Figure 1 is a schematic circuit diagram of a known cooling assembly, Figure 2 is a schematic circuit diagram of a cooling assembly according to the present invention, and Figure 3 is a schematic circuit diagram of an alternative cooling assembly according to the present invention. In Figure 1, a prior art cooling assembly 10 is shown. In Figure 2, the cooling assembly 10 of the present invention comprises an electrical component in the form of a motor drive 50. In alternative embodiments, the component can be any component which requires cooling, for example, a resistor, a capacitor, a converter, a power supply, or a transistor such as an IGBT. The drive motor 50 or other component is used in, for example, control systems of a submarine (not shown). The cooling assembly 10 further comprises a cooling circuit 12 and a heat exchanger, in this embodiment, a plate heat exchanger 14. The cooling circuit 12 is a pressurised circuit. The cooling circuit 12 includes a cooling fluid IF, in this embodiment water. In alternative embodiments, other cooling fluids can be used, for example, a synthetic ester-based dielectric fluid such as Midel 7131, or a mixture of ethylene glycol and water. The heat exchanger 14 is of the known type and includes an internal circuit 22 and an external circuit 24 of the submarine. The internal circuit 22 and the external circuit 24 are not in direct fluid communication, that is, the cooling fluid IF in the internal circuit 24 cannot flow into the external circuit 24. However, the internal 22 and external 24 circuits are in thermal communication such that heat is transferred from the internal circuit 22 to the external circuit 24 as will be described further below. The external circuit 24 is used to supply other systems of the submarine. The cooling circuit 12 is fluidly connected to the internal circuit 22 of the heat exchanger via an internal input 23 and internal output 25 such that the cooling circuit 12 and the internal circuit 22 form a closed circuit. The internal input 23 and internal output 25 allow the cooling circuit 12 to be releasably connected to the heat exchanger 14. The external circuit 24 of the heat exchanger 14 is fluidly connected to an external water supply 21 via an external input 27 and an external output 29. closed circuit. The external input 27 and the external output 29 allow the heat exchanger 14, and therefore the cooling circuit 12 to which it is fluidly connected, to be releasably connected from the external water supply 21. The cooling circuit 12 further comprises a fluid storage tank 16 and a primary pump in the form of pump 18 and a secondary of redundant back-up pump 19 connected in parallel with the primary pump 18. The pump 18 is configured to pump the cooling fluid IF around the cooling circuit such that it can cool the motor drive 12. A shuttle valve 17 is included in the cooling circuit 12 between the fluid storage tank 16 and the pump 18. The shuttle valve 17 is associated with a pressure sensor (not shown) of the cooling circuit 12 and configured to allow the cooling fluid IF to flow through the pump 18 only, i.e. bypassing the secondary pump 19, when the pressure in the cooling circuit 12 is above a pressure threshold. If the pressure in the cooling circuit 12 drops below the threshold, indicating a possible failure of the pump 18, the shuttle valve 17 moves to allow fluid to pass through the secondary pump 19 instead of the pump 18. It will be understood that the provision of the secondary pump 19 enables the cooling fluid IF to circulated, thus cooling the component 50 in the event of the primary pump 18 failing. The cooling circuit 12 further comprises an expansion vessel as is known in the art (not shown) to accommodate for changes in volume in the internal circuit due to temperature changes. The motor drive 50 includes embedded water tubes (not shown) in fluid communication with the cooling circuit to take heat away from the motor drive 50. The fluid storage tank 16 is positioned in the cooling circuit 12 adjacent the internal outlet 25 of the heat exchanger 14. The pump 18 is positioned in the cooling circuit 12 between the fluid storage tank 16 and the motor drive 50. The fluid storage tank 16 is sized such that it can contain a reserve volume V of the cooling fluid IF. The reserve volume V of cooling fluid IF in the storage tank 16 is set such that the total volume of fluid in the cooling circuit 12 is sufficient to enable the motor drive 50 to continuing operating for a specific period of extended time T at a given power output P. For example, the reserve volume V is set to run at full power Pf for a time T1 or halfpower Pf / 2 for a period of time T2 which is greater than T1. Typically, in critical systems, the motor drive, or any other component, is required to operate for at least twenty minutes at half-power when the external supply is unavailable. To determine the size of the fluid storage tank 16 to accommodate the reserve volume V for the required extended time T, experiments are conducted with different fluid storage tank sizes to establish a time constant which relates the extended run time T to the reserve volume V for a given cooling assembly 10 and given operating power requirements after the external power fails. It is then possible to determine the reserve volume V required for different extended run times T. Operation of the cooling assembly 10 is as follows: The external water supply 21 is connected to the heat exchanger 14 such that a continuous supply of cold water is circulated through the external circuit 24. The cooling circuit 12 is connected to the heat exchanger 14. The pump 18 in the cooling circuit 12 is activated such that it continuously circulates the cooling fluid IF around the cooling circuit 12 when the component 50 is operating, i.e. there is no temperature measurement or control which selectively circulates cooling fluid IF through the component 50. Specifically, the cooling fluid IF is pumped from the internal circuit 22 of the heat exchanger 14, through the fluid storage tank 16 and through the embedded water tubes of the motor drive 50, before being returned to the internal circuit 22 of the heat exchanger 14. The cooling fluid IF takes heat away from, and therefore cools the motor drive 50, resulting in a heated cooling fluid 28 flowing from the motor drive 50. The heated cooling fluid 28 then circulates through the internal circuit 22 of the heat exchanger 14 where it is cooled due to heat being taken away by the cold external fluid EF circulating in the external circuit 24 of the heat exchanger 14. The cooling fluid IF then circulates back through the pump 18 to supply cooled cooling fluid 26 to the motor drive 50. This circulation of cooling fluid IF continues when the pump is operating and ensures the motor drive 50 is cooled sufficiently to enable it to operate within its desired temperature range. In the event of the external supply 21 failing, for example, if the external water supply 21 is removed, or a physical connection between the external water supply 21 and the heat exchanger 14 breaks, then cold external fluid EF is no longer supplied to the heat exchanger 14. The circulation of cooling fluid IF continues, but the cooling fluid IF is no longer cooled by the heat exchanger 14 and therefore the temperature of the cooling fluid IF will gradually increase up to a maximum temperature, 70°C in this embodiment, at which temperature the motor drive 50 is no longer being sufficiently cooled to keep it within its desired temperature range, and will trip or shut down. The provision of the reserve volume V of cooling fluid IF in the fluid storage tank 16 increases the total volume of coiling fluid IF in the cooling circuit 12 compared to a cooing circuit without a reserve volume V, and therefore a greater volume of cooling fluid IF is available in the cooling circuit 12 at the point at which the external supply 21 fails. The time taken for the cooling fluid IF to reach that maximum temperature therefore increases, which enables the motor drive 50 to continue operating for the extended run time before tripping. Typically, the cooling assembly 10 will include additional components 80 (shown schematically in Figure 2), for example, control electronics, which are not directly cooled by the cooling circuit 12, and these additional components will tend to fail before the motor drive 50 trips out if they become too hot. That is, continued operation of a system to which the motor drive is integrated with, is not limited by the motor drive itself and the associated extended run time, but by these other components 80. In a cooling assembly that is open to the environment E, the additional components 80 are not contained, and will be cooled by the surrounding environment E as the heat dissipates naturally. It can be seen in Figure 2 that an equipment boundary exists between the cooling assembly 10 and the external cooling fluid supply 21. The equipment boundary does not represent a cooling assembly housed within a sealed box (as is the case in the cooling assembly of Figure 3 below). In Figure 3, an alternative cooling assembly 110 is shown which is identical and operates the same to cooling assembly 10 described above in relation to Figure 2 except that an additional heat exchanger, in this embodiment, an air-water tube-fin heat exchanger 60 is included, and the assembly 110 is contained within a sealed box 70 to comply with an ingress protection rating of IP56. It can be seen from Figure 3 that the additional components 80 are not exposed to the environment E and require additional cooling as will be described below. The air-water heat exchanger 60 is coupled to the cooling circuit 12 at junction 33 such that the cooled cooling fluid 26 flows through the component 50 and through an internal circuit 69 of the air-water heat exchanger 60 and re-joins the cooling circuit IF after the component 50 at junction 35 such that the heated cooling fluid 28 from the air-water heat exchanger 60 is not fed into the component 50 which would be detrimental to cooling of the component 50. In other words, the water-cooled component 50 and the air-water heat exchanger 60 are arranged in parallel so that the cooling fluid IF runs through the water-cooled component 50 and the air-water heat exchanger 60 in parallel. A fan 65 is arranged to force air over the cooled cooling fluid 26 inside the heat exchanger 60, to generate cooled air 67 which is then circulated throughout the sealed box 70 to cool the additional components 80. The cooling assembly 110 functions in the same way as cooling assembly 10 except that the cooling fluid IF is also circulated through the heat exchanger 60 to provide additional air cooling inside the sealed box 70 and the components located therein. It will be appreciated that the reserve volume V also enables cool air 67 from the heat exchanger 60 to be circulated in the box 70 for a period of time after external fluid supply failure by virtue of the internal circuit 69 being coupled to the internal cooling circuit 12. It will be understood that the cooling assembly of Figure 2 can also be housed within a sealed box, and the cooling assembly of Figure 3 need not be housed within a sealed box. In both the cooling assemblies of Figure 2 and 3, the optional second heat exchanger 60 can be added, irrespective of the cooling assembly being housed within a sealed box, and according to the cooling requirements. Typically, the greater the number of components, the more heat is generated, and therefore more cooling capacity is required, particularly if contained with a sealed box. The greater the component density, i.e., the number of components for a given box volume, the more resistance there is to air flow. It will also be understood that the cooling assembly of the present invention enables components in power dense environments to be cooled sufficiently and for an extended period of run time in the event that the external cooling fluid supply fails, which is important for critical systems. In particular, the provision of a reserve thermal store integrated into a pressurised internal circuit which continuously circulates through the component enables the component to be cooled for extended periods of operation in the event the external fluid supply fails. Furthermore, by being not in direct fluid communication with the external fluid supply 21, the cooling fluid IF in the internal circuit 22 is less impacted by any temperature fluctuations in the external circuit 21. Yet further, the provision of a secondary redundant pump within the internal circuit 22 enables the circuit to continue cooling the component in the event the primary pump fails. The use of a pressurised system also negates that need for a header tank to accommodate changes in volume due to temperature. The header tank would need to be positioned at the top of the system, as opposed to the expansion vessel of the present invention which is not only more compact, but can be positioned anywhere in the system.

Claims

1. A cooling assembly (10) comprising a pressurised cooling circuit (12) containing an internal cooling fluid (IF), a component (50) in fluid communication with the cooling circuit (12), and a heat exchanger (14), the cooling circuit (12) comprising a fluid storage tank (16) and a pump (18), the heat exchanger (14) comprising an internal circuit (22) in fluid communication with the cooling circuit (12) and an external circuit (24) in fluid communication with an external fluid supply (EF), the internal circuit (22) in thermal communication with the external circuit (24) such that the cooling fluid (IF) in the internal circuit (22) is cooled by the external fluid (EF) in the external circuit (24), the pump (18) is configured to continuously circulate the cooling fluid (IF) around the internal circuit (22) to the component (50) via the fluid storage tank (16) such that the component (50) is cooled by the cooling fluid (IF), in which the fluid storage tank (16) contains a reserve volume (V) of the cooling fluid (IF).

2. A cooling assembly (10) according to claim 1 in which the cooling circuit (12) and the internal circuit (22) are a closed circuit not in direct fluid communication with the external fluid supply (21).

3. A cooling assembly (10) according to claim 2 in which the cooling circuit (12) is releasably fluidly connectable to the internal circuit (22) of the heat exchanger (14).

4. A cooling assembly (10) according to any preceding claim in which the internal circuit (22) of the heat exchanger (14) comprises an inlet (23) and an outlet (25), in which the inlet (23) receives a heated cooling fluid (28) from the component (50) and the outlet (25) supplies a cooled cooling fluid (26) to the component (50).

5. A cooling assembly (10) according to claim 4 in which the fluid storage tank (16) is positioned in the cooling circuit adjacent the outlet (25).

6. A cooling assembly (10) according to any preceding claim in which the pump (18) is positioned in the cooling circuit (12) between the fluid storage tank (16) and the component (50).

7. A cooling assembly (10) according to any preceding claim in which the reserve volume (V) is configured to enable the component (50) to run at a specified power output (P) for a specified extended run time (T) if the external fluid supply (21) ceases to supply external fluid (EF) to the external circuit (24) of the heat exchanger (14).

8. A cooling assembly according to any preceding claim in which the cooling fluid (IF) is one of water, a synthetic ester-based dielectric fluid, or a mixture of ethylene glycol and water.

9. A cooling assembly according to any preceding claim in which the heat exchanger is one of a shell and tube, tube-fin or plate-fin heat exchanger.

10. A cooling assembly according to any preceding claim in which the component is one or more of a resistor, a capacitor, a power supply, a motor drive, a power convertor, or a transistor such as an IGBT.

11. A cooling assembly (110) according to any preceding claim further comprising a second heat exchanger (60).

12. Acooling assembly (110) according to claim 11 in which the second heat exchanger (60) is an air-water heat exchanger.13.A cooling assembly (110) according to claim 12 in which the second heat exchanger (60) is coupled to the cooling circuit (12).14.A cooling assembly (110) according to claim 13 in which the second heat exchanger (60) is arranged in the cooling circuit (12) in parallel with the component (50) such that the cooling fluid (IF) runs through the component (50) and the heat exchanger (60) in parallel.

15. A cooling assembly (110) according to any one of claims 11 to 14 in which the second heat exchanger (60) includes an internal circuit (69), the internal circuit (69) is a closed circuit not in direct fluid communication with the external fluid supply (21).

16. A cooling assembly (110) according to any preceding claim in which the cooling assembly (110) is contained with a sealed box (70).

17. A cooling assembly (10,110) according to any preceding claim, the cooling circuit (12) further comprises a secondary pump (19) connected in parallel with the primary pump (18), and a valve (17), the valve (17) configured to allow the cooling fluid (IF) to only flow through the pump (18) when a pressure in the cooling circuit (12) is above a pressure threshold, and allow the cooling fluid (IF) to only pass through the secondary pump (19) when the pressure in the cooling circuit (12) is below a pressure threshold.

18. A cooling assembly (10,110) according to claim 17 further comprising a pressure sensor to detect the pressure in the cooling circuit (12).

19. A cooling assembly (10) ) according to any preceding claim in which the internal cooling fluid (IF) is a different fluid to the fluid of the external fluid supply (EF)20. A submarine including a cooling assembly (10,110) according to any preceding claim.14

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