GB2453129A

GB2453129A - Freezing protected pump assembly

Info

Publication number: GB2453129A
Application number: GB0718765A
Authority: GB
Inventors: Peter David Hood
Original assignee: Intelligent Energy Ltd
Current assignee: Intelligent Energy Ltd
Priority date: 2007-09-26
Filing date: 2007-09-26
Publication date: 2009-04-01
Anticipated expiration: 2027-09-26
Also published as: TW200925427A; GB0718765D0; GB2453129B; AR068279A1; WO2009040515A1

Abstract

A pump assembly 10 comprises a first body portion 11, a second body portion 12, an inlet port 13, an outlet port 14 and a pumping chamber defined between the first and second body portions which encloses a pumping mechanism e.g. a gear pump, to pump fluid from the inlet to the outlet. The first and second body portions are secured together by a resiliently biased fastening mechanism 16, 19 to provide a fluid seal around the pumping chamber. The fastening mechanism may comprise one or more bolts through the body portions and a resilient ring around each bolt to allow reversible separation of the body portions by elastic deformation of at least a portion of the fastening mechanism to avoid ice damage. May be used as a submerged pump in a vehicle fuel cell pure cooling water tank which may freeze in cold conditions.

Description

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PUMP ASSEMBLY

Field of the Invention

The invention relates to a pump assembly for pumping liquids, and in particular to a pump assembly that is capable of withstanding being repeatedly frozen and thawed.

Background

Recirculating coolant systems are typically required in fuel cell systems, for example to supply coolant water to a fuel cell stack, either through an isolated coolant path or directly into and through individual cells in the stack. Further details of such systems are provided in co-pending GB applications entitled "Fuel cell system" by the present applicant.

In such systems, a pump may be disposed within a coolant reservoir, the pump being submerged in the coolant and arranged to pump coolant into the fuel cell on demand. If the coolant is high purity water, which may be required for direct cathode cooling of a fuel cell, additives to reduce the freezing point of the coolant cannot be used because these would poison the fuel cell membranes. If the coolant water is not kept above freezing point (i.e. 0 °C at normal atmospheric pressure) at all times, damage to the pump could occur when ice forms around and within the pump when temperatures drop and are maintamed for prolonged periods below freezing. Particularly for automotive applications, where subzero temperatures and intermittent use may occur, such situations need to be taken into account.

One option is to ensure that the coolant water is kept liquid at all times. This can be at least partly achieved through the use of an insulated containment vessel, with one or more heaters in the vessel to keep water within the vessel around and within the pump above freezing point. This approach can, however, only work for as long as power for heating is available, and would clearly be wasteful of battery power andlor fuel if needed for prolonged periods of time.

An alternative option is to ensure that any water in the system is flushed from the pump when the system is not in use. This, however, prevents the coolant system from being in a

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primed condition ready to start when required, and requires additional steps on shutdown and startup of the system to flush and recharge the pump.

It is an object of the invention to address one or more of the above mentioned problems.

Summary of the invention

In a first aspect, the invention provides a pump assembly comprising: a first body portion; a second body portion; an inlet port; an outlet port; and a pumping chamber defined by a volume between the first and second body portions, the pumping chamber enclosing a pumping mechanism configured to pump fluid from the inlet port to the outlet port via the pumping chamber, wherein the first and second body portions are secured together by a resiliently biased fastening mechanism to provide a fluid seal around the pumping volume, the fastening mechanism configured to allow for reversible separation of the first and second body portions by elastic deformation of at least a portion of the fastening mechanism.

In a second aspect, the invention provides a water containment vessel for a coolant system, the water containment vessel comprising: a water inlet; a water outlet; a pump assembly according to the first aspect, wherein the outlet of the pump is in fluid communication with the water outlet of the water containment vessel, and the pump is disposed within the vessel such that the pump is submerged when the vessel contains water.

The invention provides a liquid coolant pump assembly that is able to withstand freezing while staying in a fully primed condition. The pump assembly is also preferably able through its construction to respond quickly to external temperature changes, thus allowing water within the pump assembly to defrost more rapidly in response to external temperature changes.

Detailed Description

The invention will be described by way of example, with reference to the accompanying drawing in which: figure 1 shows a perspective view of an exemplary pump according to the invention; and figure 2 illustrates a schematic cross-sectional view of a water containment vessel in which the exemplary pump assembly of figure 1 can be installed.

Figure 1 illustrates a perspective view of an exemplary liquid pump assembly 10. The pump assembly 10 comprises a first body portion 11 and a second body portion 12. The first 11 and second 12 body portions are joined together either side of a third body portion along delamination interfaces 18. A pumping mechanism (not shown) is provided within a cavity formed between the first and second body portions 11, 12 and surrounded by the third body portion 15. When the pump assembly 10 is fully immersed, liquid is pumped from an inlet port 13 to an outlet port 14 (both ports being shown in figure 1 with protective covers not present in use).

The pumping mechanism in the pump assembly 10 is preferably that of a gear pump, although other types of pumping mechanisms may be suitable. One advantage of a gear pump is that a known volume of liquid can be pumped for each revolution of the mechanism within the pump assembly 10. This is advantageous when a predetermined metered rate of liquid flow is required, for example for use with a cathode injection system in a fuel cell.

Shown in figure 2 is a schematic cross-sectional view of a water containment vessel 140 containing a pump assembly 10 according to the invention. The vessel 140 comprises a thermally insulating wall 210 and a lid 211, which may also be thermally insulated.

Preferably the wall 210 of the vessel 140 is of a double wall construction, having a vacuum or other thermally insulating layer such as air or expanded polystyrene between the two walls. The inner surface 215 of the vessel 210 is preferably made from a material having a resistance to corrosion, such as stainless steel, to prevent contamination of water 212 within the vessel.

The purpose of the lid 211 is to allow connections to the various elements housed within the vessel 140, whilst also maintaining a good degree of insulation. Typically the lid 211 is manufactured from glass-reinforced nylon with an additional layer of insulating foam.

Ports in the lid to accommodate passage of the lines 125, 144, 128 are preferably configured such that when the fuel cell system to which the vessel 140 is connected is shutdown, any residual water runs back into the vessel 140. This involves using pipe of a suitably large diameter such that beads of water do not form to span the internal bore of the pipe and hang up in the line. Preferably, no fittings are used in the lid 211 so that pipes passing through the lid 211 contain no sharp bends.

A thermostatic heating element 236 within the vessel 140 is provided to maintain the temperature of water 212 within the vessel 140 above freezing point. A level sensor 233 provides a signal indicating the level of water 212 within the vessel. A heater 237 is provided in addition to the thermostatic heating element 236 in order to provide faster heating to defrost the water 212 if frozen. Due to the energy requirement of changing the phase of water from solid to liquid, this heater 237 is typically of a higher power rating than the thermostatic heating element 236, for example around 180W or higher. The thermostatic heater 236 is configured to ensure that the temperature of the water 212 in the vessel 140 remains above a set point. This set point is typically 5°C, in order to prevent the water from freezing. The thermostatic heater 236 may be powered by a I 2V battery supply, and set to operate for a prescribed period. Hence, during this period, liquid water 212 in the vessel 140 can be guaranteed. For longer periods at sub-zero ambient temperature, the thermostatic heater 236 is preferably disabled to save on battery power.

The water 212 may then freeze, and will require defrosting with the higher power heater 237. The thermostatic heater 236 is typically of a power rating such that a maximum heat output is slightly larger than the maximum rated losses from the vessel. A typical power rating is in the range of 2 to 4 W. A temperature sensor TX4, preferably comprising a submerged thermistor, is installed in order to allow the temperature of the water 212 in the vessel 140 to be monitored.

An overflow line 144 is provided to eject excess water from the contaimnent vessel if a level of water in the vessel exceeds a preset amount.

Water from an inlet line 128 enters the vessel 140 through a filter 234. The pump assembly 10, driven by the drive shaft 240 and motor 231, pumps the water 212 from the vessel 140 through a further filter 214, a reverse flow relief valve 213 and through the outlet line 125. A flow meter 235 is configured to monitor the amount of water passing through the outlet line 125.

The pump is preferably constructed such that the motor 231 is located outside the containment volume of the vessel 140 and therefore avoids being in contact directly with water 212 within the vessel 140. The drive shaft allows the motor 231 to drive the pump assembly 10. The motor 231 is preferably rated for operation at sub-zero temperatures.

The pump assembly 10 is located so as to be submerged by water 212 in the vessel 140.

This has the advantage of there being no requirement for the pump assembly 10 to be purged during shutdown or heated during startup, particularly when water 212 is maintained within the flask after shutdown. Thawing of any ice within the pump assembly is achieved via heat transferred from the surrounding water as it defrosts. On thawing, the pump assembly 10 returns to its original shape without compromising its operation.

The reverse flow relief valve 213 is constructed such that water is allowed to pass from the pump assembly 10 through the cathode water injection line 125 when the pump assembly is operational, creating a pressure drop across the valve in the direction of flow.

However, when the pump assembly 10 is stopped and pressure in the outlet line 125 is increased, the valve 213 allows water to flow back into the vessel 140 through a purge port 238.

If the pump assembly 10 is in the form of a gear pump, without the reverse flow relief valve 213 no water would flow due to the pressure required to push water back through the pump assembly 10. Therefore, the reverse flow relief valve 213 is configured such that in normal operation it allows water to pass through it from the pump assembly 10 through the outlet line 125. When subjected to a small back pressure (for example in the region of 300mBar.g) when the pump assembly 10 is not being operated, a diaphragm in the reverse flow relief valve 213 opens and allows water to flow back into the vessel 140 through the purge port 238.

The drive shaft 240 can be driven by an electric motor 231 disposed on the outside of the water containment vessel 140. A suitable sealed bearing in the lid 211 can be provided to create a watertight seal to prevent the motor 231 from coming into contact with water from within the vessel 140. Thus, electric components such as the motor 231 are separated from parts of the pump such as the drive shaft 240 and pump assembly 10 that are in contact with water. This reduces the risk of electric short circuits.

The primary feature that allows the pump assembly 10 to accommodate a volume expansion involved when water within the pumping chamber freezes is the ability to mechanically delaminate along the interfaces 18. To do this, the pumping chamber within the assembly 10 is preferably constructed in three parts, which are able to separate in a direction parallel to the rotational axis 20 of the drive shaft (not shown). The expansion is absorbed by elastomeric components such as rubber o-rings 19 provided on each of the bolts 16 holding the body portions 11, 12, 15 together. The elastomeric components 19 are sufficiently resilient to allow the body portions 11, 12, 15 to return to their original position on thawing, and to allow a seal to be re-formed at each of the delamination interfaces 18.

To allow the core temperature of the pump assembly 10 to respond quickly to external temperatures i.e. to recover to an operating state from being frozen and encapsulated within ice, an open latticework of ribs 17 and voids 21 are preferably incorporated in the design of the three body portions 11, 12, 15. This allows the internal pumping chamber to be closer to the outer environment, thus reducing the thermal lag of the pumping assembly when warming from being frozen. Preferably the nbs 17 and voids 21 are constructed such that the internal pumping chamber is no more than 3 mm away from an outer surface of the pumping assembly 10.

Other embodiments are intentionally within the scope of the invention, as defined by the following claims.

Claims

1 A pump assembly comprising: a first body portion; a second body portion; an inlet port; an outlet port; and a pumping chamber defined by a volume between the first and second body portions, the pumping chamber enclosing a pumping mechanism configured to pump fluid from the inlet port to the outlet port via the pumping chamber, wherein the first and second body portions are secured together by a resiliently biased fastening mechanism to provide a fluid seal around the pumping volume, the fastening mechanism configured to allow for reversible separation of the first and second body portions by elastic deformation of at least a portion of the fastening mechanism.

2. The pump assembly according to claim I wherein the fastening mechanism comprises: one or more bolts passing at least partially through the first and second body portions; and a resiliently flexible ring around each of the one or more bolts, the ring being compressible to allow separation of the first and second body portions.

3. The pump assembly according to claim I comprising a third body portion disposed between the first and second body portions, the third body portion being separable from the first and second body portions along delamination interfaces through elastic deformation of a portion of the fastening mechanism.

4. The pump assembly according to claim 3 wherein the third body portion comprises a plurality of ribs and corresponding voids extending from an outer surface of the third body portion towards the pumping chamber.

5. The pump assembly according to claim 4 wherein the voids extend to within 3 mm of the pumping chamber.

6. The pump assembly according to claim 1 wherein the pumping mechanism comprises one or more gears arranged to pump liquid from the inlet port to the outlet port.

7. The pump assembly according to claim 6 comprising a drive shaft extending through the first body portion and connected to an electric motor, the drive shaft being configured to drive the one or more gears through rotation of the drive shaft by means of the electric motor.

8. The pump assembly according to claim 7 wherein the first and second body portions are configured to delaminate from one another by relative movement along a rotational axis of the drive shaft.

9. A water containment vessel for a coolant system, the water containment vessel comprising: a water inlet; a water outlet; a pump assembly according to any one of claims 1 tc-8, wherein the outlet of the pump is in fluid communication with the water outlet of the water containment vessel, and the pump is disposed within the vessel such that the pump is submerged when the vessel contains water.

10. The water containment vessel of claim 9 wherein the pump assembly comprises a drive shaft extending through the first body portion and through a lid of the containment vessel, the vessel further comprising an electric motor disposed on the outside of the vessel and connected to the drive shaft for driving the pump assembly.

11. A pump assembly substantially as described herein, with reference to the accompanying drawing.

12. A water containment vessel substantially as described herein, with reference to the accompanying drawing in figure 2.