GB2596829A - Drainage of a liquid condensation from a gas conduit - Google Patents

Abstract

An arrangement for draining liquid such as water from a cryogen gas conduit 14 comprises a drain hole 220 on an underside of the gas conduit, to allow water to flow through the drain hole, out of the quench path. A differential flow restrictor 60 is provided to impede the flow of gas, while presenting little impediment to the flow of water along the same flow path 62.

Description

DRAINAGE OF LIQUID CONDENSATION FROM A GAS CONDUIT

The present invention relates to arrangement for allowing a liquid condensate, such as water, to drain from a gas 5 conduit, providing an opening for allowing condensate to escape while restricting the quantity of gas which escapes.

The present invention is particularly relevant to quench lines used to provide an egress path for cryogen gas from 10 cryostats used to cool superconducting magnets, such as superconducting magnets used in MRI equipment.

Cryogen-filled cryostats for cooling superconducting magnets are provided with large-bore quench lines to allow for egress 15 of large quantities of cryogen in case of quench of the magnet. Such quench lines are often open to atmosphere.

They are only used in times of magnet quench, which is rare. At other times, differences in humidity and temperature can cause moisture from the air to condense on inner surfaces of the quench line. Such condensation may form a puddle of water unless a drain hole is provided. If a magnet quench occurs, a large volume of cryogen gas will flow through the quench path at a temperature significantly below the freezing point of water. Any moisture within the quench line will freeze to ice. Such ice may impede the flow of cryogen.

Fig. 1 shows a conventional arrangement for addressing this issue. A cryostat 10 contains an amount of cryogen 12, typically mostly in liquid form, at a pressure somewhat in excess of atmospheric pressure. A gas conduit 14 is provided, closed from the cryostat by a pressure limiting valve 16. In case of a quench in a superconducting magnet within the cryostat 10, a flow of cryogen 18 will leave the cryostat, at temperatures of under 100K. Any water within the gas conduit will freeze to ice on contact with this cryogen.

A quench elbow 20 is illustrated. This is a bend in the quench path formed by the gas conduit 14, and such quench elbows are frequently provided to enable the gas conduit 14 to carry a flow of cryogen gas 18 from cryostat 10 to a collection receptacle or out of a building to atmosphere. Condensation of moisture is often particularly noticeable at quench elbows 20. A drain hole 22 is provided on the underside of the gas conduit 14 near the quench elbow 20. This drain hole is intended to allow water condensation 24 to drip out of the gas conduit, but is limited in size to reduce the amount of cryogen which escapes through the drain hole 22 in case of quench.

The present invention aims to provide an arrangement wherein a drain hole is provided on the underside of the quench path, the drain hole being large enough that water condensation 24 may flow relatively unimpeded from the drain hole, and that the drain hole has a reduced susceptibility to blockage from debris.

The present invention accordingly provides structures und;g4.4444, as defined in the appended claims.

The above, and further, objects, characteristics and advantages of the present invention will become more apparent from the following description of certain embodiments thereof, with reference to the accompanying drawings, wherein: Fig. 1 shows a conventional arrangement of a drain hole allowing water condensation to drip out of a quench elbow; Figs. 2(a) to 2(c) show examples of directional flow restrictors which may be employed in respective embodiments of the present invention; and Fig. 3 shows an arrangement of a drain hole allowing water 35 condensation to drip out of a quench elbow, according to an embodiment of the present invention.

The present invention provides an arrangement wherein a drain hole is provided on the underside of the quench path, the drain hole being large enough that water condensation 24 may flow relatively unimpeded from the drain hole, and that the drain hole has a reduced susceptibility to blockage from debris. The arrangement includes provision to ensure that an excessive amount of cryogen gas does not escape through the drain hole in case of quench.

The present invention employs a directional flow restrictor. Such articles will be discussed in more detail below, with reference to Figs. 2(a) to 3.

A directional flow restrictor such as employed in the present invention has the characteristic that fluid flow through it is impeded more in one direction, the "reverse direction" than in the opposite direction, the "forward direction". Certain of such devices may be colloquially known as "fluid diodes".

In the example shown in the left side of Fig. 2(a), a fluid 30 is shown flowing in the forward direction from inlet 32 to outlet 34. The inlet is a tube of constant cross-section, and laminar flow of the fluid 30 provides little impediment.

In chamber 36, the fluid 30 spreads out into a space of much greater cross-sectional area, also providing little impediment to the flow. Outlet 34 is in itself a tube of constant cross-section, and laminar flow of the fluid through outlet 34 will provide little impediment. Some impediment will be provided in the region of the outlet 34 as the fluid flows from chamber 36 into outlet 34. However, the impediment is relatively light.

In the example shown in the right side of Fig. 2(a), fluid 30 is shown flowing in the reverse direction from outlet 34 to inlet 32. In this case, laminar reverse flow of the fluid 30 through the tube of constant cross-section of the outlet 34 provides little impediment. The fluid 30 enters chamber 36 tangentially and circulates around the circular chamber, forming a type of vortex. As more fluid flow in, the fluid already in the chamber is forced radially inwards, gaining angular velocity in order to maintain angular momentum. This will cause shear forces and turbulence in the fluid, and centrifugal forces will press the fluid away from the inlet 32 located at the centre of the vortex. Even once the fluid 30 enters the inlet 32, it continues to circulate in a vortex, further impeding flow in this reverse direction.

In the example shown in Fig. 2(b), a flow channel 40 is disturbed by protuberances 42 from the walls of the flow channel. These protuberances are shaped such that flow 44 in a reverse direction is impeded to a significantly greater extent than flow 46 in a forward direction. Taking reverse flow 44, the shape of the protuberances 42 directs a partial stream of the fluid 30 into cavities 46, where the fluid impinges on the channel walls, and is deflected into conflict with another partial stream of the fluid 30. Circulating currents may be established in the cavities 46 which contribute to turbulent flow through the flow channel. Flow 46 in a forward direction is much less disturbed by the protuberances 42, which are shaped such that the fluid impinges on the channel walls at a shallow angle and does not cause as much turbulence as for the reverse flow direction 44. Cavities 46 may cause eddies in the flow, but these will not cause such impediment as for the reverse flow 44.

In the example shown in Fig. 2(c), a flow channel 50 is disturbed by vanes 52 protruding at an angle from the walls of the flow channel 50. These vanes 52 are angled such that flow 54 in a reverse direction is impeded to a significantly greater extent than flow 56 in a forward direction. Taking reverse flow 54, the angle of the vanes 52 directs partial streams of the fluid 30 into cavities 56 between vanes, where the fluid impinges on the vanes and the channel wall, and causes great turbulence in the fluid flow. Similar turbulence occurs at each cavity 56 between vanes 52. Flow 56 in a forward direction is much less disturbed by the vanes 52, which are angled such that the fluid impinges on the vane walls at a shallow angle and is directed back into the main flow, which does not cause as much turbulence as for the reverse direction. Cavities 56 may cause eddies adjacent the forward flow, but these will not cause such impediment as for the reverse flow.

Such directional flow restrictors work efficiently for fluid flow with high Reynolds number. Some examples have been found to work well when the Reynolds number is >3000. A typical magnet quench will generate a Reynolds number of -100,000 to 1,000,000 within the quench line. (e.g. see PRESSURE RISE DURING THE QUENCH OF A SUPERCONDUCTING MAGNET USING INTERNALLY COOLED CONDUCTORS, J. R. Miller, L. Dresner, J. w. Lue, S. S. Shen, and H. T. Yeh; Oak Ridge National Laboratory, Oak. Ridge, Tennessee, USA).

The following consideration is relevant to the present invention. A directional flow restrictor requires relatively fast flowing fluid in order to behave as described above. Slow moving fluid will experience less impediment in the reverse direction since the turbulence created in the flow will be much reduced. The directional flow restrictors as described may therefore operate as differential flow restrictors, acting to impede rapid flow, while having little effect on slow flow.

Turning to the present application, cryogen gas flow during a quench is fast flowing gas under high differential pressure and would experience significant restriction to flow when passed through a directional flow restrictor in the reverse direction. However, the water condensate will flow at a slow rate under little differential pressure, and will experience little restriction to flow.

Fig. 3 illustrates an arrangement of a drain hole allowing water condensation to drip out of a quench elbow, according to an embodiment of the present invention. Features in common with Fig. 1 carry corresponding reference numbers.

The arrangement according to the embodiment of the invention 5 shown in Fig. 3 differs from the conventional arrangement shown in Fig. 1 in that the drain hole 220 is significantly larger (e.g. Sum diameter as compared to 1.5mm diameter of the drain hole 22 of Fig. 1). Furthermore, a differential flow restrictor 60 it placed vertically or substantially vertically below the drain hole. The differential flow restrictor 60 is oriented vertically or substantially vertically in order to provide a path for water condensation 24 dripping from the drain hole 220. Ideally, a flow channel 62 through the differential flow restrictor 60 provides an unimpeded vertical path for drops of water condensation 24 from the drain hole 220.

The differential flow restrictor 60 may take the form of a directional flow restrictor of any suitable known form, such as those described above. Such differential flow restrictor 60 is connected such that the flow of water condensation 24 and any flow of cryogen 18 will take place vertically, or substantially vertically, downwards in the reverse direction.

The differential flow restrictor acts in substantially impeding fast flow of high differential pressure, while not impeding slow flow of low differential pressure to any significant extent. There is no flow vertically upwards -the "forward" direction where the differential flow restrictor 60 is a directional flow restrictor. The differential flow restrictor 60 is used, in the present invention, the differentiate between slow, low differential pressure flow, such as the flow of water condensate; and fast, high differential pressure flow, such as the flow of cryogen gas during a quench event in the particular example of the present invention.

Water condensation 24 is very slow moving, discontinuous fluid flow which will experience substantially no flow restriction in the differential flow restrictor 60, even though the flow is in the "reverse" direction of a directional flow restrictor. Cryogen gas, in the case of a quench event, will be a very high differential pressure flow, and will be impeded by the differential flow restrictor 60 in a manner similar to those described above in relation to directional flow restrictors.

This differential flow effect allows the size of the drain hole 220 to be significantly increased without allowing a significant increase in the escape of cryogen gas in the case of a quench. The increase in drain hole 220 size will reduce the risk of the drain hole becoming blocked by debris within the quench line. A further advantage of an increase in drain hole size is in that it will also improve air flow within the quench line under normal conditions, that is, in the absence of a quench event, to allow it to dry out quicker in humid environments. This should reduce the incidence of water condensation present in the quench line 14 at the time of a quench event.

The use of the differential flow restrictor 60 with a large bore drain hole 220 will reduce the need for cleaning/inspection of the drain hole since the risk of blockage is much reduced. The size of the drain hole can be preferably larger than is currently used, for example of 5mm diameter as compared to a conventional arrangement having 1.5mm bore drain hole.

The invention could use any of the directional flow restrictors mentioned above as the directional flow restrictor 60. The prerequisites would be to provide a relatively large passage size from the drain hole (preferably 5mm or more in diameter) and an easy drainage path for condensed water (preferably no re-entrant features, no U-bends etc).

Although the above examples cite a drain hole 220 diameter of at least 5mm, certain preferred embodiments may include a drain hole of rather larger diameter than that. Such larger 5 drain hole 220 would reduce the risk of the drain hole 220 becoming blocked due to debris that may accumulate within the gas conduit. In certain embodiments of the invention, the gas conduit leads to -cent to atmosphere, for example leading from a cryostat cooling a superconducting magnet of an MAT system 10 to an open vent external to a building housing the MAT system. In such arrangements, a mesh is typically fitted over the vent to prevent objects, animals etc. from entering the gas conduit. An example of such mesh is: mesh size of 10 + 2 / -1 mm with 1.0 ± 0.3 mm round wires, maximum mesh size is 12.7 mm square. It may accordingly be preferred to employ a drain hole 220 of diameter to match the mesh size, for example 12.7mm to match the side of squares in the mesh, or sqrt(2) * 12.7mm to match the diagonal dimension of the mesh squares. If possible, it may be preferred to provide a drain hole 22 of even slightly bigger than the mesh size to allow easy passage of objects through the drain hole 220.

Claims (3)

1. Claims 1. An arrangement for draining liquid from a gas conduit comprising -a gas conduit (14) provided with a drain hole (220) on an underside of the gas conduit, to allow water to flow through the drain hole, out of the quench path; a differential flow restrictor (60) arranged with a flow path (62) leading vertically or substantially vertically downward away from the drain hole, the differential flow restrictor acting to impede rapid fluid flow of gas at high differential pressure through the flow path (62) away from the drain hole, while presenting little impediment to slow fluid flow of water under little differential pressure, along the same flow path (62).
2. 2. An arrangement according to claim 1 wherein the flow path (62) provides an unimpeded vertical path for drops of water from the drain hole (220).J. An arrangement according to any preceding claim, wherein the differential flow restrictor (60) is a directional flow restrictor arranged such that flow of water and of gas take place in a reverse direction, vertically or substantially vertically downward away from the drain hole (220).Claims 1. An arrangement for draining water from a cryogen gas conduit comprising -a cryogen gas conduio_ (14) arranged to provide an egress path for cryogen gas from a cryostat, said conduit having a gas inlet end and a gas outlet end; provided with a drain hole (220) on an underside of the cryogen gas conduit (14), providing a further outlet to allow water to flow-through the drain hole, out of the cryogen gas conduit; a differential flow restrictor (60) arranged with a flow path (62) leading vertically or substantially vertically downward away from the drain hole, the differential flow restrictor acting to impede rapid fluid flow of gas at high differential pressure through C\I the flow path (62) away from the drain hole, while presenting little impediment to slow fluid flow of water under little differential pressure, along the CD 20 same flow path (62).LOC)J 2. An arrangement according to claim 1 wherein the flow path (62) is shaped to provide an unimpeded vertical path for drops of water from the drain hole (220).
3. 3. An arrangement according to any preceding claim, wherein the differential flow restrictor (60) is a directional flow restrictor arranged such that flow of water and of cryogen gas takes place in a reverse direction, vertically or substantially vertically downward away from the drain hole (220).