GB2394538A

GB2394538A - Cooling of a subterranean cavity

Info

Publication number: GB2394538A
Application number: GB0320412A
Authority: GB
Inventors: Stephen Forbes Pearson
Original assignee: Star Refrigeration Ltd
Current assignee: Star Refrigeration Ltd
Priority date: 2002-08-30
Filing date: 2003-09-01
Publication date: 2004-04-28
Also published as: GB0320412D0; GB0220140D0

Abstract

A subterranean cavity 17, such as a railway tunnel 5 is cooled by apparatus 10 comprising a reservoir containing a vaporisable fluid 35 which has a first part 20 located within the cavity and a cooler second part 25 located outside the cavity. Fluid in the first part absorbs thermal energy from the cavity by vaporising and moving to the cooler second part, where it condenses. The condensed fluid may return to the first part of the apparatus by gravity or a liquid pump, and can be selected from ammonia, propane, propylene, tetrafluoroethane, carbon dioxide, R404A, R407C, R417A, or R410A fluids. The second and/or first part may include a plurality of fins 22, and the parts may include tubular portions. The second tubular portion may be between 5 and 50 meters in length, and 4 to 20 cm in diameter. The first and second part may be connected together via a flange 23 and gasket to form a closed and sealed unit.

Description

SUBTERRANEAN CAVITY COOLING

FIELD OF INVENTION

The present invention relates to an apparatus and method for cooling a subterranean cavity, for example, a 5 tunnel. BACKGROUND OF INVENTION

It may be desirable to cool an underground cavity in which there is liberation of heat from people and 10 machinery. For example, in the tunnels of the underground rail system in London, at high capacity the number of people and machinery is sufficient to raise the temperature within crowded coaches to around 35 C at humidities of over 90%. It is not a solution to provide air conditioning 15 within the coaches by conventional means because the heat rejected from the air conditioning systems would raise the temperature outside the coaches within the tunnel, thus exacerbating the problem.

Furthermore, refrigerating the air within the tunnels 20 by conventional mechanical methods, for example, rejecting the heat to ground water, would require the consumption of large amounts of electrical power. A further approach would be to pump ground water at a temperature of around 20 C through air coolers over which air from the tunnel 25 would be blown using fans. This method also would consume large amounts of power necessary to drive water pumps and fans, especially for a complete underground tunnel system.

It is an object of the present invention to mitigate the above mentioned problems and to cool an underground cavity in an energy-efficient manner.

5 SUMMARY OF INVENTION

Broadly speaking, the present invention relates to an apparatus and method for cooling a subterranean cavity by making use of a vaporizable fluid for absorbing thermal energy from inside the cavity and which vaporizes and moves 10 by convention to a location outside the cavity where the vapour condenses, and thus causes a transfer of thermal energy from inside the cavity to outside the cavity. The condensed fluid flows back under gravity.

According to a first aspect of the present invention 15 there is provided an apparatus for cooling a subterranean cavity, which comprises a fluid reservoir for containing a vaporizable fluid having a first part for location inside the cavity and a second part in fluid communication with the first part and adapted for location outside the cavity; 20 whereby, in use, fluid in the first part absorbs thermal energy and vaporizes and moves into the second part wherein condensation of the vapour occurs and the fluid returns to the first part under gravity, such as to transfer thermal energy from the inside of the cavity to the outside.

25 The vaporizable fluid may, for example, be any suitable fluid such as those used as refrigerants or coolants. Examples of such fluids which may be used singly or as mixtures are carbon dioxide (R744), ammonia

(R717), propane (R290), propylene (R1270), tetrafluoroethane (R134a CF3CH2F), R404A, R407C, R417A and R410A. The last four are mixtures as follows: R404A is 44% CHF2CF3/52% CH3CF3/4% CH2FCF3 5 R407C is 23% CH2F2/25% CHF2CF3/52% CH2FCF3 R417A is 44% CHF2CF3/52% CH2FCF3/4% CH(CH3) 2CH3 R410A is 50% CH2F2/50% CHF2CF3.

Typically the first part and/or the second part comprise first and second tubular portions, respectively.

lo Generally the first tubular portion is disposed substantially horizontally within the cavity, so as to provide a large heat absorbing surface. The second tubular portion may extend from the first portion at a point intermediate the ends of the first portion.

15 In a particularly preferred embodiment, one or a plurality of second tubular portions extend outwardly from the first portion (and in fluid communication therewith) into the surroundings outside the cavity. Each second tubular portion generally extends at an angle of 10-90 to 20 the length of the first tubular portion, and is usually perpendicular thereto. Typically, each second tubular portion has a length of 500cm to 5000cm and a diameter of 4cm to 20cm.

The second tubular portion extends outside the cavity 25 and into the surrounding subterranean matter, for example, earth, soil or clay. The second tubular portion will be arranged to allow flow of condensed fluid back into the first part. This may be typically achieved by positioning

the second tubular portion such that it slopes upwardly away from the first part, typically at an angle of 10 to Doo (e.g., from 40 to 60 ) to the horizontal. It may be easily installed by drilling into the wall of the cavity.

5 Alternatively, a small liquid pump may be used to circulate the condensed fluid if natural convection is not possible. The first and/or second parts may include at least one member extending from a surface thereof such that the 10 surface area is increased, so as to improve heat transfer from the surroundings. Typically such members comprise a plurality of fins, to provide an enlarged heat exchange surface. The interior of the first part may alternatively or 15 additionally have a surface suitable to enhance vaporization of the fluid contained therein, for example by providing a surface of particles or projections which may act as vapour nucleation sites, e.g., a sputtered metal coating. 20 Typically the first and second parts are formed of a metal or metal alloy. A corrosion-resistant coating may be provided.

According to a second aspect of the present invention, there is provided a subterranean cavity provided with at 25 least one such apparatus according to the first aspect of the present invention.

Typically the subterranean cavity will be provided with a plurality of cooling apparatuses, arranged at intervals along the cavity wall. One important practical advantage of this is that accidental leaks from individual 5 cooling apparatuses do not affect the whole system and these leaks may be easily detected.

The subterranean cavity may be any cavity which is used to house or transport people or machinery, e.g., a mine, cavern, basement or tunnel.

10 The tunnel may include a rail track for use in transporting people.

According to a third aspect of the present invention, there is provided a method of cooling a subterranean cavity comprising the steps of: 15 providing a fluid reservoir containing a vaporizable fluid and having a first part and a second part; locating the first part within the subterranean cavity; locating the second part outside the cavity; 20 whereby the vaporizable fluid is allowed to absorb thermal energy and vaporize and move from the first part and to condense in the cooler second part to cause a transfer of thermal energy from the inside of the cavity to the outside.

DETAILED DESCRIPTION

The present invention will now be described by way of example with reference to the accompanying drawings in which: 5 Figure 1 is a schematic cross-sectional view (not to scale) of a cooling apparatus according to an embodiment of the present invention installed within a tunnel; Figure 2 is a plan view of the apparatus.

Referring now to Figure 1, there is shown an 10 underground tunnel 5 with an apparatus 10 fitted through the wall 15 of the tunnel.

The cooling apparatus 10 is formed from a first part 20 which in this embodiment is a metal tube positioned substantially horizontally within the air of the tunnel 15 cavity 17. Typically, the first part 20 is cylindrical of length 50 to 5000cm and diameter 1 to 10cm and is provided with fins 22.

Connected to the first part 20 is a second part 25 which in this embodiment is a metal tube extending through 20 the tunnel wall 15 and into the surrounding ground 30. It is seen that the second part 25 is sloping to allow condensed vapour to flow under action of gravity.

The parts 20 and 25 are connected together via a flange 23 and gasket (not shown) to form a closed and 25 sealed unit.

The part 20 contains an amount of vaporizable fluid which is a measured quantity of refrigerant 35. The refrigerant charge within each unit would typically be 50

to lOOOml.

As shown in Figure 2 the apparatus 15 is constructed from a first tubular part 20 and a second tubular part 25 mounted substantially perpendicular to tube 20. Such a 5 unit allows the apparatus to be formed as a modular system for instalment within underground cavities to provide a particularly practical method of construction of the apparatus because the refrigerant charge within each unit would typically be small.

10 The tube 25 may be easily installed by drilling through the tunnel wall and inserting the tube. The tube 20 may then be fitted on to the flanged end of the tube 25 to form a sealed reservoir, which is then filled with a measured amount of liquid refrigerant.

15 In use, the metal tube 20 is disposed within the air in the tunnel cavity and may, if necessary, be located in a shallow recess within the tunnel wall. The tube 20 would thus be within the space between the tunnel wall and, for example, a train travailing within the tunnel. At right 20 angles to the tube 20 is the condenser tube 25 angled up into the surrounding soil or clay 30. The refrigerant would absorb thermal energy and evaporate from within the horizontal tube 20. The vapour produced would rise up the sloping tube 25 in the cool surrounding clay or soil, where 25 it would condense and return as liquid by draining down into the horizontal tube 20 under gravity. The vaporization and condensation cycle to produce refrigeration within the tunnel may then repeat.

The refrigeration cycle would thus cool the air within the tunnel. However, the cooling apparatus itself is passive and does not generate any additional heat.

The temperature of the soil or clay surrounding the 5 tunnel would typically be in the range of 15 C to 20 C during summer conditions. The tunnel air will often be at a temperature of 25-35 C and thus there is enough temperature difference between the tunnel air and the colder surroundings to drive the refrigeration cycle. It 10 can be seen that this system has no moving parts and consumes no power.

Air currents within the tunnel induced by, for example, train movements would improve the heat transfer from the tunnel air to the cooling apparatus. Furthermore 15 air circulation within train coaches could be promoted by fitting air intake scoops and filters to provide a flow of tunnel air through the coaches.

It may be clearly seen that such a system of tunnel cooling provides cool tunnel air without using additional 20 power either within the tunnel or in the trains passing within the tunnel.

It shall be understood that the aforementioned embodiments are not to be construed as limiting the present invention. For example, other embodiments may be envisaged 25 where only one, or more than two tubes 25 extend from each horizontal tube 20 and these tubes may not be arranged in a perpendicular manner.

Although the embodiment shown in Figures 1 and 2 shows one apparatus, it should be understood that several such cooling apparatuses could be installed at intervals (say, every one to ten metres) along the tunnel wall (and 5 possibly spaced around the periphery of the tunnel).

Claims

1. An apparatus for cooling a subterranean cavity, which comprises a fluid reservoir for containing a 5 vaporizable fluid having a first part for location inside the cavity and a second part in fluid communication with the first part and adapted for location outside the cavity; whereby, in use, fluid in the first part absorbs thermal energy and vaporizes and moves into the cooler second part 10 wherein condensation of the vapour occurs and the fluid returns to the first part, such as to transfer thermal energy from the inside of the cavity to the outside.

2. An apparatus according to claim 1 wherein the 15 vaporizable fluid is selected from carbon dioxide, ammonia, propane, propylene, tetrafluoroethane, R404A, R407C, R417A or R41OA.

3. An apparatus according to any preceding claim 20 wherein the second part comprises a second tubular portion.

4. An apparatus according to any preceding claim wherein the first part and the second part comprise first and second tubular portions, respectively.

5. An apparatus according to claim 3 or 4 wherein each second tubular portion has a length of 500 to 5000cm.

6. An apparatus according to claim 5 wherein each second tubular portion has a diameter of 4 to 20cm.

7. An apparatus according to any preceding claim 5 wherein condensed fluid returns to the first part under gravity.

8. An apparatus according to claim 1 wherein the second part comprises a second tubular portion which slopes lo upwardly away from the first part to allow flow of condensed fluid back into the first part.

9. An apparatus according to any of claims 1 to 6 which further comprises a liquid pump to return the 15 condensed fluid to the first part.

10. An apparatus according to any preceding claim wherein a plurality of fins are provided on the first part.

20

11. An apparatus according to claim 1 wherein the first and second parts comprise first and second tubular portions, which are provided with a plurality of fins.

12. An apparatus according to any preceding claim 25 installed in the subterranean cavity.

13. A method of cooling a subterranean cavity comprising the steps:

- providing a fluid reservoir containing a vaporizable fluid and having a first part and a second part; - locating the first part within the subterranean 5 cavity; and - locating the second part outside the cavity; whereby the vaporizable fluid is allowed to absorb thermal energy and vaporize and move from the first part and to condense in the cooler second part to cause a transfer of 10 thermal energy from the inside of the cavity to the outside.

14. A method according to claim 13 wherein the subterranean cavity is a railway tunnel.