GB2095386A - Portable refrigeration equipment - Google Patents

Abstract

Portable refrigeration equipment which does not rely upon the existence of an electricity supply comprises first (11) and second (12) stainless-steel pressure vessels interconnected by stainless-steel pipework (13) and containing a body (17) of refrigerant-absorbent fluid such as ammonia/water solution. Pipework (13) comprises individual pipes (13A, 13B, 13C) inter-connected at boss (14) and a one-way valve (15) is provided in pipe (13A) which opens into vessel (11) at its upper end (11A) whereas pipe (13B) extends through the upper end of vessel (11) and opens at the lower end (11B) thereof. Pipe (13C) opens into vessel (12) at its upper end (12A) and is connected to a pressure-relief mechanism (16). In use when vessel (11) is heated whilst vessel (12) is cooled by a water jacket fluid is boiled off from body (17) causing valve (15) to open and transferal of the vapour along pipework (13) to the vessel (12) which, being externally cooled, causes the vapour to liquify. The internal pressure rises considerably during this process and may be monitored by a gauge or by action of the relief valve (16). Vessel (11) is then located in a cooling jacket and vessel (12) is surrounded by a medium to be refrigerated and simply left for a period of time. The medium becomes refrigerated due to volatilisation of the liquid body in vessel (12) and the vapour passes along pipe (13B) into the existing fluid body (17) in vessel (11) when absorption occurs. <IMAGE>

Description

SPECIFICATION Portable refrigeration equipment This invention relates to portable refrigeration equipment.

In the delivery of medical supplies, particularly vaccines, to remote parts of the world there is a need to maintain these supplies at an even temperature in the range 0-8"C. For the most part this is easily achieved where a supply of electricity is constantly available but there are many areas of the world where this is not the case.

It is an object of the present invention to provide portable refrigeration equipment which is simple to use and which does not rely upon the existence of an electricity supply.

According to the present invention there is provided portable refrigeration equipment comprising first and second pressure vessels interconnected by pipe means and containing a body of refrigerantabsorbent fluid, wherein said pipe means defines a first passageway containing a one-way valve permitting uni-directional fluid flow from said first to said second vessel and a second passageway permitting flow from said second to said first vessel, said first passageway opening adjacent the upper end of said first vessel and said second passageway opening adjacentthe lower end of said first vessel and said body of fluid being of such a volume that when entirely contained in said first vessel and in liquid form the liquid level thereof lies intermediate said first and second passageway openings, and said first and second passageways opening into said second vessel adjacent the upper end thereof.

Preferably said first and second passageways extend from said second vessel in a common pipe located adjacent the side wall of the second vessel proximal said first vessel.

Preferably also said common pipe incorporates a pressure relief mechanism. Said second passageway may be arranged to permit unidirectional or bidirectional flow of fluid between said first and second vessels.

The external surface of the second vessel conveniently incorporates a plurality of fins for enhancing the thermal transfer properties of the second vessel which fins may be formed integrally with the second vessel or mounted on a sleeve which is heat-shrunk onto the second vessel. The pipe means interconnecting the two vessels conveniently is surrounded by a heat shield to which handles are secured for transport of the equipment. Additionally the equipment comprises a fill plug whereby the body of fluid may be entered into the vessels. Conveniently the fill plug forms part of the pipe means.

Preferably the body of refrigerant-absorbent fluid is 35% by weight ammonia in water since at this level the ammonia content of the fluid is only slightly volatile at S.T.P. and so the equipment can be filled at ambient conditions. However a greater percentage of ammonia may be utilised if so desired and the equipment then filled under pressure. The fluid need not be a solution of ammonia in water as will become apparent. Other constituents with the required volatilisation and condensation or liquification properties would suffice.

The material used to form the pressure vessels is preferably stainless steel of 12 swg thickness (about 0.1 inches) as this gives a balance between pressure containment, corrosion resistance, thermal transfer properties and weight or portability.

In order to utilise the equipment of the present invention for refrigeration purposes the body of fluid is initially transferred to the first pressure vessel by pouring any that may be in the second vessel along the second passageway. The first vessel is then heated by means of a small fire or stove or the like causing volatilisation of part of the fluid body resulting in a pressure build-up within the first vessel. At the appropriate pressure the one way valve in the first passageway opens (preferably this occurs at a very low pressure) resulting in gaseous transfer into the second vessel which at this stage is externally cooled by means of a water jacket at a temperature of less than 40"C so that the gas entering the second vessel becomes liquefied.This process is continued for a time (e.g. 1 hour) whereafter the equipment is transferred so that the second vessel is surrounded by a medium to be refrigerated (usually water) and the first vessel is externally cooled by means or a water jacket at a temperature of less than 40"C.

Removal of the heat sourec and cooling of the first vessel together cause a rapid reduction in pressure within the equipment to a level below the volatilisation pressure of the liquid in the second vessel resulting in volatilisation thereof and transfer of the gas from the second vessel to the first vessel along the second passageway, the gas being reabsorbed in the fluid body within the first vessel and the latent heat required to volatilise the fluid in the second vessel being extracted from the medium to be refrigerated. In this way about 1 kg of ice can be made in about 2 hours and the water jackets used for cooling purposes result in heated water which can be used for various purposes.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which Fig. 1 shows a general arrangement of the principal components of the equipment according to the present invention; Fig. 2 illustrates the one-way valve of the equipment; Fig. 3 illustrates the finned sleeve of the equipment; and Fig. 4 illustrates the heat shield and handling arrangement of the equipment.

As shown in Fig. 1 the equipment 10 comprises a first stainless-steel pressure vessel 11 interconnected with a second stainless-steel pressure vessel 12 by means of stainless-steel pipework 13. Both vessels 11, 12 have domed ends to reducethether- mal mass of the vessels and pipework 13 extends between the upper ends 11 A, 1 2A of the vessels.

Pipework 13 comprises pipes 13A, 13B and 13C interconnected at boss 14 which incorporates a fill plug. Pipe 13A incorporates a one-way valve and opens into vessel 11 at its upper end 11A. Pipe 13B extends through the upper end 11A of vessel 11 and opens adjacent the lower end 11 B of this vessel. Pipe 13C opens into vessel 12 at its upper end 12Aand Zccordingly a first passageway is created between vessels 11, 12 by pipe 13C and pipe 13A and a second passageway is created by pipe 13C and pipe 13B, the first passageway being unidirectional because of the one-way valve therein and the second passageway being bidirectional.

A pressure relief mechanism 16 is mounted on pipe 13C for the purpose of ensuring that the internal pressure never exceeds a safe limit relative to the bursting strength of the vessels 11, 12 and the pipework 13. Conveniently components 11, 12 and 13 are manufactured to operate up to 1500 psi and mechanism 16 operates at 500 psi.

Within the equipment 10 there is a body 17 of refrigerant-absorbent fluid which, when entirely contained in vessel 11 and in liquid state has a liquid level 17A which is intermediate the openings into the first and second passageways so that between liquid level 17A and the one-way valve in pipe 13A is a closed volume the only outlet of which is via the one-way valve.

Fig. 2 illustrates the junction of pipes 13A, 13B and 13C at boss 14 and part of pipe 13A is shown in section to reveal the one-way valve 15. As illustrated valve 15 comprises a mount 15A welded in gas-tight manner two the interior of pipe 13A and incorporating a bore 15B defining a tepered valve seat 1 SC which is PTFE lined and against which a valve ball 15D is urged by a spring (not shown). The spring may be located in any convenient manner such as by a threaded collar secured to the mount 15A and operate to urge the ball 15D towards vessel 11 so that valve 15 only opens when the pressure within the closed volume above the liquid level 17A in vessel 11 exceeds the spring tension.The fill plug boss 14 in a screw-threaded fit and it will be evident that the illustrated arrangement permits easy replacement of worn components of the valve 15 since these are accessible via the fill plug aperture in boss 14.

Vessel 12 is externally clad with a finned sleeve 20 shown in Fig. 3 extending the full length of the cylindrical portion of the vessel, the sleeve being made of aluminium and provided for the purpose of enhancing the thermal transfer properties of vessel 12. Vessei 11 however has a relatively smooth external surface. Pipework 13 extends substantially in a single plane so that pipes 13A, 13B and 13C penetrates vessels 11, 12 on a respective diameter, with pipe 13C entering vessel 12 adjacent the side wall thereof so that prior to use of the equipment any fluid contained in vessel 12 can be poured back along pipes 13Cand 13B into vessel 11 and it is for the same reason that valve 15 is located in pipe 13A closely adjacent boss 14 and that pipe 13A lies intermediate pipes 13B and 13C.

Pressure relief valve 16 is located within a heat shield fabricated from plate metal (such as mild steel) and shown diagrammatically in Fig. 2. Shield 22 is secured to pipe 13C by clip fittings (not shown) and incorporates front and rear panels 22A, 22B which are held spaced apart on opposite sides of pipe 13C by plate spacers 22C so that the shield 22 forms a box-like structure with lateral openings 23 for venting any pressurised gas that may emerge from the relief valve 16. The shield 22 also comprises a housing 22E within which is located a pressure gauge coupled to pipe 1 3C such that the face of the gauge is visible at window 22F and from the lateral walls of housing 22E carrier handles 25 project whereby the equipment may be transported without injury to an operator even when the pipework 13 and the vessel 11 are in a heated state.

Shield 22 is asymmetric in that panels 22A, 22B have cutouts adjacent vessel 12 theses being so arranged that the panels 22A, 22B together act as a partial support for the equipment when in use.

In order to prepare the equipment for use the body 17 of refrigerant-absorbent fluid, preferably 35% ammonia by weight in water solution, is loaded into vessel 11 via the fill plug in boss 14. Air is displaced from the equipment so far as is possible by the action of vaporising ammonia which is heavier than air and the equipment is sealed by means of the fill plug. Vessel 12 is lifted above the level of vessel 11 to drain any fluid from vessel 12 as previously explained. The equipment is then mounted on a stand or other support structure so that a heat source can be played overthevesselil and vessel 12 can be located within a water jacket such as is provided by a volume of water within an open-top container.The applied heat causes ammonia to boil off from body 17 thereby opening valve 15 and transferring along pipe 13C into vessel 12.

Vessel 12, being externally cooled, causes the ammonia vapour to liquefy so that during the heating cycle liquid ammonia collects in vessel 12, the internal pressure in the equipment due to ammonia gas being within the range 30-300 psi depending upon the specific design of components which influence the rate of the volatilisation and liquification processes occurring simultaneously. When a sufficient body of ammonia is gathered in vessel 12 conveniently monitored by the pressure gauge reaching 300 psi the heating of vessel 11 is terminated. By means of the handles 25 the equipment is repositioned so that vessel 11 is located in a jacket of cooling water contained in an open-top container and vessel 12 is surrounded by a medium to be refrigerated.For the particular application for which the illustrated equiment has been designed this medium is water contained within a conventional vaccine carrier (i.e. about 4 litres capacity). Removel of the heat source together with application of the coolanttovessel 11 rapidly cause the pressure within the equipment to reduce to less than the vapour pressure of ammonia resulting in volatilisation of the liquid ammonia in vessel 12 and transfer of ammonia gas along pipes 13C and 13B into the fluid body 17 contained in vessel 11. At this stage in the process this body 17 is substantially water so that the gaseous ammonia is rapidly absorbed. However this absorption is aided by the pipe 13B extending below the level 17A of the fluid body 17 so that gaseous ammonia is constrained to have substantial transit time in the liquid before reaching level 17A if at all. The volatilisation process occurring in vessel 12 absorbs heat from the medium to be refrigerated and depending on the relative volume, temperatures and duration of this process the medium can be refrigerated into ice.

It will now be appreciated that the pressure in the volume above level 17Awithin vessel 11 provides the force required to unseat the ball valve 15. This force is partly counterbalanced by the liquid level within pipe 13B rising above that illustrated and for this reason the spring bias on the ball valve requires to be very light. In certain circumstances, depending principally upon the relative dimensions of pipe 13B and container 11 and fluid body 17 it may be sufficient to rely upon the weight of the ball alone in which case of course no spring is required in valve 15. In this case it becomes necessary to provide a ball retainer, such as a diametrical pin extending through mounting 15A or even pipe 13A. In order to simplify manufacturing tolerances as regards valve 15 it is acceptable to provide a one-way valve in pipe 13B opening so as to provide fluid flow into vessel 11 wherebythefluid head within pipe 13B no longer affects operation of valve 15. Of course, if such a valve is provided it may be installed by means of an arrangement similar two boss 14 and pipe 13B would then include a right angle.

Claims (10)

1. Portable refrigeration equipment comprising first and second pressure vessels interconnected by pipe means and containing a body of refrigerantabsorbent fluid, wherein said pipe means defines a first passageway containing a one-way valve permitting uni-directional fluid flow from said first to said second vessel and a second passageway permitting flow from said second to said first vessel, said first passageway opening adjacent the upper end of said first vessel and said second passageway opening adjacent the lower end of said first vessel and said body of fluid being of such a volume that when entirely contained in said first vessel and in liquid form the liquid level thereof lies intermediate said first and second passageway openings, and said first and second passageways opening into said second vessel adjacent the upper end thereof.

2. Equipment as claimed in claim 1, wherein said first and second passageways extend from said second vessel in a common pipe located adjacent the side wall of the second vessel proximal said first vessel.

3. Equipment as claimed in claim 2, wherein said common pipe incorporating a pressure relief mechanism.

4. Equipment as claimed in any one of claim 1-3, wherein said second passageway is arranged to permit unidirectional flow of fluid between said first and second vessels.

5. Equipment as claimed in any one of claims 1-3, wherein said second passageway is arranged to permit bidirectional flow of fluid between said first and second vessels.

6. Equipment as claimed in any preceding claim, wherein the external surface of the second vessel incorporates a plurality of fins for enhancing the thermal transfer properties of the second vessel.

7. Equipment as claimed in any preceding claim, wherein the pipe means interconnecting the two vessels is surrounded by a heat shield to which handles are secured for transport of the equipment.

8. Equipment as claimed in any preceding claim, wherein there is provided a fill plug forming part of said pipe means whereby the body of fluid may be entered into the vessels.

9. Equipment as claimed in any preceding claim, wherein the material used to form the pressure vessels is stainless steel of 12 swg thickness (about 0.1 inches).

10. Portable refrigeration equipment substantially as hereinbefore described with reference to the accompanying drawing.