GB2076133A - A respiratory heat exchanger for low temperature environments - Google Patents

Abstract

A cylindrical respiratory counter current heat exchanger comprises a first spiral passageway 14 having an inlet 38 for gas to be inspired and an outlet 34 for delivering gas to a user, a second spiral passageway 16 in heat exchanging relationship to the first spiral passageway, said second spiral passageway having an inlet 36 for receiving expired gas from the user and having an outlet 40 through which said expired gas may be exhausted from the exchanger. The heat exchanger is made from two sheets of copper 10, 12 wound in a spiral, and sealed at the ends with rubber spacing strips. The heat exchanger may find use in survival garments for cold climates or in deep sea diving apparatus. <IMAGE>

Description

SPECIFICATION A respiratory heat transfer unit for low temperature environments This invention relates to survival at low temperatures and more particularly means for conserving body heat to prevent hypothermia.

Many devices have been proposed to conserve or supplement body heat so as to prevent hypothermia. Such proposals usually comprise some sort of covering for the body which may be equipped with heating means, whereby heat losses from the skin are reduced.

In diving a much more difficult problem arises in the case of respiratory heat loss which is more serious for two reasons. Firstly, the breathing mixture has a high thermal capacity by virtue of the high pressures at which a diver in a bell may be exposed to hypothermia and therefore represents a potential thermal loss which can easily exceed metabolic heat production and can far exceed cutaneous heat loss. Hence it is now mandatory to warm the inspired breathing gas when diving to depths in excess of 1 50 m. The second reason is the intimate contact which the lungs provide between the inspired gas and the whole circulating blood volume, i.e. the body is now being cooled at its core.The lung is ideal for its primary purpose of oxygenating blood but this represents the worst configuration from the viewpoint of heat conservation, since gas-cooled blood now cools vital organs which cannot function under thermal gradients of the magnitude tolerated by skin and the underlying tissues.

During diving, moreover, the layer of non-tidal gas separating warm blood from each cold inspired breath is now largely compressed helium - a very much better heat conductor than air at normal pressure at which the lung evolved. These considerations make it most desirable to design a breathing gas device for emergency use when the power supply to a diving bell has failed as could occur if the umbilical is severed. Although the problem of respiratory heat loss is not as acute in the case of submersibles immobilised in cold water, such a device could also help in the survival of the crew until rescued. Similar problems arise at normal pressures and with cold climatic conditions and this unit will be of benefit in such situations.

The present invention has been made with these considerations in mind.

According to the invention there is provided a respiratory heat transfer unit comprising a first spiral passageway having an inlet for cold gas to be inspired and an outlet for delivering gas to the user, a second spiral passageway in heat exchanging relationship to the first spiral passageway, said second spiral passageway having an inlet for receiving expired gas from the user and having an outlet through which said expired gas is exhausted from the unit.

In a preferred embodiment of the invention the turns of the first spiral are interposed between the turns of the second spiral so that heat from expired gas is transferred through the wall dividing the second passageway from the first passageway and the incoming gas is heated. Preferably the inlet for the first passageway is provided at the radially outermost turn of the first passageway and the outlet for the first passageway at the radially innermost turn thereof. The arrangement is reversed in the second passageway with the inlet at the radially innermost turn and the outlet at the radially outermost turn.

The respiratory heat transfer unit of the invention could advantageously be used in combination with a heater adapted to preheat breathing gas admitted to the respirator inlet that is to say that the inlet to the first passageway.

Preferably the heater is of the kind described in United States Patent No. 3809526 which provides heat by controlled combustion of a charcoal fuel element, the heat so generated being distributed by means of a fan.

In a further embodiment of the invention the heater could be combined with a garment made of heat insulating material. A particularly preferred kind of material is a laminate such as described in our British Patent Application No.31226/75 (Serial No. ). The garment may be in the form of a bag which totally encloses the wearer save for his face. The bag is provided with an external pouch which receives the heater. It is particularly preferred to provide a CO2 absorber in the pouch to which the inlet to the respiratory unit can be connected by appropriate valve means.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a side elevation of a respiratory heat transfer unit; Fig. 2 is a diagrammatic transverse section on an enlarged scale through the unit of Fig. 1; Fig. 3 is a detail showing a vertical section along the line A-A' of Fig. 2; Fig. 4 is a perspective view of a survival bag; and Fig. 5 is a longitudinal section through the bag of Fig. 4.

Referring to Figs. 1 to 3 the respiratory heat transfer unit is formed from two sheets 10 and 12 of material of good thermal conductivity, for example copper, held substantially parallel to each other and wound in a spiral, thereby defining a first spiral passageway 14 and a second spiral passageway 1 6. The wound sheets 10 and 12 form a cylinder 1 8 as illustrated in Fig. 1 the top and bottom of which is closed by covers 20 and 22. Clamps 28 and 30 holds the covers in position. A spacing strip 24 (Fig. 3) surrounds the longitudinal edge portion of each sheet 10 and 12.

These spacing strips 24 maintain the spaced apart relationship of the sheets when wound into a cylinder and also seal the edges of the passageways. Preferably the strips 24 are made of resilient material such as rubber of relatively low thermal conductivity to minimize heat losses therethrough.

A divided tube 32 extends through cover 22 and is connected to the innermost ends of passageways 14 and 16. Valves 34 and 36 are provided in the tube 32 which confine flow of breathing gas through passageway 14, in the direction of the arrows, from the inlet 38 at the radially outer side of the assembly towards the middle thereof and flow of air through passageway 1 6 in the opposite direction from the centre of the assembly to the exhaust outlet 40.

The unit just described is, in effect, a counter current heat exchanger. In use tube 32 is connected to a mouth piece (not shown) which the user fixes on his face for example by straps.

Cold breathing gas inspired through inlet 38 is heated as it travels along passageway 14 by warm exhaled breathing gas passing along passageway 16. The heat recovery obtained with an assembly of 6 inches diameter and height 8 inches with sheets 10 and 12 formed of copper foil amounts to from 95 to 98%.

The respiratory heat transfer unit according to the invention has many applications but is particularly adapted for use in cold environments such as diving bells. One form of such application will now be described with reference to Fig. 4 and 5.

A hypothermia bag made of laminated heat insulating material such as described in our British Patent Application No.31226/75 (Serial No.

) is formed with a pouch 52. The pouch contains a heater 54 of the kind described in U.S.

Patent No. 3809526 which generates heat by controlled combustion of charcoal. Heat from the heater is urged into the hypothermia bag through an opening 54 by a fan included in the heater assembly. The pouch also contains a soda-lime CO2 absorber 56. The absorber is connected to a mouthpiece 58.

In normal use the breathing gas is inspired through the soda lime absorber. Absorption by soda lime of CO2 is exothermic so that under normal operating conditions breathing gas drawn through the soda lime absorber is heated.

However absorption of CO2 by soda lime is temperature sensitive. If therefore the ambient temperature falls, as may happen in a diving bell if the umbilical to the surface is damaged, the soda lime absorber may stop working added to which there is no heat of absorption to benefit the user.

In such circumstances or indeed in any circumstances when heated breathing gas is not available, breathing gas is inspired by appropriate switching of a valve (not shown) through respiratory unit 60 of the kind as has been described with reference to Figs. 1 to 3 in order to conserve body heat.

In an assembly such as described with reference to Figs. 4 and 5, it is also possible to divert heat from the heater to heat breathing gas inspired by the user. Moreover the heater can also be used, where necessary to heat the soda lime absorber sufficiently to maintain its absorptive function.

Claims (6)

1. A respiratory heat exchanger comprising a first spiral passageway having an inlet for gas to be inspired and an outlet for delivering gas to a user, a second spiral passageway in heat exchanging relationship to the first spiral passageway, said second spiral passageway having an inlet for receiving expired gas from the user and having an outlet through which said expired gas may be from the exchanger.

2. A respiratory heat exchanger according to Claim 1 wherein the turns of the first spiral passageway are interposed between the turns of the second spiral passageway.

3. A respiratory heat exchanger according to Claim 2 wherein the inlet and outlet for the first spiral passageway are located respectively at the radially outermost and the radially innermost turns of the first spiral passageway and inlet and outlet for the second spiral passageway are located respectively at the radially innermost turn and the radially outermost turns of the second spiral passageway.

4. A respiratory heat exchanger as claimed in any preceding Claim in conjunction with a garment provided with a heater.

5. A respiratory heat exchanger as claimed in any of Claims 1 to 3 in conjunction with the breathing gas of a diving apparatus.

6. A respiratory heat exchanger substantially as hereinbefore described with reference to any of Figs. 1 to 5 of the accompanying drawings.