GB2084728A - Thermal systems - Google Patents

Abstract

A thermally-responsive sealed system comprises a cylindrical phial secured to an expansible capsule by a length of capillary tube. The whole system is sealed and contains mercury and a bubble of incondensable gas, e.g. nitrogen. The bubble is introduced by placing the filled but unsealed system in an atmosphere of the gas, displacing a predetermined amount of the mercury and sealing the system in the gas atmosphere. The presence of the bubble eases the vaporisation of the mercury by reducing surface tension effects.

Description

SPECIFICATION Thermal systems This invention relates to thermally-responsive sealed systems containing a charge of liquid the pressure of which increases with increased temperature. Such systems are commonly nominally filled with a charge of mercury, which, when heated, vapourises locally so increasing the pressure.

Commonly systems of this kind, as described in our Patent No. 1,344,260, comprise a phial connected to an expansible chamber by a length of capillary tube, the whole being nominally filled with mercury and sealed. The phial is then placed to sense a varying temperature. One problem met is that there may be an oscillation set up in the mercury between the phial and the expansible chamber which leads to fatigue of the materials. It is now theorized that this oscillation is due to surface tension effects opposing the local vaporisation so that the temperature has to be increased above the normal boiling point before the surface tension is overcome and the mercury separates into two columns with a vapour bubble formed therebetween. This results in a sudden boiling at the heated point and a rapid increase in the fluid pressure exerted in the expansible chamber.The vapour/ liquid interface then moves quickly to a cooler position resulting in a converse effect of rapid cooling and the sudden reduction in effective vapour pressure and the coming together of the surfaces of separation. This sequence is then repeated causing the oscillation.

The invention provides a thermally-responsive sealed system filled with mercury having a bubble of incondensable gas introduced into the mercury to maintain a permanent separation of the mercury into two columns thereby easing the vaporisation of the mercury.

The effect of this is to provide a cushioning effect on the returning mercury so that the two columns do not combine to form a continous column and the surface tension effect is avoided.

The gas is preferably an inert gas such as nitrogen or a mixture of gases in which the inert gas is a major constituent.

The invention according to another aspect provides a method of producing a thermally-responsive sealed system as set forth above, comprising the steps of preparing a phial with an open end secured to a capillary tube which is secured to an expansible chamber, locating the system with the open end of the phial uppermost, filling the system with liquid mercury, placing it in an atmosphere of the incondensable gas, inserting a rod or the like into the open end of the phial so as to displace a predetermined volume of the liquid mercury, removing the rod so that a similar volume of the gas enters the phial, and sealing the open end of the phial.

A specific embodiment of the invention comprises a generally cylindrical phial having a length of capillary tube secured to one end. The other end of the capillary tube leads into an expansible capsule of the kind formed from two flexible diaphragms secured together about their outer edges The whole system described is sealed and contains mercury and a bubble ofnitrogen gas or a mixture in which nitrogen is the major constituent. The bubble of gas is preferably such as to occupy about 1/8 inch of the length of the phial. It is found in practice that in this system the oscillations described above are not set up.

The method of introducing a measured volume of nitrogen gas into the mercury comprises preparing the empty system with the free end of the phial open. The system is inverted so that the open end of the phial is uppermost and mercury is introduced by placing the system in a vacuum to remove the air and then pouring the mercury into the phial. The system is then placed in a nitrogen atmosphere and a rod inserted into the phial to a predetermined level, the volume of the inserted part of the rod determining the amount of gas to be introduced. This spills the same volume of mercury from the phial so that when the rod is removed the surrounding nitrogen enters the phial. The open end of the phial is then sealed.

CLAIMS (Filed 1Sept1981) 1. A thermally-responsive sealed system filled with mercury and having a bubble of incondensable gas maintaining a separation of the mercury into two columns, thereby easing vaporisation of the mercury.

2. Athermally-responsive sealed system comprising a phial connected to an expansible chamber by a length of capillary tube, the system being filled with mercury and having a bubble of incondensable gas maintaining a separation of the mercury into two columns, thereby easing vaporisation of the mercury.

3. A system as claimed in claim 2, wherein said phial is cylindrical and said bubble occupies about 1/8 inch length of said phial.

4. A system as claimed in any of claims 1 to 3, wherein said gas is an inert gas or a mixture of gases in which the inert gas is a major constituent.

5. A system as claimed in claim 4, wherein said inert gas is nitrogen.

6. A method of producing a thermallyresponsive sealed system as claimed in any of claims 1 to 5, comprising the steps of preparing the system with an open end, filling the system with mercury, placing it in an atmosphere of the incondensable gas, inserting a rod or the like into the open end so as to displace a predetermined volume of the liquid mercury, removing the rod so that a similar volume of the gas enters the system and sealing the system while still in said atmosphere.

7. A method as claimed in claim 6, wherein said filling step comprises placing the system under vacuum and pouring mercury into the open end.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Thermal systems This invention relates to thermally-responsive sealed systems containing a charge of liquid the pressure of which increases with increased temperature. Such systems are commonly nominally filled with a charge of mercury, which, when heated, vapourises locally so increasing the pressure. Commonly systems of this kind, as described in our Patent No. 1,344,260, comprise a phial connected to an expansible chamber by a length of capillary tube, the whole being nominally filled with mercury and sealed. The phial is then placed to sense a varying temperature. One problem met is that there may be an oscillation set up in the mercury between the phial and the expansible chamber which leads to fatigue of the materials. It is now theorized that this oscillation is due to surface tension effects opposing the local vaporisation so that the temperature has to be increased above the normal boiling point before the surface tension is overcome and the mercury separates into two columns with a vapour bubble formed therebetween. This results in a sudden boiling at the heated point and a rapid increase in the fluid pressure exerted in the expansible chamber.The vapour/ liquid interface then moves quickly to a cooler position resulting in a converse effect of rapid cooling and the sudden reduction in effective vapour pressure and the coming together of the surfaces of separation. This sequence is then repeated causing the oscillation. The invention provides a thermally-responsive sealed system filled with mercury having a bubble of incondensable gas introduced into the mercury to maintain a permanent separation of the mercury into two columns thereby easing the vaporisation of the mercury. The effect of this is to provide a cushioning effect on the returning mercury so that the two columns do not combine to form a continous column and the surface tension effect is avoided. The gas is preferably an inert gas such as nitrogen or a mixture of gases in which the inert gas is a major constituent. The invention according to another aspect provides a method of producing a thermally-responsive sealed system as set forth above, comprising the steps of preparing a phial with an open end secured to a capillary tube which is secured to an expansible chamber, locating the system with the open end of the phial uppermost, filling the system with liquid mercury, placing it in an atmosphere of the incondensable gas, inserting a rod or the like into the open end of the phial so as to displace a predetermined volume of the liquid mercury, removing the rod so that a similar volume of the gas enters the phial, and sealing the open end of the phial. A specific embodiment of the invention comprises a generally cylindrical phial having a length of capillary tube secured to one end. The other end of the capillary tube leads into an expansible capsule of the kind formed from two flexible diaphragms secured together about their outer edges The whole system described is sealed and contains mercury and a bubble ofnitrogen gas or a mixture in which nitrogen is the major constituent. The bubble of gas is preferably such as to occupy about 1/8 inch of the length of the phial. It is found in practice that in this system the oscillations described above are not set up. The method of introducing a measured volume of nitrogen gas into the mercury comprises preparing the empty system with the free end of the phial open. The system is inverted so that the open end of the phial is uppermost and mercury is introduced by placing the system in a vacuum to remove the air and then pouring the mercury into the phial. The system is then placed in a nitrogen atmosphere and a rod inserted into the phial to a predetermined level, the volume of the inserted part of the rod determining the amount of gas to be introduced. This spills the same volume of mercury from the phial so that when the rod is removed the surrounding nitrogen enters the phial. The open end of the phial is then sealed. CLAIMS (Filed 1Sept1981)

1. A thermally-responsive sealed system filled with mercury and having a bubble of incondensable gas maintaining a separation of the mercury into two columns, thereby easing vaporisation of the mercury.

2. Athermally-responsive sealed system comprising a phial connected to an expansible chamber by a length of capillary tube, the system being filled with mercury and having a bubble of incondensable gas maintaining a separation of the mercury into two columns, thereby easing vaporisation of the mercury.

3. A system as claimed in claim 2, wherein said phial is cylindrical and said bubble occupies about 1/8 inch length of said phial.

4. A system as claimed in any of claims 1 to 3, wherein said gas is an inert gas or a mixture of gases in which the inert gas is a major constituent.

5. A system as claimed in claim 4, wherein said inert gas is nitrogen.

6. A method of producing a thermallyresponsive sealed system as claimed in any of claims 1 to 5, comprising the steps of preparing the system with an open end, filling the system with mercury, placing it in an atmosphere of the incondensable gas, inserting a rod or the like into the open end so as to displace a predetermined volume of the liquid mercury, removing the rod so that a similar volume of the gas enters the system and sealing the system while still in said atmosphere.

7. A method as claimed in claim 6, wherein said filling step comprises placing the system under vacuum and pouring mercury into the open end.

8. Athermally-responsive sealed system substantially as described hereinbefore.

9. A method of producing a thermallyresponsive sealed system substantially as described hereinbefore.