CA2800431A1

CA2800431A1 - Expansion tank with membrane thermal protection

Info

Publication number: CA2800431A1
Application number: CA2800431A
Authority: CA
Inventors: Jean Pichette
Original assignee: 2440644 Canada Inc
Current assignee: LES SOLUTIONS CALEFACTIO Inc
Priority date: 2012-01-05
Filing date: 2012-12-20
Publication date: 2013-07-05
Also published as: US20130180993A1

Abstract

An expansion tank for accommodating hot expanded fluid in a heat transfer fluid system has a tank body defining an internal volume. A fluid inlet is provided on the tank body for connection to the heat transfer fluid system. A membrane, such as a diaphragm or a bladder, divides the internal volume into first and second sections. The first section includes a buffer zone between the fluid inlet and the membrane.
The buffer zone contains a predetermined volume of tempering fluid for cooling down the incoming hot expanded fluid at its entry in the expansion tank. The buffer zone has an air valve for venting air from the buffer zone while the buffer zone is being filled up with the tempering fluid. The second section on the opposed side of the membrane is maintained under pressure with a gas.

Description

EXPANSION TANK WITH MEMBRANE THERMAL PROTECTION
TECHNICAL FIELD
The application relates generally to heat transfer fluid systems and, more particularly, to expansion tanks suited for use in such systems.
BACKGROUND OF THE ART
It is well know to use expansion tanks in closed looped heat transfer fluid systems to accommodate increases in volume resulting from the temperature rise of non-compressible heating fluids, such as water, glycol, glycerine and propylene glycol solutions. Such expansion tanks allow controlling the system operating pressure by providing to the expanded heating fluid a place to go.
Commercially available expansion tanks typically comprises two half-shell members adapted to be assembled together to define an internal volume. A
membrane, which may be provided in the form of a diaphragm or a bladder, divides the internal volume of the tank in two sections. A first section of the tank has a heating fluid inlet connected to the pipe network of the system for accommodating the extra volume of heating fluid created by thermal expansion. The second section of the tank, sometimes referred to as the dry side, contains a compressible gas (e.g. air) under pressure. When the heating fluid is heated, it expands. The expended heating fluid enters the first section of the expansion tank. As the heating fluid pressure increases, it pushes the internal membrane against the pressurized gas on the dry side of the membrane, thereby compressing the gas.
When such an expansion tank is used in a high temperature system, such as a solar heating system, the heating fluid may reach temperatures which are potentially higher than the maximum temperature that can be withstood by the membrane.
This may result in damages to and premature wear of the membrane.
Therefore, there is a need to provide a new expansion tank arrangement wherein the internal membrane of the tank is protected from being exposed to temperatures which exceed the temperatures that can be withstood by the membrane.

DOCSMTL 4979677\1 SUMMARY
It is therefore an object to protect the membrane of an expansion tank from being damaged as a result of being exposed to excessive temperatures.
In one aspect, there is provided an expansion tank for accommodating hot expanded fluid in a heat transfer fluid system. The expansion tank comprises a tank body having an internal volume, a fluid inlet provided on the tank body and adapted to be connected to the heat transfer fluid system, a membrane for dividing said internal volume into first and second sections, said first section including a buffer zone between the fluid inlet and the membrane, the buffer zone containing a predetermined volume of tempering fluid for cooling down any incoming hot expanded fluid at its entry in the expansion tank, the buffer zone having an air valve for venting air from the buffer zone while the buffer zone is being filled up with the tempering fluid, the second section on the opposed side of the membrane being filled up with a pressurized fluid, the second section of the internal volume having a valve for allowing the second section to be maintained at a predetermined pressure.
In a second aspect, there is provided an expansion tank for use in a heat transfer fluid system, the expansion tank comprising a shell defining an internal volume, a membrane dividing said internal volume into a gas chamber and an expandable fluid receiving chamber, a fluid opening provided on said shell and communicating with said expandable fluid receiving chamber, a closable gas inlet provided on said shell and communicating with said gas chamber for allowing a pressurized gas to be directed and maintained under pressure in said gas chamber, a shell extension member mounted over one end of the shell to define therewith a thermal buffer chamber adapted to be filled with a tempering fluid, said thermal buffer chamber communicating with said expandable fluid receiving chamber via said fluid opening, an air valve provided on said shell extension member to allow air to be expelled from the thermal buffer chamber while the same is being filled up with the tempering fluid, and an inlet port provided on the shell extension member and connectable to the heat transfer fluid system, the thermal buffer being disposed between the inlet port and the fluid opening of the first shell member, whereby hot expanded fluid from the system mixes with the tempering fluid contained in the thermal buffer chamber at its entry in the expansion tank, the hot expanded fluid being cooled down by the tempering fluid.
In accordance with a still further general aspect, there is provided an expansion tank suitable for any heat transfer fluid system, filled or to be filled with potable water, glycol, a mix of water and glycol, or else. The tank can be of any volume and its construction can be of metal, plastic or equivalent and its finish may be epoxy paint, electrostatic paint powder, regular paint, or equivalent. The tank may have a Schrader-type valve or a ball valve to let air out of a first buffer section thereof when the same is being filled with a tempered or cooling fluid. The volume of the first buffer section is determined as a function of the fluid temperature, the volume being bigger when temperature is higher and smaller when the temperature is lower.
Heat exchange promoting structures, such as metal fins, may be provided on the first section of the tank to more efficiently release heat from the "cooling" fluid filling the first section of the tank. The first section may also be provided with a diffuser adapted to be connected to the heating system for homogeneously diffusing any hot expanded fluid coming from the system into the tempered cooling fluid present in the first section of the expansion tank. In the first section, the hot expanded fluid mixes with the tempered fluid and is thus cool down to an acceptable temperature. The tank has a second section connected in fluid flow communication with the first section to receive the cooled expanded fluid. The second section is separated from a third section by a membrane, such as a bladder, a diaphragm or a bladder-type diaphragm, which may be made of EPDM, butyl or any equivalent material. The third section contains a pressurized gas against which the membrane may deflect to accommodate the expanded fluid. The third section is provided with a Schrader-type valve, a ball valve or any other suitable valve to pre-charge the expansion tank at a desired pressure.
Further details of these and other aspects of the present invention will be apparent from the detailed description and figures included below.

DESCRIPTION OF THE DRAWINGS
Reference is now made to the accompanying figures, in which:
Fig. 1 is a partial cross-section of an expansion tank in accordance with an embodiment of the present invention; and Figs. 2a to 2c are cross-section views illustrating the installation and the operation of the expansion tank shown in Fig. 1.
DETAILED DESCRIPTION
Fig. 1 illustrates an expansion tank 10 suited for use with high temperature fluid heating systems, such as solar heating systems. The expansion tank 10 is configured to accommodate the expansion of the fluid in the system when the same is heated. The expansion tank 10 provides a place for the expanded fluid to go.
The fluid may be water, glycol, a mixture of water and glycol or any other fluids that may be used in a heating system.
The expansion tank 10 generally comprises first and second half-shell members 12 and 14 assembled together such as by welding or other suitable techniques. The first and second shell members 12 and 14 may form a generally cylindrical housing. The shell members 12 and 14 may be made out of plastic, metal or any suitable materials. The first and second shell members 12 and 14 define therebetween an internal volume of the expansion tank 10. As known in the art, a flexible elastomeric membrane 16 divides the internal volume of the expansion tank 10 into a heating fluid chamber 18 and a pressurized gas chamber 20. According to the illustrated embodiment, the flexible membrane 16 is provided in the form of a bladder. However, it is understood that the membrane could take various forms.
For instance, it could consist of an elastomeric diaphragm. According to the illustrated embodiment, the bladder 16 may be made out of rubber, EPDM, butyl or other suitable materials. As shown in Fig. 1, the bladder 16 may me mounted at one end thereof to a mounting flange 22 surrounding a central inlet hole 24 defined in the end wall of the first shell member 12. Bolts 26 or other suitable fasteners may be used to removably install the bladder 16 in the internal volume of the expansion tank.
The bladder 16 could also be permanently attached to the first shell member 12. A
valve 28 is mounted to the opposed end wall of the second shell member 14 of the tank 10 for allowing the gas chamber 20 to be filled with a gas under pressure. The valve 28 could be provided in the form of a Schrader-type valve or a ball valve. It is understood that other types of valves could be used as well. A cap 30 may be provided on the outer surface of the end wall of the second shell member 14 to protect the valve 28.
In order to prevent the expanded fluid from coming into direct contact with the bladder 16, it is herein proposed to install a third shell member 32 over the first shell member 12 to form therewith a buffer chamber 34 adapted to be filled with a "cooling" fluid that will mix with the incoming hot expanded fluid and thus cool the same to a temperature which is below the temperature that the can be withstand by the bladder 16. The third shell member 32 can be viewed as an extension shell member into which the cylindrical housing of the tank is nested. The third shell member 32 can be welded or otherwise suitably joined to the first shell member 12.
As shown in Fig. 1, an air valve 36 is provided on the end wall of the third shell member 32 for venting air from the buffer chamber 34 while the same is being filled up with the cooling fluid. The cooling fluid may be the same fluid as in the heat transfer system but maintained at a lower temperature, typically at room temperature.
In some applications, the cooling fluid could be different from the heating fluid of the system in which the expansion tank is installed. The temperature and volume of cooling fluid is selected to provide a generally tempered fluid body which will effectively lower the temperature of the hot expanded fluid which intermittently flows into the expansion tank 10 to a temperature which is below the maximum temperature that the bladder 16 can withstand. Accordingly, the sizing of the buffer chamber 34 is function of the temperature of the expanded fluid and of the volume of expanded fluid to be accommodated in the fluid chamber 18. Heat promoting structures (not shown), such as fins, may be provided on the outer surface of the third shell member 32 to accelerate the release of heat from the body of fluid contained in the buffer chamber 34.

A fluid inlet 38 adapted to be connected to the fluid heating system is provided on the end wall of the third shell member 32. The fluid inlet 38 may include a diffuser 40 to uniformly diffuse the incoming hot expanded fluid into the body of cooling fluid contained in the buffer chamber 34. A fitting or connector 42 is provided at the outer distal end of the diffuser 40 for connection with a mating connector mounted in a line of the system. The diffuser 40 may be removably bolted or welded on a mounting flange 44 surrounding the inlet 38 of the third shell member 32. In this way, the diffuser 40 and the connector 42 may be readily removed to provide easy access to the bladder 16 and the flange 26 to which it is mounted.
However, it is understood that the whole assembly could be welded to provide a permanently attached diaphragm and a fixed buffer chamber with a welded connection; no part being removable.
Referring now to Figs. 2a to 2c, we will now describe the installation and operation of the expansion tank 10. First, the expansion tank 10 is connected via connector 42 to the piping network N of the system as shown in Fig. 2a. The valve 28 at the bottom end of the second shell 14 is connected to a source of pressurized gas (e.g. air) and is then opened to pressurize the gas chamber 20 to a predetermined pressure. Once the desired pressure is reached, the valve 28 is closed. In this initial stage of the installation, the bladder 16 is in a collapsed state as shown in Fig. 2a.
Thereafter, the piping network N of the system is filled with the heating fluid (e.g.
glycol solution) as schematically depicted by the dash lines in Fig. 2a. The filling operation of the piping network N is typically carried on at room temperature.
The air valve 36 provided at the top of the buffer chamber 34 is opened to allow air to be expelled out of the buffer chamber 34 and to, thus, allow ingress of the tempered heating fluid into the buffer chamber 34. The tempered fluid present in the buffer chamber 34 as schematically depicted in Fig. 2b, will serve as a body of cooling fluid to cool down any incoming hot expanded fluid at its entry in the expansion tank 10. The pressure exerted by the pressurized gas in the gas chamber 20 against the bladder 16 maintains the bladder in its collapsed state during the filling operation of the buffer chamber 34, thereby preventing the tempered fluid from flowing into the bladder 16. Once the buffer chamber 34 has been full up, the air valve 36 is closed.
The system may then be operated. In use, when the heating fluid is heated, it expands and the expanded fluid flows into the expansion tank 10, thereby causing the bladder 16 to inflate in order to accommodate the expansion of the fluid in the system.
At its entry in the expansion tank 10, the hot expanded fluid is cooled down by the cooling fluid already present in the buffer chamber 34. The hot expanded fluid is cooled down to a temperature which is inferior to the limit temperature that can be sustained by the bladder. The buffer chamber 34 thus allows protecting the bladder from being exposed to excessive temperature.
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. For example, the first and second shells could for instance be replaced by a one-piece hollow container body.
Such a one-piece construction container body could be blow molded. Also it is understood that while the buffer chamber as been shown as being provided at the upper end of the tank, the expansion tank could be installed upside down wit the buffer chamber at the bottom of the tank. It is understood that in such an inverted installation, the air valve 36 would be repositioned such as to remain at the upper end of the buffer chamber.
Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

Claims

1. An expansion tank for accommodating hot expanded fluid in a heat transfer fluid system, the expansion tank comprising a tank body having an internal volume, a fluid inlet provided on the tank body and adapted to be connected to the heat transfer fluid system, a membrane mounted within said tank body for dividing said internal volume into first and second sections, said first section including a buffer zone between the fluid inlet and the membrane, the buffer zone containing a predetermined volume of tempering fluid for cooling down any incoming hot expanded fluid at its entry in the expansion tank, the buffer zone having an air valve provided at an upper end thereof for venting air from the buffer zone while the buffer zone is being filled up with the tempering fluid, the second section on the opposed side of the membrane being filled up with a pressurized fluid, the second section of the internal volume having a valve for allowing the second section to be maintained at a predetermined pressure.

2. The expansion tank defined in claim 1, wherein the tank body comprises first and second shell members, each of said first and second shell members having an end wall and a tubular side wall, said first and second shell members being assembled together with respective end walls in opposed facing relationship, and wherein the tank body further comprises a third shell member installed over said first shell member, said buffer zone being defined between said third and first shell members, the second section of the internal volume being bounded by the membrane, the first shell and the second shell.

3. The expansion tank defined in claim 2, wherein the fluid inlet and the air valve are both provided on said third shell member, and wherein the membrane is provided in the form of a bladder mounted in an inlet hole defined in the end wall of the first shell member, the bladder being in fluid flow communication with the buffer zone and expandable in the second section of the internal volume between the first and second shell members.

4. The expansion tank defined in claim 2, wherein the valve for maintaining the second section at a predetermined pressure is mounted to one of the first and second shell members.

5. The expansion tank defined in claim 1, wherein the fluid inlet includes a diffuser for diffusing incoming hot expanded fluid into the tempering fluid contained in the buffer zone.

6. The expansion tank defined in claim 1, wherein the tank body comprises a generally cylindrical housing having a side wall and opposed end walls, and a shell member having one end wall and a side wall extending from the end wall, the shell member being mounted over the housing, the buffer zone being defined between the shell member and the housing, the membrane being mounted within the housing and communicating with the buffer zone via an opening defined in one of the end walls of the housing.

7. An expansion tank for use in a heat transfer fluid system, the expansion tank comprising a shell defining an internal volume, a membrane dividing said internal volume into a gas chamber and an expandable fluid receiving chamber, a fluid opening provided on said shell and communicating with said expandable fluid receiving chamber, a closable gas inlet provided on said shell and communicating with said gas chamber for allowing a pressurized gas to be directed and maintained under pressure in said gas chamber, a shell extension member mounted over one end of the shell to define therewith a thermal buffer chamber adapted to be filled with a tempering fluid, said thermal buffer chamber communicating with said expandable fluid receiving chamber via said fluid opening, an air valve provided on said shell extension member to allow air to be expelled from the thermal buffer chamber while the same is being filled up with the tempering fluid, and an inlet port provided on the shell extension member and connectable to the heat transfer fluid system, the thermal buffer being disposed between the inlet port and the fluid opening of the first shell member, whereby hot expanded fluid from the system mixes with the tempering fluid contained in the thermal buffer chamber at its entry in the expansion tank, the hot expanded fluid being cooled down by the tempering fluid.

8. The expansion tank defined in claim 7, wherein the volume of the thermal buffer section is sufficient to cool down the hot expanded fluid to a temperature which is inferior to a maximum temperature that the membrane is able to withstand.

9. The expansion tank defined in claim 7, wherein the shell comprises first and second shell members, each of said first and second shell members having an end wall and a tubular side wall, the first and second shell members being assembled together with respective end walls in opposed facing relationship.

10. The expansion tank defined in claim 9, wherein the fluid opening is defined in the end wall of the first shell member, and wherein the shell extension member is mounted over the first shell member.

11. The expansion thank defined in claim 7, wherein the air valve is disposed at an upper end of the thermal buffer chamber.

12. The expansion tank defined in claim 7, wherein the fluid inlet includes a diffuser for diffusing incoming hot expanded fluid into the thermal buffer chamber.

13. The expansion tank defined in claim 7, wherein the membrane is provided in the form of a bladder extending from said fluid opening, the bladder being in fluid flow communication with the thermal buffer chamber.