Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
A HYDRAULIC ACCUMULATOR
Document Type and Number:
WIPO Patent Application WO/2017/089815
Kind Code:
A1
Abstract:
A hydraulic accumulator (1, 11) comprising a pressure vessel (2) having first and second chambers (6, 7) sealingly separated by a movable barrier (8); the first chamber (6) containing a first fluid; the second chamber (7) containing a second fluid; and a cooler (10) arranged in communication with the first chamber (6) and operable to solidify the first fluid in the first chamber (6).

Inventors:
RITCHIE, Charles (Blanawa, Corsekelly Place St CombsFraserburgh, Peterhead, Aberdeenshire AB43 8ZS, AB438ZS, GB)
Application Number:
GB2016/053707
Publication Date:
June 01, 2017
Filing Date:
November 25, 2016
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SCORE GROUP PLC (Glenugie Engineering Works, Peterhead Aberdeenshire AB42 0YX, AB42 0YX, GB)
International Classes:
F03G7/06; F15B1/02
Foreign References:
US4220006A1980-09-02
US5375983A1994-12-27
US20080245068A12008-10-09
US20050194054A12005-09-08
US20100270002A12010-10-28
EP0365011A21990-04-25
Attorney, Agent or Firm:
MURGITROYD & COMPANY (Scotland House, 165-169 Scotland Street, Glasgow Strathclyde G5 8PL, G5 8PL, GB)
Download PDF:
Claims:
CLAIMS:

1. A hydraulic accumulator comprising

a pressure vessel having first and second chambers sealingly separated by a movable barrier;

the first chamber containing a first fluid;

the second chamber containing a second fluid; and

a cooler arranged in communication with the first chamber and operable to solidify the first fluid in the first chamber.

2. A hydraulic accumulator as claimed in claim 1 , wherein in use the expansion of the first fluid on change of state from liquid to solid creates pressure that acts on the barrier which in turn energises the second fluid. 3. A hydraulic accumulator as claimed in claim 1 or claim 2, wherein the second chamber is connectable to a hydraulic line via a port for energising an external object.

4. A hydraulic accumulator as claimed in claim 3, wherein the port comprises a valve.

5. A hydraulic accumulator as claimed in claim 3 or claim 4, wherein the second fluid serves as a working fluid acting on the external object. 6. A hydraulic accumulator as claimed in claim 1 or claim 2, wherein the second fluid in the second chamber is the object to be pressurised.

7. A hydraulic accumulator as claimed in any preceding claim, wherein the movable barrier comprises a piston seal.

8. A hydraulic accumulator as claimed in any preceding claim, wherein the first fluid is water.

9. A hydraulic accumulator as claimed in claim 8, wherein one or more chemical additives is provided to change phase change temperature and pressure curve of the first fluid. 10. A hydraulic accumulator as claimed in claim 9, wherein the one or more additives includes a salt.

1 1. A hydraulic accumulator as claimed in any preceding claim, wherein the first fluid includes one or more materials selected from gallium, silicon, bismuth, plutonium, germanium, antimony.

12. A hydraulic accumulator as claimed in any preceding claim, wherein the cooler includes a vessel containing a cooling medium. 13. A hydraulic accumulator as claimed in claim 12, wherein the cooler includes a heat exchanger for transfer of heat between the first fluid and the cooling medium.

14. A hydraulic accumulator as claimed in claim 13, wherein the heat exchanger comprises a return pipe.

15. A hydraulic accumulator as claimed in claim 14, wherein the return pipe comprises a coil, located in or around the first chamber for accommodating and conveying the cooling medium. 16. A method of actuating a hydraulic accumulator, the method comprising the steps of:

a) providing a hydraulic accumulator comprising a pressure vessel having first and second chambers sealingly separated by a movable barrier;

the first chamber containing a first fluid;

the second chamber containing a second fluid; and

a cooler arranged in communication with the first chamber; and

b) allowing the cooler to solidify the first fluid in the first chamber and cause expansion of the first fluid thereby creating pressure on the barrier which in turn energises the second fluid.

17. A method of claim 16, wherein the method includes the step of connecting the second chamber to a hydraulic line via a port and energising an external object via the hydraulic line, wherein the second fluid serves as a working fluid acting on the external object.

18. A method of claim 16, wherein the method includes the step of using the second fluid in the second chamber as the object to be pressurised.

19. A method of any one of claims 16 to 18, wherein the method includes the step of super cooling the first fluid below its freezing point.

20. A method of claim 19, wherein the method includes the step of introducing a nucleation crystal into the first fluid.

Description:
A HYDRAULIC ACCUMMULATOR

FIELD OF THE INVENTION

The invention relates to a hydraulic accumulator.

BACKGROUND OF THE INVENTION

A hydraulic accumulator is a type of energy storage device which comprises a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. The hydraulic fluid is used to energise an external device. The external source can be a spring, a raised weight, or a compressed gas.

The most common type of hydraulic accumulators are compressed gas accumulators which use a pressurised gas to provide the energy to force hydraulic fluid at high pressure. The gas can be any suitable gas, but is normally nitrogen to minimise risks associated with the explosive nature of some other pressurised gases.

A compressed gas accumulator consists of a reservoir, also known as a pressure vessel, with two chambers that are separated by an elastic diaphragm, an enclosed bladder, or a floating piston. One chamber contains hydraulic fluid and is typically connected to a hydraulic line. The other chamber contains a gas under pressure, usually nitrogen, that provides the compressive force on the hydraulic fluid. As the volume of the compressed gas changes, the pressure of the gas and, accordingly, the pressure on the hydraulic fluid changes inversely. Existing designs are large and heavy due to the need for two storage tanks and do not have the high energy density needed for many applications. Furthermore, gas when pressurised rises in temperature and when it cools, a corresponding decrease in pressure happens. As a result charging of the accumulator can be a lengthy process where thermal equilibrium with ambient needs to occur before a set pressure can be achieved. In addition, the high temperatures generated can cause a material change in anything that is nearby. This is a particular challenge where bio- organisms or biological or genetic materials are involved, or indeed with any material that does not respond well to high temperatures, e.g. electronics, clothes, flammable objects or liquids. Additionally, a pressure port is required to inject and remove the pressure and the reservoir needs to be sufficiently thick and heavy to withstand the pressure. It is an object of the invention to obviate or mitigate the above drawbacks. SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a hydraulic accumulator comprising

a pressure vessel having first and second chambers sealingly separated by a movable barrier;

the first chamber containing a first fluid;

the second chamber containing a second fluid; and

a cooler arranged in communication with the first chamber and operable to solidify the first fluid in the first chamber.

The expansion of the first fluid on change of state from liquid to solid creates pressure that acts on the barrier which in turn energises the second fluid.

In one arrangement, the second chamber is connectable to a hydraulic line via a port for energising an external object. The port may comprise a valve. In this embodiment, the second fluid serves as a working fluid acting on the external object.

In another arrangement, the second fluid in the second chamber is the object to be pressurised. Accordingly, no port is required to be provided in the pressure vessel.

The movable barrier may comprise a piston seal. In principle, the movable barrier may be of any suitable type as would be apparent to a person skilled in the art.

The first fluid may be water, pure or with various chemical additives to change its phase change temperature and pressure curve. The additives may include salt in various concentrations. These additives also serve as a seed in the transition from liquid to solid.

Additional materials that expand when cooling from a liquid phase to a solid phase are gallium, silicon, bismuth, plutonium, germanium, antimony. Other compounds and chemicals that form spacious crystal lattices can also expand on freezing.

The cooler may include a vessel containing a cooling medium. The cooler may include a heat exchanger for transfer of heat between the first fluid and the cooling medium. In principle, the heat exchanger may be of any suitable type as would be apparent to a person skilled in the art. In one arrangement, heat exchanger may comprise a return pipe, such as, for example, a coil, located in or around the first chamber for accommodating and conveying the cooling medium.

One key limiting feature on the usability of such a device is the time taken to produce the phase change from liquid to solid. In the present invention this time is limited by setting predetermined values of relative difference in temperatures between the cooling medium and first fluid and their relative specific heat capacities, thermal conductivities of the cooling medium and the first fluid and intervening materials (e.g. the material of the pressure vessel), and specific heat of fusion of the first fluid.

Preferably, the cooling medium has a relatively high specific heat. This is desirable as the cooling medium absorbs the heat energy from the first fluid to cool it down to allow for a relatively controllable system. Preferably, the first fluid has a relatively low specific heat. This is desirable so that the first fluid can quickly get to its freezing point.

Preferably, any intervening materials (e.g. the material of the pressure vessel) have relatively high thermal conductivities. This is desirable to allow for efficient cooling of the material to change state.

Preferably, the first fluid has a relatively low specific heat of fusion.

It typically takes a long time to remove the heat energy necessary to produce a change in state, and this is largely due to the thermal conductivities and the practical offsets in temperature between the cooling medium and the material to be solidified.

In one arrangement, a material that can be super cooled below its freezing point can be employed as the first fluid. This is particularly advantageous where the generation of pressure is required in a short time, e.g. in a cell disruptor. When a phase change is required, a nucleation crystal can be introduced into the first fluid. This greatly reduces the time taken to produce the phase change. Examples of fluids that can be super cooled and that expand on freezing include water and gallium. According to a second aspect of the present invention, there is provided a method of actuating a hydraulic accumulator, the method comprising the steps of: a) providing a hydraulic accumulator comprising a pressure vessel having first and second chambers sealingly separated by a movable barrier;

the first chamber containing a first fluid;

the second chamber containing a second fluid; and

a cooler arranged in communication with the first chamber; and

b) allowing the cooler to solidify the first fluid in the first chamber and cause expansion of the first fluid thereby creating pressure on the barrier which in turn energises the second fluid.

In one arrangement, the method includes the step of super cooling the first fluid below its freezing point. The method may include the step of introducing a nucleation crystal into the first fluid. All essential, preferred or optional features or steps of one of the first aspect of the invention can be provided in conjunction with the features of second aspect of the invention and vice versa.

The invention provides a hydraulic accumulator and an associated method as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are described hereinafter with reference to the accompanying drawings in which:

Figure 1 is a side perspective schematic view of a hydraulic accumulator in accordance with the invention in accordance with one configuration;

Figure 2 is a cross-sectional perspective view of the apparatus of Figure 1 ;

Figure 3 is a front perspective view of the apparatus of Figure 1 ;

Figure 4 is a side perspective schematic view of a hydraulic accumulator in accordance with the invention in accordance with another configuration; and

Figure 5 is a cross-sectional side view of the apparatus of Figure 4.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures 1 to 5, a hydraulic accumulator apparatus in accordance with the invention is indicated generally by reference numerals 1 (Figures 1 - 3) and 11 (Figures 4 and 5). Apparatuses 1 and 1 1 are similar and for brevity common reference numerals have been used to denote common features of the apparatuses 1 , 11.

The hydraulic accumulator 1 , 1 1 comprises a pressure vessel 2 having first and second chambers 6, 7 sealingly separated by a movable barrier 8 provided in the form of a piston seal. In principle, the movable barrier 8 may be of any suitable type as would be apparent to a person skilled in the art. Although not shown in the drawings, the first chamber 6 contains a first fluid and the second chamber 7 contains a second fluid. A cooler 10 is arranged in communication with the first chamber 6 for solidifying the first fluid in the first chamber 36. The cooler 10 includes a vessel 12 containing a cooling medium (not shown) and a heat exchanger 14 for transfer of heat between the first fluid and the cooling medium. In principle, the heat exchanger may be of any suitable type as would be apparent to a person skilled in the art. The heat exchanger 14 comprises a coil 16 wound around the first chamber 6 for accommodating and conveying the cooling medium.

The expansion of the first fluid on change of state from liquid to solid creates pressure that acts on the barrier 8 which in turn energises the second fluid.

In the hydraulic apparatus 1 (Figures 1 - 3), the second chamber 7 is connectable to a hydraulic line 5 via a port 4, provided in the form of a valve, for energising an external object 9. In this embodiment, the second fluid serves as a working fluid acting on the external object 9.

In the hydraulic apparatus 11 (Figures 4 and 5), the second fluid in the second chamber 7 is the object to be pressurised. Accordingly, no port is required to be provided in the pressure vessel 2.

The first fluid may be water, pure or with various chemical additives to change its phase change temperature and pressure curve. The additives may include salt in various concentrations. These additives also serve as a seed in the transition from liquid to solid.

Additional materials that expand when cooling from a liquid phase to a solid phase are gallium, silicon, bismuth, plutonium, germanium, antimony. Other compounds and chemicals that form spacious crystal lattices can also expand on freezing.

A material that can be super cooled below its freezing point can be employed as the first fluid. This is particularly advantageous where the generation of pressure is required in a short time, e.g. in a cell disruptor. When a phase change is required, a nucleation crystal can be introduced into the first fluid. This greatly reduces the time taken to produce the phase change. Examples of fluids that can be super cooled and that expand on freezing include water and gallium.

One key limiting feature on the usability of the hydraulic accumulator 1 , 1 1 is the time taken to produce the phase change from liquid to solid. In the present invention this time is limited by setting predetermined values of relative difference in temperatures between the cooling medium and first fluid and their relative specific heat capacities, thermal conductivities of the cooling medium and the first fluid and intervening materials (e.g. the material of the pressure vessel), and specific heat of fusion of the first fluid.

Preferably, the cooling medium has a relatively high specific heat. This is desirable as the cooling medium absorbs the heat energy from the first fluid to cool it down to allow for a relatively controllable system.

Preferably, the first fluid has a relatively low specific heat. This is desirable so that the first fluid can quickly get to its freezing point.

Preferably, any intervening materials (e.g. the material of the pressure vessel 2) have relatively high thermal conductivities. This is desirable to allow for efficient cooling of the material to change state.

Preferably, the first fluid has a relatively low specific heat of fusion.

Modifications are possible within the scope of the invention, the invention being defined in the appended claims.