BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for maintaining a desired gas-liquid absorption level in a liquid irrespective of changes of temperature of the liquid. More specifically, the present invention relates to a method and apparatus for controlling the pressure of C0 ₂ gas supplied to a carbonator in order to maintain a desired carbonation level of the carbonated liquid therein, despite changes in temperature of the carbonated liquid.

Carbonators produce carbonated water of predetermined (target) carbonation levels, by absorbing C0 ₂ in water. The driving force for mass-transfer in the absorption process is equal to the difference between the saturated concentration of C0 ₂ in water and the target carbonation level. Since other mass-transfer conditions within the carbonator, such as contact surface and agitation are normally fixed, the target carbonation will be maintained provided that this driving force for mass-transfer is kept constant. However, the saturated concentration of C0 ₂ in water is dependent on pressure and temperature, according to Henry's law. As a consequence, when the water

temperature varies, the resulting change in mass-transfer driving force will cause a change in the level of final carbonation and the target carbonation level will thus not be maintained. For this reason, carbonators are usually designed to operate within a very narrow water temperature range and the C0 ₂ pressure is fixed to that the target carbonation level is attained within this temperature range.

In order to achieve the target carbonation level, regardless of the prevailing water temperature in the carbonator, the C0 ₂ gas pressure must be varied with water temperature, ideally so as to produce a constant driving force (i.e. a constant difference between saturated concentration and target concentration) . Simply changing gas pressure in relation to water temperature is not reliable, since this does not have a linear relationship to mass-transfer driving force, as illustrated by Fig. 1. No simple, direct-acting device exists either for controlling carbonator gas pressure according to water temperature, or more particularly, for controlling mass-transfer driving force according to water temperature.

SUMMARY OF THE INVENTION A primary objective of the present invention is to provide a simple, direct-acting regulator, which automatically either compensates the C0 ₂ gas pressure in a carbonator for changes in water temperature, or, more particularly, which compensates the carbonation mass- transfer driving force according to water temperature.

It is another object of the present invention to provide a method and apparatus for maintaining a desired gas-liquid absorption level in a liquid irrespective of changes of temperature of the liquid.

It is another object of the present invention to

provide a carbonation level regulator construction which is compact and inexpensive including a few injection molded or stamped metal parts.

The objects of the present invention are fulfilled by providing apparatus for maintaining a desired gas- absorption level of gas in a liquid comprising: means for providing a reference quantity of the same liquid with a desired gas-absorption level; means for sensing vapor pressure of the reference quantity of liquid; and means for controlling the gas-absorption level as a function of the vapor pressure sensed; whereby a constant mass-transfer driving force between gas and liquid is maintained irrespective of the temperature of the liquid.

In a preferred embodiment a control-signal originates from a reference standard of carbonated water close to the target carbonation level, which is sealed inside a pilot chamber. The pilot chamber is exposed to the water temperature in the carbonator system, and is shaped and sized so as to promote rapid equalization of the temperature of the reference standard with that of the carbonator water. The pressure inside the pilot chamber is equal to the equilibrium vapour pressure, according to temperature and carbonation level of the reference standard. This pressure is transmitted through a flexible membrane in one of the walls of the pilot chamber to a valve in the gas-supply line of the carbonator. This valve therefore balances the C0 ₂ gas pressure within the carbonator with the equilibrium vapour pressure in the pilot chamber. Since the equilibrium vapour pressure in the pilot chamber is precisely equivalent to the saturated concentration of the reference standard at the prevailing

temperature, the adjustment of the carbonator pressure to this equilibrium pressure results in constant carbonation driving force.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating perferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:

Fig. 1A is a graph illustrating the non-linear relationship between mass transfer driving force and temperature in a gas-liquid absorption system;

Fig. IB is a graph illustrating the linear relationship between mass-transfer driving force and equilibrium vapor pressure at target carbonation in the carbonation system of the present invention;

Fig. 2 is a cross-sectional view of one embodiment of the pilot chamber and associated regulation valve of the present invention;

Fig. 3A is a diagrammatic view illustrating the pilot chamber/regulator valve of Fig. 2 in the water supply line of the carbonator;

Fig. 3B is a diagrammatic view illustrating the pilot chamber/regulator valve of Fig. 2 in the carbonated product

output line of the carbonator;

Fig. 3C is a diagrammatic view illustrating the pilot chamber/regulator valve of Fig. 2 in a water reservoir coupled to the output product line of the carbonator; Fig. 3D is a diagrammatic view illustrating the pilot chamber/regulator valve of Fig. 2 immersed in a water bath with the carbonator; and

Fig. 4 is another embodiment of a pilot chamber/regulator valve configuration of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 2 demonstrates one embodiment and the main principles of this invention.

A regulator (1) with a pilot chamber (2) is partially filled with a reference quantity of carbonated water (3) and sealed by a flexible membrane (4) . The pressure in the pilot chamber (2) is therefore equal to the equilibrium vapour pressure of the carbonated water (3) at the prevailing temperature. The container (10) of the pilot chamber (2) is thermally-conducting and in contact with the water temperature in the carbonator so that the temperature of the reference quantity of the carbonated water (3) changes to reflect the temperature of the water in the carbonator (40) . To this end, the container (10) of the pilot chamber (2) is inserted into the water-supply line of the carbonator, as illustrated by Fig. 3A; or into the carbonator product line as in Fig. 3B. If the carbonator has an external carbonated water reservoir (42) the entire regulator (1) can be submerged in this reservoir as shown in Fig. 3C. When the entire carbonator is placed in a water bath, the regulator (1) can also be submerged in this water bath (Fig. 3D). In each of the four cases in Fig. 3, the pilot chamber (2) and the reference standard of

carbonated water inside (3) are kept at the temperature of the water within the carbonator (40) .

In order to minimize response time to water temperature variations, the container (10) must have a large external contact surface area and also enable rapid absorption/desorption of C0 ₂ within the carbonated water (3) , so that the vapour pressure in the pilot chamber (2) quickly attains the pressure level which is at equilibrium with the carbonated water temperature. In this embodiment, these two criteria are achieved by a pilot chamber (2) , which is wide and shallow. This provides a large external area for temperature equalization and, when filled with a very shallow reference quantity of carbonated water (3) , provides a large liquid surface area for rapid attainment of equilibrium vapour pressure at the prevailing temperature. Also, the container (10) is preferably made of thin sheet metal in order to improve heat transfer through the chamber walls and has a minimum of free gas space, when filled, so as to accelerate pressure response. The pressure inside the pilot chamber (2) acts upon the flexible membrane (4) , which is rigidly connected to a valve (5). The membrane (4) and the valve (5) have the same exposed surface area in contact with the gas in the high-pressure chamber (6) and the vapour pressure in pilot chamber (2) . Valve (5) regulates the pressure between the high-pressure chamber (6) , which is connected to the C0 ₂ supply by the inlet (7) , and the low-pressure chamber (8) , which is connected to the carbonator by the outlet (9) . The C0 ₂ supply in the high-pressure chamber exerts its pressure upon the valve (5) as well as upon the membrane (4) . As both have the same surface area in contact with the gas in the high-pressure chamber (6) , the forces acting on each as a result of the supply pressure are in balance,

and do not influence the position of the valve (5) . The pressure in the low-pressure chamber (8) , which is always equal to the C0 ₂ gas pressure within the carbonator, is therefore balanced by the vapour pressure in the pilot chamber (2) . When the pressure in the low-pressure chamber (8) is reduced due to absorption of gas inside the carbonator, the forces across the valve (5) are unbalanced and the valve (5) will open, allowing more C0 ₂ gas to flow from inlet (7) , through the valve (5) to outlet (9) and to the carbonator. As soon as the carbonator pressure has become equal to the pressure in the pilot chamber (2), the force balance across the valve (5) is restored and the valve (5) will close. The carbonator pressure will thus always be equal to the equilibrium vapour pressure of the carbonated water (3) which acts as a reference standard, so that the mass-transfer driving force in the carbonator is always kept constant and a constant level of carbonation is achieved in the product streams output from the carbonator.

The embodiment in Fig. 2 can be manufactured from a minimum of parts: principally a container (10) , a valve (5) , a membrane (4) , a valve seat housing (12) , and a lid (13) . The container (10) and the membrane (4) are metal parts to provide good heat transfer and avoid gas permeation, but the other parts are preferably injection moulded plastic parts to enable low-cost mass production. Upon assembly, the valve (5) is inserted into its seat (12) and the membrane (4) is attached to the valve seat housing (12), together with the lid (13). The pilot chamber (2) is filled with either chilled carbonated water, or ice and solid C0 ₂ in the correct proportion, and then sealed immediately by welding it to the membrane (4) .

The proportions of water and C0 ₂ filled into container (10) predetermine the mass-transfer driving force

provided by the regulator (1) within the carbonator. Preferably the ratio of depths of liquid to gas in container 10 is about 1:1 in a range of 2 to 5 mm. The diameter of cylindrical container 10 which defines the surface area of the liquid/gas interface is 5 to 100 mm depending on the application and preferably 20 to 25 mm.

Striction induced by the natural stiffness of parts within the regulator (1) can be overcome by adjusting the carbonation level of the carbonated water (3) . Therefore, adjustable components to bias the regulator (1) are not required, since the manufacturing tolerances of the simple moulded/stamped component parts can be kept within the tolerance limits.

A reference standard of plain C0 ₂ only can also be used instead of carbonated water within the regulator (1) , in applications where less accuracy is acceptable. A reference standard of C0 ₂ can be prepared by simply filling a weighed quantity of solid C0 ₂ into the reference chamber and sealing it immediately. An alternative embodiment, based on conventional production engineering methods, using metal components, is shown in Fig. 4. The pilot chamber (20) .is connected over a narrow channel (22) to the reference standard chamber (21) . This is partially filled, in the manner already described, with a reference standard (23) of carbonated water and is exposed to the water temperature in the carbonator system, as in Figs 3A to 3D. In the reference standard chamber (21) and the pilot chamber (20) , an equilibrium vapour pressure is established, according to temperature and carbonation of the reference standard (23) . This pressure acts upon a flexible membrane (24) , which constitutes one of the pilot chamber (20) walls and is connected to the valve pin (25) . Enclosed in the pilot

chamber is a spring (26) , which exerts a biasing force upon the membrane (24) . The pressure in the low-pressure chamber (27) , at the opposite side of the membrane, is always equal to the carbonator pressure, as this chamber is directly connected with the carbonator by the regulator outlet (28) . When the force exerted on the membrane (24) by the pressure in the low-pressure chamber (27) is lower than the force exerted by pressure in the pilot chamber (20) plus the spring (26) force, valve (25) will be opened. Gas will then enter the high-pressure chamber (29) via inlet (30) and flow through the valve (25) to low-pressure chamber (27) and to the carbonator via outlet (28) . Because of the inflow of gas, the pressure in the carbonator, and thus in chamber (27) , will rise until the forces on membrane (24) are balanced, as a result of which the valve (25) will close again.

The biasing force of spring (26) can be set with bias screw (31) . Membrane (32) allows compression of the spring (26) , whilst the pilot chamber (20) remains sealed. Whilst the concept described above related to the specific absorption process of carbonating water, a similar principle can be applied to any gas/liquid absorption system.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.