TECHNICAL FIELD The present invention relates to a slush machine of a type that is capable of dispensing a frozen "slush" beverage.

BACKGROUND ART Slush beverage systems are well known and are usually configured to dispense a beverage product with ice in a fine form to drink from a glass/cup or eat with a spoon. Such machines usually incorporate a reservoir of at least several litres with a conventional refrigeration apparatus that can take many hours to reach a suitable operating temperature/ ice content. Large machines typically rely on a scrape surface system and have a high capacity leading to significant waste of product when it is cleaned. Such wastage may be acceptable where the product is relatively cheap but is commercially prohibitive where the product is expensive such as slushes containing alcohol.

Furthermore, slush dispense machines of all types are generally expensive (particularly the motors that drive scrapers) which leads to a reluctance to offer slush beverages in bar environments and the like.

US2001/0041210 (Kauffeld) describes a "long tube" system, i.e. a coiled tube immersed in a glycol bath, for slush dispense. It further requires adding a freezing point depressing agent and particles to the beverage formulation in order to discourage ice from forming on the tube wall. Slush is recirculated constantly around the system by a pump. When utilising a "long tube" system, the primary problem encountered is the occurrence of seemingly random blocking events that a pump cannot recover from, leading to system breakdown.

Furthermore, in a simple recirculation system like US2001/0041210 there is no provision to ensure a consistent serve, specifically avoiding dispense of unfrozen (or not adequately frozen) product that has not had the required residency time in the system to become a slush with a suitable ice content (e.g. 20% ice). Such potentially unfrozen product is referred to herein as a "warm slug". To achieve a desired serve consistency and to avoid dispense of a "warm slug", product needs to spend a certain minimum residence time in the line to reach the serving temperature when it is dispensed. This is a function of flow rate, the tube length being cooled and the energy removal capacity of the total system. The use of long pipes adds to the size and cost of a unit, decreasing its commercial attractiveness.

In general, longer tubes require increased pumping power or more pumps to act as boosting pumps because of the gradual loss of pressure in a product line after a pump. Slush is a viscous fluid and, therefore, such a pressure drop is noticeable, compared to an unfrozen liquid. Both consequences result in greater cost and unit size. A further problem in such slush dispense machines is that drawing off slush product from a recirculating system is not straight forward. Opening a dispensing outlet does not necessarily direct product out of the system to be dispensed because the product flow has an opportunity to continue to recirculate. Also, because product is driven out of a reservoir (e.g. keg or bag-in-box) under pressure, as it enters a recirculating system it can flow either into the section of the system cooled by the cooling means (the first conduit according to the invention) or the wrong way into the return leg of the recirculating system (the second conduit according to the invention) toward the dispensing outlet, resulting in unfrozen product being dispensed.

DISCLOSURE OF THE INVENTION

The present invention seeks to provide a cost effective slush machine able to deliver a consistent frozen beverage product and to improve on the limitations of the system disclosed in Kauffeld .

In a first aspect the invention provides a slush machine including an inlet for receiving product from a reservoir, a fluid moving means, a first conduit including a coil associated with a cooling means downstream of the inlet, a dispensing outlet and a second conduit returning product to the first conduit for recirculation, wherein the fluid moving means is operable to cause product to flow in at least two flow rates, a first flow rate corresponding to a required dispensing flow rate and a second flow rate, less than the first, and wherein product entering the inlet is cooled to a slush in a single pass of the first conduit before reaching the dispensing outlet.

Particularly, a length of coil in the first conduit section is such that, at an average flow rate determined from the two or more flow rates caused by the fluid moving means, fresh product entering the system has time to be cooled to a consistent temperature and slush consistency in a single pass of the first conduit before reaching the dispensing outlet. Preferably the fluid moving means is a pump or series of pumps. Also, preferably, the pump(s) are operated in at least two speeds to obtain at least two flow rates in accordance with the invention. The advantage of two flow rates, e.g. by virtue of a two- speed pump, is that in normal operation product will be able to reach a desired slush consistency in a single pass through a relatively shorter conduit with a correspondingly lower pumping pressure, unit size and hence cost while being able to be dispensed at a more practical, quicker, commercially attractive speed. The quicker dispense speed is desirable in a bar environment where there is time pressure for serving the next drink. The slush machine may have a series of pumps at locations along the first (and/or second) conduit. Preferably these locations are at roughly an equal distance for standard engineering reasons. In a preferred embodiment the slush machine includes a control means capable of controlling the fluid moving means, e.g. pump(s), to adjust flow rate of the slush beverage.

A preferred embodiment of the invention features a mode where there is dispense for a predetermined time interval (e.g. 15 seconds) followed by recovery for a minimum predetermined time interval (which may also be at least 15 seconds) . This is possible by cutting supply at the inlet from the reservoir (e.g. by a solenoid valve) for a minimum 15 seconds following a serve (which is preferably 200mL in 15 seconds) . Even if the dispensing outlet (tap) is open product will not be dispensed because product flow will preferentially continue to circulate round the system than exit (until at least the predetermined recovery time interval expires) .

It will be apparent that the length of a coil submerged in a glycol bath can be calculated using standard engineering principles to establish the heat transfer requirements for the cooling mechanism so as to achieve a desired slush consistency with a single pass of the liquid whether or not the pumps are operating at a dual speed. According to the first aspect of the invention, with a dual speed pump, the product can spend the same residency time in contact with the cooling means but in a shorter coil compared to a single flow rate system. For example, in operation, a machine that dispenses at 0.8L/min for 15 seconds, followed by a recovery flow rate of 0.25L/min for 15 seconds, will require a shorter total length of coil than a system which operates at one speed of 0.8L/min.

The shortest coil length could, of course, be obtained by operating only at the lower speed, but this would not give an acceptable serve in a commercial environment. The risk of blocking may also be greater due to non-laminar flow. A yet further alternative would be to recirculate the product for two or more passes before allowing dispense but this would result in a complex monitoring problem and likely delivery of a "warm slug" as previously mentioned. In one embodiment the control means may monitor the viscosity of the beverage product. In this embodiment the control means preferably monitors current drawn by the pump as a function of viscosity of the beverage within the system, e.g. to estimate overall ice content to meet the serve requirements of a slush or at least whether the beverage has nucleated and formed ice crystals.

In connection with the further problem of drawing off slush product for dispense, this is addressed by a second broad aspect of the invention where there is provided a slush machine including an inlet for receiving product from a reservoir, a first conduit section associated with a cooling means downstream of the inlet, a dispensing outlet located downstream of the first conduit section and a second conduit section downstream of the dispensing outlet to return product to a location upstream of the first conduit section to form a recirculating product-flow system, there being a stop valve located upstream of the location where the second conduit section returns product flow to the first conduit section for recirculation .

According to the invention the stop valve, when closed, prevents any reverse flow of product up the second conduit section. Also, when the stop valve is closed and the dispensing outlet is opened, this has the effect of causing slush to be directed out of the recirculating system for serving due to the volume of product resident in the second conduit .

The stop valve may be a solenoid stop valve which operates to close in response to product being dispensed such that product cannot flow the wrong way up the second conduit section toward the dispensing outlet.

A stop valve downstream of the dispensing outlet is effectively a means for obstructing flow through the second conduit thereby converting the slush machine from a recirculating product-flow system to a one-way product-flow system via the first conduit only. This feature also avoids keg pressure from "short circuiting" the system by driving unfrozen product up the second conduit (which is the "return leg" of the recirculation circuit) and out of the dispensing outlet .

In a preferred form of either the first or second aspect of the invention the first conduit section includes a coil, immersed in a cooling means, e.g. the coolant may be glycol or any other appropriate medium.

In a preferred embodiment the slush machine operates as a combination of features of both the first and second aspects of the invention, i.e. it includes a flow directing means (the stop valve) and operates with at least two flow rates.

Preferably at least part of the first conduit section leading from contact with the cooling means to the dispensing outlet, and at least part of the second conduit section leading from the dispensing outlet to return to the first conduit section, is cooled by a "python" with coolant circulating therein. Preferably the coolant is supplied by a coolant reservoir within which the first conduit coil is submerged.

Preferably the conduits are made from plastic pipe. However, it is recognised that a longer plastic pipe will be needed to achieve the same heat transfer due to a lower heat transfer coefficient through the pipe wall, compared to metal (e.g. copper) . In further embodiments the conduit (s) may be formed from other suitable materials, preferably with a smooth inner wall, e.g. a copper pipe with an inner Teflon® coating.

As noted previously, existing slush machines can often take a significant length of time to reach a required operating temperature and corresponding ice content. If commercially desired, a variety of methods can be used to induce ice nucleation. Such methods are well known in the art and include the addition of chemicals that act as nucleators, excessive cooling of part or all of the liquid with subsequent partial melting, striking the first or second conduit with a sharp force, inducing cavitation or turbulence in the liquid with ultrasound or any other well known method.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a general view of a slush machine according to a first embodiment of the invention;

Figure 2 shows a general view of a slush machine according to a second embodiment. MODE ( S ) FOR CARRYING OUT THE INVENTION

Referring to Figure 1, the main components of a slush machine system according to a first embodiment of the invention include a reservoir 11 (e.g. pressurised keg or bag-in-box) , coupled to an optional pre-chiller 12, an inlet (pipe) 13, a first conduit section 14 comprised of both a coil 15 and transfer conduit 16, a fluid moving means in the form of a pump 17, a dispensing outlet 18, a second (or "return") conduit section 19 and a glycol bath cooling means 20.

According to the invention, pump 17 is a dual or variable speed pump that, following dispense at a desired dispense speed, slows the recirculation speed down to allow newly introduced liquid into coil 15 sufficient residency time in the glycol bath 20 to turn to slush. This aspect aims to prevent a "warm slug" from travelling around the system and being dispensed before it has become slush.

Preferably, the total length of pipe required in the first conduit (or specifically the length of coil 15 in contact with the cooling means 20) is calculated from the flow rates generated by the dual/variable speed pump and relates to the pipe length required to take product from the inlet to the outlet and remove sufficient energy in order to have a desirable slush consistency to serve. In other words, the pipe length can be determined from knowing four application variables:

beverage serving output, described as volume of slush per time frame, e.g. a 200mL drink of 25% ice content every 30 seconds,

dispense flow rate, describing the time to pour a drink, e.g. 15 seconds to serve a beverage,

the recovery flow rate, describing the time required to cool new incoming liquid,

the energy removal or 'heat lift' properties of the total system.

From these factors using standard engineering and heat transfer calculations the system ensures the product has sufficient residency time to create a consistent slush in a single pass.

By way of example, the following calculations can be used to determine the length of pipe required to create a required consistent slush drink in a single pass.

To achieve a desired serve rate of, for example, 200mL in 15 seconds, the serve speed must be 0.8L/min. Applying this to a plastic pipe with an internal diameter of 6.7mm and wall thickness of 1.4mm the material thermal conductivity is 0.4W/mK and the thermal resistances are 0.0037 K/W (Kelvin per Watt) for glycol to pipe, 0.0115 K/W through the pipe and 0.0972 K/W resistance to the product. Taking the example of requiring a product at -6.4°C with 24% ice content, it would require a coil of 105m in order to achieve the correct temperature within a single pass at this higher dispense flow rate of 0.8L/min. By taking advantage of the invention, i.e. utilising a second flow rate (a lower recovery speed) of 0.25L/min for 15 seconds and otherwise using the same pipe properties as above, the desired 200mL slush in 15 seconds can be achieved with the coil length reduced to 72m because the total average flow rate has reduced to 0.525L/min (the average of 0.8 and 0.25L/min) . This is a considerable space saving in a small unit .

According to the illustrated embodiment a 72m plastic coil with a 6.7mm internal diameter has a volume of 2.55 litres and, with an average flow rate of 0.525L/min, would result in a single pass time of 4 minutes 40 seconds. The pipe has been sized so that, at this flow rate, the product leaving the end of the coil is at -6.4°C and 24% ice and so would always be of the correct quality.

Although the average base flow is 0.525L/min (one glass served every 30 seconds), the serve rate when the dispense outlet 18 is open is intended to be 0.8L/min (one 200mL glass in 15s) . If the machine operated at this higher flow rate only, a single pass through 72m of pipe lowers the product temperature down to only -5.6°C corresponding to an estimated 20% ice. One further pass through the coil is required to achieve the temperature of -6.4°C and 24% ice.

Most obvious is to only run at the slowest speed possible to make the largest footprint saving on pipe length; however it must be remembered that if the flow rate is too low it could take several minutes to serve a drink across the bar which is unacceptable to a customer being served. Also, in practice, if the recovery flow rate is too low for too long then the possibility of a random blocking event in the pipe becomes unacceptably high which could cause a need to thaw out the machine, losing precious time in a retail outlet, potentially during a peak period for sales.

Pump speed is monitored and adjusted by a control means 21 such that pump(s) 17 delivers the required flow rate at dispense and recirculation.

A preferred method of measuring viscosity and specifically deciding whether the product has nucleated to become slush or not is monitoring the current (amps) drawn by the pump motor. A high current will correspond to a thicker, nucleated slush and therefore delivery speed can be relatively quick. By contrast, a low current will correspond to a thin beverage (i.e. it is easier to pump) and so circulation in the machine should slow down to allow ice to form. The unit, in one form, self adjusts the pump speed and corresponding serve. Alternative forms of control monitoring (viscosity measurement) are possible including ultrasound, light absorption etc, however, current monitoring has proved reliable and simple to achieve the requirements of the invention .

The slush machine incorporates a flow directing means in the form of a stop valve 22. Such a valve can be positioned within the second conduit section 19, downstream of dispensing outlet 18 where product is drawn off for dispense and upstream of the location where flow is returned to the first conduit section 14 and joined by top-up beverage from inlet 13.

Preferably stop valve 22 is in the form of a solenoid valve, activated by control means 21 in response to dispensing events. For example, valve 22 closes as dispensing outlet 18 is opened to serve product. Product resident in second conduit 19 therefore ceases to move and product following behind in the transfer conduit 16 is directed out of the dispensing outlet 18 due to the effectively incompressible nature of product trapped within second conduit 19. During this action the slush machine has become a one way system.

As illustrated in Figure 1, a sleeve or "python" 23 provides continued glycol cooling to the slush product as it leaves submerged coil 15 and travels along transfer conduit 16 toward the dispensing outlet 18 and then returning for recirculation via second conduit 19. The python 23 is intended to be in the form of a second pipe or sleeve, fed by a glycol pump 24 from the glycol bath 20 (which includes a propeller 25 therein to circulate coolant onto the coil 15), arranged closely adjacent transfer conduit 16 and second conduit 19. The multiple pipes, consisting of two slush carrying conduits 16/19 to/from dispenser 18 and two coolant pipes 23, are all covered and bound together by a suitable insulator that has the appearance of a thick elongate sleeve, hence the term "python".

Ideally, the slush carrying conduits 16/19 and corresponding glycol pipework 23 in a sleeve should be as short a distance as possible to reduce heat gain when beverage is out of the glycol bath.

As illustrated, one end of the python 23 connects to the slush supply and return product lines and to the glycol feed and return lines. At the other end, a tee piece tube connector 26 connects across the slush supply and return lines and to the dispense tap 18. The two glycol pipes 23 are connected to each other and back to the glycol pump 24.

The slush machine may use other forms of cooling the supply lines than the "python" illustrated or related glycol system.

A second preferred operating embodiment of the invention is illustrated by Figure 2. The same reference numerals have been used where possible in relation to Figure 1, however, in addition to the solenoid valve 22 as a means for directing flow there is a further flow stop valve 27 and a flow switch 28, both located on the inlet line 13 prior to the recirculating system. In a preferred experimental embodiment, the glycol bath 20 with about 48L volume of liquid is cooled by conventional means, e.g. a system including an ACC G534 1.4 kW heat lift compressor .

Temperature control of the glycol will be performed as one of the functions of the control PCB 21. The glycol chiller also contains a stirrer (not illustrated in Figure 2) to maintain a consistent temperature throughout the reservoir and a glycol pump (also not illustrated in Figure 2) to feed the python 19.

Figure 2 illustrates a dual pump/coil system (compared to the single pump/coil of Figure 1) wherein the product coil and pump assembly consists of two product coils 15a and 15b and two pumps 17a and 17b. The product supply line 13 connects to the reservoir 11 via a suitable keg connection and supplies product to the coil 15, first passing through the product flow switch 28 and flow stop valve 27.

Coil 15 is preferably constructed of plastic (e.g. food grade nylon or polyethylene such as MDP tubing made by Valpar Industries Ltd) with a 9.5mm (3/8") external diameter and 6.7mm internal diameter, i.e. a tube wall thickness of approximately 1.4mm.

Most preferably the coils 15a/15b will sit within the reservoir of the glycol chiller 20, whilst the pumps 17a/17b and flow direction control valve 22 will be positioned close but not within the reservoir to reduce ambient heating of the product. The plastic coil tubes 15 are preferably arranged with spacing (minimum 5mm) between loop passes to allow glycol to flow around. An example of a product recirculation pump 17 that will work with the invention is a Fluid-o-Tech supply gear pump 4mm, no bypass, driven by a Papst BLDC VD-3-43.10 motor capable of at least 0.8 L/min at a 5 bar pressure head. It has a magnetic coupling between the motor drive and pump head that decouples at 9bar pump pressure, capable of speed regulation down to 0.1 L/min. The pump is self priming through air with liquid product (not slush) so long as the pressure head is not too great .

As illustrated, the product coil consists of two coils (15a/15b), e.g. of at least 46m and 26m. This coil length (at least 72m total) results in a product capacity of approximately 2.5L. In the python 23 (e.g. consisting of a 10m section of the first conduit 16 to the dispensing outlet 18 and a 10m second conduit "return leg" 19 from the dispensing outlet, e.g. 20m total conduit within the python) there will be approximately 0.7L resulting in 3.2L for the whole system. Any additional part of the second conduit 19 not located in the python 23 is of negligible volume.

It will be apparent that the dispensing outlet 18, i.e. tap on a bar top, is to be located 10m from the main slush machine in the illustrated schematic embodiment.

The two pumps 17a and 17b can be relatively evenly spaced in the system. As the 26m coil 15b is the one connected to the python (which has a 20m send/return flow path therein) the total length of the recirculating system is effectively 46 + (26+20) = 92m. Note, in reference to calculations above, without a two flow rate system according to the invention, the total length would need to be 125m (105 + 20) to achieve a 0.8L/min serve for 15 seconds.

The control PCB 21 connects to the glycol chiller vapour compression system to control the glycol temperature via a temperature probe 29 positioned in the reservoir 20. The control PCB 21 is also connected to the pumps 17a and 17b, flow stop valve 22, product flow switch 28 and flow direction valve 27.

In general it can be assumed that the python 23, while it is refrigerated by virtue of the glycol lines therein, does not have sufficient cooling mass to perform further cooling on the product. It is only the coil submerged within the glycol bath 20 that is able to remove heat from the product. At best the python 23 retains product within transfer conduit 16 at its exit temperature from the coil 15b without any gain of heat before it reaches the dispensing outlet 18. Therefore, for the purpose of cooling calculations it is the length of the submerged coil section of the first conduit 14 which is important. The second conduit/python (which plays no role in cooling) is only taken into account for determining distances to be pumped.

According to the invention, the pump speed is controlled so that fresh product reaches the desired temperature in a single pass through the coil 15. After re-freezing, the system should speed up to either the dispense speed or an optional third "recirculation" speed of approximately 0.65L/min to achieve laminar flow once nucleation is achieved . An alternative dispense configuration is a pulsed dispense mode that times out after 15 seconds (sufficient to deliver a 200mL drink) upon which the product stop valve 27 closes and the pump speed reduces to recovery speed as above. After a further 15 seconds, the solenoid of the product stop valve 27 reopens and the pumps 17a/17b increase to dispense speed (e.g. 0.8L/min) . If further dispensing is detected via the product supply flow switch 28, the above cycle repeats. It is believed that pulsed dispense will be a more reliable way to maintain product consistency.

Systems designed for lower output, i.e. one 15 second serve per minute or less, can be supplied with a further reduction in coil length. Shorter coil lengths result in less waste and lower demands on pumping power, as previously stated.

The apparatus can be configured for multiple product supply lines, each including a controlled pump. This will result in further coils being submerged in a common glycol bath. A single control device 21 can be configured to manage the multiple lines and temperature control required to deliver a consistent slush. By way of example, a glycol reservoir modified for two supply line coils may need to be increased in size to 88 L to house both product lines and provide sufficient capacity for heat removal.

The slush machine of the invention may be a separate unit or be incorporated with a reservoir, e.g. keg or bag-in-box. In one form the return leg (second conduit section) 19 may return product to the reservoir 11 itself which acts as a reservoir of slush. In this sense, while there is an "inlet" to the first conduit section 14 which is effectively a coupling to the keg, it is a closed system with replenishment occurring when the keg is changed.

INDUSTRIAL APPLICABILITY

The slush machine as described and the method of pump control enables delivery of a consistent slush beverage, using generally available componentry/materials to be arranged according to the invention.