WO2008146274A2

WO2008146274A2 - Improved components, system and method for fabricating pumpable ice

Info

Publication number: WO2008146274A2
Application number: PCT/IL2008/000704
Authority: WO
Inventors: Boris M. Menin; Moshe Menchikovsky; Gregory Katz
Original assignee: Crytec Ltd.
Priority date: 2007-05-25
Filing date: 2008-05-25
Publication date: 2008-12-04
Also published as: WO2008146274A3

Abstract

A slurry ice crystallization chamber unit comprising: a crystallization chamber for crystallizing ice dendrites out of an aqueous solution, the chamber having a smooth inner wall, fabricated from a material having a high heat conductivity coefficient, that is chemically compatible with the aqueous solution and with the refrigerant; the cylindrical chamber being surrounded by an evaporator chamber which is coupled in series with a compressor, a condenser and an expansion valve to provide a closed recirculating refrigerant loop; a wiper arrangement being provided within the crystallization chamber that is configured to wipe the smiooth inner wall of the chamber, preventing ice build up thereupon.

Description

Improved components, system and method for fabricating pumpable ice Field of the Invention

The present invention is directed to providing pumpable ice for refrigeration purposes and particularly but not exclusively to improved systems and methods for cooling fluids to below their freezing point, causing nucleation of the solid phase whilst preventing crystal growth, thereby keeping the resultant material, though substantially frozen, flowable through pipes. Background

Most reactions follow an Arrhenius type relationship wherein, over an appropriate range, the reaction rate increases with temperature. The reverse is also true, and a well known technique for slowing or even preventing a thermodynamically favorable reaction from occurring is to lower the temperature of the reacting species.

It has long been appreciated that the rate of food spoilage may be slowed by refrigeration. Freezing to temperatures of between 0⁰C and -4⁰C arrests the bacterial and fungal decay of many foods, preventing spoilage and increasing the shelf life thereof. Deep freezing to lower temperatures is even more effective, particularly for meat products.

A wide variety of frozen fruit and vegetables are commercially available. Frozen vegetables are blanched, i.e. cooked for a short time in boiling water prior to freezing, which adds color and preserves texture. Other than losing some water- soluble vitamins during the blanching process, frozen fruit and vegetables are often at least as healthy as the 'fresh' equivalent, since they are harvested at the height of the season and frozen immediately, which is advantageous over out-of-season produce that may linger in warehouses, transit trucks, supermarkets and the kitchen before being cooked and eaten.

Foodstuffs that freeze satisfactorily include corn, spinach, peas, chicken breasts, chicken livers, ground turkey, puff pastry, fish fillets, whole fish and raw meat.

Raw, whole chicken is widely available frozen, and is acceptable for many dishes. It is, nevertheless, less tasty than fresh chilled chicken, albeit with a much longer shelf life. Ice-cream and sorbets require freezing. Finally, cakes, biscuits, sliced cooked meat, chicken and turkey schnitzel and fried fish are widely prepared in advance and frozen by busy housewives and even by restaurants, hotels and the like.

As a rule, fruit and vegetables may be successfully frozen for around eight months, meat and poultry for three, and fish and shellfish for up to nine months. There are, however, inherent problems with freezing many foodstuffs, in that as water content within the cells of the foodstuff turns to ice, it may damage the cell wall. Consequently, frozen and then defrosted vegetables tend to be flaccid, and though acceptable when subsequently cooked, are not of a quality for eating raw. Fresh fish is tastier, and even suitable for eating raw (sushi). Consequently, it commands a higher price than frozen fish. It is possible to keep fish fresh on ice for two or maybe three days. The short shelf life results in fish requiring rapid transport from netting on the trawler or fishing boat via refrigerated trucks or trains to a wholesale fish-market such as Billingsgate in London, for distribution to the fishmongers slab. Fresh fish distribution in this manner works in the UK with its mild temperatures aided by ships unloading the fish at night when it is cool, a rail network of lines converging on London, which is, itself only an hour or so from the coast by train, and the wholesale market being at its most active between 3 am and 4:30 am.

In many places, such as in land-locked countries and warmer climates, it takes appreciable time to bring fish to market and fresh fish is thus more and sometimes prohibitively expensive if available at all. Fish can be frozen of course. Indeed minced fish and meat freeze well. Whole fish or large fish fillets take a while to freeze and the fish may start to decay before being properly frozen through.

Using crushed ice for keeping fish fresh also has its associated problems. Rapidly chilled fish may suffer ice burns from contact with the ice. Fish packed within crushed ice may be damaged by sharp corners of the ice particles, which may puncture the skin of the fish. Furthermore, crushed ice does not flow well, and some of the fish surface may be inadequately covered and thus improperly chilled. The thennal center of the fish may take a long time to reach freezing temperatures and decay processes may commence before this is achieved. Poorly frozen fish tends to have slimy skin, softened flesh, stale flavor and an unpleasant odor. Warm, freshly slaughtered chickens, particularly when stacked in several layers on pallets in industrial freezers, may take a while to freeze, and chickens in the center of the stack may start to spoil prior to becoming too cold to retard microbe reproduction. This occurrence results in a degrading in quality of the chicken, and may in extreme cases, pose a health hazard.

These and other problems are largely addressed by slurry ice, which consisting of microscopic ice crystallites having a typical grain size of about 5 microns, surrounded by a minimal quantity of liquid water. Although consisting mostly of solid particles, slurry ice is fully flowing and may be pumped through pipes. If poured over fish, for example, tends to spread out over the surface of the fish, thereby ensuring good contact over a large area and a more even, faster cooling. In consequence, slurry ice wrapped fish is rapidly chilled through to the core. Indeed, the shelf life of fish chill-killed with slurry ice and shipped to market therein, has been demonstrated to be significantly better than fish killed and kept fresh with conventional methods. If allowed to cool further, the crystallites of the slurry ice will grow and eventually solid ice will result. If kept at a higher ambient temperature, the ice will remain at the triple point until all the crystallites have melted. Typically, such systems use salt water rather than pure water to lower the freezing point of the slurry. Sometimes however, such as for keeping fresh-water fish fresh, or for freezing fruit and the like, this is not an option.

It is noted that slurry ice technology has been around for decades. One prior art slurry ice manufacturing system is described in United States Patent Number US 6,305,189 titled "Method and installation for continuous crystallization of liquids by freezing" to Boris Menin, the inventor of the present invention as described hereinbelow. Whereas, most slurry ice systems produce slurries containing about 30% ice crystals and 70% water, Menin's slurry ice technology achieves an impressive 50% ice content. The present invention relates to a crystallizer chamber and wiper arrangement for the production of slurry ice that has a marked improvement over the system described in that publication and known in the prior art. Summary of the Invention

A slurry ice crystallization chamber unit comprising: a crystallization chamber for crystallizing ice dendrites out of an aqueous solution, the chamber having a smooth inner wall, fabricated from a material having a high heat conductivity coefficient that is chemically compatible with both aqueous solutions to be frozen and with a refrigerant; the cylindrical chamber being surrounded by an evaporator chamber coupled in series with a compressor, a condenser and a thermal expansion valve to provide a closed, recirculating refrigerant loop; the crystallization chamber being provided with a wiper arrangement configured to wipe the smooth inner wall, preventing ice build up thereupon.

Typically the aqueous solution comprises dissolved NaCl.

Alternatively, the aqueous solution comprises a solute selected from the list comprising sea water, alcohol, sugar, and ethylene-glycol.

Typically, said material comprises alpha brass. Optionally, said material comprises Naval Brass or Red Brass.

Typically, the smooth inner wall of the crystallization chamber has a surface roughness of less than 1 micron.

In another aspect of the invention, the wipers comprise a drive shaft and two rows of pivoting polymeric wiping blades coupled to the drive shaft; a first row on a first side of the drive shaft and a second row on the second side of the drive shaft; such that pivoting polymeric blades on the first side are staggered with respect to pivoting polymeric blades on the second side, such that rotation of the drive shaft generates a centrifugal force that pushes the wipers against the inner surface of the crystallization chamber to wipe the inner surface preventing deposition and growth of ice thereupon.

Optionally, the polymeric blades are fabricated from high density polyethylene.

Optionally, the polymeric blades are coupled to the drive shaft by stainless steel threaded pins that engage blind holes drilled tangentially to the drive shaft. Typically, the wipers rotate at a speed of between 300 and 1,500 rpm. In a third aspect of the invention, a proximal end of the drive shaft has a bearing bolted thereupon that freely rotates in a bearing mount that is bolted to a base by bolts; a plug carving is provided around a distal end of the drive shaft and is coupled thereonto and a seal is provided between the plug carving and a flange that is bolted to the base by bolts; the seal comprising a plurality of turns of a lock cord that is sealingly wedged between base, flange and plug carving to provide a water tight fit; pressure being exertable onto the lock cord by tightening the bolts that connect the flange to the base.

Preferably, the drive shaft, bolts, bearing, bearing mount, plug carving and flange are fabricated from 316L stainless steel, the base is fabricated from Delrin and the lock cord is fabricated from PTFE.

In a further aspect of the invention, the evaporator is a cylindrical chamber sandwiched between the slurry ice crystallization chamber and an outer sleeve; the evaporator is serially couplable to a compressor, condenser and thermal expansion valve in a closed refrigeration loop such that a gaseous refrigerant is compressed in the compressor, liquefied in the condenser and expanded through the thermal expansion valve into the evaporator where it boils, and the gaseous, evaporated refrigerant expands into the compressor.

In preferred embodiments, the evaporator has an inlet at a first end thereof for the influx of liquid refrigerant, and an outlet at a second end thereof for venting refrigerant vapor, the slurry ice crystallization chamber having an inlet at the second end for inflow of liquid to be frozen and an outlet at the first end for outflow of slurry ice, such that the liquid to be frozen is in counter flow to the refrigerant vapor.

In a further aspect, use of PTFE lock cord to provide a fluid seal between a shaft of a wiper unit of a slurry ice crystallization chamber and its bearing is claimed.

In a further aspect of preferred embodiments of the invention, there is provided a cylindrical slurry ice crystallization chamber unit comprising a slurry ice crystallization chamber separated from an evaporator chamber therearound by a brass wall. In yet a further aspect of preferred embodiments of the invention, there is provided: a sleeve like cylindrical evaporator chamber mounted coaxially around a cylindrical refrigeration chamber; for boiling and evaporating a refrigerant within the evaporator chamber for cooling the refrigeration chamber; the evaporator having an inlet at a first end thereof for influx of liquid refrigerant, and an outlet at a second end thereof for venting refrigerant vapor, the slurry ice crystallization chamber having an inlet at the second end for inflow of liquid to be frozen and an outlet at the first end for outflow of slurry ice, such that the liquid to be frozen is in counter flow to the refrigerant vapor.

Brief Description of the Figures

For a better understanding of the invention and to show how it may be carried into effect, reference will now be made, purely by way of example, to the accompanying drawings. It is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention; the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the accompanying drawings:

Fig. 1 is a schematic isometric projection of a crystallization chamber in accordance with an embodiment of the invention; Fig. 2 is a schematic cross section through an evaporator unit in accordance with a preferred embodiment of the invention;

Fig. 3 is an isometric projection of a wiper unit;

Fig. 4 shows a bearing and flange assembly in accordance with a preferred embodiment of the present invention; Fig. 5 and 6 are workshop plans of the drive shaft in accordance with one embodiment of the wiper unit assembly;

Fig. 7 is a workshop plan of the bearing base in accordance with an exemplary embodiment;

Fig. 8 is a workshop plan of the bearing cover in accordance with an exemplary embodiment;

Fig. 9 is a workshop plan of the base of the wiper unit in accordance with an exemplary embodiment;

Fig. 10 is a workshop plan of the evaporation chamber in accordance with an exemplary embodiment, and Fig. 11 is a workshop plan of the wiping blade in accordance with an exemplary embodiment.

Description of the Preferred Embodiments

With reference now to Fig. 1, a crystallization chamber 10 of the invention is shown. Crystallization chamber 10 is cylindrical, and is fabricated from an alloy or metal that is resistant to corrosion, has a high thermal conductivity, a low specific heat and is able to stand thermal shock. Although crystallization chamber 10 may be fabricated from 316L stainless steel which is a popular choice for refrigeration systems and for use with sea water, it is a particular feature of embodiments of the invention that the crystallization chamber 10 may be fabricated from an alloy of copper and zinc, typically alpha brasses Cu-38%Zn, the so called naval brass and 'red brass' (Cu-15%Zn with traces of lead and iron), for example. These brass alloys are easily machined, have a high thermal conductivity, typically in the range of 140- 160 W/(mK), and are widely used in pipes, connectors, faucets, meters and the like for drinking water. They are not believed to cause illness or pose any other health risks. Furthermore, brasses, particularly naval brasses, are resistant to corrosion by sea water, and so can be used in refrigeration systems for installing on ocean going fishing boats, and the like. Due to its high thermal conductivity, brass allows a large heat flux there-through and crystallization chambers walled by this material are efficiently cooled.

The crystallization chamber 10 is cylindrical in shape and has an inner cylindrical tube 12, surrounded by an outer sleeve 14 separated therefrom by a small distance d, forming an evaporator 16 therebetween. A refrigerant fluid is passed around a closed loop between this evaporator 16, compressor 40, condenser 20 and thermal expansion valve 41. As refrigerant liquid boils, it evaporates into the gas phase 22, sucking heat (the latent heat of evaporation) from its surroundings. This has a chilling effect on the inner cylindrical tube 12, cooling same. The wall 13 of the crystallization chamber 10 is chilled, and a heat flux ΔH out of the crystallization chamber 10 results, cooling the aqueous solution 24 therein to below freezing, thereby resulting in the nucleation of ice crystals. The coldest part of the crystallization chamber 10 is the outer wall 13 thereof, and this provides a surface on which ice dendrites nucleate.

Due to the expansion valve 41, the liquid refrigerant 18 influxes into an inlet 15 at a one end of the evaporator 16, and evaporates as it passes along the evaporator to an outlet 17 at the other end thereof where the refrigerant vapor 22 is vented. The liquid to be frozen, typically an aqueous solution 24, is pumped into the crystallization chamber 10 through an entry port 19 near the first end, and, due to the partial crystallization thereof, into ice nuclei, slurry ice outflows through an exit port at the other end. The refrigerant 18 vaporizes slowly as it passes along the evaporator 16, sucking heat from the aqueous solution, causing a thermal gradient and resulting in the nucleation of solvent dendrites, typically ice crystallites, on the wall 13 of the crystallization chamber 10. As the liquid refrigerant boils, because of the narrowness of the evaporator 16, a foam is formed. The thermal rise along the evaporator is kept to a minimum, since the most efficient cooling effect is due to the latent heat of evaporation, and it is this latent heat that sucks heat out of the aqueous solution 24 flowing through the crystallization chamber 10, which results in deposition of dendritic ice crystals on the outer wall 13 of the crystallization chamber 10.

With additional reference to Figs. 2 and 3, a novel wiping unit 28 is provided. Wiping unit 28 consists of staggered plastic wiping blades 30a, 30b, 30c... mounted on alternate sides of a central drive shaft 32. The drive shaft 32 is typically fabricated from 316L stainless steel. Plastic wiping blades 30a, 30b, 30c... may be fabricated from high density polyethylene (HDPE), such as that marketed as Delrin. Preferably all edges are rounded and all burrs removed.

The plastic wiping blades 30a, 30b, 30c... are fastened to the central drive shaft 32 by pins 34 - also typically from 316L steel, and are free to rotate thereabout. As the wiping unit 28 rotates about the axle of the central drive shaft 32, the plastic wiping blades 30a, 30b, 30c... are driven outwards by centrifugal force and the ends thereof are brought into contact with the outer wall 13 of the crystallization chamber 10. The wiping unit 28 rotates contantly, wiping the wiping blades 30a, 30b,

30c... over the outer wall 13 of the crystallization chamber 10, removing the microscopic ice crystal dendrites nucleated (i.e. seeded) thereupon, and preventing the deposition and build up of an insulating ice layer which would otherwise adversely affect the efficiency of the crystallization process. Typically, the wiping unit 28 rotates at between about 300 rpm (revolutions per minute) and about 1500 rpm, and most typically at about 600 rpm. In addition to preventing ice build up on the outer wall 13 of the crystallization chamber 10, the wiping unit 28 also serves to stir the ice- fluid mixture 26 within the crystallization chamber 10, ensuring the formation of a quality slurry. In the past, scrapers were required, but due to the smooth surface of outer wall 13, the wiping blades 30a, 30b, 30c are merely required to wipe the inner surfaces of the outer wall 13 of the crystallization chamber 10 to prevent ice build up thereupon, but not to scrape off accumulated ice; it being appreciated that any mechanical energy exerted to break up or scrape off ice is ultimately converted into heat that has to be removed, therefore minimizing such wasted energy increases the efficiency of the system and lowers running costs.

The wiping unit 28 is coupled to a motor at one end, and is fixed to the crystallization chamber cylinder by a bearing and flange assembly 100 described hereinbelow with reference to Fig. 4. With reference now to Fig. 4, a cross-section through the bearing and flange assembly 100 of the wiping unit 28 in accordance with a preferred embodiment of the invention is shown. The bearing and flange assembly 100 comprises a plain bearing 102 that rotates with a plain bearing case 103, both of which are optionally machined from 316 L stainless but could also be tooled from brass, HDPE or any other materials having appropriate coefficients of thermal expansion, so as not to lock in a freezing (and in many applications - salty) environment. The plain bearing 102 is bolted onto the proximal end of shaft 32E and turns in a socket machined in the bearing case 103 which separates into two parts around the plain bearing 102; the parts being typically held together by bolts 110. The bearing case 103 has a circular slot therethrough of internal diameter 25 mm providing clearance for the reduced diameter shaft 32F, having a diameter of 24.85 mm providing clearance to freely rotate within the circular slot. It will be appreciated that other dimensions are possible, so long as adequate clearance is provided, taking into account the thermal contraction and expansion as the system is operated or switched off. The bearing case 103 of plain bearing 102 is bolted by bolts 110 to the base

104 which is machined from black Delrin, i.e. HDPE with carbon filler. Helical inserts 109 are provided within the bolt holes in base 104 for engaging the shafts of the bolts 110. The drive shaft 32 is reduced in diameter to a diameter of 25 mm (32F) and this reduced diameter section 32F protrudes through the base 104. Figs. 5 and 6 are workshop drawings of the drive shaft 32 in accordance with an exemplary embodiment of the invention. The proximal end of the shaft 32 is reduced in diameter twice more: firstly, it is machined down to a narrower diameter of 20 mm (Section 32C) , the edge of the step being tapered D (Fig. 5) and a close fitting plug carving 106 (sleeve type element) is provided therearound that is sealed to the 20 mm diameter section (Section 32C) with an O-ring 107 that may be of felt, for example. The plug carving 106 is bolted onto the driveshaft 32 and rotated therewith. A flange 105 from 316L stainless steel is coupled to the base 104 by bolts 113 with spring disk, helical inserts again being provided in the base 104. Typically four such bolts 113 are provided. A bearing cover (see Fig. 8), which may be fabricated from 316L stainless steel, for example, may be provided to give a neat finish.

It is a particular feature of the bearing and flange assembly 100 of the present embodiment, that the water tight seal between the plug carving 106 and the flange 105 is provided by a protective seal 108 that is fabricated by a few turns of PTFE lock cord. This provides a low maintenance water tight seal that can be periodically tightened by minor adjustments (typically quarter of a turn) of bolts 1 13, of which four are typically provided.

A slot 115 is machined through reduced diameter section 32A of the driveshaft 32, allowing the secure fixing of a coaxial gear wheel therearound (not shown) for coupling to the spindle of a motor via a gear train or belt for rotation of the driveshaft 32 thereby. In this manner, wiping means 28 is rotated at 300 to 12500 RPM. The rotation of the wiping means 28 serves three purposes: (i) the blades 30a, 30b, 3 Oc... thereof wipe the inner surface of wall 13 of crystallization chamber 10, dislodging ice nuclei and crystallites and preventing the build up of ice thereupon, (ii) wiping means 28 stirs the slurry ice-water mixture 26 within the crystalization chamber 10, keeping it fairly homogeneous, (iii) it helps move the slurry ice-water mixture 26 along the crystallization chamber 10, allowing fresh (i.e. not iced up, it may be salt water) water 24 to be pumped in and slurry ice 26 to be removed.

It will be noted that instead of the simple PTFE lock cord seal 108 described hereinabove, prior art wiping units 28 such as that described in US 6,305,189 to Menin, use expensive bearings and mechanical seals such as BT-AR 14, supplied by Pac-Seal. Such bearings and mechanical seals are not only expensive, but, being moving parts and operating in extreme conditions, are not particularly reliable and need periodic replacement, typically every 3 months or so. It will be appreciated that slurry cooling systems, such as installable on deep sea fishing boats and the like, are required to be reliable and to operate for maximum time between maintenance.

In contradistinction, the preferred bearing and flange assembly 100 of Fig. 4 described hereinabove does not use a conventional mechanical seal with bearings. Instead, it is closed with a polytetrafluoroethylene (PTFE) lock cord 108, which is cheaper to install. More importantly, instead of requiring skilled maintenance personnel, leakage of seal may be achieved by any technician who is merely required to periodically tighten the seal 108 by rotating bolts 113 through a small arc, thereby applying a pressure onto the lock cord. This keeps the bearing sealed, and can be performed periodically or simply whenever the technician notices a dripping of fluid. This novel sealing concept minimizes maintenance down time, and is a simple, reliable alternative to the more sophisticated and costly mechanical bearing seals of the prior art.

The proximal end of shaft 32 may be supported by a simple mount having a clearance hole therethrough, or, as shown in Fig. 1, shaft 32 may be unmounted, the shaft 32 canterlevering from the bearing and flange assembly 100. Being unmounted actually makes the wiping more efficient, in that additional vibrations typically result.

By way of exemplary enablement only, workshop plans of bearing base, bearing cover, body of crystallization and evaporation chamber and wiping blades are given in Figs. 7-11 respectively. It will be appreciated that other embodiments may vary somewhat in design, while nevertheless retaining novel and inventive features as described herein.

In prior art crystalization chamber units, the throttled refrigerant entered the evaporation chamber at both ends and expanded as it passed along the evaporation chamber. As it expanded, the refrigerant boiled and was vaporized, drawing heat from the warmer water-ice mixture within the crystalizer through the wall thereof. The refrigerant vapor exited the evaporator in the middle, with a temperature difference between the refrigerant entrance and exit ports of about 1.5⁰C to 2⁰C. Now, the temperature of the liquid refrigerant is sufficiently low to have a cooling effect on the crystallization temperature. Once vaporized, as the vapor expands, the temperature drops, as known.

The most significant cooling effect for removing heat from the crystallization chamber is the latent heat of vaporization, where the boiling refrigerant sucks heat from its surroundings in order to overcome the intermolecular bonds within the liquid phase as it vaporizes. In the crystalization chamber 10 of the preferred embodiment shown in Fig. 1, throttled refrigerant 18 enters the evaporator 16 at one end and the vapor 22 is exhausted at the other end. In consequence of this unique design, the vaporization zone of the refrigerant is twice as long as in prior art systems. Furthermore, for most of the length of the evaporator 16, the refrigerant 18 is in a whipped up, foam-like state. This provides a large surface area for evaporation and increases the evaporation rate. In consequence, the resulting ice crystallite yield is significantly greater. The net result is lower operating costs and higher production rates. In addition to having only one inlet 15 for the influx of liquid refrigerant 18 at one end of the evaporator 16 and one outlet 17 for venting the vaporized refrigerant 22, the distance d between inner wall 13 and outer wall 14 of the evaporator 16 is set to between about 3 mm and about 10 mm. This aids the foaming effect, which wets and thus most efficiently sucks heat through the inner wall 13, as the refrigerant evaporates (boils).

Using the R507 Refrigerant, (Trade mark "GenetronAZ50" by "Allied Signal") which is an environmentally friendly refrigerant with low Ozone depletion potential (ODP = 0) and global warming potential (GWP = 3900), with the contra-flow along the entire length of the evaporator and crystallization chamber and with an appropriate separation d of between about 3 mm and about 10 mm between outer 14 and inner 13 walls of the evaporator 16, the temperature difference along the evaporator 16 may be as low as 0.5 ⁰C to 1 ⁰C, thereby resulting in a significantly increase in the heat transfer coefficient of the evaporator, which may be as much as 15-20%.

The slurry ice producer described hereinabove may be used for chilling fish, shrimps, fruit and vegetables, chickens, meat and other foodstuffs. It may also be used for cooling air for keeping flowers fresh, for air-conditioning units, thermal energy storage, in the production of iced wines, ice-cream and other foods and beverages.

Thus an improved slurry ice producer is described, having a number of unique features that, in combination, provide greater efficiencies, i.e. lower operating costs, and cheaper slurry ice than hitherto attainable. These features include:

1. A novel, improved wiping unit for efficient removal of ice crystals from the chilled wall of the crystallization chamber

2. Fabrication from brass rather than stainless steel

3. Piping throttled refrigerant into the evaporator from one end and venting saturated refrigerant vapor at the other end, thereby boiling the refrigerant along the full length of the evaporator which is the most efficient cooling regime with the highest cooling rates

4. Pumping aqueous solution into the crystallization chamber at one end and removing slurry ice at the other end. 5. Pumping the aqueous solution to be cooled along the crystallization chmaber in counterflow to the flow of refrigerant.

6. Low maintenance, cheap, polytetrafluoroethylene. seal, removing need for conventional cryogenic bearings It will be appreciated that any of the above listed features taken individually could be used to modify prior art crystalization units for slurry manufacture, lowering operating costs and provide slurry more efficiently. Although each of these features is believed to be novel and inventive in its own right, the effects thereof are additive and slurry producing system including all the above elements are 30-50% more efficient than prior art systems.

Thus the scope of the present invention is defined by the appended claims and includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications thereof, which would occur to persons skilled in the art upon reading the foregoing description. In the claims, the word "comprise", and variations thereof such as

"comprises", "comprising" and the like indicate that the components listed are included, but not generally to the exclusion of other components.

Claims

1. A slurry ice crystallization chamber unit comprising: a crystallization chamber for crystallizing ice dendrites out of an aqueous solution, the chamber having a smooth inner wall, fabricated from a material having a high heat conductivity coefficient that is chemically compatible with aqueous solution and with a refrigerant; the cylindrical chamber being surrounded by an evaporator chamber coupled in series with a compressor, a condenser and a thermal expansion valve to provide a closed, recirculating refrigerant loop; the crystallization chamber being provided with a wiper arrangement configured to wipe the smooth inner wall, preventing ice build up thereupon.

2. The slurry ice crystallization chamber unit of claim 1, wherein the aqueous solution comprises dissolved NaCl.

3. The slurry ice crystallization chamber unit of claim 1, wherein the aqueous solution comprises a solute selected from the list comprising sea water, sugar, juice, alcohol and ethylene glycol.

4. The slurry ice crystallization chamber unit of claim 1, wherein the material comprises alpha brass.

5. The slurry ice crystallization chamber unit of claim 1, wherein the material comprises a brass selected from the list of naval brasses and red brasses.

6. The slurry ice crystallization chamber unit of claim 1, wherein the smooth inner wall has a surface roughness of less than 1 micron.

7. The slurry ice crystallization chamber unit of claim 1, wherein the wipers comprise an drive shaft and two rows of pivoting polymeric wiping blades coupled to the drive shaft, a first row on a first side and a second row on the second side, such that pivoting polymeric wiping blades on the second side are staggered with respect to pivoting polymeric wiping blades on the second side, such that rotation of the drive shaft generates a centrifugal force that pushes the wipers against the inner surface of the crystallization chamber to wipe the inner surface preventing growth of ice crystals thereupon.

8. The slurry ice crystallization chamber unit of claim 7, wherein the polymeric wiping blades are fabricated from high density polyethylene.

9. The slurry ice crystallization chamber unit of claim 7, wherein the polymeric wiping blades are coupled to the drive shaft by stainless steel pins that engage blind holes drilled tangentially to the drive shaft.

10. The slurry ice crystallization chamber unit of claim 7, wherein the wipers rotate at a speed of between 300 and 1,500 rpm.

11. The slurry ice crystallization chamber unit of claim 1 wherein a proximal end of the drive shaft has a bearing bolted thereupon that freely rotates in a bearing mount that is bolted to a base by bolts; a plug carving is provided around a distal end of the drive shaft and is coupled thereonto and a seal is provided between the plug carving and a flange that is bolted to the base by bolts; the seal comprising a plurality of turns of a lock cord that is sealingly wedged between base, flange and plug carving to provide a water tight fit; pressure being exertable onto the lock cord by tightening the bolts that connect the flange to the base.

12. The slurry ice crystallization chamber unit of claim 11 wherein drive shaft, bolts, bearing, bearing mount, plug carving and flange are fabricated from 316L stainless steel.

13. The slurry ice crystallization chamber unit of claim 11 wherein the base is fabricated from HDPE.

14. The slurry ice crystallization chamber unit of claim 11 wherein the lock cord is fabricated from PTFE.

15. The slurry ice crystallization chamber unit of claim 1, wherein the evaporator is a cylindrical chamber sandwiched between the slurry ice crystallization chamber and an outer sleeve; the evaporator is serially couplable to a compressor, condenser and thermal expansion valve, via a closed refrigeration loop such that gaseous refrigerant is liquefied in the condenser and expanded into the evaporator where the liquefied refrigerant boils and expands to be compressed by the compressor in a circulating cycle.

16. The slurry ice crystallization chamber unit of claim 15, wherein the evaporator comprises an inlet at a first end thereof for influx of liquid refrigerant, and an outlet at a second end thereof for venting refrigerant vapor, the slurry ice crystallization chamber having an entry port at the first end for inflow of liquid to be frozen and an exit port at the second end for outflow of slurry ice, such that the liquid to be frozen is in counter-flow to the refrigerant vapor.

17. A slurry ice crystallization chamber unit as described hereinabove and illustrated in the Figures.

18. Use of PTFE lock cord to provide a fluid seal between a shaft of a wiper unit of a slurry ice crystallization chamber and its bearing.

19. A cylindrical slurry ice crystallization chamber unit comprising a slurry ice crystallization chamber separated from an evaporator chamber therearound by a brass wall.

20. A sleeve-like cylindrical evaporator chamber mounted coaxially around a cylindrical refrigeration chamber; for boiling and evaporating a refrigerant within the evaporator chamber for thereby cooling the refrigeration chamber; the evaporator having an inlet at a first end thereof for influx of liquid refrigerant, and an outlet at a second end thereof for venting refrigerant vapor, the slurry ice crystallization chamber having an inlet at the second end for inflow of liquid to be frozen and an outlet at the first end for outflow of slurry ice, such that the liquid to be frozen is in counter flow to the refrigerant vapor.