DIRECT-CONTACT ICE-GENERATION DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of devices that provide refrigeration for commercial applications. More particularly, the invention relates to refrigeration systems having multiple cooling loops. Still more particularly, the invention relates to refrigeration systems that use either an aqueous solution or an aqueous- solution/ice slurry ("slurry") as a coolant and that entail the direct co-mingling of coolant and refrigerant. Even more particularly, the invention relates to such refrigeration systems that can use the high cooling capacity of a slurry as a coolant and also provide storage of that cooling capacity, sometimes designated"thermal storage." 2. Description of the Prior Art For many decades, the need to provide large scale refrigeration in commercial establishments has given rise to one of the larger costs in the annual expense outlay by such establishments. Here"refrigeration"is used in its general sense and encompasses applications ranging from office and factory air conditioning, cooling of foodstuffs in supermarkets, low-temperature maintenance in cold-storage warehouses, cooling of turbine blades, and so on. In these applications, not only is it costly to meet the refrigeration demand, but other problems arise from the need to extend that refrigeration over large areas and, in the case of supermarkets, to many small spaces distributed throughout large areas that are not to be refrigerated. Although all operators of such equipment face the problem of the high cost of electricity to operate them, many operators also have to contend with constraints on the nature of the cooling substance. Because of the potential for leakage in systems requiring extended piping to bring the cooling substance to the point that is to be refrigerated, such substances cannot be toxic.

Also because of the potential for leakage, there is increasing concern that the

coolant not be expensive and that, in addition to being non-toxic, that it not be harmful to the environment in other ways.

For many reasons, including concern over the loss of expensive coolant and the need to use an environmentally benign substance as the coolant in close proximity to the areas to be refrigerated, there is widespread use in commercial refrigeration systems of a two-tier approach. In the two-tier approach, two substances, each circulating within its own sealed piping circuit are used to extract heat from the areas to be cooled and to dump it remotely. The first substance (the "coolant") is a liquid medium that is brought into close thermal contact with the areas to be refrigerated (cooled), from which areas it extracts heat and conveys that heat back to the region where the coolant is in thermal contact with the second substance (the"refrigerant"). The refrigerant is contained in a much shorter piping circuit within which it is subjected to a traditional refrigeration cycle, by which is meant that the refrigerant undergoes evaporation at one point and subsequently is condensed back to a liquid. In the evaporation region the refrigerant absorbs heat from its environment; in the condensation region it gives up heat to its environment. In the two-tier system under discussion, the coolant is brought into thermal contact with the refrigerant at the evaporation region of the latter. (Usage of the word"coolant"in the present context is equivalent to the phrase"secondary coolant"as used, for example, in Chapter 18 of the 1981 ASHRAE HANDBOOK, Fundamentals: any liquid cooled by the refrigerant and used for the transmission of heat without a change in its state.) The refrigerant absorbs the heat needed to evaporate (vaporize) it from the coolant. Thus the refrigeration system can be pictured as the coolant picking up heat from the areas to be refrigerated, handing that heat on to the refrigerant, which then, at a separate place, gives that heat up to the outside environment, to be conveyed by some means away from the building containing the refrigeration system. Traditionally, the refrigeration is carried out continuously and maintained as long as the need for cooling continues.

The region where the coolant gives up heat to the refrigerant, thereby vaporizing the latter, is referred to as the"heat exchanger. "Traditionally, the heat

exchanger consists of two circuits of interwoven conduits, one being part of the refrigerant's piping circuit ("primary circuit"or"primary line"), the other being part of the coolant's piping circuit ("secondary circuit"or"secondary line"). Heat flows from the warmer substance (the coolant in this case) to the colder (the refrigerant). The capacity of the two-tier refrigeration system depends to a high degree on the heat flux between the coolant and the refrigerant in the heat exchanger. From basic thermodynamics, it is known that, all other things being constant, the heat flux will be proportional to the temperature difference between the coolant and the refrigerant at each point within the heat exchanger. The flux will also be strongly dependent on the thermal resistance that the materials of the heat exchange impose on this heat flow. Stated more concisely, the heat flux at a given point in the heat exchanger is directly proportional to the temperature gradient between the coolant and refrigerant and to the thermal conduction of the heat exchanger materials at that point.

Using a two-tiered system enables selection of a refrigerant based on its condensation and evaporation characteristics without concern for expense or toxicity, the characteristics that typically govern selection of the coolant. Once the refrigerant is selected, the design problem reduces to increasing the efficiency of the heat exchange between refrigerant and coolant. Large-area commercial refrigeration is very expensive, even when the maximum efficiency allowed by the laws of thermodynamics is approached. Thus, even with high-efficiency heat exchangers in use, there remains an incentive (in those markets where time-of-day pricing of electric energy is in effect) to shift one's use of electricity to those hours of the day when it is least expensive, or at the very least, away from those times of day when it is most expensive. Stated concisely, one would like to use the electricity during"off-peak"hours. This can be achieved by adding to the refrigeration system a tank in which the cooling capacity of the coolant can be accumulated as the system operates during off-peak hours, to be used during peak hours to obtain the needed refrigeration. Since the use of the accumulated cooling capacity does not involve operating the refrigerant loop, this means that heavy power demand can be shifted to off-peak hours. The storage of coolant that makes this possible is one

example of what is called"thermal storage,"even though what is being stored here is cooling capacity rather than heating capacity.

A water-ice combination is the most common thermal storage medium used today because of its many positive characteristics, such as availability, low cost, non-toxicity, nonflammability, high density, high heat of fusion (for latent heat storage), high specific heat (for sensible heat storage) and high heat transfer characteristics. See Chapter 40 of the 1995 ASHRAE HANDBOOK, HVAC Applications. When the coolant consists of ice particles suspended in an aqueous solution (pumpable slurry), the cooling capacity of the coolant is increased due to the latent heat of fusion (144 Btu/Ib.) of the ice particles. See Bel, Hunyadi et al. : Thermal Study of an/ce Slurry Used as Refrigerant in a Cooling Loop, preprint from : Applications for Natural Refrigerants, Chapter 12, Danish Technological Institute, Aarhus, Denmark, 1996.

Neither the concept of the two-tier refrigeration system nor that of generating cooling capacity during off-peak hours to be used during peak hours is new. For example, Wildfeuer (U. S. Patent 4,334,412, issued 1982) describes a cooling system having cooling and refrigeration zones connected through a heat exchanger, for use in air conditioning a building. Wildfeuer teaches the use of a water/ice slurry as a coolant, which varies in composition as it is cooled (by the refrigerant) and which extracts heat from the areas to be air conditioned. Furthermore, the Wildfeuer system incorporates a means of storing this slurry for later use. It is to be noted that the Wildfeuer device uses the traditional heat exchanger design, in which the primary and secondary circuits are brought into localized thermal contact with one another while maintaining the refrigerant and the coolant, physically separated from one another. It therefore suffers from the inefficiencies referenced above, in particular from the need for the refrigerant to be significantly colder than the coolant when both are within the heat exchanger. This is also true of the thermal storage device of McCracken et al. (U. S. Patent 5,005,368, issued 1991), which seeks to store cooling capacity by producing solid ice during off-peak periods and storing the ice in modular tanks to provide cooling to meet daytime loads on an

air conditioning system. The ice is produced by circulating a glycol-containing coolant through plastic tubing submerged in a tank of water. In order to freeze portions of this water, the coolant itself must be cooled to temperatures considerably below 32F. That is accomplished by a third medium, a refrigerant cycling through a standard evaporation/condensation process.

Running through all of the known art related to the present subject is the stated or implied conviction that the coolant and refrigerant must be kept separated if the coolant is water based. This is because of the detrimental effect that water- contamination of the refrigerant has on the performance of the refrigerant. See, for example,"Control of Moisture and other Contaminants in Refrigerant Systems," Chapter 6 of the 1996 ASHRAE HANDBOOK, Refrigeration: Excess moisture in a refrigerating system can cause one or all of the following undesirable effects : 1./ce formation in expansion valves, evaporators, and the like 2. Corrosion of metals 3. Copper plating 4. Chemical damage to motor insulation... or other system materials 5. Hydrolysis of lubricants and other materials.

Because of the concern about moisture-contamination of the refrigerant stated above, heat exchangers have always been used to cool water-based coolants, so that the coolant and refrigerant can be brought into thermal contact with one another while remaining physically separate. That is, it has been accepted that the heat transfer between refrigerant and coolant can only be done across an impermeable- to-fluids barrier, in spite of the inherent inefficiencies in heat transfer that this entais. As stated above, these include the resistance of this barrier to heat flow.

The thermal resistance arises not just from the materials of the heat exchanger, but also from ice build-up on the surface of the coolant piping within the heat exchanger.

Because of the detrimental effect of the ice build-up, some of the prior art provides for the periodic scraping of the ice, a process that gives rise to added expense and to other problems in operation. In summary, a substantial temperature differential must be maintained between the refrigerant and coolant in order to overcome the

intrinsic thermal resistance of the heat exchanger. A Carnot-type energy analysis, however, shows that the lower the refrigerant temperature at its evaporative stage (where it is absorbing heat from the coolant), the lower the efficiency of the cycle.

Thus, the need to maintain a temperature differential across the heat exchanger runs contrary to the effort to maximize the efficiency of the refrigerant cycle.

In an attempt to overcome the inefficiencies inherent in the heat-exchange stage of the two-tier system, Zakeri describes a one-tier refrigeration system in which water is the refrigerant. To establish the standard evaporation/condensation refrigeration cycle (the Carnot cycle), the refrigeration loop in the device of Zakeri operates under temperature and pressure conditions such that the water is at its "triple point" (the point at which liquid water, gaseous water, and solid water (ice) co- exist in equilibrium with each other). See Zakeri, G. Reza; Vacuum Freeze Design forEnergy Effective Production of Ice Slurry, published as a preprint from: Applications for Natural Refrigerants, Chapter 12, Danish Technological Institute, Aarhus, Denmark, 1996. By drawing heat away from the liquid phase, water vapor acts as the refrigerant. To the extent that the water can thereby be used as the refrigerant, the system of Zakeri overcomes the inefficiency imposed by the heat exchanger in the two-tier systems. However, the low pressure that must be maintained within the Zakeri refrigerant conduit is an overwhelming disadvantage.

That is, the temperature and pressure of water at its triple point are 32°F and 0.0887 psi, respectively, that is, a pressure equal to 0.006 atm (0.6% the atmospheric pressure). This means effectively that the ambient air will exert a pressure of 14.7 psi all along that part of the refrigeration conduit within which the water refrigerant is at its triple point; this pressure differential makes the system vulnerable to air leaking into it. The presence of air within this system is highly deleterious to the heat transfer process and can lead to harmful corrosion. Thus, because of the very low operating pressures of the Zakeri system, extraordinary effort is required to prevent air from contaminating the refrigerant, thus making the Zakeri system impracticable. Moreover, because of the high specific volume of gaseous water, the Zakeri system requires very large compressor capacity compared to the capacity required for more traditional refrigerants.

No known prior art mentions a two-tier refrigeration system wherein the refrigerant is introduced directly into the coolant at the stage where heat is to be transferred from the latter to the former. Given the problems that arise in other parts of the refrigerant circuit when the refrigerant becomes contaminated with moisture, it is clear that if the coolant is water, then there must be some method of re-separating coolant from refrigerant before the latter re-cycles through the compressor, etc.

Although not involving a simple two-tier system such as discussed here, the device of Gainer (U. S. Patent 4,302,944; issued 1981) does deal with the mixing of two coolants so as to increase heat transfer efficiency, followed by the re-separation of these substances. This mixing and re-separation takes place in a vertical storage tank through the bottom regions of which passes a closed conduit of refrigerant.

The two coolant components are of different densities, such that they become stratified, with the region through which the refrigerant conduit passes being occupied essentially entirely by the higher density component, typically methyl chloroform. The upper region of the tank is occupied predominantly by the lower- density coolant, typically a solution of water and methyl alcohol. The object of the system of Gainer is the production and storage of ice at one time for cooling at a later time. More particularly, the thermal storage is achieved during an off-peak time, as for example when a truck is parked at night at its home base. The high- density coolant (which has an extremely low freezing temperature and hence never forms heat-flow-impeding"ice"on the outside of the refrigerant circuit), is conducted from the bottom of the tank up to the top, where, chilled, it is sprayed or otherwise deposited at the upper surface of the low-density coolant. It then sinks down through the lower-density coolant to be bottom of the tank, whence it is again circulated to the top. As the process continues, the low-density coolant begins to turn to slush as it is cooled while at its freezing temperature. Because of the high heat of fusion (better stated, of melting) this ensures that a high cooling capacity will be available the next day, when the higher-density coolant is then circulated through the truck to be cooled, and then back into the top of the storage tank. The slush itself stays in the storage tank to receive heat from the higher-density coolant. This example is mentioned because it exemplifies one method of separating liquid coolants once they have been put into intimate contact for high-efficiency heat

transfer. However, this separation-by-settling method is a time-consuming approach, useful only in small systems.

What is needed, therefore, is a refrigeration system that permits the use of a refrigerant, having the evaporation/condensation advantages of traditional refrigerants, and a coolant for the production of ice within a water-based coolant, without having the energy-transfer inefficiencies of the prior-art two-tier systems.

What is further needed is such a refrigeration system that allows for thermal storage and the concomitant shifting of energy demand away from peak hours while permitting the cooling itself to continue throughout part or all of the peak hours of the day. What is yet further needed is such a system that will maximize the cooling capacity of the coolant by generating the coolant in the form of a pumpable slurry.

What is still further needed is such a system that is efficient, inexpensive, compact in size, easily assemble and operated, and applicable to large-scale commercial cooling demands.

SUMMARY OF THE INVENTION It is an object of the present invention to produce a refrigeration system that permits the use of a refrigerant having the evaporation/condensation advantages of traditional refrigerants, and of a coolant for production of ice within a water-based coolant, without having the energy-transfer inefficiencies of the prior art two-tier systems. It is further an object of the present invention to produce such a refrigeration system that allows for thermal storage and the concomitant shifting of energy demand away from peak hours while permitting the cooling itself to continue throughout part or all of the peak hours of the day. It is yet further an object of the present invention to produce a refrigeration system that will maximize the cooling capacity of the coolant by generating the coolant in the form of a pumpable ice slurry. It is still further an object of the present invention to produce a refrigeration system having the above features that is also efficient, inexpensive, compact in size, easily assembled and operated, and applicable to large-scale, commercial cooling

demands.

In order to achieve these objects as energy-efficiently as possible, the present invention attacks the inefficiencies inherent in the physical separation of coolant and refrigerant at the heat exchanger by directly injecting the refrigerant physically into the coolant. This disperses the refrigerant throughout the coolant and provides an extremely large surface area over which heat can be transferred.

This method also eliminates heat transfer impediments due to the thermal resistance of the heat exchanger tubes and ice build-up. Thus, the key source of inefficiency, of having to produce and maintain a high temperature differential between refrigerant and coolant, is eliminated and the heat transfer from the coolant to the refrigerant maximized. Indeed, just the elimination of the traditional heat exchanger simplifies and makes less expensive the construction of the refrigeration system.

Finally, the present invention further achieves the object of efficiency by efficiently producing ice for thermal storage, and also producing ice to form a pumpable water/ice slurry that can be used directly as the coolant.

The present invention, by physically mixing the refrigerant and the coolant, now needs to incorporate a way to re-separate coolant and refrigerant once the desired heat transfer has been effected. Rather than using the separation-by- settling method of Gainer, the present invention introduces an active means of separation, namely evaporating the refrigerant out of the coolant. The refrigerant, in liquid form, is introduced into a vessel that contains the coolant. At the same time, vapor pressure inside the vessel is maintained at a value sufficiently low to cause the refrigerant to evaporate at a temperature below the freezing point of the coolant (without being so low as to increase the likelihood of leaks into the system from the ambient atmosphere). The refrigerant thus absorbs heat from the coolant and causes ice to form within the coolant. The refrigerant vapor then quickly rises out of the coolant and is drawn away from the mixing tank. The vapor is then condensed back to a liquid and is re-introduced into the coolant to complete the cycle.

Various methods can be used to maintain the vapor pressure inside the

vessel sufficiently low to form ice within the coolant. The preferred method is to use a compressor to remove the refrigerant vapor from the vessel. The compressed vapor is then condensed back to a liquid at a pressure and temperature substantially above the freezing point of the coolant. This liquid refrigerant is then routed back into the coolant to complete the cycle.

Another method is to provide a heat exchanger that is in contact with the vapor refrigerant that has evaporated from the coolant. With the temperature of the heat exchanger lowered to a value below the freezing point of the coolant, the refrigerant vapor condenses on the heat exchanger and drops back into the coolant to complete the cycle.

The water/ice slurry formed by this method can be used in several different ways. It may, for example, be pumped directly into the external coolant circuit so as to provide refrigeration in the areas to be refrigerated. In this way, the circuit has additional cooling capacity due to the suspended ice particles. Alternatively, it may be pumped to a storage tank, to be held until some later time when refrigeration is desired. Once in the storage tank, it may later be circulated as a slurry or it may be filtered so that the ice remains behind and only the liquid water travels to the area to be refrigerated, and then back to the tank where it is re-cooled by contact with the ice that remained behind. In this way, the system of the present invention can be operated so as to provide cooling capacity during peak periods, thus"load-shifting" electric power usage to off-peak periods.

The coolant may be pure water or an aqueous solution-such as brine- containing a solute that will effectively lower the freezing point of the coolant, thereby allowing the present invention to be used for applications in which a temperature substantially lower than the freezing point of water is need. Clearly, for the system of the present invention to work as described, the refrigerant must be almost totally immiscible with the coolant; that is, it must flow through the coolant without becoming dissolve in it to any significant degree. Also, the refrigerant must be essentially non-reactive with the coolant, so that the system can have a stable,

trouble-free service life. Furthermore, the refrigerant should operate near atmospheric pressure, to minimize air leakage and avoid subjecting the associated vessels to excessive stress.

During the development of this invention, it has been discovered that various hydrocarbon refrigerants satisfy the latter requirements and would therefore be suitable for this application. Listed below are the vapor pressure values at the freezing point of pure water for several hydrocarbon refrigerants. Vapor Pressure at3Z°F Refrigerant PSIA PSIG R-290 (propane) 68.8 54.1 R-600 (n-butane) 15.0 0.3 R-600a (isobutane) 22.7 8.0 R-1270 (propene) 84.8 70.1 Table 1. Vapor Pressure Data Refrigerant % by weight R-290 (propane) 0.0007 R-600 (n-butane) 0.0093 1 R-600a (isobutane) 0.0085 1 Table 2. Solubility of Hydrocarbon Refrigerant in Water Research by the inventor has confirmed that all of the refrigerants listed in Table 1 are nearly immiscible with water and are essentially non-reactive with water.

The vapor pressure of the hydrocarbon refrigerant at 32°F is also an important consideration in the present invention. By inspection of the vapor pressure data shown in Table 1, it is evident that the operating pressures of these refrigerants are in a practical range, i. e. they are not at extremely low pressures such as that of the water at its triple point that might lead to air leaks, nor are they at extremely high

pressures that might place excessive stress on the containment vessels.

Hydrocarbons have several characteristics or advantages that make them particularly desirable as refrigerants. Hydrocarbons occur naturally in petroleum and are abundant and inexpensive. Moreover, the ozone depletion potential of hydrocarbons is zero and their environmental impact low. Hydrocarbons are essentially non-reactive with water and their solubility in water is very low. As shown in Table 2, the solubility of propane in water at 70°F is less than 10 parts per million (ppm). Hydrocarbons are flammable, but can be effectively and safely used with simple precautions, as is evidenced by their increasing use in automobile air- conditioning systems and in domestic refrigerators in many countries in the world.

See Comprehensive TeX Archive Network (CTAN) website of the University of New South Wales, Sydney, Australia, on Hydrocarbon Refrigerants on October 27,1999.

Further research by the inventor has shown that conventional refrigerants such as hydrofluorocarbons (HFCs), particularly R-1 34a (tetrafluoroethane), and chlorofluorocarbons (CFCs), particularly R-12 and R-22, are less effective than hydrocarbons as refrigerants in the direct-contact ice-generation method and apparatus of the present invention because the use of HFCs or CFCs leads to the formation of crystals called solid hydrates as the cooling process approaches 32°F.

The formation of hydrates is a process which binds some of the refrigerant, thereby removing the refrigerant from the evaporation process and, consequently, reducing the ice-producing capacity of the refrigeration process. See 1998 ASHRAE

Handbook: Refrigeration, Chapter 6, page 6.1. Thus, although these conventional refrigerants are capable of producing ice, they are not ideal refrigerants in a direct- contact ice-generation process. Studies by the inventor have shown that hydrocarbon refrigerants do not result in the formation of crystals.

In conclusion, by directly co-mingling the coolant and refrigerant, the method and apparatus of the present invention provide a simple, economic means of generating ice for thermal storage, thereby permitting the user to shift loads on cooling systems to take advantage of off-peak utility rates. Furthermore, by introducing a pumpable ice slurry, the method and apparatus of the present invention maximize the cooling capacity of the coolant. Finally, by using hydrocarbon refrigerants, the method and apparatus of the present invention provide a means for cooling that has zero ozone depletion potential and has generally a low impact on the environment.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic diagram of a first embodiment of the present invention, an embodiment in which the refrigerant is directly removed from the coolant using a compressor and the coolant is pumped as an ice slurry directly to the cooling load.

FIGURE 2 is a schematic diagram of a second embodiment of the present invention, an embodiment similar to the first embodiment, but one in which the cooling capacity of the coolant is stored in a storage tank for later use.

FIGURE 3 is a schematic diagram of a hydrocarbon refrigeration circuit usable as a variant with either of the embodiments depicted in FIGURE 1 and FIGURE 2.

DETAILED DESCRIPTION OF THE INVENTION There are two primary embodiments of the invention: a first embodiment in which the coolant is circulated directly to the cooling load after being cooled by mixing with the refrigerant, and a second embodiment in which the coolant is delivered to a storage tank to provide cooling capacity at some later time. Within those two primary embodiments there are variants as well. A schematic representation of the first embodiment of the direct-contact ice-generation device 100 of the present invention is shown in Fig. 1. The heart of the device is a mixing tank 3, the site where a liquid refrigerant 1 is brought into direct contact with a coolant 2. In both primary embodiments, the refrigerant used is propane, commonly known by the designation R-290, and the coolant used is a water-based solution, selected for its heat capacity and freezing temperature. With continuing reference to Fig. 1, note that the liquid refrigerant 1 is introduced into the coolant 2 contained in the mixing tank 3. During this process, the pressure at the top of mixing tank 3 is maintained at a level sufficiently low to cause the liquid refrigerant 1 to evaporate readily at a temperature somewhat below the freezing point of the coolant 2. As the liquid refrigerant 1 evaporates to a gaseous-state refrigerant 13, it absorbs heat from the coolant 2, thereby lowering the temperature of the coolant 2 and causing solid crystals of the coolant 2 to form within the mixing tank 3.

Because the density of the refrigerant 1 in its gaseous state is much lower than that of the coolant 2, the gaseous-state refrigerant 13 state quickly rises through and out of the mixing tank 3. The refrigerant 1 must then be re-condensed into its liquid state. In the primary embodiments of the present invention, this is achieved through traditional compressor/condenser means. To effect this, the gaseous-state refrigerant 13 is moved through the circuit containing a compressor 4 by means of a motor 5. It is important that the compressor 4 not introduce into the refrigerant contaminants such as oil that would otherwise be conveyed to the mixing tank 3 where it would react with the mixture of the refrigerant 1 and the coolant 2.

Any one of the several types of oil-free compressors already available in the

marketplace can be used for this purpose.

At any event, the gaseous-state refrigerant 13, after compression by compressor 4, is at a temperature considerably above the freezing point of the coolant 2 and needs to be cooled and liquefied before being reintroduced to the mixing tank 3. In the primary embodiments, and as shown in Fig. 1, this is accomplished by using a common condenser 6 such as is used in typical refrigerator systems. As it is condensed, i. e., as the gaseous-state refrigerant 13 goes to liquid refrigerant 1, the gaseous-state refrigerant 13 gives off its heat of condensation, which is carried away by any convenient means (not shown). The liquid refrigerant 1 is then passed through an expansion valve 7 so as to cool it further and ensure that the pressure of liquid refrigerant 1 is made substantially equal to the pressure within the mixing tank 3 at the point that the liquid refrigerant 1 is introduced to the mixing tank to complete the cycle.

The coolant 2, which when circulated to the cooling load comprises an ice/water slurry as described above, can be cooled and circulated either in a continuous process or in a batch process. For definitiveness, consider it as a batch process wherein after a specific period of time the slurry has reached the desired ratio of ice to liquid. By the nature of the process there may still be some liquid refrigerant 1 within the coolant 2 residing in the mixing tank 3; that is, even after the majority of the liquid refrigerant 1 has been vaporized to the gaseous-state refrigerant 13 and removed from the coolant, there may remain a small amount of liquid refrigerant 1 admixed with the slurry, creating a slurry/refrigerant admixture 9.

In the primary embodiments, the admixture 9 is transported by an admixture pump 8 to an admixture tank 10, wherein the liquid refrigerant 1 is allowed to evaporate to gaseous-state refrigerant 13 and be drawn off through compressor pipe 25 by compressor 4. Because the evaporation of liquid refrigerant 1 that occurs in admixture tank 10 draws yet more heat from the coolant 2, the slurry comprising the coolant 2 in the admixture tank 10 will be shifted further into the solid component direction, resulting in a secondary slurry 12. Ideally, following the refrigerant

extraction that takes place in the admixture tank 10, the concentration of refrigerant will be on the order of its saturation concentration, which for the refrigerant/coolant combination used in the primary embodiments, will be on the order of 10 ppm.

At this point, as shown in Fig. 1, the secondary slurry 12, which in the primary embodiments of the present invention remains pumpable, is conveyed from the admixture tank 10 via a coolant delivery pipe 29 directly to the cooling load by means of pump 11, the ice component in the slurry providing added cooling capacity as it melts. Alternatively, a filtering device consisting of a screen 36 is used at the outlet of admixture tank 10 to prevent the ice component of the secondary slurry 12 from entering coolant delivery pipe 29, thereby ensuring that only the liquid component of coolant 2 is delivered to the cooling load. Whichever form of the coolant 2 delivered to the cooling load, it is returned from the cooling load (bearing heat extracted from the cooling load) via coolant return pipe 30. Fig. 1 shows the coolant 2 being returned directly to the mixing tank 3. However, depending on the particular needs of the operator of the system, it is envisioned that it could in the alternative be returned to the admixture tank 10.

The second primary embodiment of the present invention incorporates a cooling-capacity-storage section, as shown in Fig. 2. With such a setup, the operator can run the refrigerant circuit (including the compressor/condenser) during the hours of iow electric power consumption, and yet have cooling capacity throughout the rest of the 24-hour cycle. Since many electrical utilities now provide time-of-day pricing (with lower charges for off-peak consumption) this approach can reduce the amount the operator pays for electricity. Referring to Fig. 2, one can see a holding tank 130 interposed between the system shown in Fig. 1 and the cooling load. It is the holding tank 130 that is used for thermal storage of the cooling capacity, and, more specifically, for storing the coolant 2 after heat has been removed from it during its circulation through the refrigerant circuit. As in the first primary embodiment of the present invention, the secondary tank 10 is shown. Now, however, the secondary pump 11 is used not to circulate the secondary slurry 12 to

the cooling load, but rather to the holding tank 130. Although the screen 36 is shown in conjunction with the secondary tank 10, just as it was in the embodiment set out in Fig. 1, screen 36 would not normally be used to strain the secondary slurry 12 emanating from the secondary tank 10 and carried to the holding tank 130. In other words, the secondary slurry 12 would normally contain the same mixture of solid and liquid as is produced in the refrigerant circuit, including the secondary tank 10.

In general, the secondary slurry 12, after being delivered to the holding tank 130, remains in the holding tank 130 for a number of hours, until it is needed to refrigerate the cooling load. When the post-storage coolant 9 is drawn from the holding tank 130 for circulation to the cooling load, it is post-storage pump 110 that effects this circulation. In the embodiment presently being discussed, and as can be seen with continuing reference to Fig. 2, the holding tank 130 is fitted with a first holding-tank screen 360, giving the operator the option of adjusting the liquid/solid mix of the post-storage coolant 9, including ensuring that it is completely liquid, with a storage-ice residue 20 being left behind in the holding tank 130. Also as shown in Fig. 2, the post-storage coolant 9 is, after extracting heat from the cooling load, circulated back to the storage tank 130 through storage-tank-return-line 30.

Fig. 2 depicts the re-charging of the holding tank 130 with cooling capacity, by extracting coolant through a second holding-tank screen 46, and recirculating it in its liquid form back to the mixing tank 3 through return-pipe 120. This re-charging would be normally be done while the refrigerant circuit (including the compressor 4) is operating.

In summary, the process using the second primary embodiment of the present invention, as represented in Fig. 2, will create an ice-pack 20 in holding tank 130, which can be used to during peak-hours to re-cool the post-storage coolant 9 that is returned from the site to be cooled after having taken up the heat of the cooling load, without being cycled through the refrigerant circuit. Thus, the post- storage coolant 9 is cycled through the holding tank 130 to the cooling load and

back to the holding tank 130 until the cooling capacity of the holding tank 130 is exhausted. The post-storage coolant 9 can be pumped as a pumpable slurry or, through use of the first storage-tank screen 360, as a liquid.

Fig. 3 depicts a variant that can be used with either of the two primary embodiments of the present invention. It shows a conventional refrigeration system 26 used to cool the gaseous-state refrigerant 13, returning it to the liquid refrigerant 1 for use in the mixing tank 3. In other words, instead of running the gaseous-state refrigerant 13 directly through a refrigerant cycle (including compressor 4), the variant shown in Fig. 3 allows one to use a sealed loop containing the gaseous- state refrigerant 13 and the liquid refrigerant 1, an approach to preventing oil or other contaminants being introduced to the working substances used in the present invention. In greater detail, the variant depicted in Fig. 3 may be described as follows. Gaseous-state refrigerant 13 is cooled by contact with a conventional heat exchanger 220 of the conventional refrigeration system 26 so as to form a low- pressure refrigerant liquid 23. The low-pressure refrigerant liquid 23 then is passed through a low-pressure liquid feed line 24 into the mixing tank 3, which is coupled into an extended system comporting to either the present invention's first primary embodiment 100, as shown in Fig. 1 or to the second primary embodiment 200, as shown in Fig. 2.

Although the use of a heat exchanger introduces heat transfer inefficiencies discussed earlier, it does have the advantage of ensuring that no oil or other contaminants are introduced into the refrigerant by the compressor, as the compressor/condenser loop is external to the refrigerant circuit.

The refrigerant used in the present invention, regardless of its embodiment, must be almost totally immiscible with water. While small amounts of refrigerant may dissolve or become entrained in the coolant or ice, any substantial solubility and its subsequent release would not be tolerated. Propane-commonly known by the designation R-290-is a commercially available hydrocarbon that is used as

the refrigerant in the primary embodiments of the invention. It is within the scope of the present invention, however, to use other refrigerants as long as they have properties suitable for application in systems of the present invention.

It should be understood that the primary embodiments and variants thereof mentioned herein are merely illustrative of the present invention. Numerous variations in design and use of the present invention may be contemplated in view of the following claims without straying from the intended scope and field of the invention disclosed herein.