WO1999030013A1

WO1999030013A1 - Additives to freeze point suppressants and to heat transfer fluids in heat exchangers

Info

Publication number: WO1999030013A1
Application number: PCT/US1998/025944
Authority: WO
Inventors: Robert R. Holcomb; John W. Evans
Original assignee: Holcomb Robert R; Evans John W
Priority date: 1997-12-08
Filing date: 1998-12-07
Publication date: 1999-06-17
Also published as: AU2198799A

Abstract

A product (figure) which is mixed with water based heat transfer fluids to provide a heat exchange fluid in which some or all of the additives used with standard freeze temperature depressants, such as ethylene glycol or propylene glycol, are no longer required. In addition, for non-aqueous coolants or for mixtures of water with either ethylene glycol or propylene glycol, the viscosity of the resultant mixtures is significantly decreased by addition of this invention.

Description

PATENT APPLICATION TITLE OF THE INVENTION "Additives to Freeze Point Suppressants and to Heat Transfer Fluids in Heat Exchangers"

INVENTOR(S): Robert R. Holcomb and John W. Evans

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/067,717, filed December 8, 1997, and incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable

REFERENCE TO A "MICROFICHE APPENDIX" Not applicable

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a heat transfer fluid for use in heat exchanger systems including cooling systems for internal combustion engines and to freeze suppressant fluids used in deicing applications where the freeze suppressant is used to remove ice from exposed surfaces by lowering the freeze point of water. 2. General Background of the Invention

Some current formulations of heat tr.ansfer fluids typically utilize the characteristics of water as the prim.ary heat removal fluid. The water content of a coolant is typically 30% to 70% by weight, depending on the severity of the winter climate.

Another component of these conventional heat transfer fluids is a freeze point depress.ant. Currently, the freeze point depress.ant in most cases is ethylene glycol (EG) although propylene glycol (PG) has been used recently because of its low toxicity characteristics. In some warm weather areas, freezing temperatures are not encountered and only water or water with a corrosion inhibitor package is used. Addition of PG to the heat transfer fluid as a low toxicity freeze point depressant introduces a mixture of water and PG which is more viscous, causing a decrease in the flow rate of the fluid through the heat exchanger, and has inferior heat transfer characteristics when compared with conventional water and ethylene glycol heat exchange fluids.

The EG heat transfer fluids that are currently used create continuing environmental problems and raise concerns about toxicity, health effects and disposal problems. EG leads to acute short term oral toxicity in humans and other mammals. For that reason recently PG based coolants have become popular. An additive package containing numerous different chemicals is initially added to the freeze point depressant to form an antifreeze concentrate, and eventually blended with water to form the coolant. These additives are designed to prevent corrosion, deposit formation and foaming, and are in concentrations of .5% to 3% by weight. In heavy duty engine cooling applications supplemental additives are used to prevent cavitation erosion of cylinder liners (iron).

Because the additives commonly used in water based heat exchange fluids have a tendency to foam, anti-foaming additives are usually included in 50/50 EG/PG water based heat exchange fluids.

One problem that arises from the use of EG and PG as freeze protection is instability of the additives. A small amount of water is intentionally added to EG/PG concentrate to keep the water soluble additives in solution, while being stored, however that amount is insufficient for long periods of time. If storage as a concentrate is too long a period (over 6-8 months) then the water soluble additives begin to "fall-out" of suspension and will accumulate in the bottom of the container as a "gel". The "gelled" additives will not return to solution even with agitation. This problem, however, is not limited to the stored concentrate only. Even when fully mixed with water, as 50/50 EG/PG/W, the water soluble additives will "gel-out" if not agitated regularly. This can be a severe problem for engines used in stationary emergency pumps and generators as well as military and other limited use engines. In heating applications where heat transfer fluids are not used during off season similar problems occur.

One difficulty with the large water fraction of the diluted heat exchange fluids, typically a 50/50 ratio of concentrate to water, is the emergence of precipitates of heavy metals, such as lead and copper contaminants, that dissolve into the water portion of the heat exchange fluids of the heat exchanger. The water reacts with lead and copper materials from heat exchanger which are the source of not only brass, and thereby copper, but also lead solder. Chronic health problems .are associated with coolant contamination from elemental heavy metal precipitates.

Water is also highly reactive with light alloys, such as aluminum, and the water fraction of the coolant can generate large amounts of aluminum precipitates, which increase proportionally with higher coolant temperatures. Water soluble additives are used for these reactions, but cannot totally eliminate the reaction, and aluminum is constantly lost to the 50/50 EG/PG water based heat exchange fluid.

Heat exchange systems contain many different metals and alloys, and corrosion of these metals by heat exchange fluids has been unavoidable because of the inclusion of water with the diol-based antifreezes, such as EG or PG. Corrosion occurs because of the formation of organic acids in the coolant, such as pyruvic acid, lactic acid, formic acid, and acetic acid. The organic diols produce acidic oxidation products when in the presence of hot metal surfaces, oxygen from either entrapped air or water, vigorous aeration, and metal ions, each of which catalyze the oxidation process. Moreover, formation of lactic acid and acetic acid is accelerated in coolant solutions at 200° F or above while in the presence of copper. Formation of acetic acid is further accelerated in the presence of aluminum in coolant solutions at 200° F or above.

Among the metals and alloys found in heat exchange systems, iron and steel are the most reactive in the formation of acids, whereas light metals and alloys such as aluminum, are considerably less reactive. As the oxidation of diols progresses, the level of organic acids formed with the water fraction rises and the pH of the coolant decreased, and therefore, the corrosion of the metal surfaces increases.

Currently known .and utilized water based heat exchanger fluids include buffers to counteract these organic acids. The buffers act to create a heat exchange fluid with a higher initial pH of approximately 10 or 11. Thus, as the oxidation occurs, the pH decreases accordingly. Some examples of typically utilized buffers include sodium tetraborate, sodium tetraborate decahydrate, sodium benzoate, phosphoric acid and sodium mercaptobenzothiazole. Buffers, in turn, also require water in order to enter into and remain in solution. As the buffer portion of the solution becomes depleted over time, the water fraction of the heat exchange fluid reacts with the heat, air and metals of the heat transfer system, and as a result, the pH decreases because of the acids that form. Thus, corrosion remains a large problem in coolants that utilize water. All known heat exchange fluid formulations require the addition of water to solubilize additives used as buffers and anti- foam agents and for prevention of aluminum corrosion. Examples of such additives include phosphates, borates, silicates or phosphoric acids. In addition, these additives require heat, extreme agitation, and extensive time for the water to react and cause the additives to dissolve.

These requirements add significant cost and complexity to the formulation and packaging of antifreeze concentrates. The handling costs, energy costs and time required for blending are major factors in processing costs. Also, the constant requirement to monitor the formulating process to assure a "proper blend" has become extremely costly as many of today's additives, for aqueous concentrates, interfere with each other and can cause an incomplete solution and failure of the formulation process.

All currently used and previously known water based heat exchanger fluids require inhibitors to control the corrosive effects from the required water content. The inhibitors must be balanced so that they do not react with each other because that would otherwise minimize their individual purposes. For instance, phosphates and borates would decease the protection of silicates on aluminum. Moreover, the inhibitors must not be in excess concentration, which is usually done to extend the depletion time, because that causes damage to system components. For example, "fall-out" from solution causes plugging of radiator and heater core tubing. In addition, silicates, silicones, borates and phosphates are abrasive and erode heat exchanger core tubes and pump impellers. Nevertheless, the inhibitors must still exist in a concentration which is adequate to protect all metals.

In many marine and boat engine applications here the vessels are powered by internal combustion engines, the water in which the vessel is riding is pumped through the cooling jackets of the internal combustion engines without any corrosion or scaling inhibitors, removing excess heat from the engine. After cooling the engine, the water is returned to the body of water from which it was taken. Use of chemical based inhibitors would introduce pollutants back into natural waterways and the apparatus to disperse additives would be difficult and expensive to produce. As a result of having no inhibitors in the cooling water, engines and cooling systems of these boats and ships undergo excessive corrosion and scaling causing premature destruction of the engine and other cooling system parts.

When propylene glycol is used as the freeze suppressant, the viscosity of propylene glycol is considerably higher than that for a similar mixture of ethylene glycol. This viscosity reduces the speed of the heat exchange fluid when flowed through the heat exchanger system and hence decreases the ability of the propylene glycol and water (PGW) solution to transfer heat.

Another current heat exchanger fluid formulation contains a substantially non- aqueous, boilable heat exchange fluid, having a saturation temperature higher than that of water. Examples of such heat exchanger fluids are ethylene glycol, propylene glycol, tetrahydrofuryl alcohol, and dipropylene glycol. The viscosity of some of these heat exchanger fluids is high, especially operating at cold temperatures of 10° F or below requiring significantly higher pump energy to circulate the heat exchanger fluids. U.S. Patent Number 5 ,031 ,579 (Evans), dated July 16, 1991, shows a condenserless apparatus for cooling an engine with a substantially non-aqueous fluid, which is hereby expressly incorporated by reference as part of this disclosure. In addition the rate of heat transfer between substantially non-aqueous fluids and the heat exchanger surfaces is considerably poorer than for similar water based heat exchange fluids. This inferior heat exchange rate dictates the use of higher coolant flow rates with higher energy requirements to operate. In some instances, heat exchange systems where a water based heat exchanger fluid is replaced by such a substantially non- aqueous fluid, pump flow rates may need to be increased adding cost to the heat exchange system.

Non-aqueous propylene glycol, one heat transfer fluid which is currently being used as an engine coolant is highly hydroscopic and absorbs considerable water causing system design problems and considerations. The water content of the coolant must be kept at levels low enough to prevent corrosion and the generation of excess water vapor.

Typically attention to design of the cooling must be observed to insure that the water content of the non-aqueous propylene glycol remains at or below 5%. In another application when freeze temperature depressants are sprayed onto aircraft and other structures requiring de-icing in below freezing temperatures, the amount of time the de-icing compound stays on the aircraft or structures and keeps ice from re-forming is a critical aspect of de-icing formulations. Currently, de-icing compounds remain active for approximately 80 minutes. The longer this time can be extended, the more effective the de-icing compound. When a heavily viscous fluid is used, equipment needed to spray the fluid is significantly more expensive to build. Recently there has been a trend to use propylene glycol instead of ethylene glycol which has been used in the past as the freeze point suppress.ant. Propylene glycol is considerably less toxic than ethylene glycol. BRIEF SUMMARY OF THE INVENTION

The present invention solves the aforesaid heat transfer fluid problems by providing a product which is mixed with water based heat transfer fluids to provide a heat exchange fluid in which some or all of the additives used with standard freeze temperature depressants, such as ethylene glycol or propylene glycol, are no longer required. In addition, for non-aqueous coolants or for mixtures of water with either ethylene glycol or propylene glycol, the viscosity of the resultant moisture is significantly decreased by addition of this invention. The invention is classified as generally regarded as safe "GRAS" under federal regulations and is non-toxic. The new heat exchange fluid can be formulated by mixing water, or "neat"

(substantially pure) ethylene glycol or propylene glycol with water, preferably in concentrations of 30% to 70% ethylene glycol, or propylene glycol, or substantially non- aqueous boilable heat exchange fluids with an aqueous suspension of colloidal silica. Depending on the content of metals in the heat exchanger system other additives may or may not be needed.

The active component of the invention comprises an aqueous suspension of colloidal silica particles, preferably an aqueous solution with silica suspending herein. The silicon particles are preferably from about 10 to 100 angstroms in size and have an electrical charge thereon. The solution is preferably mixed in such a way that the colloidal particles become electrically charged, preferably by circulation of the solution through a magnetic field, and further, that the solution pass through a magnetic void during mixing so that the charged particles assume a stable configuration in relation to internal bonding. The charge on the colloidal particles is stabilized to remain during a relatively long shelf life of the final product by the mixing process and by the addition of molar amounts of citrate or citrate salts. The colloidal particles are also believed to carry several layers of water bound to the particle. The aqueous suspension of colloidal silica is preferably specially processed as described in US Patent Application No. 60/048,766 (Holcomb).

We have discovered that the colloidal silica in the product removes scale build-up on the surfaces of the heat exchange system, inhibits the formation of new scale, reduces the viscosity of the resultant fluid, increases the speed of heat transfer from heat generating surfaces to the heat exchange fluid, which is hereby expressly incorporated by reference as part of the present disclosure, inhibits the interaction of both the glycol and/or water with various metals in the heat exchange system, and eliminates the expensive process of mixing at least some of the various chemical additives with the cooling system water or the ethylene glycol, propylene glycol or some other freeze depressant additive normally used in heat exchange applications. In substantially non- aqueous propylene glycol the colloidal silica is more hygroscopic than propylene glycol minimizing any special design considerations to keep water content of the substantially non-aqueous propylene glycol at acceptable levels. Unlike most additives to current heat exchange fluids, the colloidal silica additive does not readily deplete and hence requires no replenishment.

In another application we have discovered that, by introducing an aqueous solution of colloidal silica, preferably in concentrations of 1 ppm to 500, into the cooling water used by vessels which extract their cooling water from and then return the cooling water to the water in which the vessels are riding, scale and corrosion within the vessel's cooling system are inhibited .and even removed without introducing any harmful elements back into the waterways. In a similar way the aqueous solution of colloidal silica can be introduced into any engine which uses water in a flow through manner where the water is used for a single pass through the engine .and then discarded wither into the reservoir from which the water is drawn or to a waste disposal system. In yet another application we have found that by mixing an aqueous suspension of colloidal silica with typical freeze point depressant fluids, we have been able to increase the amount of time the mixture can keep ice from forming on aircraft in deicing applications as well as decrease the pressure required and equipment costs required to pump the mixture.

BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements and wherein:

Figure 1 is a side view of a cartridge which holds the crystalloid from of the colloidal silica and releases colloidal silica slowly into the flow through engine cooling system.

Figure 2 is a comparison of viscosities of a standard propylene glycol and water heat transfer fluid mixed in a ratio of 60% propylene glycol and 40% water with a similar mixture containing 150 ppm of the colloidal silica. Figure 3 is a comparison of viscosities of commercially available substantially anhydrous propylene glycol with a similar mixture containing 150 ppm of the colloidal silica.

DETAILED DESCRIPTION OF THE INVENTION

In one preferred embodiment of the present invention heat exchange fluids which are cycled inside a heat exchange system can be formulated by mixing "neat" (substantially pure) ethylene glycol or propylene glycol (preferable in concentrations of 30% to 70% ethylene glycol or propylene glycol) with water and optional chemical additives depending on the composition of materials in the heat exchange system, and adding an aqueous suspension of colloidal silica to bring the concentration of colloidal silica within the composition to a preferred range of 1 ppm to 900 ppm. Although concentrations of a 1 ppm and more than 900 ppm have been shown to be effective in many applications.

In another embodiment of the invention cyclable heat exchange fluid can be formulated by mixing a substantially non-aqueous, boilable liquid including but not limited to ethylene glycol or propylene glycol, with a limited number of chemical additives such as those made up of nitrates, molybdate salts, and azoles, which is discussed in further detail in co-pending continuation in part of application serial No. 08/119,514 (Evans), entitled "Non- Aqueous Heat Transfer Fluid and use Thereof and co-pending application No. 08/449,338 (Evans), entitled "A method of Cooling a heat Exchange System using a Non-aqueous heat Transfer Fluid", which are hereby expressly incorporated by reference as part of the present disclosure, with an aqueous suspension of colloidal silica to bring the concentration of colloidal silica within the composition to a preferred range of 1 ppm to 900 ppm.

A third flow through heat exchange fluid can be formulated by introducing preferably 1 to 900 ppm of a colloidal silica into water which is passed through the heat exchanger and then either returned to the reservoir from which the water came (in the case of boats back into the water in which the boat is riding) or otherwise discarded with no ill effects to the environment. The colloidal suspension can be introduced as either a liquid suspended in water and infused into a cooling water or as a crystalloid form of the colloidal silica held in a flow through cartridge. The negatively charged silica colloid sequesters the positive ions of minerals in the water rendering them inactive and reducing significantly any potential scale build-up inside the heat exchanger. Similarly the silica colloid sequesters positive ions which would normally form oxide inside the heat exchanger reducing oxidation of the heat exchanger.

To introduce the colloidal silica, a flow through cartridge device as depicted in FIG. 1 is placed in the inlet of the cooling water prior to the heat exchanger. When water passes through the cartridge portion of the water is directed into a cavity which holds the colloidal silica in a crystalloid form.

When the water mixes with the crystalloid silica, small amounts of about 1 to 900 ppm of the colloidal silica are released into the cooling water. In another application a system for infusing the aqueous suspension of colloidal silica into the flowing water from a reservoir of a highly concentrated aqueous colloidal silica may be used. There are numerous ways known to anyone skilled in the art to infuse one liquid into a second flowing liquid.

To prepare the inventive colloidal silica suspension, as an example, an aqueous solution of colloidal silicon dioxide is first made up. This can be done by starting with a solution that is about 27% silicon dioxide in about 3 to about 4 molar NaOH. As one option, it has been found that citric acid or citric acid salts added in molar amounts about equal to the molarity of the NaOH improve the stability of the end solution. The starting solution and citric acid or citric acid salts, if present, is diluted very slowly, while stirring. Preferably, this is done by slow titration with about 0.5 - 1.0 molar of an acid, usually hydrochloric or acetic acid, to a pH of between about 7.6 and 8.2. This is preferably done over a period of several hours with constant stirring. The final concentration is a solution of colloidal silica. At this time the silica is present as colloidal particles of between 10 to 10 Angstroms in size. The Patent Application No. 60/048,766 (Holcomb), which is hereby expressly incorporated by reference as part of the present disclosure.

In order to generate a charge on the silica particles, it is preferred that, during the mixing of the colloidal silica solution, the solution be circulated through a magnetic field so that movement of the silica particles through the magnetic field generates the electrical charge on the silica particles. If the silica particles are passed through to a magnetic field so as to cut through the lines of flux of the field, an electrical charge is generated on the particles as they cut through the lines of flux. The particles act as both a conductor and a capacitor, i.e., they generate a charge and store the charge. After passing through a magnetic field to generate a charge on the silica particles, it is preferred that the particles be passed through a space substantially void of any magnetic fields. This space allows each of the charged particles to then assume a configuration based on the charges on the particle and the internal bonding of the particle without regard to external fields. It is currently understood that this provides formation of a very stable colloidal particle.

Circulation through the magnetic field and the magnetic void preferably takes place on the repetitive basis during generation of the colloidal solution. It has been found that with circulation through a magnetic field, the silica particles take on a net negative electrical charge. On apparatus which has been found advantageous for mixing the colloidal solution is shown in US Patent Application Number 60/0849,766 (Holcomb).

Once a mixture of water and the colloidal silica have been formed, the resulting mixture added to water and freeze point depressants, such as ethylene glycol and propylene glycol with or without chemical additives, as well as to substantially non- aqueous propylene glycol with and without chemical additives, is introduced into the heat exchange system in a way well known to anyone skilled in the art. Although the preferred embodiment of the invention uses either PG or EG as freeze protection or as a non-aqueous fluid, the two can be mixed together and used as freeze protection additives or any combination of PG and EG with other freeze protection additives could be used as well. Additionally the two may be used in any combination as a non-aqueous fluid with any number of additives well known in the field.

It is presently understood that the colloidal silica has substantial negative charge on the outside of the colloidal silica particles. The negative charge is postulated to "capture" positive ions because of the attraction of the positive ions in the coolant to the negative silica particles. In addition it is further postulated that the silica is a dipole moment with negative charge on one end of the silica particle and a positive charge on the other. The positive end attracts and "captures" negative ions in a similar manner although the attraction to positive ions is significantly stronger. The capturing of positive and/or in some cases negative ions inactivates the normal chemical scaling and corrosion process which requires chemical activity between positive and negative ions. In this way the silica inactivates oxidation and scaling of some or all of the surfaces which form a boundary between the heat exchanging surfaces and the heat exchange fluid.

If scale already exists on any of the surfaces of the heat exchange system, it is currently understood that the scale and oxidation is held to the surface by the electrostatic forces between substantially negative charge on the surface of metallic parts in the heat exchange system. When the negatively charged silica colloid particles are introduced and come in contact with the positive ions they counteract the electrostatic attraction of the ions to the metal surface and "capture" the positive ions in the silica. In this way the coolant which contains the colloid silica removes existing scale and oxidation from heat exchanger surfaces. DESCALING

CHARGED COLLOIDAL SILICA, AS A COOLANT FORTIFIER 1. Basics of Technology

Simply stated, the colloidal silica invention, in solution with the coolant medium (water, 50/50 EG or PG and water, or NPG) introduces colloidal silica particles with massive negative charges to the liquid. The negative charge is so dominant that it quickly introduces a negative charge to all it comes into contact with. Once corrosion, and scale receives a large negative charge, it loses its adherence to the metal component, which is also (always) negative in its charge, as the "like" charges repel each other and the corrosion, and scale deposits quickly fall away from the coolant surfaces of the engine, radiator, and heater core. Any further build-up of deposits is eliminated because of the continuing massive amount of negative charge which continues residually in the fluid. Heat transfer is also improved as the highly charged silica ions move around at a rapid rate because of their natural tendency to repel each other. These moments, in turn, cause an increased movement (rate) of the liquids molecules which results in the fluids having an increased ability to move heat into, out of, and through the liquid. 2. Benefits as an additive to 50/50 EG or PG and water a. Increased Heat Transfer

Better cooling performance any liquid cooling system (especially desirable race cars, performance cars, trucks and construction equipment). b. Extends the corrosion protection in all EGW or PGW antifreezes. *Especially if high mineral (or salt) content water is introduced to the coolant (as in many house water supplies)

* Will not allow scale build-up or corrosion to cause blockage of radiator or heater core tubes. c. Will "free-up" systems which are already clogged with scale build-up *Within minutes of adding the colloidal silica, the scale deposits will start to release from the entrances to heater and radiator tubes.

*In relatively short time, (presumably about one day), full flow should return to the radiator and heater which will return them to their original performance levels. d. Simply by adding the colloidal silica, a heater system which was not producing heat, for the passenger area, will return to full heater out-put. This should result in no more than 24 hours and would avoid a heater core replacement costing from

$500.00 to $1,500.00 or more (many current heater cores require the dashboard to be removed in order to replace). ii Radiator replacement, to cure over heating, would also be very often avoided as "clogging" is most often the cause for replacement (also a cost of up to $1,500.00)

** Note: Industry tests have shown that after only 20,000 miles of operation 30%) of cooling system capacity is lost due to surface build-up on components, (internal heat transfer blockage to the system). d. All the build-up of scale, on cooling system surfaces, would be eliminated for the life of the cooling system if the colloidal silica is added, as a fortifier, when the car is new. 3. Dynamics of de-scaling:

Once the scale is released, (See #1 above/"Basics"), the scale particles become suspended in the coolant. Many breakdown to "ionic" size and remain in suspension. Because they are so small they will cause no damage. Larger particles will fall out of the coolant and accumulate, harmlessly, in the bottom of the radiator tank. Most all will drawn out with a coolant draining as they have no affinity to adhere to the cooling system components (being "Negatively" charged). An effective de-scaling procedure would be to: a. Add the colloidal silica to the old coolant b. Drive the vehicle for a relatively short period (at least one 24 hour period). c. Drain the fluid after the "drive" period and replace with new coolant and a final charge of colloidal silica.

* Compare this colloidal silica "fortifier" method with the descalers which are currently used, (commonly called "system flushes"), especially in class 6-8 trucks; d. Chemicals used are usually acids e. Time periods, for the treatment, is critical as the acids can cause extensive damage if left in too long. f. Neutralizers must be used to stop the acids reaction with the system, (after the acid solution is drained.

*That which is drained out is a dangerous solution which is a highly toxic waste. g. The acid descalers never get all the scale removed, the colloidal silica will remove 100% of the scale deposits.

4. Benefits of the colloidal silica as an additive to 100% Water Systems: (Primarily race cars, agricultural, and some construction systems and about all boiler systems). These system are run on 100% water because the operators feel they are getting maximum heat transfer with water (many times that is wrong, due to massive water vapor entrained within the system). With the use of water there is no protection at all from corrosion and scale, colloidal silica as an additive, will give a significant level of corrosion protection, eliminate any build up of corrosion deposits, or scale, and keep the surfaces clean for maximum cooling. Additionally, the colloidal silica will improve the heat transfer ability of the water (See #1 above/"Basics") making the pure water, at 100%, cool better.

5. Testing ("A" Flow Benefit Tests, "B" Vehicle Test) A) Laboratory Dynomometer Bench Testing was performed to verify the effect of the colloidal silica added to a 50/50 mixture of water and ethylene glycol (antifreeze), as an additive usable on a universal basis as a true "pour-in" answer to the world wide problem of heat exchanger clogging as related to system scale build-up within water based cooling systems. A servo-controlled DC motor was used to drive a bench mounted conventional coolant pump (ford V-8) which was connected in series, by conduits, with a helical gear type spiral rotor flow meter and a coolant heater tank, housing three (3) 1500 watt heating elements. A conventional radiator 28" wide by 18" high (Chevrolet light duty V-8 truck) was selected from field use after being removed due to excessive engine temperature; ("over heating" due to poor coolant flow through the core tubes which were clogged from scale build-up). The radiator was placed in series with the pump, flow meter, and heater tank. Pressure recording points were tapped into the conduits at the inlet, and outlet, of the radiator to record the pressure drop (flow resistance) of the radiator core tubes. Testing was performed at a stabilized 200° F ± 1 ° F and progressive results, over time, were taken at the following RPM points; 1000 RPM ±1 2000 RPM ±1 3000 RPM ±1 4000 RPM ±1

Results:

The bench was warmed up to 200° F and operated at that stabilized point for eight hours with the baseline 50/50 EGW (No IPE added). At the 8 hour point an initial baseline reading was taken (chart "A" below) quantifying the limited coolant flow and higher pressure differential; CHART "A" BASELINE

The colloidal silica was then added making a solution level of 2400 parts per million (6% of 40,000 PPM concentrate). The bench was then operated on a cycle of 8 hours at 200 ° F and 16 hours of "cool-down" each day with data points taken at the end of each 8 hours of 200° F of operation. At the 3rd 8/16 hour cycle the maximum results were achieved;

CHART "B" 24 HRS AT 200° F

The bench was then run for an additional three 8 hour/ 16 hour cycles during which there was no additional flow improvement noted. A visual inspection of the radiator was then performed and a complete removal of all scale deposits, at the core tube openings, was noted as well as an extremely clean appearance of the tube header flange. The test results revealed that the effective cleaning (de-scaling) period, of the test, had been during the first 24 hours of running time.

B. Vehicle Testing was performed on a 1986 model 944 Porsche with 130,000 miles on the original radiator. The car had been rendered "undriveable" due to severe coolant temperatures and overheating. It was concluded that the cause was excessive scale clogging of the radiator in that when the radiator was in cycle, (thermostat open), the engine would run hot (approximately 210° F) and the radiator would be operating much cooler (approximately 110° F). This was a clear indication that the coolant flow, through the radiator, was almost completely blocked. The upper radiator hose was also noted to be similarly hot, as the engine, but immediately upon entering the radiator the coolant within the core tubes dropped rapidly across the face of the radiator. This indicated that there was some flow but not very much.

The colloidal silica was subsequently added to the system through the vehicles pressure cap on the expansion reservoir. A solution of 2400 PPM was used similar to the bench test described above. The engine was then allowed to idle for four hours thereby mixing the colloidal silica into solution and passing the mixture on through whatever passages were open in the radiator core. After approximately 1¹/_ hours the temperature level of the radiator began to rise, and by the 4th hour, the engine had returned to normal operating temperature of 195° F (Thermostat control) and the radiator was hot, indicating good coolant flow. The vehicle was returned to the road and has exhibited normal coolant temperatures including operation at higher ambient temperatures (80° F). The coolant was observed to have particles of scale, and corrosion, suspended in it and a sample was taken out and analyzed at the end of 60 days of post treatment operation. REDUCING VISCOSITY WITH THE COLLOIDAL SILICA The viscosity of a heat exchange fluid is an indication of the electrostatic force of attraction between various molecules within the fluid. The introduction of the negatively charged silica colloid into the liquid decreases those forces of attraction causing a corresponding reduction of viscosity. FIG 2 demonstrates the reduction in viscosity actually measured in a 60/40 mixture of propylene glycol/water heat exchange fluid with and without addition of 150 ppm of silica colloid . Measurements of viscosity were made at - 36° F showing a decrease in viscosity from about 1250 centipoise to 650 centipoise. Figure 3 demonstrates the reduction in viscosity, at the same 36° F for a mixture of non-aqueous propylene glycol (NPG) with the colloidal silica as compared to NPG without the colloidal silica. CONTROL OF WATER CONTENT WITH THE COLLOIDAL SILICA

The colloidal silica added to NPG has shown that water levels may be kept well below 0.5% when the NPG is used as a heat transfer fluid.

In an internal combustion engine heat exchange system application as detailed in Patent No. 5,031,579, operating with substantially non-aqueous propylene glycol formulated with at least one of an appropriate molybdate salt, nitrate compound, and an azole compound, the hygroscopic nature of propylene glycol was sufficient to increase the water content of the mixture to levels of about 3%. After adding colloidal silica in concentrations of 150 ppm to the mixture maximum levels of water were reduced to 0J % which eliminates the necessity to take special steps to insure that the percentage of water inside the heat exchange fluid is controlled. It is understood that the colloidal silica is so hygroscopic that it attracts water from the propylene glycol thus limiting the maximum amount of water which is absorbed by propylene glycol. The colloidal silica "sequesters" some of the water preventing the water from reacting with propylene glycol, and some of the water is additionally driven off into the ambient atmosphere.

We have discovered that adding colloidal silica to propylene glycol reduces the hygroscopic nature of propylene glycol. Propylene glycol which is left open to atmosphere with some water content in the atmosphere traditionally increases the water content in the propylene glycol up to 10% in a given time period at 70° humidity. However, if approximately 150 ppm of an aqueous suspension of colloidal silica is added to the propylene glycol, the amount of water found in propylene glycol is limited to approximately less the 0.1% in most ambient applications. Since water content in propylene glycol produces unwanted water vapor and corrosion of metal parts in cooling systems for internal combustion engines, the addition of the aqueous suspension of colloidal silica reduces those unwanted effects of water. In many typical applications this reduction relieves the necessity to provide for mechanical or other chemical ways to control the water content in propylene glycol for cooling applications. Three vehicle and one bench tests have been conducted with various concentrations of the colloidal silica ranging from 300 PPM to 1200 PPM. In all cases the initial water content was above 3% in the total solution, with the highest content being a maximum of 6%. In all cases the water fraction dropped to below 0.1% within 24 hours of operation at about 200° F. The fraction of 0.1% was then maintained throughout the following operating of the vehicles, in the test, during normal cold and hot seasonal changes in the North East, and Central U.S. regions. Each test was similarly constructed to the structure of the Evans 08/449,388 patent application, specifically using the expansion reservoir to raise the vapor pressure of the NPG. That configuration has previously been shown to keep the water fraction of the NPG coolant at about 3.0%. The three vehicle and the one bench tests are described below with observed (measured results). 1. Bench Test

The same flow dynamometer test bench was used, for the test, as was used and described in the report on colloidal silica Descaling Tests. The bench test system was filled with a fresh charge of Evans NPG coolant with a water content of 0.02%. The fluid was tested for water content to verify the baseline of the test. An industrial/chemical industry refractometer was used to make the measurement which is accomplished by light penetrating (passing through) the fluid and refracting off the water, if present, and resultantly being read on a precise scale of graduations on the refracted lens. The reading confirmed the fluid was "neat" (water free) with a reading of below 0.1% water content. At that point a 6% fraction of the colloidal silica was added to the coolant volume for a total system volume of 2.0 gallons. The volume was unchanged as the same 6% fraction of NPG was removed from the system just prior to the addition of the colloidal silica. The bench was then operated for three 8 hour hot cycles, each followed by a 16 hour cool down, at 1000 pump speed RPM. At the time of the addition of the 6% fraction of the colloidal silica, the water content was measured and found to be about 5.5%. The colloidal silica used was a concentrate of 15,000 PPM therefore a resultant volume of 900 PPM colloidal silica was added to the total volume.

The results observed were that the water fraction reduced by about 3/4's of its content during the first two hot cycles (16 hours), and became non-detectable during the last cycle (8 hours) with a reading, on the refractometer, of below 0.1% total content. 2. Vehicle #1

A new 1997 Jeep Grand Cherokee; 5.2L V-8, was filled with NPG coolant and a charge of 3.0% colloidal silica (using a 15,000 PPM concentrate) resulting in a 450 PPM colloidal silica solution and about 3.0% water fraction. The water content, after the addition, measured to be 2.8% on the refractometer.

The test was then started on 6/21/97 with an odometer reading of 45 miles. The system was operated with a 7.0 PSI pressure cap and a 195° F thermostat. The vehicle was operated in rural driving, accumulating about 40 miles per week. After one week of operation, 280 miles, the fluid was measured for water content and found to be below

0.1% fraction on the refractometer test equipment which was used for the bench test, described above. The vehicle has remained in constant service since the initial start-up in 6/97. The water has been monitored each month and found to be below 0.1% fraction during the entire period of 6/97 to 11/98 with an accumulated mileage of coolant samples have been taken to quantify "stability" (life of the coolant). The following chart details the test results over the two year period of 4/21/97 to

10/11/98; Mode Date Mileage Water Fraction

Start (Baseline) 4/21/97 45 2.8% NPG/colloidal silica 4/28/97 280 <0.1% NPG/colloidal silica 10/15/97 14,218 <0.1% NPG/colloidal silica 04/22/98 20,332 <0.1% NPG/colloidal silica 10/11/98 24,659 <0.1% NPG/colloidal silica (continuing)

3. Vehicle #3 A 1996 Dodge (Intrepid); 3.3L V-6, which had been operated since new (6/96) on NPG, was measured for water content and found to have a 2.9% water fraction on the refractometer test equipment described previously in the "bench test" section, after 19 months of operation in the Detroit, Michigan area. At that time, during January of 1998 a 6% charge of colloidal silica was added to the coolant volume resulting in a solution of 900 PPM colloidal silica (6% of 15,000 concentrate in the total system volume) which additionally raised the water content to about an 8.7% fraction of the total system volume. The vehicle was then subsequently operated in the Detroit, Michigan area until April of 1998 (3 mos.) when it was driven to Sharon, CT and the water content measured on the refractometer test equipment. At the time, the water fraction was observed to have dropped to below 0.1 % fraction of the total volume. The vehicle was then placed back into service to continue operation, and evaluation.

4. Vehicle #4

A 1997 Jeep Grand Cherokee; 4.0L V-6, was converted from new (36 miles) with a complete drain, and fill, with NPG coolant. The system pressure was reduced to 7.0 PSIG and the vehicle was placed into a light duty service operation with intermittent short operating periods where by a minimal amount mileage was accumulated (3642 miles) during the period of 4/97 to 11/98. On 11/20/98 the water fraction was measured to be 2.8% of the total coolant volume. The vehicle was then driven for a distance of 1002 miles over a period of 17 hours (2 days; 8 hrs, and 9 hrs respectively). The water fraction was then measured and found to have dropped to below 0.1% total volume of the system. COLLOIDAL SILICA USED TO IMPROVE HEAT TRANSFER

Although the substantially non-aqueous heat transfer fluid is normally propylene glycol it can be ethylene glycol or any mixture of both propylene glycol and ethylene glycol as well or one of any other normally used organic heat transfer fluids.

We have discovered that the colloidal silica (preferably specially processed as described in US Patent Application 60/048,766 [Holcomb]) in the produce in concentrations of approximately 150 ppm decreases the time required to bring the temperature of a fixed volume of non-aqueous propylene glycol with anti-corrosive additives in a metal container from 62° F to 230° F by a factor of 6 to 8% when compared to a like fluid with no colloidal silica added and that different concentrations of the colloidal silica change the time in differing amounts. It is concluded from the experiment that the rate of transfer of heat from the metal surface to the heat transfer liquid is increased by about 6 to 10%. IMPROVED DE-ICING WITH THE COLLOIDAL SILICA

In yet another application we have discovered that the amount of time a de-icing compound can keep ice from reforming on air-craft is a function of how viscous the fluid is when it is on the wings, the hygroscopic nature of the fluid and the ability of the fluid to adhere to the surface of the aircraft. Typically propylene or ethylene glycol is used. By adding approximately a preferred 1 to 900 (however, more may be desirable) ppm of an aqueous suspension of silica particles to the non-aqueous propylene or ethylene glycol, the viscosity is significantly decreased causing the fluid to flow better .and assure an even distribution of de-icing fluid over the aircraft. The lower viscosity reduces the cost of the equipment needed to spray the de-icing fluid. The hygroscopic sequestering and moisture repelling nature of the colloidal silica tends to limit the amount of water which is absorbed by the de-icing fluid. For example, the less water in the propylene glycol the lower is freeze point will be. Hence by using the colloidal silica, the freeze point is decreased, increasing the time before re-freezing occurs. In addition, because of the highly negative charge of the colloidal silica and the positive charge on the aircraft, the fluid formulated with the colloidal silica adheres more readily to the aircraft surface. The application is not limited to aircraft but can be used in any system where ice needs to be removed from any surface.

The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.

Claims

CLAIMS L A method of cooling a heat exchange system which comprises circulating a composition in said system, said composition consisting of a suspension of negatively charged particles, thereby inhibiting and/or removing formations of scale and/or corrosion of at lease one surface of heat exchange system components.

2.. A method of cooling a heat exchange system which comprises circulating a composition in said system, said composition consisting of a suspension of negatively charged particles, thereby lowering the viscosity of a heat transfer fluid containing water and at least one freeze point depressant substance.

3. A method of cooling a heat exchange system which comprises circulating a composition in said system, said composition consisting of a suspension of negatively charged particles, thereby lowering the viscosity of a heat transfer fluid which contains a substantially non-aqueous, boilable liquid.

4. A method of cooling a heat exchange system which comprises circulating a composition in said system, said composition consisting of a suspension of negatively charged particles, thereby increasing the rate of heat transfer from at least one surface of a heat exchange system to a heat transfer fluid.

5. A method of cooling a heat exchange system which comprises circulating a composition in said system, said composition consisting of a suspension of negatively charged particles, thereby decreasing the hygroscopic properties of a substantially non- aqueous propylene glycol by introducing into the propylene glycol an aqueous suspension of charged colloidal silica particles.

6. A method as defined in claim 2 where the freeze point depressant substance is either ethylene glycol or propylene glycol.

7. A method as defined in claim 1, 2, 3, 4 or 5 where the heat exchange system is an engine cooling system where at least one engine coolant chamber is formed adjacent to heat-rejecting components of the engine.

8. A method as defined in claim 2 where at least one additional buffer, defoamer, surfactant, chelate, dye, corrosion inhibiting, cavitation inhibiting, or scale inhibiting chemical is introduced into the heat exchange fluid.

9. A method as defined in claim 3 or 4 where the non-aqueous heat transfer fluid is propylene glycol or ethylene glycol or any mixture of the two.

10. A method as defined in claim 9 where the heat transfer fluid consists essentially of propylene glycol, and at least one additive soluble in propylene glycol, said additive inhibiting corrosion of at least a first metal used to form the heat exchange system.

11. A method as defined in claim 10 where the heat transfer fluid consists essentially of propylene glycol, and at east one second additive soluble in propylene glycol, said second additive inhibiting corrosion of a second metal used to form the heat exchange system.

12. A method as defined in claim 11 where the heat transfer fluid consists of a third additive which is soluble in propylene glycol which third additive inhibits corrosion of a third metal used to form the heat exchange system.

13. A method defined in claim 10, 11, or 12 where the soluble additives are selected from a group consisting of a molybdate salt, a nitrate compound, or an azole compound.

14. A method as defined in claim 4 where the heat exchange fluid contains water and at least one additive to lower the freeze point of the fluid.

15. A method of inhibiting the formation of scale in an open loop flow through heat exchange system wherein an aqueous suspension of charged colloidal silica particles is added to the cooling water which is flowed through the heat exchange system and then discarded.

16. A method as defined in claim 15 where the suspension of negatively charged particles is introduced from a flow through cartridge wherein the charged particles are held in a chamber through which at least part of the cooling water passes or from which the solution can be otherwise infused into the cooling water.

17. A heat transfer fluid composition for use in a heat exchange system where an additive comprising of a suspension of negatively charged particles is added to the heat exchange fluid.

18. A heat transfer fluid composition of claim 17 wherein said heat exchange fluid is made up of at least one of a substantially water, a mixture of water with at least one freeze point depressant, or a non-aqueous fluid.

19. A heat transfer fluid composition of claim 18 wherein said heat exchange fluid has at least one additive inhibiting the corrosion of at least a first metal used to form the heat exchange system.

20. A freeze suppression fluid for use in de-icing of surfaces of structures exposed to temperatures below the freezing temperature of water, such freeze suppression fluid comprised of a substantially non-aqueous base liquid and at least one additive comprised of a suspension of negatively charged particles.

21. A freeze suppression fluid as defined in claim 20 where the substantially non-aqueous freeze suppression fluid is either ethylene or propylene glycol.