FI101547B - Method of cooling an object with a heat transfer agent using the change of agent and heat transfer agent - Google Patents

Description

1 101547

Method of cooling the object with a heat transfer medium, use of the substance and heat transfer medium

The invention relates to a method for cooling an object with a heat transfer medium, wherein the cooling takes place by heat transfer to a heat transfer medium containing potassium formate. The invention also relates to the use of the substance and to the heat transfer medium to be pumped.

Particularly at low operating temperatures, the aim is to use a heat transfer medium 10 to cool the object so that the heat transfer medium does not solidify at any stage of the process or that the solutes in it do not crystallize. In order to replace the dangerous ethylene glycol, a lot of water-based heat transfer agents have been used, in which various salts have been dissolved to lower the freezing point. For example, U.S. Patent No. 15,510,456 discloses a heat transfer agent, the most preferred composition of which is 1 mole of potassium formate per 6 moles of potassium acetate dissolved in water.

As already stated above, the heat transfer medium should remain liquid at its operating temperatures. In indirect cooling, the heat transfer medium is cooled to its lowest temperature, after which it is brought into heat transfer contact with the object to be cooled, which is then cooled so as to transfer heat to the heat transfer medium. Heat transfer is also affected by the viscosity of the substance.

According to U.S. Pat. No. 5,104,562, a salt / water molar ratio of 1: 4.72 could, in the case of pure potassium formate, reach a freezing point of -35 ° C, but with an acetate / formate molar ratio of 6: 1 even as low as -70 ° C.

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However, it is obvious that these measurements have been made by methods which determine the freezing point without taking into account the effect of mixing the test solution. It has now been found that if the heat transfer medium is circulated, its freezing properties and, as a result, its cooling properties change decisively.

2 101547

It has been found that if the cooled liquid is mixed in concentrated solutions, the acetate-containing solution crystallizes at lightning speed and its pumpability properties change substantially.

5 Coolants are used in many cases under conditions in which they remain stationary for long periods of time, whereby the solution of the aforementioned U.S. patent remains non-solidifying, but solidifies when subjected to vibration, agitation or pumping.

The object of the invention is to provide a method by which the reliability of the cooling process can be improved. To achieve this purpose, the process is mainly characterized in that the heat transfer medium is an aqueous solution of potassium formate, in which the molar amount of dissolved potassium formate is at least 80% of the molar amount of all water freezing point depressants and the heat transfer medium mixes with the object to be cooled.

It has now been found that, contrary to the information of the above-mentioned U.S. patent, potassium formate has excellent properties for its use as a heat transfer agent.

Low operating temperatures are achieved by using potassium formate in a sufficient concentration, preferably at a concentration of at least 30% by weight.

25 The behavior of a concentrated solution is of great importance, because over time, for example, as a result of the evaporation of water, the solution may concentrate and thus blockages in the piping of cooling systems. On the other hand, indirect cooling systems operating at very low temperatures, such as below -30 to 40 ° C, in any case require the use of fairly concentrated solutions, and thus potassium formate achieves greater reliability even at very low temperatures due to better solubility and lower freezing point of acetate. Concentrated potassium formate also has a lower viscosity than potassium acetate. 35

The experiments leading to the invention will now be described in more detail with reference to the accompanying drawings, in which Figure 3 shows a phase diagram of an aqueous solution of potassium formate, Figure 2 shows the viscosity of an aqueous solution of potassium formate as a function of temperature, and Figure 3 shows the viscosity of potassium formate.

EXAMPLE

The freezing point was measured from the solution as follows. The test solution was dispensed (ca. 15 ml) into a test tube with a stopper. Prior to sealing, an additional 8 mm diameter glass ball was placed in the test tube. A test tube (about 30) was placed in a rack which was immersed in the cooling tank of a refrigerating machine. The coolant temperature was lowered from 5 ° C / day to 0 ° C to 60 ° C. Inspection of the test tube was performed daily by lifting each test tube from the cold bath, tilting the tube so that the glass ball moved back and forth in the test tube, and caused the solution to stir. The formation of ice crystals in test tubes 20 was observed visually.

Formate and acetate solutions according to Table 1 were prepared for freezing experiments. Solutions were prepared by mixing stoichiometric amounts of formic acid / acetic acid and potassium hydroxide.

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Table 1. Freezing point tests and kinematic viscosities of solutions measured at room temperature.

4 101547

Experience K-for- K-asc- Water- I freeze is- Throw- Uaom.

mate pacifier toint point cSt __% __% __% ° C __ (20 * C) __ 1 <0 __- 40 * 55__237K-formate lyose 2 SO - 50 -40 L91___ 3 40 - 60 -25 1.46 4 30 __-__ 70 __- 15 132___ 5 50 10 40 -60 __-__ K-form / K-set »5/1 6 41.7 83 50 * 40__L94 __-_ 7 333 6.7 60 -2S __-__-_ g 25.0 5 70 -15 - 9 40 20 40 -40 __- __K-forai / K-set = 4/2 10 333 16.7 50 -40 2J9__ · _ 11 26.7 133 60 -2S __-__ * · _ 12 20 10 70 -15 __-__ · _ 13 30 30 40 -40 __- K- form / K-sets = 1/1 14 25 25 50 __- 45__2M__ "15 20 20 60 -25 __-__” _ 16 15 15 70 __- 15 __-__ "_ 17 20 40 40 crystallizes - K-form / K-sets = 2/4 18 16.7 333 50 -40__2 £ 7 __ * _ 19 133 26.7 60 __- 25 __- "_ 20 10 20__70 __- 15 __-__ * _ 21 10 50 40 crystallizes - K-form / K-settings s 1/5 22 83 41.7 50 -35__2-98 __ ”_ 23 6.7 333 60 -35 __-__" _ 24 5.0 25 70 -20__ · __ "_ 5 101547

It can be seen from the results that K-formate-rich solutions (Experiments 1 and 5) were able to achieve a lower freezing point than K-acetate-rich solutions of the same concentration. With concentrated K-acetate solutions, crystallization occurred immediately after the solution 5 was introduced by means of a glass ball. Prior to its rapid crystallization, the solution was completely transparent. After crystallization, the sample solution became cloudy and very solid.

Figure 1 shows a phase diagram of potassium formate, in which the freezing-point curve is a polynomial fit to the freezing points of potassium formate solutions of different concentrations measured by the applicant and the solubility curve is a polynomial fit to the solubility values obtained from the literature. At the eutectic point, the potassium formate concentration is about 68% by weight and the freezing point is about -70 ° C.

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The results also show that the viscosity of the concentrated K-formate solutions (50% K-formate solution, 1.91 cSt, experiment 2) is clearly lower than that of the corresponding K-acetate solutions (50% K-acetate / K-formate solution, 2.98 cSt, experiment 22). . This is of great importance for the pumpability of the coolant. Figure 2 shows the viscosity measured with a potassium formate in a Ostwald capillary viscometer tube held in a cold bath at different concentrations as a function of temperature, and Figure 3 shows the viscosity dependence of the operating temperature with potassium formate and known heat transfer agents. The operating temperature in this case is 10 ° C above the freezing point of the solution used, i.e. if it is desired to use a heat transfer agent at -15 ° C, a solution with a freezing point of -25 ° C is selected, in the case of potassium formate a solution with a viscosity of about 35% by weight. at operating temperature is about 4.2 mPas. It can be seen from the figure that the viscosity of potassium formate is below the viscosities of known heat transfer agents, and the difference increases with the transition to low operating temperatures. The pH values of potassium formate solutions are also in the range where they do not require special materials for piping. The pH values of the 35 and 50 wt% solutions are 6.17 and 6.71, respectively.

35 In terms of properties, potassium formate solution as such is the best coolant option. The freezing point of potassium formate could not be reduced by the additives tested by the applicant, which were potassium acetate, sodium formate, sodium acetate, ethylene glycol, ethanol, urea and potassium chloride. If other substances are mixed with the potassium fibromate used as the coolant, the molar amount of the dissolved parts formed by the potassium fibromate must be at least 80% of the 5 molar amount of all the dissolved parts in the heat transfer medium which lower the freezing point of water. These dissolved moieties can be ions or undissociated molecules.

The following Table 2 shows the effect of some of the above additives on the freezing point of the potassium formate solution.

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Table 2. Effect of different additives on the freezing point of aqueous solution of K-formate at three different concentrations. The amount of each additive is 20% of the amount of K-formate.

K-formate solution + _ Solution concentration_ additive__20% 35% 50%

K-form. (clear solution) -10 ° C -25 ° C -50 ° C

K-Fonn. + K-position, __- 15 ° C -25 ° C -50 ° C

K-form. + Na-form .__- 10 ° C -20 ° C -40 ° C

K-form. + Na-acet .__- 15 ° C -25 ° C -45 ° C

K-form. + EtyLglyk. -15 ° C -20 ° C crystallized K-form. + Ethanol -10 ° C -20 ° C crystallized 7101547

The preparation method used in the process according to the invention is simpler, since no harmful acetate is required and in this respect the manufacturing costs are reduced. The potassium formate used in the invention 5 can be prepared by direct synthesis in the presence of a suitable catalyst from carbon monoxide and potassium hydroxide. Potassium acetate cannot be prepared by direct synthesis, so it is considerably more expensive than potassium formate made in the manner in question. Thus, it is apparent that potassium formate, made by the direct synthesis of carbon monoxide and potassium hydroxide, is a useful coolant suitable for heat transfer in most applications where the solution must remain molten down to -40 ° C. It should also be noted that potassium formate has significantly better heat transfer properties than the currently commonly used ethylene glycol. In addition, unlike ethylene glycol, potassium formate is less toxic and the decomposition products are harmless to nature.

Potential corrosion problems can also be avoided by adding suitable inhibitors.

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The invention can be applied to many refrigeration equipment in use and in general to objects requiring low temperatures.

Claims (9)

101547 A method for cooling an object with a heat transfer medium, wherein the cooling takes place by heat transfer to a heat transfer medium containing potassium formate, characterized in that the heat transfer medium is an aqueous solution of potassium formate. . 2. For the purposes of paragraph 1, the amount of molar game 15 is determined to be 90% of the total potassium form. Process according to Claim 1, characterized in that the molar amount of the dissolved parts formed by the potassium formate is at least 90% of the total molar amount. 3. A compound of formula 1 or 2 is used, the concentration of which is potassium formate in a solution of at least 30% by weight, the yield being 40% and 65% by weight. 20 Process according to Claim 1 or 2, characterized in that the concentration of potassium formate in the solution is at least 30% by weight, preferably between 40 and 65% by weight. 20 4. For the purposes of paragraph 3, the potassium formate is treated with a minimum of 98% by weight of the compound in the watten and the wattage, with a corrosion inhibitor. 25 5. Förfarande enligt nägot krav ovan, kännetecknat därav, att potassiumformiatlösningen används i ätminstone en del av kylnings-processen vid emperat temperat temperā. Process according to Claim 3, characterized in that the potassium formate is present in an amount of at least 98% by weight of the amount of substances dissolved in the water, the remainder being excipients, such as corrosion inhibitors. Process according to one of the preceding claims, characterized in that the potassium formate solution is used in at least part of the cooling process at a temperature below -20 ° C. 6. For the purposes of item 5, the temperature of the drift is 30 ° C and the temperature is below -30 ° C, the temperature is below -40 ° C. Process according to Claim 5, characterized in that the operating temperature in at least part of the cooling process is below -30 ° C, preferably below -40 ° C. 7. Envändning av en potassiumformiatvattenlösning i en concentration av minst 30 vikt-%, företrädesvis 40-65 vikt-% som ett pumpbart värme- 35 överföringsmedel. 7. Use of an aqueous solution of potassium formate having a content of at least 30% by weight, preferably 40-65% by weight, as a heat transfer medium to be pumped. 35 9 101547 8. In the case of a pump, the use of potassium forms in an object, which is determined by the addition of potassium formate in accordance with Article 11 101547, in which case, both parts of the potassium form are not subject to a maximum of 80% of the effect. 8. A pumpable heat transfer medium for cooling an object, characterized in that it contains potassium formate dissolved in water in an amount such that the molar amount of dissolved parts formed by potassium formate is at least 80% of the molar amount of all dissolved parts lowering the freezing point of water. Heat transfer medium according to Claim 8, characterized in that the concentration of potassium formate in the solution is at least 30% by weight, preferably between 40 and 65% by weight. 101547 5 1. For example, an object with an object with a water treatment medium, with a view to the genome of an energy test, with an indication of the amount of the substance used in the water, of which 80% of mol-10 play down to the bottom of the sink water frost point and the color of the frying point of the sample is relative to the relative object of the scaly. 9. To Värmeöverföringsmede! According to claim 8, the concentration of potassium formate in the solution is at least 30% by weight, the yield is 40% and 65% by weight. «