CS251794B2 - Heat transfer fluid - Google Patents

Abstract

The heat sharing fluid comprises 2 to 12 parts by weight of water, urea and/or formamide and/or dimethylformamide, in an amount of not more than 4 parts by weight, ammonium nitrate in an amount of not more than 7 parts by weight and optionally ethylene glycol in an amount of not more than the same volume as the above-mentioned components, as the main components, and not more than 0.3% by volume or weight of a corrosion inhibitor, based on the volume or weight of the fluid as a whole. The use of this fluid eliminates the disadvantages associated with the use of glycol completely or to a large extent, and the fluid also constitutes a non-toxic heat sharing fluid suitable for isopiestic drying.

Description

The present invention relates to a multi-component heat transfer fluid which is widely used. The heat transfer fluids of the present invention can be used for cooling internal combustion engines, non-polluting thermal central cooling systems, industrial refrigerating and freezing machines, and household and open and closed solar collectors, chemical industrial duplicators and refrigerators. autoclaves and for isopiocene drying.

Various types of heat transfer fluids are used in industry. Water is used wherever it can be used, since it is cheap, does not pollute the environment and has no adverse health effects, is non-flammable, has only slight corrosion and its specific heat is high. A major drawback of this application is that the water volume increases by 9% after freezing and therefore the closed devices are damaged. From the point of view of heat centers requiring a large cooling capacity, another drawback, which is of great importance in water scarce areas, is that the water has a very low boiling point and therefore a relatively high pressure. Therefore, the evaporation rate is high and any undesirable water losses can be significant.

The relatively low boiling point can also be disadvantageous, since boiling water, for example in solar collectors and vehicle cooling systems, causes serious operational problems. It is therefore desirable to extend the temperature range in which the heat transfer fluid can be used, i.e., to increase its boiling point.

A further drawback of water is that it cannot be used for isopesticic drying. Isopestic drying means processes in which the water content of the heat-sensitive dried substance (e.g. corn, wheat) is removed with a water-absorbing liquid at room temperature. The dried substance and liquid are kept in the same enclosed drying chamber, with air circulating through the fan. The water absorbed by the liquid is removed by continuous or continuous distillation of the liquid and the liquid is periodically or continuously returned to the drying chamber. This not only prevents unwanted heating of the dried substance, but also saves more energy compared to the hot air drying technique.

The freezing point may be lowered and the boiling point may be increased by mixing well soluble compounds in water. These phenomena, the so-called cryoscopic phenomena, can multiply if strong electrolytes dissolve in water, since electrolytic dissociation in water leads to an increase in the apparent concentration even in concentrated solutions. A widely used, well soluble, three-ion dissociating strong electrolyte is calcium chloride. The disadvantage of its use is, as in the case of other chloride compounds, the rapid corrosion of the metal components, especially when the temperature is permanently or periodically high. A particular drawback of chloride ions is that they cause local corrosion (such as pitting, joint corrosion and intercrystalline corrosion), which in some cases wears the device even when its walls are substantially intact. Similar problems are encountered with other chloride compounds , while the use of acidic and alkaline solutions restricts the regulations on health and environmental cleanliness in addition to its corrosive action.

Lower alcohols, ketones, hydrocarbons (e.g., gasoline, and cyclohexanone are preferred for their antifreeze properties, but are flammable, their vapors with water form foaming compositions, most of which are toxic and have a low boiling point. Another disadvantage of the above-mentioned solvents is that its heat capacity, based on weight unit (specific heat), is small (approximately 30 to 40% specific heat of water).

When their density is less than one, its specific heat per unit weight is much less. This is of practical significance since heat transfer fluids are used in equipment with a predetermined volume.

Aqueous solutions of ethylene glycol are widely used in practice as heat transfer fluids because of their numerous advantages. Glycol is miscible with water in any ratio, is slightly flammable and explosive, its specific heat is approximately twice as high as the above organic compounds, is colorless and relatively resistant to freezing. The specific heat and freezing point depend on the glycol / water ratio, with the specific heat rising and the freezing point decreasing as the water content decreases. The lowest freezing point is the eutectic mixture containing 60% glycol. Another advantage is that the volume of the glycol-water mixture does not increase after freezing, so that the equipment is not damaged.

However, the above advantages are associated with some technical drawbacks that limit the further usability of the glycol / water mixture, although the cost of the glycol is not significant. Ethylene glycol is highly toxic and can be fatally poisoned as it easily confuses with ethanol. Due to its toxicity it pollutes the environment and therefore cannot be discharged into waste water. On the other hand, its use is limited by the fact that the 1: 1 consistency of the mixture, which is important from a practical point of view, is a non-thixotropic mass even at -31 ° C (although the freezing point of the mixture is -38 ° C) and therefore this mixture cannot be pumped. So it is necessary to consider not only the freezing point of the mixture, but also a relatively narrow temperature range at which the mixture has a nonhitropic viscous consistency, hereinafter referred to as the flow limit, which is also of great practical importance. By varying the glycol to water ratio, the glycol / water mixture cannot be used for heat transfer at temperatures below -30 ° C. The antifreeze character and flow characteristics of the mixture change with time. Due to the slow polymerization of glycol, the mixture has to be replaced by a fresh mixture, which presents further technological and economic drawbacks.

It is therefore an object of the present invention to provide a new heat transfer fluid that meets the following requirements:

- its boiling point would be higher than that of water,

- its specific heat would be similar to that of water,

- its freezing point would be varied by varying the composition, if necessary the flow limit could be reduced below -31 ° C,

- its volume would not increase after freezing,

- would be miscible in any proportion with water,

- it would not be toxic, explosive and flammable and would not pollute the environment,

- it would be miscible with a mixture of glycol and water,

- it would be odorless (to avoid air pollution),

- it would be non-corrosive and would not be more corrosive than mixtures of glycol and water.

Accordingly, the present invention provides a heat transfer fluid consisting of water, urea and ammonium nitrate and optionally glycol as the main constituents, wherein the weight ratio of urea and ammonium nitrate is from 1: 1.50 to 1: 2.00, preferably 1: 1 , 75. The solution may further comprise a buffer to adjust the pH to 8.0 to 8.5 and a corrosion inhibitor to prevent corrosion of the metal parts.

The invention is based on the theoretical knowledge that the -NH ₂ groups of certain water-soluble amide compounds (e.g. formamide, urea, ethanolamine, phenylenediamines, dimethylformamide or mixtures thereof) tend to protonate, to form prototropic associations and hydrogen bridges in the presence of water and salts If this protonation is associated with the formation of ammonium hydroxide, salinisation occurs, the amide compound and the acid-hydrolysing amine salt increase their mutual solubility, and this is also used in the preparation of liquid fertilizers. the urea and ammonium nitrate are dissolved together in water, the concentration of both urea and ammonium nitrate substantially exceeds the saturation concentration of aqueous urea and aqueous ammonium nitrate solutions in the thus obtained solutions of the three components water, urea and nitrogen. ammonium stannate, although the chemical reaction does not occur.

The invention is further based on the finding that in a system of water, an ammonium compound, an ammonium salt, in particular water, urea, ammonium nitrate, the properties cannot be predicted by a simple sum of the parameters of the characteristics of the various solutions. This means not only solubility conditions, but also freezing point, boiling point, flow limit and specific heat, especially when glycol is added as a major component. In this case, the solution is not favorable from the point of view of environmental contamination, but the advantageous properties of both liquid systems are favorably combined. For example, the flow limit can be substantially extended compared to the water-glycol system. On the other hand, if the glycol-containing heat transfer fluid is diluted with another non-flammable and non-toxic solvent, the hazardous properties of the glycol are reduced in direct proportion to the dilution.

Experiments have confirmed that the corrosive action of the urea-water-ammonium nitrate solution is less than the glycol-water system if the pH value of the urea-water-nitrate system. the ammonium is adjusted to 8.0 to 8.5 and the inhibitors, preferably additives containing thiomycin, alkylpolyglycol ester and / or hexamethylenetetramine as active ingredient are added in a concentration of 0.1 to 0.2, at most 0.3%, with percentages being by weight or by volume.

Solutions containing the above ingredients meet the above requirements. At the same time, the ratio of the components may vary within wide concentration limits, thereby obtaining the most advantageous results in terms of pour point and flow limit when the weight ratio of ammonium nitrate to urea is 1.50 to 2.0, preferably 1.75.

The invention is illustrated by the following non-limiting examples.

Example 1

Heat transfer fluid suitable for isopestyl drying

2 parts by weight of water, 4 parts by weight of urea and 7 parts by weight of ammonium nitrate are mixed. Since dissolution is a strongly endothermic reaction, mixing is performed in a heatable duplicator equipped with a stirrer. The pH of the mixture is adjusted to

7.2 by the addition of potassium carbonate, followed by the addition of 2.5 liters of potassium hydrogen phosphate and hexamethylenetetramine per 1 m of mixture as inhibitor. The dense, viscous liquid thus prepared has the following characteristics:

freezing point +7.5 ° C boiling point 123.0 ° C density 1,348.0 kg / m ³

The liquid is preferably used for isopestic drying because of its high boiling point.

On the other hand, it is suitable as an antifreeze if water is added as its freezing point drops rapidly after the addition of water. The blend can be directly prepared in a urea and ammonium nitrate plant, saving an expensive distillation step. Antifreeze solutions can be prepared by adding water and optionally glycol to said mixture. Transporting the concentrate is more economical compared to transporting antifreeze containing larger amounts of water.

Example 2

Glycol-free antifreeze

A solution containing 8 parts by weight of water, 4 parts by weight of urea and 7 parts by weight of ammonium nitrate is prepared in two different ways: by direct mixing the individual components and diluting the solution of Example 1 with water; the additives listed in Example 1 are also added to the solution. The mixture thus obtained has the following characteristics:

freezing point boiling point boiling point density specific heat

-28.8 ° C -28.8 ° C 110.5 ° C

234.0 kg / m ³

3.24 j / ° C.cm ^ (at 20 to 25 ° C)

It is recalled that the specific heat of the preferred mixture of glycol and water in a ratio of III is the same as the liquids prepared according to this example. The composition of this example does not contain glycol, but has a flow limit of -31 ° C, which is the value achievable at the most preferred glycol / water ratio.

The urea may be partially or completely replaced by the other amide compounds mentioned above. Thus, the properties of the liquid can vary widely, for example, the freezing point can be reduced below -30 ° C. However, such a requirement occurs only in special cases, since there is rarely a need for antifreeze liquids satisfying below -30 ° C.

The volume of the liquid according to the example does not increase after freezing and since the precipitated crystals do not completely fill the space, they do not interfere with the metal wall of the device. The liquid is not toxic when it comes into contact with the skin or when it comes into the mouth and can be used as a valuable fertilizer. Optionally, it can be mixed with a phosphate and a potassium compound and can then be converted to a mixed fertilizer after removal from the apparatus. If it is considered that it is generally not necessary to cool to temperatures around -30 ° C and below -30 ° C, freezing the mixture (since it does not damage the apparatus) is not disadvantageous since the melting of the mixture is endothermic and cools the system. In such cases, heat transfer refers to the use of latent heat, since when the environment is colder than -30 ° C, heat is dissipated from the refrigerated machine operating at a temperature higher than -30 ° C.

If the freezing point and flow limit are to be further reduced, for example, to values for a glycol / water mixture, this can be achieved by adding glycol or a glycol / water mixture, as will be shown in the following examples.

Example3

Glycol-containing antifreeze

A mixture is prepared containing 43.2 liters of water, 28 liters of glycol, 15.6 kg of urea and 27.3 kg of ammonium nitrate and the additive listed in Example 1. The same solution can be obtained if 28 volumes of glycol and 12 volumes of water are obtained. to 60 parts by volume of the composition of Example 2. The composition obtained has the following properties:

freezing point boiling point boiling point density specific heat

-38.0 ° C -37.0 ° C 112.5 ° C

178.0 kg / m ³

2.56 J / ° C.cm ³ (at 20 to 25 ° C)

The mixture contains 28% by volume glycol. If a mixture of glycol and water of the same pour point is prepared, 50% by volume of glycol is required. However, the flow limit of such a glycol / water mixture is only -31 ° C, although this is the optimal case. At the same time, the composition according to the invention makes it possible to reduce the flow limit and to save 22% or 44% glycol compared to conventional solutions. Certain deficiencies resulting from the presence of glycol are also diminished.

According to Example 1, 39.9 liters of water, 38.5 liters of glycol, 11.7 kg of urea,

20.5 kg of ammonium nitrate and additive according to example 1. The same mixture can be obtained by mixing 38.5 parts by volume of glycol and 16.5 parts by volume of water into 45 parts by volume of the liquid according to Example 2. The mixture obtained has the following characteristics:

Example 4

Super antifreeze coolant containing glycol freezing point liquidity limit boiling point density specific heat

-48.5 ° C -45.0 ° C 113.0 ° C

156.0 kg / m ³

3.0 J / ° C.om ³ (at 20 to 25 ° C)

It can be observed that after the freezing point has decreased, the difference between the freezing point and the flow limit increases gradually. If only the freezing point reduction is to be achieved without regard to the flow limit, then the freezing point can even reach -69 ° C for the mixture by adding 59.9 parts by volume of glycol and 25.5 parts by volume of water to 15 parts by volume of the mixture of Example 2 Conversely, the lowest freezing point of the glycol / water mixture is -57 ° C. The freezing point of the glycol-water system of the eutectic composition can be reduced by about 12 ° C using approximately the same amount of glycol, although the practical use of such a system is limited by the fluidity problems.

The advantage of the heat transfer fluid according to the invention is that the drawbacks of using glycol are completely or largely eliminated, whereby the freezing point and the liquid flow limit of the solution can be substantially reduced, so that liquids can be used in a wide range of temperatures. At the same time, a nontoxic heat transfer fluid suitable for isopesthic drying has been developed, so that not only can a considerable amount of energy be saved, but heating can be eliminated in the case of heat-sensitive substances.

Claims (3)

1. Heat transfer fluid, characterized in that it contains 2 to 12 parts by weight of water, urea and / or formamide and / or dimethylformamide, in an amount of not more than 4 parts by weight of ammonium nitrate in an amount of not more than 7 parts by weight and such as the aforesaid substances as the main component and not more than 0.3% by weight or 0.3% by volume or by volume of the total liquid. 2. A liquid according to claim 1, characterized by 1.5 to 2.0, preferably 1.75. 3. The liquid according to claim 1, characterized in that 7.5. of a corrosion inhibitor calculated on the total that it contains ammonium nitrate and urea in a ratio that has a pH adjusted to a maximum of 4 by the buffer. 3. The liquid according to claim 1, wherein the alkylpolyglycol esters or hexamethylenetetramine comprises thiourea, preferably a mixture thereof, as inhibitors.