RU2137798C1 - Composition of low-temperature heat carrier - Google Patents

Abstract

FIELD: special compositions. SUBSTANCE: composition has the following components, wt.-%: glycerol 30-32; sodium molybdate 1-3; disodium phosphate 0.5-2; sodium tetraborate 1-3; benzotriazole 0.01-0.2, and water - the rest. Heat carrier exhibits the low corrosion activity with respect to metals, low viscosity, stability of properties and impossibility of formation of insoluble deposits that ensures to use its as a heat carrier in thermoregulation systems of cosmic apparatus. EFFECT: high quality and properties of the composition. 1 tbl

Description

 The invention relates to low temperature coolants (antifreezes) and can be used as a coolant for thermal control systems (CTP) of spacecraft (SC).

Special requirements are imposed on the heat transfer fluids for the manned missile spacecraft with long-term operation: firstly, the coolant must be non-toxic in order to protect the crew in case of accidental leakage from the man-ship; secondly, it should not be corrosive to metal materials STR; thirdly, it must be chemically resistant for a long time (10 or more years), not change its properties and not form insoluble precipitates, which can lead to contamination of filters and slotted gaps of STR, and, finally, it must have good physicochemical and thermophysical properties: freezing temperature below minus 8 ^o C and viscosity no more than 3 cSt, high thermal conductivity and heat capacity.

 Known antifreezes based on ethylene glycol with special additives that reduce the corrosion effect on the inner surfaces of the STR [1 G.P. Pokrovsky "Fuel, lubricants ...", M, 1985, p. 162-167]. A complex hydrocarbon, dextrin, is introduced to protect against destruction of copper, aluminum and lead-tin solder; disodium phosphate (2.5-3.5 g / l) is added to protect cast iron, steel and brass; and sodium molybdenum acid is used to protect zinc and chromium coatings ( sodium molybdate) (7-8 g / l) [1, p. 164]. Other corrosion inhibitors of ethylene glycol antifreezes are known: triethanolamine phosphate (3%), mercaptobenzothiazole or benzotriazole (0.2-0.3%), sodium benzoate (5-7.5%) sodium tetraborate (decahydrate) (2.4- 3.0) [2, "Non-combustible coolants and hydraulic fluids", ed. Sukhotina A.M., 1979, p. 275 and 289] and other substances [2, p. 290 and 291].

The disadvantages of these coolants are:
- high toxicity;
- high viscosity (4.4-7.3 cSt), which entails the need for increased energy consumption during the operation of electric pumps for pumping the coolant in the STR.

 Ethylene glycol is a powerful food poison. If it enters the body, even in small amounts, it causes severe poisoning. The lethal dose of ethylene glycol for humans is only 20-30 g.

 A known composition of a low-temperature coolant containing glycerin, water and benzotriazole [2, p. 312, Fig. 10.10. (prototype)].

The disadvantages of this technical solution is the high viscosity (45 cSt at a temperature of 20 ^o C) [2, p.299]; high corrosion activity in relation to metallic materials and chemical instability, leading to the formation of an insoluble precipitate, which is unacceptable for STRS, since it leads to contamination of filters and small gaps in the system.

When choosing components for the preparation of a new coolant, we were guided by the following basic principles: firstly, the main component of the coolant should provide a freezing temperature of the solution not higher than minus 8 ^o C; secondly, all components of the coolant should be low toxic and chemically inert with respect to each other; thirdly, all components of the coolant must have a sufficiently high solubility in water.

 As the main component that lowers the freezing point of the solution, glycerin was chosen, the low toxicity of which is well known.

 In addition to the main components, the new coolant must contain corrosion inhibitors. Corrosion inhibitors should be chemically inert with respect to glycerin and to each other.

 Based on the foregoing, sodium molybdate, sodium tetraborate, disodium phosphate and benzotriazole were selected for the preparation of the coolant.

 The chemical composition of the new coolant, along with low corrosion activity with respect to metallic materials, ensures its low viscosity, stability of properties, and the impossibility of the formation of insoluble precipitates, which makes it possible to use it in STR.

The essence of the invention lies in the fact that the composition of the low-temperature coolant, consisting of glycerol, water and benzotriazole, additionally contains sodium molybdate, sodium tetraborate and disodium phosphate in the following ratio of components (wt.%):
glycerin - 30-32
sodium molybdate - 1-3
disodium phosphate - 0.5-2
sodium tetraborate - 1-3
benzotriazole - 0.01 - 0.2
water - the rest
The use of the specified amount of glycerol provides the required crystallization temperature (freezing) of the coolant. The use of sodium molybdate, sodium tetraborate, disodium phosphate and benzotriazole provides the required corrosion inertness of the coolant with respect to metallic materials.

 For the preparation of coolant samples, the procedure described below was used.

 1. The calculated amount of glycerol, sodium molybdate, sodium tetraborate, disodium phosphate and benzotriazole were successively dissolved in a glass container. The mixture was stirred until the components were completely dissolved. In the resulting solution can be added fluorescein (uranium) in an amount of 0.01 g / l for tinting and to ensure identification of the coolant fluorescence method.

 2. After dissolving the components, the solution was allowed to stand for at least 8 hours.

 3. After settling, the coolant was filtered through a paper filter and poured into a hermetically sealed container for storage.

 The coolant samples were tested according to the methods described below.

 1. The appearance of the coolant was determined visually in transmitted light in a test tube P2-19-150XC or P1-16-150XC according to GOST 25336-82E.

2. The kinematic viscosity at a temperature of 20 ^o C was determined according to GOST 33-82.

 3. The crystallization temperature was determined by the method, namely, that the test coolant was cooled to form ice crystals visible to the naked eye, then it was heated and the temperature was fixed at which the last ice crystal disappeared (melted).

For this, 20 cm ^{3 of} coolant was placed in a test tube with a diameter of 20 ± 1 mm, closed with a stopper in which a thermometer and a stirrer were inserted, and placed in a thermostat bath with a cooling mixture (isopropanol - dry ice or liquid nitrogen). The temperature of the cooling mixture in the bath was maintained at 10-12 ^o C below the expected freezing temperature of the coolant. The coolant was cooled with constant stirring until ice crystals appeared. After the appearance of ice crystals, the device was removed from the thermostat bath and the state of the liquid was observed with stirring in transmitted light. The crystallization temperature of the coolant was taken as the temperature at which the last ice crystal disappears.

 4. The corrosive effect on metals was determined according to GOST 29117-76.

Example 1. The optimal content of additives
The composition of the coolant (wt.%):
glycerin - 31
sodium molybdate - 2
disodium phosphate - 1
sodium tetraborate - 2
benzotriazole - 0.1
water - the rest
Example 2. The minimum content of additives
The composition of the coolant (wt.%):
glycerin - 30
sodium molybdate - 1
disodium phosphate - 0.5
sodium tetraborate - 1
benzotriazole - 0.01
water - the rest
Example 3. The maximum content of additives
The composition of the coolant (wt.%):
glycerin - 32
sodium molybdate - 3
disodium phosphate - 2
sodium tetraborate - 3
benzotriazole - 0.2
water - the rest
Example 4. The average content of additives
The composition of the coolant (wt.%):
glycerin - 31
sodium molybdate - 1.5
disodium phosphate - 0.75
sodium tetraborate - 1.5
benzotriazole - 0.05
water - the rest
Example 5. The average content of additives
The composition of the coolant (wt.%):
glycerin - 32
sodium molybdate - 2.5
disodium phosphate - 1.75
sodium tetraborate - 2.5
benzotriazole - 0.15
water - the rest
Example 6. The content of additives is less than the lower limit.

The composition of the coolant (wt.%):
glycerin - 25
sodium molybdate - 0.5
disodium phosphate - 0.5
sodium tetraborate - 0.5
benzotriazole - 0.1
water - the rest
The coolant had an insufficient freezing temperature, and corrosion of metal samples was observed.

 Example 7. The content of additives exceeds the upper limit.

The composition of the coolant (wt.%):
glycerin - 35
sodium molybdate - 4
disodium phosphate - 3
sodium tetraborate - 4
benzotriazole - 0.25
water - the rest
The coolant had a high viscosity and formed insoluble precipitates.

 Example 8. The composition of the coolant corresponds to the prototype.

 The coolant had a high viscosity, formed insoluble deposits and corrosion of metal samples was observed.

 The properties of the obtained laboratory batches of coolant are given in the table.

 Thus, the coolant obtained according to the recipe and technology developed by us has significant advantages compared to the prototype, which is confirmed by the data in the table, and can be used for thermal control systems of spacecraft.

Claims (1)

The composition of the low-temperature coolant, consisting of glycerol, water and benzotriazole, characterized in that it additionally contains sodium molybdate, sodium tetraborate and disodium phosphate in the following ratio, wt.%:
Glycerin - 30 - 32
Sodium Molybdate - 1 - 3
Disodium phosphate - 0.5 - 2
Sodium tetraborate - 1 - 3
Benzotriazole - 0.01 - 0.2
Water - Else

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