DE3909105A1 - Heat pipe - Google Patents

Abstract

The invention relates to a thermal syphon and a heat pipe having special working liquids which can be used in principle over the entire temperature range. However, in this case the range between -10 and +40@C is especially preferred, because so far no optimum working liquids have been available here. The heat-transporting capacity of the known working liquids of methanol and ethanol is not very high. The temperature range mentioned above is too low for water, which is overwise the ideal working liquid. The invention makes available a heat pipe having different working liquids based on azeotropic mixtures which not only cover a wide temperature range, but at the same time also have a very high heat-transporting capacity.

Description

The invention relates to a thermosiphon or a heat pipe a special internal working fluid, such as z. B. to Transport of heating or cooling energy and to the isostatic Use tempering.

As is well known, a thermosiphon is a closed container, in usually in the form of a tube with a small amount filled with a working fluid and then under setting of a certain internal pressure is sealed gas-tight. Now this container is set up essentially vertically and warmed at its lower end, the accumulated there begins Working fluid to warm up and evaporate. The Steam spreads evenly inside the container. When the steam hits cooler zones of the container wall it condenses there, the condensate forming droplets and runs down the container wall due to gravity, to the liquid supply in the sump of the container again complete. When the working fluid evaporates, it becomes warm Zone of the container deprived of heat. This latent energy will transported by steam and condensed to the colder zone of the container released again. So it takes place both a material and energy transport within the thermosiphon instead, which is phenomenal without any moving or wearing components only is started by supplying heat, and completely runs silently. With thermosiphon this process can be due to the gravity dependency is only in a circular direction, which is why it is also called a thermal diode.

The so-called heat pipe is the thermosiphon similar. It also has a capillary structure inside, which serves to absorb the working fluid. A Swamp with a supply of working fluid is normal not present, that is, the amount of working fluid is approximately such that it is complete in the working state is sucked up by the capillary structure. For the transport of the Working liquid in the liquid state are the capillary forces responsible, so that a heat pipe is also overhead or can be used in zero gravity in space travel.  

With a vertical arrangement of the heat pipe, the return can of the condensate are supported by gravity if the evaporation zone is at the bottom and the condensation zone is at the top.

Special forms of heat pipes have separate lines, so-called Arteries, for returning the condensate. They can do that Improve heat transport capacity of a heat pipe in that the droplet entrainment of condensate is prevented by the steam flow becomes.

As working fluid of thermosyphons and heat pipes Substances are required whose enthalpy of vaporization reaches high values. At the same time, these substances have good wetting properties have to be thermal in the working temperature range be stable, the construction materials must not attack and should be physiologically safe. For one A number of applications also play an acceptable price important role.

So far, working fluids are according to the working temperature range quite a number of substances for use came. These are both organic and inorganic Substances, as well as metals. In the temperature range between around 30 and 200 ° C water is a working fluid dominant place. No other known substance reached similarly high in terms of heat transport capacity Values. They also sum up its other positive qualities makes water an unbeatable candidate. The little one Vapor pressure of water at low temperatures, however, requires very small internal pressures within the system and leads too high flow rates due to the low evaporation rate of steam. This results in approximately below 80 ° C a greater decrease in the heat transport capacity. At very low working temperatures in the range from 0 to about 30 ° C Therefore, the use of water as the working fluid is eliminated out.

In the low temperature range described was used as working fluid previously mainly used ammonia. Towards water is the heat transport capacity of ammonia as a working fluid however significantly reduced. Because of the physiological concern There are also efforts to reduce ammonia health replace harmless working fluid.

As working fluids in the low temperature range Time methanol and ethanol were also used. Compared to ammonia the heat transport capacity of these alcohols is reduced again.

There was therefore the task of creating a thermosiphon and a heat pipe with working fluids, which either expand the range of applications for known working fluids, or at given working temperatures and internal pressures Should increase heat transport capacity.  

The task is according to the in claim 1 and in the subclaims given teaching solved. Then the invention Thermosiphon or the heat pipe according to the invention with an azeotrope mixed working fluid. According to the invention is a choice between the different forms of Given azeotropy. Are proposed as mixture components organic or inorganic substances and their subgroups Alkanes, alcohols, ketones and cycloalkanes, alkane amines, alkane diamines or water, ammonia or hydrazine.

Azeotropic mixtures are known to have the property of Boiling into a vapor phase of the same composition, the boiling point of the mixture compared to the boiling points of the pure substances is shifted at the same pressure. Positives Azeotropes show a lower boiling point, while negative ones Azeotropes have an increase in boiling point. Man this property can also be seen as an increase or decrease interpret the vapor pressure at a given temperature.

By using azeotropic mixtures as working fluids in thermosyphones and heat pipes is thus by the invention opens up the possibility of using the known range Expand working fluids. Are the azeotropic mixtures e.g. B. composed with water, its boiling point can, for. B. by adding a certain proportion by weight of hydrazine the new boiling temperature of 120 ° C can be brought to normal pressure. In the same way, for. B. a reduced to 87 ° C. achieve a new boiling point if the water contains a certain percentage of propyl alcohol (1-propanol) is added. According to the invention such azeotropic working fluids also come as tertiary, quaternary, quaternary or higher quality mixtures for use.

When using water as a mixture component azeotropic Working fluids are particularly preferred such mixtures, that have a relatively high proportion of water. This makes the extremely high evaporation enthalpy of water in strong Measures the evaporation enthalpy of the azeotropic mixture, so that despite a z. B. reduced boiling temperature still the enthalpy of vaporization of the azeotropic mixture is quite high remains.

With the use of azeotropic mixtures as working fluids in thermosyphons and heat pipes are mainly compared to the Use of pure water gives further advantages that depending on the type and amount of admixture, the freezing point of the Working fluid is degradable, which makes a certain Frost protection is achievable, and in addition better ones Wetting properties by reducing the surface tension surrender.

To clarify the possibilities given by the invention are shown in Tables 1 to 4 azeotropic mixtures based on Examples between water and various admixtures in their respective proportions by weight and the new boiling temperatures  listed. Table 1 shows these values for additives of various alkanes, table for 1-alkanols, while in Table 3 ternary mixtures between water, 1-butanol and various alkanes are compiled. In addition, Table 4 shows various examples of other mixtures shown. The invention is not based on the examples shown limited. Because of the large number of azeotropic mixing possibilities would be a complete listing within the scope of this Blast patent application.

With the invention thus a thermosiphon and a heat pipe provided with working fluids, which are opposite pure substances either in an extended working temperature range can be used, or a higher heat transfer capacity have. The invention further opens up the possibilities, at the same time better wetting properties to realize and in certain cases an anti-freeze to realize.  

Table 1

Table 2

Table 3

Table 4

Claims (15)

1. Thermosiphon, consisting of a gas-tight container, preferably a tube-like configuration with a supply of enclosed working fluid and a specific internal pressure or heat pipe (heat pipe), consisting of a gas-tight container, preferably a tube-like configuration with an internal capillary structure, a supply of enclosed working fluid and a specific one Internal pressure, whereby in both cases the working liquid is evaporated by applying a temperature difference to the warmer zone and condensed in the colder zone, thereby using the steam flow to heat energy from the warmer zone to the colder zone and by means of the backflow of the condensate on the wall of the container , in the capillary structure, or via a separate artery, cold energy is transported from the colder zone to the warmer zone, characterized in that the working fluid has an azeotropic mixture at least is at least two substances. 2. thermosiphon or heat pipe according to claim 1, characterized in that the mixture has a positive azeotropy. 3. thermosiphon or heat pipe according to claim 1, characterized in that the mixture has a negative azeotropy. 4. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that the mixture is a has positive-negative azeotropy (saddle azeotropy). 5. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that the mixture is a Owns homoazeotropy. 6. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that the mixture is a Possesses heteroazeotropy. 7. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is an organic substance.   8. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is an inorganic substance. 9. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is water. 10. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is an alkane. 11. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is an alcohol. 12. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is a cycloalkane. 13. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component the working fluid is a ketone. 14. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component is an aminoalkane. 15. Thermosiphon or heat pipe according to one or more of the aforementioned Claims, characterized in that a mixture component is a diamino alkane.