Ripe (technology)
Technical maturity arises in technical processes in which air with a temperature of below −2 ° C is cyclically conveyed into a vortex ; also needs the vortex steadily cooling power to be supplied.
There are relevant maturations in technology in the following processes:
- Frost formation on aircraft
- Snow cannons
- Zureifung the evaporator of an air / water heat pump or a refrigeration system .
At the moment there is no possibility to simulate frost or snow formation processes . The reason is that these processes have not yet been understood physically. This applies in particular to air / water heat pumps; none of the formulas published so far allow a physical understanding of the maturation of an evaporator.
Emergence
The formation of a snowflake begins (according to studies by Prof. Kenneth G. Libbrecht at the California Institute of Technology ) at atmospheric pressure at a temperature below −2 ° C with a microscopic, floating mineral or biological freezing germ. If such a germ solidifies to a freezing germ, then constantly supercooled water molecules attach to it and solidify to ice. The growth of the frozen germ into a snowflake through this process is called the Bergeron-Findeisen process .
If there are no freezing germs in the air, the snowflake only develops at temperatures below −40 ° C via supercooled water germs.
In addition, the above-mentioned investigations at the CIT showed that the above Conditions also more complex ice crystals can be formed, which are known as dendrites . They are only formed when the air is clearly oversaturated with water; The humidity therefore plays a major role in the formation of frost and snow. In addition, the cyclical circulation of the air in a vortex from a cold surface, which must be colder than −2 ° C, to an environment, which must be warmer than 0 ° C, is necessary for the formation of complex snow crystals from freezing germs.
meaning
In aircraft technology
In the case of an aircraft, technical frost is created by vortices in the area of the inflow surface of the wing or the propeller as well as by smaller drag vortices in the area of the frontal surface . In order to prevent the windows from icing up on the front surface of the aircraft, they are heated with embedded resistance layers or wires so that they do not frost up (see aircraft de-icing ).
With fan guns, too, the propeller is stripped by means of electrical heating. The energy requirement for such thermal de-icing using electricity is extremely high. Therefore, this method is used more as an emergency procedure. In order not to overload the electrical power of the aircraft, not all heating surfaces are switched on at once and continuously, but only individual ones (in pairs, symmetrical) and at intervals (e.g. every 5 minutes). In the case of electrical de-icing on the four-blade propeller, two propeller blades opposite each other must be de-iced at the same time. One problem would be asymmetrical de-icing on the propeller, which can lead to strong vibrations (e.g. with a frequency of 42 Hz at a speed of 2500 revolutions per minute), which u. a. possibly damage the motor. In the event of strong vibrations, the speed must therefore be reduced as much as possible immediately.
By snow cannons
The basic principle of a snow cannon was discovered by chance in Canada at the end of the 1940s, when a team of researchers led by the Canadian Raymond T. Ringer sprayed water into a wind tunnel at low temperatures in order to investigate the icing of jet engines - which resulted in unwanted snow.
With a snow cannon, air that has to be colder than −2 ° C is pumped, swirled and injected with water. This process for the formation of frost or snow requires that the cooling capacity of the conveyed air with its freezing germs allows the injected water to be cooled to a temperature of below -2 ° C. If this is not the case, the freezing nuclei recrystallize so that no frost or snow is formed in the snow cannon.
In the inflow area of an air heat pump
If you analyze the frost pattern in the front area of the lamella of an evaporator of an air / water heat pump or refrigeration system, then it is frost or snow with a dendrite structure. Due to the swirling of the conveyed air, part of the air in the inflow area is continuously and cyclically swirled in a small dragging vortex. In addition, the conveyed air in the vortex must be cooled to a temperature of −2 ° C. This also has the effect that the air in the drag vortex is heavily oversaturated with water. As soon as the first freezing germs are formed in the drag vortex, the snow formation process begins in the front area of the evaporator lamella.
Since the heat exchanger in the inflow area only starts to close at a limit temperature of −2 ° C, the temperature can be raised to above −2 ° C by punching in the front area of the evaporator fin. This is a very effective way of preventing the evaporator of an air heat pump from ripening. This allows the annual coefficient of performance JAZ (similar to the efficiency ) of an air / water heat pump to be increased from currently 3 to 3.75, i.e. H. Generate 3.75 kilowatts of heating energy from one kilowatt of electricity . The heat pump manufacturer Viessmann Group applied for a patent in 2015 .
