In ballooning, we deal with gases, liquids and solids. We are now primarily interested in the substances we encounter in their various states of aggregation.

Question: Which substances do we encounter in at least two different states of aggregation in ballooning?

The transition from a solid to a liquid state is called melting. To melt a solid such as ice, heat must be added; the solid must be warmed up. The solid can be warmed up

• by exposing it to radiation, such as sunlight.
• by direct heat transfer from one medium to another.
• by convection of a surrounding medium, which then transfers the energy to the surface of the solid by direct heat conduction.
• by exerting pressure on the body, causing it to compress.

The transition from a liquid to a solid state is called freezing, and heat is released. There are several ways to cool a liquid:

Through direct heat transfer from one medium to another, for example when water comes into contact with a cold surface or the temperature of the ambient air falls below the freezing point of 0°C/273K.

By radiation. For example, at night when the heat radiation emitted by the medium is greater than the radiation received.

By convection of a surrounding medium such as air. For example, cold air can flow down into a valley and lower the air temperature there until it eventually falls below the freezing point of water, 0°C/273K.

Beim Verdunsten geht ein Stoff vom flüssigen in den gasförmigen Zustand über, wobei die Flüssigkeit nicht die Siedetemperatur erreicht. Voraussetzung ist aber dass das Gas, oder Gasgemisch über der Flüssigkeit nicht gesättigt ist. Übertragen auf die Luft bedeutet das, dass die relative Luftfeuchtigkeit geringer als 100% ist.

Beispielsweise können sich Lebewesen nicht mehr durch Schwitzen abkühlen, wenn die Luftfeuchtigkeit 100% beträgt, da dann keine Verdunstung mehr stattfindet.

Ein Beispiel wo ein anderer Stoff als Wasser verdunstet ist das Benzin im Tank des Gebläses. Allerdings ist Benzin kein Stoff sondern ein Gemisch, und Teile davon verdunsten rascher als andere.

Eine Flüssigkeit verdampft, wenn sie die Siedetemperatur, den Siedepunkt überschreitet.

Achtung: Umgangssprachlich sprechen wir von Wasserdampf, wenn wir tatsächlich eine Ansammlung kleinster Tröpfchen sehen. Der Kaffee dampft. Wasserdampf ist wie alle Gase transparent und damit unsichtbar.

Beim Betrieb unserer Ballone verdampfen wir das Propangas. Der Siedepunkt von Propan liegt bei -42°C/231K bei einem Druck von 1013hPa, dem Normaldruck. Wenn der Druck erhöht wird, erhöht sich auch der Siedepunkt, wir kennen das Prinzip vom Dampfkochtopf.

Dadurch dass das Propan in der Flasche unter Überdruck ist, bleibt es flüssig. Da die Flasche nicht vollständig mit flüssigem Propan gefüllt wird, bildet sich oberhalb des flüssigen Propans ein Gaspolster. Das flüssige Propan wird mit einem Tauchrohr entnommen, und in den Brennerspiralen überhitzt, so dass beim Austritt aus den Brennerdüsen es schlagartig verdampft.

Sowohl zum Verdunsten als auch zum Verdampfen wird Wärmeenergie benötigt. Würde die Menge Propan die zum Betrieb des Brenners benötigt wird, in der Flasche verdampfen, dann würde diese so stark abkühlen dass sie vereist.

Wie bereits ausgeführt, erhöht sich die Siedetemperatur wenn der Druck erhöht wird. Umgekehrt sinkt die Siedetemperatur, wenn der Druck verringert wird. Das ist das Prinzip des Vergasers beim Motor. Hier wird an einer Stelle wo Unterdruck herrscht flüssiger Treibstoff hinzugeführt, so dass dieser vergast. Wie wir gelernt haben, wird zum Verdampfen - Vergasen Wärmeenergie benötigt. Und diese wird aus der Umgebung entnommen. Beim Vergaser kann das, wenn sich Wasser im Benzin befindet, zur Vergaservereisung führen. Und damit kann der Vergaser ausfallen.

When operating a hot air balloon, there are two cases of undesirable conversion of liquid propane to gaseous propane: In the pressure regulator, if the regulator is not fed from the gas cushion above the liquid propane when the cylinder is lying down, but directly from the liquid propane. This causes the pressure regulator to ice up.

And on the burner control valve, if this is not fully opened and the reduced cross-section causes a drop in pressure, the liquid propane turns into gas. This can cause the control valve to freeze. If the propane contains water, there is a particular risk of the valve freezing inside and no longer functioning as intended. Therefore, always open and close the control valve fully.

The gases used as carrier gases, hydrogen and helium, require such low temperatures and such high pressures to liquefy that they always remain gaseous in the balloon. However, in rare cases, the lifting gas is supplied in liquid form for events. It is transported in specially insulated containers at a temperature of -259°C/14K and must be vaporised before the balloons can be filled. To do this, it is passed through an evaporator, usually a cold evaporator, which extracts heat energy from the ambient air. Given the amount of hydrogen or helium required to fill the balloons in a short time, the cold gasifier tends to freeze, and its performance decreases because the ice has an insulating effect.

Water condenses as soon as saturation of 100% is exceeded. In the atmosphere, the dew point, the point at which 100% relative humidity prevails, is reached through cooling. Relative humidity is the ratio of the absolute amount of water vapour contained in the air to the maximum possible amount of water vapour that could be contained in the air. And this amount depends on the temperature.

Cooling in the atmosphere occurs

• adiabatically, in which air rises, expands and thus the pressure decreases.
• on surfaces that cool down through radiation and thus cool the air in direct contact with them through direct heat conduction. This surface can also be the balloon envelope.
• by mixing with cooler air.
• by advection, when air flows over a cooler surface.

The condensate usually occurs as microdroplets, which then lead to cloud formation, and as dew on surfaces. During condensation, heat is released and counteracts cooling, but cannot prevent it completely. For adiabatic cooling, this means that it is reduced by the amount of heat supplied by condensation. The cooling due to the adiabatic lapse rate is approximately 1°C/1K per 100m and the moist adiabatic lapse rate is approximately 0.6°C/0.6K per 100m. The moist adiabatic gradient applies in the area where condensation takes place. This is because the adiabatic temperature change depends on the pressure change, and the pressure change is not linear with altitude in the atmosphere, but decreases with increasing altitude.

Sublimation: There is also a direct transition from a gaseous to a solid state. The most well-known examples of this are the formation of frost – the icing of aircraft surfaces is often related to frost formation – and ice flowers on windows.

The reverse process occurs when ice crystals do not melt first, but change directly into a gaseous state. Examples of this are freeze-drying or drying laundry in frost.

The process is referred to as sublimation in both directions.

Question 2: What changes in the state of aggregation have you experienced yourself? And how?

Question 3: During which changes in the state of matter is heat released?

Question 4: When changes in the aggregate state occur, must heat energy be supplied?

Answer form about aggregate states