When one designates heat distribution media a medium, which (in a cool and/or a heating cycle) warmth transports along a temperature gradient, i.e. from the place of higher temperature to a place of lower temperature. Heat distribution media become depending upon application purpose and temperature range also as heating medium (heating medium), when cooling carrier calls or cooling agent.

In contrast to it a refrigerant in a refrigerant cycle against the temperature gradient, i.e. of a place of lower temperature can transport warmth to a place of higher temperature. In this way temperatures can be produced below the ambient temperature and thus "cold weather". For goal temperatures below the ambient temperature therefore always the combination of a cooling circuit with a refrigerant cycle is necessary.

In order to minimize the transportation losses, as short and well isolated a piping guidance as possible are aimed at.

Characteristics

Heat distribution media should ideal-prove the following characteristics to possess:

• high specific thermal capacity and/or large specific fusion enthalpy
• large heat transmission coefficient
• high heat conductivity
• sufficiently low freezing point/solidification point
• sufficiently high boiling point/point of decay
• low viscosity
• not inflammable or explosively
• not malicious

Usually heat distribution medium used

• Water
• Air

Water

Water is due to its very high specific thermal capacity of approx. 4.2 kJ/kg K and/or its high specific evaporation enthalpies of approx. 2000 kJ/kg and its fusion enthalpy 333 kJ/kg a very good warming and/or cooling carrier. Water works in connection with ions or oxygen corrosively. However also no demineralized water should be used, since it can deposit on the one hand no protective layer, on the other hand changes of the pH value abpuffert and therefore in particular corrosively works and also attacks seal material.

Water is used not only in the liquid, but also in gas and/or vaporous condition as heat distribution medium and in partial solid and/or state than cooling carriers.

The use as steam offers the advantage to be able to make transport in long-distance heating pipelines in form of overheated high pressure steam with relatively small losses of energy. Then at the destination overheated steam (superheated steam) is converted into steam transforming stations (pressure reduction with water injection) into saturated steam. The saturated steam can deliver then in the following heat exchanger very effectively its warmth by condensation again (similar: High voltage transmission line, transformer station). With shorter distances from the boiler to the consumer (also here similar to current transport) lower transportation pressures can be used.

The use as ice offers the advantage, relatively high achievements with small flow rates to transfer to be able (see specific thermal capacity and fusion enthalpy). In order to remain fluid (ice mash), the water must be shifted in addition however with anti-freezes.

Water is used both in open and in closed cycles.

Air

Air is nearly everywhere available and in open cycles is mostly used.

can exhibit different characteristics depending upon their chemical composition. They can be divided into low viscose rayon, easily inflammable oils with deep solidification and boiling points and high viscose rayon, with difficulty inflammable oils with higher solidification and boiling points. According to their origin they can be differentiated in

• Mineral oils (e.g. frame of diesel oils)
• (e.g. frame of silicone oils)
• Biological oils (e.g. frame (--> D-Limone))

Diesel oils are hydrocarbons and from oil are won. They are relatively cheaply, however usually inflammable and chemically aggressive opposite many seal materials.

Silicone oils are polymers Methylsiloxane or polymers Phenylsiloxane. Silicone oils are corrosive and not poisonous; the high-viscous silicone oils are certified also for the food technology. However the specific thermal capacities are relatively small.

are won from the bowls by and are food-technically harmless. E.g. frame orange oil under the trade name D-Limone is used for the cooling of molds in chocolate production.

are used naturally in closed cycles.

Cooling carrier

Cooling carriers heat distribution media are usually called, which are intended for the use below 0"°C. Due to its high specific thermal capacity also in this temperature range gladly water is used. However pure water already freezes with 0"°C, i.e. the polar water molecules arrange themselves to ice crystals. In order to be able to use even at lower temperatures the good heat distribution medium characteristics of the water, this order must be disturbed. For it the admixture of polar or amphoteren materials is suitable; in this way the 0"°C-Grenze can be fallen below partly clearly, and which knows mixture of water and anti-freeze as single-phase cooling carriers is used. At far sinking temperature then first a partial separation takes place, and small ice crystals develop surrounded from approx. 0.01 to 0.1 mm in diameter, by a ever more highly concentrated anti-freeze solution, so that scarcely above the solidification temperature an ice mash is present. This represents a two-phase cooling carrier. In order to work against a solidification by connection of the ice crystals, the ice mash must be always held in motion; so for example are to be equipped with agitating devices. The more deeply the application temperature, the more highly is the necessary portion of anti-freezes (naturally only up to the eutectic). The behavior of mixtures from anti-freeze and water can be represented by the freezing point curve.

In order to protect the cooling system, the added anti-freeze is shifted with inhibitors; the water used as cooling carriers should be degassed after possibility. As anti-freezes to be used alcohols and salts.

Alcohol-water solutions

Alcohols leave themselves, according to the number of OH-groups for each to molecule, divide into

univalent alcohols, like for example methanol CH3OH

Ethanol (Weingeist) C2H5OH

Propanol C3H7OH bivalent alcohols, like for example Ethandiol (ethyl glycol) C2H4 (OH) 2

Propandiol (propylene glycol) C3H6 (OH) of 2 trivalent alcohols, like for example 1,2,3-Propantriol (glycerin) C3H5 (OH) of 3 and higher alcohols.

Cooling carriers made of water and alcohol are not hardly corrosive or. They are to be kept however absolutely oxygen-free, since from alcohols in connection with oxygen strongly corrosively working organic acids develop (for example from ethanol "acetic acid "). As anti-freeze to be used above all glycols such as ethyl glycol, propylene glycol and higher alkyl glycols. Glycols taste (iglykos = sweetly, "wine scandal ") and are only weakly poisonous.

Ethyl glycol exhibits the best physical characteristics, is not certified however not for the food technology. Propylene glycol is used, if the cooling carrier in contact with drinking water or food can turn out. Higher alkyl glycols are used, even if stability is necessary at higher temperatures. Since glycols exhibit a clearly smaller specific thermal capacity as well as a higher viscosity than water, the cooling carrier characteristics of the mixture worsen with increasing glycol portion.

Seawater solutions

Seawater solutions can be divided into

chloridhaltige seawater solutions, like for example sodium chloride (NaCl) - water solution, magnesium chloride (MgCl2) - water solution, calcium chloride (CaCl2) - water solution

chloride-free seawater solutions, like for example potassium carbonate (K2CO3) - water solution. Contrary to chloridhaltigen solutions cooling carriers from solutions of chloride-free salts with high-grade steel are well compatible.

Salt solutions (brines) can be used also in the food technology. Their viscosity is low.

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