Refrigerant-Absorbent Combinations
Refrigerant-absorbent combinations (the so-called working fluids) are mostly used in the absorption refrigerating systems and heat pumps. Inorganic and organic groups, are the main sources of refrigerants and absorbents. Some organic groups for refrigerants amines, alcohols, Противотум. headlights, and utilities, and for absorbents, alcohols, ethers, alcohol content-esters, amides, amines, Amin-alcohols, esters, ketones, acids, aldehydes or can be used.
Two well-known examples are ammonia-water and water-lithium bromide. In some literature, absorbent also called solvent. Absorbent, should have more chemical affinity for refrigerant than that indicated by the ordinary law of solubility. Very little heat is released when freons, nitrogen substances, as well as a number of other gases dissolved in water. However, the water has a high chemical affinity for ammonia and a significant amount of heat is produced in the process of absorption. For example, on 15 C one unit of water can absorb about 800 units of ammonia.
Thus, the amount of heat released in absorption a rough estimate of the chemical affinity.
In practical absorption cooling in addition, ammonia-water and lithium bromide combinations of different refrigerant-absorbent combinations were considered such as:
- ammonia/calcium chloride,
- ammonia/strontium chloride,
- ammonia/heptanoyl,
- ammonia/triethanolamine,
- ammonia/glycerin,
- ammonia/silicone oil,
- ammonia/lithium nitrate,
- ammonia/lithium bromide,
- ammonia/zinc, bromine,
- ammonia/tetraethylene glycol dimethyl ether (DMETEG),
- ammonia/dimethyl formamide (DMF),
- methyl amine/water
- methyl chloride/tetraethylene glycol,
- R12/dimethyl acid amide,
- R12/cyclohexanone,
- R21/dimethyl ether,
- R22/DMETEG,
- R22/DMF, and
- R22/dimethyl acid amide.
an interest in finding new refrigerants and fluids brought R134a as the alternative refrigerant with DMETEG and DMF forefront for absorption refrigerating systems and heat pumps.
Preferably refrigerant-absorbent combination must have the property of the high solubility in conditions of shock, but should have a low solubility in the conditions of a generator. In absorption refrigerating systems and heat pumps, the following are useful properties and the impact of absorbents:
- a negligible vapour pressure at the generator, compared with the steam pressure of the refrigerant 37.5 C affecting rectifier losses and operational costs;
- good temperature, pressure, concentration relations (absorbent should remain in a liquid state during the whole cycle, and the relationship should be in accordance with the practical capacitor, absorber, and generator temperature and pressure);
- high stability, affecting the ability to withstand heating mode, with maximum temperatures occurring in the generator;
- low heat affecting the heat exchange requirements;
- low surface tension, influence on heat transfer and absorption;
- low viscosity influence the transmission of heat and electricity for pumping.
In addition, the refrigerant-absorbent combinations must meet the following requirements:
- Solubility (high solubility of refrigerant cooling medium temperature, e.g. air , water, and the pressure corresponding to the pressure of the refrigerant vapor in 5 C, plus low solubility of refrigerant to a drain on the generator temperature and pressure corresponding to the pressure of the refrigerant vapor cooling medium temperature);
- stability (refrigerant and absorbent should be incapable of any irreversible action of chemical substances with each other within a practical temperature range, for example, from 5 to 120 C); and
- superheating and subcooling (influencing on operation).
Properties combinations are liquid and/or vapor state, as found in normal operation absorption systems using such combinations, and to crystallization boundary of the liquid phase, where applicable. These properties can be classified as follows:
- vapor-liquid equilibria,
- crystallization temperature,
- corrosion characteristics,
- heat mixing,
- liquid density,
- the vapor-liquid-phase densities,
- specific heat
- thermal conductivity,
- viscosity,
- stability,
- heat-mass exchange rates,
- entropy,
- refractive index
- surface tension,
- toxicity and
- Flammability.
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Refrigerants