Secondary Refrigerant

Refrigerant, Secondary

 

(also secondary coolant), a liquid or gas that is used in refrigerating systems as an intermediate medium for heat transfer from the object to be cooled to the refrigerant, which boils in the evaporator of the refrigerating machine. Systems that operate with secondary refrigerants are used in cases where the direct cooling of an object by means of a boiling refrigerant is impossible, difficult, or uneconomical, for example, when there are many users or when the users are far from the machine room.

Secondary refrigerants should have a low freezing point, a low viscosity, a high specific heat, and a high thermal conductivity. They should be nontoxic, flameproof, and neutral with respect to building materials.

Solutions of salts in water, called refrigeration brines, are used as secondary refrigerants. Sodium chloride brine is employed for temperatures down to – 15°C; magnesium chloride brine, down to – 27°C; and calcium chloride brine, down to – 45°C. Antifreezes and Freons are used in low-temperature refrigerating systems. Aqueous solutions of propylene glycol are employed for temperatures down to – 47°C; aqueous solutions of ethylene glycol, down to – 60°C; Freon-30, down to – 90°C; and Freon-11, down to – 100°C.

Water is used as the secondary coolant in air-conditioning systems.

V. A. GOGOLIN

References in periodicals archive ?
By applying C[O.sub.2] as the secondary refrigerant, pumping power can be reduced to about 1 kW (1.3 hp) compared with traditional fluids, which require 5 kW to 15 kW (6.7 hp to 20.1 hp).
The Kuehne+Nagel system features two air-cooled Azanechillers with ammonia as primary and glycol as secondary refrigerant. Each unit has a cooling capacity of 400kW and features a low ammonia charge of less than 0.45kg/kW.
In preference to a conventional 'direct expansion' (DX) cooling system, Coolmation proposed a 'secondary refrigerant system' because of its reduced reliance on large volumes of potentially harmful refrigerants and the contained application of them.
"Weltweit erste eislaufbahn mit C[O.sub.2] als kaltetrager" ("The world's first ice rink with C[O.sub.2] as secondary refrigerant").
For that reason CO2 was chosen as the secondary refrigerant. To achieve the enhanced thermal storage capacity of the 3" thick inner concrete layer several PCM technologies were evaluated.
Water is been used by the system as its secondary refrigerant. In order to remove heat from the water, chillers are used, which is further circulated through other components for absorbing heat from the space.
The Kuehne + Nagel system features two air-cooled Azanechillers with ammonia as primary and glycol as secondary refrigerant. Each unit has a cooling capacity of 400kW and features a low ammonia charge of less than 0.45kg/kW.
The Culina system features two AA750 air-cooled Azanechillers with ammonia as primary and glycol as secondary refrigerant. Each Azanechiller has an operating capacity of 450kW to maintain the chill store at +2 to +5 [degrees] C.
Furthermore, as a secondary refrigerant, C[O.sub.2] has shown significant potential.
With Second Nature systems, refrigerated display cases and walk-in coolers/freezers are redesigned to benefit from the latest advances in secondary refrigerant technology.
For normal-temperature refrigeration a mixture of ethanol and water is employed as the secondary refrigerant. Temperature refrigeration calls for use of silicone oil.