Steam-Jet (or Steam Vacuum) Refrigeration Cycle

Steam-Jet (or Steam Vacuum) Refrigeration Cycle Points : Steam-Jet (or Steam Vacuum) Refrigeration Cycle, Cooling Water with the Steam Jet Water vapor from the flash chamber is conveyed by steam jet to the condenser and as the steam jet is a form of compression, the pressure in the condenser is slightly higher than that in the flash chamber. The vapor and steam jet effluents are condensed by cooling water circulated through the condenser. Thee condensate is then returned to the flash chamber in the form of a spray, and because there is a fall in pressure, some of the condensate will vaporize and produce a fall in temperature by extracting latent heat from the remaining liquid condensate. The condensate is then circulated as chilled water through the air conditioning system and the, returning chilled water is sprayed, with the condensate, into the flash chamber. Further vapor is flashed off and again extracts heat from the remaining liquid. The excess condensate arising from the condensation of the steam jet is pumped back to the boiler feed tanks. The whole cycle is maintained at high vacuum in order to obtain the low temperatures required. At a chilled water temperature of 7°C the equivalent saturation pressure in the flash chamber must be 990 mbar.

The practicable compression pressure which can be obtained by steam jet compression is in the order of 950 mbar in the condenser.

The amount of flash vapor produced in the flash chamber is very small with the flash chamber at 7°C and the returning chilled water at 13.5°C, the proportion of vapor produced is only about 1 percent. Cooling Water with the Steam Jet Where water and high, pressure steam are available at relatively moderate cost, the steam jet unit for cooling water has many advantages. It has no moving parts except those in the centrifugal pumps used to circulate the water. The weight of the equipment in moderate and it can be Iodated almost anywhere, even on the roof a building if necessary. Because of the absence of reciprocating parts there is no vibration. No costly chemical refrigerant which may require replacement is used. Because of the absence of such a refrigerant, the steam jet unit it especially suitable for installations where hazards due to fire and toxicity must be reduced to a minimum.

Water cannot remain liquid at a temperature higher than the boiling temperature Corresponding to its pressure. For instance, if water at a temperature higher than 45 F is delivered to a tank which the pressure is maintained at 0148 Psia, the water will immediately cool to 45 .F. in doing so, it surrenders heat. Inasmuch as there is not other medium at a temperature low enough to receive this heat, a portion of the water itself will be vaporized. Therefore, the heat surrendered by the water in cooling is immediately unitized as latent heat which vaporized a small part of water delivered to the tank. In .this way, the relatively warm water retuning to the tank is cooled to a temperature corresponding to the pressure being maintained in the tank. The cooling of water in this manner depends altogether upon maintaining the low pressure that corresponds to the desired water temperature. This process is exactly the same as the cooling of liquid refrigerant flowing through an expansion valve.

Because a part of the water delivered to the tank is continually flashing into the steam, the tank in which this takes place is known as the flash tank. The chilled water is removed front the flash tank by a pump, which increase its pressure and delivers it to an air coil or air washer.

Obviously, the vapor produce by the flashing to water must be removed as fast as it is found, if the required low pressure is to be maintained, inasmuch as the pressure inside the flash tank is Considerably below atmospheric pressure, the vapor can be removed only by means of a compressor.

However, the vapor removed will now be compressed to atmospheric pressure. It must be compressed only to such a point that it can be condensed at a temperature above the temperature of water available for condensing purpose.

Ordinarily the pressure of the vapor must be increased to such a point that it can be condensed at about 100 F. the pressure corresponding to this temperature is about b.95 psia If chilled water is being maintained at 45 F. the pressure in the flash tank will be about 0.15 psia. In order to condense the flash vapor, it must be compressed form 0. 15 to 0.95 psia.