Steam jet cooling system
A steam jet refrigeration system is a thermal refrigeration system or the application of a cold vapor process in which water vapor is used as a propellant, refrigerant and refrigerant.
A first patent application was made in 1884 and Leblanc designed a usable refrigeration machine in 1910. A first application was the cooling of ammunition on warships.
description
In the steam jet cooling system, water is used as the refrigerant. Water vapor must be generated as a thermal energy carrier. The steam is fed into a driving nozzle , which is designed as a Laval nozzle . The motive steam is accelerated and, with a supercritical pressure ratio, reaches the speed of sound in the narrowest cross-section and in the enlarged part of the motive nozzle, supersonic speed is reached when a supercritical pressure ratio is present. The pressure energy is converted into kinetic flow energy. The high flow velocity creates a negative pressure and water vapor is sucked in from the evaporator in the mixing chamber and it mixes with the motive steam, whereby the flow velocity is reduced. The mixed jet is accelerated again in the collecting nozzle and decelerated in the diffuser outlet. If there is a supercritical pressure ratio, a vertical shock wave occurs in the area of the narrowest cross section of the diffuser or behind it.
The water introduced into the evaporator evaporates in order to maintain the saturated steam equilibrium between pressure and temperature in the evaporator. The warm water returned to the evaporator is sprayed in order to achieve an effective heat and mass transfer.
Through the evaporation process and the suction, heat is extracted from the water reservoir of the evaporator and the liquid cools down. The cooled water can be pumped to the cooling point via a pump and returned to the evaporator after it has absorbed heat.
The jet of motive steam is directed into a condenser . This can be designed as a heat exchanger or as a co-condenser into which cold water is sprayed and the steam is precipitated. The pressure in the evaporator corresponds to the water vapor pressure at the cold water inlet temperature (1 to 3 mbar) and is lower than the condenser pressure. The resulting condensate must be cooled in a cooling tower. A vacuum pump, usually a water ring pump, must be connected to the condenser in order to discharge the inert gases. Multi-stage systems are often used to increase efficiency.
Application area
Due to the freezing point of water, steam jet cooling systems can only be used for cooling applications above 0 ° C. The advantage of the steam jet cooling system is that, apart from the pumps, no moving parts and no environmentally harmful or toxic refrigerant are used. With a cold water temperature of 8 ° C / 16 ° C, cooling water temperature of 29 ° C and a saturated steam pressure of 3.6 bar (absolute) of the motive steam jet, the value 0.5 is specified as the COP of the process, so that the use only makes sense in terms of energy is when exhaust steam is available in sufficient quantities. In connection with the use of high-pressure steam for electrical energy and the use of low-pressure steam for heating and / or cooling, one speaks of combined heat, power and cooling (CHP).
swell
- Dubbel, paperback for mechanical engineering, 18th edition, ISBN 3-540-57650-9
- Peter Noeres, Thermal cold generation with steam jet chillers, concepts and experiences in KI -cold-air-air-conditioning technology 11/2006