XI Международная студенческая научная конференция Студенческий научный форум - 2019

Currently, special fortification structures for cooling various equipment (diesel engines, ventilation systems, frequency converters, main switchboards, transformer substations, etc.) mainly use compressor refrigerating machines. There are some refrigeration units that will have several advantages over the compressor ones. In particular, one of them is an ejector refrigerating unit.

In ejector refrigerating units the energy expended to implement the refrigeration cycle is introduced as heat. Some freons and their mixtures, ammonia and other substances that meet the requirements for refrigerants may serve as the working medium for such machines. But most often such refrigerators work on water.

In ejector refrigerating units cooled water circulates through the evaporator, which is both a working fluid and a coolant. The water is cooled by its partial evaporation, while the latent heat of vaporization is removed from the main mass of water entering the evaporator through the control valve. Condensate is returned from the condenser to the evaporator, compensating the evaporated part of the water.

Suction of water vapor from the evaporator of steam jet machines occurs due to the kinetic energy of the steam jet, which expands in a special apparatus - a jet ejector.

Since the working fluid of steam ejection chillers is water, they can produce relatively high temperatures (at least 5 ÷ 7 ° C).

To obtain 1000 kcal of cold, it is necessary to evaporate 1.68 kg of water, but under high vacuum, which has to be maintained in the evaporator of the steam ejector machine, the specific volume of vapor increases sharply (at + 5 ° C it is 147 m³/kg). No compressor could suck such large volumes of steam, so water, despite its excellent thermodynamic properties, is not used as a working fluid of compression refrigeration machines.

Various ejector refrigerating units differ mainly in condensers. They can be superficial and confusing.

In machines with surface condensers, steam is separated from the cooling water by tubes that form a heat transfer surface. These machines have relatively less weight and size and can be installed close to cold consumers.

In machines with mixing condensers, condensation occurs through direct contact of steam with cooling water. Condensate is not stored, which causes additional costs for the preparation of boiler water.

The reverse refrigeration cycle of a steam-water ejector machine proceeds under high vacuum conditions.

For the thermodynamic analysis of the operation of ejector refrigerating units it is necessary to know the mass flow ratio of active M and passive M₀ steam. Assuming that the removal of 1 kg of passive steam from the evaporator consumes at active steam, we obtain the flow coefficient (multiplicity of circulation) of the active steam.

It is important to note that in the considered scheme ejector refrigerating unit electrical energy is used only in small quantities to drive the pump. If it were not for this moment, then ejector refrigerating unit would receive an important operational advantage in comparison with compressor refrigerating machines - independence from stationary power supply.

The using advantages of ejector refrigerating units in special fortifications are obvious, since as a heat source for heating water in their cycle, you can use the heat generated during the operation of various equipment, for example: diesel engines, ventilation systems, frequency converters, main switchboards, transformer substations, etc. This is cost-effective, since a large amount of energy is not needed to operate the machine. Ejector refrigerating units have smaller dimensions than compressor ones, which is very important for special fortifications. The lack of a bulky and expensive compressor in the installation is also a significant advantage of ejector refrigerating units. In addition, the advantages of ejector refrigerating units are their explosion safety, the absence of harmful emissions and ease of manufacture.

Thus, the use of ejector refrigerating units in special fortifications allows the equipment to be cooled, consuming less energy due to the use of heat generated by other equipment.