Power unit with low-temperature Stirling engine and vortex tube. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Alternative energy sources

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The conversion of low-temperature thermal energy into industrial heat is possible using a heat pump or a Stirling cycle engine. Stirling cycle heat pumps are widely covered in the literature; here we consider the use of a vortex tube, which makes it possible, due to the Ranque-Hilsch effect, to obtain heat at a temperature sufficient for heating and cold for refrigeration units.

The general scheme of the installation is shown in fig. 2.4.1. As a heat source, the heat of wastewater, the heat of reservoirs, the heat of the earth (wells) can be used. Heat transfer to the heated part of the Stirling engine is carried out by a heat pipe. The cooler is a low-temperature environment - atmospheric air in winter, stored ice mass in summer.

The Stirling cycle engine can be a Beale free piston engine or a diaphragm driven engine. The characteristics of such engines differ from engines with a crank mechanism; they are completely hermetic, which allows the use of almost any working fluid.

Ris.2.4

Engine fig. 2.4.2. consists of three main elements: a heavy working piston, a light displacer and a cylinder with seals. The working cavity is located above the piston and is divided into a compression cavity between the working piston and the displacer and an expansion cavity - above the displacer. The expansion cavity interacts with the heater, the compression cavity interacts with the cooler.

The engine (in this scheme) is used as a gas compressor, i.e. the oscillating working piston also acts as a compressor piston. The performed studies of this type of engine (Agbi, 1971) showed its quite satisfactory operation.

Even more promising for this scheme is a membrane-type compressor engine with absolute sealing of the motor cavity.

An analysis of the thermodynamic efficiency of the cycle of a low-temperature Stirling engine in comparison with normal conditions reveals, as expected, low operating parameters: for example, at a heater temperature of 300 K and a coolant temperature of 250 K, thermal efficiency cycle is only 17%, but taking into account the fact that waste low-temperature renewable heat is processed here, the system becomes quite competitive.

Fig.2.4.2. Free-piston Stirling engine (Beale W.'s scheme): 1. Heat pipe of the heater; 2. Heater; 3. Displacer; 4. Housing; 5. Cooler; 6. Displacer rod; 7. Piston; 8. Compressed air outlet; 9. Air inlet; 10. Heavy piston; 11. Carter

Of particular interest is the use of a two-phase working fluid in the engine. Stirling engine theory shows that in order to increase the specific power of the engine, it is necessary to increase the average pressure of the working process. The ratio of working volumes for such engines rarely exceeds 2-2,5 and pressure changes are entirely determined by these figures. At a lower pressure equal to or close to atmospheric, the upper pressure does not exceed 0,3-0,5 MPa. However, two-phase working fluids - for example (Butadiene-1,3, whose boiling point is 4,4°C; ammonia - 33°C; cis- and trans-Butene-2 ​​+3 and 0, respectively°C, etc.) allow to obtain a higher average cycle pressure.

For any working fluid, the specific volume of liquid is much less than the volume of saturated steam. With an increase in the average pressure, the output power increases and the heat transfer through the evaporation and condensation processes improves.

Thus, when using a two-phase working fluid, it is possible to increase the working power by 2-3 times at the same temperature limits.

The well-known advantages of the Stirling engine - quiet operation, the absence of harmful emissions, tightness, and the absence of vibrations - are especially valuable in this scheme, since they allow the power unit to be placed in close proximity to the living quarters.

The vortex tube is today the most simple and studied tool for the simultaneous production of heat and cold. The ratio between hot and cold gas flows is quite simply regulated, i.e. In winter, most of the energy is spent on heating, in summer - on cooling.

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