Gravity cycle

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This article describes the gravity cycle in geothermal systems. For the gravity cycle in steam boilers, see natural circulation boilers .

The gravity circuit ( Engl. Heat pipe or thermosyphon cycle ) tries specific, not only thermodynamic , advantages and disadvantages of geothermal to come into view heat sources. Since the operating losses in addition to the thermodynamic problems in the low efficiencies falling more and more significant, was looking for ways the losses of the feed pump and the feed pump to eliminate. The great depths are specific to geothermal springs. This disadvantage becomes an advantage or a prerequisite for the construction of very extensive systems in the Z-axis.

Akbarzadeh et al combine a gravity cycle with a generator . The gravity cycle is based on natural convection as a result of changes in density and offers very good heat and mass transport properties. In 1944 Gaugler patented a heat exchanger that was essentially identical to today's heat pipe . However, the technology was forgotten again until the 1960s. In connection with the space program , it was rediscovered by Grover and others. The heat pipe is now used to solve a variety of problems of heat transfer and temperature control.

The basic structure consists of a closed vertical cylinder that contains an evaporator , a separating layer and a condenser . The turbine is arranged in the area of ​​the separating layer. The working medium is evaporated in the lower end of the cylinder and flows upwards. Here the vapor is condensed again and the liquid returns to the evaporator with the help of gravity. Between the evaporator and the condenser, the steam flows through the turbine, which converts the energy of the steam into mechanical or electrical energy.

Akbarzadeh and others were able to achieve quite remarkable results with a sample system. At a source temperature of 55 ° C and a condenser temperature of 25 ° C, the prototype achieved an efficiency of 3% and was therefore in the order of 33% based on the theoretical Carnot efficiency. The targeted costs of only approx. € 1,200 / kW are also remarkable. The greatest advantage of the proposed system, its simplicity, is, however, at the same time an obstacle to further improvements. B. the integration of a recuperator is hardly possible.