Mobile measurements for thermal water

Thanks to the energy turnaround, increasing interest is being taken in geothermics as a regenerative energy source. The principle is that geothermal energy, for example in the form of thermal water, is used either directly for heating purposes or to generate electricity. Already before a geothermal power station is built, the local thermal water has to be examined, and its properties must be determined, since the efficiency and size of the plant significantly depend on the water’s heat content.

State of the art

In order to calculate this heat content, it is necessary to know the thermodynamic material properties of the thermal water – in particular, the specific, isobar heat capacity. A partly high salt and gas content of the water complicates the predictability of these variables. So far, it has only been possible to analyse samples in the laboratory. However, by taking samples on site and transporting them, the thermal water is depressurised and cooled down, which changes the water’s composition, and hence also its thermodynamic material properties.

Technology

Scientists at the KIT Institute for Nuclear and Energy Technologies (IKET) have therefore developed a fluid calorimeter that can analyse thermal water of up to 170 degrees Celsius directly on site. Thus the water can also readily be checked when the geothermal plant is in operation, with the calorimeter being used as a mobile test stand that is directly linked to the power station network via a “bypass”. The thermal water is immediately fed from the plant into the flow tube of the calorimeter. Here, it flows past temperature probes at the tube entry and outlet as well as past an Ohm heater. Given a certain fluid mass flow, the heat capacity can be determined using the amount of heat contributed by the heater and the difference in temperature between the two probes. Here, the calorimeter ensures that pressure of up to 30 bar is maintained, and it also compensates heat losses.

Advantages

The test stand can be supplemented by further measurement apparatus to determine viscosity and density as well. Thus the mobile test stand is suitable for comprehensive measurement campaigns to determine the material sizes of thermal water and other liquids.

Options for companies

KIT is looking for industrial partners to develop the fluid calorimeter as a stand-alone measurement apparatus for client-friendly use.