Delicate Masterpieces Withstanding Extreme Temperatures
Experts from the Technology House Business Unit on KIT’s Campus North know how to produce individual technical items of high complexity or prototypes. Examples are highly sensitive measuring lances for the Karlsruhe Liquid Metal Laboratory KALLA. They are about to be taken into operation.
The longest lance is 2 meters and 70 centimeters long and has a diameter of a few centimeters only. The other four temperature probes are a little longer than a meter. Their special features are integrated very thin wires of 0.5 mm in diameter, the pointed tips of which serve as highly precise temperature sensors. The longest lance contains an array of 97 wires. The temperature-sensitive tips protrude from small boreholes precisely arranged on the surface of the measurement instrument. There, they can survive and measure temperatures of up to 700°C in molten metal.
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The highly sensitive measuring lances can survive and measure temperatures of up to 700 °C
Parts that Cannot Be Purchased off the Shelf
Neither the extremely thin temperature sensors nor the lances can be bought off the shelf. They are manufactured by specialists for scientific apparatus engineering and manufacture from the Technology House. This work, from the idea to implementation, was organized under the project “Temperature Measurement Lances” by researchers from the Institute for Thermal Energy Technology and Safety (ITES) in cooperation with engineer Daniel Kuntz from the Technology House. “I cooperate very closely with the scientists who want to test their high-temperature heat storage systems in practice,” he says and adds: “My team realizes technical drawings and I provide for the necessary material and listen to the researchers’ wishes.“
Forging, soldering, and welding are the key skills of precision mechanic Paul Wagner-Nagy. During his vocational training many years ago, he would never have imagined himself working on a microscope, soldering wires as fine as a hair, welding them with a laser, and stringing them in well-ordered arrays. “It is fun to fabricate such delicate pieces,” Wagner-Nagy says. “You need a steady hand and inventiveness. To bend the wires at the end without breaking them, we have developed special pliers.” In addition, the team designed a spacer with 97 boreholes such that the wires do not get entangled when they are inserted into the tube of the lance.
Prototype for Industrial use
Frank Fellmoser, engineer at ITES and head of the project at the Karlsruhe Liquid Metal Laboratory, ordered the lances. “It is an advantage that the Technology House is located in the vicinity of our lab,” Fellmoser explains. “Together, we had a look at the workpieces and thought about how they can be optimized before they are permanently installed.”
Once they have arrived at the experimental hall of the Karlsruhe Liquid Metal Laboratory and been installed in the plant, the very long thermometers can no longer be exchanged or repaired. Their place of installation is a large steel cylinder which has also been made in the workshops of the Technology House. The cylinder is about 2 meters long and has a diameter of nearly 1 meter. It will be filled with ceramic beads and operated as a heat storage system. The heat transfer medium is liquid metal.
Lead-bismuth, for example, has a high thermal conductivity. Compared to conventional liquids, such as oils, liquid salts, and gases, its heat transfer rate is up to 100 times better. This makes heat storage systems based on liquid metals interesting for use in industry, as they can directly store thermal energy from waste or process heat and release it again.
Pilot Plant to Be Commissioned Soon
First tests are planned to reveal the temperature distribution in the tank at up to 450 °C. Fellmoser explains: “Simulation calculations have resulted in a prognosis as to how temperature will initially develop in the tank, how it will behave over time, and how cooling will develop. The experiment is now aimed at finding out whether our simulation calculations are correct or whether they can be improved by experimental data.” And this is why the temperature lances are used. The longest of the five probes passes the tank vertically in the middle. The other four are arranged horizontally and diagonally on different levels. The numerous temperature measurement points of the lances will then document thermal dynamics during the experiments: How do warm and cold areas mix? Is the heat storage capacity of the ceramic beads maintained over longer terms?
“We can’t wait to see the results,” Fellmoser says. “In the meantime, the tank has been filled with 1.5 tons of ceramic beads without damaging the temperature lances. In spring, liquid lead-bismuth will be passed through the tank for the first time.” The experiments at the pilot plant will also show whether the operation of heat storage systems based on liquid metals is feasible in industry.