Researchers at Eindhoven University of Technology use a nine-metre long ‘cooking tube’ to study the behaviour of the combination of steam and hot water flowing together through a pipe. The system is designed for water-steam flows with a pressure up to 40 bar and a temperature up to 250 degrees Celsius. By varying the pressure and water temperature, it is possible to determine the ideal ratio of a combination of steam and water for maximum heat dissipation, for example. This cooktube is new and special because of its size (nine meters high) and the possibility to record the flow pattern with cameras.

Flow pattern against dangerous bubbles

Because the water then boils, a so-called two-phase system is created: part of the water remains liquid and part becomes gaseous steam. How these two phases flow together, the flow pattern, depends on the temperature, pressure, steam fraction, speeds of the different phases and other parameters. A flow pattern map of the measured flow patterns can then be used to make installations safer and more efficient.

The flow pattern in the cooktube can be monitored in high resolution on monitors.

Magna-Power controls the heating

In order to ensure uniform heating up to the saturation point and during evaporation, extra attention has been paid to the heaters.  Several options were considered for both heating elements, the preheater and the heating of the test section. The main purpose of preheating is to heat the supercooled mixture with a pre-defined ratio of liquid to vapour. The test section will either maintain the flow state or add extra heat to achieve a new flow regime.

The preheater consists of a nearly four metre long stainless steel tube with an inner diameter of 20 mm and a wall thickness of 2.5 mm. The current required to generate 70 kW of heating power can be derived from the electrical resistance of the pipe material. This is 18 mΩ at 100 °C and 20 mΩ at 250 °C over the four metre length. At 100 °C, a current of 1950 A and a voltage of 36.8 V is required. The Magna-Power power supply MTA50-2000 provides the electrical power here. A higher voltage has been chosen to compensate for the losses in the connections between the power supply and the preheater. The connection was made with thick copper strips with a resistance of 15 µΩ per meter. The sense-wires of the Magna-Power power supply are connected to the connection points on the preheater tube itself, so that the voltage across the heating part itself is measured. In this way, the losses in the connection are compensated for when determining the added power to the preheater.

The heating of the test section is very similar to the preheating. Only the length and the power are different. The tube is almost one meter long and has the same diameter and connections as the preheating. The required power is 30 kW. At the electrical resistance of this tube (4.6 mΩ at 100 °C and 5.1 mΩ at 250 °C over the one meter length) a current of 2552 A at a voltage of 11.8 V is needed. The TSA16-2700, a Low Voltage – High Current DC power supply from Magna-Power provides this power.

Magna-Power 100 kW MTA50-2000

Again, the voltage is higher to compensate for the losses and sense wires are connected to the heater section so that the power generated in the tube can be measured and controlled.

The two MagnaDC programmable DC power supplies are equipped with programmable settings for voltage and current. The power supplies use high-frequency IGBT-based electrical power conversion into Current-fed topology. This adds an extra step compared to conventional voltage-powered topology for better control and system protection, so that the power supply protects itself even in the event of a failure. The self-protecting properties of this topology exclude the possibility of rapidly increasing current peaks and magnetic core saturation. In addition to the robust topology, MagnaDC power supplies have an accurate programming of voltage and current. Each power supply is tested at 90% to 125% nominal line voltage to ensure correct operation even under the worst mains voltage conditions.

Magna-Power 43,2 kW TSA16-2700 programmable DC power supply

Safer and more efficient

Typical applications for TU/e research are power plants (coal, gas, biomass and nuclear power plants) using a steam turbine, various systems in the chemical industry (such as high-temperature reactors for the production of plastics and oil), and cooling in the food industry. It is expected that the systems will become safer and more efficient in use. Power plants will also have to close less frequently.

The cooktube was put into operation after an introduction by the chairman of the NWO’s domain of Technical and Applied Sciences and former dean Prof. Jaap Schouten. The section leader of the research group Multiphase and Reactive Flows, Prof. Niels Deen, explained the set-up.

Source: Thesis Giel Priems, TU Eindhoven website, Magna-Power datasheets.

You can find Giel’s thesis on https://research.tue.nl/files/105419442/20181001_Priems.pdf

Click here for more information about Magna-Power or watch this movie on their website.

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