Joshua Feldman with adviser K. Haran

Interest in electric aircraft has grown as the aviation industry seeks to reduce its reliance on fossil fuels. Large commercial passenger planes will require electric motors with high specific powers to achieve payload and range targets competitive with that of conventional aircraft. The use of superconducting windings could enable these high specific powers, though they require effective cooling at cryogenic temperatures. This project investigates flow-boiling of hydrogen as a cooling method, and the hydrogen is envisioned to have a double-use as the plane’s energy storage.

Fluid flow in helically coiled tubes is known to form secondary flow patterns, which may enhance heat transfer when compared to flow in straight tubes. This effect can be leveraged for better cooling of superconducting motors, though an accurate heat transfer model is needed for effective heat exchanger design. While this effect has been studied in water and some other common refrigerants, it has not been studied for hydrogen. Hence, this project includes a series of flow-boiling experiments in straight  (Figure 1) and coiled tubes (Figure 2 and on report back cover) to investigate how this phenomenon occurs in hydrogen. Tests involving nitrogen are being conducted currently, and results will be extrapolated to hydrogen. This project is funded by NASA/CHEETA.

Figure 1: Test of flow-boiling nitrogen in a straight tube.

Figure 2: Coiled tubes intended for experiment