Experimental results from the Bathμ-wave rotor turbine performance tests

Abstract

Abstract This paper details an extensive experimental investigation of a novel throughflow micro-wave rotor with symmetrically cambered passage profiles designed for shaft power output as well as pressure exchange. This is the first time comprehensive experimental data from a power generating wave rotor is presented in a peer-reviewed journal. Moreover, the significance and renewed interest in wave rotors for a wide range of applications from refrigeration to micro-gas turbines makes this experimental programme extremely valuable to many fields of research. The wave rotor is a four port, three-cycle unit of 60 mm in diameter, 30 mm in length and houses 46 channels. The unit was experimentally tested on a gas stand in open-loop configuration using electrical heaters as a source of heat for the high pressure inlet and pressurised air for both inlet ducts. Throughout testing, the mass flow rates among high pressure in- and outlet were balanced. A series of tests were conducted investigating the effect of variation in rotational speed, ratio of inlet mass flow rates (loop flow ratio), axial clearances and peak inlet temperature on wave rotor performance. The results show the importance of minimum axial clearance for maximum energy transfer as well as for reduced mixing of hot and cold flows. The competing relationship between pressure ratio, high pressure zone pressure difference, internal exhaust gas recirculation and fresh air exhaustion is also highlighted. Finally, measurements of the temperature distributions in the high pressure outflow show the effect of rotational speed, loop flow ratio and centrifugal forces on the fresh air stream location and its mixing with the hot gas stream. A peak shaft power of 450 W and a peak pressure ratio of approximately 1.63 were obtained close to the design speed that were in line with expectations for clearances and temperatures under investigation. Using a new approach to calculating efficiency that assumes equal values for expansion and compression, a peak figure of 80% was obtained indicating the superiority that such designs have over similarly sized traditional turbomachinery.