Abstract: A novel design of a pulse expansion wave tube (PEWT) for the study of homogeneous nucleation in mixtures of vapours and gases is presented. The main difference with the previous design consists in a test section with flat walls, which avoid that optical windows and pressure transducers do affect the flow field locally. Additionally, the test section length is reduced by a factor two. The performance of the wave tube is investigated both experimentally and numerically. The thermal insulation of the piezoelectric pressure sensor is proved to be beneficial for accurate measurements. The smallest thickness possible of the diaphragm, initially separating the high- and low-pressure sections of the PEWT, is also shown to be crucial. The flow phenomena are simulated with a 2D numerical model. It is shown to correctly predict the gasdynamic features of the PEWT and the effects of the diaphragm opening process. Nucleation rates for water in helium are determined as a function of supersaturation for two different pressure conditions, 1 MPa and 0.1 MPa, at a temperature of 240 K. The good agreement with results from previous experiments shows that the geometrical mismatch of optical windows and pressure transducers in the original wave tube did not affect the nucleation rates significantly and that both the original and the new wave tube produce reliable measurement data. Graphic abstract: [Figure not available: see fulltext.].