A PULSE-EXPANSION WAVE TUBE FOR NUCLEATION STUDIES AT HIGH-PRESSURES

The design and performance of a new pulse-expansion wave tube for nucl eation studies at high pressures are described. The pulse-expansion wa ve tube is a special shock tube in which a nucleation pulse is formed at the endwall of the high pressure section. The nucleation pulse is d ue to reflections of the initial shock wave at a local widening situat ed in the low pressure section at a short distance from the diaphragm. The nucleation pulse has a duration of the order of 200 I-is, while n ucleation pressures that can be achieved range from 1 to 50 bar total pressure. Droplet size and droplet number density can accurately be de termined by a 90 degrees-Mie light scattering method and a light extin ction method. The range of nucleation rates that can be measured is 10 (8) cm(-3)s(-1)<J<10(11) cm(-3)s(-1). We will illustrate the functioni ng and possibilities of the new pulse-expansion wave tube by nucleatio n rate measurements in the gas-vapour mixture nitrogen/water in the te mperature range 200-260 K, and in the mixture methane/n-nonane as a fu nction of supersaturation S at various total pressures up to 40 bar an d temperatures around 240 K.