Venturi investigations into cavitation in ethylene glycol/water mixtures

Abstract

The objective of the investigation was to study cavity formation with various concentrations of ethylene glycol/water (EG/W) in order to gain an insight into the previously observed anomalous thermal effects in these mixtures. The normal thermal effect is for the apparent cavitation coefficient to decrease with increase in fluid temperature whereas in EG/W mixtures it has been observed to increase. Cavities in a cavitating venturi tube were observed and photographed. The cavity pressure was measured, together with cavity temperatures at various distances along the cavity. The measured temperatures confirmed that the cavity temperature depression, which is responsible for the normal thermal effect, is present in EG/W mixtures and, if this were the only factor, these mixtures should exhibit the same thermal effect as other liquids. However, the cavity pressure measurements showed that a gas (undoubtedly air) was present in the cavity, the proportion of air increasing with the concentration of ethylene glycol (EG). This air is responsible for the reverse thermal effect with EG/W mixtures, a phenomenon previously observed at higher temperatures with water. It is thought that microbubbles of air observed circulating in the rig are responsible for the collected air in the cavity, the persistence of these bubbles increasing with increasing concentration of EG.