Constant heat outflow rates for air/surge vessel modelling during pressure transients

Abstract

Air/surge vessels protect water pipelines during pressure transients. A Rational Heat Transfer (RHT) model and Polytropic (PVn=C) model exists for predicting the thermodynamic behaviour of the enclosed air in the vessel during pressure transients. The RHT model is not used today for design of air vessels because of the difficulty involved in the substitution of the correct form of the heat outflow rate. This work investigated through modelling and simulation, the constant heat outflow rates suitable for predicting the thermodynamic behaviour of the entrapped air. Initial laboratory data and experimental results obtained from literature were used. The results show that when constant heat outflow rate values of 0.7124 W and 0.98 W are assumed, the thermodynamic behaviour of the enclosed air closely matches those obtained from the Polytropic model at index values of 1.0 and 1.4 respectively. These rates are independent of the vessel size, and initial pressure transient event type.