Thermodynamic Behaviour and Heat Transfer in Closed Surge Tanks for Hydropower Plants

A numerical model of a hydraulic system with a closed surge tank is developed for evaluating the thermodynamic behavior during slow transients in the air pocket. The numerical model is used to evaluate the polytrophic equation against a Modified Rational Heat Transfer (MRHT) method, and the results are compared to field observations. The original RHT method considers heat transfer to walls and water as a lumped quantity, and the method is modified in this work to evaluate these two processes separately. The field observation dataset contains pressure and water level measurements from a 3,050 m33,050 m3 closed surge tank during a pressure increase from 805 to 1543 kPa over 40 min, thus providing a unique opportunity to investigate the thermodynamic behavior during slow transients. This paper will show how the accuracy of modeling slow transient events in a closed surge tank may be improved by applying the MRHT method, which accounts for heat transfer to enclosing media