Physically modeling and mathematically simulating pressure transients in transfer lines

Abstract

Characterizing transient flow is not a trivial venture. It provides an excellent challenge for a senior mechanical engineering lab class. This project aimed at developing a new physical system for such a class based on the benefits and short comings of the previously used physical system. A physical system was developed to vary key parameters, such as run length and pipe diameter. Pipe diameter was previously not a variable parameter. The physical system was designed to help the operator's intuition in developing a mathematical model for said system. The design incorporated solenoid valves and clear pipe. In contrast to the previous system that used ball valves and copper pipe. These features were chosen so that those using the system could neglect human error and visually inspect the flow. The system was designed to increase variation between runs so that a more robust model could be developed. The flexibility of the physical system allows for the examination of more complex flows than the previous system. The mathematical model that was developed characterized the flow reasonably well. The unsteady Bernoulli equation was implemented with major and minor losses. The model revealed several aspects of the physical system that were not immediately obvious from the data. The unpredicted aspects of the physical system were the fluctuation in tank pressure over the test duration and the correlation between tank pressure and the loss coefficient of the main solenoid valve. The higher the pressure the lower the loss coefficient across the valve. The mathematical model did not account for losses that increase as the water air interface moves through different fittings. This was a major shortcoming of the mathematical model that was developed.