ABSTRACT

The aim of this paper is to fill the gap between theory and practice concerning the dynamic behavior of a gas transport pipeline. The different aspects are ordered according to the level of importance. The first level is the resistance of a pipeline. Some remarks will be made concerning the friction factor and the compressibility factor. The second level is conservation of mass. As a result of these two levels there is the concept of time constant of a pipeline. At the third level the temperature behavior will be analyzed. At the fourth level the Zhukovsky shock is shown.

1 Introduction

This paper describes the behavior of a Gas Transport Pipe in a dynamic environment. The intention of this paper is to give people full understanding of this topic without the need for advanced mathematics and without using a simulator. In the course of this presentation simplified formulas will be presented with limited accuracy. There are different approaches to modeling. One can mix all details together and hope that is will give a stable and accurate model. The other approach is to bring a problem to the bare minimum and only add details if necessary and if it does not hurt. The most important properties of a pipeline are that it has resistance and does not lose gas during transport. The last property is so obvious that we often do not mention it. In section 2 we will treat resistance. The friction factor, the compressibility factor and the temperature will be treated in subsections in connection with the resistance. In section 3 the conservation of mass will be treated. With this property we enter the dynamic aspects of a pipeline. The pipeline can act as a buffer. Here the conservation of mass will be treated in isolation. It takes time to unload a buffer via a resistance. So a pipeline has a time constant. The time constant will be presented as an easy formula in section 4. This is done by replacing the pipe that has distributed volumes and resistances, by a artificial pipe that consists of a concatenation of volumes and resistances. Calculations will be done and simulations will be performed in order to get a good feeling for the time constant. In section 5 we will treat the temperature behavior. The temperature along a pipeline is caused by heat exchange between gas and environment and the Joule-Thompson effect. Velocity plays an important role. The concept of target temperature will be introduced. Gas in a pipeline has a small momentum. The effect can be seen in combination with the buffer property in the Zhukovsky shock. This will be treated in section 6. It is the relation between instantaneous pressure and ow change at the end of a pipeline. The Zhukovsky shock will also be enlightened by calculations and simulations. If not mentioned otherwise, the units of table 1 will be used, and constants based on the British units will be put in brackets().

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