Users of simulation packages are interested rather in accuracy of simulated scenarios (usually, in terms of differences between calculated values and measured data known for test cases) than in precise description of heat dynamics phenomenon. Heat transfer between gas and surroundings of pipe legs can be simulated if relevant parameters of surroundings are known. The main parameters are material properties of the surrounding materials (heat conductivity, heat capacity and density), the appropriate geometry and the undisturbed (far soil) temperature. We shall discuss impact of the surroundings' parameter values on the results that are usually considered by the users as a measure of accuracy, as the uncertainty of these parameters is usually very high. A case study will be presented, illustrating the influence of heat transfer parameters in situations mostly met in practical tasks (steady-state and transient ones). The aim is to bring reasonable engineering guidelines about how to cope with this uncertainty.
Thermal balance is a standard option for gas network simulators. The heat exchange between gas and surrounding environment is rather a complex phenomenon and requires good understanding by the user in order to supply the necessary input data for setting up the model as well as using it in a technically sound way. Theoretical background of the heat exchange models was discussed in several PSIG papers in previous years (see e.g. PSIG9201) and illustrated by interesting examples, e.g. during the PSIG 2007 Showcase as the latest. User of gas network simulators faces the need to gather the necessary inputs for his/her calculations, build the configuration (network model, scenario - task definition) for the simulator and interpret the results obtained correctly. This is not always straightforward and easy chain of tasks and still requires qualified attention; see e.g. PSIG 0309 for nice overview of common issues. Practical experience shows that the setup of heat exchange model is a frequently asked question because of user's uncertainty of input data and the way how to handle the information available. In particular, such question is asked by typical offline users performing system planning or design simulations. This paper aims to illustrate the impact of expectable range of input values and tries to give simple but safe guidelines.
Heat balance model has two main parts: Energy equation for gas coupled with continuity and momentum equations Heat exchange between gas and surrounding environment (soil) and it's coupling to the energy equation It is commonly understood that the exchange gas-soil is a radial phenomena only (no longitudinal heat transfer in the soil takes role). The coupling between gas energy equation and radial heat exchange model is done by the heat flux at the internal wall surface.
