Subarea: Qualitative Physic s

This paper describes a qualitative domain theory developed for modeling fluids and thermodynamics scenarios in On. This work builds on the domain models of [4], adding process definitions for pumps (fo r liquids), compressors (for gasses), and a phase-change process for condensation. The model includes a complete qualitative account of the thermodynamic behavior of fluids associate d with each type of process. It allows significant flexibility and composability in assembling new scenarios; the user need only describe the structural configuration to be modeled, and qPE does the rest. It has been used to model a variety of fluid system scenarios, including a two-phase refrigeration system described i n detail. Lessons learned from putting together a large qualitative model are discussed, hopefully preventin g future model builders from falling into the same traps. Area