| dc.description.abstract | A dynamic model for a heat exchanger with multicomponent phase change, part of
reliquefaction cycle of natural gas, is developed. The finite control volume method is
used to spatially discretize the heat exchange intro a series of lumps with constant volume.
Vapor-liquid equilibrium is assumed in the vapor-liquid region of the phase envelope.
The model is written in terms of differential and algebraic equations applied to
each lump (or cell).
Different algebraic equations are valid in each of the phase regions (e.g. vapor, liquid,
vapor-liquid), namely the vapor-liquid equilibrium condition is not satisfied in either
of the single phases. Therefore, each phase region has its own set of differential and
algebraic equations. The number required to describe the two-phase region is higher
compared to the single regions. Hence, dummy variables and equations (without a
physical meaning) are used in the single regions to in order to have the same number
of equations in all phases such that the same model can be used for simulating all
phase regions. A logical conditions is implemented to select the corresponding set of
equations.
The model is written and implemented in Matlab® for simulation purposes. The
phase change detection is automatically handled by an event function inside the solver.
A few additional examples are used to investigate how the ode15s solver treats nonsmooth
systems, or how the algebraic equations are solved.
The possibility of formulating the model as a mathematical problem with complementarity
constraints is also investigated. | |
