Speaker
Description
District heating grids (DHGs) are considered a key technology for decarbonizing the heating sector. In a DHG, heat energy is transported from heat sources to heat sinks through a network of pipes. Heat sources and heat sinks are connected to the district heating network usually via counter-flow heat exchangers so that they are hydraulically separated but thermally coupled. Therefore, a precise understanding of the behavior of heat exchangers is required for efficient control of heat sources and heat sinks in DHGs.In this context, usually reduced order models based on ordinary differential equations (ODEs) are utilized to derive control strategies.
State-of-the-art ODE-based models rely on empirical Nusselt correlations in order to describe the dependence of the heat transfer on the mass flow rates. This approach assumes fully developed flow and statistically stationary operation conditions, which is insufficient in various respects, especially when considering the requirements for modern multi-energy systems. As an alternative, computational fluid dynamics (CFD) could be utilized to more accurately capture the non-linear heat exchanger dynamics. However, CFD-based models are too costly for direct derivation of control strategies. Nevertheless, in order to utilize CFD results in ODE-based models, in this work CFD-based parameter identification for ODE-based heat exchanger models is performed, adapting ODE-based models from the literature.
In the contribution, the CFD model of an idealized counter-flow heat exchanger will be formulated and validated for transient flow and conjugate heat transfer. After that, it is demonstrated how CFD-based predictions of the heat transfer can be utilized for parameter identification of selected ODE-based heat exchanger models. The forthcoming analysis extends to a quantitative assessment of the differences and improvements.
