Numerical methods for solving complex heat exchanger models in transient operation

Abstract

Heat exchangers are important in many industrial systems. In order to maximizeheat transfer while fulfilling requirements to size and weight, it is crucial to havegood numerical tools available. Sintef has developed a modelling framework forsolving a variety of different heat exchangers in steady-state. This thesis containsthe work done to extend the framework with a transient solver. Dynamical aspectsof heat exchangers can not be investigated by steady-state solvers, and a transientformulation is needed to explore these phenomena.The transient formulation that has been attempted has proven to form a set of stiffequations. The stiffness is related to the size of the control volumes used by thesolver. Furthermore, the transient solver is unable to solve a base case for thereference heat exchanger that has been investigated. In order for the solution toconverge, the tube diameters need to be multiplied by a factor of 30. Increasing thetube diameters does not only violate potential size requirements, but it also resultsin a lower heat transfer. Thus, the transient formulation that is implemented isnot robust enough to solve compact heat exchangers.