Transient Thermohydraulic Modeling of Capillary Pumped Loop 2011-01-2587

“More electric” aircraft requires more power electronics integration. Traditional cooling systems reach their maximal performances because of too high thermal dissipation of these components. Thanks to their heat transport capacity and their passive pumping, two-phase fluid capillary pumped loops appear among identified alternative solutions. Before being used in aircrafts, some investigations are needed to estimate the ability of these systems to ensure thermal transfer under harsh environment: vibrations, accelerations, cooling temperature range … If lots of steady state modeling are available in the literature, few transient models exist. However, transient phases set the main problem for two-phase fluid capillary pumped loops in airplane environment. This paper proposes a transient thermohydraulic modeling approach of a capillary pumped loop developed for gravitational applications: the Capillary Pumped Loop for Integrated Power (CPLIP).

As hydraulic transfers are the driving phenomena during transient states, the present model transcribes accurately the fluid mechanical aspects. It relies on mass, momentum and energy conservation equations, using finite volumes method. Mass enthalpy, pressure and mass flow rate are considered as variables. Temperature is calculated thanks to the mass enthalpy and the pressure and is used to estimate these latters. This strong coupling between the four variables sets the major difficulty of two-phase fluid heat transfer devices transient modeling. The fluid is considered homogeneous to answer to a system approach modeling. Then the comparison between modeling results and experimental data highlights a good correlation between numerical estimations and measured temperature evolution. Furthermore, even if the accuracy may be improved, this model is able to represent the dynamic evolution (“overshoots” and “undershoots”) of the hydraulic variables (pressure, mass flow rate). Eventually, some ways of improvement are identified, particularly concerning two-phase tank and evaporator modeling in order to increase the model accuracy and to extend its validity field.