Complex Ventilation of Multiple Electrical Enclosure Systems. Development and comparision of 1D pipe-flow models.

Abstract

The nature of fluid flows in pipes is highly relevant to planning and constructing cooling systems. Although general, conventional computational fluid dynamics solutions such as ANSYS FLUENT, OpenFOAM or similar software exists, these solutions are computationally expensive and require hours, if not days, to give results. This study aims to explore and compare implicit solutions for complex pipe networks that can be generated in a much quicker fashion. In this context, implicit solutions refer to 1D-implementations which solve the entire pipe network as a set of simultaneous equations, or in other words, a matrix. In order to evaluate the accuracy of any such implicit solver, the results that the solver produces are validated against a simulation run in ANSYS FLUENT using, to the extent that it is possible, identical settings. A set of different cases are run through this validation procedure in order to observe how the implicit flow rate solver compares across a number of cases. The results show that while the implicit flow rate solver manages to mimic the fluid flow of the ANSYS FLUENT simulations with only small errors that arise primarily from observed asymmetries in the ANSYS FLUENT simulation. The implicit flow rate solver does however produce significant errors in temperature prediction when cooling systems that have heat sources approximating 2 · 105 W/m3 applied at smaller regions. Additionally, the results show an extreme benefit in terms of run-time, on the order of 103 compared to ANSYS FLUENT. These results suggest that the implicit solver fails to capture a variety of phenomena, particularly related to cases applying larger additional heat sources. These phenomena would need to be captured if it is to act as a predictor of the behavior of such cases. For cases without the previously mentioned large heat source however, the results suggest that the implicit solver can serve as a semi-accurate run-time efficient predictor. Additionally, the results suggest that the usage of minor loss coefficients or length-equivalents for estimating the pressure drop over a pipe bend, T-junction or similar structures is insufficient to capture combined effects of said structures in more complex pipe networks. Finally, observation of the errors in temperature prediction suggest an approximately linear behavior. On this basis, the implicit solver or a variant of it could very well serve as an early predictor when iterating through system design in order to quickly find designs that will fail to fulfill certain criteria.