Implementation Of A Nucleate Boiling Flux
Partitioning Model For A CFD Simulation Of
Compact Heat Exchangers Based On The Local
Estimation Of Bulk Properties
Author(s)
C. Paz, J. Porteiro, A. Copo & A. Díaz
Abstract
The widely used implementation of wall heat flux partitioning during subcooled
flow nucleate boiling has a number of limitations when it is applied on a local
cell basis as is done in CFD codes. The main limitations reported generally have
their origin in the bulk formulation of the proposed submodels being transferred
to a local balance at the cell near the wall whose volume and flow conditions
strongly differ from those employed in the experimental calibration of the model
imposed. Several models developed for nucleate boiling are based on a so-called
wall heat flux partitioning strategy that consists of a modification of the
convective heat transfer law at the wall to include evaporation. However, it is
known that the local movement of the subcooled liquid to replace the volume of
vapour represents an enormous contribution to heat flux enhancement, a process
that is known as quenching. Therefore, when a 3D, local formulation of a wall
heat flux partitioning boiling submodel is implemented at the cell scale in a CFD
code, it must take into account that most of the available correlations and the
physical phenomenon itself are strongly connected with regions of the fluid that
are quite distant from the wall, normally around 0.5 mm. The numerical structure
of CFD codes is not suitable for a non-local formulation. Therefore, this study
attempts to address these limitations to implement a flux partitioning boiling
model at the local cell scale but employs distant properties of the fluid for bulk
conditions and heat exchange. This method has been validated in several
geometries, allowing parallelisation and full grid size and shape versatility. The
results obtained when applied to an EGR cooler indicate an important
improvement with respect to other models, and the results obtained are more
Keywords
nucleate boiling, Chen’s model, CFD, local properties
Related Book
Other papers in this volume
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