Towards Improved Understanding and Modelling of Compact Heat Exchangers
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Date
2021-06-02
Authors
Buckrell, Andrew
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
The present work pursues the ability to increase the fundamental understanding of and to
improve numerical modelling capabilities for Compact Heat Exchangers (CHE). This goal
is achieved by numerically and experimentally studying the small scales of flow, then in-
corporating these results into a novel reduced order model (ROM) of a full heat exchanger.
The result is a numerically efficient modelling approach that significantly improves numer-
ical modelling of CHE’s.
The heat transfer enhancement surface of focus, the turbulizer, is studied in great de-
tail with high resolution Computational Fluid Dynamics (CFD), using experimental flow
visualisation and Laser Doppler Velocimetry (LDV) measurements to validate the results.
The modelling process explores a variety of turbulence models and simulation methodolo-
gies, finding that a Large Eddy Simulation (LES) model with several modifications to the
turbulizer geometry to replicate manufacturing process pressure drop predictions within
7% of experimental results and heat transfer within 15% of experimental results. Excellent
correlation is also observed with predictions of transition to unsteady flow. Flow visualisa-
tion provides excellent correlation with predicted flow patterns at low
Re
. The validated
turbulizer model is used to investigate flow conditions through a wide range of
Re
andflow
incidence angles, which have not been previously studied.
Construction of the reduced order model leverages data obtained during the detailed
simulation of the turbulizer under a variety of flow conditions, mapping the appropriate
Nu
and
f
D
to a porous media heat transfer framework. This framework is used to enforce
the heat transfer and pressure drop calculated based on the detailed modelling phase.
Model lookup performance is investigated using both an artificial neural network (ANN)
and bi-linear interpolation. The ANN approach provides the best overall performance.
Implementation of the ROM and turbulizer flow data is undertaken within the frame-
work of STAR-CCM+, using
fieldfunctions
and
user defined code
to interact with the
proposed model. Heat transfer is validated against experimental test results of a heat
exchanger design which has previously been problematic for analytical models to accom-
modate. The results indicate an approximate halving of the error in pressure drop and
heat transfer predictions made by numerical and analytical models, respectively. This in-
dicates that the proposed novel ROM methodology provides a significant increase in the
numerical predictive capabilities of complex heat exchanger models under a wide variety
of flow conditions.
Description
Keywords
heat transfer, compact heat exchanger, fluid dynamics, reduced order modeling, cfd, automotive