Paper 5
Comparison between Numerical and
Observed Air and Contaminant Distribution for Mechanical Mixing and
Displacement Ventilation Coupled with a Local Exhaust - Lessons Learnt
Barbara Lipska
Department of Heating, Ventilation and Dust Removal
Technology, Faculty of Power and Environmental Engineering. Silesian
University of Technology, Gliwice, Poland
Abstract
CFD modelling can be used in the design of ventilation systems.
However, simplifications in room airflow models may lead to errors and
discrepancies between predictions and reality. The aim of this paper is to
present the problems and errors connected with the prediction of the air
distribution based on CFD codes. The sources of error are pointed out, as
well as possibilities for eliminating or reducing them based on program
options and experimental identification of the predicted flows. As an
example, a real complex room was considered. The investigations consisted
of a test room with heat and contaminant sources and a local exhaust.
Mixing ventilation using a ceiling square cone diffuser and a displacement
system with laminar diffusers were applied. Numerical calculations were
carried out using Flovent 6.1. The correctness of the predictions of the
airflow pattern and contaminant propagation was assessed by comparison
with visualization of actual flow. The predicted profiles of the
parameters of air and tracer gas were compared with the results of
measurements. Discrepancies were found and attempts were made to reduce
them. It was found that some of these discrepancies could be eliminated by
applying respectively the options which are available in the program,
including an adequately selected discretization grid. Unfortunately,
however, there were also problems which were difficult to overcome. These
include the impossibility of the simulation to exactly represent the
complicated construction of the diffusers and the characteristics of the
jet leaving them.
Key words: CFD simulation, experimental control, heat source,
contamination, local exhaust, mixing, displacement ventilation.
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