Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
The paper presents analysis of the high-pressure gas
quenching of metal elements, after their vacuum carbonisation
process, based on the computer simulation. The ANSYS-CFX
code has been used for this purpose. This transient quenching
process includes challenging problems, which requires deep
knowledge and application of heat transfer, fluid mechanics and
thermodynamics. The numerical simulation analysis method
focuses on a single element contained in an elementary,
repeatable section (usually a cuboid) of the whole batch. In this
study quenching of a steel cylinder of diameter d = 20mm and
length L = 150 mm is analysed. This approach allows defining
precisely: (i) the geometries of the metal element and of the
elementary cubical section associated with it and, also, (ii) flow
and thermal boundary conditions on the walls of this
elementary section. Above definition of the elementary section
(a computing domain) allows using the whole available
computing power for the quenching process simulation in it.
The ratio of volumes mentioned in (i) defines a “porosity of
batch” and the analysis covers the range from 7 to 70%. The
number of grid points used for the elementary section varies
from 55000 to 240000. The influence of the pressure gradient
value (a flow “driving force” through the elementary section)
and its direction – on temperature and quenching rate time
distributions in a steel element – is analysed and presented. The
use of periodicity and symmetry conditions, for the velocity
field, on the elementary section walls, allows simulating
different single element quenching conditions – reflecting its
position in the batch. The transient quenching has been usually
analysed for a fixed velocity field. However, the steel element
body thermal properties in this transient process varied –
appropriately to its time dependent temperature distribution.
The initial element temperature is assumed to be equal 1300 K.
The influence of different gases, i.e. argon, helium, nitrogen
and hydrogen, and their static pressures (up to 30 bar), on the
steel element quenching process, is analysed and presented.