Investigation of Porous Metals as Improved Efficiency Regenerators

In these past few years the subject of porous metals has gained considerable
attention. The area of flow and heat transfer behaviour in porous metals used
as regenerators is the focus of this work.
A total of 37 porous metal samples have been produced to evaluate their
characteristics as regenerators, these include 12 replicated porous metal
samples made from commercially pure aluminium using three different NaCl
preform particle sizes and two packing methods. The replication method using
argon only was improved to become more efficient, tests were done to
determine adequate time and temperature for uniform porous metal sample
production. In total 4 different protocols (W, X, Y and Z) were developed to
produce different levels of porosity (from 61 to 78%) by changing certain
variables in the production process.
Other porous metal samples were manufactured with the objective of having a
wide range of structures and material comparisons; 7 SS304L wire mesh
samples, 3 wire felt samples (Al, Cu and SS304L), to evaluate the effect of pore
size, 5 packed sphere samples (Al, AISI 52000 chrome steel, Cu, soda glass
and SS420) and 10 additive layer manufactured samples (SS316L and Ti6Al4V)
to evaluate the effect of material and porosity levels.
All the samples were tested on pressure drop and heat transfer capabilities,
they were compared with the literature using Reynolds and Stanton numbers,
the thermal conductivity was also measured, a characteristic that had to be
estimated in previous work due to a lack of an experimental test rig, which was
developed during this research.
It was found that the best performing ones were the stainless steel wire
meshes, the wire felts and the replicated porous metals. Several correlations
involving pore size, porosity and material effects were proposed as an aid for
designing regenerators obtained from the experimental results. The replicated
porous metals have the potential of being used as regenerators if they can be
made from high efficiency materials and of a smaller pore size than the ones
discussed here, their advantage is that they may be modified to a large range of
specifications, being able to replicate the behaviour of other structures.