Development of an apparatus to investigate the thermal characteristics of regenerative heat exchangers

Cyclic thermal regenerators have an important industrial
application, however most of the design techniques are old and
use many simplifying assumptions. With the advent of digital
computers many of these simplifying assumptions can be examined,
however there is very little scope for practical verification.
An apparatus has been designed, built and fully commissioned to
investigate thermal regenerator characteristics. The analog
operation of the apparatus is enhanced by four computer aspects.
Commissioning of the regenerator highlighted how the response
of apparatus can be influenced by the peripheral pipework around
the test section, radiation effects from the heaters and jetting
of air into the regenerator packed bed section.
A series of experiments, comprising runs (a maximum of
ten period changes) within a set-up (a known air flowrate and
packed bed length) were formulated to examine the regenerator
response, using three types of spherical packing, steel lead
glass and alumina. A method of obtaining convective heat
transfer coefficients was produced and represented in two
forms. One in a graphical form which can be used for cyclic
regenerator designs without the prior knowledge of a heat
transfer coefficient, whilst the other form is data stored
on a computer disc which produces convective heat transfer
coefficients for regenerator raw data. Analysis of the
practical data clearly shows the importance of the number of
cycles required to reach equilibrium, test bed heat leak and
packing intraconduction.
Finally, prior to each cyclic set-up a single shot run was
performed and the convective heat transfer coefficient obtained
using Darabi's(1981) graphical technique. This offered a
unique opportunity to compare cylic and single shot
characteristics for the same physical system.