Page 335 - Design and Operation of Heat Exchangers and their Networks

Dynamic analysis of heat exchangers and their networks 321

the measurement of heat transfer coefficients of compact heat transfer sur-
faces and developed a transient experimental method—the single-blow
testing technique. Different kinds of the mathematical models for the
single-blow problem were later further developed and will be introduced
in Chapter 8 in detail.
The boom of the modeling and investigation of transient behavior of
two-stream heat exchangers came in the 1950s. However, the researches
were limited to obtaining the transfer functions of outlet fluid temperatures
to the variations in inlet fluid temperatures and mass flow rates, that is, the
solutions in the Laplace domain (Takahashi, 1952). The fluid temperature
responses in real-time domain were obtained by means of numerical
methods such as finite-difference method (Dusinberre, 1954). Only for
some simplest cases, the analytical solutions of the outlet fluid temperatures
were obtained; for example, one fluid has phase change, and the heat transfer
resistance between this fluid and the wall is negligible so that the wall tem-
perature is constant.
After the 1960s, research was extended to more general cases and com-
plicated types of heat exchangers. A historical review of earlier investigations
on modeling and dynamics of heat exchangers were given by Kanoh (1982),
in which more than 200 references were cited. Shah (1981) formulated the
transient response problems of one-dimensional flow heat exchangers and
summarized the available solutions for counterflow and crossflow heat
exchangers and thermal regenerators subjected to a step change in inlet tem-
perature and/or mass flow rate of one or both fluids. New developments in
dynamic analysis of heat exchangers were reviewed by Roetzel (1996). The
cited 76 references cover the topics of dynamic responses of parallel-flow
and counterflow heat exchangers to the disturbances in inlet fluid temper-
atures and mass flow rates, dynamic characteristics of crossflow heat
exchangers, single-blow problems, and axial heat dispersion model. The
axial heat dispersion model was proposed by Roetzel and Xuan (1992b)
for taking into account the effect of flow maldistribution on the dynamic
behavior of heat exchangers, especially the fluid temperature responses at
the exchanger outlets. A systematic description of the transient behavior
of heat exchangers was provided by Roetzel and Xuan (1999), in which
the new developments in dynamic analysis of tube bundle heat exchangers,
plate heat exchangers, and crossflow heat exchangers as well as the applica-
tion of the axial dispersion model in dynamic simulation of heat exchangers
are summarized. A general solution for real-time dynamic responses of par-
allel channel multistream heat exchangers and their networks to the