Page 19 - Design and Operation of Heat Exchangers and their Networks

6 Design and operation of heat exchangers and their networks

by Desideri et al. (2016). Compared with the experimental data, both of
them are well suited for dynamic modeling of two-phase heat exchanger
components being characterized by a low error on the total conservation
of energy and mass, but the moving boundary model proves much faster
compared with the finite-volume model. However, the finite-volume for-
mulation was found to be more robust through start-up transients
(Bendapudi et al., 2008).
With the rapid development of computer technology, the computa-
tional fluid dynamics (CFD) techniques have been increasingly applied
for the design of heat exchangers in recent years. Sunden (2011) discussed
the applications of computational methods in heat transfer equipment and
presented some examples of application of CFD methods for real heat
exchangers. Bhutta et al. (2012) reviewed the applications of CFD in design,
simulation, and optimization of various types of heat exchangers. The qual-
ity of the solutions obtained from these simulations are largely within the
acceptable range, proving that CFD is an effective tool for predicting the
behavior and performance of a wide variety of heat exchangers. Besides
the well-known commercial CFD software such as FLUENT and ANSYS,
recently, OpenFOAM, an open-source CFD code has often been used for
the numerical simulation of heat exchangers (Selma et al., 2014; Gomez
et al., 2018).

1.3 Heat transfer enhancement
Heat transfer enhancement is always an important topic for design and
development of heat exchangers. A lot of techniques have been invented
and developed. One aspect is the development and application of a variety
of compact heat exchangers, including plate heat exchangers, plate-fin heat
exchangers, tube-fin heat exchangers, and microchannel heat exchangers.
These compact heat exchangers have very high ratio of the heat transfer area
2 3
to the exchanger volume (greater than 700m /m ). Meanwhile, their struc-
ture can produce higher heat transfer rate. As a result, a small heat exchanger
can have a larger heat transfer area and higher heat transfer coefficient and
offer much higher heating (or cooling) load.
The second aspect of heat transfer enhancement is the development of a
variety of enhanced surfaces, including externally finned tubes, internally
finned tubes, roughened surfaces, and integral low finned tubes.
These enhanced surfaces have larger heat transfer area than the plain ones.
Furthermore, suitable use of the roughness, ribs, and low fins can increase