Page 16 - Design and Operation of Heat Exchangers and their Networks

Heat exchangers and their networks: A state-of-the-art survey 3

exchangers handle most of services in a vast range of applications and will be
the topic in this book.
Recuperative heat exchangers have many variations but can be broadly
classified into the tubular and plate types. Tubular heat exchangers have
tubes (mostly but not always circular in cross section) for the flow passage
for one or both fluids. Plate heat exchangers have stacks of die-formed plates
in which the fluid flow passages are impressed. The stacks of plates may
be brazed or welded in a permanent assembly (plate-fin types) or simply
compacted in a frame by compression bolts with sealing gaskets between
the plates (plate-and-frame type).
The tubular heat exchangers are found in the great majority of applica-
tions, primarily for historical and economic reasons. They have been in use
for a long time and familiar to many engineers. Standard models provided by
well-established manufactures are available in a wide range of capacities at
reasonable cost, as are the custom-made units found in oil refineries and
chemical process plants and in the power industry. Standards for design
and procedures for use, maintenance, and inspection are well known and
familiar. Furthermore, in many cases, the fluid streams are substantially pres-
surized, and the exchanger serves as a pressure vessel as well as to transfer heat
energy. Circular tubes and shells are in a good shape for high-pressure fluids.
Very high pressure and temperature can be handled in tubular heat
exchangers. Similarly, there is no foreseeable limit to the range of flow
capacities that can be accommodated. Nevertheless, in some applications,
appreciable savings in cost, weight, and space can be gained with plate heat
exchangers, and these kinds of exchangers have an established and growing
place in the technology. Increasing numbers of plate heat exchangers are
being used presently.
Recently, microchannel heat exchangers have been extensively applied
for high-heat flux cases, especially for cooling of electronic equipment.
Microchannel heat exchangers have a flow passage with the hydraulic diam-
eter less than 1mm, and the heat transfer surface density can reach more than
3
2
10,000m /m . Tuckerman and Pease (1981) reported their pioneering
work on the cooling of very large-scale integrated circuits with microchan-
nel heat sinks. A new review on the application of microchannel heat sinks as
a thermal management for high-heat flux electronic devices was presented
by Naqiuddin et al. (2018).
According to the flowing patterns of fluids in the heat exchangers,
recuperative heat exchangers can also be classified into parallel flow and
crossflow. In the parallel flow heat exchangers, the hot and cold fluids (could