Unit lab 2

DEFINITION AND TYPES OF HEAT EXCHANGER

HEAT EXCHANGER

Definition and Types of Heat Exchanger

JOSEPH ESTUR

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ENGR. MICHAEL MANGAOANG


Heat Exchanger

The general function of a heat exchanger is to transfer heat from one fluid to another.
The basic component of a heat exchanger can be viewed as a tube with one fluid
running through it and another fluid flowing by on the outside. There are thus three heat
transfer operations that need to be described:

Convective heat transfer from fluid to the inner wall of the tube,
Conductive heat transfer through the tube wall, and
Convective heat transfer from the outer tube wall to the outside fluid.

Heat exchangers are typically classified according to flow arrangement and type of
construction. The simplest heat exchanger is one for which the hot and cold fluids move
in the same or opposite directions in a concentric tube (or double-pipe) construction. In
the parallel-flow arrangement, the hot and cold fluids enter at the same end, flow in the
same direction, and leave at the same end. In the counterflow arrangement, the fluids
enter at opposite ends, flow in opposite directions, and leave at opposite ends.

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Types of Heat Exchanger

A. Shell-and-Tube Heat Exchangers – These are exchangers that have bundles of
tubes contained in ‘shells’ or pressure vessels. Like in osmosis, the fluid or gas that has
to be treated will flow through a series of tubes. Depending on the temperature of the
input, the result would be the exact opposite. For example, if the liquid on the first series
of tubes is hot, the second group of tubes will help initiate the process of temperature
change in order to produce cooler fluid. Perhaps the only drawback of these exchangers
is the complexity of their design. Some considerations are being measured just to
ensure its efficiency in large-scale processes. Aside from the built, the amount of
workload and the maintenance costs are also taken into account by most industrial
engineers.

B. Plate Heat Exchangers – These are units that use thin sheets of aluminum
instead of tubes. Although they basically function in the same manner as the
aforementioned, these exchangers are rather more efficient in the process of heat
transfer. Its structure is composed of ‘plates’ that are grouped as a stack in a frame,
having gaps several inches wide so that they do not touch each other. They are usually
held together by gaskets, which are detachable in order to be able to access the plates
effortlessly for cleaning and tune-ups. The main advantage of plate exchangers from the
traditional shell-and-tubes is the large amount of surface area provided to allow the fast
transfer of heat. However, it is this same mechanism that these exchangers have that
can be of a disadvantage to them. Due to the rapid expansion of fluids over the plates,
leakages are likely to happen during the exchange process. They are also susceptible
to fouling or contamination because of the narrow space between the plates in which
the liquid flows. Overall, the plate exchangers are by far the most practical devices
given their compactness and low maintenance costs.

C. Regenerative Heat Exchangers – As the term might suggest, these exchangers
promote energy conservation. They have this design that allows a cycle of heat transfer.

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The exchange takes place on both sides of the machinery. The exiting fluid is used
again as an input, and the whole process of heat exchange continues as a cycle. This
type of heat exchangers can be adopted by using either the tube bundles or plate
exchangers.

D. Adiabatic Wheel Heat Exchangers – The term ‘adiabatic’ pertains to the
thermodynamic process that happens without any loss or gain in heat. As a heat
exchanger, the adiabatic wheel acts as a mechanism for storing the heat before it is
eventually released.

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Unit lab 2

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Unit lab 2