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The principal types of heat exchangers used in
chemical and allied industries which will be discussed in this chapter, are
listed below:
1. Double-pipe exchanger: the simplest type, used for cooling and heating.
2. Shell and tube exchangers: used for all applications
3. Plate and frame exchangers (plate heat exchangers): used for heating and
cooling.
4. Plate-fin exchangers.
5. Spiral heat exchangers.
6. Air-cooled: coolers and condensers.
7. Direct contact: cooling and quenching.
8. Agitated vessels.
9. Fired heaters.
Heat exchanger types are also classified according to the direction of flow of
the hot and cold fluids with respect to each other, or according to the
temperature distribution of the two fluids along the exchanger length. Thus, we
may have the following types of heat exchanger:
a) Parallel-flow exchanger
b) Counter-flow exchanger
c) Cross-flow exchanger
d) Condenser or evaporators
Parallel-flow exchangers: The hot fluid and
cold fluids flow in the same direction, hence the name parallel-flow. Many
devices, such as water heaters, oil heaters and oil coolers, etc., belong to
this class.
The temperature difference between hot and cold fluid keeps on decreasing from
inlet to exit as shown in following fig.1.2
Counter-flow Exchangers: In this case the
fluids flow through exchanger in opposite directions, hence the name counter
flow. The temperature distribution in counter-flow exchanger is shown in fig.1.3
Below:
It can be seen that the temperature difference between the two fluids remains
more nearly constant as compared to the parallel-flow type. This arrangement
gives maximum heat transfer rate for a given surface area. If the fluid flows
through the exchanger only once, it is called a single pass heat exchanger. In
many designs, one or both fluids may traverse the exchanger more than once. Such
exchangers are called multi-pass exchangers.
Cross-flow exchangers: Here the two fluids
flow at right angles to each other. Two different arrangements of this exchanger
are commonly used. In one case, each of the fluids is unmixed as it flows
through the exchanger. As a result, the temperatures of the fluids leaving the
exchanger are not uniform. An automobile radiator is an example of this type of
exchanger. In other case, one fluid is perfectly mixed while the other is
unmixed as it flows through the exchanger.
Condenser: In a condenser the condensing
fluid (hot fluid) remains at constant temperature throughout the exchanger while
the temperature of the colder fluid gradually increases from inlet to outlet.
Similarly in an evaporator the boiling fluid (cold fluid) remains at constant
temperature while the hot fluid temperature gradually decreases. The temperature
distribution in condenser is shown below. Since the temperature of one of these
fluids remains constant, it is immaterial whether the two fluids flow in the
same direction of opposite direction.
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Introduction |
Combined heat transfer process |
Heat transfer in cooling tower |
Variables affecting performance of CT heat transfer |
Heat transfer within
cooling system (heat exchanger) |
Types of heat exchanger |
Basic design
procedure and theory |
Designing a test heat exchanger |
Log Mean Temperature
difference | L.M.T.D. Correction factors |
Overall heat transfer coefficient |
Elaborated method for calculating U values |
Effect of scale formation |
Condensation of steam |
Condenser, where the hot fluid temperature varies |
Significance of pressure |
Significance of flow rate |
Methods of checking steam
condenser performance |
Common conversion factors
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