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CHAPTER
II

 

LITERATURE
REVIEW

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Shell
and helical coiled tube heat exchangers are the most sought after heat
exchangers due to their compactness, ease of manufacture and high heat transfer
ability in given space limitation. The coil curvature provide centrifugal
forces to act on the fluid flowing inside heat exchanger, which result in
secondary flow pattern which is perpendicular to the axial flow pattern. This
secondary pattern consists of two vortices. Heat transfer rates are increased
by secondary flow as it moves fluid across the temperature gradient. Hence,
there is an additional convective heat transfer mechanism that is perpendicular
to the axial flow, which does not exist in straight tube heat exchangers.

Several
researchers have analyzed the helical coil heat exchangers, which involves
various dimensionless numbers and geometric parameter variation in order to
improve the heat transfer rate and effectiveness of heat exchanger and some
studies are focused towards either constant wall temperature or constant wall
heat flux boundary conditions of heat exchanger. However some studies are
focused on the effect of air bubble injection into helical coil heat exchanger,
the variations of NTU and effectiveness due to the air bubbles injection with
different air flow rates.

In
last few years more computational methods have been developed to help
researchers in analyzing combustion, fluid dynamics and behaviour of different
models of heat transfer etc. The heat exchangers have wide range of
applications in various industries, which have attracted more researchers to
work in this field.

Following
articles presents a review of important published literature in the current
work:-

 

2.1.        
Previous work

Austen
et al. (1988) analysed the influence of pitch on the
pressure drop and heat transfer characteristics of helical coils for the
uniform input heat flux. Two pairs of coils were tested; each pair corresponds
to the same diametric ratio but substantially different pitch ratio. Water (3

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