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Heat transfer enhancement technology has been developed and is widely
applied to heat exchanger applications, leading to a reduction in size and cost of the
heat exchangers. In laminar flow, the heat transfer coefficient is generally low in
a plain tube, and hence any means of improving the heat transfer rate without
adding extra cost for energy is well acceptable. Bergles (1985 and 1988) reported an
overall view of heat transfer enhancement by various techniques. Among the
many techniques (both passive and active) investigated for enhancement of heat
transfer rates inside circular tubes, a tube fitted with full length twisted tape inserts
(also called as swirl flow device) was found to be very effective due to the imparting
of helical path to the flow. Today Computational Fluid Dynamics (CFD) plays a
major role in understanding the heat transfer and fluid flow mechanism in tube
flow with much easier and economical means, than experiments. Also, CFD
simulation is useful for predicting the flow behavior in a wide range of flow conditions
for various geometries. Good literature is available on CFD modeling of
convective heat transfer and heat transfer augmentation process using swirl flow
devices. Michiel and Dixon (2001) presented the comparison of CFD simulations
to experiment for convective heat transfer in a gas-solid fixed bed. Hilde et al. (2003) reported the validation of the CFD model of a three dimensional
tube-in-tube heat exchanger. Modeling of heat transfer augmentation in a circular
tube fitted with twisted tape inserts in a laminar flow using CFD was reported
by Sivashanmugam et al. (2007 and 2008). At higher heat flux conditions,
the conventional fluids are not capable of achieving the desired heat transfer
rate and hence research is underway to apply nanofluids in those environments.
Choi (1995) was the first to use the term nanofluids referring to fluids
with suspended nanoparticles. Nanofluids were created by dispersing
nanometer-sized particles (< 100 nm) in a base fluid such as water, ethylene glycol
or propylene glycol. Use of high thermal conductivity metallic nanoparticles
like Copper, Aluminum, Silver and Silicon increase the thermal conductivity of
such mixtures, thus enhancing their overall energy transport capability. Due to
their excellent thermal performance, nanofluids have attracted the attention
of researchers as a new generation of heat transfer fluids in building heating,
heat exchangers, and automotive cooling applications. Various benefits of
the application of nanofluids include: improved heat transfer, heat transfer
system, size reduction, minimal clogging, microchannel cooling and miniaturization
of systems. Numerous heat transfer studies (Yimin and Qiang, 2000; Xuan and
Li, 2003; Dongsheng and Yulong, 2004; Sidi et
al., 2004 and 2005; Ying et al., 2005; Yurong et al., 2008; Praveen et al., 2009; Xiang-Qi Wang et al., 2009; and Zeinali et al., 2009) were reported using nanofluids. An attempt to use swirl flow
devices for nanofluids can reap the benefits of heat transfer enhancement by both
swirl flow devices and nanofluids. Therefore, the present paper reports the
CFD analysis of heat transfer behavior of a circular tube fitted with helical tape
inserts at constant heat flux using CuO nanofluids.
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