Heat transfer can be enhanced by
employing various techniques and methodologies, such as increasing either the
heat transfer surface or the heat transfer coefficient between the fluid and
the surface that allow high heat transfer rates in a small volume. Cooling is
one of the most important technical challenges facing many diverse industries,
including microelectronics, transportation, solid-state lighting, and
manufacturing.
There is, therefore, an urgent need for new and innovative
coolants with improved performance. The addition of micrometer- or
millimetre-sized solid metal or metal oxide particles to the base fluids shows
an increment in the thermal conductivity of resultant fluids. But the presence
of milli- or microsized particles in a fluid poses a number of problems. They
do not form a stable solution and tend to settle down. Apart from the
application in the field of heat transfer, nano fluids (nano meter particles in
a fluid) can also be synthesized for unique magnetic, electrical, chemical, and
biological applications. They also cause erosion and clogging of the heat
transfer channels.
The novel concept of “nano fluids” has
been proposed as a route to surpassing the performance of heat transfer fluids
currently available. A very small amount of nano particles, when dispersed
uniformly and suspended stably in base fluids, can provide impressive
improvements in the thermal properties of base fluids. Nano fluids, which are a
colloidal mixture of nano particles (1–100 nm) and a base liquid (nano particle
fluid suspensions), is the term first coined by Choi in 1995 at the Argonne
National Laboratory to describe the new class of nanotechnology-based heat
transfer fluids that exhibit thermal properties superior to those of their base
fluids or conventional particle fluid suspensions.
Several investigations have revealed that
the thermal conductivity of the fluid containing nano particles could be
increased by more than 20% for the case of very low nano particles
concentrations. Nowadays a fast growth of research activity in this heat
transfer area has arisen. In fact, the exponential increase in the number of
research articles dedicated to this subject thus far shows a noticeable growth
and the importance of heat transfer enhancement technology in general.
Just to
give some data in table is given the number of papers from 1993 to 2010 (up to
April) found in SCOPUS under “Nano fluids” and the other two columns are the
papers found under “Nano fluids AND Heat Transfer” and “Nano fluids AND
Properties”. Moreover, in SCOPUS under “Nano fluids and Review” about 34 papers
were given as that result. This indicates a the high interest in nano fluids
activity research and the potential market for nano fluids for heat transfer
applications is estimated by the CEA in 2007 to be over 2 billion dollars per
year worldwide, with prospect of further growth in the next 5–10 year.
The aim of this special issue is to
collect basic, application and review articles of the most recent developments
and research efforts in this field, with the purpose to provide guidelines for
future research directions. The order of the papers is given presenting a
possible range of applications, a review on specific heat capacity, and an
experimental study to evaluate the effects of particle species, surface charge,
concentration, preparation technique, and base fluid on thermal transport
capability of nano fluids. A survey on heat transfer in nano fluids is
summarized in order to analyze the theories regarding heat transfer mechanisms
in nano fluids and to discuss the effects of clustering on thermal
conductivity.
After some considerations to address whether the heat transfer in
nano fluids still satisfies the classical energy equation are theoretically
examined by the macro scale manifestation of the micro scale physics in nano
fluids, an experimental investigation on natural convection heat transfer
characteristics in nano fluids in an enclosure and a numerical study on
turbulent forced convection flow of nano fluids in a circular tube subjected
are presented in the last two papers.
In the dimensional scale a nanometre is a billionth of
a meter. Nano scale science and engineering has revolutionized the scientific
and technological developments in nano particles, no structured materials, nano
devices and systems. National Science Foundation (2004) defines nanotechnology
as the creation and utilization of functional materials, devices, and systems
with novel properties and functions that are achieved through the control of
matter, atom-by-atom, and molecule by molecule or at the macro molecular level.
A unique challenge exists in restructuring teaching at all levels to include
nano scale science and engineering concepts and nurturing the scientific and
technical workforce of the future.This is because nanoparticles are usually
used at very low concentrations and manometer sizes. These properties prevent
the sedimentation in the flow that may clog the channel. From these points of
view, there have been some previous studies conducted on the heat transfer of
nanoparticles in suspension. Since Choi wrote the first review article on nanofluids [1],The advances in nanotechnology have resulted in the
development of a category of fluids termed nano fluids, first used by a group
at the Argonne National Laboratory in 1995 (Choi 19952).
Nano fluids are
suspensions containing particles that are significantly smaller than 100 nm
(Wen and Ding 2004), and have a bulk solids thermal conductivity of orders of
magnitudes higher than the base liquids. Experimental studies conducted have
shown Wanget .al.,1999, Lee et.al
1999,Keblinski et.al 2002) that the effective thermal conductivity increases
under macroscopically stationary conditions. Lee and Choy (1996), under laminar
flow conditions, nano fluids in micro channels have shown a twofold reduction
in thermal resistance (Lee and Choi, 1996) and dissipate heat power three times
more than that of pure water.
Studies conducted using water-Cu nano fluids
(Xian and Li, 2003) of concentrations approximately 2% by volume was shown to
have a heat transfer coefficient 60% higher than when pure water was used. Such
advances must have a broader impact culminating in promoting teaching, training
and learning. Dissemination of research results will enhance the scientific and
technological understanding of nanotechnology.
This effort aims at bringing nanotechnology to the
undergraduate level, especially at the applied level in engineering and
technology curricula. The focus is to incorporate nanotechnology into existing
course curricula such as heat transfer and fluid mechanics. The intention of
the work described here is to introduce a simple experimental procedure in a
heat transfer course to facilitate the understanding of the convective heat
transfer behaviour of nano fluids.