Technical Seminar :)

1. Al2O3/Water Nanofluid as Coolant in
Double-Tube Heat Exchanger
Mr.V.S. PATNAIK Presented By,
(Guide) K.S.SUMAN KRISHNA KANTH

2. Advanced Flow and Heat-Transfer
Challenges
• Cooling becomes one of the top technical challenges faced by high-tech
industries such as microelectronics, transportation, manufacturing, and
metrology.
• Conventional method to increase heat flux rates:
 extended surfaces such as fins and micro-channels
 increasing flow rates increases pumping power.
• However, current design solutions already push available technology to its
limits.
• New Technologies and new advanced fluids with potential to improve
flow & thermal characteristics are of critical importance.
• Nanofluids are promising to meet and enhance the challenges.

3. Concept of Nanofluids
Thermal conductivity (W/m-K)
• Conventional heat transfer fluids 2500
have inherently poor thermal 1-Engine Oil
conductivity compared to solids. 2000
2-Ethylene Glycol
3-Water
• Conventional fluids that contain
4-Alum ina
1500
5-Silicon
mm- or m-sized particles do 6-Alum inum
7-Copper
not work with the emerging 1000 8-Silver
“miniaturized” technologies 9-Carbon
because they can clog the tiny 500
channels of these devices.
• Modern
0.15 0.25 0.61
nanotechnology 0
1 2 3 4 5 6 7 8 9
provides opportunities to Material
produce nanoparticles. Thermal conductivity of typical materials
• Nanofluids are a new class of
advanced heat-transfer fluids
engineered by dispersing Solids have thermal conductivities
nanoparticles smaller than 100 that are orders of magnitude larger
nm (nanometer) in diameter in than those of conventional heat
conventional heat transfer fluids. transfer fluids.

4. NANOFLUIDS
• A recent advancement in nanotechnology has been the
introduction of nanofluids, that is, colloidal suspensions of
nanometer-sized solid particles instead of common working
fluids.
• Nanofluids were first innovated by Choi and Eastman in 1995
at the Argonne National Laboratory, USA.
• Nanofluids have novel properties that make them potentially
useful in many applications in heat transfer, including
microelectronics, fuel cells, pharmaceutical processes, and
hybrid-powered engines, engine cooling/vehicle thermal
management, domestic refrigerator, chiller, heat
exchanger, nuclear reactor coolant, in grinding, machining, in
space technology, defense and ships, and in boiler flue gas
temperature reduction

5. Why Use Nanoparticles?
• The basic concept of dispersing solid particles in fluids to enhance thermal
conductivity can be traced back to Maxwell in the 19th Century.
• Studies of thermal conductivity of suspensions have been confined to
mm- or mm-sized particles.
• The major challenge is the rapid settling of these particles in fluids.
• Nanoparticles stay suspended much longer than micro-particles and, if
below a threshold level and/or enhanced with
surfactants/stabilizers, remain in suspension almost indefinitely.
• Furthermore, the surface area per unit volume of nanoparticles is much
larger than that of microparticles .
• These properties can be utilized to develop stable suspensions with
enhanced flow, heat-transfer, and other characteristics.

6. Materials for Nanoparticles and Base Fluids
1. Nanoparticle materials include:
– Oxide ceramics – Al2O3, CuO
– Metal carbides – SiC
– Nitrides – AlN, SiN
– Metals – Al, Cu
2. Base fluids include:
– Water
– Ethylene- or tri-ethylene-glycols and other coolants
– Oil and other lubricants

7. Methods for Producing
Nanoparticles/Nanofluids
 Two nanofluid production methods has been developed in ANL
to allow selection of the most appropriate nanoparticle material
for a particular application.
• In two-step process for oxide nanoparticles (“Kool-Aid” method),
nanoparticles are produced by evaporation and inert-gas
condensation processing, and then dispersed (mixed, including
mechanical agitation and sonification) in base fluid.
• A patented one-step process simultaneously makes and
disperses nanoparticles directly into base fluid; best for metallic
nanofluids.
• Other methods: Chem. Vapor Evaporation; Chem. Synthesis.

8. • Realizing the modest thermal conductivity enhancement in
conventional nanofluids, a team of researchers at Indira
Gandhi Centre for Atomic Research Centre, Kalpakkam
claimed developing a new class of magnetically polarizable
nanofluids where the thermal conductivity enhancement up
to 300% of base fluids is demonstrated.

9.  The objective of this paper is to provide improvements through
nanofluids in place of pure working fluid in heat exchangers
with a view of decreasing the mass flowrate for providing the
same heat exchange capacity.
• 7nm- Al2O3 nanoparticle with concentration up to 2vol.% has
been selected as a coolant in a typical horizontal double-tube
heat exchanger because of its good thermal properties and
easy availability.
• Water has been chosen as heat transfer base fluid.
• Al2O3 nanoparticles are generally considered as safe material
for human being and animals that are actually used in the
cosmetic products and water treatment.
• In addition, Al2O3 nanoparticles are stabilized in the various
ranges of PH.

10. Thermophysical properties of nanoparticle and
base fluid
• Density of Al2O3/water nanofluid can be calculated using mass
balance
ρnf =(1 – φ)ρbf + φρp
• specific heat of nanofluids
cp,nf =[(1 – φ)ρbfcp,bf + φρpcp,p ]/ρnf

11. Thermophysical properties of nanoparticle and
base fluid

12. Mathematical Modeling
 HOT SOLVENT SIDE CALCULATION:
• The rate of heat transferred to the hot solvent in a double-
tube heat exchanger can be written as follows :
Q.given = m˙ hcp,h(T1 − T2) ≡m˙nfcp,nf(t2 – t1)
• The heat exchange capacity of exchanger (Q.given ) is equal to
15.376kW, the inlet outlet temperatures of hot solvent stream
are equal to 400C and 300C respectively, the flowrate of hot
solvent stream is 0.8kg.s-1 and its specific heat capacity is
equal to 1922 Jkg-1K-1.
• The heat transfer coefficient of hot solvent flowing inside the
tube under a turbulent regime(Re>10000) can be calculated
as

13. • where Di is the internal diameter of the internal tube(μnf/μwnf)0.14
is the viscosity correction factor. In the previous
equation the Reynolds and Prandtl numbers and heat transfer
coefficient of hot solvent are calculated as follows :

14. Nanofluids Side Calculation
• The heat transfer coefficient of the nanofluid as coolant flowing in the
annular can be calculated considering the turbulent Nusselt number
presented by Li and Xuan as follows:
• where Ped is the nanofluid Peclet number and is defined in the following
form:
• where dp is the diameter of the nanoparticles and αnf is the nanofluids
thermal diffusivity which is defined as follows:

15. • The Reynolds and Prandtl numbers in are calculated considering the
nanofluid properties as follows:
• where Deq is the equivalent diameter which is expressed in the following
form:
where Ds is the internal diameter of the external tube.
• Tw is calculated by equating the heat transfer rates at both sides of the tube
wall as follows:

16. • The friction factor of Al2O3/water nanofluid can be calculated using the
formula presented as follows :
Where
• The pressure drop (Δpnf) and pumping power (PP) for Al2O3/water
nanofluid used as a coolant in a double-tube heat exchanger are
calculated as follows
• where L is the length of the tube, D|eq is the equivalent diameter of an
annulus given by D|eq= Ds − Do, and as is the annular flow area.

17. Total Heat Transfer Area and Coefficient Calculation
• The total heat transfer coefficient can be calculated as follows:
• where Rf is the fouling resistance, hh,o is heat transfer coefficient of hot
solvent that referred to the external area, and hnf is the heat transfer
coefficient of the nanofluid coolant. In this work, the fouling resistance is
assumed to be 5×10−4m2KW−1.
• The total heat transfer area of a double-tube heat exchanger, A, is
computed from the following equation:
• where U is the total heat transfer coefficient and F is the temperature
correction factor, which in the case of the countercurrent flow can be taken
equal to 1.

18. • The thermal conductivity of Al2O3 /water nanofluid with
different concentrations (0-2% volume fraction) has been
calculated using Kang model.
• As can be seen, thermal conductivity increases with increasing
the nanoparticles volume concentration.

19. • Results show that heat
transfer coeffcient and
Nusselt number can be
enhanced by adding
nanoparticles to the
base fluid.
• For volume concentration of 2%, the heat transfer coefficient increase about
64.65%, while the increase of thermal conducitivity is below 40%

20. • Increasing the
particles
concentration raises
the fluid viscosity
and decreases the
Reynolds number
and consequently
decreases the heat
transfer coefficient
• It can be concluded that the change in the coolant heat transfer
coefficient is more than the change in the fluid viscosity with
increasing nanoparticles loading in the base fluid.

21. • This figure reveals that as the concentration
increases, the effect of increasing nanoparticles
concentration on changing the thermal conductivity
is lower than changing the heat transfer coefficient.

22. • The total heat transfer
coefficient of the
Al2O3/water nanofluid for
volume concentrations in the
range of 0.1% to 2%
increases by 0.55%–3.5%.
• The total heat transfer coefficient is high when the probability
of collision between nanoparticles and the wall of the heat
exchanger has increased under higher concentration
conditions. It confirms that nanofluids have considerable
potential to use in cooling systems.

23. • Figure 7 shows the
reduction percent of
wall temperature and
heat transfer area in a
double-tube heat
exchanger that utilizes
Al2O3/water nanofluid
as a coolant under
turbulent flow
conditions.
• The wall temperature and total heat transfer area decrease with the
increasing of volume concentration of nanoparticles. For example, the
reduction percent of wall temperature at 0.5%, 1%, 1.5%, and 2% volume
concentrations is about 5.35%, 9.32%, 11.74%, and 13.72%, respectively.
Moreover, the reduction of the total heat transfer area at 2% volume
concentration is about 3.35%.

24. • This figure reveals that at the same heat exchange
capacity, the flowrate of nanofluid coolant decreases with the
increasing concentration of nanoparticles. For a volume
concentration range of 0.1% to 2%, the mass flowrate
decreases by 4.73% to 24.5%.

25. • The results show that nanofluid friction factor and pressure
drop increase with increasing nanoparticles loading in the base
show that using the Al2O3/water nanofluid at higher particle
volume fraction creates a small penalty in pressure drop.

26. CONCLUSIONS
• The results confirm that nanofluid offers higher heat
performance than water and therefore can reduce the total
heat transfer area and also coolant flowrate for providing the
same heat exchange capacity.
• Inorder to determine the feasibility of Al2O3/water nanofluid
as a coolant in a double-tube heat exchanger, the effects of
nanoparticles on the friciton factor, pressure drop, and
pumping power have been evaluated.
• The results show that using Al2O3/water nanofluid at higher
particle volume fraction creates a small penalty in pressure
drop.

27. REFERENCES
[1] S. U. S. Choi and J. A. Eastman, “Enhancing thermal conductivity of fluids
with nanoparticles,” in ASME International Mechanical Engineering Congress
and Exhibition, San Francisco, Calif, USA, 1995.
[2] M. Shafahi, V. Bianco, K. Vafai, and O. Manca, “An investigation of the
thermal performance of cylindrical heat pipes using nanofluids,” International
Journal of Heat and Mass Transfer, vol. 53, no. 1–3, pp. 376–383, 2010.
[3] P. Naphon , P. Assadamongkol, T. Borirak , “Experimental investigation of
titanium nanofluids on the heat pipe thermal efficiency”, International
Communications in Heat and Mass Transfer ,vol 35, pp.1316–1319, 2008.
[4] Navid Bozorgan, Mostafa Mafi, and Nariman Bozorgan, “Performance
Evaluation of Al2O3 /Water Nanofluid as Coolant in a Double-Tube Heat
Exchanger Flowing under a Turbulent Flow Regime,” Advances in Mechanical
Engineering, vol. 2012, Article ID 891382, 8 pages, 2012.

28. Q &A