1. CSG
Latest Technology in Refrigeration and Air Conditioning
Under the Auspices of the PRESIDENCY OF THE COUNCIL OF MINISTERS
XV EUROPEAN CONFERENCE MILANO 7th-8th JUNE 2013
THE POTENTIAL HVAC&R
APPLICATION OF NANOFLUIDS
Sergio BOBBO, Laura COLLA, Matteo SECURO, Laura FEDELE
Consiglio Nazionale delle Ricerche
Istituto per le Tecnologie della Costruzione - sede di Padova
Corso Stati Uniti, 4, 35127 Padova, Italy
Telefono: +39.049.8295736 Fax: +39.049.8295728
e-mail: sergio.bobbo@itc.cnr.it

2. SUMMARY
• What are Nanofluids?
• Nanofluid Characterization at ITC-CNR
• Stability
• Thermal Conductivity
• Dynamic Viscosity
• Heat Transfer Coefficient
• HVAC&R Applications

3. WHAT ARE NANOFLUIDS
Solids have thermal
conductivity (l) orders of
magnitude higher than liquids
Dispersion of solid particles in
liquids enhances the thermal
conductivity of the base fluids.
0
500
1000
1500
2000
2500
Nanotubi
Diamante
Grafite
Fullereni(film)
Argento
Rame
Alluminio
Nickel
Silicio
Allumina(Al2O3)
Sodioa644K
Acqua
Glicoleetilenico
Oliopermotori
ConduttivitàtermicaaTambiente(Wm-1
K-1
)
Thermal conductivity of solids and liquids
0.613
0.253
0.145
Non
metallic
Carbon Metals Met.
Liq.
Non
Metallic
liquids

4. WHAT ARE NANOFLUIDS
Nanofluids are colloidal suspensions of nanoparticles in common fluids:
water
BASE FLUIDS oil
ethylene glycol
refrigerants
oxides
NANOPARTICLES metals
carbon nanotubes

5. WHAT ARE NANOFLUIDS
Nanofluids promise to significantly enhance thermal, rheological and
tribological properties of technological fluids
FACTORS INFLUENCING NANOFLUIDS PERFORMANCE:
• Colloidal solutions Zeta potential and pH
• Nanoparticles concentration
material, shape and size
• Dispersants type and concentration

6. Heat Transfer
Coefficient
Measurem. (a)
Nanofluids
preparation
Measurement
-dimens. distrib.
-Zeta potential
Thermal
Conductivity
Measur. (l)
NANOFLUIDS LAB AT ITC-CNR
Viscosity
Measur. (m)
Calculation
Density (r)
Specific Heat (cp)
IENI-CNR
Commercials

7. STUDIED NANOFLUIDS
• Single Wall Carbon Nanohorns (SWCN) in Polyolester (POE) oil (Bobbo et al., 2010);
• Titanium oxide (TiO2) in POE oil (Bobbo et al., 2010);
• Copper (Cu) in water (Fedele et al., 2011);
• TiO2 in water (Fedele et al., 2011, Bobbo et al., 2012, Fedele et al., 2012);
• SWCNH in water (Fedele et al., 2011, Bobbo et al., 2012);
• Silicon oxide (SiO2) in water (Bobbo et al., 2011);
• Iron oxide (Fe2O3) in water (Colla et al., 2011);
• Silicon Carbide (SiC) in ethylene glycol (Bobbo et al., 2012a);
• Zinc Oxide (ZnO) in water (Bobbo et al., 2012b);
• Gold (Au) in water (Colla et al., 2013a);
• TiO2 in POE (Colla et al., 2013b).

8. NANOFLUID STABILITY
Nanoparticle mean diameter in relation to the
time elapsed from the day of preparation in
water-based nanofluids containing TiO2 at 1
wt%. ( ) static and (•) stirred samples at the
DLS (Fedele et al., 2012)
45
50
55
60
65
70
75
80
85
0 10 20 30 40
Meandiameter(nm)
Day from preparation
 Nanofluids stability:
• Particle diameter should not change
with particle concentration;
• No aggregation after 30 days;
• No partial precipitation.
Malvern Zetasizer Nano ZS, Dynamic
Light Scattering (DLS) Technique

9. THERMAL CONDUCTIVITY
 Nanofluids Thermal Conductivity:
• strongly dependent on concentration;
• function of temperature;
• influenced by size and stability of particles.
TPS 2500 S (Hot Disk) was used to determine thermal conductivity and thermal
diffusivity, knowing density and specific heat of the analysed material
accuracy better then 5%.

10. THERMAL CONDUCTIVITY
0.95
1.00
1.05
1.10
1.15
1.20
1.25
0 20 40 60 80
lexp/lwater
T / °C
Au 0.02%
citrato 0.03%
Au 0.05%
citrato 0.07%
Thermal conductivity enhancement of nanofluid
water+Au as a function of temperature

11. DYNAMIC VISCOSITY
A rotational Rheometer AR G2 (TA Instruments) with a cone and plate geometry
 Nanofluids Dynamic Viscosity:
• m essential to evaluate increase/decrease of energy required to pump the
fluid through the hydraulic circuits;
• dependent on concentration;
• size of particles can influence the viscosity (aggregation of nanoparticles
strongly enhances viscosity)

12. DYNAMIC VISCOSITY
0.00126
0.00128
0.00130
0.00132
0.00134
0.00136
0.00138
0.00140
0 200 400 600 800 1000 1200 1400
m(Pas)
shear rate (s-1)
water
0.1%
1%
5%
Refprop9.0
Dynamic viscosity data for water and ZnO-water nanofluids at 10°C

13. HEAT TRANSFER COEFFICIENT
The heat transfer coefficient is useful to understand nanofluids energy behaviour
At ITC-CNR in Padova, a hydraulic apparatus, based on constant heat flux, was
specifically built for the single phase heat transfer coefficient measurement.
gear pump
Ismatec MCP-
Z
Coriolis mass flow
meter Emerson
Process
cooling
machine
Polyscience
measurement
sectionFLUID
COPPER
PIPE
INSULATION
HEATING ELECTRICAL
RESISTANCES
HEAT FLUX

14. HEAT TRANSFER COEFFICIENT
The measured fluids until now did not show significant heat transfer coefficient
enhancement:
 ZNO 10%WT IN WATER (Bobbo et al.,2012b)
• coefficient increase up of 7% only
• temperature range between 19 C and 41 C
• Re=16000;
 AU 0.02% WT IN WATER (Colla et al.,2013)
• coefficient increase up of 5% only
• in the temperature range between 19 C and 41 C
• turbulent flow.

15. HEAT TRANSFER COEFFICIENT
Tin = 19°C 0.02 wt% Tin = 41°C 0.02 wt%
An enhancement of the heat transfer coefficient has been found, depending on Re and temperature:
Tin = 19 °C from 4% Re 5000 to 1% Re 10000
Tin = 41°C about 5% Re from 7000 to 16000

16. HVAC&R Applications
SECONDARY FLUIDS
commercial refrigeration, chiller, solar panels
NANOREFRIGERANTS
nanoparticles dispersion directly in the refrigerant
NANOLUBRICANTS
they can improve thermal dissipation, anti-wear and extreme pressure
properties of compressors lubricants

17. Applications in vapour
compression systems
R134a with TiO2-mineral oil in a domestic refrigerator
(Bi et al., Application of nanoparticles in domestic refrigerators, Applied
Thermal Engineering, 28:1834, 2008)
Domestic refrigerator
Capillary expansion device; reciprocating compressor
Refrigerant: R134a
Lubricant: i) POE oil ii) mineral oil+nanoparticles
0.1 wt% of TiO2 dispersed in MO by ultrasonic homogenizer
Experimental results
- R134a and MO+nanopartciles worked normally and efficiently
- energy consumption reduced by 26.1% in comparison to R134a and
POE oil
- the same tests with Al2O3 showed similar results

18. Applications in vapour
compression systems
R134a/R600/R290 with Al2O3-mineral oil
(Jwo et al., Effects of nanolubricant on performance of hydrocarbon
refrigerant system, J. Vacuum Sci. Tech. B, 27:147, 2009)
Domestic refrigerator (50 l capacity)
Replacement of R134a with mixture butane/propane/R134a
Replacement of POE oil with mineral oil
Mineral oil added with Al2O3 nanoparticles (0.05, 0.1, and 0.2 wt%)
Experimental results:
‒ Optimal mixture: 60% R134a 0.1 wt% of Al2O3
‒ Power consumption reduced of about 2.4%
‒ COP was increased by 4.4%.

19. Applications in vapour
compression systems
R134a with Al2O3 in mineral oil
(Subramani and Prakash, Experimental studies on a vapour compression
system using nanorefrigerants, Int. J. Eng. Sci.Tech., 3(9): 95, 2011)
Experimental refrigeration circuit
Thermostatic expansion valve; reciprocating compressor
Refrigerant: R134a
Lubricant: i) POE oil ii) mineral oil iii) mineral oil+nanoparticles
0.06 wt% of Al2O3 dispersed by ultrasonic homogenizer
Experimental results
- power consumption reduced by about 25% with reference to POE oil
- COP increased by 33% with reference to POE oil

20. Applications in vapour
compression systems
R134a with Al2O3 in polyalkylene glycol (PAG) oil
(Kumar and Elansezhian, Experimental Study on Al2O3-R134a Nano
Refrigerant in Refrigeration System, Int. J. Mod. Eng. Res., 2(5):3927 (2012)
2012)
Experimental refrigeration circuit
Capillary expansion device; reciprocating compressor
Refrigerant: R134a (150 g)
Lubricant: PAG oil
0.2% of Al2O3 dispersed by magnetic stirring and ultrasonic
homogenizer
Experimental results
- energy consumption reduced by about 10% with reference to pure oil

21. Applications in vapour
compression systems
Refrigerants with TiO2 in mineral oil (Padmanabhan and Palanisamy,
2012)
Experimental refrigeration circuit
Capillary expansion device; reciprocating compressor
Refrigerant: R134a, R436A (R290/R600a-56/44 wt%) and R436B
(R290/R600a-52/48 wt%)
Lubricant: i) POE oil ii) mineral oil+nanoparticles
0.1 g/L of TiO2 dispersed in MO by ultrasonic homogenizer
Experimental results
- exergy efficiency with R134a, R436A and R436B and nanolubricant
increases by 6%, 8% and 12%, respectively with reference to R134a
and POE oil

22. CONCLUSIONS
• Nanofluids are colloidal suspensions of nanoparticles in common fluids that
promise to significantly increase the energetic performance of thermal systems
and the tribological properties of lubricants.
• They could be applied in HVAC&R systems, both as refrigerant or lubricant, and
present literature show a good potentiality in common applications
• However, literature results are frequently controversial and relatively scarce.
• For this reason, a huge experimental and theoretical work is still necessary to
select and optimise nanofluids on the application requirements;
• Future works will be devoted to study the effect of metal nanoparticles in
suspension on the thermophysical properties of nanofluid and directly the
influence of nanoparticles in working fluid of vapour compression cycle.

23. THANKS FOR YOUR ATTENTION

24. THERMAL CONDUCTIVITY
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0 20 40 60 80
l(W/mK)
T (°C)
water+SiO2 1%
water+SiO2 5%
water+SiO2 25%
water+SiO2 50%
Buongiorno et al. (2009)
water (experimental)
water (Lemmon et al., 2010)

25. R134a with TiO2-mineral oil in a refrigerating machine (Wang et al., 2003)
Nanoparticles enhanced the solubility of R134a in mineral oil (MO) and
improved the performance by returning more lubricant oil back to the
compressor compared to R134a and POE oil.
Applications in vapour
compression systems

27. HOW TO PRODUCE NANOFLUIDS
The first need is to obtain a stable and homogenous colloidal solutions
TWO-STEP METHOD
• nanoparticles powder is put into the
base fluids, physically dispersed by
strong mechanical stirring (low or
high energy ultrasounds, ball milling,
high pressure homogenisation).
• this technique is suitable for the
dispersion of oxide nanoparticles
SINGLE-STEP METHODS
• synthesis and dispersion of nanoparticles
into the fluid take place simultaneously
• Various techniques are available:
− direct dispersion of nanoscale vapour
from metallic source material into low-
vapour-pressure fluids;
− physical process set up by wet grinding
technology with bead mills;
− chemical reduction method for
producing metallic nanofluids;
− optical laser ablation in liquid.
Dispersants (with steric or ionic effects) and optimisation of parameters, such as
pH and Zeta potential, could be necessary to ensure stable solutions.

28. 1.00
1.05
1.10
1.15
1.20
1.25
1.30
0 20 40 60
lwater+SiO2/lwater
Temperature / °C
1% wt
5% wt
25% wt
50% wt
NANOFLUIDS PROPERTIES
Water-SiO2
0.5
1.0
1.5
2.0
2.5
3.0
0 20 40 60 80
mwater+TiO2/mwater
Temperature / °C
Constant shear rate: 550 (1/s)
1%
5%
25%
THERMAL CONDUCTIVITY RATIO
Water-SiO2
VISCOSITY RATIO
wt
wt
wt

29. WHAT ARE NANOFLUIDS
NANOPARTICLES
 more stable fluids
 no obstruction
 low wearing
 enhancements of thermal conductivity and heat transfer
coefficients
 improvements of tribological properties
MILLI/MICROMETRIC PARTICLES
 fast deposition
 channels obstruct
 high wearing

30. WHAT ARE NANOFLUIDS
Nanofluids are colloidal suspensions of nanoparticles in common fluids:
100 nm
SEM (Scanning Electron Microscope) images
CuO TiO2 SWCNH
water
BASE FLUIDS oil
ethylene glycol
refrigerants
oxides
NANOPARTICLES metals
carbon nanotubes

31. NANOFLUID STABILITY
 FeO3 in water (Colla et al.,2011)
• is a stable nanofluid with a mean particle diameter arown 67nm;
 SiO2 in water (Bobbo et al.,2011)
• the average of nanoparticles size depend of nanoparticles concentration
and the diametres were costant for more than 20days;
 SiC in ethylene glycol (Bobbo et al.,2012)
• is a stable nanofluid with costant values, around 100-120nm;
Manca immagine

32.  SiC in ethylene glycol (Bobbo et al., 2012b)
• 1%wt conductivity increases from 5% to 10%;
• 10%wt conductivity increases of 16% compared to the base fluid;
• 30%wt conductivity increases of 20% (in literature);
 Au in H20 (Colla et al., 2013a)
• 0.02% wt conductivity increases of 21% at 70 C respect the pure
water;
THERMAL CONDUCTIVITY

33.  SiC in ethylene glycol (Bobbo et al., 2012a)
• 1% wt Viscosity is similar to the base fluid;
• 5% wt Viscosity is greater of about 80%.
 ZnO in water (Bobbo et al., 2012b)
• 1% wt Viscosity is very similar to that of water;
• 5% wt Viscosity increase of about 5%;
• 10% wt Viscosity increase of about 12%.
DYNAMIC VISCOSITY

34. HEAT TRANSFER COEFFICIENT
 Heat transfer coefficient:
It is useful to understand nanofluids energy behaviour;
At ITC-CNR in Padova was built an apparatus for mesure this coefficient;
The measured fluids until now did non show significant increases in heat transfer
coefficient:
 ZnO 10%wt in water (Bobbo et al.,2012b)
• coefficient increase up only of 7% in the temperature range between
19 C and 41 C and Re=16000;
 Au 0.02% wt in water (Colla et al.,2013)
• coefficient increase up only of 5% in the temperature range between
19 C and 41 C.