Sergio Bobbo - CNR DI PADOVA - APPLICAZIONI DEI NANOFLUIDI

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 RicercheIstituto per le Tecnologie della Costruzione - sede di Padova

Corso Stati Uniti, 4, 35127 Padova, ItalyTelefono: +39.049.8295736 Fax: +39.049.8295728

e-mail: [email protected]

SUMMARY

• What are Nanofluids?

• Nanofluid Characterization at ITC-CNR• Stability• Thermal Conductivity• Dynamic Viscosity• Heat Transfer Coefficient

• HVAC&R Applications

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.

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Thermal conductivity of solids and liquids

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Carbon Metals Met.Liq.

Non Metallicliquids

WHAT ARE NANOFLUIDS

Nanofluids are colloidal suspensions of nanoparticles in common fluids:

waterBASE FLUIDS oil

ethylene glycolrefrigerants

oxidesNANOPARTICLES metals

carbon nanotubes

WHAT ARE NANOFLUIDSNanofluids 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

Heat Transfer Coefficient Measurem. (a)

Nanofluids preparation

Measurement- dimens. distrib.- Zeta potential

Thermal ConductivityMeasur. (l)

NANOFLUIDS LAB AT ITC-CNR

Viscosity Measur. (m)

CalculationDensity (r) Specific Heat (cp)

IENI-CNRCommercials

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).

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)

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Mea

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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

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%.

THERMAL CONDUCTIVITY

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l exp

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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

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)

DYNAMIC VISCOSITY

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shear rate (s-1)

water0.1%1%5%Refprop9.0

Dynamic viscosity data for water and ZnO-water nanofluids at 10°C

HEAT TRANSFER COEFFICIENTThe 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

INSULATIONHEATING ELECTRICAL RESISTANCES

HEAT FLUX

HEAT TRANSFER COEFFICIENTThe 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.

HEAT TRANSFER COEFFICIENTTin = 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

HVAC&R Applications

SECONDARY FLUIDScommercial 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

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


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%.


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


- power consumption reduced by about 25% with reference to POE oil

- COP increased by 33% with reference to POE oil


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)



Refrigerant: R134a (150 g)

Lubricant: PAG oil

0.2% of Al2O3 dispersed by magnetic stirring and ultrasonic homogenizer


- energy consumption reduced by about 10% with reference to pure oil


Refrigerants with TiO2 in mineral oil (Padmanabhan and Palanisamy, 2012)



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


- exergy efficiency with R134a, R436A and R436B and nanolubricant increases by 6%, 8% and 12%, respectively with reference to R134a and POE oil

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.

THANKS FOR YOUR ATTENTION


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water+SiO2 50%

Buongiorno et al. (2009)

water (experimental)

water (Lemmon et al., 2010)

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.


HOW TO PRODUCE NANOFLUIDSThe 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.

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NANOFLUIDS PROPERTIES

Water-SiO2

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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

WHAT ARE NANOFLUIDSNanofluids are colloidal suspensions of nanoparticles in common fluids:

100 nm

SEM (Scanning Electron Microscope) imagesCuO TiO2 SWCNH

waterBASE FLUIDS oil

ethylene glycolrefrigerants

oxidesNANOPARTICLES metals

carbon nanotubes

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

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;


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

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.

Sergio Bobbo - CNR DI PADOVA - APPLICAZIONI DEI NANOFLUIDI

Technology

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