Sergio Bobbo - CNR DI PADOVA - APPLICAZIONI DEI NANOFLUIDI
CSGLatest Technology in Refrigeration and Air ConditioningUnder the Auspices of the PRESIDENCY OF THE COUNCIL OF MINISTERSXV EUROPEAN CONFERENCE MILANO 7th-8th JUNE 2013THE POTENTIAL HVAC&RAPPLICATION OF NANOFLUIDSSergio BOBBO, Laura COLLA, Matteo SECURO, Laura FEDELEConsiglio Nazionale delle RicercheIstituto per le Tecnologie della Costruzione - sede di PadovaCorso Stati Uniti, 4, 35127 Padova, ItalyTelefono: +39.049.8295736 Fax: +39.049.8295728e-mail: firstname.lastname@example.org
SUMMARY• What are Nanofluids?• Nanofluid Characterization at ITC-CNR• Stability• Thermal Conductivity• Dynamic Viscosity• Heat Transfer Coefficient• HVAC&R Applications
WHAT ARE NANOFLUIDSSolids have thermalconductivity (l) orders ofmagnitude higher than liquidsDispersion of solid particles inliquids enhances the thermalconductivity of the base fluids.05001000150020002500NanotubiDiamanteGrafiteFullereni(film)ArgentoRameAlluminioNickelSilicioAllumina(Al2O3)Sodioa644KAcquaGlicoleetilenicoOliopermotoriConduttivitàtermicaaTambiente(Wm-1K-1)Thermal conductivity of solids and liquids0.6130.2530.145NonmetallicCarbon Metals Met.Liq.NonMetallicliquids
WHAT ARE NANOFLUIDSNanofluids are colloidal suspensions of nanoparticles in common fluids:waterBASE FLUIDS oilethylene glycolrefrigerantsoxidesNANOPARTICLES metalscarbon nanotubes
WHAT ARE NANOFLUIDSNanofluids promise to significantly enhance thermal, rheological andtribological properties of technological fluidsFACTORS INFLUENCING NANOFLUIDS PERFORMANCE:• Colloidal solutions Zeta potential and pH• Nanoparticles concentrationmaterial, shape and size• Dispersants type and concentration
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 STABILITYNanoparticle mean diameter in relation to thetime elapsed from the day of preparation inwater-based nanofluids containing TiO2 at 1wt%. ( ) static and (•) stirred samples at theDLS (Fedele et al., 2012)4550556065707580850 10 20 30 40Meandiameter(nm)Day from preparation Nanofluids stability:• Particle diameter should not changewith particle concentration;• No aggregation after 30 days;• No partial precipitation.Malvern Zetasizer Nano ZS, DynamicLight 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 thermaldiffusivity, knowing density and specific heat of the analysed materialaccuracy better then 5%.
THERMAL CONDUCTIVITY0.951.001.051.101.151.201.250 20 40 60 80lexp/lwaterT / °CAu 0.02%citrato 0.03%Au 0.05%citrato 0.07%Thermal conductivity enhancement of nanofluidwater+Au as a function of temperature
DYNAMIC VISCOSITYA 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 thefluid through the hydraulic circuits;• dependent on concentration;• size of particles can influence the viscosity (aggregation of nanoparticlesstrongly enhances viscosity)
DYNAMIC VISCOSITY0.001260.001280.001300.001320.001340.001360.001380.001400 200 400 600 800 1000 1200 1400m(Pas)shear rate (s-1)water0.1%1%5%Refprop9.0Dynamic viscosity data for water and ZnO-water nanofluids at 10°C
HEAT TRANSFER COEFFICIENTThe heat transfer coefficient is useful to understand nanofluids energy behaviourAt ITC-CNR in Padova, a hydraulic apparatus, based on constant heat flux, wasspecifically built for the single phase heat transfer coefficient measurement.gear pumpIsmatec MCP-ZCoriolis mass flowmeter EmersonProcesscoolingmachinePolysciencemeasurementsectionFLUIDCOPPERPIPEINSULATIONHEATING ELECTRICALRESISTANCESHEAT FLUX
HEAT TRANSFER COEFFICIENTThe measured fluids until now did not show significant heat transfer coefficientenhancement: 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 10000Tin = 41°C about 5% Re from 7000 to 16000
HVAC&R ApplicationsSECONDARY FLUIDScommercial refrigeration, chiller, solar panelsNANOREFRIGERANTSnanoparticles dispersion directly in the refrigerantNANOLUBRICANTSthey can improve thermal dissipation, anti-wear and extreme pressureproperties of compressors lubricants
Applications in vapourcompression systemsR134a with TiO2-mineral oil in a domestic refrigerator(Bi et al., Application of nanoparticles in domestic refrigerators, AppliedThermal Engineering, 28:1834, 2008)Domestic refrigeratorCapillary expansion device; reciprocating compressorRefrigerant: R134aLubricant: i) POE oil ii) mineral oil+nanoparticles0.1 wt% of TiO2 dispersed in MO by ultrasonic homogenizerExperimental results- R134a and MO+nanopartciles worked normally and efficiently- energy consumption reduced by 26.1% in comparison to R134a andPOE oil- the same tests with Al2O3 showed similar results
Applications in vapourcompression systemsR134a/R600/R290 with Al2O3-mineral oil(Jwo et al., Effects of nanolubricant on performance of hydrocarbonrefrigerant system, J. Vacuum Sci. Tech. B, 27:147, 2009)Domestic refrigerator (50 l capacity)Replacement of R134a with mixture butane/propane/R134aReplacement of POE oil with mineral oilMineral 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%.
Applications in vapourcompression systemsR134a with Al2O3 in mineral oil(Subramani and Prakash, Experimental studies on a vapour compressionsystem using nanorefrigerants, Int. J. Eng. Sci.Tech., 3(9): 95, 2011)Experimental refrigeration circuitThermostatic expansion valve; reciprocating compressorRefrigerant: R134aLubricant: i) POE oil ii) mineral oil iii) mineral oil+nanoparticles0.06 wt% of Al2O3 dispersed by ultrasonic homogenizerExperimental results- power consumption reduced by about 25% with reference to POE oil- COP increased by 33% with reference to POE oil
Applications in vapourcompression systemsR134a with Al2O3 in polyalkylene glycol (PAG) oil(Kumar and Elansezhian, Experimental Study on Al2O3-R134a NanoRefrigerant in Refrigeration System, Int. J. Mod. Eng. Res., 2(5):3927 (2012)2012)Experimental refrigeration circuitCapillary expansion device; reciprocating compressorRefrigerant: R134a (150 g)Lubricant: PAG oil0.2% of Al2O3 dispersed by magnetic stirring and ultrasonichomogenizerExperimental results- energy consumption reduced by about 10% with reference to pure oil
Applications in vapourcompression systemsRefrigerants with TiO2 in mineral oil (Padmanabhan and Palanisamy,2012)Experimental refrigeration circuitCapillary expansion device; reciprocating compressorRefrigerant: R134a, R436A (R290/R600a-56/44 wt%) and R436B(R290/R600a-52/48 wt%)Lubricant: i) POE oil ii) mineral oil+nanoparticles0.1 g/L of TiO2 dispersed in MO by ultrasonic homogenizerExperimental results- exergy efficiency with R134a, R436A and R436B and nanolubricantincreases by 6%, 8% and 12%, respectively with reference to R134aand POE oil
CONCLUSIONS• Nanofluids are colloidal suspensions of nanoparticles in common fluids thatpromise to significantly increase the energetic performance of thermal systemsand the tribological properties of lubricants.• They could be applied in HVAC&R systems, both as refrigerant or lubricant, andpresent 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 toselect and optimise nanofluids on the application requirements;• Future works will be devoted to study the effect of metal nanoparticles insuspension on the thermophysical properties of nanofluid and directly theinfluence of nanoparticles in working fluid of vapour compression cycle.
THERMAL CONDUCTIVITY0.550.600.650.700.750.800.850.900 20 40 60 80l(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)
R134a with TiO2-mineral oil in a refrigerating machine (Wang et al., 2003)Nanoparticles enhanced the solubility of R134a in mineral oil (MO) andimproved the performance by returning more lubricant oil back to thecompressor compared to R134a and POE oil.Applications in vapourcompression systems
HOW TO PRODUCE NANOFLUIDSThe first need is to obtain a stable and homogenous colloidal solutionsTWO-STEP METHOD• nanoparticles powder is put into thebase fluids, physically dispersed bystrong mechanical stirring (low orhigh energy ultrasounds, ball milling,high pressure homogenisation).• this technique is suitable for thedispersion of oxide nanoparticlesSINGLE-STEP METHODS• synthesis and dispersion of nanoparticlesinto the fluid take place simultaneously• Various techniques are available:− direct dispersion of nanoscale vapourfrom metallic source material into low-vapour-pressure fluids;− physical process set up by wet grindingtechnology with bead mills;− chemical reduction method forproducing metallic nanofluids;− optical laser ablation in liquid.Dispersants (with steric or ionic effects) and optimisation of parameters, such aspH and Zeta potential, could be necessary to ensure stable solutions.
WHAT ARE NANOFLUIDSNANOPARTICLES more stable fluids no obstruction low wearing enhancements of thermal conductivity and heat transfercoefficients improvements of tribological propertiesMILLI/MICROMETRIC PARTICLES fast deposition channels obstruct high wearing
WHAT ARE NANOFLUIDSNanofluids are colloidal suspensions of nanoparticles in common fluids:100 nmSEM (Scanning Electron Microscope) imagesCuO TiO2 SWCNHwaterBASE FLUIDS oilethylene glycolrefrigerantsoxidesNANOPARTICLES metalscarbon 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 concentrationand 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 purewater;THERMAL CONDUCTIVITY
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 transfercoefficient: ZnO 10%wt in water (Bobbo et al.,2012b)• coefficient increase up only of 7% in the temperature range between19 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 between19 C and 41 C.