research article flow boiling heat transfer enhancement by...

Research ArticleFlow Boiling Heat Transfer Enhancement byUsing ZnO-Water Nanofluids

Om Shankar Prajapati1 and Nirupam Rohatgi2

1 Department of Mechanical Engineering Rajasthan Technical University Kota Rajasthan 324010 India2Department of Mechanical Engineering Malaviya National Institute of Technology Jaipur Rajasthan 302017 India

Correspondence should be addressed to Om Shankar Prajapati omshankarprajapatigmailcom

Received 31 May 2013 Accepted 11 November 2013 Published 2 February 2014

Academic Editor Mohamed Awad

Copyright copy 2014 O S Prajapati and N Rohatgi This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

Nanofluids are liquid suspensions containing nanoparticles that are smaller than 100 nmThere is an increased interest in nanofluidsas thermal conductivity of nanofluids is significantly higher than that of the base liquids ZnO-water nanofluids with volumeconcentration of ZnO particles varying from 00001 to 01 were prepared using ultrasonic vibration mixer Thermal conductivityof the ZnO-water fluids was investigated for different sonication time using thermal property analyzer (KD2 Pro) Thermalconductivity of nanofluids for a given concentration of nanoparticle varies with sonication time Heat transfer coefficient andpressure drop in an annular test section with variable pressure (1ndash25 bar) and heat flux (0ndash400 kWm2) at constant mass fluxof 400 kgm2s were studied for samples having maximum thermal conductivity Surface roughness of the heating rod was alsomeasured before and after the experimentation The study shows that heat transfer coefficient increases beyond the base fluid withpressure and concentration of ZnO

1 Introduction

Heat transfer enhancement is an important method to saveenergy in different engineering processes Use of solid parti-cles in conventional fluids because of their higher thermalconductivity has been considered for decades to enhanceheat transfer However because of practical problems likefouling sedimentation and increase in pressure drop interestof the industry in this technique never really picked up Inrecent years significant advances in nanotechnology havemade it possible to overcome these problems by producingparticles in nanometer size ranges

A nanofluid is a fluid with a colloidal dispersion ofnanosized particles of another substance in water or otherbase fluids In a colloid two substances are distinguishablebut can interact through weak surface molecular forcesThe nanoparticles used in nanofluids commonly have anaverage size below 100 nm Relatively large surface area ofnanoparticles increases the stability of nanofluid and reduces

the problem of sedimentation of nanoparticles Heat transferincreased with increase in surface area of nanoparticlescompared to microparticles because of increased stability ofnanofluids A lot of research has been undergone for thelast twenty years in pool boiling of nanofluids You et al [1]reported that nanofluids have great potential for enhancingthe heat transfer coefficients and critical heat flux (CHF)They showed that nanofluids can improve the critical heatflux (CHF) by as much as 200 Kim [2] reported thatheat transfer coefficient for Alumina and Zinc-oxide basednanofluid in flow boiling did not statistically improve evenfor much higher mass fluxes at 1 bar He also reportedincreased CHF for Alumina and Zinc-oxide based nanofluidWhile nanofluids in pool boiling conditions are being studiedbroadly data for nanofluid flow boiling which is the situationof interest for the nuclear applications are very scarce

Nanofluids are gaining popularity among academicresearchers and receiving more attention from industry asthey continue to demonstrate improvements in heat transfer

Hindawi Publishing CorporationScience and Technology of Nuclear InstallationsVolume 2014 Article ID 890316 7 pageshttpdxdoiorg1011552014890316

2 Science and Technology of Nuclear Installations

properties of liquid cooling processes ldquoNanofluidsrdquo is theaccepted nomenclature for slurries containing nanoparticlessuspended in a base fluid Conventional heat transfer fluidsincluding oil water and ethylene glycol mixture are poorheat transfer fluids since the thermal conductivity of thesefluids plays an important role in the heat transfer coefficientbetween the heat transfer medium and the heat transfersurface Therefore numerous measures have been taken toimprove the thermal conductivity of these fluids by suspend-ing nanomicro-or larger-sized particle materials in liquids[3]

Nanoparticle suspensions in fluidsmake a new innovativecategory of fluids called nanofluids These kinds of fluids arenow of great interest not only for modifying heat transferperformance of fluids but also for improving other charac-teristics such as mass transfer and rheological properties offluids [4ndash7]

From a relatively limited amount of experimental data(see in particular [8ndash14]) it has been found that nanofluidsgenerally possess thermal conductivities well higher thanthose of the base fluids

Prajapati andRajvanshi [15]measured the effect ofAl2O3-

water nanofluid onheat transfer characteristics in convectionThey observed that heat transfer increases with additionof the Al

2O3nanoparticles in the base fluid because of

increased thermal conductivity of Al2O3nanofluid heat

transfer through increased solid-liquid interface layers heatconduction through nanoparticles and nanoparticle drivennatural convection

He et al [16] observed enhancement in the convectiveheat transfer coefficient in laminar as well as turbulent flowregimes and the enhancement increased with increase inparticle concentrationThe enhancement in the laminar flowregime was much smaller than that in the turbulent flowregime At Re = 1500 the maximum enhancement wasabout 12 for nanofluid having 11 of TiO

2by volume

whereas at Re = 5900 the maximum enhancement for thesame nanofluid that is 11 of TiO

2by volume exceeded by

40 Experiments were also conducted for nanofluid havingfixed volume of TiO

2but with different sizes of TiO

2

nanoparticles The average particle size had marginal effecton heat transfer

Duangthongsuk and Wongwises [17] presented exper-imental investigations on convective heat transfer perfor-mance and flow characteristic of a TiO

2-water nanofluid

for a horizontal double tube counterflow heat exchangerExperiments were carried out under turbulent flow con-ditions The results indicate that heat transfer coefficientincreases with increase in Reynolds number The convectiveheat transfer coefficient of the nanofluid was higher than thatof the base fluid (water) at any given Reynolds number Thenanofluid having 02 of TiO

2by volume had approximately

6ndash11 higher heat transfer coefficient than that of the purewater The convective heat transfer coefficient increased withincrease in Reynolds number and it increased with increasein mass flow rate of the heating fluid

Heris et al [18] observed that nanofluids can conduct heatone order of magnitude faster than scientists had predictedpossible Because of their considerable promise nanofluids

have become a rapidly emerging field where nanoscalescience and engineering meet

Bang et al [19] measured the effect of pressure on heattransfer coefficient Experimental data for only two pressures(2 and 16 bar) were compared At low vapor quality where theslug flow pattern seemed to be dominant the heat transfercoefficient was slightly higher at the higher pressure At highvapor quality where the flow pattern is annular flow the effectof pressure was not significant

Rana et al [20] performed experiments in subcooled flowboiling of ZnO-water nanofluids with different low particleconcentrations (le001 volume ) in horizontal annulus atheat fluxes from 100 to 450 kWm2 and flow rates from 01to 0175 lps at 1 bar inlet pressure and constant subcoolingof 20∘C to determine bubble behavior and heat transferwith flow rates of ZnO They observed that increase in heatflux leads to increase in bubble diameter the heat transfercoefficient increases with increase in heat flux and particlevolume fraction of ZnO

Moosavi et al [21] measured thermal conductivity vis-cosity and surface tension of ZnO nanofluids with ethy-lene glycol (EG) and glycerol (G) as the base fluids Theyobserved that the thermal conductivity of ZnOEG andZnOG nanofluids increased nonlinearly up to 105 and72 respectively as the volume fraction of nanoparticlesincreased up to 3 by volume The ratio of the viscosity ofthe nanofluid and the viscosity of the base fluid increasedwith increase in concentration and decrease in temperatureThe ratio of surface tension of the nanofluid and the surfacetension of the base fluid increasedwith increase in the volumefraction of the solid nanoparticles

Based on the following key properties ZnO nanomaterialis selected for experimentation

(1) corrosive resistant(2) the antibacterial behavior(3) good thermal conductivity(4) easy availability in purity ranges from 94 to 999(5) excellent size and shape capability(6) low costBy suspending nanophase particles in heating or cooling

fluids the heat transfer performance of the fluid can besignificantly improved The main reasons for this effect arelisted below

(1) The suspended nanoparticles increase the effectivethermal conductivity (Wm K) of the fluid Thermalconductivity of nanoparticles is in order of 1000+when mixed with fluids of low thermal conductivitythat is of the order of 001 to 1 the mixture obtainedhas higher thermal conductivity compared to the basefluid

(2) The interaction and collision among particles fluidand the flow passage surface are intensified

(3) The mixing fluctuation and turbulence of the fluidare intensified by Brownian motion due to increasedenergy level of electron at higher temperature

Science and Technology of Nuclear Installations 3

2 Experimental Setup

Preparation of nanofluid is the first key step towards usingnanophase particles to enhance the heat transfer performanceof conventional fluids The nanofluid does not simply referto a liquid-solid mixture of base fluid and nanoparticles Ananofluid has some special requirements such as uniformitystability low agglomeration of particles and no change inchemical and physical properties of the fluid In general thefollowing are the effective methods used for preparation ofsuspensions (1) changing the pH value of suspension (2)using surface activators andor dispersants and (3) usingultrasonic vibrations These methods can change the surfaceproperties of the suspended particles and can be used tosuppress the formation of particle clusters in order to obtainstable suspensions The use of these techniques depends onthe application for which the nanofluid is to be used

Toshcon make ultrasonic vibration mixer (UVM) of 27 plusmn3 kHz frequency and 1500W ultrasonic capacity was usedto prepare the nanofluids In UVM the ultrasonic energyis produced by converting electrical energy into mechanicalvibrations by using generator and piezoelectric transducersThe required weight of the nanoparticles was mixed withdistilledwater inUVMand vibrated for 3 to 4 hours Preparednanofluid was placed in the storage reservoir An immersedelectrical heater was provided in the storage reservoir toregulate the temperature of the nanofluid It also consists oftemperature control device The storage reservoir was madeof stainless steel

The closed fluid loop test facility (Figure 1) of 10-liter capacity consists of mainly an ultrasonic vibrationmixer storage reservoir circulating pump flowmeter heaterinserted horizontal annular test section condenser and heatexchanger The working fluid is pumped from the reservoirto the test section through flow meter that measures fluidflow rate The working fluid or the mixture of working fluidand steam from the exit of the test section passes througha horizontal condenser and counterflow heat exchangerbefore returning to the reservoir In boiling flow condensercondenses the steam into water and heat exchanger reducesthe excess temperature and controls the temperature ofworking fluid before recirculation The inlet temperatureof the working fluid at test section is maintained constantby using an electrical heater controlled by a temperaturecontroller in the reservoir tank The fluid loop was designedto work in range of variable parameters like heat supply inletpressure type of the fluid flow rate inlet temperature of thefluid and the degree of subcooling

Pressure drop in test section also measured for varyingconcentration of nanofluids with pressure sensors at inlet andoutlet The annular test section as shown in Figure 2 andphotograph in Figure 3 is 780mm long and consists of anelectrically heated rod and an outer borosilicate glass tubeof 218mm inner diameter The heater is 127mm diameterhollow stainless steel rod welded to solid copper rods at bothends The test section is easily dismountable The heater rodis fitted with transparent glass tube by two teflon corks atboth ends The test section was not insulated to facilitatethe visualization studies Adhesive was applied at the ends

Table 1 Experimental range

Serialnumber Parameter Range

1 Pressure (bar) 1ndash252 ZnO volume fraction () 00001ndash013 Heat flux (kWm2) 0ndash4004 Diameter of nanoparticles (nm) 30ndash50

Table 2 Results of uncertainty analysis

Serial number Parameter Uncertainty ()1 Temperature plusmn042 Pressure plusmn1583 Volumetric flow plusmn164 Heat flux plusmn114

of tubes over teflon corks and thermocouples to removeleakage problem at high heat flux In the glass tube the fluidflows over the surface of the heater rod The heated length of500mm is located 230mm downstream of the inlet plenumand thus allowing for the flow to fully develop An input 415V3-phase AC power is stepped down to 0ndash32V DC power byusing 64 kVA DC regulated power supply by which a largerange of heat fluxes are applied to the test section

Two pressure transducers are installed at both ends ofthe test section to measure the pressure drop along thetube Static pressure at the inlet and the outlet of the testsection are measured using Keller make pressure sensorswhich have a range of 1ndash10 bar with an accuracy of plusmn01The pressure drop in single-phase flow and two-phase flow ofnanofluids was measured Measured data including pressuresand temperatures are recorded by a data acquisition system(Omega OMB-DAQ-55) which is connected to a computer

Temperatures at the inlet and the outlet of the testsection and the heater surface were measured with J-typeungrounded thermocouples Temperatures at various loca-tions on the surface of the heater rod were measured usingfive miniature thermocouples which were embedded on itAll the thermocouples were connected to the data acquisitionsystem 4-wire turbine type flow meter (Electronet FL-204)with flow range of 002ndash03 lps was used for measuring themass flow rate Its time response was 100ms with accuracy ofplusmn1

A hollow pipe of stainless steel was fitted in the placeof test section to clean the experimental test fluid loop with1388 normal H

2SO4in distilled water before final cleaning by

distilled water at 90∘C and atmospheric pressure to removeoxides and other residues after every experimental set Theexperimented test section was used to measure surfaceroughness separately A new heater rod of test section wascleaned with very fine (grade P-220) sand paper to maintainsimilar surface characteristics of the test surface

The experimental boundary conditions and results ofuncertainty analysis for measured parameters are shown inTables 1 and 2 respectively The experimental uncertainty ofthe present work was determined by ASME guidelines on


Test section

Data acquisition

Reservoir with heater

Ultrasonic vibration mixer

Heat exchanger

Turbine type

flow meter

Pump

Thermocouples

Con

dens

er

Water in

Water out

Wat

er in

Wat

er o

ut

ToPoTi Pi

Figure 1 Experimental flow fluid loop

Glass tubeStainless steel hollow heater rodSolid copper rod

Inle

t

Out

let

780

218127

Indicates thermocouples

Sketch is not to scale All dimensions are in mm

50500

100 100 100 100 100

Figure 2 Annular test section

uncertainties in experimental measurements in multiphaseflow [22]

3 Experimental Procedure

The following procedure was adopted for conducting theexperiment

(1) According to the required concentration of nanofluidthe required weight of the nanoparticles was calcu-lated and this amount of nanoparticles was mixedwith distilled water

(2) ZnO-water nanofluid was prepared in ultrasonicvibration mixer machine for 3 to 4 hrs based onmaximum thermal conductivity

(3) Thermal conductivity of ZnO-water nanofluid wasmeasured with thermal property analyzer KD2-Pro

(4) The test section and heater surface were cleaned withdilute H

2SO4solution to remove oxides and fouling

residues

(5) The fluid loop was filled with working fluid distilledwater or ZnO-water nanofluid

(6) Degassing of distilled water or ZnO-water nanofluidwas done to remove dissolved and entrapped air fromthe fluid loop using degassing valve This process wasrepeated 2-3 times before each experiment until nobubbles were observed

(7) After degassing parameters like pressure heat fluxand inlet temperature were set according to experi-mental boundary conditions

(8) Heat flux was gradually increased upto 04MWm2


Figure 3 Photograph of test setup during experiment

(9) For each concentration of ZnO-water nanofluid andpressure temperature voltage and current weremea-sured

(10) For the next set the pressure and the volumefraction of nanofluids were changed and similarreadings were taken at each heat flux

(11) Surface roughness measured for bare heater rod andnanoparticles coated heater rod after a set of experi-ments for each volume fraction of nanofluids

4 Results

The heat transfer coefficient ℎ is calculated from knowledgeof Newtonrsquos law of cooling

ℎ =

119902

119879119904minus 119879119887

(1)

Here heat flux 11990210158401015840

calculated as joule power (119881 lowast 119868)divided by area and the surface temperature 119879

119904and the bulk

temperature 119879119887measured at the steady-state condition by

ensuring that temperatures of all the thermocouples havebecome steady The surface temperature 119879

119904was the average

of all the five imbedded thermocouplesExperimental data in Figure 4 shows heat transfer coef-

ficient of distilled water Results show that heat transferincreases with heat flux for all pressures due to increasedenergy gain by the water

Experimental data in Figures 5 6 7 and 8 shows heattransfer coefficient of 00001 ZnO-water nanofluid 0001ZnO-water nanofluid 001 ZnO-water nanofluid and01 ZnO-water nanofluid Results show that heat transferincreases with heat flux for all concentrations of ZnO-waternanofluids due to increased energy gain by the nanoparticleswhich is in similar trend with previous researches [20] Theincrease in heat transfer coefficient was significant at 01volume concentration of nanoparticles because at higherconcentration of nanoparticles (01) 120 increased ther-mal conductivity of ZnO-water nanofluid 1367 increasedsurface roughness of heater rod due to deposition of ZnO-water nanofluid the nanoparticles were deposited more onheater surface thereby increasing the surface area of heater

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Distilled water

1bar 15 bar2bar 25 bar

Heat flux (kWm2)

Poly (1 bar) Poly (15 bar)Poly (2 bar) Poly (25 bar)

Figure 4 Variation of heat transfer coefficient ℎ (kWm2K) ofdistilled water with heat flux at 400 kgm2s mass flow rate

0

10

20

30

40

50

60

0 100 200 300 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)

00001 ZnO-water

1 bar-water 1 bar15 bar 2 bar25 bar Poly (1 bar-water)Poly (1 bar) Poly (15 bar)Poly (2 bar) Poly (25 bar)

Figure 5 Variation of heat transfer coefficient ℎ (kWm2K) ofZnO-water nanofluid with heat flux at 00001 ZnO nanoparticlevolume fraction and 400 kgm2s mass flow rate

rod and thus increasing the heat transfer by convection alsodue to increased Brownian motion particle driven naturalconvection and increased conduction between nanoparti-cles

The heat transfer coefficient also increased with appliedpressure because at higher pressure effective cooling ofheater rod was observed possibly due to increased Brownianmotion particle driven natural convection and conductionbetween nanoparticles viamore force applied at same heatingarea

Figure 9 shows pressure drop Δ119875 (bar) in an annulartest section for different ZnO-water nanofluid with varyingconcentration of ZnO There was no significant pressuredrop observed at lower concentrations however at higher


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


0001 ZnO-water


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


001 ZnO-water


concentrations (0001 to 01) pressure drop was increaseddue to increased viscosity of nanofluids

Figure 10 shows that the surface roughness Ra (120583m) ofheater rod for ZnO-water nanofluid increases gradually withincrease in concentration of ZnO particles in the nanofluidbecause of deposition of nanoparticles on heating surfacearea

5 Conclusion

An experimental facility was developed to study heat transfercharacteristics of ZnO-water nanofluid The working fluid

0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


01 ZnO-water


0100

0105

0110

0115

0120

0125

0130

00000 00001 00010 00100 01000

Pres

sure

dro

p (b

ar)

ZnO-water nanofluids ()

Pressure drop with ZnO-water nanofluid

Figure 9 Pressure drop in an annular test section with ZnOnanoparticle volume fraction

0001020304050607080910

00000 00001 00010 00100 01000

Surface roughness of heater surface

Surfa

ce ro

ughn

ess (120583

m)


Figure 10 The surface roughness of heater rod of deposited ZnO-water nanoparticles with volume fraction


was electrically heated in horizontal annular test sectionAll the instruments in test setup were properly calibratedas per guidelines given by American Society of Mechan-ical Engineers Flow boiling heat transfer experiments insubcooled region were carried out to study heat transfercharacteristics of ZnO-water nanofluid The results of thepresent investigation are summarized as follows

(1) Heat transfer coefficient increases by 126 over waterwith applied pressure and particle volume fraction ofZnO-water nanofluid within the given range of heatflux adopted

(2) No significant pressure drop change relative towater only was observed with low concentrations ofnanofluid but 23 pressure drop increases with 01concentration of ZnO particles in the nanofluid

(3) The surface roughness of the heating surface increasesby 1367 with increase in concentration of ZnOparticles in the nanofluid over the water

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The guidance by Late Professor A K Rajvanshi and thefinancial help from the ldquoBoard of Research inNuclear Science(BRNS) Department of Atomic Energy Indiardquo (Sanction no20093695-BRNS3234) are gratefully acknowledged

References

[1] S M You J H Kim and K H Kim ldquoEffect of nanoparticles oncritical heat flux of water in pool boiling heat transferrdquo AppliedPhysics Letters vol 83 no 16 pp 3374ndash3376 2003

[2] S J Kim Subcooled flow boiling heat transfer and critical heatflux in water-based nanofluids at low pressure [PhD thesis]Nuclear Science and Engineering Department MassachusettsInstitute of Technology 2009

[3] S Kakac and A Pramuanjaroenkij ldquoReview of convective heattransfer enhancement with nanofluidsrdquo International Journal ofHeat and Mass Transfer vol 52 no 13-14 pp 3187ndash3196 2009

[4] X Ma F Su J Chen T Bai and Z Han ldquoEnhancementof bubble absorption process using a CNTs-ammonia binarynanofluidrdquo International Communications in Heat and MassTransfer vol 36 no 7 pp 657ndash660 2009

[5] O N Sara F Icer S Yapici and B Sahin ldquoEffect of suspendedCuOnanoparticles onmass transfer to a rotating disc electroderdquoExperimental Thermal and Fluid Science vol 35 no 3 pp 558ndash564 2011

[6] E Nagy T Feczko and B Koroknai ldquoEnhancement of oxygenmass transfer rate in the presence of nanosized particlesrdquoChemical Engineering Science vol 62 no 24 pp 7391ndash73982007

[7] P K Namburu D P Kulkarni D Misra and D K DasldquoViscosity of copper oxide nanoparticles dispersed in ethyleneglycol and water mixturerdquo Experimental Thermal and FluidScience vol 32 no 2 pp 397ndash402 2007

[8] H Masuda A Ebata K Teramae and N Hishinuma ldquoAlter-ation of thermal conductivity and viscosity of liquid by dispers-ing ultra-fine particles (dispersions of 120574 -Al

2O3 SiO2 and TiO

2

ultra-fine particles)rdquo Netsu Bussei vol 4 no 4 pp 227ndash2331993

[9] X Wang X Xu and S U S Choi ldquoThermal conductivity ofnanoparticle-fluid mixturerdquo Journal of Thermophysics and HeatTransfer vol 13 no 4 pp 474ndash480 1999

[10] C H Chon K D Kihm S P Lee and S U S Choi ldquoEmpiricalcorrelation finding the role of temperature and particle size fornanofluid (Al

2O3) thermal conductivity enhancementrdquoApplied

Physics Letters vol 87 no 15 Article ID 153107 pp 1ndash3 2005[11] S U S Choi Z G Zhang W Yu F E Lockwood and E

A Grulke ldquoAnomalous thermal conductivity enhancement innanotube suspensionsrdquo Applied Physics Letters vol 79 no 14pp 2252ndash2254 2001

[12] J A Eastman S U S Choi S Li W Yu and L J ThompsonldquoAnomalously increased effective thermal conductivities ofethylene glycol-based nanofluids containing copper nanoparti-clesrdquo Applied Physics Letters vol 78 no 6 pp 718ndash720 2001

[13] G Roy C T Nguyen D Doucet S Suiro and T Mare ldquoTem-perature dependent thermal conductivity evaluation of aluminabased nano-fluidsrdquo in Proceedings of the 13th InternationalSymposium on Hyphenated Techniques in Chromatography andSeparation Technology (IHTC rsquo06) p 12 Begell House SydneyAustralia August 2006

[14] H A Mintsa G Roy C T Nguyen and D Doucet ldquoNewtemperature dependent thermal conductivity data for water-based nanofluidsrdquo International Journal ofThermal Sciences vol48 no 2 pp 363ndash371 2009

[15] O S Prajapati and A K Rajvanshi ldquoAl2O3-water nanofluids in

convective heat transferrdquo Applied Mechanics and Materials vol110ndash116 pp 3667ndash3672 2012

[16] Y He Y Jin H Chen Y Ding D Cang and H Lu ldquoHeattransfer and flow behaviour of aqueous suspensions of TiO

2

nanoparticles (nanofluids) flowing upward through a verticalpiperdquo International Journal of Heat and Mass Transfer vol 50no 11-12 pp 2272ndash2281 2007

[17] W Duangthongsuk and S Wongwises ldquoHeat transfer enhance-ment and pressure drop characteristics of TiO

2-water nanofluid

in a double-tube counter flow heat exchangerrdquo InternationalJournal of Heat and Mass Transfer vol 52 no 7-8 pp 2059ndash2067 2009

[18] S Z Heris M N Esfahany and S G Etemad ldquoExperimen-tal investigation of convective heat transfer of Al

2O3water

nanofluid in circular tuberdquo International Journal of Heat andFluid Flow vol 28 no 2 pp 203ndash210 2007

[19] K H Bang K K Kim S K Lee and B W Lee ldquoPressureeffect on flow boiling heat transfer of water in minichannelsrdquoInternational Journal ofThermal Sciences vol 50 no 3 pp 280ndash286 2011

[20] K B Rana A K Rajvanshi and G D Agrawal ldquoA visualizationstudy of flow boiling heat transfer with nanofluidsrdquo Journal ofVisualization vol 16 pp 133ndash143 2013

[21] M Moosavi E K Goharshadi and A Youssefi ldquoFabricationcharacterization and measurement of some physicochemicalproperties of ZnOnanofluidsrdquo International Journal of Heat andFluid Flow vol 31 no 4 pp 599ndash605 2010

[22] R B Abernethy R P Benedict and R B Dowdell ldquoASMEmeasurement-uncertaintyrdquo Journal of Fluids Engineering vol107 no 2 pp 161ndash164 1983

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properties of liquid cooling processes ldquoNanofluidsrdquo is theaccepted nomenclature for slurries containing nanoparticlessuspended in a base fluid Conventional heat transfer fluidsincluding oil water and ethylene glycol mixture are poorheat transfer fluids since the thermal conductivity of thesefluids plays an important role in the heat transfer coefficientbetween the heat transfer medium and the heat transfersurface Therefore numerous measures have been taken toimprove the thermal conductivity of these fluids by suspend-ing nanomicro-or larger-sized particle materials in liquids[3]

Nanoparticle suspensions in fluidsmake a new innovativecategory of fluids called nanofluids These kinds of fluids arenow of great interest not only for modifying heat transferperformance of fluids but also for improving other charac-teristics such as mass transfer and rheological properties offluids [4ndash7]

From a relatively limited amount of experimental data(see in particular [8ndash14]) it has been found that nanofluidsgenerally possess thermal conductivities well higher thanthose of the base fluids

Prajapati andRajvanshi [15]measured the effect ofAl2O3-

water nanofluid onheat transfer characteristics in convectionThey observed that heat transfer increases with additionof the Al

2O3nanoparticles in the base fluid because of

increased thermal conductivity of Al2O3nanofluid heat

transfer through increased solid-liquid interface layers heatconduction through nanoparticles and nanoparticle drivennatural convection

He et al [16] observed enhancement in the convectiveheat transfer coefficient in laminar as well as turbulent flowregimes and the enhancement increased with increase inparticle concentrationThe enhancement in the laminar flowregime was much smaller than that in the turbulent flowregime At Re = 1500 the maximum enhancement wasabout 12 for nanofluid having 11 of TiO

2by volume

whereas at Re = 5900 the maximum enhancement for thesame nanofluid that is 11 of TiO

2by volume exceeded by

40 Experiments were also conducted for nanofluid havingfixed volume of TiO

2but with different sizes of TiO

2

nanoparticles The average particle size had marginal effecton heat transfer

Duangthongsuk and Wongwises [17] presented exper-imental investigations on convective heat transfer perfor-mance and flow characteristic of a TiO

2-water nanofluid

for a horizontal double tube counterflow heat exchangerExperiments were carried out under turbulent flow con-ditions The results indicate that heat transfer coefficientincreases with increase in Reynolds number The convectiveheat transfer coefficient of the nanofluid was higher than thatof the base fluid (water) at any given Reynolds number Thenanofluid having 02 of TiO

2by volume had approximately

6ndash11 higher heat transfer coefficient than that of the purewater The convective heat transfer coefficient increased withincrease in Reynolds number and it increased with increasein mass flow rate of the heating fluid

Heris et al [18] observed that nanofluids can conduct heatone order of magnitude faster than scientists had predictedpossible Because of their considerable promise nanofluids

have become a rapidly emerging field where nanoscalescience and engineering meet

Bang et al [19] measured the effect of pressure on heattransfer coefficient Experimental data for only two pressures(2 and 16 bar) were compared At low vapor quality where theslug flow pattern seemed to be dominant the heat transfercoefficient was slightly higher at the higher pressure At highvapor quality where the flow pattern is annular flow the effectof pressure was not significant

Rana et al [20] performed experiments in subcooled flowboiling of ZnO-water nanofluids with different low particleconcentrations (le001 volume ) in horizontal annulus atheat fluxes from 100 to 450 kWm2 and flow rates from 01to 0175 lps at 1 bar inlet pressure and constant subcoolingof 20∘C to determine bubble behavior and heat transferwith flow rates of ZnO They observed that increase in heatflux leads to increase in bubble diameter the heat transfercoefficient increases with increase in heat flux and particlevolume fraction of ZnO

Moosavi et al [21] measured thermal conductivity vis-cosity and surface tension of ZnO nanofluids with ethy-lene glycol (EG) and glycerol (G) as the base fluids Theyobserved that the thermal conductivity of ZnOEG andZnOG nanofluids increased nonlinearly up to 105 and72 respectively as the volume fraction of nanoparticlesincreased up to 3 by volume The ratio of the viscosity ofthe nanofluid and the viscosity of the base fluid increasedwith increase in concentration and decrease in temperatureThe ratio of surface tension of the nanofluid and the surfacetension of the base fluid increasedwith increase in the volumefraction of the solid nanoparticles

Based on the following key properties ZnO nanomaterialis selected for experimentation

(1) corrosive resistant(2) the antibacterial behavior(3) good thermal conductivity(4) easy availability in purity ranges from 94 to 999(5) excellent size and shape capability(6) low costBy suspending nanophase particles in heating or cooling

fluids the heat transfer performance of the fluid can besignificantly improved The main reasons for this effect arelisted below

(1) The suspended nanoparticles increase the effectivethermal conductivity (Wm K) of the fluid Thermalconductivity of nanoparticles is in order of 1000+when mixed with fluids of low thermal conductivitythat is of the order of 001 to 1 the mixture obtainedhas higher thermal conductivity compared to the basefluid

(2) The interaction and collision among particles fluidand the flow passage surface are intensified

(3) The mixing fluctuation and turbulence of the fluidare intensified by Brownian motion due to increasedenergy level of electron at higher temperature




















Test section

Data acquisition



Heat exchanger

Turbine type

flow meter

Pump

Thermocouples

Con

dens

er

Water in

Water out

Wat

er in

Wat

er o

ut

ToPoTi Pi



Inle

t

Out

let

780

218127



50500

100 100 100 100 100










residues










4 Results


ℎ =

119902

119879119904minus 119879119887

(1)

Here heat flux 11990210158401015840


119904and the bulk







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Distilled water


Heat flux (kWm2)



0

10

20

30

40

50

60

0 100 200 300 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)

00001 ZnO-water







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


0001 ZnO-water


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


001 ZnO-water




5 Conclusion


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


01 ZnO-water


0100

0105

0110

0115

0120

0125

0130

00000 00001 00010 00100 01000

Pres

sure

dro

p (b

ar)




0001020304050607080910

00000 00001 00010 00100 01000


Surfa

ce ro

ughn

ess (120583

m)










Acknowledgments


References









2O3 SiO2 and TiO

2













2



2-water nanofluid



2O3water










FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of




































Test section

Data acquisition



Heat exchanger

Turbine type

flow meter

Pump

Thermocouples

Con

dens

er

Water in

Water out

Wat

er in

Wat

er o

ut

ToPoTi Pi



Inle

t

Out

let

780

218127



50500

100 100 100 100 100










residues










4 Results


ℎ =

119902

119879119904minus 119879119887

(1)

Here heat flux 11990210158401015840


119904and the bulk







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Distilled water


Heat flux (kWm2)



0

10

20

30

40

50

60

0 100 200 300 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)

00001 ZnO-water







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


0001 ZnO-water


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


001 ZnO-water




5 Conclusion


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


01 ZnO-water


0100

0105

0110

0115

0120

0125

0130

00000 00001 00010 00100 01000

Pres

sure

dro

p (b

ar)




0001020304050607080910

00000 00001 00010 00100 01000


Surfa

ce ro

ughn

ess (120583

m)










Acknowledgments


References









2O3 SiO2 and TiO

2













2



2-water nanofluid



2O3water










FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of






















4 Results


ℎ =

119902

119879119904minus 119879119887

(1)

Here heat flux 11990210158401015840


119904and the bulk







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Distilled water


Heat flux (kWm2)



0

10

20

30

40

50

60

0 100 200 300 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)

00001 ZnO-water







0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


0001 ZnO-water


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


001 ZnO-water




5 Conclusion


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


01 ZnO-water


0100

0105

0110

0115

0120

0125

0130

00000 00001 00010 00100 01000

Pres

sure

dro

p (b

ar)




0001020304050607080910

00000 00001 00010 00100 01000


Surfa

ce ro

ughn

ess (120583

m)










Acknowledgments


References









2O3 SiO2 and TiO

2













2



2-water nanofluid



2O3water










FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of


















0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


0001 ZnO-water


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


001 ZnO-water




5 Conclusion


0

10

20

30

40

50

60

0 50 100 150 200 250 300 350 400

Hea

t tra

nsfe

r coe

ffici

ent

Heat flux (kWm2)


01 ZnO-water


0100

0105

0110

0115

0120

0125

0130

00000 00001 00010 00100 01000

Pres

sure

dro

p (b

ar)




0001020304050607080910

00000 00001 00010 00100 01000


Surfa

ce ro

ughn

ess (120583

m)










Acknowledgments


References









2O3 SiO2 and TiO

2













2



2-water nanofluid



2O3water










FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of
























Acknowledgments


References









2O3 SiO2 and TiO

2













2



2-water nanofluid



2O3water










FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of





















FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















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