Paper presented at the 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 30 June - 2 July, 2008.Recently, a new class of fluid made up of metal nano-particles in suspension in a liquid, called nanofluid, appeared. Some numerical studies have shown that these new fluids have a higher heat transfer performance, compared with the conventional liquids. In the present study, we have attempted to study, by experimentation, the thermal performances of a particular nanofluid composed of aluminum oxide (γAl2O3) particles dispersed in ethylene glycol 30% for various concentrations ranging from 0 to 2 %. The experimental set up is a coaxial exchanger, which is destined to solar application, in which the heating liquid used is the nanofluid studied.vk201

Luciu, Razvan

Mare, Thierry

Sow, Ousmane

Van Vaerenbergh, Stephan

UPSpace at the University of Pretoria

HEFAT2008 6th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics Pretoria, South Africa Paper number: MT1  EXPERIMENTAL STUDY OF HEAT TRANSFER IN A DOUBLE PIPE EXCHANGER  USING NANOFLUIDS: SOLAR APPLICATION   Thierry Maré a*, Razvan Luciu b, Ousmane Sow c, Stephan van Vaerenberghd a* LGCGM, INSA de Rennes, IUT Saint Malo, 35043 Rennes, France  b LGCGM, INSA de Rennes , facultad Iasi Rounamia c Laboratoire d’Energie Appliquée, Ecole supérieure Polytechnique, Dakar, Sénégal d laboratory micogarvity Bruxelle Belgium   ABSTRACT Recently, a new class of fluid made up of metal nano-particles in suspension in a liquid, called nanofluid, appeared.  Some numerical studies have shown that these new fluids have a higher heat transfer performance, compared with the conventional liquids.  In the present study, we have attempted to study, by experimentation, the thermal performances of a particular nanofluid composed of aluminum oxide (γAl2O3) particles dispersed in ethylene glycol 30% for various concentrations ranging from 0 to 2 %. The experimental set up is a coaxial exchanger, which is destined to solar application, in which the heating liquid used is the nanofluid studied.  NOMENCLATURE  D Tube diameter [ m] k Conductivity [W/m k]  K        Conductance [W/K] Nu Nusselt number Pr        Prandtl number Re       Reynolds number  S         annular Section [m2] P         Perimeter [m]   Dh       Hydraulic diameter [m] c         Specific capacity  [J/kg K] h         Convection heat transfer coefficient  [W/m2 K] ρ         Density [kg/m3] Ф        Heat flux [W] vφ       Volumetric Concentration [%] µ         Dynamic viscosity [kg/ms] V Velocity [m/s]  indices f           cool fluid (water in annulus) o          basic fluid b          bulk n          nanofluid EG      Ethylene Glycol m         nano particle  INTRODUCTION Nanofluids, a two-phase mixtures composed of very fine particles in suspension in a continuous and saturated liquids (water, ethylene glycol, engine oil), may constitute a very interesting alternative for advanced thermal applications (Lee and Choi [1]; Chein and Huang [2]. It has been found that important heat transfer enhancement may be achieved while using nanofluids compared to the use of conventional fluids; furthermore, some oxide nanoparticles exhibit an excellent dispersion properties in traditional cooling liquids. In spite of their remarkable features, only few published results on nanofluids use in confined flow situations have been reported – see Daungthongsuk and Wongwises [3] for a partial review. Pak and Cho [4] and Li and Xuan [5] have provided the first empirical correlation for computing Nusselt numbers in laminar and turbulent tube flows using water-based nanofluids. Others considered the use of nanofluids in microchannel heat sinks (Chein and Huang,[2]). Recent author’s works  Maïga [6], Nguyen [7], Palm [8] and Roy [9] - have clearly confirmed the heat transfer enhancement due to nanofluids in tube flow and in radial flow between heated disks.  Research efforts were mostly concerned with the characterization of nanofluids thermal and physical properties, among which, a good proportion of works was of experimental nature and focused on the determination of effective thermal conductivities In this work, we have experimentally measured the heat performance of ethylene glycol-based nanofluids, Al2O3 with 47nm particle-sizes, and this in heat exchanger to solar application condition. Indeed, to reduce the fossil energy utilization and to save energy, the passive solar application is in constant progress in the world.  The countries of the North develop this technology     principally for sanitary warm water production ADEME [10], and the countries of the South use it for news technique of production of fresh water, Sow [11]. The problem of the countries of the North is to perform the incidental solar energy, either by an improvement of the solar collectors, or by the increase of the exchange surface, or by the optimization of the inclination and the orientation. The countries of the South are interested in the energy autonomy; it is to be told to decrease the consummation of energy of the pumps of circulation of fluid. Whatever the objective (decrease the surface of exchange or the circulation pump flow), the solution can be brought by the thermal improvement of the performances of the coolant. The idea of our study is to change the usual ethylene glycol by ethylene glycol - Al2O3 nanofluid.  In the present work, the thermal performances, Nusselt number and convection heat transfer are obtained for different volume concentration. The nanofluid is introduced in the inner tube of a coaxial heat exchanger for co and counter current configuration. EXPERIMENTAL SET UP  The schematic representation of the system studied is presented figure 1. The interior diameter of the inside tube is D4 = 6 mm, The exterior diameter is D3 = 8 mm. The second tube has an inner diameter D2 = 16 mm, 2 mm thick (D1 = 18 mm). The heat exchanger is being a length of 680 mm.   Figure 1 Schematic representation   This exchanger is cover of an insulated sheath 4 cm thick with conductivity performance k =0.004 W/mK. These are U-Tubes and in inox made. (Picture 1).  The temperatures of the two fluids circulating respectively in the tube and in the annular space are controlled by Platinum type sunder, measuring 0.1 °C, placed at the entrances and exits.  The entrance of the tube and of the annular space (between the internal and external tube) are each linked to a thermal reservoir with a constant level.  The mass flow of the fluid entering into the tube as well as into the annular space is controlled by a miniature flow meter. These mass flows are measured at the exit with the aid of a graduated vase with an absolute uncertainty of 1 ml/s.  The average of heat transfer surface is 0,015 m².      Picture 1 Experimental set up   Water pump is used for fluid circulation inside and outside the inner tube with a maximum mass flow of 48 l/h. Two configurations (co and counter current) are possible.  To place our exchanger in a solar collector application, we put a cooling water fluid in the channel with temperature of 15 °C at the entrance and a constant mass flow of 30 l/h.  The heater fluid, inside the inner tube, is use to going from a solar collector; at temperature 16°c to 80°c.The flow is constant and around 30 l/h. The fluid used in the inner tube is composed of ethylene glycol 30% and water 70%, with nanoparticle concentration varying from 0% to 2%.  THERMAL PROPERTIES OF NANOFLUID  The nanoparticles used are aluminium oxide (γAl2O3) particles having the following characteristic:  density ρm = 3880 kg/m3, specific heat cm = 773 J/kgK and thermal conductivity km= 36 W/mK; mean particle diameter is 47nm.  The following formula has been employed to relate the Ethylene Glycol pure data.    %30%30 7,03,0 EGEGpureEG ρρρ +=%30%30 7,03,0 EGEGpureEG ccc += %30%30 7,03,0 EGEGpureEG μμμ +=  %30%30 7,03,0 EGEGpureEG kkk += Density: We will assume that the density and heat capacity of the aluminium oxide nanoparticles is constant over the entire range of temperature considered; however for ethylene glycol 30%, we will take into account its density variation with respect to the temperature. The following relation has been used to compute the nanofluid density and heat capacity:    mvvn ρφρφρ +−= 0)1(       mvvn ccc φφ +−= 0)1(   Figure 2 shows the variation of the density of the nanofluid considered as function of the temperature as well as of the particle volume concentration.   950980101010401070110011301160273 293 313 333 353T  [K ]ρ [kg/m³]water ethylene glycol 30% 1% 1,50% 2%  Fig. 2. Variation of nanofluid density with temperature      Figure 3 shows the variation of heat capacity of the nanofluid considered as function of the temperature as well as of the particle volume concentration.                                   350036003700380039004000410042004300273 283 293 303 313 323 333 343 353T [K]c [J/kg K]water ethylene glycol 30% 2% 1,50% 1%  Fig. 3. Variation of nanofluid heat capacity with temperature  Dynamic viscosity: The viscosity of the nanofluid can be estimated with the existing relations for the two phase mixture. Drew and Passman introduced Einstein’s formula for evaluating the effective viscosity. Fluid is containing a dilute suspension of small rigid spherical particles.  )5,21(0 vn φμμ −=    This formula is restricted for low volumetric concentration of particle, under 0.05%. Brinkman proposed to extend Einstein’s formula by:  5,20 )1( vn φμμ −=   Other relations of effective viscosity of two phase mixture exist in the literature. Each relation has it own limitation and application. Some complex reaction has been observed by N Guyen [12]. Unfortunately results reveal that Brinkman’s formula underestimates the few experimental data present in literature.  We have some experimental results in literature for viscosity of nanofluid with pure ethylene glycol. But it’s seems there are no data for nanofluid with ethylene glycol 30%. Finally we choose the polynomial approximation based on experimental data Nguyen [13], for pure ethylene glycol- γ Al2O3 nanofluid.  02 )119,0306( μφφμ +−= vvn   We replace µ0 by µEG30%    Figure 4 shows the variation of viscosity of the nanofluid considered as function of the temperature as well as of the particle volume concentration  0,0000,0020,0040,0060,0080,0100,0120,014273 283 293 303 313 323 333 343 353T  [K ]µ [kg/ms]water ethylene glycol 30% 1% 1,50% 2%  Fig. 4. Variation of nanofluid viscosity with temperate           Conductivity : Lots of experimental researches have measured the thermal nanofluid conductivity and its evolution with temperature, but all data results are for the same nanofluid. It’s because lots of parameters influence this thermal conductivity (concentration, shape and size of particles, dispersant, active or not mixed, agglomeration etc.). We adopted the Hamilton and Crosser [14] formula.   )(2)(2200000 mvmmvmnkkkkkkkkkk−−+−−+= φφ  Figure 5 shows the variation of conductivity of the nanofluid considered as function of the temperature as well as of the particle volume concentration.     0,350,400,450,500,550,60273 283 293 303 313 323 333 343 353T  [K ]k [W/m K]water ethylene glycol 30%1% 1.5 %2%     Fig. 5. Variation of nanofluid conductivity with temperature                   Nusselt number and Heat flux  In the channel  Knowing temperature in and out, we can calculate the bulk temperature Tb  212 TTTbf+=   In our case we are in a short tube  PrRe1.0<hDL   The Nusselt number for laminar flow in tube is done by Sider and Tates equation:  33.0)/Pr(Re86.1 LDNu h=    With Reynolds Number  μρ hVD=Re   With hydraulic diameter  424 DDPSDh −==   And Prandlt Number  ffkc μ=Pr   And heat convection coefficient number for water hf:  hff DkNuh =  In the inner Tube It is possible to determine the heat flow absorbed by the nanofluid  by making the following relation:   In the channel           2nfmoyΦ+Φ=Φ  With  )( 12 TTcm fff −=Φ  and      )( 43 TTcm nnn −=Φ                               The heat lost through the walls; is obtained by calibration using water data for various flow rates and is around 5%. Knowing the thermal power absorbed by the nanofluid   and the bulk temperature in the inner and channel tube.  243 TTTbn+=    We can determinate the convection coefficient number for nanofluid hn:  244424 12)ln(1DDhkDDDKLDhfinoxn−−= π  With  bfbnmoyTTK −=φ Nusselt number is:  nnkDhnNu 4=   RESULTS  Table 1 shows the average of nanofluid Nusselt number obtained as function of the particle volume concentration, for co current and counter current.  Volumetric concentration Co-current Counter-current 0% 3,78 3,85 1% 3,59 3,78 1,5% 3,58 3,61 2% 3,59 3,55  Table 1.  Average nanofluid Nusselt number in the inner tube  We can show that Nusselt average number is close to 3,66, the value for laminar flow fully developed in isothermal tube. This  value is constant independently of concentration.      That would be interesting is to know how temperature distribution is and develop length of flow.  Figure 6 shows the variation of convection heat transfer coefficient of the nanofluid considered as function of the temperature as well as of the particle volume concentration, for co current and counter current  C o‐current3003103203303403500 500 1000R e hnE G 30% 2% 1.5% 1%C ounter‐current3003103203303403500 500 1000 1500R e hnE G30% 2%1.5% 1%  Fig. 6. Variation of convection heat transfer coefficient of nanofluid with Reynolds number   For a laminar flow, Nusselt number is independent of the Reynolds number, so the evolution of convection heat transfer coefficient is essentially due to the evolution of conductivity with temperature.  Convection increase with volume concentration, but difference is not significant between Co and counter current.  Figure 7 shows the variation of convective coefficient of the nanofluid considered as function as volume concentration, for co current and counter current  It is clearly observed, from figure 7, that for a given Reynolds number, the convective heat transfer coefficient has increased considerably with the particle volume concentration. On the other hand, for a same particle concentration, the fact of increasing the flow rate has also a great beneficial effect on the convective coefficient.  C o‐current2702903103303500,0 0,5 1,0 1,5 2,0% hnre100re300re500re800re1000C ounter‐current2702903103303500,0 0,5 1,0 1,5 2,0% hnre100re300re500re800re1000  Fig. 7. Variation of convection heat transfer coefficient of nanofluid with volumetric concentration   Conclusions  An experimental study was carried out in order to investigate the heat transfer enhancement as provided by replacement of conventional fluid, water by a nanofluid with ethylene glycol inside a double pipe exchanger destined for solar application. The nanofluid used, which composed of aluminium oxide particles in suspension in ethylene glycol 30% solution, has been provided at various volume concentration ranging from 0% to 2%. Experimental data have clearly shown that the use of such a nanofluid has provided a significant enhancement of heat transfer. The heat transfer coefficient has been found to increase with augmentation of volume concentration as well with augmentation of flow rate. New measured data where also provided regarding the temperature dependence of the nanofluid viscosity and this for various particle concentrations.     Aknowledge : AUF support      REFERENCE  [1] LEE S, CHOI S.U.S, LI S and EASTMAN J.A, Measuring thermal conductivity of nanofluids containing oxide nanoparticuls, J of heat transfer, vol 121, pp 280-289, 1999 [2] R. CHEIN, G. HUANG , Analysis of microchannel heat sink performance using nanofluids, Applied Thermal Engineering, Volume 25, Issues 17-18, December 2005, Pages 3104-3114 [3] DAUNGTHONGSUK S; WONGWISES , a critical review of convective heat transfer of nanofluids Renewable and Sustainable energy review pp 1-23,2005 [4] PAK, B. C. et CHO, Y. I., Hydrodynamic and Heat Transfer Study of Dispersed Fluids with Submicron Metallic Oxide Particles, Experimental Heat Transfer, Vol. 11, No. 2, pp. 151-170, 1998. [5] LI Q, XUAN Y, Conductive heat transfer performance of fluids with nano-particles, Proc of twelfth International Heat Transfer, pp 483-488, Heat transfer 2002   [6] MAIGA, S.E. B., PALM, S.J., CONG, T., N., ROY, G., et GALANIS, N., Heat transfer enhancement by using nanofluids in forced convection flows, Int. J. Heat Fluid Flow, Vol. 26, pp. 530- 546 (2005). [7] NGUYEN C. T., G. ROY, P.R. LAJOIE, Refroidissement des microprocesseurs  à haute performance en utilisant des nano fluides, Congrès Français de Thermique, SFT 2005, Reims, 30 mai-2 juin 2005                                [8] PALM, S.J., ROY, G., et NGUYEN C. T., Heat transfer enhancement with the use of nanofluids in radial flow cooling  systems considering temperature- dependant properties, Applied Thermal Engineering, 26 pp. 2209- 2218 (2006). [9] ROY, G.., NGUYEN, C.T., DOUCET, D., SUIRO, S., et MARE, T. Temperature dependant thermal conductivity evaluation of alumina based nanofluids, Proc. 13th IHTC, 13- 18 august, Sydney, Australia (2006). [10] ADEME french website  [11] O SOW, T MARE, J. MIRIEL, M. ADJ, C. TAYA Optimization of the number of effects in the desalination plants for multiple effects ISJAEE  march 2008 accepted [12] C.T. NGUYEN, F. DESGRANGES, N. GALANIS, G. ROY, T. MARÉ, S. BOUCHER, H. A. MINTSA, Viscosity data for Al2O3–water nanofluid—hysteresis: is heat transfer enhancement using nanofluids reliable?, International Journal of Thermal Sciences 47 (2008) 103–111. [13] C.T. NGUYEN, F. DESGRANGES, G. ROY, N. GALANIS, T. MARE, S. BOUCHER, H.A. MINTSA « Données de viscosité yAl2O3-Eau, phénomène d’hystérésis », Colloque Interuniversitaire Franco-québécois Montréal (Canada) Mai 2007  [14] HAMILTON, R.L et CROSSER, O.K., Thermal conductivity of heterogeneous two-component systems, I&EC Fundamentals, Vol. 1, pp. 182-191, 1962.                                

Experimental study of heat transfer in a double pipe exchanger using nanofluids: solar application

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Experimental study of heat transfer in a double pipe exchanger using nanofluids: solar application

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