EXPERIMENTAL STUDY ON HEAT TRANSFER COEFFICIENT AND FRICTION FACTOR OF Al 2 O 3 NANOFLUID IN A PACKED BED COLUMN

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1 Journal o Mechanical Engineering and Sciences (JMES) ISSN (rint): ; e-issn: ; Volume 1, pp. 1-15, December 2011 Universiti Malaysia ahang, ekan, ahang, Malaysia DOI: EXERIMENTAL STUDY ON HEAT TRANSFER COEFFICIENT AND FRICTION FACTOR OF Al 2 O 3 NANOFLUID IN A ACKED BED COLUMN G. Srinivasa Rao 1, K.V. Sharma 2*, S.. Chary 3, R.A. Bakar 2, M. M. Rahman 2, K. Kadirgama 2 and M.M. Noor 4 1 Department o Mechanical Engineering Kakatiya Institute o Technology and Science Warangal, Andhra radesh, India, 2 Faculty o Mechanical Engineering, Universiti Malaysia ahang, ekan, ahang, Malaysia * kvsharma@gmail.com 3 Andhra University, Visakhapatnam , India 4 Department o Mechanical and Mechatronic Engineering, University o Southern Queensland, Australia ABSTRACT The orced convection heat transer coeicient and riction actor are determined or the low o water and nanoluid in a vertical packed bed column. The analysis is undertaken in the laminar and transition Reynolds number range. The column is illed with spherical glass beads as the bed material. The heat transer coeicients with Al 2 O 3 nanoluid increased by 12% to 15% with the increase o volume concentration rom 0.02% to 0.5% compared with water. The experimental values o axial temperature are in good agreement with the NTU-ε method proposed by Schumann s model. Keywords: acked bed; Al 2 O 3 nanoluid; convective heat transer; riction actor; heat transer enhancement. INTRODUCTION The process o orced convection is employed in various installations, such as boilers, solar collectors, heat exchangers, and electronic devices. However, the low thermal conductivity o heat transer luids, such as water, oil, and ethylene glycol mixture limits seriously improvement o their perormance. To overcome this, there is need to develop advanced heat transer luids with signiicantly higher conductivity. An innovative means o improving the thermal conductivities o luids is to suspend nanosized solid particles in the luid. Tuckerman and ease (1982) conducted experiments or laminar low in a channel. The heat transer coeicient estimated is inversely proportional to the width o the channel, because the limiting Nusselt number is constant. Mahalingam (1985) conirmed the superiority o micro-channel cooling on a silicon substrate with a surace area o 5 5 cm using water and air as coolants. Many studies have been directed towards the evaluation o heat transer coeicients or luid low in micro-channels. orous structures are also used or heat transer augmentation as these augment the mixing o the lowing luid and improve the convection heat transer. Hence, studies are undertaken due to its broad applications. Early works have considered the eects o various parameters through experimental and statistical methods and have developed a 1

2 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column set o equations based on theoretical models or packed beds in tubular low (Sadri, 1952). Jeigarnik, Ivanov and Ikranikov (1991) investigated experimentally the convection heat transer o water on lat plates and in channels packed with sintered spherical particles, nets, porous metal, and elt. The majority o the experiments is or the evaluation o heat transer coeicients with dierent thickness (0.86 to 3.9 mm) and particle diameters (0.1 to 0.6 mm). They ound that the porous media increased the heat transer coeicient by 5 10 times; however, the increase in hydraulic resistance is even more. Experiments to study the percolation behavior o luids through a packed bed were undertaken by Yagi, Kunii and Endo (1964), Gunn, Ahmad and Sabri (1987), and Lamine, Colli Serrano and Wild (1992a). Analyses o heat transer coeicients by Weekman and Myers (1995), Silveira (1991), and Lamine, Colli Serrano and Wild (1992b) on gas-liquid low, however, presented limited results. Adeyanju (2009) experimentally determined the velocity variations within a porous medium or packed beds. He concluded that the pressure drop across the porous medium was due to various actors, which included orm drag, viscous drag rom the bounding wall, and inertia orce. The results rom this study conirmed that the pressure drop is a linear and quadratic unction o low velocity at low and high Reynolds number, respectively. You, Moon, Jang, Kim and Koo (2010) analyzed the thermal characteristics o an N 2 O catalytic igniter as a hybrid system or small satellites. The authors analyzed the problem theoretically, in order to determine the thermal perormance o the catalytic igniter results on porosity, pumping capacity, and the ratio o length to diameter. Using six hydrodynamic models, Carlos, Araiza and Lopez-Isunzay (2008) predicted a generalized equation or radial velocity distribution in a packed bed with a low tube-toparticle diameter ratio. Their calculations show that the use o an eective viscosity parameter to predict experimental data could be avoided i the magnitude o the two parameters in Ergun s equation, related to viscous and inertial energy losses, are reestimated rom velocity measurements or the packed beds. Maxwell (1904) showed the potential or increasing the thermal conductivity o a solution by mixing it with solid particles. Fluids containing small quantities o nanosized particles are called nanoluids. The particles, which are less than 100 nm in size, are dispersed uniormly within a liquid. The dispersion o nanoparticles in normal luids enhances heat transer, even when added in small quantities. The nanoluids show great potential or increasing heat transer rates in a variety o cases. Lee, Choi, Li and Eastman (1999) demonstrated that CuO or Al 2 O 3 nanoparticles in water and ethylene glycol exhibit enhanced thermal conductivity. The thermal conductivity increased by 20% at 4.0% concentration, when 35-nm-sized CuO nanoparticles were mixed in ethylene glycol. Mansour, Galanis and Nguyen (2007) used Al 2 O 3 particles with a mean diameter o 13 nm at volume concentration o 4.3%, and reported an increase in thermal conductivity by 30%. Xuan and Roetzel (2000) presented a relation or the evaluation o the orced convection heat transer coeicient or low in tubes with Cu nanoluid. Various concepts have been proposed to explain the reasons or the enhancement o heat transer. Xuan, Li and Hu (2004) have identiied two causes or the improvement o heat transer with nanoluids: the increased dispersion due to the chaotic motion o nanoparticles that accelerates energy exchange within the luid, and the enhanced conductivity o nanoluids considered by Choi (1995). Thermal conductivity o Al 2 O 3 nanoluid has been evaluated by Das, utra, Thiesen and Roetzel (2003) within the temperature range o C. They observed a two to our-old enhancement o thermal conductivity within the range o concentration tested. Wen and 2

3 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 Ding (2004) evaluated the heat transer o nanoluid in the laminar region through experiment. They used equations available in the literature to determine viscosity at bulk temperature. Maiga, alm, Nguyen, Roy and Galanis (2005) investigated water- Al 2 O 3 and Ethylene-glycol-Al 2 O 3 nanoluids and observed the adverse eects o wall shear when tested with the latter. The heat transer enhancement o nanoluids can be expected owing to intensiication o turbulence, suppression o the boundary layer as well as the dispersion or back mixing o the suspended particles, a large enhancement in the surace area o nanoparticles, and a signiicant increase in the thermo-physical properties o the luid. Thereore, the convective heat transer coeicient with nanoluids is a unction o the physical properties o the constituents, dimension and volume raction o the suspended nanoparticles, and low velocity. Sarma, Subramanyam, Kishore, Dharma Rao and Kakac (2003) and Sharma, Suryanarayana, Sarma, Rahman, Noor and Kadirgama (2010) developed a theoretical model or the estimation o the heat transer coeicient under laminar low in a tube with twisted tape inserts. Syam Sundar, Sharma and Ramanathan (2007) investigated heat transer enhancement or nanoluid low in a circular tube with twisted tape inserts. The impact o operating parameters on heat transer o nanoluid low in a packed bed has not been attempted previously. The inluence o nanoluid concentration on parameters aecting orced convection heat transer in a vertical tube illed with packing materials is undertaken. The temperatures are measured at dierent axial positions with p-type thermocouples, as shown in Figure 1. Al 2 O 3 nanoluid at 0.02%, 0.1%, and 0.5% volume concentration is pumped through the test section against gravity, both at dierent low rates and at dierent inlet temperatures. The Nusselt number, riction actor and heat transer coeicients are evaluated next. Figure 1. Experimental test rig or packed bed. MODELS FOR REDICTING THERMAL ANALYSIS OF A ACKED BED In order to determine the heat transer o a packed bed system, several theoretical models have been reported in literature based on experimental investigations. A bed is o height L B, diameter D p and cross-sectional area A and packed with material having a 3

4 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column void raction ε, as shown in Figure 2. It is assumed that the temperature o the bed is uniorm at an initial value T Bi. The luid enters at T i with a mass low rate m and leaves the bed at T 0. The bed height L B is divided into a certain number o elements o thickness x. The temperature at the entry o the element is T m and on exit, it is at T m+1. Schumann Model Schumann (1929) has modeled the thermal behavior o packed beds, which was extended by Sagara and Nakahara (1991). The model estimates the mean luid and solid material temperatures at a given cross section as a unction o time and axial position. The assumptions made by Schumann, according to Duie and Beckman (1991), are: 1. The bed material has ininite thermal conductivity in the radial direction with plug low, i.e., no temperature gradient in the radial direction. 2. Bed material has zero thermal conductivity in the axial direction. 3. Thermal and physical properties o the solid and luid are constant. 4. The heat transer coeicient does not vary with time and position inside the bed. 5. No mass transer occurs. 6. No heat loss to environment. 7. No phase change o the luid in the axial direction. 8. The low is steady and uniorm. Fluid out X L B Fluid in Figure 2. Elemental representation o packed bed domain. The energy balance equation or the luid and solid components in the Schumann model or a packed bed can be written as: Energy in luid at entry to bed = (Energy transerred to bed) + (Energy in the luid in the bed) + (Energy in the luid leaving the bed) + (Energy lost to environment) T Ti m Cp T h T T Adx C Adx m C T dx Ul xt T (1) i v b p t p i x mb 4

5 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 Energy in the luid in the bed and energy lost to the environment can be neglected as per the assumptions. Based on the assumptions stated, Eq. (1) becomes T hv ALB (2) X m The above equation can be also written as where X = L B T X hv AL m C x, NTU (Number o transer units) = B p C p T T T T NTUT T S h V AL m C Energy transerred to the material = Energy stored by the material Ts hv T Ts Acsdx scps( 1 )Acsdx (4) t The above equation can be expressed as Ts (5) NTU(T where (dimensionless time) = m C C ps 1 ta cs L B ) Eqs. (3) and (5) give the thermal perormance o the packed bed. The exit luid temperature rom the bed is obtained by integrating Eq. (3) and can be written as NTU N Th 1 e (6) The rate o heat transer rom luid to bed element o thickness x is given by; Q = m Cp T,m1 T,m (7) Eq. (7) with the aid o Eq. (6) can be written to determine the exit temperature o the luid m Cp T,m1 T,m = NTU / N m Cp T,m TS,m 1 e (8) Similarly, Eq. (8) can be modiied to calculate the mean temperature o bed elements m as given below dt S, m d CN T N where C is a constant and equal to 1 e NTU /. Eq. (9) permits energy loss to environment at temperature T amb and can be written as dt UmΔA S,m CS,m CNT T T T (10) dτ,m, m S,m T s T ) S, m B p m C FABRICATION OF THE EXERIMENTAL SETU The experimental setup consists o a packed column 4 cm in diameter and 50-cm high. Figure 3 shows a diagram o the process and instrumentation o the experimental setup. An immersion heater heats the water, which is connected to a eed water storage tank o 50-liter capacity. A pump with low control and bypass valves supplies a regulated low o circulating working luid through the test section. Suitable instrumentation is used to measure the low rate o the working luid, the pressure drop across the bed, and the variation o axial temperature. The working luid lows through a helical coil immersed in the hot water tank under the action o a pump. It achieves the desired temperature beore it enters the test section. The interaction between the cold bed and the hot luid takes place. As a result, the luid temperature at the bed outlet decreases. The luid recirculates in a closed circuit. When the bed reaches steady state, the pressure drop S atm S S,m (3) (9) 5

6 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column across the bed and temperatures along the bed length are obtained by personal computer through use o a data logger or glass beads o two dierent sizes: 6- and 14.6-mm diameter. ESTIMATION OF RESSURE DRO O interest or the low through the packed beds is the relationship between low velocity and the drop in pressure across the bed. Many theoretical correlations are available in the literature to calculate this. However, Sadri (1952) equation is used to calculate the pressure drop through a packed bed, given by μ V0 LB 1 ε 1.75ρ V0 LB 1 ε ΔTh (11) 2 3 D 3 D ε ε where the bed void raction can be determined rom the relation Vol and p Vol are the volume o particles and bed, respectively, B 0 ε 1 Vol Vol B, in which V is supericial velocity, 6V D is the equivalent particle diameter given by D, and S is surace area. S The experimental pressure drop is calculated with the help o dierential height in a mercury manometer given by the equation R ( ) g / g (12) Exp m A The pressure drops obtained rom Eq. (11) or dierent low rates are compared with the experimental values and presented. The riction actors are calculated using the equation o Sadri (1952) by applying pressure drop relations and are presented as Ex b 3 thd 2 L B VS 1 c (13) 2 C with data Logger Rotometer ACKED BED TEST SECTION GV1 GV2 1 Supply tank ump Heating tank Manometer Figure 3. Schematic diagram o experiment setup o packed bed column. 6

7 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 CALCULATION OF HEAT TRANSFER COEFFICIENT The energy balance equation or the packed bed can be estimated rom the relation Q mc ( T T ) (14) O Exp where m is the mass low rate. The heat transer coeicient is estimated using Q Exp and the dierence between the surace temperature o the bed and the bulk mean temperature o the luid is given by QExp h (15) Exp L A (T T ) i8 where T T /8 s and T Si b (TI TO )/ 2. The experimental Nusselt number is i1 estimated by using the relation h D Nu Exp (16) Exp k Alazmi and Vaai (2000) derived a correlation by conducting experiments with air, hydrogen, carbon dioxide, and water. Experiments are undertaken in a narrow range o randtl numbers or a packed bed Reynolds number with the characteristic dimension in Re taken as the bed particle diameter D. The validation o the correlation has been undertaken by Gnielinski (1980) who presented the relation as hd p 0.5 1/3 Nulam 0.664Re p r (17) k 0. 8 hdp Re r Nu (18) tub k. Re r / 1 Gunn et al. (1987) presented an equation that is similar to Eq. (17) o Gnielinski (1980) in the absence o Nu tub as hdp / 3 Nu Re r (19) k Figure 4 represents the pressure drop in the packed bed with water and nanoluids at various volumetric concentrations. The pressure drop decreases with an increase in bed particle diameter and Reynolds number. The pressure drop increases with an increase in volume concentration o the nanoluid. The values o riction actor rom theory are compared with those rom experiment in Figure 5. The values are compared or water and nanoluid at various concentrations or 6- and mm particles. A regression equation is developed or the estimation o riction actor with an average deviation o ±0.08% and standard deviation o 1.68% as φ 0.. Re 2919 (20) p Figures 6 to 9 represent the variation o heat transer coeicient or various concentrations o nanoluid. Figure 6 shows the variation o heat transer coeicient with particle Reynolds number. Nanoluids predict higher heat transer coeicients compared with base luid water. A regression equation is developed or the estimation o the Nusselt number as a unction o the Reynolds number, randtl number, and volume concentration o the nanoluid. It is obtained with a standard deviation o 1.56% and an average deviation o 3.92%, as given by Nu S S b I Re p r (21) 7

8 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column Figure 4. Comparison o experimental and theoretical pressure drop or water and nanoluids or and 6-mm particles in packed bed. Figure 5. Comparison o experimental and theoretical riction actor or water and nanoluids or and 6-mm particles in packed bed. 8

9 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 Figure 6. Comparison o heat transer coeicient in packed beds with particle Reynolds number with 6 and mm glass particle beds with water and nanoluids. Figure 7 represents the variation o heat transer coeicient with nondimensional axial distance along the bed length at 40 C or minimum and maximum low rates o water and nanoluid at two dierent concentrations or the two particles. The heat transer coeicient increases with increasing low rate and concentration o the nanoluid. Figure 8 represents the variation o heat transer coeicient or 6- and mm particles or dierent operating conditions. The low rate is 150 LH at 40 C or water and nanoluids at dierent concentration. The heat transer coeicient increased with decreasing particle diameter. Figure 7. Eect o Al 2 O 3 concentration on heat transer coeicient comparison with non-dimensional axial distance with beds o mm particles with water and nanoluids. 9

10 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column Figure 8. Heat transer coeicient vs. particle Reynolds number at luid rate 150 LH or 6- and mm particles. Figure 9 shows the variation o heat transer coeicient o water and nanoluid at high low rates or two temperatures and particle concentrations. At higher low rates and temperatures, the heat transer coeicient is greater or 6 mm-particles compared with mm particles. Figure 9. Heat transer coeicient vs. particle Reynolds number at luid rate 300 LH or 6- and mm particles. Figures 10 to 11 represent the temperature distribution o the bed or two particle sizes. The experimental values are in agreement with the Schumann-NTU method and other authors rom the literature. There is a reasonable agreement o 10

11 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 experimental data with other theoretical investigations. The pressure drop with nanoluids is higher by 10% and it increases with concentration o the nanoluid. Figure 11 shows a comparison o temperature proiles at minimum and maximum low rate or a bed o mm particles. At the low low rate, the temperature is greater than at high low rate. There is no signiicant temperature variation with low rate. The temperature variation is signiicant at higher concentrations o the nanoluid. Figure 12 represents the non-dimensional luid exit temperature distribution or 6-mm particles at dierent low rates in comparison with the NTU method. The temperatures obtained with the nanoluid are higher than or water. The theoretical results indicate reasonable agreement with the experimental values with a deviation o 10%. Figure 10. Comparison o non-dimensional temperature distribution with nondimensional axial distance with NTU-ε method at 150 LH and 300 LH. Figure 11. Comparison o non-dimensional temperature distribution with nondimensional axial distance with NTU-ε method at 150 LH and 300 LH or 6-mm particles. 11

12 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column CONCLUSIONS Heat transer in a packed bed column illed with 6- and mm-diameter glass beads, is employed to determine the heat transer coeicient and pressure drop. The riction actor increases with decreasing particle diameter and increasing volume concentration o nanoluids compared with the base luid. The pressure drop is higher with nanoluids than with water by 10% to 15%. The pressure drop increases with nanoluid concentration. At lower concentration, the deviation o the riction actor with nanoluid and water is more signiicant than at higher concentration. The heat transer coeicient is higher with 6-mm particles owing to the larger surace area and the number o particles. Similarly, the heat transer coeicient is greater at higher concentrations o the nanoluid. With an increase in volume concentration, the heat transer is greater and it increases with the low rate and inlet luid temperature. The enhancement in heat transer coeicient with nanoluids compared with the base luid lies between 10% and 15% due to higher values o thermal conductivity. The values rom the Schumann model agree with the experimental data or the two bead sizes o 6.0 and mm. The deviation between the two is less than 10%. REFERENCES Alazmi, B., & Vaai, K. (2000). Analysis o variants within the porous media transport models. Journal o Heat Transer, 122(2), Adeyanju, A. A. (2009). Eect o luid low on pressure drop in a porous medium o a packed bed. Journal o Engineering and Applied Sciences, 4(1), Araiza, C. C. O., & Isunzay, F. L. (2008). Hydrodynamic models or packed beds with low tube-to-particle diameter ratio. International Journal o Chemical Reactor Engineering, 6(A1), 1-8. Carlos, O. Araiza, C., & Lopez-Isunzay, F. (2008). Hydrodynamic models or packed bedswith low tube-to-particle-diameter ratio. International Journal o Chemical Rector Engineering, 6(A1): Choi, S. U. S. (1995). Enhancing thermal conductivity o luid with nanoparticles. Developments and applications o non-newtonian low. ASME, FED 231/MD, 66, Das, S. K., utra, N., Thiesen,., & Roetzel, W. (2003). Temperature dependence o thermal conductivity enhancement or nanoluids. ASME Journal o Heat Transer, 125, Duie, J. A., & Beckman, W. A. (1991). Solar engineering o thermal processes. 2 nd ed. New York: John Wiley& Sons Inc. Gnielinski, V. (1980). Warme- und Sto ubertragung in Festbetten, Chemical Engineering & Technology, 52, Gunn, D. J., Ahmad, M., & Sabri, M. N. (1987). A distributed model or liquid phase heat transer in ixed beds. International Journal o Heat and Mass Transer, 30, Jeigarnik, U. A., Ivanov, F.., & Ikranikov, N.. (1991). Experimental data on heat transer and hydraulic resistance in unregulated porous structures. Teploenergetika, 12, Lamine, A. S., Colli Serrano, M. T., & Wild, G. (1992a). Hydrodynamics and heat transer in packed beds with liquid up low. Chemical Engineering and rocessing: rocess Intensiication, 31,

13 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 Lamine, A. S., Colli Serrano, M. T., & Wild, G. (1992b). Hydrodynamic and heat transer packed beds with concurrent up low. Chemical Engineering Science, 47, Lee, S., Choi, S. U. S., Li, S., & Eastman, J. A. (1999). Measuring thermal conductivity o luids containing oxide nanoparticles. Journal o Heat Transer, 121, Mahalingam, M. (1985). Thermal management in semiconductor device ackaging. roceedings o IEEE 73(9), Maiga, S. B.,alm, S. J., Nguyen, C. T., Roy, G., & Galanis, N. (2005). Heat transer enhancement by using nanoluids in orced convection lows. International Journal o Heat and Fluid Flow, 26: Mansour, R., Galanis, N., & Nguyen, C. (2007). Eect o uncertainties on orced convection heat transer with nanoluids. Applied Thermal Engineering, 27(1), Maxwell, J. C. (1904). A treatise on Electricity and magnetism. Cambridge: Oxord University ress. Sadri, E. (1952). Fluid low through packed bed vertical column. Chemical Engineering rogress, 48: Sagara, K., & Nakahara, N. (1991). Thermal perormance and pressure drop o rock beds with larger storage materials. Journal o Solar Energy, 47(3), Sarma.. K., Subramanyam. T, Kishore,. S., Dharma Rao, V., & Kakac, S. (2003). Laminar convective heat transer with twisted tape inserts in a tube. International Journal o Thermal Sciences, 42(9), Schumann, T. E. W. (1929). Heat transer: a liquid lowing through a porous prism. Journal o the Franklin Institute, 208(3), Sivleira, A. M. (1991). Heat transer in porous media one phase model in ixed beds. h.d. Dissertation, EQ-COE/UFRJ. Sharma, K. V., Suryanarayana, K. V., Sarma,. K., Rahman, M. M., Noor, M. M., & Kadirgama, K. (2010). Experimental investigations o oxygen stripping rom eed water in a spray cum tray type deaerator. International Journal o Automotive and Mechanical Engineering, 1, Syam Sundar, L., Sharma, K. V., & Ramanathan, S. (2007). Experimental investigation o heat transer enhancements with Al 2 O 3 nanoluid and twisted tape insert in a circular tube. International Journal o Nanotechnology and Applications, 1(2), Tuckerman, D. B., & ease, R. F. (1982). Ultra high thermal conductance microstructures or cooling integrated circuits. IETE, 781(4), Weekman, V. W., & Myers, J. E. (1995). Heat transer characteristics o concurrent gasliquid low in packed beds. American Institute o Chemical Engineers Journal, 11, Wen, D., & Ding, Y. (2004). Experimental investigation into convective heat transer o nanoluid at the entrance region under laminar low conditions. International Journal o Heat and Mass Transer, 47(24), Xuan, Y. M., & Roetzel, W. (2000). Conceptions or heat transer correlation o nanoluids, International Journal o Heat and Mass Transer, 43(19), Xuan, Y. M., Li, Q., & Hu W. (2004). Aggregation structure and thermal conducting o nanoluids. American Institute o Chemical Engineers Journal, 49(4),

14 Experimental Study on Heat Transer Coeicient and Friction Factor o Al 2 O 3 Nanoluid in a acked Bed Column Yagi, S., Kunii, D., & Endo, K. (1964). Heat transer in packed beds through which water is lowing. International Journal o Heat and Mass Transer, 7, You, W. J. Moon, H. J., Jang S.., Kim, J. K., & Koo, J. (2010). Eects o porosity, pumping power, and L/D ratio on the thermal characteristics o an N 2 O catalytic igniter with packed bed geometry. International Journal o Heat and Mass Transer, 53, NOMENCLATURE 2 A area o the bed, m C constant in Equation (9) C speciic heat, J kgk D diameter, m riction actor 2 g local acceleration o gravity, m s 2 g gravitational constant, kg m N s c h heat transer coeicient, W m 2 K h average heat transer coeicient, W m 2 K h volumetric heat transer coeicient, W/m -3 K -1 V k thermal conductivity, W mk L length, m m mass low rate, kg s N number o grids in axial direction, x / L NTU Number o Transer Units Nu Nusselt number, h D k pressure, a pressure drop, a r randtl number, C L k rate o heat transer, W Q R e Reynolds number, s Re p packed bed Reynolds number, s ( 1 ) R m dierential height in manometer luid T temperature, K T mean temperature, K Vol 3 volume, m V velocity, m s X x Subscripts LB A B b Ex I mercury bed bulk luid experimental inlet 14

15 Srinivasa Rao et al. / Journal o Mechanical Engineering and Sciences 1(2011) 1-15 lam laminar low O outlet luid L liquid particle 0 supericial S surace Th theoretical tub turbulent low x local values Nano nanoluid Greek Symbols non-dimensional luid temperature 3 density o the luid, kg m dynamic viscosity, N s m void raction volume concentration 15