PREDICTION OF PRESSURE DROP AND HEAT TRANSFER IN MICRO-HEAT EXCHANGERS WITH NANO CRYOGENIC FLUIDS USED IN THE COOLING OF ELECTRONIC DEVICES

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1 International Journal o Mechanical Engineering and Technology (IJMET) Volume 8, Issue 7, July 2017, pp , Article ID: IJMET_08_07_138 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed PREDICTION OF PRESSURE DROP AND HEAT TRANSFER IN MICRO-HEAT EXCHANGERS WITH NANO CRYOGENIC FLUIDS USED IN THE COOLING OF ELECTRONIC DEVICES Vishnu Saini Research Scholar, School o Mechanical Engineering, Lovely Proessional University, Punjab, India. Abhinav Kumar Research Scholar, School o Mechanical Engineering, Lovely Proessional University, Punjab, India. Kumari Neelam Verma Graduate Student, School o Mechanical Engineering, Lovely Proessional University, Punjab, India. Raja Sehar Dondapati Associate Proessor, School o Mechanical Engineering, Lovely Proessional University, Punjab, India. ABSTRACT Microelectronic devices are the integral part o advanced technologies such as space technologies. However, the cooling o these microelectronic devices encounters various challenges due to large aspect ratios. Further, the conventional liquid coolants could not dissipate the heat aster due to limited thermal conductivity and speciic heat values. Hence, in the present wor, a computational investigation is done on the easibility o using cryogenic coolants with nanoparticles such as CuO, SiO2, SiC, Al2O3 and TiO2 dispersed in the cryogenic coolant (Liquid Nitrogen). A computational geometry is developed in ANSYS and the pressure drop and heat transer analysis is done using FLUENT. Relevant boundary conditions are applied to relect the practical operating conditions o microelectronic devices. It is observed rom the results that the pressures drop decreases with suspension o CuO. Further, the heat transer is observed to be increasing with the addition o Al2O3 and SiO2 nanoparticles with the volume concentration o 3%. Finally, it can be concluded that the dispersion o the nanoparticles in Liquid Nitrogen (LN2) will be beneicial to use in microelectronic devices editor@iaeme.com

2 Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati Key words: Liquid Nitrogen, Micro Heat Exchangers, Nanoluid, Metal Oxide Nanoparticles, Micro-electronic devices. Cite this Article: Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati Prediction o Pressure Drop and Heat Transer in Micro-Heat Exchangers with Nano Cryogenic Fluids Used in The Cooling o Electronic Devices. International Journal o Mechanical Engineering and Technology, 8(7), 2017, pp INTRODUCTION With the increasing demand or various electronic devices such as integrated circuits [1], microreactors [2], microprocessors and laser diodes [3], cooling o these devices is become essential due to their higher heat dissipation. These demands can be ulilled by incorporation o micro-heat exchangers woring with nanoluids. These nanoluids play a vital role in enhancement o thermophysical properties by which desired result o higher heat transer rate can be achieved. Koo et al. [4], reported that the perormance o micro-heat sins increased with addition o CuO nanoparticles with a concentration o 1-4%. Further, Lee et al. [5], investigated that the heat transer coeicient increased with decreasing the channel diameter at a given low rate. Furthermore, Lelea et al.[6], investigated the numerical modeling o Al2O3 with water and observed that heat transer is increased in axial direction with suspension o Al2O3 nanoparticles. In addition, Kamyar et al. [7], reviewed that computational simulation has good agreement with experimental wor and nanoluids leads to enhancement o heat transer. Later, Sey et al. [8], numerically studied the enhancement in convective heat transer by using nanoluid in micro-pin-in heat sin. Shalchi-Tabrizi et al. [9], numerically investigated the eect o volume concentration and particle diameter on entropy, hydrodynamic and heat transer perormance o tangential micro-heat sin. Sohel et al. [10], reported that use o nanoluids enhanced the thermal perormance o micro-channel heat sin to be used in electronic heat sin. Moreover, Azari et al. [11], investigated the heat transer enhancement in water/al2o3 based nano luids using Computational Fluid Dynamics (CFD). Bianco et al. [12], reported that nanoluids (Al2O3 with water) allows to obtain higher heat transer coeicient in circular tubes. Furthermore, Peyghambarzadeh et al. [13], experimented that higher heat transer can be obtained by using micro channel with incorporation o nanoluids and showed good agreement with conductive and convective heat transer mechanisms. Ray et al. [14] experimentally and numerically investigated the enhancement o heat perormance in compact plate heat exchangers. Later, Solomon et al.[15], observed that addition o nanoparticles in screen mesh pipe increased the eective thermal conductivity by which enhancement in heat transer is obtained. Salman et al. [16], reported that maximum heat transer enhancement was about 22% when using the nanoluids. R.S. Dondapati [17], investigated the perormance o various nano luids or cooling o transormers. Motivated by the challenges involved in cooling o micro-electronic devices, in the present wor, the nano particle such as CuO [18], [19], SiO2 [20], [21] SiC, Al2O3 [22], [18], [23] and TiO2 [24], [25] is dispersed in Liquid Nitrogen (LN2) and thermophysical properties is evaluated to investigate the perormance o micro-electronic devices. Further, Computational analysis is done to assure the use o these nanoluids in micro-electronic devices or better heat transer perormance. 2. STUDY OF THERMOPHYSICAL PROPERTIES OF NITROGEN Nanoparticles such as CuO, SiO2, SiC, Al2O3 and TiO2 with 3% volume concentration are dispersed in LN2 (baseluid) to obtain the nanoluid to be used in micro-electronic devices. In order to evaluate the perormance o micro-electronic devices, it is essential to study the editor@iaeme.com

3 Prediction o Pressure Drop and Heat Transer in Micro-Heat Exchangers with Nano Cryogenic Fluids Used in The Cooling o Electronic Devices thermophysical properties such as density, viscosity, thermal conductivity and speciic heat using theoretical and experimental model. However, these correlations are applicable or water, oil and ethylene glycol baseluid with suspension o nanoparticles. These correlations implied approximate desired result with 3% o volume raction nanoparticles suspended in base luid (LN2).These thermophysical properties will be used to solve governing conservation equations. 3. THERMOPHYSICAL PROPERTIES OF LIQUID NITROGEN BASED NANOFLUID Thermophysical properties such as density, speciic heat, with viscosity and thermal conductivity o nanoluid are computed as unction o temperature rom 65 to 83K at a pressure o 2bar. In equation (1) [26], ρ NF shows the eective density o Nanoluid φ volume raction o nanoparticle ( NP ) and ρ density o baseluid ( BF ). ρ = (1 φ ) ρ + φρ NF BF NP In equation (2) [27], C pnf shows the eective speciic heat o Nanoluid withφ volume raction o nanoparticle (NP), C is speciic heat and ρ is density o base luid (BF). p (1) C p N F = (1 φ ) ( ρ C ) + φ ( ρ C ) p B F p N P (1 φ ) ρ + φ ρ B F N P (2) TABLE 1 Theoretical and Experimental correlation or Thermal Conductivity Model Reerence Correlation Theoretical Experimental Maxwell Li and Peterson e p φ ( p ) = + 2 φ ( ) e e p p = 0.764φ ( T ) = 3.761φ ( T ) Relevant inormation Liquid and solid suspension Al 2O 3/water Nanoluid CuO/water Nanoluid Table 1 shows both the experimental and theoretical correlations or eective thermal conductivity o nanoluid ( e ) withφ volume raction o nanoparticle or ( ) thermal conductivity (base luid) and p thermal conductivity o nanoparticle. To compute the eective thermal conductivity o LN2, Maxwell correlation [28] and Li and Peterson [29] corelation are considered. Table 2 shows both experimental and theoretical ormulas o eective viscosity o nanoluid ( µ e ) withφ volume raction o nanoparticle or ( µ ) viscosity o baseluid. To evaluate the eective viscosity o LN2 and LHe, Einstein [30], Drew and Passman [31] correlation are considered editor@iaeme.com

4 Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati TABLE 2 Theoretical and Experimental correlation or Viscosity Model Reerence-Year Correlation Relevant inormation Theoretical Einstein-1906 µ µ e = ϕ Ininitely dilute suspension o spheres Experimental Drew and passman µ µ e = φ Concentration is than less 5 vol% 4. COMPUTATIONAL STUDY ON LIQUID NITROGEN BASED NANOFLUID In FIG 1, geometrical coniguration o micro tube used in micro-electronic device is shown. To model this device the mesh generation using ANSYS [32] is shown in FIG 2. In this present study the luid enters through inlet with uniorm temperature and the wall heat lux is considered uniorm. Figure 1 Geometrical coniguration o micro tube used in micro heat exchanger 4.1. Governing Equations To obtain numerical results in this geometry, governing equations are to be solved. There are three governing equation such as conservation o mass, momentum and energy equation. These equations or single phase luid are given in (3) to (5). Mass Conservation equation: ρ +.( ρ v) = Sm t Where, Sm is the source term or mass. Momentum Conservation equation: ρ v + ρ v v = p + τ + ρ g+ F t (4) ( ).( ). ( ) Energy Conservation equation: ( ρe) +.( v( ρe + p)) =. hjj j + S (5) h t j (3) editor@iaeme.com

5 Prediction o Pressure Drop and Heat Transer in Micro-Heat Exchangers with Nano Cryogenic Fluids Used in The Cooling o Electronic Devices 4.2. Discretization To convert the governing equation in to algebraic orm inite volume method (FVM) Descritization is done. FLUENT [33] is used to solve these equations to obtain numerical result. In this wor Descritization o momentum and energy equation with second order upwind scheme, turbulent inetic energy and turbulent dissipation rate with irst order upwind scheme, pressure with standard scheme and solution o linear equation with least square cell based is done. For pressure-velocity coupling SIMPLE (semi implicit method or pressure lined equation) algorithm is used. Transport equation [34] or the Realizable - model is: µ t ( ρ) + ( ρ u ) = µ + + G + G ρε Y + S t t xi σ xi j b M 2 µ t ε ε ( ρε ) + ( ρε u j ) = µ + + ρc1sε ρc 2 t x j x j σ ε x j + vε ε + C1ε C3ε Gb + Sε η Where C 1 = m a x 0.4 3, η + 5, η = S ε (6) (7) Figure 2 Mesh generation o micro tube used in micro heat exchanger 4.3. Boundary Conditions At inlet o exchanger, the luid low with 0.1 to 0.14 g/s mass low rate at 65 K temperature. Moreover, ully developed low is dominated at outlet o exchanger. To compute the Reynolds Number temperature dependence properties, viscosity and density, is taen. Uniorm heat lux o W/m 2 is applied on exchanger wall and no slip condition is considered Solution The present descritized model is solved by using FLUENT [33] or urther analysis. To simulate the present model residuals are considered to iterate the equations. To initialize the solution standard method is considered. Assumption o this wall unction gave desired result editor@iaeme.com

6 Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati 5. RESULTS AND DISCUSSIONS 5.1. Pressure Drop Analysis In this study, Computational Fluid Dynamics (CFD) is used to investigate the pressure drop and heat transer with the combined eect o temperature dependent thermo-physical properties and suspension o nanoparticles due to turbulent low o LN2. FIG 3 and FIG 4 shows the velocity proiles o ully developed low at outlet o circular pipe or Maxwell theoretical [28] and Li and Peterson experimental model [29] respectively with dispersion o nanoparticles at 0.13 g/s mass low rates. Firstly, Pressure drop is computed or circular channel with 3% volume concentration o nanoparticles. FIG 5 shows increase in pressure drop with increase in Reynolds Number and decrease in pressure drop with suspension o nanoparticles. Moreover, Pressure drop is less or CuO nanoparticles with 3% o volume concentration in LN2. For circular pipe riction actor is computed rom equation (8) or turbulent low. Reynolds Number is can be calculated rom equation (9) τ 8 wall 2 ρvavg = (8) DhV avg ρ Re = (9) µ FIG 6 and FIG 7 shows the riction actor or Maxwell theoretical [28]and Li and Peterson experimental model [29] with dispersion o 3% o nanoparticles. It is observed that riction actor decrease with increase with increase in Reynolds Number and with dispersion o nanoparticles. Moreover, Fiction actor is less or Al2O3nanoparticles with 3% o volume concentration inln Pumping Power To pump the nanoluids in micro channels, Pumping power at various mass low rates with 3% volume concentration o nanoparticles is calculated as W = P V (10) In FIG 8, pumping power has been shown or various mass low rates. It is observed that pumping power increases with increase in mass low rate whereas decreases with the dispersion o dierent nanoparticles at 3% volume concentration editor@iaeme.com

7 Prediction o Pressure Drop and Heat Transer in Micro-Heat Exchangers with Nano Cryogenic Fluids Used in The Cooling o Electronic Devices Figure 3 Velocity proiles with dierent nanoparticles at 0.13 g/s mass low rate or Maxwell theoretical model Figure 4 Velocity proiles with dierent nanoparticles at 0.13 g/s mass low rate or Li and Peterson experimental model [32] Figure 5 Pressure drop o Liquid Nitrogen with dierent nanoparticles editor@iaeme.com

8 Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati Figure 6 Friction actor with dierent nanoparticles or Maxwell theoretical model [31] This is due to decrease in riction actor and wall shear stress. Moreover, pumping power is very less or CuO dispersed nanoluid which is desirable result to pump the nanoluids in micro heat exchangers Heat transer analysis To cool the microelectronic devices, LN2 based nano-cryogens is passed the through circular channels. The heat dissipates rom these devices transer their heat to the channels. Hence, temperature dierence will be created between outlet and inlet sections. FIG 9 shows these dierences or dierent low rate. It is ound that temperature dierence decreases with increase in mass low rate and increase with the dispersion o nanoparticles. Moreover, temperature dierence is more or suspension o CuO in Liquid Nitrogen. Figure 7 Friction actor with dierent nanoparticles or Li and Peterson experimental model [32] editor@iaeme.com

9 Prediction o Pressure Drop and Heat Transer in Micro-Heat Exchangers with Nano Cryogenic Fluids Used in The Cooling o Electronic Devices Figure 8 Pumping power o Liquid Nitrogen at dierent mass low rate FIG 10 and FIG 11 shows Nusselt Number with Reynolds Number or Maxwell theoretical model [28] and Li and Peterson experimental model [29] respectively. It is detected that Nusselt Number increases with increase in Reynolds Number and with the suspension o dierent nanoparticles. Moreover, Nusselt Number is higher with dispersion o Al2O3 nanoparticles or Maxwell theoretical model and with dispersion o SiO2 nanoparticles or Li and Peterson experimental model. Furthermore, increase in Nusselt Number shows increases the heat transer which is desirable property to use nanoparticles in LN2. Enhancement in heat transer due to increase in thermal conductivity o LN2 with suspension o dierent nanoparticles with 3% volume concentration. Figure 9 Temperature dierence Vs mass low rate with dierent nanoparticles 5.4. Cooling Capacity Cooling capacity o nanoluids is estimated as Qcc = V ρcp ( Tinlet Toutlet ) (11) FIG 12 shows the cooling capacity o LN2 with suspension o dierent nanoparticles at various mass low rates. It is observed that cooling capacity decrease with increase in mass low rate and also with the suspension o dierent nanoparticles editor@iaeme.com

10 Vishnu Saini, Abhinav Kumar, Kumari Neelam Verma and Raja Sehar Dondapati Figure 10 Nusselt Number Vs Reynolds No o LN 2 with dierent nanoparticles or Maxwell theoretical model [28] Figure 11 Experimental Nusselt Number Vs Reynolds No o LN 2 with dierent nanoparticles or Li and Peterson experimental model [29] Figure 12 Cooling Capacity o LN 2 at dierent mass low rate 6. CONCLUSIONS The present wor shows the pressure drop and heat transer analysis using FLUENT code. The suspension o nanoparticles with 3% volume concentration in LN2 shows increase in heat transer and decrease in pressure drop. Heat transer is high with the suspension o Al2O3 (Maxwell theoretical model) and SiO2 or Li and Peterson (experimental) model. Moreover, Pressure drop is less with the suspension o CuO nanoparticle in LN2. Further, pumping power and cooling capacity o nanoluids decreases with 3% dispersion o nanoparticles. It editor@iaeme.com

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