Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 189 A comparative Study on the Thermal Conductivity of Micro and Nano fluids by Using Silver and Zirconium Oxide Layth W. Ismael Dr. Khalid Faisal. Sultan Lecturer Lecturer Materials . Eng. Dept. Electromechanical. Eng. Dept. University of Technology University of Technology Ph. .D. Student – Ozyegin university E-Mail: alfahadlwi@yahoo.com E-Mail: ksultan61@yahoo.com Received 12 November 2012 Accepted 17 March 2014 ABSTRACT In this article experimentally investigations have been carried out to study the effect of the size and type particles on the thermal conductivity of micro and nanofluids. The study investigated nanofluids and microfluids which containing silver (Ag) and zirconium oxide (Zr2O3) as well as in the size and type of micro and nanoparticles in distilled water as base fluid with different particles size and concentrations. The experimental results emphasized the enhancement of the thermal conductivity due to the nanoparticles presence in the fluid greater than microfluids, also shown the effect of the particle size and concentration on the thermal conductivity. It has been recognized that the addition of highly conductive particles can significantly increase the thermal conductivity of heat – transfer fluids. Particles in the micro and nano – size range have attracted the most interest because of their enhanced stability against sedimentation and, as a result, reduction in potential for clogging a flow system. Furthermore the results showed that, the obtained thermal conductivities doubtlessly revealed that size and type particles was a key factor affecting conductive heat transport in suspensions. The aim of this article is an experimental exploration of the thermal conductivity of micro – and nano – particles and Compared with them as well as type particles and the method used in this researcher know Lee's disc technique. These results show noticeable enhancement in the thermal conductivity were evaluated to be ( 7.66 %, 2.35 %) for the Ag, Zr2O3 – distilled water nanofluid while reaches to (3.23 %,1.02 %) for the Ag , Zr2O3 – distilled water micro fluids at the concentration of (0.05 vol. %) and at the room temperature. A good agreement was found between the experimental obtained data for this paper and other results from published papers. mailto:alfahadlwi@yahoo.com mailto:ksultan61@yahoo.com Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 190 وأوكسيد الفضة باستخدام والنانوية المايكروية للموائع الحراري التوصيل بين مقارنة دراسة الزركونيوم فيصل سلطان د. خالد ليث وضاح اسماعيلمدرس الكهرو ميكانيكيةقسم الهندسة قسم هندسة المواد الجامعة التكنولوجية الجامعة التكنولوجية الخالصة يتضمن البحث الحالي دراسة عملية للموصلية الحرارية للموائع التي تحتوي على حبيبات نانوية وما يكروية مخلوطة مع المائع الزركونيوم وأوكسيد Ag فضة وكذلك تأثير حجم ونوع الجزئيات. الدراسة تضمنت سوائل نانوية وما يكروية مكونة من االساسي Zr2O3 على شكل حبيبات نانوية وما يكروية مختلطة مع الماء النقي كمائع اساسي بكسور حجمية وتراكيز مختلفة. أكدت النتائج التجريبية تحسين الموصلية الحرارية بسبب وجود الجسيمات النانوية في المائع أكبر من الموائع الميكروية ، أظهرت أيضا تأثير حجم يمكن أن تزيد بشكل كبير من الموصلية ا لحرارية وصيل الحراري. وقد تم االعتراف بأن إضافة جزيئاتالجزيئات والتركيز على الت في انتقال الحرارة بالموائع . الجزيئات ذات الحجم النانوي والميكروي اجتذبت قدر كبير من االهتمام بسبب تحسين األستقرارية ضد دفق بالنظام وعالوة على ذلك أظهرت النتائج أن التوصيالت الحرارية التي تم الحصول الترسيب وبالنتيجة ،الحد من احتمال انسداد الت عليها كشفت بال شك أن حجم و نوع الجزيئات كان عامال رئيسيا يؤثر على انتقال الحرارة بالتوصيل في الموائع الميكروية والنانوية . رية للجزئيات النانوية والميكروية و بالمقارنة بينهما ، فضال عن نوع الهدف من هذه المقالة هو دراسة عملية في الموصلية الحرا الجزيئات و الطريقة المستخدمة في هذا الباحث تعرف بتقنية قرص لي. كما بينت النتائج العملية تحسن ملحوظ في الموصلية الحرارية بسبب الحبيبات الما يكروية والنانوية المضافة الى المائع، كذلك ر بينت تأثير الحجم الحبيبي والتركيز على الموصلية الحرارية. النتائج بينت ايضا ان الموصلية الحرارية الى المواد النانوية تكون اكب من الموصلية الحرارية للمواد المايكروية بسب صغر حجم الجزئيات النانوية بالمقارنة مع الحجم المايكروية. وان نسب التحسين في مع الماء النقي على التوالي Zr2O3 الزركونيومأوكسيد و Agالى المائع النانوي الفضة (%2.73,7.66)الحرارية كانت الموصلية وبتركيز مع الماء النقي Zr2O3 الزركونيومأوكسيد و Agالى المائع المايكروية الفضة (%3.23 ,1.02). بينما كانت هذه النسب وبدرجة حرارة الغرفة. وجد توافق جيد بين النتائج العملية المستحصلة من هذه الدراسة ونتائج اخرى في بحوث منشورة (0.05%) سابقة. Keywords: Nano fluid, Micro fluid, thermal conductivity, Enhancement. Nomenclature d Thickness of the discs mm ds Thickness of the sample mm e Heat loss Watt I Current A V Voltage V K Thermal conductivity W/m 2 .k Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 191 n Empirical shape factor __ r The radius of the disc mm T1, T2, T3 The temperatures of the through discs. k Ф Volume fraction % subscripts nf Nanofluid __ p Nanoparticles __ b Base __ 1- INTRODUCTION Heat transfer fluids can exhibit significant increases in thermal conductivity with the addition of highly conductive particles. Recent attention has focused on micro – and nano – particle suspensions because of their enhanced stability against sedimentation, reduction in potential for clogging a flow system, as well as the tantalizing possibility of unexpected enhancements in thermal conductivity. The later has been spurred by reports of large increases in the thermal conductivity in very – low – volume fraction nanoparticle (up to 100 nm in size) suspensions. For instance, the effective thermal conductivity of an ethylene-glycol-based nanofluid containing copper nanoparticles with diameters less than 10 nm was reported to increase by up to 40% at 0.3% vol of dispersed particles [1]. Another example is silver nanoparticles in water and toluene[2], where thermal conductivity enhancement of 5- 21% was observed at a loading of only 0.026% vol. The addition of less conductive aluminum oxide particles were reported to increase the resulting thermal conductivities of base fluids by up to 30% at particle volume fraction of Al2O3 of 5% [3], [4], 4% [5] or 3% [6]. In each case, the enhancements in thermal conductivity were reported to be greater than predicted by macroscopic theory for the given particle volume fraction and thermal conductivity. Among nanoparticle suspensions, those containing carbon nanotubes (CNTs) have attracted some of the most interest. Discovered in 1991, carbon nanotubes have already entered the realm of practicality, finding use in the aerospace, automotive and telecommunications industries because of their interesting characteristics. Single – walled carbon nanotubes are 100 times stronger than steel at one-sixth the weight, and their thermal conductivity is about 5 – 10 times greater than that of very conductive materials like aluminum or copper. Nanotubes can be electrical conductors or semiconductors depending on their crystal structure. Moreover, many physical properties of nanotubes, including their thermal conductivity, are expected to be highly anisotropic. One of the emerging miniaturization techniques is the nanofluid technology which meets the shortcomings of the earlier used bulk fluids and conventional base fluids. Nanofluids exhibit large thermal conductivity compare to traditional (base) fluids and are suitable for heat transfer applications Choi et al. [7]; Das et al. [8]; Murshed et al. [9]; Xuan and Li [10]. There is a great attraction towards Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 192 nanofluids because they are proved to be far more superior when compared to the conventional bulk fluids. Nanofluids offer promising heat transfer applications which is of major importance to industrial sectors including transportation, power generation, micro-manufacturing, electronics, engines, thermal therapy, heating, cooling, ventilation and air conditioning. Many of the reported anomalous enhancements in thermal conductivities in nanofluids were non – reproducible Keblinski et al. [11]. Recent experimental studies suggest that nanofluids exhibit thermal conductivity enhancement within Maxwell’s limit (Philip et al. [12]; Timofeeva et al. [13]; Eapen et al. [14];Shima et al. [15]. Zhang et al. [16]) measured the effective conductivity and thermal diffusivity of Au/totuene, Al2O3/water, TiO2/water, CuO/water nanofluids using the transient short-hot-wire (SHW) technique, which was developed from the conventional transient hot wire (THW) technique and is based on the numerical solution of two dimensional transient heat conduction for a short wire with the same length- to-diameter ratio and boundary conditions as those used in the actual measurements. The diameters of Au, Al2O3, TiO2 and CuO spherical particles were 1.65, 20, 40 and 33nm, respectively. The effective thermal conductivities of the nanofluids show no anomalous enhancement and can be predicted accurately by the equations of the Hamilton and Crosser model. Liu et al. [17] measured the thermal conductivities of nanofluids containing CNTs n dispersed in ethylene glycol and a synthetic engine oil. The increase of thermal conductivity is up to 12.4% for CNT – ethylene glycol suspensions at 1.0 vol% and 30% for CNT – synthetic engine oil suspensions at 2 vol%. One possible reason for this is that the thermal conductivity is highly dependent on important factors such as the structure of the CNTs, clustering, temperature, etc. Further systematic research is necessary to obtain a whole map for the thermal conductivities of CNTs. Hwang et al. [18] compared the thermal conductivity of four kinds of nanofluids such as MWCNTs in water, CuO in water, SiO2 in water, and CuO in ethylene glycol. They found that the thermal conductivity of MWCNT nanofluid was increased up to 11.3% at 1 vol%, which is relatively higher than that of the other groups of nanofluids .Zhang et al. [16] investigated the effective thermal conductivity and thermal diffusivity of CNT/water nanofluids using the transient short – hot – wire technique. The average length and diameter of CNTs are 10 μm and 150 nm, respectively. However, the measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancements and can be predicted accurately by the unit – cell model equation of Yamada and Ota [19] for carbon nanofibers. There are few studies made on ultrasonic propagation in magnetic nanofluids by some researchers (Sayan and Ulrich [20]; Motozawa et al,[21]; Raj et al. [22]) no systematic research efforts have been carried out to compare the behavior of micro and nanofluids in terms of acoustical and thermal parameters. The fundamental understanding of exact mechanisms responsible for the anomalous values of ultrasonic wave propagation is unclear because of the lack of molecular level understanding of the ultrafine particles (Raj et al. [22]) that warrant systematic studies. A systematic study on the micro and nanofluids is required for the basic understanding of how the nanoparticles behave in fluids. The objective of this work is an experimental exploration of the thermal conductivity of micro – and nano – particle and Compared thermal conductivity increase in suspensions containing micro – and nano – sized particles as well as study the type and particles agglomeration effect on the thermal conductivity of micro and nanoparticle suspensions. 2-THEORETICAL FORMULATION Currently, there is no reliable theory to predict the anomalous thermal conductivity of nanofluids. From the experimental results of many researchers, it is known that the thermal conductivity of nanofluids depends on parameters including the thermal conductivity of the base fluid and the Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 193 nanoparticles , the volume fraction, the surface area, and the shape of the nanoparticles , and the temperature. There are no theoretical formulas currently available to predict the thermal conductivity of nanofluids satisfactorily. For particle – fluid mixtures, numerous theoretical studies have been conducted dating back to the classical work of Maxwell. Yu and Choi [23] proposed a modified Maxwell considering to account the effect of the nano-layer by replacing the thermal conductivity of solid particles kp in Eq. (1) with the modified thermal conductivity of particles kp, which is based on the so called effective medium theory.     b k Φ 3 β1 b k p k2 b 2k p k Φ 3 β1 b k p k2 p 2k p k nf k                            ……………………………………………..…….(1) where kp is the thermal conductivity of the particle, kb is the thermal conductivity of the base fluid and is the particle volume fraction in the suspension The thermal conductivity of the nanofluid is calculated from Hamilton& Crosser [24] using the following equation:       b k Φ p k b k b k1 p k Φ p k b k1 b k1 p k nf k                n nn …………………………………………………..(2) Where: knf is the thermal conductivity of the nanofluid, kp is the thermal Conductivity of the nanoparticles , kb is the thermal conductivity of the base fluid Furthermore, the thermal conductivity of the nanofluid is calculated from Wesley Charles –Williams [25]. 1Vol%) (T)(4.5503 b k nf k  …………………………………………………………………(3) One well – known formula for calculating the thermal conductivity of nanofluid is Timo Feera et al. [13]. b )k3(1 nf k  …………………………………………………………………………….……(4) Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 194 3-EXPERIMENTAL INVESTIGATION 3.1-Sample Preparation Nanofluid samples were prepared by dispersing pre – weighed quantities of dry particles in distilled water. The pH of each aqueous mixture was measured, the mixtures were then subjected to ultrasonic mixing (Sonics &Materials, Inc. Vibra - Cell VCX 750) for one hour to break up any particle aggregates. The acidic pH is much less than the iso electric point of these particles (6 – 8 for zirconium oxide and 5.5 – 8 for silver), thus ensuring a positive surface charge on the particles. The surface charge enhanced repulsion between the particles, which resulted in uniform dispersions for the duration of the experiments. Fig.(1) depicted an aqueous nanofluids Oxide (Zr2O3) and silver (Ag). The same preparation for micofluids and Fig.(2) shows an aqueous micofluids Oxide (Zr2O3) and silver (Ag). (A) (B) Figure (1): Aqueous nanofluids (A) containing zirconium Oxide(Zr2O3) and (B) containing silver (Ag) nanoparticles Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 195 (A) (B) Figure (2): Aqueous micro fluids (A) containing zirconium Oxide(Zr2O3) and (B) containing silver (Ag) micro particles 3.2-Thermal conductivity Measurement Since thermal conductivity is the most important parameter responsible for enhanced heat transfer many experimental works been reported on this aspect. Lee's disc technique was used for the measurement of the thermal conductivity for nanofluids and microfluds. The apparatus which is used in the measurement of the thermal conductivity is shown in the Figs.(3 and 4). Figs.(3) reveal the built – up cell which is used to measure the thermal conductivity, the cell contains three parts, on the two sides of the cell there is two copper discs (1 and 2) as shown in the figure. While the third part of the cell located between the two copper discs and contains the experimental fluid. Fig.(4) represents the test apparatus (Lee's disc apparatus) type (Griffin and George) with tested sample disc and some accessories to measure the temperature on both sides of the sample disc in order to calculate the thermal conductivity, the heater is switch on from the power supply with(V = 6 V and I = 0.2 A) to heat the copper discs ( 2 and 3) and the temperature of the all discs increases in nonlinear relationships and at different rates with the time according to its position from the heat source, and the temperatures were recorded every (5 minutes) until reach to the equilibrium temperature of all discs. Then the thermal conductivity can be calculated by using the following form Murthy et al [26] and Rondeauz & Bready [27]:                       2 Tds 2 1 1 Tds 2 1 1 d r 2 1 Te ds 1 T 2 T K ……………………………………………….(5) And can calculate the value of e as follows:            3 T 3 d 2 T 2 d 2 T 1 Tds 2 1 1 T 1 derπ2 3 T 1 Te 2 rπIV …………………………..(6) Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 196 The experimental results for the thermal conductivity were compared with the equations or models of thermal conductivity developed by researchers such as Yu and Chio model [23], Hamilton & Crosser model [24], Wesley Charles – Williams model [25] and Timo Feeva et al model [13], Figure (3): Testing cell Figure (4): Thermal conductivity test apparatus 4-RESULTS AND DISCUSSION In order to verify the accuracy and the reliability of the experimental apparatus , the thermal conductivity are experimentally measured for distilled water ethylene glycol ethanol before obtaining those of micro and nanofluids (Ag+ DW) , (Zr3O2+ DW). Fig.5 shows the variation of theoretical values with experimental values for thermal conductivity to three types of fluids (distilled water, ethylene glycol, methanol, ethanol). As it is seen from this figure, the deviation of the experimental data from the theoretical less than 5%. Figs. (6 and 7) show that the ratio of the thermal conductivity ( K nano/ K base) increases significantly with the increasing of concentration, and the relation between the thermal conductivity with the concentration is a leaner relation. The enhancement in the thermal conductivity were evaluated to be ( 7.66%,2.35%) for the Ag, Zr2O3 – distilled water nanofluid while reaches to (3.23%,1.02%) for the Ag, Zr2O3 – distilled water micro fluids at the concentration of (0.05 vol. %). The results obtained from these figures indicate that the silver particles have thermal conductivity higher than that of the Zirconium oxide particles. The experimental results for this investigation were compared with other data from published papers at the same field, very good agreement was found between the experimental data and model R.L. Hamilton, O.K. Crosser [11], is the closest to practical by difference does not exceed 1.25%. Thermal conductivity was increased for the nanofluids and microfluids which contains large particle size compared with that contains small particle size as shown in figs. (8 and 9), these figures show the effect of the particle size on the thermal conductivity. Figs. (10 and 11) shows a comparison between the experimental data for thermal conductivity of (Ag , Zr2O3 – distilled water ) nanofluids and micro fluids at (dp= 20, 30, 50 nm and 20, 30, 50 µm) particle size, this comparison shows the enhancement of the thermal conductivity for the two types of nanofluids are greater than two types of microfluids (Ag , Zr2O3 – distilled water ) and the effect of the particle size on this enhancement. It has been TT T Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 197 recognized that the addition of highly conductive particles can significantly increase the thermal conductivity of heat – transfer fluids. Particles in the microand nano – size range have attracted the most interest because of their enhanced stability against sedimentation and, as a result, reduction in potential for clogging a flow system . Furthermore the results showed that, the obtained thermal conductivities doubtlessly revealed that size and type particles was a key factor affecting conductive heat transport in suspensions. For nanofluids, despite the promise of enhanced stability due to the nanoscale size of particles, particle agglomeration state can have a profound effect on the resulting thermal conductivity of the suspension. Figs.(12) and (13) reveal the experimental data of thermal conductivity to nanofluids and microfluids for two types of particles Ag , Zr2O3 – distilled water. 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Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 200 Figure (5): Thermal conductive calibration results Figure.(5) Thermal conductive calibration results Figure (6): Thermal conductivity ratio of distilled water – based Ag nanofluid Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 201 Figure (7): Thermal conductivity ratio of distilled water – based Zr2O3 nanofluid Figure (8): Thermal conductivity ratio of distilled water – based Ag nanofluid With different particles diameter Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 202 Figure (9): Thermal conductivity ratio of distilled water – based Zr2O3 nanofluid With different particles diameter Figure (10): Experimental data for thermal conductivity of nanofluids versus particle size Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 203 Figure (12): Experimental data for thermal conductivity of microfluids versus particle size Figure (11): Experimental data for thermal conductivity of micro fluids versus particle size Al-Qadisiya Journal For Engineering Sciences, Vol. 7……No. 2 ….2014 204 Figure (13): Experimental dat for thermal conductivity of microfluid (Ag – DW ) and nanofluid (Ag – DW ) for different particle size Figure (14): Experimental dat for thermal conductivity of microfluid (Zr2O3 – DW ) and nanofluid (Zr2O3– DW ) for different particle size