Optical Thermal Lens Technique To Measure Thermo-Optical Properties of Nano-Engine Oil Lubricant

Faris Mohammed Ali

Department of Communication, Engineering Technical college\Najaf, Al-Fourat Al-Awssat Technical University, Kufa, Najaf, Iraq

E-mail\ ,

HP:009647704149998

Abstract:

Nano engine oil (Nanofluids), a mixture of nanoparticles or nanotube and fluids, have exceptional potential to enhancement their thermal properties. The single wall carbon nanotube (SWNT) was suspended in engine oil lubricant: Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30 with 0.5% volume fraction, and Titanium dioxide (TiO2) 18 nm was suspendedin engine oil lubricant: Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30 with 0.2% volume fraction. Sonication processing with high-powered pulses was used toensure the dispersion of nanotube and nanoparticles in good uniformity in the engine oil lubricant. The optical thermal lens technique was used to measurethermo-optical properties of nano-engine oil lubricant.The results show that the thermo-optical properties of the samples have higher than the base fluid (engine oil). In addition to, the particles materials have significant influence on thermo-optical properties, where it is increased with the single walled carbon nanotubes more than titanium dioxide nanoparticles.

Introduction:

superlative performance cooling is one of the most essential needs of many industrial technologies[1]. However, a primary limitation in developing energyefficient heat transfer fluids which have low thermal conductivity required for superlative performance cooling. wherefore, modern nanotechnology can produce nonmetallic or metallic particles of nano size dimensions, these nanomaterials have unique thermal, optical, mechanical,electrical and magnetic properties. Therefore, nanofluidscan beproduced by suspending nanomaterials with average sizes below 100 nm in base fluids[2]. The use of nanofluids in heat exchangers, especially in micro-cooling systems, may result in energy and cost savings and should facilitate the trend of device miniaturization[3]. The experimental work has been focused on measurements of thermal conductivity as a function of type of nanoparticles, size, concentration, and temperature. The most popular techniques for measuring thermal properties of nanofluids are the transient hot-wire method [4; 5; 6; 7; 8]3-ω method[9; 10] and temperature oscillation method [11; 12]. The effective thermal diffusivities and thermal conductivities of nanofluids were typically measured using a transient hot wire (THW) method, which is regard one of the most accurate ways to determine the thermal properties of nanofluids [13].The enhancement of thermal conductivity of CuO-water, Al2O3-water and Cu-Oil nanofluids have been reported by Eastman and Choi [14]by using the transient hot wire THW method. Ehsan-o-llahEttefaghi et al. have used Multi-walled carbon nanotube (MWCNTs) dispersed in engine oil SAE 20 W 50 as base fluid which is prepared by planetary ball mill. They have reported the thermal conductivity increased by 22.7% at 0.5 wt% concentration and the amount of flash point and pour point increased by 13% and 3.3%, respectively[15].

The hot wire-laser beam displacement technique havebeen proposed by Faris Mohammed A. and W. Mahmood Mat Yunus to measure thermal diffusivity and thermal conductivity of the aluminum and aluminum oxide nanoparticles dispersed inside distilled water, ethylene glycol (EG), and ethanol base fluids. They found that that the thermal conductivity and thermal diffusivity increased linearly with increasing volume fraction concentration of nanoparticles in the respective base fluids. In addition, the thermal conductivity and thermal diffusivity increased faster in the Al2O3 nanofluids than in all the three base fluids [16].

MohammadhassanVasheghani et al. studied the effect of Al2O3 phases on the enhancement of thermal conductivity and viscosity of nanofluids in engine oil by using hot wire method, their results showed that by adding 4wt% of α-Al2O3 and ɤ-Al2O3 nanoparticles to the base fluid engine oil thermal conductivity have increased by 31% and 37%,respectively. In addition, they were observed that the differences in thermal conductivity comes from higher specific surface area of ɤ-Al2O3compared to the α-Al2O3which is theresult of porosity difference[17]. Karthik R. et al. [18] have investigated the enhancement thermal conductivity of copper (II) oxide-DI water nanofluids using a tailor- made measurement device that uses the 3ωtechnique, they concluded that The enhancement in thermal conductivity over the base fluid for the tested conditions is observed to be 13 to 25%. A comparison between the measured data and the predicted ones using established correlations reveals that the deviation in prediction is within ±10%.

Recently a few optical techniques for measuring thermal conductivity or thermal diffusivity of nanofluids. Putnam et al.[19] have used an optical beam deflection technique for measurements of the thermal diffusivity of fluid mixtures and suspensions of nanoparticles with a precision of better than 1% . Veneruset al.proposed an optical technique called forced Rayleigh scattering to measure thermal diffusivity of Au nanoparticle suspension in water and an Al2O3 nanoparticle suspension in a petroleum oil [20]. Shaikhet al. used amodern laser flash technique (LFA 447) to measure the effectivethermal conductivity of exfoliated graphite, heat treated nanofibers, and CNTs in polyalphaolefin oil as the base fluid [21].

To the best of our knowledge there are few systematicstudies of thermal conductivity and thermal diffusivity reportedin the literature regarding the use of single walled carbon nanotubes (SWCNT)and Titanium dioxide TiO2 suspensions in engine oil lubricant (SAE 10W30)and (SAE 5W30), particularlyat smaller volume.

In the present work a new model of optical thermal lens techniquewas developed for measuring new thermo-optical propertiesof nanofluids.

Materials and Methods:

1-Theory

The optical thermal techniques have used electromagnetic radiation to induce non radiative de-excitation of excited states which have led to change in temperature of sample. This a rise in temperature can be measured by different techniques, these techniques have used laser beam as the excitation. Optical thermal lens techniques deserve attention because it is a high sensitivity optical technique. Furthermore, it is noninvasive, nondestructive, considerably faster and simpler than photothermal techniques which reported previously [19-21] and it does not require any particular sample treatment.in addition, it reduces the heat transfer due to radiation andconvection when compared to steady state techniques, since it consists of a transient method. Indeed, it has been used to obtain optical and thermal properties at room temperature of nanofluids and nanomaterials.

The optical thermal lens effect is caused by the deposition of heat via non-radiative decay processes after the laser beam has been absorbed by the sample which has Gaussian intensity profile (TEM00).

The first step in the development of the optical thermal lens modelis to consider the heat source profile Q(r) is proportional to the Gaussian intensity profile, which can be expressed as:

) (1)

Where, Pe(mW) is the excitation laser power, we (µm)is the excitation beam waist at the sample position.

By the heat conduction equation which is depend on the employed boundary condition that have been developed the infinitive aberrant model for the optical mode mismatched thermal lens configuration. Using the conditions the temporal evolutionof the temperature profile in the sample is given by[22]

(2)

In which Aethe optical absorption coefficient at the excitation beam wavelength (cm-1 ), Cthe specific heat (J K-1 g-1 ), ρ is the density (g cm-3) and tcthe characteristic optical thermal lens time constant (s) which is defined by:

(3)

Where D is thermal diffusivity (m2 s-1) and K is thermal conductivity(W/ m. K).

The temperature evolution of the optical thermal lens depends on the parameter tc given by Eq. (3), which is related to the thermal diffusivity D. Therefore, parameters Ae and D which are related to the amplitude and tcof the optical thermal lens signal, respectively, can be determined by optical thermal lens experiment.

However, this temperature rise, which carries a Gaussian profile, induces a slight distortion in the probe beam wave front that can be associated with the optical path length change of the sample with respect to the axis of the beam as:

(4)

In which is the phase shift induced when the probebeam passes through the optical thermal lens,is the probe beam wavelength, is the sample thickness andis the temperature coefficient of the optical length at the probe beam wavelength. Finally, using Fresnell diffraction theory, the probe beam intensity at the detector plane can be writtenas an analytical expression for absolute determinationof the thermo-optical properties of the sample as[22];

(5)

Where, and in which .

Here,

Here,(µm)is the probe beam radius at the nanofluid sample, Zcis the confocal distance of the probe beam, Z1 is the distance from the probe beam waist to the nanofluid sample, Z2 the distance between the nanofluid sample and the detector, I(t) is the temporal dependence of the probe beam intensity at the detector, I(0) is the initial value of I(t), and I(0) equal to I(t) when the transient time t or is 0, and is approximately the thermally induced phase shift of the probe beam (atr = 0 and r=) after passing through the nanofluid sample,which is given by:

(6)

It is important to note that the parameter have described the whole optical path length change induced by the excitation beam, that means for nanofluid samples (liquid) we have . While, for solid material it depends on several mechanisms such as the stress optical coefficient, end-face curvature, and the sample bulging during the illumination.

By using least square curve fitting of the optical thermal lens experimental data with Eq.(5),tcand θcan be determined.

In this project, we have used Zcis (2.5 cm), Z1 is (5.5 cm), is (198 µm) andis (45 µm). Therefore, m is 19.36, V is 2.2.

2-Experiment

The schematic diagram of the optical mode mismatched thermal lens experimental setup is shown in Figure 1, where these mode configuration has been shown the most sensitive experimental setup for the optical mismatched thermal lens measurements.This experimental arrangement used two laser beams with different spot sizes at the nanofluids sample position as shown in Figure 2. The measurement wasperformed bya CW He-Ne (2 mW) laser operated at wavelength of 632.8 nm was used as a probe laser beam and a 165 LG Argon-Ion laser (10 mW) operated at wavelength of 514 nm was used as an excitation source. The lasers were mounted on a stage completed with alignment facilities.

The optical mode mismatched thermal lens measurements were performed using timeresolved method. The time-resolved method permits the measurement of the development of the thermal lens in a short period oftime, and the advantage of this procedure is that it allows to measure the sample thermal diffusivity.

The excitation laser beamwas modulated by Shutter System SR470 then the excitation beam was focused by a lens (Plano-Convex PCX1304) of focal length of 50 mm to focus the excitation beam onto a nanofluids sample which is resides in a Cole-Parmer quartz cell with dimension of (20.5 x 10.5) mm. The quartz cell was fixed on a three-dimension position mechanism stage .The probe beam (He-Ne ) laser was focused by a lens (Plano-Convex PCX1304) of 60 mm focal length away from the quartz cell and it is aligned at asmall angle (about 2°) with respect to the excitation beam. A pinhole positioned in front of the position sensitive detector (PSD, S1880) (PSD2) to select the probe beam central part only.

the excitation beam is used to induce the thermal lens in the central part of the probe beam and a consequent change in its intensity in the position sensitive detector, PSD1.

The output voltage of the position sensitive detectors (PSDs) were coupled to a digital storage oscilloscope (Lecroy 9310A) to record the time evolution of TL signal. The LABVIEW software was used to capture the TL data from oscilloscope.

Fig. 1Schematic diagram of the optical mode mismatched thermal lens experimental setup

Fig. 2 Geometric diagram excitation and probe beams position

3-Prepare of Nanofluid Samples

Nanofluids sample are prepared by using onestep technique method, similar to the one reported by Choi [23]. With single step method (one step) technique the nanoparticles are directly dispersed in the base fluids in a single process. The single wall carbon nanotube (SWNT), 0.7-1.3 nm diameter (704113 ALDRICH, Sigma Aldrich Co. LLC, Malaysia),Titanium dioxide (TiO2), 18 nm (798525 ALDRICH, Sigma Aldrich Co. LLC, Malaysia) were suspended in engine oil lubricant as base fluid: Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30.The single wall carbon nanotube of volume fraction 0.5%, Titanium dioxide (TiO2) of volume fraction 0.2%nanoparticles are dispersed in engine oil lubricant were mixed and kept in an ultrasonic bath (SW12H)for more than 3 hours to ensure properly dispersion. Furthermore, the nanofluids is subjected to intensified ultra-sonication by immersing a probe type sonication (Scientz-IID, 950W) for 6 hours to achieve maximum possible de-agglomeration of particles. sodium deoxycholate (DOC) was used as a surfactant for the mixture SWNT with engine oil lubricant as reported by Wenseleers et al. [24], while, hexadecyltrimethylammonium bromide (CTAB) was used as a surfactant for the mixture Titanium dioxide (TiO2)withengine oil lubricant. A Transmission Electronic Microscopy TEM (Hitachi 7100 TEM) was used to measure the particle size, the particle distribution, and the morphology of SWNT and nanoparticles in the base fluids(engine oil lubricant).as shown in Figure 1-4.

Fig.1 TEM image single wall carbon nanotube (SWNT) dispersed in Fuchs TITAN universal HD SAE 10w/30 at volume fraction 0.5 %

Fig.2 TEM image single wall carbon nanotube (SWNT) dispersed in Fuchs TITAN GT1 pro-flex SAE 5w/30 at volume fraction 0.5 %

Fig.3 TEM image Titanium dioxide (TiO2) dispersed in Fuchs TITAN universal HD SAE 10w/30 at volume fraction 0.2 %

Fig.4 TEM image Titanium dioxide (TiO2) dispersed in Fuchs TITAN GT1 pro-flex SAE 5w/30 at volume fraction 0.2 %

Result and Discussion

The optical thermal lens effect of nanofluids was based on their laser induced heating and time resolved monitoring on the thermal effects. So, to verify and evaluate the reliability of the experimental measurement of optical thermal lens, firstly we measure the thermo-optical properties of engine oil lubricant unused, then compare this result with the literature result of engine oil lubricant and showed a good agreement with references[25; 26; 27]. The results have shown in Table1.

Table 1 Results ofengine oil lubricant unused

engine oil / Thermal
Diffusivity x10-8 (m2/s) / Reference value of Thermal Diffusivity x10-8 (m2/s) / Thermal Conductivity (W/m.K) / Reference value of `(W/m.K)
Fuchs TITAN SAE 10w/30 / 8.54 / 8.5325
8.5326
8.5527 / 0.144 / 0.14425
0.14527
Fuchs TITAN SAE 5w/30 / 8.57 / 8.5525
8.5727 / 0.145 / 0.14426
0.14627

The measurement of the thermo-optical propertiesof single walled carbon nanotube SWNT(0.7-1.3 nm diameter) and Titanium dioxide TiO2(18 nm) suspension in engine oil lubricant which are Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30nanofluid samples were conducted. The single walled carbon nanotube SWNT were prepared at volume fraction 0.5% and Titanium dioxide were prepared at volume fraction 0.2% suspension in different engine oil as base fluids; Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30.

Figures 1 to 4 show TEM for the SWNT and TiO2nanoparticle distribution of the sample in engine oil as base fluids (Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30) after 9 hours in the sonication process (ultrasonic bath and probe type sonication). The images 1 and 2 show that the SWNT were aggregated to form nanotubes clusters and evenly distributed in the engine oil base fluids. These TEM images reveal that the single walled carbon nanotubeare highly cluster-dispersed. while, the images 3 and 4 show that the TiO2 nanoparticles were aggregated to form nanoparticle clusters and evenly distributed in the engine oil. These TEM images show that the nanoparticles are highly cluster-dispersed with an average size of about 25-50 nm and are spherical in shape.

The thermally induced phase shift of the probe beam θ and the characteristic optical thermal lens time constanttc were obtained by fitting equation 5 to the normalized optical thermal lens time evolution data and finally the thermo physical properties (thermal diffusivity and thermal conductivity) can be calculated from equation 3. Where, the specific heat Cp have been determined by ordinary calorimetry and the density ρ have been determined by Archimedes' method. the experimental have been conducted at room temperature. Figures 5 and 6show the typical time evolution of optical thermal lens signals for the SWNTnano-lubricant engine oil (Fuchs TITAN SAE 10w/30) and TiO2 nano-lubricant engine oil (Fuchs TITAN SAE 5w/30) samples respectively, where the solid line represent the best fit of equation 5 to the experimental data and the symbols (o) denote to the experimental data.

The thermo-optical properties of nano-lubricant engine oil samples have listed in Table 2.

Table 2 Results ofthermo-optical properties of nano-lubricant engine oil

Nanofluid samples / θ / tc (s) / Thermal Diffusivity x10-8(m2/s) / Thermal Conductivity (W/m.K)
SWNT+SAE 10w/30 / 0.09861±0.0002 / 0.00342±0.00001 / 14.64±0.114 / 0.465 ±0.002
SWNT+ SAE 5w/30 / 0.09135±0.0001 / 0.00332±0.00003 / 15.23±0.158 / 0.489±0.003
TiO2+ SAE 10w/30 / 0.08736±0.0001 / 0.00441±0.00002 / 11.47±0.245 / 0.291±0.001
TiO2+ SAE 5w/30 / 0.08487±0.0003 / 0.00427±0.00004 / 11.83±0.188 / 0.315±0.003

The results of thermal diffusivity of SWNT(0.7-1.3 nm diameter) Nanotubes dispersion in Fuchs TITAN SAE 10w/30 and Fuchs TITAN SAE 5w/30 at volume fraction 0.5% were14.64x 10-8±0.114, 15.23 x 10-8 ± 0.158(m2/s)respectively. while Thermal conductivity were0.465 ±0.002, 0.489±0.003 (W/m.K) respectively. Inaddition, The results of thermal diffusivity of TiO2 (18 nm) nanoparticles dispersion in Fuchs TITAN SAE 10w/30and Fuchs TITAN SAE 5w/30 at volume fraction 0.2% were 11.47 x 10-8± 0.245, 11.83 x 10-8 ± 0.188 (m2/s) respectively. While, thermal conductivity were 0.291±0.001, 0.315±0.003 (W/m.K) respectively.

So, the enhancements in thermal diffusivity and thermal conductivity have an obvious increase by adding nanotubes and nanoparticles. This observation can provide an insight into the mechanism of thermal exchanger transport in nanofluids. We particularly mention the volume fraction of nanoparticles or nanotubes dependence of thermal diffusivity and thermal conductivity, because thermal diffusivity and conductivity would show more enhancements if the nanoparticles or nanotubes formed suspensions in base fluids (engine oil).Single Walled Carbon Nanotubes (SWNT)nanofluid exhibits 71.42% enhancement in thermal diffusivity with 0.5% volume fraction of nanotubes in Fuchs TITAN universal HD SAE 10w/30, while Single Walled Carbon Nanotubes (SWNT) nanofluid presents 77.71% enhancement with 0.5% volume fraction nanotubes in Fuchs TITAN GT1 pro-flex SAE 5w/30. Moreover, the enhancement in thermal conductivity were 222.91% and 237.24% for SWNT suspension in Fuchs TITAN universal HD SAE 10w/30 and SWNT suspension in Fuchs TITAN GT1 pro-flex SAE 5w/30 respectively.

The enhancement of thermo physical properties (diffusivity and conductivity) of TiO2 nanofluids suspension in Fuchs TITAN universal HD SAE 10w/30 and Fuchs TITAN GT1 pro-flex SAE 5w/30at volume fraction 0.2% were 34.3%, 38.03%, 102.08%, and117.24%, respectively.We observed also that SWNT suspension in Fuchs TITAN GT1 pro-flex SAE 5w/30 have higher thermal diffusivity and thermal conductivity values compared to the TiO2 nanoparticles in Fuchs TITAN GT1 pro-flex SAE 5w/30.The comparison between thermal diffusivityand conductivity of SWNT and TiO2 nanofluids in different base fluid at same volume fraction, the Fuchs TITAN GT1 pro-flex SAE 5w/30 base fluid has the highest thermal diffusivity and thermal conductivity.According to the results which are presented above, the nano (nanotube and nanoparticle) suspension in engine oildemonstrates some unique and novel thermal properties when compared to the traditional heat transfer of engine oil.There are several mechanisms that will enhance the thermal properties of nano-engine oil: Brownian motion of nano, interfacial liquid layer (liquid layer at liquid particle interface), nano- structuring / aggregation, and effects of nano clustering[28; 29].