Experimental investigation of convective heat transfer coefficient of Al2O3/water nanofluid at lower concentrations in a car radiator

For many years, water and ethylene glycol were used as conventional coolants in automotive car radiators, but these coolants offer lower thermal conductivity than is required. This study is focused on the application of water‐based Al₂O₃ nanofluid at lower concentrations in a car radiator. The Al₂O₃ nanoparticles with an average diameter of 50 nm are dispersed in demineralized water at four different volume concentrations (0.1 vol. % to 0.4 vol. %) without any dispersant or stabilizer. Flow rate is varied in the range of 2 l/min to 5 l/min and inlet coolant temperature to the radiator is set to 50 °C, 60 °C, and 70 °C. The results show that the heat transfer coefficient increases with an increase in particle concentration, flow rate, and inlet temperature of coolant and the maximum increase in heat transfer coefficient is 45.87 % compared to pure water. However, the Nusselt number increases with the increase in particle concentration, Reynolds number, and inlet temperature of the coolant. In addition with the experimental study, a regression analysis is performed by using the ANOVA method and generates a correlation for the convective heat transfer coefficient.     

Experimental study on the thermo-physical properties of car engine coolant (water/ethylene glycol mixture type) based SiC nanofluids

The engine coolant (water/ethylene glycol mixture type) becomes one of the most commonly used commercial fluids in cooling system of automobiles. However, the heat transfer coefficient of this kind of engine coolant is limited. The rapid developments of nanotechnology have led to emerging of a relatively new class of fluids called nanofluids, which could offer the enhanced thermal conductivity (TC) compared with the conventional coolants. The present study reports the new findings on the thermal conductivity and viscosity of car engine coolants based silicon carbide (SiC) nanofluids. The homogeneous and stable nanofluids with volume fraction up to 0.5 vol.% were prepared by the two-step method with the addition of surfactant (oleic acid). It was found that the thermal conductivity of nanofluids increased with the volume fraction and temperature (10–50 °C), and the highest thermal conductivity enhancement was found to be 53.81% for 0.5 vol.% nanofluid at 50 °C. In addition, the overall effectiveness of the current nanofluids (0.2 vol.%) was found to be ~ 1.6, which indicated that the car engine coolant-based SiC nanofluid prepared in this paper was better compared to the car engine coolant used as base liquid in this study.     

Performance investigation of an automotive car radiator operated with nanofluid-based coolants (nanofluid as a coolant in a radiator)

Water and ethylene glycol as conventional coolants have been widely used in an automotive car radiator for many years. These heat transfer fluids offer low thermal conductivity. With the advancement of nanotechnology, the new generation of heat transfer fluids called, “nanofluids” have been developed and researchers found that these fluids offer higher thermal conductivity compared to that of conventional coolants. This study focused on the application of ethylene glycol based copper nanofluids in an automotive cooling system. Relevant input data, nanofluid properties and empirical correlations were obtained from literatures to investigate the heat transfer enhancement of an automotive car radiator operated with nanofluid-based coolants. It was observed that, overall heat transfer coefficient and heat transfer rate in engine cooling system increased with the usage of nanofluids (with ethylene glycol the basefluid) compared to ethylene glycol (i.e. basefluid) alone. It is observed that, about 3.8% of heat transfer enhancement could be achieved with the addition of 2% copper particles in a basefluid at the Reynolds number of 6000 and 5000 for air and coolant respectively. In addition, the reduction of air frontal area was estimated.     

Experimental investigation on the effect of SiO2 secondary phase on thermo-physical properties of SiC nanofluids

Nanofluids (NFs), wherein solid nanoparticles (NPs) are dispersed in traditional heat exchange fluids, are recognized for improving the performance of traditional fluids by enhancing their thermal conductivity (TC). The presence of impurities or undesired phases in commercial NPs may influence the thermo-physical properties of NFs including TC and viscosity, which makes it difficult to understand the real effect of NPs on heat transport characteristics of NFs. Moreover, the presence of these impurities in commercial NPs is unavoidable and their removal from commercial NPs with no negative impact on composition of NPs is challenging. To study the impact of impurities on thermo-physical properties of NFs a systematic experimental work was performed using commercial α-SiC and SiO₂ NPs as the secondary phase as it commonly co-exists in commercial SiC batches. For this purpose, a series of NFs containing 9 wt% of α-SiC/SiO₂ NP mixture with different content of SiO₂ NPs from 5 to 50% were fabricated and investigated. The results show that as the undesired impurity phase (SiO₂) increases, TC of NFs decreases slightly while viscosity increases dramatically. This may be a sound path to tuning the viscosity of the NFs while the achieved high TC is mildly influenced by the secondary phase.     

A time variant investigation on optical properties of water based Al2O3 nanofluid

Optical properties of nanofluids are vital for calculating performance of a Direct Absorption Solar Collector (DASC). Characteristics of nanofluids are not constant; they vary with time and growth of nanoparticles. For current investigation, nanofluids were prepared to obtain considerable stability. Stability ratio of our nanofluids was 100 times larger than the threshold limit. Here, we have investigated aggregation process and its effect on optical characteristics of the nanofluids using Transmission Electron Microscopy (TEM) imaging, Dynamic Light Scattering (DLS) approach and UV–visible spectroscopy. Steps of aggregation are broadly described with TEM images. Our results indicate that extinction coefficients of the nanofluids reduce rapidly with time within visible to near IR region. Quasi Crystalline (QC) and Rayleigh Approaches were used to compare the experimental behavior of optical properties of nanofluids. It was found that both of these approaches are weak to predict the optical behavior, especially at UV region and scattering of light is found responsible for high extinction with the experimental results. More experimental effort is still required to get an appropriate explanation.     

Experimental investigation of free single jet impingement using Al2O3-water nanofluid

Four volume fractions Al₂O₃-water nanofluids (0.5%, 1%, 1.5% and 2%) are introduced into free single jet impingement experiment as working fluids. The Reynolds numbers, impact angles and nozzle-to-plate distances (H/D) are variable for investigating the heat transfer performance. As to get observation of flow characteristics in nanofluid, heat transferring performance would be studied in this case. Experimental results show that there is a relationship between convective heat transferring coefficient and nanoparticles suspendability within base fluid. Convective heat transfer coefficient is proportional to the extent of nanoparticles concentration, Reynolds number while it decreases with the increasing angle of impacting. In addition, considering the influence of the suspended nanoparticles and the condition of impinging jet, a heat transfer correlation has been proposed combining the influence of the suspended nanoparticles and the condition of impinging jet.     

Experimental and analytical investigation on an automobile radiator with CuO/EG‐water based nanofluid as coolant

In the present study, experimental and analytical thermal performance of automobile radiator using nanofluids is investigated and compared with performance obtained with conventional coolants. Effect of operating parameters and nanoparticle concentration on heat transfer rate are studied for water as well as CuO/EG‐water based nanofluid analytically. The results are presented in the form of graphs showing variations of net heat transfer rate for various coolant flow rate, air velocity, and source temperature for various CuO/EG‐water based nanofluids. Experimental results indicate that with the increase in coolant flow rate and air velocity, heat transfer rate increases, reaches maximum and then decreases. Experimental investigation of a radiator is carried out using CuO/EG‐water based nanofluids. Results obtained by experimental work and analytical MATLAB code are almost the same. Maximum absolute error in water and air side is within 12% for all flow condition and coolant fluids. Nusselt number of nanofluid is calculated using equation number 33[9]. The results obtained from experimental work using 0.2% volume CuO/EG‐water based nanofluids are compared with the results obtained from MATLAB code. The results show that the maximum error in the outlet temperature of the coolant and air is 12% in each case. Thus MATLAB code can be used for different concentration of nanofluids to study the effect of operating parameters on heat transfer rate. Thus MATLAB code developed is valid for given heat exchanger applications. From the results obtained by already validated MATLAB code, it is concluded that increase in coolant flow rate, air velocity, and source temperature increases the heat transfer rate. Addition of nanoparticles in the base fluid increases the heat transfer rate for all kind of base fluids. Among all the nanofluid analyzed in this study, water‐based nanofluid gives highest value of heat transfer rate and is recommended for the heat exchanger applications under normal operating conditions. Maximum enhancement is observed for ethylene glycol‐water (4:6) mixture for 1% volume concentration of CuO is almost equal to 20%. As heat transfer rate increases with the use of nanofluids, the heat transfer area of the radiator can be minimized.     

Experimental study on thermal performance of optimum PG brine as a radiator coolant

The present study deals with the experimental impact of an alternative heat transfer fluids for overall performance improvement for radiators. Water and water mixed with anti‐freezing agents such as ethylene glycol (EG) and propylene glycol (PG) are the traditional coolants for an automotive radiator. Comparison of experimental and numerical analysis of optimum brine solution, that is 25% of propylene glycol and water as coolant for the rectangular fin radiator, has been well discussed. A closed loop test rig was designed, and fabricated with a wind tunnel section to achieve uniform velocity at the test section of the rectangular radiator and was tested for performance. Experimental runs were conducted at varying operating temperatures which included the runs for water, and an optimum propylene glycol brine solutions at 70 °C and 80 °C with various flow rates. Results show the energy performance of an optimum brine solution was nearly similar to that of water at high temperatures. The Nusselt number, heat transfer coefficient, and heat transfer rate for an optimum propylene glycol brine is nearly the same as water at 80 °C with a maximum deviation of 15%, 5.7%, and 6.6%, respectively, for theoretical and experimental result comparisons. Air side and coolant side pressure drops had a maximum deviation of 3.66% and 6.6%, respectively. Air and coolant exit temperatures had a deviation of 5% and 3.5%, respectively, with an air frontal velocity of 4.6 m/s in a rectangular fin radiator for an optimum brine solution used as coolant for the automotive radiator. The optimum propylene glycol brine may be environmentally beneficial.     

Experimental investigation of Al2O3–MgO hot hybrid nanofluid in a plate heat exchanger

Exergy–energy analysis of the plate heat exchanger is experimentally performed with different Al₂O₃–MgO hybrid nanofluid (HyNf) as a hot fluid. There were six combinations of fluids, namely, deionized (DI) water, ethylene glycol–DI water brine (1:9 volume ratio), propylene glycol–DI water brine (1:9 volume ratio), base fluids and their respective Al₂O₃–MgO (4:1 particle volume ratio) HyNfs of 0.1% total volume concentration. The effects of different flow rates and hot inlet temperatures on the heat transfer rate, heat transfer coefficient, pump work, irreversibility, and performance index (PI) are investigated. It is witnessed that the heat transfer rate, heat transfer coefficient, pump work, and irreversibility enhances with the flow rate and nanoparticle suspension. While the PI declines with a rise in the flow rate, the heat transfer rate, heat transfer coefficient, PI, and irreversibility rise up maximum for MgO–alumina (1:4) DI water HyNf upto 11.8%, 31.7%, 11.1%, and 4.05%, respectively. The pump work enhances upto 1.6% for MgO–alumina (1:4)/EG–DI water (1:9) HyNf.     

Kinetic investigation on butanol steam reforming over Ru/Al2O3 catalyst

Steam reforming of biomass-derived oxygenates is an attractive technique for the renewable production of hydrogen (H₂). In this work, steam reforming of n-butanol – a representative of bio-oxygenates – was studied over commercial 5% Ru/Al₂O₃ catalyst in a fixed-bed reactor. Kinetics of butanol reforming was investigated between temperatures 623 and 773 K at steam/carbon (S/C) ratio equal to 33.3 mol/mol. The W/F_A0 ratio (W: mass of catalyst, F_A0: molar flow rate of butanol in feed) was varied between 3.3 and 16.7 g h/mol. At T = 773 K, butanol conversion and H₂ yield were 93.4% and 0.61 mol/mol. Evaluation of the kinetic data showed that reaction order with respect to butanol was unity. The activation energy for the investigated reaction was 78 kJ/mol. Finally, a Langmuir-Hinshelwood model that assumed the surface reaction between the adsorbed reactants as rate-determining was used to describe the kinetic data.     

Thermal conductivity measurement of methanol-based nanofluids with Al2O3 and SiO2 nanoparticles

In this study, the methanol-based nanofluids with Al₂O₃ and SiO₂ nanoparticles are prepared by dispersing nanoparticles in pure methanol using an ultrasonic equipment. The main objective of this paper is to measure the thermal conductivity of the methanol-based nanofluids. We have also measured the zeta potential, particle size and Tyndall effect for the present nanofluids. The transient hot-wire method is applied for measuring the thermal conductivity of methanol-based nanofluids. The measurement uncertainty in repeatability is obtained as 1.95% for deionized (DI) water and 1.34% for pure methanol, respectively. The effective thermal conductivity of methanol-based nanofluids is measured at a temperature of 293.15 K. The results show that the thermal conductivity increases with an increase of the nanoparticle volume fraction, and the enhancement is observed to be 10.74% and 14.29% over the basefluid at the volume fraction of 0.5vol% for Al₂O₃ and SiO₂ nanoparticles, respectively. Clustering of nanoparticles is considered to be the main reason for the thermal conductivity enhancement.     

Characterization of molten salt doped with different size nanoparticles of Al2O3

This paper aims to study the effect on the characteristics of molten salt because of the dispersion of different size nanoparticles of Al₂O₃. The eutectic mixture of 54 wt% KNO₃ and 46 wt% NaNO₃ was selected as the base salt. Five different size nanoparticles of Al₂O₃, 80, 135, 200, 300, and 1000 nm, were dispersed into the base salt at a mass concentration of 1% to make the nanomaterials by a two‐step method, respectively. Thermal properties of the base salt and the samples with Al₂O₃ nanoparticles, including the melting point temperature, fusion heat, specific heat capacity, and thermal diffusivity, were measured with differential scanning calorimeter (DSC) and Xenon Flash Apparatus (XFA). On the basis of the measured specific heat capacities and thermal diffusivities, their thermal conductivities in the solid state were calculated at discrete specified temperatures. The results showed that the dispersions of 200‐ and 135‐nm Al₂O₃ nanoparticles could enhance the average solid and liquid specific heat capacities by up to 17.2% and 19.7%, respectively. The research on thermal diffusivity and thermal conductivity also verified that the influences of different size nanoparticles were different. Although no new strong intensity peaks or peak position variations were found in the diffraction patterns of the two samples with 80‐ and 1000‐nm nanoparticles of Al₂O₃, the larger deviations in the lower wavenumber region still meant possible crystalline structure variation because of the dispersion of Al₂O₃ nanoparticles. Scanning electronic microscope (SEM) images showed the inhomogeneity and the agglomeration of dispersed nanoparticles in the base salt, and the formation of a nanolayer around the nanoparticles could be a possible explanation to the thermal‐physical property variation.     

Experimental investigation of the thermophysical properties of AL2O3-nanofluid and its effect on a flat plate solar collector

Experimental investigations have been carried out for obtaining the thermophysical properties of 60:40 (by mass) ethylene glycol/water mixture and water based alumina nanofluids. The effect of density and viscosity on the pumping power for flat plate solar collector has been investigated as well. Nanofluids of 0.05–0.1%v/v concentrations were prepared and characterized. Water based alumina nanofluids were found more preferable against sedimentation and aggregation than ethylene glycol/water mixture based nanofluids. The measured thermal conductivities of both types of the nanofluids increased almost linearly with concentration and are consistent in their overall trend with previous works done at lower concentrations by different researchers. In contrast to thermal conductivity, viscosity measurements showed that the viscosity of the Al₂O₃–water nanofluids exponentially decreases with increasing temperature. Furthermore, the measured viscosities of the Al₂O₃–water nanofluids showed a non-linear relation with concentration even in the low volume concentration except 0.05%v/v at below 40 °C. On the other hand, Al₂O₃–EG/water mixture exhibited Newtonian behavior. Existence of a critical temperature was observed beyond which the particle suspension properties altered drastically, which in turn triggered a hysteresis phenomenon. The hysteresis phenomenon on viscosity measurement, which is believed to be the first observed for EG/water-based nanofluids, has raised serious concerns regarding the use of nanofluids for heat transfer enhancement purposes. Results suggest that nanofluids can be used as a working medium with a negligible effect of enhanced viscosity and/or density. Results also show that the pressure drop and pumping power of the nanofluid flows are very close to that of the base liquid for low volume concentration.     

保温材料热物性测试的实验及数值研究

针对保温材料导热系数低,采用常规的导热系数测试方法难以获得准确结果的问题,根据瞬态法导热系数测试原理,对常功率平面热源法进行了研究。建立传热的二维瞬态数学模型,借助FLUENT有限体积软件对常功率平面热源法中试样的温度分布和热量传递规律进行数值模拟,开发了一套保温材料导热系数测试装置。测试结果与文献数据能较好的吻合,最大误差不超过4％。测试结果可靠,测试精度较高。     

封闭腔内Al_2O_3-EG纳米流体自然对流传热特性的数值研究

对梯形封闭腔内Al2O3-EG纳米流体自然对流传热进行了数值模拟,讨论了封闭腔尺寸比、瑞利数、纳米颗粒体积分数以及布朗运动对自然对流流动与传热特性的影响。数值模拟结果表明在考虑布朗运动时,腔体尺寸比与瑞利数对流动传热均有很大影响,且尺寸比为0.5时,对流换热平均Nusselt数达到最大值。随着纳米颗粒体积分数的增加,纳米流体换热效果逐渐增强;但当忽略布朗运动时,添加纳米颗粒削弱了换热效果。     

基于模板法制备氧化铝纤维及其石蜡复合相变材料热性能

石蜡是一种高储热密度的有机相变材料,但是热导率低和易泄漏的缺点限制其进一步发展。为提高石蜡的导热和防泄漏性能,本研究以天然纤维为模板制备了具有高导热性的纤维状氧化铝导热填料,通过真空浸渍混合法制备了氧化铝纤维/石蜡复合相变材料,并对其形貌、热导率、相变循环稳定性、防泄漏性能以及热响应性能进行测试。结果表明,随着填料含量的增加,复合相变材料的导热系数近似线性增加。1200℃高温烧结形成的α型Al₂O₃比1000℃低温烧结γ型Al₂O₃具有更高的导热性能,且α型氧化铝纤维填充量达到45%(质量分数,余同)时,导热系数达到最高值为0.69 W/(m·K),是纯石蜡的2.9倍。通过对3种不同填充量Al₂O₃纤维进行100次的热循环测试,复合相变材料的相变焓值基本不变,说明了其具有良好的热循环稳定性。同时对复合相变材料的防泄漏性能以及热响应性能进行测试,结果显示30%和45%填料的α型Al₂O₃纤维均具有较好的防泄漏以及快...     

Numerical investigation of hydrogen production via autothermal reforming of steam and methane over Ni/Al2O3 and Pt/Al2O3 patterned catalytic layers

In this study a numerical analysis of hydrogen production via an autothermal reforming reactor is presented. The endothermic reaction of steam methane reforming and the exothermic combustion of methane were activated with patterned Ni/Al₂O₃ catalytic layer and patterned Pt/Al₂O₃ catalytic layer, respectively. Aiming to achieve a more compacted process, a novel design of a reactor was proposed in which the reforming and the combustion catalysts were modeled as patterned thin layers. This configuration is analyzed and compared with two configurations. In the first configuration, the catalysts are modeled as continuous thin layers in parallel, while, in the second configuration the catalysts are modeled as continuous thin layers in series (conventional catalytic autothermal reactor). The results show that the pattern of the catalyst layers improves slightly the hydrogen yield, i.e. 3.6%. Furthermore, for the same concentration of hydrogen produced, the activated zone length can be decreased by 38% and 15% compared to the conventional catalytic autothermal reforming and the configuration where the catalysts are fitted in parallel, respectively. Besides, the oxygen consumption is lowered by 5%. The decrement of the catalyst amount and the oxygen feedstock in the novel studied design lead to lower costs and compact process.     

Experimental investigation of the thermal transport properties of graphene oxide/Co3O4 hybrid nanofluids

The in-situ growth and chemical co-precipitation method was used for the synthesis of uniform dispersion of Co₃O₄ nanoparticles on the graphene oxide (GO) nanosheet. The reductions of aqueous cobalt chloride in the presence of GO with sodium borohydrate result in the formation of hybrid GO/Co₃O₄ nanoparticles. The synthesized GO/Co₃O₄ nanoparticles were characterized using X-ray power diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The hybrid nanofluids were prepared by dispersing synthesized GO/Co₃O₄ nanoparticles in water, ethylene glycol, and ethylene glycol/water mixtures. The properties such as thermal conductivity and viscosity were estimated experimentally at different volume concentrations and temperatures. The thermal conductivity enhancement of water-based nanofluid is 19.14% and ethylene glycol-based nanofluid is 11.85% at 0.2% volume concentration and at a temperature of 60 °C respectively compared to their respective base fluids. Similarly, the viscosity enhancement of water-based nanofluid is 1.70-times and ethylene glycol-based nanofluid is 1.42-times at 0.2% volume concentration and at a temperature of 60 °C respectively. The obtained thermal conductivity and viscosity data is compared with the literature values.     

Experimental investigation on the effect of MgO and TiO2 nanoparticles in stepped solar still

This work aims at augmenting the amount of potable water using MgO and TiO₂ in stepped solar still. Experiments were carried out for the climatic conditions of Chennai, India, with two different concentrations of nanofluids inside a stepped basin under three different cases. Results show that there is an improvement in yield of fresh water from stepped solar still by 33.18% and 41.05% using 0.1% and 0.2% volume concentration of TiO₂ nanofluid, respectively, whereas the freshwater yield from stepped still with MgO nanofluids improved by 51.7% and 61.89%. Furthermore, the economic analysis revealed that the cost of potable water from the modified solar still reduced from 0.029 to 0.016 $/kg. Similarly, the useful annual energy, yearly cost per kilogram, and annual cost per kilowatt hour are significantly profitable with the use of MgO nanofluid in the stepped basin and found as 512.46 kWh, 0.025 $/kg, and 0.026 $/kWh, respectively. It is also found that the cost of potable water from the modified still significantly increases as the amount of fresh water produced is decreased with increased fabrication cost of the solar still.