New Measurements of the Apparent Thermal Conductivity of Nanofluids and Investigation of Their Heat Transfer Capabilities (original) (raw)
Related papers
Comparison of Heat Transfer and Fluid Dynamic Performance of Nanofluids
TechConnect Briefs, 2007
Many recent studies have shown that nanofluids with metallic nanoparticles as suspension increase the thermal conductivity of base fluid by a substantial amount. First, we investigated the rheological properties of SiO 2 , Al 2 O 3 and CuO nanofluids at different volume percentages at varying temperatures. The fluids were tested over temperatures ranging from-35˚C to 50˚C. The viscosity trends showed the great influence of temperature on various nanofluids. Also, we investigated the particle diameter effect (20 nm, 50 nm, 100 nm) on nanofluid viscosity. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in a turbulent regime. During analysis of the convection coefficient, the measured viscosity values of the nanofluids were used as well as the thermal conductivity and specific heats were used from the available correlations in the current literature. Heat transfer coefficients of nanofluids increase with volume concentration, for example, a typical enhancement of a heat transfer coefficient of a 6% concentration of 45 nm CuO is about 54% at a Reynolds number of 8,000. Similar results were investigated for aluminum and silicon oxide nanofluids in ethylene glycol/water base fluid. Pressure loss was observed to increase with nanoparticle volume concentration and also with increasing particle diameter. It was observed that an increase in particle diameter increased the heat transfer coefficient. Applications of nanofluids will be in heating building and in automobiles in northern climates.
Investigations of thermal conductivity and viscosity of nanofluids
International Journal of Thermal Sciences, 2008
A combined experimental and theoretical study on the effective thermal conductivity and viscosity of nanofluids is conducted. The thermal conductivity and viscosity of nanofluids are measured and found to be substantially higher than the values of the base fluids. Both the thermal conductivity and viscosity of nanofluids increase with the nanoparticle volume fraction. The thermal conductivity of nanofluids was also observed to be strongly dependent on temperature. Two static mechanisms-based models are presented to predict the enhanced thermal conductivity of nanofluids having spherical and cylindrical nanoparticles. The proposed models show reasonably good agreement with the experimental results and give better predictions for the effective thermal conductivity of nanofluids compared to existing classical models. Based on the calibration results from the transient hot-wire method, the measurement error was estimated to be within 2%. In addition, the measured values of the effective viscosity of nanofluids are found to be underestimated by classical models.
Experimental evaluation of heat transfer coefficient for nanofluids
2014
The paper reports the results of heat transfer experimental tests on nanofluids. Measurements were performed in a two-loop test rig for immediate comparison of the thermal performances of the nanofluid with the base-fluid. The convective heat transfer was evaluated in a circular pipe heated with uniform heat flux and with flow regimes from laminar to turbulent. Tests have been performed to compare the heat transfer capability of nanofluids and water at the same velocity or Reynolds number , and they have been compared with values calculated from widely used correlations. In particular ten different nanofluids and three base fluids (in addition to the water) have been used. The analysis of the experimental data shows a different behavior depending on the parameter used in the comparison, and, as a consequence, the addition of nanoparticles to the heat transfer fluid can result advantageous or not, depending on the specific point of view. Furthermore some classical correlations have been used to estimate the heat transfer coefficients, and the analysis shows that they are able to provide good agreement with the experimental data both for the nanofluid and water.
Nanofluids for Heat Transfer : An Analysis of Thermophysical Properties
2015
Nanofluids have emerged as a new class of fluids with special characteristics of enhanced heat transfer characteristics. It is designed by suspending nanoparticles of dimension ranging from 1nm-100nm into a base fluid like water ,ethylene glycol or oil. The volume fraction of particles under study ranges from 2% to 8%. A higher volume fraction results in the particles agglomerating as well as causing abrations in the walls through which it flows. Nanofluids for heat transfer has managed to overcome both these problems. The suspensions are more stable and cause lesser damage to the walls along with better heat transfer characteristics than the base fluids. It is therefore possible to design lighter and more compact heat exchangers as the quantity of the fluid required is much smaller than the base fluid. The suspension of metal and metal oxides in base fluids which are the conventional heat removing fluids, are the nanofluids under study in this paper. Investigating the thermophysica...
Thermal conductivity, viscosity and heat transfer process in nanofluids: A critical review
Journal of Composites and Compounds, 2020
Heat transfer efficiency has always been at the center of attractions for many researchers and industries, and demand for higher efficiency methods and materials are increased in the last decades. Among the different methods of heat transfer enhancement, using nanofluids has proven to be an effective technique. In the present paper, the properties of nanofluids including viscosity, thermal conductivity as well as convective heat transfer are discussed and useful conclusions about the reported results by different researchers are presented. The effect of volume fraction, temperature, size and shape of particles, base fluid properties, and other factors on viscosity, and thermal conductivity of nanofluids are reviewed. Also, in the present manuscript, the methods of stable nanofluid preparation, and the effective factors on the stability of nanofluids are exhibited in detail. Besides, a summarized number of experimental and mathematical studies on the properties, and stability of nanofluids are listed, compared, and analyzed. The works about the Nusselt number in fluids and nanofluids are presented in detail to determine the future challenges of nanofluids.
A comprehensive review of last experimental studies on thermal conductivity of nanofluids
Journal of Thermal Analysis and Calorimetry, 2015
C p,nf Specific heat capacities of nanofluid C p,np Specific heat capacities of nanoparticle C p,bf Specific heat capacities of base fluid t Time T Temperature (°C) a Aspect ratio of nanoparticles Nanoparticles Base fluid Al 2 O 3 Water Fe 3 O 4 Oil (engine oil) ZnO (zinc oxide) Diesel CuO Glycol TiO 2 Ethylene glycol SiO 2 Polyethylene glycol (PEG)
A Comprehensive Review on Thermal Conductivity and Viscosity of Nanofluids
Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 2022
The innovation of nanofluids, a novel working fluid, has presented the development of heat transfer properties in machining, automotive engine cooling systems, pumping power and others to optimize the overall system. Nanofluids have pulled in scientists' cogitation from various fields in designing new thermal systems for different engineering applications due to their distinctive thermophysical properties and prospective applications. Long term stability, improved thermal conductivity, and viscosity are the principal fundamental expectations in nanofluids research to achieve better heat transfer performance. In the previous couple of decades, various investigations have been completed to explore the nanofluids properties augmentation. For instance, kerosene-based oleic acid-coated Fe3O4 nanofluids showed 300% improvement of thermal conductivity, and water-based single-walled carbon nanotube revealed 320% improvement of viscosity. This paper presents a survey of recent exploratio...
Energy has been rated as the single most important issue facing humanity in the current as well as next 50 years. Securing clean energy has become the top priority of most developed countries. Considering the rapid increase in energy demand worldwide, intensifying the heat transfer process and reducing energy loss due to ineffective use have become an increasingly important task. Fundamentally, energy conversion and transportation occur at atomic or molecular levels, Nanoscience and nanotechnology are expected to play a significant role in revitalizing the traditional energy industries and stimulating the emerging renewable energy industries. Nanofluid is a modern engineering heat transfer fluid with superior potential for enhancing the heat transfer performance of conventional fluids such as water, ethylene glycol and oils. It is consisting of solid nanoparticles with sizes typically of 1-100 nm suspended in base fluids. Many attempts have been made to investigate its important thermal properties, i.e. thermal conductivity; however, no definitive agreements and idea have emerged about this property. This article reports the effect of different nanomaterial on the thermal conductivity enhancement of nanofluids experimentally. TiO 2 , Fe 3 O 4 and Al 2 O 3 nanoparticles dispersed in water and ethylene glycol with volume concentration of 1-7.5 vol. % is used in the present study. A transient hot-wire apparatus (KD2 pro) is used for measuring the thermal conductivity of nanofluids. The results show that all the heat transfer fluids show an increase in thermal conductivity with the addition of nanoparticles in it. The measured thermal conductivity of nanofluids increased as the particle concentrations increased and are higher than the values of the base liquids. This confirms the effect of volume concentration of nanoparticles on the thermal conductivity enhancement.
Influence of Viscosity of nanofluids on heat transfer Rate
Heat exchangers are devices for almost all manufacturing, power production and automobile applications. In this paper, the influence of dynamic viscosity on heat transfer characteristics of pure water and water mixed with copper oxide, Iron oxide and aluminum oxide nanoparticles with different mass concentration in a horizontal circular pipe under constant heat flux condition are studied. All the nanofluids are made in three different mass concentrations i.e. 0.5%, 1.0%, 1.5 % and 2%. Influence of nanofluid temperature on dynamic viscosity is presented. The results show that when the mass concentration percentage is increasing, the viscosity is also increasing.