Analysis of heat transfer of different nanofluids flow through an abrupt expansion pipe (original) (raw)
Extensive research has gone into enhancing the thermal efficiency of heat pipes using conventional fluids for over a decade. The enhanced thermal properties of heat pipes using nanofluids has also been researched upon by various researchers over the past few years. The study shows that the thermal characteristics of the heat pipe are enhanced using nanofluids in comparison to conventional working fluids. This paper summarizes our research on the thermal effect of four different nanofluids in heat pipe and identifies the possibility of nanofluid that can be successfully used to improve thermal efficiency of heat pipes.
Flow and heat transfer of nanofluids with temperature dependent properties
3rd Joint US-European …, 2010
Numerical simulations of laminar convective heat transfer with nanofluids in two different geometries involving a straight pipe and a 90 o curved pipe are presented. The Navier-Stokes and energy equations for an incompressible Newtonian fluid are solved in a body fitted coordinate system using a control-volume method. In the present work, the nanofluid is a mixture of water and alumina particles, and its thermophysical properties are considered as a function of temperature as well as particle concentration. The accuracy of the models employed for estimating the effective thermophysical properties of this nanofluid are first evaluated using available experimental data for heat transfer in a straight pipe. The same models are then employed for the simulation of flows in a curved pipe.
Internal convective heat transfer of nanofluids in different flow regimes: A comprehensive review
Physica A: Statistical Mechanics and its Applications, 2019
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Evaluation of Heat Transfer Mechanisms in Heat Pipe Charged with Nanofluid
Arabian Journal for Science and Engineering, 2019
The nanofluid is a colloidal solid-liquid mixture obtained by the dispersing nanoparticles with a high heat transfer coefficient in the base fluid. In general, metal, metal oxide, ceramic and magnetic nanoparticles are used in nanofluids. The nanoparticles suspended in the base fluid of heat pipes effectively increased the heat transfer rate and thermal conductivity properties of the base fluid. The nanofluids have been found to be acting much better for some problems such as sedimentation, erosion, clogging and pressure drop compared to common slurries. The energy transfer is carried out by two-phase heat transfer mechanism in heat pipes. There are many parameters and factors that have an effect in the boiling heat transfer coefficient. It is not easy to understand the positive and negative changes caused by nanofluids in this complex heat transfer mechanism. The surface geometry is a significant indicator on the boiling heat transfer mechanism. Investigation into nanofluid effects besides the surface geometry is very important in the experimental studies. In addition, it is known that nanofluids change the properties of the heater surface, apart from the thermophysical properties. The synthesis methods of nanofluids are presented in this article. Then, the physical and chemical mechanisms determining the long-term stability of nanofluids are explained in detail. Finally, some useful information about the use of nanofluids in heat pipes and pool boiling of nanofluids is given. The presented study also describes the pool boiling mechanism of nanofluids to understand the positive effects of nanofluids on the heat pipes heat transfer mechanism.
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.
Analysis of flow and thermal field in nanofluid using a single phase thermal dispersion model
Applied Mathematical Modelling, 2010
Flow and thermal field in nanofluid is analyzed using single phase thermal dispersion model proposed by Xuan and Roetzel [Y. Xuan, W. Roetzel, Conceptions for heat transfer correlation of nanofluids, Int. J. Heat Mass Transfer 43 (2000) 3701-3707]. The non-dimensional form of the transport equations involving the thermal dispersion effect is solved numerically using semi-explicit finite volume solver in a collocated grid. Heat transfer augmentation for copper-water nanofluid is estimated in a thermally driven two-dimensional cavity. The thermo-physical properties of nanofluid are calculated involving contributions due to the base fluid and nanoparticles. The flow and heat transfer process in the cavity is analyzed using different thermo-physical models for the nanofluid available in literature. The influence of controlling parameters on convective recirculation and heat transfer augmentation induced in buoyancy driven cavity is estimated in detail. The controlling parameters considered for this study are Grashof number (10 3 < Gr < 10 5 ), solid volume fraction (0 < / < 0.2) and empirical shape factor (0.5 < n < 6). Simulations carried out with various thermo-physical models of the nanofluid show significant influence on thermal boundary layer thickness when the model incorporates the contribution of nanoparticles in the density as well as viscosity of nanofluid. Simulations incorporating the thermal dispersion model show increment in local thermal conductivity at locations with maximum velocity. The suspended particles increase the surface area and the heat transfer capacity of the fluid. As solid volume fraction increases, the effect is more pronounced. The average Nusselt number from the hot wall increases with the solid volume fraction. The boundary surface of nanoparticles and their chaotic movement greatly enhances the fluid heat conduction contribution. Considerable improvement in thermal conductivity is observed as a result of increase in the shape factor.
A critical review of convective heat transfer of nanofluids
Renewable and Sustainable Energy Reviews, 2007
A nanofluid is a suspension of ultrafine particles in a conventional base fluid which tremendously enhances the heat transfer characteristics of the original fluid. Furthermore, nanofluids are expected to be ideally suited in practical applications as their use incurs little or no penalty in pressure drop because the nanoparticles are ultrafine, therefore, appearing to behave more like a single-phase fluid than a solid-liquid mixture. About a decade ago, several published articles focused on measuring and determining the effective thermal conductivity of nanofluids, some also evaluated the effective viscosity. There are only a few published articles on deriving the forced convective heat transfer of nanofluids. The purpose of this article is to summarize the published subjects respect to the forced convective heat transfer of the nanofluids both of experimental and numerical investigation.
Journal of Thermal Science and Technology, 2018
The present work is concerned of numerical simulation of three dimensional laminar forced and mixed convection of two nanofluids; 2 3-water and-water flowing through a horizontal tube submitted to a constant and uniform heat flux. Based on single-phase approach, three dimensional conservation equations of mass, momentum and energy with the appropriate boundary conditions have been solved using finite volume method with the schemes of spatial and temporal discretization of second order precision and by using the SIMPLER algorithm with the Tri-Diagonal Matrix Algorithm (TDMA). At a fixed Reynolds number = 300 and Grashof number equal to 0 and 5×10 5. The results show an increase in heat transfer ratio compared to pure water at several volume fractions for both alumina and copper based nanofluids. At a fixed volume fraction = 4%, the axial Nusselt number does not increase significantly in forced convection case. However, in mixed convection case the axial Nusselt number augments considerably especially with-water nanofluid. On the other hand, secondary flow and axial velocity are slightly affected by nanoparticles volume fraction. It is proved in this study that nanofluids can also contributes to optimise pipes compactness, using 2% and 4% of alumina and copper respectively dispersed in water flowing through a pipe with given length gives higher axial Nusselt number ratio compared to pipes larger length but containing pure water.
Correct interpretation of nanofluid convective heat transfer
International Journal of Thermal Sciences
Engineers and scientist have a long tradition in trying to improve the thermophysical properties of convective heat carriers such as water and transformer oil. Technological developments of the last decades allow the dispersion of particle of sizes ranging between 10 and 100 nm in these liquids. In a large number of recent studies the resulting nanofluids have been reported to display anomalously high increase of convective heat transfer. The present study compiles experiments from five independent research teams investigating convective heat transfer in nanofluid flow in pipes, pipe with inserted twisted tape, annular counter flow heat exchanger, and coil and plate heat exchangers. The results of all these experiments unequivocally confirm that Newtonian nanofluid flow can be consistently characterized by employing Nusselt number correlations obtained for singlephase heat transfer liquids such as water when the correct thermophysical properties of the nanofluid are utilized. It is also shown that the heat transfer enhancement provided by nanofluids equals the increase in the thermal conductivity of the nanofluid as compared to the base fluid independent of the nanoparticle concentration or material. These results demonstrate that no anomalous phenomena are involved in thermal conduction and forced convection based heat transfer of nanofluids. The experiments are theoretically supported by a fundamental similarity analysis of nanoparticle motion in nanofluid flow. where Nu denotes the Nusselt number (h l/k), GEO is some geometry
Heat transfer measurment in water based nanofluids
International Journal of Heat and Mass Transfer, 2018
Nanofluids are a class of heat transport fluids created by suspending nano-scaled metallic or nonmetallic particles into a base fluid. Some experimental investigations have revealed that the nanofluids have remarkably higher thermal conductivities than those of conventional pure fluids and are more suited for practical application than the existing techniques of heat transfer enhancement using millimeter and/or micrometer-sized particles in fluids. Use of nanoparticles reduces pressure drop, system wear, and overall mass of the system leading to a reduction in costs over existing enhancement techniques. The focus of this study is to determine the role of nanoparticle motion in the enhancement of the overall heat transfer coefficient of a nanofluid at different nanoparticle loadings. The enhancement of the heat transfer coefficient is determined experimentally by dispersing CuO nanoparticles (40 nm) with different particle loadings (0.25 wt% and 1 wt%) into water and then flowing the resulting nanofluid through a heated copper tube. The experimental results illustrated that numerous factors including Reynolds number and particle concentration are all capable of impacting the enhancement ratio. To further explain the impact of these variables on the hydrodynamic and thermal parameters of a nanofluid, we developed a CFD model using a Eulerian-Lagrangian approach to study the nature of both the laminar and turbulent flow fields of the fluid phase as well as kinematic and dynamic motion of the dispersed nanoparticles. The main goal is to provide additional information about the fluid and particle dynamics to explain the observed behavior in the experimentally observed trends of the heat transfer coefficient enhancement relative to both nanoparticle concentrations and fluid flow behavior. Our results indicate that heat transfer enhancement significantly depends on particle motion within the system and is highly dependent upon the position of nanoparticles relative to the tube wall.