A numerical investigation of natural convection heat transfer of copper-water nanofluids in a rectotrapezoidal enclosure heated uniformly from the bottom wall (original) (raw)
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International Communications in Heat and Mass Transfer, 2019
This paper deals with heat transfer and fluid flow of natural convection in enclosures (square enclosure and enclosures with concave/convex walls) filled with water based Cu, and subjected to a constant imposed wall temperature. The governing equations of momentum and energy are formulated using the dimensionless form of transport equations in bipolar coordinates for a laminar two-dimensional incompressible and Newtonian flow which is expressed in terms of stream-function, vorticity and temperature. The resulting equations are numerically solved using the finite volume method (FVM) implemented in an in house-built computer code. The key parameters governing the problem are the Rayleigh number up to 10 5 , the Prandtl number of 6.2 and nanoparticles' volume fraction from 0 to 0.2. The relevant results are presented in terms of isotherms and streamlines. It is found that the heat transfer increases with nanoparticles' volume fraction for the entire range of Rayleigh number considered. Besides this, heat transfer in the square enclosure remains better than for the other enclosures with curved walls.
International Journal of Simulation Modelling, 2012
Numerical analysis is performed to examine the heat transfer enhancement of Au, Al 2 O 3 , Cu and TiO 2 water-based nanofluids. The analysis uses a two-dimensional enclosure under natural convection heat transfer conditions and has been carried out for the Rayleigh number range 10 3 ≤ Ra ≤ 10 5 , and for the nanoparticles' volume fraction range 0 ≤ φ ≤ 0,10. The governing equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. Highly accurate numerical results are presented in the form of average Nusselt number and heat transfer enhancement. The results indicate clearly that the average Nusselt number is an increasing function of both, Rayleigh number and volume fraction of nanoparticles. The results also indicate that heat transfer enhancement is possible using nanofluids in comparison to conventional fluids, resulting in the compactness of many industrial devices. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.
Enhancement of Heat Transfer in a Cavity Filled with Cu-water Nanofluid
This paper summarizes a numerical study of natural convection in a square cavity with a corner heater filled with water based nanofluid (water with Cunanoparticles). Finite volume method is used for solving momentum and energy equations in the form of stream function-vorticity. One wall of the enclosure is isothermal but its temperature is colder than that of heaters while the remaining walls are adiabatic. Calculations were performed for Rayleigh number (10 3 ≤ Ra≤ 10 6); dimensionless lengths of heater in x and y directions (0.25 H≤ H x ≤ 0. 5 H, 0.25 H ≤ H y ≤ 0.5 H) and volume fraction of nanoparticles (0 ≤ φ ≤ 0.1). The results indicate that dimensionless lengths of heater are an important parameter affecting the flow pattern and temperature field. Nusselt number increases with increasing both the Rayleigh number. It is also observed that at a given Rayleigh number and definite dimensionless lengths of heaters, the average Nusselt number increases linearly with the increase in the solid volume fraction of nanofluid.
Procedia Engineering, 2014
The existing work is focused on the numerical modelling of mixed convection of Cu-water nanofluid in a square enclosure filled with non-darcian fluid saturated porous medium. The enclosure object has cooled vertical walls and insulated horizontal walls. Finite volume method has been employed to solve the generalised Darcy-Brinkmann Forchheimer extended momentum and energy equations. The parametric study has been taken out for wide ranges of Richardson number, Darcy number and solid volume fraction. The performance of nanofluid is tested inside an enclosure by using solid volume fraction and compared with respect to base fluid (water). A fair degree of precision can be found between the present and previously published work. The results are presented in the form of streamlines, isotherms, average nusselt number and velocity graphs; it clearly explained the influence of flow governing parameters on heat transfer rate and fluid flow within the enclosure.
Heat transfer enhancement of copper-water nanofluids in a lid-driven enclosure
Communications in Nonlinear Science and Numerical Simulation, 2010
A numerical study is conducted to investigate the transport mechanism of mixed convection in a lid-driven enclosure filled with nanofluids. The two vertical walls of the enclosure are insulated while the horizontal walls are kept at constant temperatures with the top surface moving at a constant speed. The numerical approach is based on the finite volume technique with a staggered grid arrangement. The SIMPLE algorithm is used for handling the pressure velocity coupling. Numerical solutions are obtained for a wide range of parameters and copper-water nanofluid is used with Pr ¼ 6:2. The streamlines, isotherm plots and the variation of the average Nusselt number at the hot wall are presented and discussed. It is found that both the aspect ratio and solid volume fraction affect the fluid flow and heat transfer in the enclosure. Also, the variation of the average Nusselt number is linear with solid volume fraction.
International Journal of Thermal Sciences, 2008
Effect of copper-water nanofluid as a cooling medium has been studied to simulate the behavior of heat transfer due to laminar natural convection in a differentially heated square cavity. The transport equations for a non-Newtonian fluid have been solved numerically following finite volume approach using SIMPLER algorithm. The shear stresses have calculated using Ostwald-de Waele model for an incompressible non-Newtonian fluid. The thermal conductivity of the nanofluid has been calculated from the proposed model by Patel et al. Study has been conducted for Rayleigh number (Ra) 10 4 to 10 7 while solid volume fraction (φ) of copper particles in water varied from 0.05% to 5%. It has been observed that the heat transfer decreases with increase in φ for a particular Ra, while it increases with Ra for a particular φ. The copper nanoparticle diameter has been taken as 100 nm for all of the studies.
In this study, a rectangular enclosure with thin fin attached and filled with Cu-water nanofluid under external magnetic field is numerically analyzed. A highly conductive thin fin is attached at the bottom wall. Numerical simulations have been carried out for wide variety of Rayleigh numbers (Ra = 10 3 ~ 10 6), Hartmann number (Ha = 0-100) and solid volume fraction (φ = 0 ~ 0.15). Galerkin weighted residual method of finite element analysis is used in this investigation to find the solution. Numerical accuracy is ensured by the grid independency test. Flow and thermal behavior are discussed on the basis of streamlines, isothermal lines respectively. Nusselt number (Nu) plot on cold wall and average temperature of the working fluid are shown to quantify the overall heat transfer rate. Results show that heat transfer rate increases with the increment of Rayleigh number, solid volume fraction and decreases with the increment of Hartmann number. More than 40% better heat transfer is recorded for lower strength of magnetic field. There is no significant change in overall heat transfer at Ha > 40, even with increasing Ra
International Journal of Thermal Sciences, 2009
Effect of copper-water nanofluid has been studied as a cooling medium to simulate the heat transfer behaviour in a two-dimensional (infinite depth) horizontal rectangular duct, where top and bottom walls are two isothermal symmetric heat sources. The governing continuity, momentum and energy equations for a laminar flow are being discretized using a finite volume approach using a power law profile approximation and has been solved iteratively, through alternate direction implicit, using the SIMPLER algorithm. The thermal conductivity of nanofluid has been determined by model proposed by Patel et al. Study has been conducted considering the fluid as Newtonian as well as non-Newtonian for a wide range of Reynolds number (Re = 5 to 1500) and solid volume fraction (0.00 φ 0.050). It has been observed that the heat transfer augmentation is possible using nanofluid in comparison to conventional fluids for both the cases. The rate of heat transfer increases with the increase in flow as well as increase in solid volume fraction of the nanofluid. Unlike natural convection the increase in heat transfer is almost same for both the cases.
In the present work, the enhancement of natural convection heat transfer utilizing nanofluids as working fluid from horizontal circular cylinder situated in a square enclosure is investigated numerically. Different types of nanoparticles were tested. The types of the nanofluids are Cu, Al2O3 and TiO3 with water as base fluid. A model is developed to analyze heat transfer performance of nanofluids inside an enclosure taking into account the solid particle dispersionrs on the flow and heat transfer characteristics. The study uses different Raylieh numbers (104, 105, and 106), the enclosure width to cylinder diameter ratio W/D is 2.5 and volume fraction of nanofluids is between 0 to 0.2. The work included the solution of the governing equations in the vorticity-stream function formulation which were transformed into body fitted coordinate system. The transformations are based initially on algebraic grid generation, then using elliptic grid generation to map the physical domain between the heated horizontal cylinder and the enclosure into a computational domain. The disecritization equation system are solved by using finite difference method. The code build using Fortran 90 to execute the numerical algorithm. The results display the comparisons between different types of the nanofluids based on the effect of Raylieh number, and volume fractions on the thermal and hydrodynamic characteristics. The results were compared with previous numerical results, which showed good agreement. For all types of the nanofluids, the Nusselt number increases with increasing the volume fraction of the nanofluids. The results show that the streamlines change with changing the type of the nanofluid, while the isotherms remain unchanged. The Nusselt number of Cu nanofluids is more than the those for other types of the nanofluids.
In industries such as power generation, chemical production, air conditioning, transportation, and microelectronics the cconventional heat transfer fluids such as water, mineral oil, and ethylene glycol are used to transfer heat from one fluid to another. The low thermal conductivity of conventional fluids increase the size of the heat transfer device for the given heat transfer. So there is a need to develop energy-efficient heat transfer fluids that are required in a plethora of heat transfer applications. Modern materials technology provided the opportunity to produce nanometer-sized particles which are quite different from the parent material in mechanical, thermal, electrical, and optical properties. The heat transfer properties of these conventional fluids can be significantly enhanced by dispersing nanometer-sized solid particles such as Al 2 O 3 , Cu, CuO and Fe 2 O 3. The suspended nano-sized metallic and metal oxide particles change the transport properties and heat transfer characteristics of the base fluid. Thus the preparation of nanofluids using metal and metal oxide nanoparticleswill play an important role in developing the next generation of cooling technology. The CuO nanoparticles are prepared by adopting sol-gel techniquein the present work. The CuO nanoparticles are prepared from copper nitrate by passed it through different stages such as dissolving, preparation of solution, formation of gel, filtration and drying to get the nano-sized CuO particles. The nanoparticles are sintered for 3 hours at a temperature of 200 0 C in the furnace to remove the liquid traces completely from nanoparticles. TheCuO-water nanofluids are prepared at different volumetric concentration of CuO nanoparticle in the base fluid. To find the heat transfer rates of CuO-water nanofluid for different Reynolds numbers and for different volume fractions of nano-particles in the base fluidthe experiments are conducted in a double pipe counter flow heat exchanger. The experimental overall heat transfer coefficients calculated are compared with the base fluid water. Also the theoretical overall heat transfer coefficients of CuO-water nanofluid are determined by evaluating the physical and thermal properties of nanofluid with the correlations available in the literature.