Current Issue : April - June Volume : 2012 Issue Number : 2 Articles : 6 Articles
Nanofluids are colloidal suspensions made of nanometer-sized particles dispersed in a conventional fluid. Their unusual\nthermal properties explain intensive investigations for several thermal and industrial applications. In this work, an experimental\ninvestigation was performed to measure the freezing point and to study the supercooling point made of alumina ?-Al2O3\nnanoparticles with 30nm diameter size and deionized water. Particles� volume fraction used in this work is ranging from 1% to\n4%. The T-historic method based on the measurement of the point of inflexion was performed to measure the thermal properties\nsuch as the freezing point and the latent heat of solidification of the nanofluids for different concentrations. The results show that\nthe supercooling degree decreases for the high particles volume concentrations and that the agglomeration does not influence the\ntemperature of the freezing point. However, it makes the freezing process longer....
This study was carried out on medium carbon steel subjected to various form of heat treatment\noperations by assessing the temperature distribution during the machining process. The model of\noblique band heat source, moving in the direction of cutting in an infinite medium with an appropriate\nimage heat source was used in this investigation. The model analysis was carried out separately on the\nchip, the tool and the work material to numerically determine the temperature distribution during\nmachining process using finite element method with nodal grids. Johnson-Cook model was used to\ndetermine the work materials flow stress upon which the material properties were determined.\nStress/strain tests were conducted on the specimens to determine the materialsâ�� constant parameters\nwhich were used as the input parameters to the modeling equation written in Visual Basic 6.0. The\noptimum shear angle of 20�° was used for the machining process and the frictional characteristics were\nalso determined. The temperature along the shear plane AB was determined with reference to\ncoordinate axis within the tool, workpiece and the chip using the model. The results which compare\nfavorably with other results from literatures, provide basis for the design of machining variables for\noptimum and quality machined products which can also be applied in the computer programming of NC\nmachine for precision machining....
This paper reports a numerical study on natural convection from a protruding heater located at the bottom of a square cavity\nfilled with a copper-water nanofluid. The vertical walls of the cavity are cooled isothermally; the horizontal ones are adiabatic,\nand the heater is attached to the bottom wall. The heat source is assumed either to be isothermal or to have a constant heat\nflux. The effective viscosity and thermal conductivity of the nanofluid are modeled according to Brinkman and Patel, respectively.\nNumerical solutions of the full-governing equations, based on the lattice Boltzmann method, are obtained for a wide range of the\ngoverning parameters: the Rayleigh number, Ra; the Prandtl number, Pr; the geometrical parameters specifying the heater; the\nvolume fraction of nanoparticles, F. For a particular geometry, it has been found that, for a given Ra, heat transfer is enhanced\nwith increasing F, independently of the thermal boundary condition applied on the heater....
Convective heat transfer can be enhanced passively by changing flow geometry and boundary conditions or by improving the\r\nthermal conductivity of the working fluid, for example, introducing suspended small solid nanoparticles. In this paper, a numerical\r\ninvestigation on laminar mixed convection in a water-Al2O3-based nanofluid, flowing in a triangular cross-sectioned duct, is\r\npresented. The duct walls are assumed at uniform temperature, and the single-phase model has been employed in order to analyze\r\nthe nanofluid behaviour. The hydraulic diameter is equal to 0.01 m. A fluid flow with different values of Richardson number\r\nand nanoparticle volume fractions has been considered. Results show the increase of average convective heat transfer coefficient\r\nand Nusselt number for increasing values of Richardson number and particle concentration. However, also wall shear stress and\r\nrequired pumping power profiles grow significantly....
A solution to obtain efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover,\r\nthe possibility of improving the thermal performances of the working fluids can be taken into account and the introduction of\r\nnanoparticles in a base fluid can be considered. In this paper, a numerical investigation on confined impinging slot jet working\r\nwith a mixture of water and Al2O3 nanoparticles is described. The flow is laminar and a uniform temperature is applied on the\r\ntarget surface. The single-phase model approach has been adopted. Different geometric ratios, particle volume concentrations, and\r\nReynolds numbers have been considered in order to study the behaviour of the system in terms of average and localNusselt number,\r\nconvective heat transfer coefficient and required pumping power profiles, temperature fields, and stream function contours....
Centrifugal separation of oil and water from streams that is concentrated with oil such as the ones from\r\nthe oil spill disasters is investigated in this study. The existing theories are largely for Stokes settling of\r\noil drops. In this study, two layers, one rich in oil and another rich in water are allowed to spin in a\r\ncentrifuge. The tangential velocity profile is derived from the equations of continuity and motion. The\r\npower drawn at the inner rotor is calculated for a set of parameters for the system and an angular speed\r\n RPM (revolutions per minute). Each simulation required the solution of four simultaneous equations\r\nand simultaneous unknowns. The power draw was found to be linear with angular rotor speed on a loglog\r\nplot. The viscosity of the oil was increased five times to study the effect on the power draw. An\r\nexpression of the interlayer thickness ratio () was obtained by use of a component mass balance on\r\noil streams that flow in and out of the continuous centrifuge....
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