The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy

The effects of sample position and gas flow pattern on the sintering of a 7xxx aluminum alloy Al-7Zn-2.5Mg-1Cu in flowing nitrogen have been investigated both experimentally and numerically. The near-surface pore distribution and sintered density of the samples show a strong dependency on the sample separation distance over the range from 2 mm to 40 mm. The open porosity in each sample increases with increasing separation distance while the closed porosity remains essentially unchanged. A two-dimensional computational fluid dynamics (CFD) model has been developed to analyze the gas flow behavior near the sample surfaces during isothermal sintering. The streamlines, velocity profile, and volume flow rate in the cavity between each two samples are presented as a function of the sample separation distance at a fixed nitrogen flow rate of 6 L/min. The CFD modeling results provide essential details for understanding the near-surface pore distribution and density of the sintered samples. It is proposed that the different gas flow patterns near the sample surfaces result in variations of the oxygen content from the incoming nitrogen flow in the local sintering atmosphere, which affects the self-gettering process of the aluminum compacts during sintering. This leads to the development of different near-surface pore distributions and sintered densities

Numerical simulation of mixed convection in a rectangular enclosure with different numbers and arrangements of discrete heat sources

The objective of this paper is to numerically investigate the cooling performance of electronic devices with an emphasis on the effects of the arrangement and number of electronic components. The analysis uses a two dimensional rectangular enclosure under combined natural and forced convection flow conditions and considers a range of Rayleigh numbers. Heat sources in the enclosure generate the natural convection flow and an externally sourced air stream through the enclosure generates the forced convection flow. The results show that increasing the Rayleigh number significantly improves the enclosure heat transfer process. At low Rayleigh numbers, placing more heat sources within the enclosure reduces the heat transfer rate from the sources and consequently increases their overall maximum temperature. The arrangement and number of heat sources have a considerable contribution to the cooling performance. However, increasing the Rayleigh number reduces this contribution

The effect of a baffle on the heat transfer in underground auxiliary ventalitation systems

This paper presents a computational fluid dynamics simulation to examine the effects of the baffle on the air flow field and the heat transfer rate in a space located beneath a ventilation channel. The computational model consists of a two-dimensional channel equipped with a thin baffle hanging from the top wall and a cavity located underneath simulating the underground space. Air flows trough the channel at a uniform velocity, uc , and temperature, Tc . The cavity base is assumed to be heated at a constant temperature, Th , while the vertical walls of the cavity are well-insulated. The top wall of the channel is maintained at a constant temperature, Tc . The continuity, momentum and energy equations are solved numerically using the control-volume approach to examine a combination of natural and forced convection flows. The results show that even though the existence of the baffle improves the cavity ventilation performance at low Richardson numbers, it has a negative impact at high Richardson numbers

A numerical study on the forced convection of laminar nanofluid in a microchannel with both slip and no-slip conditions

This article provides numerically study of the thermal performance of a microchannel, cooled with either pure water or a Cu-water nanofluid, while considering the effects of both slip and no-slip boundary conditions on the flow field and heat transfer. The microchannel is partially heated at a constant temperature and cooled by forced convection of a laminar flow at a relatively lower temperature. The effects of pertinent parameters such as Reynolds number, solid volume fraction, and slip velocity coefficient on the thermal performance of the microchannel are studied. The results of the numerical simulation indicate that the heat transfer rate is significantly affected by the solid volume fraction and slip velocity coefficient at high Reynolds numbers

Natural convective heat transfer of magnetite/graphite slurry under a magnetic field

This paper presents a numerical analysis of the natural convective heat transfer of magnetite/graphite slurry non-Newtonian ferrofluid in a square enclosure under a variable external magnetic field. A heat source with variable temperature distribution is located at the bottom of the enclosure. The left and right walls of the enclosure are at a relatively low temperature. The top wall and part of the bottom wall are thermally insulated. Experimental results are used to obtain the non-Newtonian behavior of graphite slurry and to obtain the properties of its temperature function. The governing equations take into account the effects of ferrohydrodynamics, magnetohydrodynamics, and non-Newtonian fluid behavior. The effects of the Rayleigh number, magnetic number, and Hartmann number on the heat transfer and fluid flow are studied. The results show that, at low Rayleigh numbers, the increase in the Hartmann number does not have any effect on the heat transfer. At high Rayleigh numbers, the heat transfer decreases as the Hartmann number increases. This decrease becomes less significant at higher Rayleigh numbers. The results also show that the strength of the applied magnetic field (the Kelvin force) should reach a certain value (Mn∗f≥104) so that it can affect the heat transfer

Natural convection in two porous media separated by a solid wall

This paper numerically examines natural convection in a square enclosure in which two porous media are separated by a vertical solid wall. The effects of pertinent parameters such as location, thickness and thermal conductivity of the solid wall on the flow and temperature fields as well as the heat transfer rate of the enclosure are studied. Moreover, the effects of effective heat transfer coefficient and permeability of both porous media on the results are investigated. The analysis is based on a control volume approach in which the non-dimensional governing equations simulating the fluid behaviour in the enclosure are solved. The vertical walls of the enclosure are maintained at different temperatures while the horizontal walls are thermally insulated. The results show that a higher heat transfer rate is achieved as the solid wall moves away from the centre of the enclosure. Moreover, at high Rayleigh numbers, the heat transfer rate increases as the thickness of the solid wall increases. It is also shown that the thermal conductivity and permeability of the solid wall affect the heat transfer mechanism within the enclosure

Enhanced natural convection in an isosceles triangular enclosure filled with a nanofluid

Natural convection is studied in an isosceles triangular enclosure with a heat source located at its bottom wall and filled with an Ethylene GlycolCopper nanofluid. This paper examines the effects of pertinent parameters such as the Rayleigh number, the solid volume fraction, the heat source location, and the enclosure apex angle on the thermal performance of the enclosure. The thermal performance of the enclosure is improved with an increase in the Rayleigh number and solid volume fraction. The results also show that the variation of heat transfer rate with respect to the enclosure apex angle and heat source position and dimensions is different at low and high Rayleigh numbers. A comparison is also presented between the results obtained from the modified and original Maxwell models. The results show that the heat transfer is generally higher based on the modified Maxwell model. © 2011 Elsevier Ltd. All rights reserved