Heat-generating Element Research Articles

Natural convection of Al2O3/H2O nanofluid in a cavity with a heat-generating element. Heatline visualization

Cooling of electronic devices is a very important topic. The present paper deals with numerical simulation of natural convection cooling of heat-conducting and heat-generating source using an alumina-water nanofluid under the effect of cold vertical walls. Governing equations formulated in dimensionless stream function, vorticity and temperature variables have been solved by the finite difference method. The effects of nanoparticles concentration, heat source location, internal heat generation flux and heat source material on fluid flow and heat transfer have been studied. It has been found that an addition of nanoparticles can intensify the cooling process when the heat is located near the vertical cold wall.

Impacts of moving wall and heat-generating element on heat transfer and entropy generation of Al2O3/H2O nanofluid

Development of various electronic devices demands to create effective cooling complexes. The present paper deals with computational analysis of mixed convection cooling of heat-conducting and heat-generating element located inside an alumina–water nanofluid enclosure with upper moving wall. Usage of upper moving wall, nanofluid and cooling vertical walls allows to create the effective cooling process. Analysis has been performed numerically using the Oberbeck–Boussinesq equations. The effects of nanoparticles concentration, heat source location and upper wall velocity on flow structures, heat exchange and entropy generation have been investigated. It has been ascertained that effective cooling of the heated element occurs for high Reynolds number and central position of the heat-generating element.

Natural convection of Al2O3/H2O nanofluid in an open inclined cavity with a heat-generating element

Free convection of alumina-water nanofluid in a tilted open cavity with a heat-generating solid element has been studied. The considered topic allows understanding an opportunity of nanofluids for cooling of the heat-generating elements in open cavities. Upper border is supposed to be open where nanofluid penetrates into the cavity. Simulation has been performed using the Oberbeck–Boussinesq equations formulated in non-dimensional stream function, vorticity and temperature. Finite difference method of the second order accuracy has been applied. The effects of cavity inclination angle (0≤γ≤π/2), heater location (0.1≤δ≤0.7, where δ is the dimensionless distance between the heater and left wall) and nanoparticles volume fraction (0≤ϕ≤0.04) have been analyzed. It has been found that the considered parameters allow minimizing average heater temperature. The cavity inclination angle of π/3 characterizes the heat transfer enhancement (average Nusselt number has the maximum value), while the heater average temperature has the minimum value. At the same time, a proximity of the heater to the cavity wall characterizes non-essential cooling of the heat-generating element. The most effective cooling of the heat-generating element occurs for central heater location with cavity inclination angle of π/3. The considered alumina-water nanoparticles do not allow to intensify the cooling process for the heater element.

Convective-radiative heat transfer in a rotating square cavity with a local heat-generating source

Development of passive cooling systems for electronic devices demands the multiparametric analysis of main heat transfer mechanisms inside the domains with heat-generating elements. Such analysis can allow to find optimal parameters for the heated elements in order to decrease the working temperature of these elements. Nowadays many electronic units are mounted in rotating systems. The present work is devoted to numerical investigation of convective-radiative heat transfer in a rotating square cavity with a local heat-generating and heat-conducting source. The considered cavity has horizontal adiabatic walls, isothermal cooled vertical borders and a heat-generating element located on the bottom wall. Mathematical model formulated in non-dimensional stream function, vorticity and temperature have been solved by finite difference method. The influence of surface emissivity, Taylor number, and Ostrogradsky number on streamlines, isotherms, average Nusselt number, fluid flow rate and average temperature inside the heater have been studied. The heat transfer enhancement with rotation for moderate values of the Taylor number has been shown. It has been found that in the case of heat-generating and heat-conducting element the periodicity in fluid flow intensity and heat transfer rates can be obtained after a lot of complete revolutions. A growth of the surface emissivity can essentially reduce the average temperature inside the heated element, while an intensive rotation also allows to decrease this temperature.

Natural convection melting of nano-enhanced phase change material in a cavity with finned copper profile

Present study is devoted to numerical simulation of heat and mass transfer inside a cooper profile filled with paraffin enhanced with Al2O3 nanoparticles. This profile is heated by the heat-generating element of constant volumetric heat flux. Two-dimensional approximation of melting process is described by the Navier-Stokes equations in non-dimensional variables such as stream function, vorticity and temperature. The enthalpy formulation has been used for description of the heat transfer. The influence of volume fraction of nanoparticles and intensity of heat generation on melting process and natural convection in liquid phase has been studied.

Effect of oxidation and nitriding on the properties of zirconium alloys

In contrast to a large number of publications about the influence of interstitial elements (O, N) on the physical-mechanical properties of zirconium alloys, insufficient attention at present is paid to examining their influence on the characteristics of near-surface layers of the shells of heat generating element (HGE). Therefore, it is expedient to widen the knowledge about the influence of interstitial elements on the properties of zirconium HGE tubes. Authors experimentally established the influence of treatment in the controlled oxygen- and nitrogen-containing gas media on the mass increment and properties of the near-surface layer of samples-rings, cut out of the shells of heat generating elements. Differences in the saturation of internal and external surfaces of zirconium pipes were described. It was shown that roughness of the internal surface is less compared to that of the external surface. Results of examining the hardness of external and internal surfaces of the samples-rings after oxidizing and nitriding are presented here. For example, treatment of the samples-rings in the oxygen-containing medium (T=650 °C, t=20 h) leads to the formation of hardness at the external surface HV 0.49 =1190±90, and at the internal surface HV 0.49 =1190±90. However, after treatment in the nitrogen-containing medium (T=650 °C, t=20 h), the hardness on external surface is HV 0.49 =615±35, while on the internal surface it is HV 0.49 =445±35. For example, after treatment in the oxygen-containing medium (T=650 °C, t=20 h), depth of the strengthened layer at the external surface is l=70…75 μm and at the internal surface, it reaches l=60…65 μm. Treatment in the nitrogen-containing medium (T=650 °С, t=20 h) causes the formation of a strengthened layer on the external surface l=60…65 µm and on the internal surface – l=55…65 µm. The duration of isothermal holding in the oxygen mixture, which can lead to the crack initiation at the internal surface of zirconium HGE pipes, was experimentally discovered. Results of present work may be taken into account for the development of modes of treatment of zirconium alloys.

Natural convection of water in a partially porous enclosure with a heat-generating element

Paper presents the numeral results of transient natural convection in a partially porous enclosure with a heat-conducting and heat-generating element. The horizontal walls of the cavity are adiabatic, while the vertical ones are isothermal and have low temperature. A mathematical model formulated in dimensionless variables such as vorticity, stream function and temperature have been solved by means of the finite difference method. The governing parameters are the porous layer thickness and dimensionless time. The effects of these parameters are shown using streamlines, isotherms and average temperature of the heat-conducting element. The results demonstrate an opportunity to intensify the passive cooling system using the porous layer.

Mathematical simulation of convective-radiative heat transfer in a ventilated rectangular cavity with consideration of internal mass transfer

Mathematical simulation of the nonstationary regimes of heat-and-mass transfer in a ventilated rectangular cavity with heat-conducting walls of finite thickness in the presence of a heat-generating element of constant temperature has been carried out with account for the radiative heat transfer in the Rosseland approximation. As mechanisms of energy transfer in this cavity, the combined convection and the thermal radiation in the gas space of the cavity and the heat conduction in the elements of its fencing solid shell were considered. The mathematical model formulated in the dimensionless stream function–vorticity vector–temperature–concentration variables was realized numerically with the use of the finite-difference method. The streamline, temperature-field, and concentration distributions reflecting the influence of the Rayleigh number (Ra = 104, 105, 106), the nonstationarity (0 < τ ≤ 1000), and the optical thickness of the medium (τλ = 50, 100, 200) on the regimes of the gas flow and the heat-and-mass transfer in the cavity have been obtained.

Effect of baffle on convective heat transfer from a heat generating element in a ventilated cavity

This paper reports the results of a numerical and experimental investigation of mixed convection from a heat-generating element in a vented cavity with/without a baffle arrangement. Numerical investigations are carried out to determine the best position of the baffle on the walls of a rectangular chamber. The effect of varying the baffle heights and the position on the enhancement of heat transfer from the heater is investigated. Experiments were carried out for a heater located centrally in a parallelepiped that has an air inlet and an outlet port. The vertical baffle is fixed on the bottom wall of the chamber. After a detailed parametric study, correlations have been developed for the average Nusselt number and the maximum dimensionless temperature occurring in the heat generating element. Comparison of the numerical and experimental results for the geometry considered showed good agreement.

Nonstationary temperature conditions of windings of transformers-betatrons with a limited repeat number of heating-cooling

The exact analytical solution of the nonstationary problem of thermal conductivity for a rod-type heat-generating element is obtained.