Air-cooled Electronic Equipment Research Articles

Numerical analysis of fluid flow due to mixed convection in a lid-driven cavity having a heated circular hollow cylinder

Mixed convection heat transfer in a lid-driven cavity along with a heated circular hollow cylinder positioned at the center of the cavity has been analyzed numerically. The present study simulates a realistic system such as air-cooled electronic equipment with a heat component or an oven with heater. A Galerkin weighted residual finite element method with a Newton–Raphson iterative algorithm is adopted to solve the governing equations. The computation is carried out for wide ranges of the Richardson numbers, cylinder diameter and solid fluid thermal conductivity ratio. Results are presented in the form of streamlines, isothermal lines, average Nusselt number at the heated surface and fluid temperature in the cavity for the mentioned parameters. It is found that the flow field and temperature distribution strongly depend on the cylinder diameter and also the solid–fluid thermal conductivity ratio at the three convective regimes.

A numerical study on the effect of a heated hollow cylinder on mixed convection in a ventilated cavity

The present work is aimed to study mixed convection heat transfer characteristics within a ventilated square cavity having a heated hollow cylinder. The heated hollow cylinder is placed at the center of the cavity. In addition, the wall of the cavity is assumed to be adiabatic. Flows are imposed through the inlet at the bottom of the left wall and exited at the top of the right wall of the cavity. The present study simulates a practical system such as air-cooled electronic equipment with a heat component or an oven with heater. Emphasis is sited on the influences of the cylinder diameter and the thermal conductivity of the cylinder in the cavity. The consequent mathematical model is governed by the coupled equations of mass, momentum and energy and solved by employing Galerkin weighted residual method of finite element formulation. A wide range of pertinent parameters such as Reynolds number, Richardson number, cylinder diameter and the solid-fluid thermal conductivity ratio are considered in the present study. Various results such as the streamlines, isotherms, heat transfer rates in terms of the average Nusselt number and average fluid temperature in the cavity are presented for different aforesaid parameters. It is observed that the cylinder diameter has significant effect on both the flow and thermal fields but the solid-fluid thermal conductivity ratio has significant effect only on the thermal field.

4322 自然空冷電子機器密閉筐体内の熱挙動(J05-1 放熱設計・評価,J05 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)

This paper describes experimental results on thermal behavior in sealed natural air-cooled electronic equipment casing. One of the authors has already proposed a simple practical equation for thermal design of a sealed natural convection air-cooled electronic equipment casing. However in that study the casing was made of plastic and had a cube shape of side length of 0.4m. Therefore, in the present work, an aluminium casing having length, width and height of 0.1m, 0.4m, and 0.3m, respectively, was used. The temperature of casing surfaces and air inside the casing were measured with various inclinations and for three different ways of casing setting on the floor. Results indicated only a small change in value of the coefficients used in the equation developed by one of the author.

Study on Chimney Effect in Natural Air Cooled Electronic Equipment Casings under Inclination (2nd Report, The Proposal of a Thermal Design Correlation including Porosity Coefficient of an Outlet Opening)

Natural air cooling technologies of electronic equipment have important advantages of no fan and high reliability. However, natural air cooling has lower cooling capability than fan air cooling, so the cooling capability enhancement has been required. In this paper are presented the results of the experimental casings on the chimney effect in natural air-cooled electronic equipment. The system box is inclined for the purpose to enhance the capability of natural air-cooling. Experiments have been carried out using a model of thin laptop PC. The influence of the box inclination, outlet positions and numbers, and the porosity coefficient of outlet openings on the cooling capability was investigated. The results show that the temperature values inside casing and heater surface are gently diminished by the effect of increase in inclination and porosity coefficient of outlet openings. Moreover, the increase in natural circulation flux in the box is quantitatively proven by experiments. The experimental data were reduced to a Nusselt number-Rayleigh number correlation by using modified the reference length.

D131 傾斜薄型筐体に追加した煙突効果の影響 : 2種類の煙突材質による比較(OS-15 電子機器・デバイスの熱問題と現状技術IV)

In this paper are presented the results of an experimental study on the two different material chimneys in a natural convection air-cooled electronic equipment casing. In order to promote the natural convective air-cooling capability, we have focused on chimney effect by casing inclining. Moreover, we came up with assembling the chimneys on casing with inclination. For evaluating thermal behavior of inclination and chimney, experiments have been carried out using a thin electronic equipment casing that has inlet and outlet in front-top side and chimneys with four different heights and two different materials. As a result, chimneys had effects on cooling of air inside casing and heater, but alternations of chimney height had a little effected on thermal behaviors. In addition, acrylic chimneys had a little more cooling effect than aluminum one, due to adiabatic efficiency.

1863 傾斜薄型筐体における煙突の影響(J09-5 電子機器の放熱設計,J09 電子情報機器,電子デバイスの熱制御と強度・信頼性評価)

In this paper are presented the results of an experimental study on the chimney in a natural air-cooled electronic equipment casing. In order to promote the natural convective air-cooling capability, we have focused on about chimney effect by casing inclining. Moreover, we came up with assembling the chimneys on inkling casing. For evaluating thermal behavior of inclination and chimney, experiments have been carried out using a thin electronic equipment casing that has inlet and outlet in front-top side, and 4 highs chimneys. As a result, chimney was decreased a temperature inside casing and heater, but alternations of chimney height had a little effected on thermal behaviors.

Study on Chimney Effect in Natural Air Cooled Electronic Equipment Casings under Inclination (The Proposal of a Thermal Design Correlation with Inclination)

Natural air-cooling needs neither a fan nor a blower. However, cooling capability of natural air-cooling is low, so the improvement of its capability is indispensable. In this paper are presented the results of the experimental casings on the chimney effect in natural air-cooled electronic equipment. The system box is inclined for the purpose to raise the capability of natural air-cooling. Experiments have been carried out using three models of thin laptop PC that have two kinds of heat sources. It has inlet and outlet vents on the front and rear walls of the casing. The box was inclined 0 to 90 degrees up from the horizontal plane. The influence by the box inclination, the box dimensions, and the heating element size was investigated. The result shows that the temperature inside casing and heater surface temperature are gently diminished by the effect of inclination, and the increase in natural circulation flux in the box is quantitatively proven by experiments. But, a substantial benefit of casing inclination is only at angles lower than about 40 degree. In the other hand, the experimental data were reduced to a Nusselt number-Rayleigh number correlation by using modified the reference length we supposed that does not include explicitly the box dimensions, the heat source size, and the inclination angle. The experimental data almost fall on a straight line which gives a correlation Nu* =0.0038 Ra*0.6, and are collapsed in a narrow band.

自然空冷機器における障害物が及ぼす流体抵抗の影響(J01-5 筐体放熱設計,J01 エレクトロニクス実装における熱制御および信頼性評価)

自然空冷機器における障害物が及ぼす流体抵抗の影響(J01-5 筐体放熱設計,J01 エレクトロニクス実装における熱制御および信頼性評価)

1840 自然空冷筐体の熱性能に対する体積空隙率の影響

In this paper are presented the results of an experimental study on the chimney effect in a natural air-cooled electronic equipment casing. In order to evaluate the natural convective air-cooling capability, the chimney height that is defined as the distance between the main heat dissipated component and outlet vent has been varied. Experiments have been carried out using a ventilated electronic equipment-casing model, with a wire-heater inside and inlet and outlet vents on the walls of the casing. And, volume porosity coefficient in the casing was also varied from 46.4% to 100.0% with flow obstacles when power dissipation was 30W. The result is that average temperature rise in the casing didn't increase until volume porosity coefficient was about 50%, but maximum and wall temperature rise were increase almost linearly.

Mixed convection in an enclosure with a heat-conducting body

Combined free convection and forced convection in a square enclosure with a finite-size heat source is studied numerically. A square heat-conducting body is located somewhere within the enclosure. The present study simulates a practical system, such as an air-cooled electronic equipment with heat components or an oven with heaters. Emphasis is placed on the influences of the configurations and physical properties of the enclosure. The developed mathematical model is governed by the coupled equations of stream function, vorticity transport, and energy, and is solved by employing the cubic spline collocation method. The computation is carried out for wide ranges of Reynolds and Grashof numbers. The results indicate that both the heat transfer coefficient and the dimensionless temperature in the body center strongly depend on the configurations of the system studied, such as size, location, and thermal conductivity of the conducting body and the location of the outflow opening. Detailed results of the interaction between forced airstream and the bouyancy-driven flow by the heat source are demonstrated by the distributions of the isotherms and streamlines and the variations of the heat transfer coefficient.

Transient mixed convection in a partially divided enclosure

Transient laminar mixed convection in a two-dimensional enclosure partitioned by a conducting baffle is investigated numerically. The enclosure has a finite-size heat source imbedded on a vertical wall. The present work simulates a practical system such one with air-cooled electronic equipment with heated components. Emphasis is placed on the transient behavior affected by the geometric arrangements in the enclosure. The developed mathematical model is governed by the coupled equations of stream function, vorticity transport, and energy, and is solved by employing the cubic spline collocation method. The effects of divider and Reynolds numbers on the heat transfer mechanism are found to be significant. The results indicate that steady time depends strongly on the governing parameters and the configuration of the divider. The transient nature of the interaction between the external forced airstream and the buoyancy driven flow by heat source is explained by the streamlines and the isotherms in the enclosure.

The effects of the outlet area and the location of the main power supply unit on the cooling capability through naturally air-cooled electronic equipment casings

This paper describes a practical thermal design approach to natural air-cooled electronic equipment casings. A set of simplified equations for the thermal design of natural air-cooled electronic equipment casings has been proposed. The proposed set of equations satisfied the demand of practical air-cooling systems, since it takes account of factors such as the stack effect, the air flow resistance and the heat transfer due to natural convection. The effects of the outlet area and the location of the main power supply unit on the natural cooling capability of electronic equipment casings were studied using a set of equations. The results have shown that a uniform temperature distribution could be achieved when the main power supply unit was placed at the bottom of the casing. It has also been suggested that the value of the heat removed from the casing surface could be more significant than that from the outlet vent in the thermal design of natural air-cooled electronic equipment casings.

MIXED CONVECTION IN A PARTIALLY DIVIDED RECTANGULAR ENCLOSURE

Combined free convection and forced convection in a partially divided enclosure with a finite-size heat source is studied numerically. The enclosure is partially divided by a conductive vertical divider protruding from the floor or the ceiling of the enclosure. The present study simulates a practical system such as air-cooled electronic equipment with heated components. Emphasis is placed on the influence of the location and the height of the divider, as well as the locations of the source and the outflow opening. The developed mathematical model is governed by the coupled equations of stream Junction, vorticity transport, and energy and is solved by employing the cubic spline collocation scheme. The computation is carried out for wide ranges of Reynolds and Grashof numbers. The results indicate that the average Nusselt number and the dimensionless surface temperature on the heat source strongly depend on the location and the height of the divider. The basic nature of the resulting interaction between the forced external airstream and the buoyancy-driven flow by the heat source is explained by the heat transfer coefficient and the patterns of the streamlines and the isotherms.