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Effects of power pulsations on natural convection from discrete heat sources
Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics 143
Thermal Visualization Study of Friction Surface and Its Estimation T. Inagaki Y. Okamoto F. Kaminaga M. Sekiya H. Nakamura
Department of Mechanical Engineering University of Ibaraki, Nakanarusawa Cho Hitachi City, Ibaraki, Japan M. Sato
Oiles Industry Co. Ltd., Kirihara Cho Fujisawa City, Kanagawa, Japan A tribological surface under reciprocating motion or rotating motion generates heat, which is caused by friction force at the moving interface. It is very difficult to measure and visualize the transient temperature distribution on a friction surface. In the case when a friction surface is visible, its temperature distribution can be observed by means of the infrared radiometer. A radiation temperature Ts must first be calibrated by measuring the real temperature Ts of a tested material at the friction interface (for example, steel, pom [polyoxymethylen] resin, brass, etc.). In this study, experiments were performed under several friction conditions, and a friction surface was visualized by an infrared radiometer, which can measure a two-dimensional radiation temperature distribution on the surface. Generated heat at a friction surface is transferred to both interfacial materials by thermal conduction and is transferred to the surroundings by convective heat transfer and thermal radiation. The transient temperature field at the friction surface was recorded by the data recorder and analyzed by a personal computer. In estimating the friction surface, friction force ~F, reciprocating speed V, and rotating speed to, which are characteristic quantities in this study, were measured, and the relation between friction force /~F and radiation temperature rising ATs' at the friction interface was studied experimentally. The transient behavior of the temperature field at the friction interface is also discussed.
Natural and Mixed Convection Effects of Power Pulsations on Natural Convection from Discrete Heat Sources Yogendra Joshi Stephen Larsen Ethan M. Akdeniz
Department of Mechanical Engineering Naval Postgraduate School Monterey, California The natural convection heat transfer response of discrete heaters flush mounted on a vertical test surface immersed in water to periodic input power was investigated. The test surface consisted of a plexiglass substrate containing a single column of 15 heat sources. Identical periodic input power patterns were generated within selected heaters using a computer-controlled DC power supply. The mean power levels were varied in the range of 0.2-3.0 W, the amplitude to mean ratios of power pulsations in the range of 0.17-1.0, and the pulsation frequencies from 0.025-0.1
Hz. The resulting heater temperatures over several cycles were measured and compared with corresponding responses for steady input power equal to the mean of the periodic variation. For a single heater powered case a triangular wave input pattern was examined. Two types of periodic input power variations were examined with a column of heat sources powered: a triangular wave and an approximate square wave. The responses clearly indicated heat transfer enhancement due to the power pulsation for certain conditions. With the triangular wave pattern, enhancement was most pronounced when the ratio of amplitude to mean power input was the largest and for the highest pulsation frequency. For the square wave power input, the maximum temperature during the cycle was never below the response to steady input power, in contrast to the triangular input power pattern.
Analysis of Natural Convection on a Horizontal-Edge Convex Dihedron With On-Both-Sides Step Discontinuity in Heat Production M. Cappelli D'Orazio C. Cianfrini M. Corcione
Department of "Fisica Tecnica" University "La Sapienza" Roma, Italy A theoretical and experimental analysis of local thermal field, flow, and heat transfer was conducted for steady laminar-free convection in air on a horizontal edge convex dihedron. The dihedron consisted of two superimposed fiat plates charaterized by the same value of internal thermal resistance and different values of internal heat production near their boundary surface. A specific thermofluid dynamic model is defined and solved by a specific numerical method, referring the dihedron behavior to that one of an equivalent wall inclined by the same angle of the upper plate, with step discontinuity in heat production at a distance from the leading edge depending on the angle of inclination of the wall. Moreover, the local thermal fields for different values of the dihedron angle, internal heat production ratio and distance from the discontinuity point are investigated with a Schlieren method. The local profiles of temperature and temperature gradients along the normal to the walls inside the thermal boundary layer were obtained experimentally. Calculations were made for the local convection coefficient values, and the experimental correlations between dimensionless parameters are pointed out.
Electronic Cabinet Cooling by Natural Convection: Influence of Vent Geometry Mario Misale
Energy Engineering Department University of Genoa Genova, Italy An experimental investigation of the natural air cooling of vertical circuit cards, packaged within a ventilated enclosure was carried out. Tests were performed on a box provided with two vents and containing six uniformly heated circuit boards. The size and shape of each opening
Thermal Visualization Study of Friction Surface and Its Estimation T. Inagaki Y. Okamoto F. Kaminaga M. Sekiya H. Nakamura
Department of Mechanical Engineering University of Ibaraki, Nakanarusawa Cho Hitachi City, Ibaraki, Japan M. Sato
Oiles Industry Co. Ltd., Kirihara Cho Fujisawa City, Kanagawa, Japan A tribological surface under reciprocating motion or rotating motion generates heat, which is caused by friction force at the moving interface. It is very difficult to measure and visualize the transient temperature distribution on a friction surface. In the case when a friction surface is visible, its temperature distribution can be observed by means of the infrared radiometer. A radiation temperature Ts must first be calibrated by measuring the real temperature Ts of a tested material at the friction interface (for example, steel, pom [polyoxymethylen] resin, brass, etc.). In this study, experiments were performed under several friction conditions, and a friction surface was visualized by an infrared radiometer, which can measure a two-dimensional radiation temperature distribution on the surface. Generated heat at a friction surface is transferred to both interfacial materials by thermal conduction and is transferred to the surroundings by convective heat transfer and thermal radiation. The transient temperature field at the friction surface was recorded by the data recorder and analyzed by a personal computer. In estimating the friction surface, friction force ~F, reciprocating speed V, and rotating speed to, which are characteristic quantities in this study, were measured, and the relation between friction force /~F and radiation temperature rising ATs' at the friction interface was studied experimentally. The transient behavior of the temperature field at the friction interface is also discussed.
Natural and Mixed Convection Effects of Power Pulsations on Natural Convection from Discrete Heat Sources Yogendra Joshi Stephen Larsen Ethan M. Akdeniz
Department of Mechanical Engineering Naval Postgraduate School Monterey, California The natural convection heat transfer response of discrete heaters flush mounted on a vertical test surface immersed in water to periodic input power was investigated. The test surface consisted of a plexiglass substrate containing a single column of 15 heat sources. Identical periodic input power patterns were generated within selected heaters using a computer-controlled DC power supply. The mean power levels were varied in the range of 0.2-3.0 W, the amplitude to mean ratios of power pulsations in the range of 0.17-1.0, and the pulsation frequencies from 0.025-0.1
Hz. The resulting heater temperatures over several cycles were measured and compared with corresponding responses for steady input power equal to the mean of the periodic variation. For a single heater powered case a triangular wave input pattern was examined. Two types of periodic input power variations were examined with a column of heat sources powered: a triangular wave and an approximate square wave. The responses clearly indicated heat transfer enhancement due to the power pulsation for certain conditions. With the triangular wave pattern, enhancement was most pronounced when the ratio of amplitude to mean power input was the largest and for the highest pulsation frequency. For the square wave power input, the maximum temperature during the cycle was never below the response to steady input power, in contrast to the triangular input power pattern.
Analysis of Natural Convection on a Horizontal-Edge Convex Dihedron With On-Both-Sides Step Discontinuity in Heat Production M. Cappelli D'Orazio C. Cianfrini M. Corcione
Department of "Fisica Tecnica" University "La Sapienza" Roma, Italy A theoretical and experimental analysis of local thermal field, flow, and heat transfer was conducted for steady laminar-free convection in air on a horizontal edge convex dihedron. The dihedron consisted of two superimposed fiat plates charaterized by the same value of internal thermal resistance and different values of internal heat production near their boundary surface. A specific thermofluid dynamic model is defined and solved by a specific numerical method, referring the dihedron behavior to that one of an equivalent wall inclined by the same angle of the upper plate, with step discontinuity in heat production at a distance from the leading edge depending on the angle of inclination of the wall. Moreover, the local thermal fields for different values of the dihedron angle, internal heat production ratio and distance from the discontinuity point are investigated with a Schlieren method. The local profiles of temperature and temperature gradients along the normal to the walls inside the thermal boundary layer were obtained experimentally. Calculations were made for the local convection coefficient values, and the experimental correlations between dimensionless parameters are pointed out.
Electronic Cabinet Cooling by Natural Convection: Influence of Vent Geometry Mario Misale
Energy Engineering Department University of Genoa Genova, Italy An experimental investigation of the natural air cooling of vertical circuit cards, packaged within a ventilated enclosure was carried out. Tests were performed on a box provided with two vents and containing six uniformly heated circuit boards. The size and shape of each opening