Size Of Heat Source Research Articles

Design Optimization for Pin-Fin Heat Sinks

An effective method for performing the thermal optimization of fully confined pin-fin heat sinks under constraints of pressure drop, mass, and space limitations has been successfully developed. This study shows how automated design optimization techniques can be successfully applied to optimal design of pin-fin heat sinks, which allows the thermal engineer to meet several design objectives and constraints simultaneously. The thermal and hydrodynamic models for pin-fin heat sinks have been developed. A statistical method for sensitivity analysis of the design factors, including the size of heat source and sink footprint, conductivity of sink base, fin material, fin pitch, fin diameter, fin height, thickness of sink base, and upstream mass flowrate, is performed to determine the key factors that are critical to the design. A response surface methodology is then applied to establish regression models for the thermal resistance and pressure drop in terms of the design factors with an experimental design. By employing the gradient-based numerical optimization technique, a series of constrained optimal designs can be efficiently performed. Comparisons between these predicted optimal designs and those evaluated by the theoretical calculations and numerical simulations are made with satisfactory agreements.

Distribution of heat sources in vertical open channels with natural convection

In this paper we use the constructal method to determine the optimal distribution and sizes of discrete heat sources in a vertical open channel cooled by natural convection. Two classes of geometries are considered: (i) heat sources with fixed size and fixed heat flux, and (ii) single heat source with variable size and fixed total heat current. In both classes, the objective is the maximization of the global thermal conductance between the discretely heated wall and the cold fluid. This objective is equivalent to minimizing temperature of the hot spot that occurs at a point on the wall. The numerical results show that for low Rayleigh numbers (∼10 2), the heat sources select as optimal location the inlet plane of the channel. For configuration (i), the optimal location changes as the Rayleigh number increases, and the last (downstream) heat source tends to migrate toward the exit plane, which results in a non-uniform distribution of heat sources on the wall. For configuration (ii) we also show that at low and moderate Rayleigh numbers ( Ra M ∼ 10 2 and 10 3) the thermal performance is maximized when the heat source does not cover the entire wall. As the flow intensity increases, the optimal heat source size approaches the height of the wall. The importance to free the flow geometry to morph toward the configuration of minimal global resistance (maximal flow access) is also discussed.

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.

Thermal Analysis of Welding on Aluminum Plates

This study investigated the temperature distribution of aluminum plates welded by gas tungsten arc. The heat of fusion, the size and distribution of heat source, the travel speed, the heat conduction in the welding direction and the surface heat loss during welding were considered. A numerical scheme was developed to solve the three-dimensional problem. With the help of a mathematical model, the effect of welding parameters such as heat input of the weld, preheating of the workpiece and moving velocity of heat source on weld penetration in moderately thick plates were discussed. The steady-state temperature profiles of the welded plate were solved by finite difference method. In addition, an experiment was conducted to verify the theoretical results. The predicted values from the proposed model compared favorably with the experimental data.

Performance characterization of a novel flat plate micro heat pipe spreader

A combined numerical and experimental investigation was conducted on a novel flat plate micro heat pipe spreader, to better understand the effect of primary operating parameters governing the performance of such devices. A numerical thermal model was developed to predict the temperature response with variation in the leading geometrical, material and boundary parameters of the spreader, viz. wall thickness, thermal conductivity, power input and heat source size. The results showed that, unlike conventional heat pipes, wall thermal conductivity is a major factor in such thin, flat spreaders. The spreader performance also degrades with decrease in heat source size. Visualization experiments have been conducted to qualitatively understand the heat transfer phenomena taking place on these devices. These confirmed that the primary limitation to heat transfer from these devices was due to the capillary limitation of the wick structures.

Heat sources — technology, economy and environment

Heat sources for heat pumps in buildings as well as in industry are discussed. Furthermore, some environmental aspects concerning choice of heat source are highlighted. Only systems for heat pumping are included, i.e. air-conditioning types which can also partly work as heat pumps are excluded. Recent heat pump installations in Sweden are mainly in small systems. Ambient air, exhaust air, soil and rock are the most common heat source types. Data on COP, investment costs, working fluids, present Swedish market etc. for these types of heat sources are given. Data on industrial heat pump installations in some countries and distribution of these according to heat pump type and industry sector as well as heat source temperatures are reported. Process integration aspects when choosing heat source size and temperature are also discussed as well as the relation between these parameters and the choice of heat pump type. Finally, the influence on the economy of the heat source temperature is presented. The cost-effectiveness of heat pumps for reducing CO 2 emissions compared with other heating technologies is discussed. The main results are: (1) heat pumps can in many cases in the future contribute to a reduction of CO 2; (2) there is a rather big difference, for larger systems a major difference, between the water-based and the ambient air-based heat pumps in terms of efficient reduction of greenhouse gas emissions.

Heat Transfer of a Smoldering Flammable Substrate. Part 1. Development of a Theoretical Model for the Heat Transfer of a Smoldering Substrate

Part 1 of this two part paper describes the development of a theo retical model for the interaction of the moving heat source and a solid substrate when they are in contact. For purposes of the model the substrate is assumed to act as a continuum and the Fourier equation for transient, three-dimensional conduction is solved using Laplace and Fourier transformations. Unlike most previous models, this model shows the explicit relations between the properties of the heat source and those of the substrate. Since the size, shape and speed of the heat source impact the ignition of substrate, considerable attention is devoted to evaluating these parameters. Results are presented which show the effects of the size, shape and speed of the heat source of the substrate.

Volcano detection and monitoring using AVHRR data: the Krafla eruption, 1984

Abstract Abstract. Many volcanic eruptions go essentially unmonitored. Potentially the Advanced Very High Resolution Radiometer (AVHRR), with its global coverage, frequent return period, and sensitivity in the thermal infrared, represents a data source capable of monitoring surface volcanic activity unrecorded by ground observations or other satellite sensors. In this study an attempt is made to demonstrate this potential by extracting information for the 1984 eruption at Krafla, Iceland. Seven cloud-free AVHRR images were available for the 14 day period of eruptive activity. The surface activity was detectable as a major thermal anomaly in all three of the longer wavelength channels and was vigorous enough during one night-time pass to be detectable in the near-infrared channel (0.725-1.1μm). Channel 2 and 4 radiance data were used to calculate the size and temperature of sub-pixel heat sources within the lava flow field, and a heat source at 1050° C was estimated as occupying an area of approximately 240000 m2, which was distributed across 20 pixels. Detection and measurement of volcanic heat sources at such short wavelengths using low spatial resolution data has rarely been reported before. Field reports and maps were used to guide and confirm the analysis. Digital number variations within the anomaly could be related to various known features of the eruption. To monitor the eruption a weighted average method was derived and used to sharpen up the images, and the density sliced sharpened images enabled the development of the eruption to be mapped. Results compared well with field reports, suggesting that AVHRR and similar systems could be a useful source of data for monitoring eruptions where contemporaneous field observations are unavailable or incomplete.

Industrial fuel ignition conditions by flame radiation

Abstract With the aim of developing and testing the model of liquid fuel ignition by flame heat flux a simplified approach is presented to evaluate the ignition conditions on the basis only of well-known fuel characteristics. The case of a sufficient size of heat source which enables boundary effects to be ignored and the case of local ignition are considered. In accordance with the presented model, critical parameters of ignition (heat flux power, exposure time, heat source size) of typical heavy fuels are determined. Direct experimental validation for the model is presented. Experimentally-determined critical parameters for diesel fuel are in a good agreement with calculated results.

Numerical study of natural convection from discrete heat sources in a vertical square enclosure

A numerical finite difference technique based on the Marker and Cell (MAC) method is used to obtain solutions of a two-dimensional model of a square enclosure with laminar natural convection heat transfer from discrete heat sources. A discrete heat source is located in the center of one vertical side representing a high- power integrated circuit (IC). The conservation equations are solved using the primitive variables: velocity, pressure, and temperature. Computations are carried out for Pr = 0.72, A = 1 and 0 5 Ra 5 lo6 (Rayleigh number is based on the length of the heat source S divided by the aspect ratio A). The ratio E of the heat source size to the total height lies in the range 0.25 5 E 5 1.0. Verification of numerical results are obtained at Ra = 0 (conduction limit) with an analytical conduction solution, and the dependence of Nu and total resistance on Ra, E , and boundary conditions are studied. Relationships between Nu and Ra based on different scale lengths are examined. In addition, a relationship between Nu and Ra, based on SIA, are correlated as Nu = Nu (Ra, E ) and extrapolation equations are developed to cover the range of Ra from 0 5 Ra < lo9.

Numerical simulations of hydrothermal circulation resulting from basalt intrusions in a buried spreading center

A two-dimensional, one by two-kilometer section through the seafloor was simulated with a numerical model to investigate coupled fluid and heat flow resulting from basalt intrusions in a buried spreading center. Boundary and initial conditions and physical properties of both sediments and basalt were constrained by field surveys and drilling in the Guaymas Basin, central Gulf of California. Parametric variations in these studies included sediment and basalt permeability, anisotropy in sediment permeability, and the size of heat sources. Faults were introduced through new intrusions both before and after cooling. Background heat input caused fluid convection at velocities ≤ 3 cm a −1 through shallow sediments. Eighty to ninety percent of the heat introduced at the base of the simulations exited through the upper, horizontal surface, even when the vertical boundaries were made permeable to fluid flow. The simulated injection of a 25–50 m thick basalt intrusion at a depth of 250 m resulted in about 10 yr of pore-fluid expulsion through the sea-floor in all cases, leaving the sediments above the intrusions strongly underpressured. A longer period of fluid recharge followed, sometimes accompanied by reductions in total seafloor heat output of 10% in comparison to pre-intrusion values. Additional discharge-recharge events were dispersed chaotically through the duration of the cooling period. These cycles in heat and fluid flow resulted from the response of the simulated system to a thermodynamic shock, the sudden emplacement of a large heat source, and not from mechanical displacement of sediments and pore fluids, which was not simulated. Water/rock mass ratios calculated from numerical simulations are in good agreement with geochemical estimates from materials recovered from the Guaymas Basin, assuming a bulk basalt permeability value of at least 10 −17 m 2/(10 −2 mD). The addition of faults through intrusions and sediments in these simulations did not facilitate continuous, rapid venting. Increased heat input at the base of the faults resulted in temporarily greater fluid discharge, but the flow could not be sustained because the modeled system could not recharge cold fluid quickly enough to remove sufficient heat through the vents.

Model-Dependence of Size and Position of Heat Source in a Geothermal Reservoir

Model-Dependence of Size and Position of Heat Source in a Geothermal Reservoir

Thermal properties of the multilayer infinite plate structure

Using the double Fourier integral transform method, the analytical temperature solutions to the single-layer and multilayer structures with infinite lateral dimensions have been derived. For the single-layer structure, temperature dependence of the thermal conductivity has been taken into account using the Kirchhoff transformation. The use of discrete rectangular heat sources rather than circular heat sources on the top surface of the structure makes this model particularly useful for the thermal analysis of common solid-state and integrated circuit devices and packages. For studying the thermal properties of a large class of solid-state device geometries, this model can be utilized to approximate actual devices with reasonable accuracy. The general device geometries for which this model can be employed to represent the actual devices are determined. Compared with the model where the finite extent of the chip lateral dimensions is considered, the present model is much more computationally efficient for cases where the heat source size is much smaller than the substrate or package size.

静止アーク溶接における溶融池内の対流と溶け込み形状

The importance of convective heat transfer in the weld pool has been widely recognized in relation to the penetration shapes of base metal.The main causes that associate streaming in molten pool are the electro magnetic force, buoyancy force, surface tension and aero dynamic drag force. But, the mechanism of heat transfer has not yet been clarified well. Therefore, in this work, they have paid special attension on the importance of convectional heat transfer in the weld pool and the anode size or heat source size under the same heat input, or same current value. A finite difference method was employed to solve above-mentioned mechanism. The results obwere tained as follows.1) When arc length is short, the velocity field induced by outward surface shear strss consists of two flow loops of opposite directions in the molten pool, which lead to comparatively deep weld shape.2) In case of short arc length and positive temperature coefficient of surface tension, surface tension is predominant. Accordingly, penetration shape is deep.3) In case of long arc length aero dynamic drag force is predominant, which leads to the 'shallow' center and 'deep' peripheral penetration.

Effect of a Surface Film on the Surface Temperature of a Rotating Cylinder

Solution to the steady heat conduction problem of a rotating layered cylinder is presented. The governing differential equations (for the film and the substrate) are solved by using an integral transform technique. It is shown that the presence of a surface film measured in micrometers can substantially change the level of the surface temperature. The effect of the surface film on the surface temperature depends on: respective thermal properties of the film and the substrate; relative surface speed; heat source (contact) size; and surface film thickness. However, the range in which the effect of the film on the surface temperature is dependent on these parameters is limited. Outside this range (i.e., thin film/low speed or thick film/high speed) the surface temperature rise is determined by the thermal properties of the substrate, or by the properties of the film alone, respectively. Hence, outside this range, a further change in the film thickness does not influence the surface temperature rise. Dimensionless plots showing the change in surface temperature rise as a function of material thermal properties, surface speed, heat source size, and film thickness are presented. Behavior for specific material combinations are also presented. The present information can be utilized to predict the layer effect on the partition of heat between the layered cylinders.

Geometric Reconstruction of Buried Heat Sources from a Surface Thermogram

Attempts to reconstruct the spatial location, size, and form of buried heat sources from the measured pattern of thermograms are, in general, prohibited by the lack of a priori information about the thermal (flow) model and the source structure. In this paper, a method is introduced based on geometric reconstruction of a buried heat source configuration. This configuration must contain point sources and/or sharp edges and be confined to a plane region parallel to the surface. The medium, in which the heat source is embedded, is assumed to be homogeneous, isotropic, and of large size compared to the size of the source and to its depth below the surface. The heat flux from the surface to the ambient is assumed to follow the Newtonian cooling law. The spatial density distribution of the flux can be described by a Green function with coefficients determined by the depth of the source plane. It is possible to approximate a corresponding inverse mapping algorithm (reconstruction filter) for each source plane depth, with only one (depth) scaling parameter. The density distribution of the source structure is optimally deblurred when the reconstruction filter's scaling parameter matches the actual depth of the source plane below the surface. In the reconstruction procedure, this reconstruction filter is consecutively applied for several values of the scaling parameter. The so-called ``deblurring quality'' of the point or edge information is utilized to decide which scaling parameter achieves the sharpest image. This procedure resembles the focusing of a lens.

Liquid immersion cooling of small electronic devices

The primary purpose of this investigation was to examine liquid immersion techniques for cooling minute heat sources. The study demonstrated that nucleate boiling is an effective means of cooling larger heat sources. However, for heat sources with surface areas less than 0·01 sq. cm, nucleate boiling was found to offer very little improvement in convective heat transfer over free convection with the same liquid. In addition, nucleate boiling may introduce mechanical stresses, contamination and physical design problems. For these reasons, two alternatives to boiling (forced convection and bubble induced mixing) were also investigated which reduced (or bypassed) some of these problems. In the forced convection study, boundary layer analysis showed the convective heat transfer coefficient would increase significantly as the heat source size decreased. This was verified experimentally with two different liquids. The experiments found the convection coefficient increased by a factor of 15 when the source size was decreased from 2·00 to 0·01 sq. cm. A similar increase was noted in the free convection and bubble induced mixing experiments. In addition, with small sources both bubble induced mixing and forced convection gave significantly larger heat transfer coefficients than were practical with boiling.

Analytical and Experimental Thermal Analysis of Multiple Heat Sources in Integrated Semiconductor Chips

Because of the complexity and interconnection density of today's integrated circuit chips, experimental measurement of individual transistor or diode junction temperatures under typical powered conditions has become increasingly difficult. In order to provide meaningful thermal data, other approaches have had to be devised. In the work described by this paper, an analytical model has been used to determine the steady state junction temperature rise on an integrated circuit chip. The effect on junction temperature of heat source size, geometry, and number of adjacent heat sources has been studied. Experimental testing on specially prepared chips has verified the analytical results.