Showing papers on "Thermal energy published in 1991"

Molded circuit package having heat dissipating post

Abstract: A major issue in the semiconductor industry is the amount of power that a silicon device dissipates. As the density of silicon integrated circuits increases with improvements in wafer processing, so does the amount of heat which must be evacuated. If the power of the silicon devices exceeds one watt, the plastic encapsulating material normally yields to the more expensive ceramic or metal packages which can dissipate thermal energy more efficiently. The conventional molded package is a silicon device such as a chip mounted onto a copper paddle which spreads the heat radially in the material and is bonded to leads via thin wires. The three major paths for the heat to escape are by conduction through the molding compound to the surface of the package where removal is by convection, and by conduction from the silicon device through the thin wires to the leads of the package and then to the printed circuit board, and by a heat conducting paddle which radially spreads the heat through the molding compound. In each instance, the heat dissipating path is through a relatively poor thermal conductor. In accordance with the principles of the invention, there is provided an improved thermal path for conducting heat from the silicon device to the surface of the plastic package. The improved thermal path comprises a post of heat conducting material positioned to extend from the silicon device to a surface of the plastic package. One end of the post is positioned to receive heat generated by the silicon device and the other end is exposed to air at the surface of the plastic package. A waist section of the post located between the ends of the post has a dimension which is different than that of the end. Additionally the ends can have dimensions which are either equal or unequal. The post configuration enables the molded package to capture the post without creating cracks in the molded package.

Effect of Varying Ladle Stream Temperature on the Melt Flow and Heat Transfer in Continuous Casting Tundishes

Abstract: The effect of varying ladle stream temperature on the fluid flow and heat transfer phenomena in a typical twin strand slab caster tundish has been mathematically modeled in the present study. The model involves solution of the transient, three dimensional form of the turbulent Navier-Stokes' equation, along with the equations of turbulence energy, energy dissipation rate of turbulence energy and thermal energy conservation. The incoming melt stream temperature has been assumed to decline at a constant rate of 0.5°C/min over a casting period of 50 min. Under the conditions examined in the present mathematical model, the temperature of the incoming melt stream becomes lower than the bulk temperature of the melt in the tundish by about 1-2°C, after 25 min from the start of teeming of a heat. Due to buoyancy effects, the cooler incoming melt starts to flow along the bottom of the tundish instead of the normal top free surface directed flow. The calculations show that the inverse flow pattern develops over the remainder of the teeming period and persists for about 1 min into the teeming of the next heat. Thus, the inclusion flotation and removal of the non-metallic inclusions during the later half of the casting period are expected to be worse compared to the first half.

Heat and mass transfer in unsaturated porous media at a hot boundary: I. One-dimensional analytical model

Abstract: We present a model of heat and mass transfer in an unsaturated zone of sand and silty clay soils, taking into account the effects of temperature gradients on the advective flux, and of the enhancement of thermal conduction by the process of latent heat transfer through vapor flow. The motivation for this study is to supply information for the planned storage of thermal energy in unsaturated soils and for hot waste storage. Information is required on the possibility of significant drying at a hot boundary, as this would reduce the thermal conductivity of a layer adjacent to the boundary and, thus, prevent effective heat transfer to the soil. This study indicates the possibility that the considered system may be unstable, with respect to the drying conditions, with the occurrence of drying depending on the initial and the boundary conditions. An analysis performed for certain boundary conditions of heat transfer and for given soil properties, disregarding the advective flux of energy, indicated that there are initial conditions of water content for which heating will not cause significant drying. Under these conditions, fine soils may be better suited for heat transfer at the hot boundary, due to their higher field capacity, although their heat conduction coefficients at saturation are lower than those of sandy soils. At present, these conclusions are limited to the range of 50–80°C. Potential effects of solute concentration at the hot boundary are indicated.

Spacecraft thermal energy accommodation from atomic recombination

Abstract: Measurements of atomic recombination probabilities important in determining energy release to reusable spacecraft thermal protection surfaces during reentry are presented. An experimental apparatus constructed to examine recombination of atomic oxygen from thermal protection and reference materials at reentry temperatures is described. The materials are examined under ultrahigh vacuum conditions to develop and maintain well characterized surface conditions that are free of contamination. When compared with stagnation point heat transfer measurements performed in arc jet facilities, these measurements indicate that a significant fraction of the excess energy available from atom recombination is removed from the surface as metastable O2.

Solar thermal energy receiver

Abstract: A plurality of heat pipes in a shell receive concentrated solar energy and transfer the energy to a heat activated system. To provide for even distribution of the energy despite uneven impingement of solar energy on the heat pipes, absence of solar energy at times, or failure of one or more heat pipes, energy storage means are disposed on the heat pipes which extend through a heat pipe thermal coupling means into the heat activated device. To enhance energy transfer to the heat activated device, the heat pipe coupling cavity means may be provided with extensions into the device. For use with a Stirling engine having passages for working gas, heat transfer members may be positioned to contact the gas and the heat pipes. The shell may be divided into sections by transverse walls. To prevent cavity workihg fluid from collecting to the extensions, a porous body is positioned in the cavity.

Heat transfer mechanisms and their effects on microstructure during spray atomization and codeposition of metal matrix composites

Abstract: In the present study, the thermal mechanisms affecting the evolution of microstructure during spray atomization and codeposition of metal matrix composites were investigated, with particular emphasis on the effect of the ceramic phase on the resulting microstructure. The present results suggest that the grain size refinement that is commonly observed when a distribution of ceramic particulates is coinjected into a metallic spray during spray atomization and deposition processin may be rationalized by considering heat transfer effects and solid state cooling effects. In order to provide insight into the heat transfer effects, a heat transfer model was formulated on the basis fundamental heat transfer considerations. In this model, the transfer of thermal energy from the atomized metal to the ceramic phase was computed for two separate stages: (a) atomization and (b) deposition. The numerical results obtained using SiC particulates in an aluminum matrix show that 9% of the nethalpy of the atomized spray is transferred to the ceramic particulates during atomization, whereas 8% of the thermal energy available after deposition will be consumed in the process of equilibrating the temperature of the SiC particulates to that the matrix. Regarding solid state cooling effects, preliminary results suggest that the presence of a dispersion of ceramic particulates in the aluminum matrix will drastically reduce the rate of grain growth. This observation was corroborated through an experimental investigation of the changes in grain size after isochronal thermal anneals.

Solar roofing system

Abstract: A solar roofing panel system for use in residential and commercial buildings employing conventional metal roofing components. The system collects and supplies thermal energy from the sun to heat the interior thereof and also is capable of providing solar generated electricity for powering the normal complement of household appliances. The system can also be adapted to provide a thermal energy source for absorption cooling for commercial applications such as supermarkets or the like. The system employs an air-to-liquid system in the preferred embodiment. The alternative embodiment has an air-to-air heat exchange system.

Magnesium hydride for thermal energy storage in a small-scale solar-thermal power station

Abstract: Magnesium hydride is a very promising thermal energy storage material. It will be used in a small-scale solar-thermal power station for terrestrial applications. During insolation the hydride will be decomposed by part of the concentrated sunlight. The released hydrogen gas will be stored either in a pressure vessel or as a hydride in a low temperature alloy. With the other part of the solar energy electricity will be generated in a power conversion unit consisting of a Stirling engine and a generator. In times without insolation the Stirling engine can be driven with the heat of reaction released when hydrogen is recombined with magnesium. Simultaneously with the electricity generation process, heat can be provided by the power station. For the heat transfer between solar receiver, thermal energy store and Stirling engine, two potassium heat pipes will be used. The system will be operated between about 300°C and 480°C. The first two laboratory models will contain 20kg of magnesium powder with a storage capacity of about 12 kWh. A detailed description of the laboratory model design and the expected operational characteristics is given.

Analysis of lunar regolith thermal energy storage

Abstract: The concept of using lunar regolith as a thermal energy storage medium was evaluated The concept was examined by mathematically modeling the absorption and transfer of heat by the lunar regolith Regolith thermal and physical properties were established through various sources as functions of temperature Two cases were considered: a semi-infinite, constant temperature, cylindrical heat source embedded in a continuum of lunar regolith and a spherically shaped molten zone of lunar regolith set with an initial temperature profile The cylindrical analysis was performed in order to examine the amount of energy which can be stored in the regolith during the day At night, the cylinder acted as a perfect insulator This cycling was performed until a steady state situation was reached in the surrounding regolith It was determined that a cycling steady state occurs after approximately 15 day/night cycles Results were obtained for cylinders of various diameters The spherical molten zone analysis was performed to establish the amount of thermal energy, within the regolith, necessary to maintain some molten material throughout a nighttime period This surrounding temperature profile was modeled after the cycling steady state temperature profile established by the cylindrical analysis It was determined that a molten sphere diameter of 476 m is needed to maintain a core temperature near the low end of the melting temperature range throughout one nighttime period

Thermal management in fuel cell system by feed gas conditioning

Abstract: A process for thermal management by feed gas conditioning in high temperature fuel cell systems wherein at least a portion of a fuel feed stream is chemically reacted in an exothermic chemical reaction in an external zone thermally separated from the fuel cell system and at least a portion of the products of such exothermic chemical reaction are passed to an internal zone in thermal exchange with the fuel cell system and reacted in an endothermic chemical reaction thereby absorbing heat from the exothermic electrochemical reaction within the fuel cell system producing a process stream of higher thermal energy. At least a portion of the higher thermal energy stream is removed from the fuel cell system, thereby maintaining the desired operating temperature in the fuel cell system. The process significantly reduces energy requirements of the system and significantly increases overall system efficiency and the output voltage of the system. The process is especially suited to molten carbonates electrolyte and solid oxide fuel cells.

Thermal budget of multicomponent porous ices

Abstract: A relation for the temperature evolution of multicomponent porous ices is derived from the energy equation of multicomponent systems. It is demonstrated that the predominant energy transfer mechanisms can be incorporated into an effective thermal conductivity (λeƒƒ), which is strongly temperature dependent, and that the heat conduction equation can be written in a Fourier type form. The vapor of volatile ices significantly contributes to λeƒƒ by the transfer of latent heat of sublimation but otherwise hardly affects the energy balance. The general results are applied to porous water ice, porous H2O–CO2 ice and porous H2O–CO ice. In all cases it is found that the major part of the deposited energy per unit volume is consumed for heating of the ice. Depending on the material parameters and temperature, energy is transferred mainly by solid state conduction or by the transport of latent heat due to sublimation-condensation processes.

Analysis of Shear and Thermal History During Co‐Rotating Twin‐Screw Extrusion

Abstract: A computation procedure was developed for calculating contributions of frictional and viscous heat generation during co-rotating twin-screw extrusion. Application of energy balance to experimental data (mechanical energy input, feed rate, feed moisture, screw speed, die pressure, barrel wall and dough temperature profiles) indicated how conditions affected fill, filled length, shear and thermal energy inputs to the foods. Kneading blocks increased degree of fill in partially filled sections, and dissipated 4–6 times more viscous heat than conveying elements in completely filled sections. Energy input profiles along extruder screw axis clearly demonstrated how heat generation from shear and heat transfer between extruder and foods influenced total energy input.

Method of remotely characterizing thermal properties of a sample

Abstract: A sample in a wind tunnel is radiated from a thermal energy source exteriorly of the wind tunnel. A thermal imager system, also located exteriorly of the wind tunnel, reads surface radiations from the sample as a function of time. The produced thermal images are characteristic of the heat transferred from the sample to the flow across the sample. In turn, the measured rates of heat loss of the sample are characteristic of the flow and the sample.

Two component cutting/cooling fluids for high speed machining

Abstract: A method of obtaining enhanced thermal energy between a material forming apparatus and a cooling fluid is disclosed. A two component heat transfer fluid of the type including a carrier fluid and a plurality of discrete particles that undergo a reversible latent energy transition upon the transfer of thermal energy thereto. The temperature of the particles is adjusted (heated or cooled as necessary) to the point of the beginning of latent energy transition of the particles. The fluid is then brought into contact with a heat source such as a metal forming apparatus and a workpiece, proximate the interface therebetween. The slurry may then be collected, adjusted to the point of the beginning of latent energy transition and re-circulated to the heat source.

Enhanced discharge recovery for ink jet recording apparatus

Abstract: A recovery method, for an ink jet recording apparatus having a recording head for recording by discharging the ink with bubbles formed by thermal energy applied to a heat acting area and an energy supplying device for providing the thermal energy, includes a compulsory recovery mode in which more than 10 3 predischarges are performed by supplying energy exceeding 1.48 times the minimum energy Eo necessary for producing the bubbles.

A PCM/forced convection conjugate transient analysis of energy storage systems with annular and countercurrent flows

Abstract: Latent heat energy storage systems with both annular and countercurrent flows are modeled numerically. The change of phase of the phase-change material (PCM) and the transient forced convective heat transfer for the transfer fluid are solved simultaneously as a conjugate problem. A parametric study and a system optimization are conducted. It is found that the energy storage system with the countercurrent flow is an efficient way to absorb heat energy in a short period for pulsed power load space applications.

Alkali metal thermoelectric power generator

Abstract: Disclosed is an alkali metal thermoelectric power generator comprising a plurality of thermoelectric converters, which are connected in electrical series to one another by an external electronic conductor device, each of the converters converting thermal energy into electrical energy by utilizing the phenomenon that an alkali metal, arranged on each side of a solid electrolyte, diffuses across the electrolyte if the density thereof on one side of the electrolyte differs from that on the other side of the same. The generator further comprises a piping consisting of a plurality of connection pipes for returning the alkali metal condensed in a second spatial region of each thermoelectric converter to a first spatial region thereof through a common pump. Further, the respective open ends of the connection pipes, which connect the respective first regions of the converters to one another, are positioned in those portions of the respective first regions where only the vapor phase alkali metal exists.

Thermal power generation method

Abstract: This invention relates to a thermal power generation method for power generation and for driving machinery by burning a fuel and converting its combustion heat energy to power A fuel and at least 54 wt % of oxygen are mixed and ignited in a combustor (4) and burnt in a combustion chamber (5), producing a combustion gas consisting of a high temperature steam and carbonic acid gas at a high pressure of at least 50 atms Water is sprayed into the combustion chamber (5) via a water spray nozzle (12) so as to generate the steam exceeding in weight the combustion gas by the combustion heat energy The combustion gas and the steam are mixed, are introduced into turbines (13, 14) and expand so that the thermal energy is converted to power The combustion gas and steam discharged from the low pressure turbine (14) are introduced into carbonic acid gas absorbers (18, 20) and steam condensors (19, 21), where absorption of the carbonic acid gas and condensation of the steam are effected The finally remaining gas is discharged into air by a vacuum pump (22) This thermal power generation method provides a high entropy head and power conversion efficiency of heat can be improved Since the fuel is burnt with oxygen, the amount of nitrogen oxides in the exhaust gas can be reduced

Off-peak thermal storage system providing a plurality of selected temperature outlets

Abstract: A thermal storage system (10) provides a means for storing thermal energy acquired from electricity purchased at off-peak demand times and from other fuel sources such as fossil fuels, waste heat, and solar energy. The thermal storage system (10) is also designed to supply a plurality of system outputs (124) at individually selected temperatures. The thermal storage system (10) includes a storage tank (12) for storing and heating fluids. Insulation (44) is provided to prevent energy from being transferred to the environment surrounding the storage tank (12). An external housing (46) is provided to protect the insulation (44) and to further insulate the storage tank (12). Heating elements (76) are included for the heating of the stored fluid. A fluid circulator (22) is provided for circulating the fluid to obtain a substantially constant temperature throughout the storage tank (12). An exchange assembly (24) is provided for drawing high temperature fluid from the storage tank (12), mixing the high temperature fluid with lower temperature fluid to obtain at least one selected temperature system water, and dispensing the desired temperature water to the appropriate systems. A control cabinet (26) is carried by the external housing (46) for housing the electrical components of the thermal storage system (10).

The current status of geothermal direct use development in the united states update: 1985-1990

Abstract: Information is provided on the status of geothermal direct heat utilization in the United States, with emphasis on developments from 1985 to 1990. A total of 452 sites, which include approximately 130,000 individual installations, have been identified with an annual energy use of 19.7 x 10 12 kJ. Approximately 44 % of this use is due to enhanced oil re­ covery in four midwestern states, and 30 % is due to geother­ maJ heat pumps. Since 1985, 25 new projects, which include approximately 200 individual installations, and representing a thermal capacity of 106.7 MWt and annual energy utilization of 1.1 x 10 12 kJ, have become operational or are under con­ struction. Earth-roupled and groundwater heat pumps, repre­ senting the largest growth sector during this period, add an additional 400 MWt and 1.2 x 10 12 kJ to these figures. Geo­ thermal heat pumps have extended geothermal direct heat use into almost every state in the nation. Slightly over 200 direct heat geothermal wells, averaging 150 m in depth, along with approximately 30,000 heat pump wells, have been drilled for these projects. Between 20 and 25 professional man-years of effort are estimated to have been allocated to geothermal direct heat projects during each of the five years.

Thermal power loops

Abstract: The concept of a thermal power loop (TPL) to transport thermal power over relatively large distances is presented as an alternative to heat pipes and their derivatives. The TPL is compared to heat pipes, and capillary pumped loops with respect to size, weight, conservation of thermal potential, start-up, and 1-g testing capability. Test results from a proof of feasibility demonstrator at the NASA JPL are discussed. This analysis demonstrates that the development of specific thermal power loops will result in substantial weight and cost savings for many spacecraft.

Method and apparatus for calculating thermal sensitivity

Abstract: According to a method and apparatus for calculating thermal sensitivity, a set temperature θ.sub.(th) is calculated on the basis of an air temperature Ta and a clothing thermal resistance Icl. Thermal energy Hθ.sub.(th) is supplied to a heater capable of adjusting a sensor temperature Tcr so as to set the sensor temperature Tcr to be equal to the set temperature θ.sub.(th). The thermal sensitivity is calculated on the basis of the air temperature Ta, the clothing thermal resistance Icl, the set temperature θ.sub.(th), and the thermal energy Hθ.sub.(th).