Showing papers on "Thermal energy published in 1986"

Explosive magma-water interactions: Thermodynamics, explosion mechanisms, and field studies

Abstract: Physical analysis of explosive, magma-water interaction is complicated by several important controls: (1) the initial geometry and location of the contact between magma and water; (2) the process by which thermal energy is transferred from the magma to the water; (3) the degree to and manner by which the magma and water become intermingled prior to eruption; (4) the thermodynamic equation of state for mixtures of magma fragments and water; (5) the dynamic metastability of superheated water; and (6) the propagation of shock waves through the system. All of these controls can be analyzed while addressing aspects of tephra emplacement from the eruptive column by fallout, surge, and flow processes. An ideal thermodynamic treatment, in which the magma and external water are allowed to come to thermal equilibrium before explosive expansion, shows that the maximum system pressure and entropy are determined by the mass ratio of water and magma interacting. Explosive (thermodynamic) efficiency, measured by the ratio of maximum work potential to thermal energy of the magma, depends upon heat transfer from the pyroclasts to the vapor during the expansion stage. The adiabatic case, in which steam immediately separates from the tephra during ejection, produces lower efficiencies than does the isothermal case, in which heat is continually transferred from tephra to steam as it expands. Mechanisms by which thermal equilibrium between water and magma can be obtained require intimate mixing of the two. Interface instabilities of the Landau and Taylor type have been documented by experiments to cause fine-scale mixing prior to vapor explosion. In these cases, water is heated rapidly to a metastable state of superheat where vapor explosion occurs by spontaneous nucleation when a temperature limit is exceeded. Mixing may also be promoted by shock wave propagation. If the shock is of sufficient strength to break the magma into small pieces, thermal equilibrium and vapor production in its wake may drive the shock as a thermal detonation. Because these mechanisms of magma fragmentation allow calculation of grain size, vapor temperature and pressure, and pressure rise times, detailed emplacement models can be developed by critical field and laboratory analysis of the resulting tephra deposits. Deposits left by dense flows of tephra and wet steam as opposed to those left by dilute flows of dry steam and tephra show contrasts in median grain size, dispersal area, grain shape, grain surface chemistry, and bed form.

Air cycle thermodynamic conversion system

Abstract: An air cycle thermodynamic conversion system compresses a compressible gas in a multi-stage compression process with intercoolers (128, 130) between each adjacent pair of compressors (108, 110, 112). The intercoolers (128, 130) return the compressed gas temperature to about; ambient temperature before each succeeding compression operation. The compressed gas is heated in a heat exchanger .(76) passing a heated exhaust gas (24) in counterflow with the compressed gas to increase the thermal energy of thereof. A minimum temperature gradient is maintained between the heating compressed gas and the cooling exhaust gas by establishing the two flows such that they both have about equal heat capacities. The heated compressed gas is expanded in a turbine (130) to produce at least enough torque to drive the multi-stage compression system. Additional torque may be produced in the turbine for driving a using process. Alternatively, an excess of heated gas, beyond that required for driving the turbine, may be fed directly to a using process. Further heat capture may make use of the effluent heated medium from the intercoolers as well as the exhaust from the turbine. In the preferred embodiment, the working gas in the compressors, intercoolers and turbine is air.

Thermal electron transport in direct-drive laser fusion

Abstract: Thermal electron transport plays a key role in direct-drive laser fusion (1). In efficient high-gain targets illuminated by submicrometre laser light, the laser light is absorbed by inverse bremsstrahlung in the low-density corona up to the critical density where the light is fully reflected. The energy absorbed is then conducted by electron thermal transport to the ablation surface where the cold, solid target material is ablated producing the "rocket" action that drives the target inwards. Figure 1 describes schematically the processes and the conditions in the target that pertain to the thermal electron transport. The absorbed laser energy creates a heat front that progresses through the cold target material; the corona, the region outside the critical surface, is almost isothermal because of the good thermal conductivity and the low density of the blowoff material. The primary effect of the thermal electron transport is on the efficiency of the drive; any reduction in the heat flux between the corona and the ablation surface directly results in diminished drive efficiency. When the thermal flux is reduced, the energy not transported into the ablation region accelerates the coronal material. A secondary effect of the thermal heat transport is on the absorption fraction. When the thermal flux is reduced, the excess

On Radiation-Affected Flame Propagation in Gaseous Mixtures Seeded with ln´ert Particles

Abstract: Abstract–We employ asymptotic techniques to study the propagation of a planar premixed flame in a gaseous mixture sceded with small, inert particles. Assuming that: i) the particles to gas heat capacity ratio is very small, ii) the phases are in local thermal and mechanical equilibrium, iii) the attenuation to conduction-convection length ratio is very large. iv) the radiant to convective energy flux ratio is small, v) the activation to thermal energy ratio is large we get the changes in flame structure and its increase in speed due to radiative (self-) preheating. The theory is applied first to steady flames, by using differential approximations of the radiative transfer equation. It is then extended to take account of a better description of radiative exchanges. including scattering and spectral effects, and is used to investigate the propagation of unsteady, planar flames.

Coating thickness measurement

Abstract: In the present invention, a discrete region of the TBC is heated, as by applying a controlled quantity of laser energy onto the region for a time interval. Then, the radiant thermal energy of a region outside the laser strike region is measured at a predetermined time following the termination of the laser pulse. The intensity of this measured radiant energy is then compared with the radiant intensities which have been experimentally obtained from known thickness specimens and the thickness is inferred therefrom.

System for solar energy collection and recovery

Abstract: A system for the collection of solar radiation and the recovery of thermal energy therefrom includes solar radiation receiver means (18) at or near the focus (24) of a solar radiation concentrating means (16) for absorbing the solar radiation, converting it to thermal energy and transferring the thermal energy to ambient air drawn over the receiver means (18) and, thereafter, directed to an energy reclamation unit (200). In the energy reclamation unit (200) the heated ambient air deposits a portion of its thermal energy in regenerators (50, 52), from which it is recovered by a compressed air stream, and transfers a portion of its thermal energy to a power fluid. The thermal energy of the ambient air is reclaimed from the compressed air stream and the power fluid as shaft work in expansion turbines (72,88). In a preferred embodiment, the solar radiation receiver (18) means comprises a high temperature resistant, porous, convex enclosure having inner (45) and outer (44) porous, convex surfaces arranged in spaced apart nested relationship for defining therebetween an annular space (46) which is randomly filled with a plurality of close to ideal black body solar radiation absorbing elements (47).

Effects of vibrational enhancement of N2 on the cooling rate of ionospheric thermal electrons

Abstract: It is shown that the cooling rate of ionospheric thermal electrons by molecular nitrogen may be reduced by more than a factor of 3 as a result of the enhanced vibrational excitation of N2 from a number of chemical sources. Furthermore, under conditions of enhanced F region electron densities (greater than 10 to the 6 per cubic centimeter), N2 may act as a small net source rather than as a sink of electron thermal energy. The object of the study is to use results of the Atmospheric Explorer program and improved laboratory reaction rate measurements to evaluate the impact of N2 vibrational on the transfer of energy between N2 and thermal electrons.

Study of solids by use of nonthermalized positrons

Abstract: We have measured the energy distribution of positrons reemitter from the surfaces of solids after being implanted at low energy. It is shown that this provides a unique possibility to study energy losses of a charged particle down to near thermal energy. Such measurements are used to estimate the positron thermalization time in Al. A dramatic change in this energy distribution was observed after oxidation of the Al surface. We attribute this to the band gap of the oxide. Trapping of epithermal positrons with a remarkably high cross section was observed for both Al and Cu.

Heat pump systems

Abstract: The present invention relates to an improved heat pump system of a heating system which also comprises a utilization circuit. The heat pump system comprises a generator (2), an absorber (1), a condenser (5) and an evaporator (7), and the utilization circuit for circulation of a heat carrier medium comprises heat exchanger means (1a, 5g, 15, 17) for removing thermal energy from the heat pump system. To supplement the thermal output of the heat pump system, when the utilization circuit requires a greater thermal output than can efficiently be achieved by the heat pump system alone, a supplementary condenser (25) is proved in the generator, the condenser comprising a heat exchanger - (25a) in heat exchange with vapour in the generator which can be connected in the utilization circuit by operation of a valve (WV) when additional thermal energy is required. Opening of the valve (WV) occurs simultaneously with an increase in the energy provided to the generator.

Building perimeter thermal energy control system

Abstract: A microprocessor-based perimeter thermal energy control system regulates heating and cooling in the perimeter area of a building in accordance with instantaneous and integrated heat flow measurements and instantaneous temperature deviation measurements. Control of heat pumps and air conditioning units is provided as is automatic switching between heating and cooling. The inherent thermal parameters of the space are inductively determined and used by the system to continually self-adapt to the heat flow properties of the space. The gain of the heat flow based control system is varied automatically as a function of the deviation between the actual space temperature and the desired set point temperature. Morning recovery is initiated and regulated in response to instantaneous and integrated heat flow measurements and inductively determined thermal space parameters and produces a near linear stepwise change in the temperature of the space from night setback to occupancy temperature.

Energetics of multiple oxides with spinel structure

Abstract: A thermodynamic model for multiple oxides with spinel structure based on the atomistic approach (lattice energy, enthalpy, bulk modulus) and semiempirical estimates (heat capacity functions, entropy, thermal expansion) is presented. The model fits the experimental high temperature free energy values of the reference compounds, with a mean absolute error of 0.65 percent (19 values). The standard state stable configuration of most reference compounds is shown to be achieved at a local minimum in the free energy vs. degree of inversion function. This is interpreted as evidence of internal consistency of the model.

Low-Temperature Specific Heat

Abstract: Numerous discussions of lattice specific heat are available in the literature; for descriptive introductory summaries, the reader is directed to standard texts, such as that of Kittel [Kit68], and a cryogenic monograph in this series by Gopal [Gop66]. In developing the Debye equations, it is usual to begin by calculating the thermal energy associated with the vibrations of N atoms of a solid. The resulting quantity is conveniently referred to as the “heat capacity” of the assembly. The Debye calculation takes place implicitly at constant volume, and leads accordingly to the constant-volume heat capacity, C v , which is, therefore, associated with some fixed volume, V, of material. If the solid is heated at constant pressure it generally expands, and in so doing absorbs some extra energy. The difference between the associated constant-pressure heat capacity, C p , and C v at some temperature T, is C p — C v = TVβ v 2 K, where β v is the volume expansion coefficient and K is the bulk modulus. Unless lattice expansion and its consequences are of special interest, as in Chapter 9, the difference C p – C v may be neglected, particularly below room temperature [Kit68, p. 165], and the bare symbol, C, may be assigned to the general heat capacity. In what follows that symbol will also be assigned to the molar heat capacity or the molar specific heat, while the superscripts v and g will designate specific heats per unit volume (cm3) and per gram, respectively. A subscript g may be employed to indicate lattice1 specific heat if a distinction between it and the electronic specific heat component of metals (see below) is to be made.

Method for regulating the energy supply to a sealing device for the sealing of thermoplastic material

Abstract: A method for regulating the supply of energy to a sealing device for the sealing of thermoplastic material includes supplying electric energy to a sealing device pressed against the combined thermoplastic material with whose help the said electric energy is converted to thermal energy. The amount of energy supplied to the sealing device is variable to compensate for heat losses brought about by heat leakage during the sealing opertion. An arrangement for carrying out the method is also disclosed.

Phase change thermal energy storage material

Abstract: A thermal energy storge composition is disclosed. The composition comprises a non-chloride hydrate having a phase change transition temperature in the range of 70°-95° F. and a latent heat of transformation of at least about 35 calories/gram.

Chemical heat pipe employing self-driven chemical pump based on a molar increase

Abstract: A chemical pump system that utilizes a self-driven compressor to increase the system pressure while obviating the need for a one-way valve and liquid head to provide the driving force for the reactants, thus enhancing long distance transport. The system comprises a chemical heat pipe employing reversible endothermic/exothermic chemical reactions to transfer thermal energy between a heat source and a heat sink. At least one reactant is self-driven substantially unidirectionally through the heat pipe by compressing the reactant(s) with a compressor and heating the reactant(s) to a predetermined pressure and temperature sufficient to form a reaction product having at least a 150% molar increase. The reaction product is expanded with an expander that is linked mechanically to the compressor. The expansion energy is sufficient to compress the reactants to the predetermined pressure while maintaining the self-driven unidirectional flow.

Turbulent thermal in a stratified atmosphere

Abstract: An approximate analytical model of a turbulent thermal in a stratified atmosphere is proposed. This model makes it possible to predict the dynamics of the ascent, suspension and oscillation processes of a buoyant cloud both within the troposphere and on entering the stratossphere. The values of the heat energy needed for the thermal to penetrate the tropopause in northern and southern latitudes are estimated. Estimates are obtained for the amount of material dumped into the stratosphere. A method of determining the thermal energy of volcanic eruptions of the explosive type is proposed.

Thermochemical method and device for storing and discharging heat

Abstract: Thermotransformer for storing and unstoring heat with a double raise in thermal potential by performing thermo-chemical processes that present Clapeyron curves that intersect in the temperature range involved, this device being applicable to heat pumps and the handling of thermal energy.

Community thermal energy exchange system

Abstract: A system of interconnecting a plurality of users of low grade thermal energy exchange has a number of users which are heat sources and a number of users which are heat sinks to balance heat flux. Heat is exchanged between a nontoxic primary heat transfer liquid and secondary heat transfer fluids for serving such users. The users are charged in proportion to the amount of heat transferred. Separate means are provided for selectively exchanging heat with the primary heat transfer liquid for maintaining the average temperature of the liquid within a desired temperature range. A municipal water main is a desirable source or sink of low grade thermal energy and nontoxicity of primary heat transfer liquid maintains the integrity of the water system.

Analysis and Measurements of Interzonal Natural Convection Heat Transfer in Buildings

Abstract: Natural convection heat transfer through doorways can be an important process by which thermal energy is transferred from one zone to another zone of a building. The topic of this paper is interzonal natural convection in a two zone and a three zone multilevel full scale building. Aperture velocity and temperature distributions are measured and the experimental interzonal mass flow rate and heat transfer are determined. A Bernoulli model is derived to predict the neutral heights, velocity profiles, and interzonal heat transfer. The measured and predicted interzonal flow rate and heat transfer are compared and found to be in good agreement.

Predicting the thermal protective performance of heat-protective fabrics from basic properties

Abstract: Novel experimental techniques were developed to measure changes in the weight, thickness, density, heat capacity, heat conductivity, and infrared (IR) transmission of protective fabrics occurring during a thermal protective performance (TPP) test. Comparisons are made between polybenzimidazole (PBI), aramid, a PBI/aramid blend fabric, and flame-retardant (FR) cotton fabrics in the 250 g/m 2 (7.5-oz/yd 2 ) weight range. This research analyzes changes in fabric heat transfer properties produced through mechanisms of pyrolysis, char formation, and shrinkage. Fiber character is shown to play a decisive role in determining the direction and extent of change in thermophysical properties. Retention of air volume is found to be critical to prolonged thermal protection performance. Experimental data indicate that air and fiber conduction dominate in intense exposures to a mixture of radiant and convective thermal energy; direct radiant transmission is not an important contributor to the total heat transferred in these exposures. The ability of fabrics to maintain surface fibers is thought to have significant impact in blocking convective heat transmission. The degradation behaviors of different materials are compared and related to their thermal protective performance.

The development of large-scale thermal_plasma systems

Abstract: This paper descriptionbes the development of large-scale thermal-plasma systems, which was motivated, in general, by the potential cost savings that could be achieved by their use as a replacement for the more conventional methods used in the generation of thermal energy. The anticipated cost savings arise not only from the use of plasma-generating devices but from the manner in which they have been interfaced with a furnace to process particular materials, mostly as fines. Thermal-plasma systems fall into two categories: non-transferred-arc and transferred-arc devices. In general, transferred-arc devices have been interfaced with open-bath furnaces in which melting or smelting processes are carried out, while non-transferred-arc devices have normally been applied to shaft furnaces. Water-cooled transferred-arc devices are somewhat limited in power (about 5 MW) because of the relatively Iow voltages (300 to 500 V) that can be attained in open-bath furnaces, where very long arcs are undesirable, and because only relatively Iow levels of current can be carried. Graphite electrodes can overcome the restriction of current, and power levels of 30 to 50 MW seem feasible, even with one electrode, if direct current is used. Multiple water-cooled devices are capable of attaining similar power levels, but the capital costs are much higher. Costs due to electrode wear are lower for water-cooled systems, but expensive gases are needed for transferred-arc devices. Mintek conducted extensive pilot-plant work in which water-cooled devices were used initially but graphite electrodes were used subsequently to produce ferrochromium from fines. Transferred-arc open-bath configurations were used. This work led to a decision by Middelburg Steel & Alloys (MS&A) to install a 16 MVA furnace of semiindustrial scale to produce ferrochromium alloys based on the ASEA d.c. arc furnace developed for the Elred process. Non-transferred-arc devices have attained reasonable scale-up to the 6 to 8 MW power level, and high-voltage operation, which is inherent in such devices, has enabled lower currents to be used. Nevertheless, multiple systems are still necessary to accommodate large-scale applications, and this can be costly from a capital point of view. The cooling requirements are large, and can represent a considerable loss of electric energy. Shaft furnaces equipped with non-transferred-arc devices are suitable for the processing of materials that have volatile species, e.g. silica or manganese, or where the shaft is used to prereduce oxides that are amenable to gas-solid reactions. It is probably in the treatment of light and refractory metals that plasma technology will achieve its greatest development in the years to come. The energy requirements for the production of these metals are high, and very Iow oxygen potentials are necessary. These are factors that favour thermal plasma. Much developmental work is still needed in this interesting field. It should be remembered that electrically generated thermal energy is a unique temperature source that, in many instances, cannot be replaced technically or economically by the combustion of a fuel.

Mixed convection flow over localized multiple thermal sources on a vertical surface

Abstract: A theoretical study of the effect of an aligned, aiding, externally induced free stream on the buoyancy‐induced flow adjacent to a vertical surface, on which isolated thermal sources are located, is carried out. The thermal sources are taken as long planar sources of finite height and the resulting two‐dimensional flow is numerically studied. The nature and the basic characteristics of the mixed convection flow that arises are investigated. Of particular interest is the interaction of the wakes generated by the sources and the dependence of this interaction on the thermal energy input and the distance between the sources. The distance beyond which the two sources may be treated as independent is investigated. The governing parameters are varied over wide ranges and their effect on the flow and on the transport mechanisms is studied in detail. The flow over and heat transfer from a thermal source located in the wake of an upstream source are determined. The parametric range for which a boundary‐layer treatment is satisfactory is determined by solving the full elliptic equations. Several other important features are obtained and considered in terms of the underlying mechanisms.

Solid-state image pick-up device

Abstract: PURPOSE:To alleviate the after-image phenomenon by applying bias charges to the photodiode of a solid state image pick-up derive or applying thermal energy to signal charges stored in the photodiode when the illumination of an object is low or when the temperature of the solid state image pick-up element is low CONSTITUTION:Illumination information on an object obtained from an IL-CCD output signal is supplied to a bias light controller 4 to control a voltage applied to a bias light bulb 5 to control the quantity of the bias light, thereby controlling the bias charge amount applied to a photodiode When the illumination of the object is low, the transfer efficiency is remarkably improved by slightly applying the bias charge The output signal of a temperature detector 8 is supplied to a heating temperature controller 9 to control a voltage or a current supplied to a heater 10, thereby controlling the thermal energy to a solid state sensor 1 When the sensor is used at low temperature such as 0 degC, the thermal energy is supplied externally to the sensor to remarkably improve the transfer efficiency

Process for the storage of a mechanical or thermal energy in chemical form and for recovery of at least a part of the said stored energy in mechanical form and plant for implementing this process

Abstract: The storage of a mechanical or thermal energy in chemical form and the recovery of the stored energy in mechanical form. An evaporator-separator 1 into which heat is introduced at a level T1 is employed, together with a condenser 2 in connection with a cold source at a temperature T2 which is lower than T1. Between the evaporation chamber 11 of the evaporator-separator and the condensation chamber 22 of the condenser, solvent vapour is circulated in order to store the energy, during the energy storage stage, by producing the solvent S and the concentrate C which are delivered to storages 4, 5 and, in an energy production stage, to reemploy the solvent and the concentrate which is stored to drive a vapour engine 6. The invention applies especially to the control of the supply of electrical energy.

Detailed thermal performance data on conventional and highly insulating window systems

Abstract: Data on window heat-transfer properties (U-value and shading coefficient (SC)) are usually presented only for a few window designs at specific environmental conditions With the introduction of many new window glazing configurations (using low-emissivity coatings and gas fills) and the interest in their annual energy performance, it is important to understand the effects of window design parameters and environmental conditions on U and SC This paper discusses the effects of outdoor temperature, wind speed, insolation, surface emittance, and gap width on the thermal performance of both conventional and highly insulating windows Some of these data have been incorporated into the fenestration chapter of the ''ASHRAE Handbook - 1985 Fundamentals'' The heat-transfer properties of multiglazed insulating window designs are also presented These window systems include those having (1) one or more low-emittance coatings; (2) low-conductivity gas-fill or evacuated cavities; (3) a layer of transparent silica aerogel, a highly insulating microporous material; or (4) combinations of the above Using the detailed building energy analysis program, DOE 21B, we show that these systems, which all maintain high solar transmittance, can add more useful thermal energy to a space than they lose, even in a northern climate Thus, in terms of seasonal energy flows,more » these fenestration systems out-perform insulated walls or roofs« less

Thermally regenerative hydrogen/oxygen fuel cell power cycles

Abstract: Two innovative thermodynamic power cycles are analytically examined for future engineering feasibility. The power cycles use a hydrogen-oxygen fuel cell for electrical energy production and use the thermal dissociation of water for regeneration of the hydrogen and oxygen. The TDS (thermal dissociation system) uses a thermal energy input at over 2000 K to thermally dissociate the water. The other cycle, the HTE (high temperature electrolyzer) system, dissociates the water using an electrolyzer operating at high temperature (1300 K) which receives its electrical energy from the fuel cell. The primary advantages of these cycles is that they are basically a no moving parts system, thus having the potential for long life and high reliability, and they have the potential for high thermal efficiency. Both cycles are shown to be classical heat engines with ideal efficiency close to Carnot cycle efficiency. The feasibility of constructing actual cycles is investigated by examining process irreversibilities and device efficiencies for the two types of cycles. The results show that while the processes and devices of the 2000 K TDS exceed current technology limits, the high temperature electrolyzer system appears to be a state-of-the-art technology development. The requirements for very high electrolyzer and fuel cell efficiencies are seen as determining the feasbility of the HTE system, and these high efficiency devices are currently being developed. It is concluded that a proof-of-concept HTE system experiment can and should be conducted.