Showing papers on "Thermal energy published in 1996"

Introduction to thermodynamics and heat transfer

Abstract: Intro to Thermodynamics and Heat Transfer 2e 1 Introduction and Overview Part 1 Thermodynamics 2 Introduction and Basic Concepts 3 Energy, Energy Transfer, and General Energy Analysis 4 Properties of Pure Substances 5 Energy Analysis of Closed Systems 6 Mass and Energy Analysis of Control Volumes 7 The Second Law of Thermodynamics 8 Entropy Part 2 Heat Transfer 9 Mechanisms of Heat Transfer 10 Steady Heat Conduction 11 Transient Heat Conduction 12 External Forced Convection 13 Internal Forced Convection 14 Natural Convection 15 Radiation Heat Transfer 16 Heat Exchangers Appendix 1 Property Tables and Charts (SI Units) Appendix 2 Property Tables and Charts (English Units)

Amplitude-Modulated Lock-In Vibrothermography for NDE of Polymers and Composites

Abstract: We present a nondestructive testing method based on lock-in thermography with mechanical heat excitation. Stresses are generated in the sample by vibrating it with a mechanical shaker. The mechanical energy is converted to thermal energy due to the acoustical damping. The defected regions have a stronger damping and also a stress concentration next to them, both of which result in a higher temperature generation. Because of the changes of the thermal properties, the defects also affect the heat conduction. These phenomena result in thermal anomalies due to the defects. The high-frequency vibration used for excitation is amplitude-modulated with a low frequency. The magnitude and phase of the sample temperature with respect to the modulation are measured with an infrared camera and a software lock-in technique. The use of phase information increases the reliability of the defect detection, and the application of high vibration frequencies results in a good thermal signal even at low stress levels,...

A perspective on thermal energy storage systems for solar energy applications

Abstract: The use of thermal energy storage (TES) systems is essential for solar power systems because of fluctuations in the solar energy input. Several classes of storage may be required for a single installation, depending on the type and scale of the solar power plant itself, and the nature of its integration with conventional utility systems. For heating and hot water applications, water and phase change materials (PCMs) constitute the principle storage media. Soil, rock and other solids are used as well. Water has the advantage of approximately 80% less volume than that of water for a temperature variation of 10°C, which is the difference between temperatures of a fully charged and a fully discharged storage tank. Some PCMs are viscous and corrosive, and must be segregated within the container in order to be used as a heat transfer medium. For heat storage, two PCMs must be available, unless heat pumping is employed. A variety of solids is also used; rock particles of 20 to 50 mm in size are most prevalent. Well-designed packed rock beds have several desirable characteristics for energy storage. The heat transfer coefficient between the air and the solid is high, the cost of the storage material is low, the conductivity of the bed is low when air flow is not present and a large heat transfer area can be achieved at low cost by reducing the size of particles. TES systems have also been suggested for storing thermal energy at medium (38–304°C) and high temperatures (120–566°C). For instance, systems in an oil-rock system for hot water and heat-recovery applications are examples of medium-temperature applications, while those in molten nitrate salt systems (an excellent storage medium) for steam production for process applications are for high temperatures. Oil-rock TES, in which the energy is stored in a mixture of oil and rock in a tank, is less expensive than molten nitrate salt TES, but is limited to low-temperature applications. However, this oil-rock TES has been proven successful for solar thermal applications. The selection of the type of TES depends on various factors such as the storage period (diurnal or seasonal), economic viability, operating conditions, etc. In this article, a study of TES systems (including materials) is presented particularly with solar thermal applications in mind. The evaluation of their performances, cost and economic viability, ease of installation, cleanliness, environmental impact, safety factors, technological usability and applicability are discussed.

Thermal energy storage and delivery system

Abstract: Described is a thermal energy storage and delivery system for delivering thermal energy to both a passenger compartment of a vehicle and a component, such as a battery, located externally of the passenger compartment. The system capitalizes on excess capacity stored in a thermal energy storage apparatus, to heat the external component in addition to the passenger compartment.

Correlated energy landscape model for finite, random heteropolymers.

Abstract: In this paper, we study the role of correlations in the energy landscape of a finite random heteropolymer by developing the mapping onto the generalized random energy model ~GREM! proposed by Derrida and Gardner @J. Phys. C19, 2253~1986!# in the context of spin glasses. After obtaining the joint distribution for energies of pairs of configurations, and by calculating the entropy of the polymer subject to weak and strong topological constraints, the model yields thermodynamic quantities such as ground-state energy, entropy per thermodynamic basin, and glass transition temperature as functions of the polymer length and packing density. These are found to be very close to the uncorrelated landscape or random energy model ~REM! estimates. A tricritical point is obtained where behavior of the order parameter q changes from first order with a discrete jump at the transition, to second-order continuous. While the thermodynamic quantities obtained from the free energy are close to the REM values, the Levinthal entropy describing the number of basins which must be searched at the glass transition is significantly modified by correlations. @S1063-651X~96!02406-3#

Applicability of Carbonation/Decarbonation Reactions to High-Temperature Thermal Energy Storage and Temperature Upgrading

Abstract: Storing thermal energy by thermochemical means seems very attractive since large amounts of energy can be stored per unit mass, and such systems can function as a heat pumps. For storing high temperature heat energy such as concentrated solar energy at 773 K, various candidate chemical reactions have been evaluated in terms of energy storage density, turning temperature, toxicity, corrosiveness, and other factors. The dissociation reaction of CaCO3 is found to be very promising. Three methods for storing the dissociation product CO2 gas; (i) storing as a compressed gas, (ii) letting the CO2 gas react with a metal oxide and storing it in the form of another carbonate, and (iii) adsorbing with an appropriate adsorbent and storing as an adsorbed gas; have been proposed and the respective thermal operating efficiencies at various upgraded temperatures are evaluated. The CaO-CO2 metal oxide system seems very effective for temperature upgrading around 1273 K and the CaO-CO2-compressor system seems suitable for storing and delivering heat energy at the same temperature. Whether the efficiency of the CaO-CO2-Adsorbent system is comparable to one of the other two systems or not greatly depends upon the adsorptivity of the adsorbent.

Sensitivity of buoyant plume heights to ambient atmospheric conditions: Implications for volcanic eruption columns

Abstract: A theoretical model is developed to investigate the sensitivity of buoyant atmospheric plumes to a wide range of ambient atmospheric conditions, including the temperature gradient, the latitude of the source, and the season. The formulation highlights the compressibility of an ideal gas, internal consistency between the governing equations for the conservation of momentum and energy, and the explicit use of the equation of state. Specific results are presented for water vapor plumes and implications are developed for multicomponent (water vapor, silicate particles, and condensates) volcanic plumes. If plume cooling is due solely to adiabatic expansion and the entrainment and mixing of ambient air, then the atmospheric temperature gradient is shown to be a dominant influence on plume height. Changes in the atmospheric gradient of 10 K/km cause the height of a low-level plume to diifer by a factor of 2. We estimate the magnitude of this effect on volcanic plumes by considering water vapor erupted with equivalent heat fluxes. The sensitivity of plumes to ambient conditions is a result of the small density difference driving buoyancy. The plume density, in turn, is strongly controlled by the thermal energy of the system. Sensitivities associated with the thermal energy balance in the eruption column are also investigated. A modest thermal loss (1–2%/km) from the column by a process other than entrainment can result in a plume height significantly lower than one that cools by entrainment alone. Additional cooling of this magnitude could be caused by a variety of combinations of phenomena, including radiative heat loss and, possibly, the conversion of heat energy into turbulent rotational energy. For particle-laden plumes, there is the possibility of additional heat loss through the fallout of solids from the eruption column. To understand the details of the thermal energy balance in a plume, measurements must be made of the bulk plume temperature profile under known atmospheric conditions.

Energy system for buildings

Abstract: The invention relates to an energy system for buildings using solar absorbers, heat exchangers and heat accumulators, which has the following features in order to improve the thermal energy balance of the building: the solar absorber has tubes or pipes (7, 8) laid to form meanders between the roofing and an insulating layer arranged thereunder; the solar absorber is subdivided into at least two zones each with its own liquid circulation system (7, 8); there is arranged below the building a solid heat-accumulator to which heat can be supplied or removed using embedded tubes or pipes (21, 23, 24, 26); the heat accumulator is subdivided into at least two zones, i.e. a central zone (21, 22) and an outer zone (23, 24) each with its own liquid circulation system; during operation of the heat accumulator, liquid is supplied by way of thermally controlled valves from the liquid circulation system of each zone (7, 8) of the solar absorber firstly to the liquid circulation system (21) of the central heat accumulator zone and, secondly to the liquid circulation system (23, 24) of the outer heat accumulator zone, when the temperature of the liquid from the circulation system of the respective zone is greater at least by one value ranging from 2 to 8 °C, preferably 2 °C, than the temperature of the respective solid accumulator zone; and during heat removal, liquid is pumped into a heating system (17, 18) of the building by thermally controlled valves, firstly from the liquid circulation system (23, 24) of the outer heat accumulator zone and, secondly, from the liquid circulation system (21) of the central heat accumulator zone.

Non-polluting open Brayton cycle automotive power unit

Abstract: Stored thermal energy absorbed by a working fluid (22) from hot thermal-energy-storage material (16) energizes an open-Brayton-cycle automotive power-generation unit (10). Sealed ceramic tubes (28), filled with a material that melts within thermal-energy-storage material's operating temperature range provides thermal energy storage. A rotary impeller (36) draws the flow of working-fluid (22) into the unit's compressor (32) from the surrounding atmosphere for discharge into a heat regenerator (56). The regenerator (56) warms working fluid (22) using thermal energy extracted from hot turbine exhaust that is then discharged into the atmosphere. Working-fluid (22) from the compressor (32) flows from the regenerator (56) through a heating vessel (12) into the turbine (76). The unit (10) includes an alternator (102) which generates electricity for powering an automobile's electric drive motors (194). Stored thermal energy may be regenerated either by a combustible-fuel burner (174) and/or an electrical heated (112) located within the heating vessel, or by an automated regeneration station (124).

Thermosyphon-powered jet-impingement cooling device

Abstract: A thermosyphon-powered jet-impingement cooling device delivering superior thermal energy dissipation for compact heat sources such as electronic devices. Thermal energy from a heat source travels through the heat source/heat spreader plate interface to the heat spreader plate and heat spreader plate extended surface. Thermal energy is transferred by convection to a single or two-phase coolant media. The heated and/or boiling, less dense coolant begins to expand and rise. The rising coolant or vapor approaches a cold plate and velocity slows due to the greater cross-sectional flow area. The coolant heat energy is released by convection or condensation to the heat dissipation/fluid interface surface, and is then conducted through the cold plate, across the cold plate/heat dissipating device thermal interface, and then to the heat dissipating device. As the cooled media contracts and/or condenses to form droplets, the coolant or droplets begin to fall. As heated or boiling coolant continues to rise, the falling coolant or droplets are both pushed from the high pressure (heated) annulus and pulled from the low pressure (cooled) center through an impingement jet orifice. The coolant impinges against a concave heat/fluid interface surface. The impinging jet of coolant media of the present invention greatly reduces the thermal boundary layer at the point of impingement.

Atomic-Scale Origins of Friction†

Abstract: The fundamental origins of friction, an important physical phenomenon in light of both its everyday familiarity and its enormous economic impact, have been discussed and debated for at least 300 years, with very little resolved. Recent experimental investigations at atomic length and/or time scales are shedding new light on the manner in which mechanical energy is converted to thermal energy, i.e., heat.

TED - a mobile equipment for thermal response test : testing and evaluation

Abstract: The study treats the advantage of using a mobile equipment for measuring the thermal resistance in a borehole, to determine the thermal properties of the entire borehole system. Suggestions for f ...

Analysis of ac temperature wave during the measurement of thermal diffusivity of two‐layered platelike samples

Abstract: A theoretical consideration of two‐dimensional ac temperature waves in a two‐layered platelike sample for application to thermal diffusivity measurement parallel to a sample surface using an ac calorimetric method is presented. The analysis is based on the Fourier‐transformed Green’s function technique. It is concluded that this thermal system deviates from an apparent one‐layered system of which the thermal diffusivity parallel to a sample surface is calculated based on steady state heat flow under the following conditions: (a) the frequency of the supplied ac thermal energy is high, (b) the difference between the thermal diffusivities of the layers is large, and (c) the layer with higher thermal diffusivity is thin. This deviation is due to the inhomogeneous ac temperature distribution normal to the sample surface. If experimental conditions are the reverse of conditions (a)–(c), an ac calorimetric method can be used to measure the thermal diffusivity of thin samples on substrates.

An energy model for artificially generated bubbles in liquids

Abstract: A mathematical analysis is carried out to model the series of processes following the occurrence of an electron avalanche in a liquid right through to the emission of a pressure transient and the formation of a bubble. The initial energy distribution is chosen to be Gaussian and it is assumed that the electrical energy injected into the system is transformed into thermal and mechanical components. From the mechanical point of view, an outgoing spherical pressure transient is formed at the edge of the plasma region, and at a later time a bubble is also formed. Theoretically, the pressure transient accounts for about 15% of the total injected energy, while it is necessary to revert to experimental results to fix the energy associated with the bubble (about 2%). A minimum such value can, however, be estimated. The maximum pressure amplitude is calculated. Concerning the thermal component of the energy, some is absorbed as internal energy by the liquid, while the remainder is stocked as latent heat of vaporization. The maximum temperature difference is derived as are the different energies as functions of the total injected energy. The advantage of this type of model is that the gas/vapour temperature in the bubble can continue to rise after the phase change takes place. The maximum bubble size following a given energy injection is calculated assuming an adiabatic expansion process. A mathematical expression for the liquid flow induced by the outgoing pressure transient is also found. Comparison between experimental and theoretical results is particularly good.

Filter array for modifying radiant thermal energy

Abstract: A system for modifying the radiant energy spectrum of a thermal energy source to produce a desired spectral bandwidth profile including a frequency-selective resonant micromesh filter (50) confronting a thermal energy source (80). 'Micromesh filter (50) includes an array of resonant-conductive antenna elements (50', 50'') and a substrate (56) for supporting the antenna elements. Thermal radiation (82) emitted from energy source (80) is filtered by micromesh filter (50), wherein radiant energy at particular wavelengths is reflected back to the energy source, while certain wavelength photons are transmitted through the micromesh filter.

Dibasic ester based phase change material compositions

Abstract: A process for moderating the thermal energy content of a body with a container enclosing a phase change material (PCM) is detailed. The phase change material comprises a high molecular weight dibasic organic acid and mixtures thereof. Miscible aliphatic and aryl monobasic acids are also suitable as PCM constituents. The PCM is capable of absorbing thermal energy from a variety of bodies including air, heat transfer fluids, combustion reactions, radiation sources and the like. In the course of absorbing thermal energy the PCM undergoes a reversible melt. Upon the PCM being exposed to a temperature below its melting temperature, the PCM releases the stored latent heat of fusion energy absorbed upon melting and undergoes a reversible freeze.

An eight‐moment approximation two‐fluid model of the solar wind

Abstract: In fluid descriptions of the solar wind the heat conductive flux is usually determined by the use of the classical Spitzer-Harm expression. This expression for the heat flux is derived assuming the gas to be static and collision-dominated and is therefore strictly not valid in the solar wind. In an effort to improve the treatment of the heat conductive flux and thereby fluid models of the solar wind, we study an eight-moment approximation two-fluid model of the corona-solar wind system. We assume that an energy flux from the Sun heats the coronal plasma, and we solve the conservation equations for mass and momentum, the equations for electron and proton temperature, as well as the equations for heat flux density in the electron and proton fluid. The results are compared with the results of a “classical” model featuring the Spitzer-Harm expression for the heat conductive flux in the electron and proton gas. In the present study we discuss models with heating of the coronal protons; the electrons are only heated by collisional coupling to the protons. The electron temperature and heat flux are small in these cases. The proton temperature is large. In the classical model the transfer of thermal energy into flow energy is gradual, and the proton heat flux in the solar wind acceleration region is often too large to be carried by a reasonable proton velocity distribution function. In the eight-moment model we find a higher proton temperature and a more rapid transfer of thermal energy flux into flow energy. The heat fluxes from the corona are small, and the velocity distribution functions, for both the electrons and protons, remain close to shifted Maxwellians in the acceleration region of the solar wind.

Supersonic Collisions between Two Gas Streams

Abstract: A star around a massive black hole can be disrupted tidally by the gravity of the black hole. Then, its debris may form a precessing stream which may even collide with itself. In order to understand the dynamical effects of the stream-stream collision on the eventual accretion of the stellar debris onto the black hole, we have studied how gas flow behaves when the outgoing stream collides supersonically with the incoming stream. We have investigated the problem analytically with one-dimensional plane-parallel streams and numerically with more realistic three-dimensional streams. A shock formed around the contact surface converts the bulk of the orbital streaming kinetic energy into thermal energy. In three-dimensional simulations, the accumulated hot post-shock gas then expands adiabatically and drives another shock into the low density ambient region. Through this expansion, thermal energy is converted back to the kinetic energy associated with the expanding motion. Thus, in the end, only a small fraction of the orbital kinetic energy is actually converted to the thermal energy, while most of it is transferred to the kinetic energy of the expanding gas. Nevertheless the collision is effective in circularizing the debris orbit, because the shock efficiently transforms the ordered motion of the streams into the expanding motion in directions perpendicular to the streams. The circularization efficiency decreases, if two colliding streams have a large ratio of cross sections and a large density contrast. But even in such cases, the main shock extends beyond the overlapping contact surface and the high pressure region behind the shock keeps the stream of the larger cross section from passing freely. Thus the stream-stream collisions are still expected to circularize the stellar debris rather efficiently, unless the ratio

Lock-in thermography as a measurement technique in heat transfer

Abstract: An experimental temperature oscillation technique is described for determining local distributions of the heat transfer coefficient or local distributions of the thermal diffusivity of heat transferring walls. By heating uniformly one surface of the wall with sinusoidally modulated energy a temperature oscillation is generated which results in a wavelike propagation behavior of heat flow and temperature within the wall. The characteristic of the temperature oscillations at both faces of the wall depends directly on the local heat transfer conditions and the thermal diffusivity of the wall material. So the local values of the heat transfer coefficient or the thermal diffusivity can be calculated from the measured amplitudes or from the phases of the temperature waves at the surfaces. To demonstrate the applicability of the method first experiments were performed. The measured results agree reasonably well with data obtained from literature. 1. Introduction Because of their simplicity and accuracy temperature oscillation techniques obtained an increasing importance for measuring purposes in heat transfer. The basic idea of these techniques is to supply modulated energy to the testing object which results in a wavelike propagation behavior of heat flow and temperature within the object material. By measuring and analyzing the temporal and spatial propagation behavior of the thermal waves, numerous thermophysical parameters of the testing object can be determined. With an earlier developed method [1] for measuring the local heat transfer coefficient or the local thermal diffusivity periodic temperature oscillations are optically generated at one spot of the object surface by periodic heating with a focused laser beam. This method was then refined by Wandelt [2] to achieve a much higher accuracy. Measurements which cover the whole object surface have to be performed point by point in a rasterlike fashion. At each pOint one has to wait a minimum time, until the local stationary state is achieved. So measuring times can be long which might be not acceptable for practical applications. The technique presented overcomes the restrictions of the method described above. Local distributions of the heat transfer coefficient as well as local distributions of the thermal diffusivity can be determined for the whole testing object within a short time. 2. Measurement principle The measurement principle is illustrated in figure 1. Sinusoidally modulated thermal energy is supplied uniformly to the whole surface of the object under consideration. From the surface a nearly plane thermal wave propagates into the material after the initial transient behavior. The local amplitudes and phases of the temperature waves at both sides of the wall depend on the properties of the wall, the frequency of the oscillation and the heat flux to the surrounding. By measuring the local temperature oscillations at each surface point and by evaluating the local phases and amplitudes of these oscillations, a phase angle image and an amplitude image can be extracted for the whole surface. In principle, a map of the local heat transfer coefficient or a map of the locally varying thermal diffusivity can now be calculated from the data of both the images. For monitoring and recording thermal waves a rapid infrared scanning device (AGEMA THV900LW/ST) is used, which allows a non-contacting measurement of the small wall temperature changes with high thermal, spatial and time resolution. The thermal information from all scanned pOints are analyzed with a PC.

Utilization of low-value heat in a supercharged thermal engine

Abstract: A power plant comprises a combustion engine having a supercharger for receiving low pressure feed air and delivering compressed feed air to the engine, a feed air heater for transferring low-temperature thermal energy from a heat source to the low pressure feed air, and a feed air cooler for recovering higher-temperature thermal energy from the compressed feed air.

Effect of glass cover inclination and parametric studies of concentrator‐assisted solar distillation system

Abstract: In this communication, a thermal analysis of concentrator-assisted solar distillation unit has been developed to optimize the glass cover inclination. The thermal energy is based on the energy balance equation for each component of the distillation unit by incorporating the proposed modified Dunckle's relation for internal heat loss. An analytical expression for various parameters, namely the water and glass cover temperatures, hourly and daily yield and an instantaneous thermal efficiency, has been derived. Numerical computations have been carried out and it has been observed that the daily output increases with inclination.