Showing papers on "Thermal reservoir published in 1987"

Steady state heat flow in a random medium and the linear heat flow‐heat production relationship

Abstract: The heat transfer in the earth's crust is described by three-dimensional steady state heat conduction in a heterogeneous medium with randomly varying thermal conductivity and heat production. The heat flow-heat production relationship generally emerges as the regression of the surface heat flow on surface heat production. The case of normally distributed thermal conductivity and heat production in an upper heterogeneous slab yields a linear relation, the slope and intercept of which depend on the horizontal and vertical correlation scales of heterogeneity, the correlation between thermal conductivity and heat production, and the ratio of heat produced within the zone of heterogeneity to heat from deeper origin. The model is a stochastic extension of the traditional homogeneous slab model, and the intercept of the linear relationship predicts the true average heat flow at a depth equal to the slope, when this depth is smaller than the true slab thickness.

Freezing and thawing of soils and permafrost containing unfrozen water or brine

Abstract: An analytical solution is presented for freezing and thawing of soils and permafrost containing unfrozen water or brine and with temperature dependent thermal properties. Latent heat effects are incorporated into an apparent heat capacity. The partially frozen soil is divided into layers, each with constant thermal properties and with fixed temperatures at the layer boundaries which move with time in a multiple moving boundary problem. Solutions are obtained for the positions of the layer boundaries and for the temperature distribution within each layer. The theory is used to predict the maximum depth of ice penetration and the temperature profile in a large artificial island. Maximum ice penetration in the island is greater than that determined from the two-layer Neumann solution. Predicted temperature profiles are relatively smooth and do not exhibit a sharp break at the phase boundary. The solution procedure is also applicable to other heat conduction problems in permafrost containing unfrozen water or brine.

The dynamics of a solid-adsorption heat pump connected with outside heat sources of finite capacity

Abstract: The problem of the response of a heat pump to the solicitations of the heat reservoirs is an important problem which has not been extensively studied up to now In this publication, a case study concerning a solid adsorption heat pump working with the zeolite water pair in a single state cycle is presented The equations needed to solve the problem are presented and are solved numerically in a particular case The numerical simulation is validated by experimental results A sensitivity study of the results of the numerical simulation is then presented vs the most important parameters The thermodynamic cycle is seen to be very sensitive to the values of the various heat exchange coefficients as well as to the heat rates exchanged between the heat pump and the heat reservoirs

Time-dependent canonical formalism of thermally dissipative fields and renormalization scheme

Abstract: The canonical formalism of thermally dissipative semifree fields in the time‐dependent situation is presented. The use of thermal covariant derivatives simplifies the formulation considerably. With this formalism one can unambiguously obtain the interaction Hamiltonian under any thermal situation which together with the free propagator enables perturbative calculations to be performed. The ‘‘on‐shell’’ renormalization condition in the time‐dependent case is also discussed. The model of a system with a thermal reservoir illustrates how the present formalism works in time‐dependent situations.

Available work from a finite source and sink: How effective is a Maxwell’s demon?

Abstract: The maximum work obtainable from a finite heat source and finite heat sink, initially at respective temperatures T+ and T−, is determined as a function of the temperature ratio τ=T−/T+ and the heat capacities of the source and sink. The thermal efficiency with which this work is delivered is found to be well approximated by η*=1−τ1/2 for τ≥0.1, independent of the source and sink heat capacities. It is noted that η* occurs in other contexts for which work or power output is optimized, and is a surprisingly ‘‘universal’’ efficiency. A reversible polycycle that delivers the maximum work using an ideal gas working fluid is found to exist only if the heat capacity of the heat sink exceeds that of the working fluid. An example of a finite source/sink combination from which work can be generated is an enclosed gas, divided in half by a partition with a small, controllable trap door operated by a Maxwell’s demon. If the demon opens and closes the door selectively, so as to achieve a temperature difference across ...

Limitation in the Apparent Heat Capacity Formulation for Heat Transfer With Phase Change

Abstract: Of the various approaches for modeling problems in heat conduction with phase change (the classical Stefan problem) the apparent heat capacity formulation still appears to be one of the preferred methods, judging from the recent literature. The principal advantage of this approach is that temperature is the primary dependent variable that derives directly from the solution. However, it is well known that this formulation suffers from a singularity problem for a phase change that occurs at a fixed temperature. This difficulty can be circumvented by assuming that the phase change occurs over a small temperature interval [Hashemi and Sliepcevich (1)]. Another alternative would be to utilize an enthalpy formulation [Civan and Sliepcevich (2,3)]. However, the purpose of this presentation is to quantify the error introduced in the apparent heat capacity formulation as a consequence of assuming a finite temperature interval for the phase change. To investigate the effect of this phase change temperature interval the two-phase Stefan problem for a one-dimensional system undergoing a phase transition at a fixed temperature will be solved for the case of constant physical properties in each phase. The results will be compared with the analytical solution given by Neumann in Carslaw and Jaeger (4). For this purpose, a simple and accurate computational method developed in previous work by the authors for semi-infinite media will be used. Normalized variables, along with the Boltzmann similarity variable and coordinate mapping transformation eliminate computational difficulties and problems that frequently arise with conventional techniques, such as the finite difference method [Goodrich (5)]. For the present purpose, a typical example of a pure incompressible substance undergoing cooling and freezing (or conversely, heating and melting) will be solved. (This same methodology can be applied to other processes involving discontinuities, such as shock phenomena and interfacial mass transport.)

Heat Transfer During Melting Around an Isothermal Vertical Cylinder

Abstract: Research on alternative energy resources has intensified during the past few decades as a consequence of the alarming increase in energy cost. Effective thermal energy storage systems have become a true necessity, especially in solar energy applications. Using the phase change of some materials in thermal energy storage systems is advantageous in various ways. For example, the heat capacity of the storage reservoir is tremendously increased (on a unit volume basis), since latent heat of fusion is involved. In addition, there are advantages as far as heat transfer from and to the reservoir is concerned. Until recently, most papers on phase change dealt exclusively with conduction heat transfer, although it has been known for some time that natural convection may play a key role during melting and freezing. Lately, however, several studies (Viskanta, 1983) considering buoyancy effects on phase-change heat transfer have been reported. The present paper reports on experimental measurements undertaken to investigate outward melting around a vertical cylinder embedded in a solid initially at its fusion temperature. The cylinder is maintained at a uniform temperature that exceeds the fusion temperature. The top and bottom of the phase-change material are adiabatic, and a small air gap provides a slipmore » boundary condition at the top. The main objective of the research reported here was to obtain experimental data for the above mentioned configuration. It is remarkable that, although the isothermal boundary condition at the heat source has been extensively studied experimentally for melting to a vertical plate (e.g., Ho and Viskanta, 1984; Okada, 1983), there are very few experimental data available for melting to an isothermal cylinder positioned vertically.« less

Device for conversion of heat energy

Abstract: The device for conversion of heat energy into mechanical work or into electrical or storable energy exhibits at least two heat reservoirs at different temperatures, each with a liquid medium and at least one heat exchanger. Arranged downstream of each heat reservoir is a device with a heat exchanger and with a piston displaceable under the pressure of an enclosed amount of gas, which device moreover is arranged in a closed hydraulic circuit with a hydraulic motor. The heat reservoir with the higher temperature alternatingly supplies heat to the devices, and the heat reservoir with the lower temperature alternatingly removes heat from the devices, the hydraulic motor producing work. The piston rods can also be directed towards the outside, exhibit a piston of ferromagnetic material, and in each case work together with a coil according to the immersion coil principle. A heat pump is also arranged between the two heat reservoirs. The heat reservoir with the higher temperature can be in radiation contact with the sun, in heat-conducting contact with waste water or used water giving off heat, and/or in radiation contact with a device giving off waste heat. An electric generator can be connected downstream of the hydraulic motor, and a device for electrolysis of water and a hydrogen reservoir can be connected downstream of the generator.

Heat reservoir (heat accumulator) for large amounts of liquids and method for operating said reservoir

Abstract: In a heat reservoir for liquids heated by solar or waste heat, the storage space of the storage tank intended in particular for large amounts of liquid is divided up into storage chambers (6, 7, 8) by advantageously displaceable or deformable separating floors (4, 5), so as to create storage spaces for liquids at different temperatures.

Electrically insulating heat tube

Abstract: The invention relates to a heat tube for transmitting high thermal power from a heat source which is at a relatively high electrical potential to a heat sink at a relatively low potential. As a result of the fact that the heat tube is split between the heat source and the heat sink, and a tubular insulating body, which does not impede the thermodynamic process, is inserted there, a considerably higher thermal power can be transferred, with a reduced temperature gradient, from a heat source which is at a high voltage to a heat sink which is at earth potential. A ceramic tube can be used as the insulating body.

Steady state swimming pool heat exchanger

Abstract: A steady state swimming pool heat exchanger designed to warm the water in swimming pools by the conducting of heat from the constant heat reservoir of the earth into the water in the pool through a heat-conducting rod sunk vertically into the earth beneath the pool. Attached to the rod is a contact plate, mounted on the floor of the pool, which transfers heat energy from the rod to the water. In temperate climates, the earth maintains a constant level of heat of 65 to 70 degrees at a depth of approximately 10 meters. The contact between the earth and the water in the pool provides a steady state transfer of heat to warm the water when the water temperature is below that of the earth reservoir. A non-conducting cover is provided to restrict the heat flux when heating or cooling of the water is not desired.

Quantum coherence: the two-state system in a thermal environment

Abstract: The real-time dynamics of a quantum mechanical particle moving in a symmetric double-well potential weakly coupled to a thermal reservoir is obtained in a simple manner in the Heisenberg picture.

Method and device for converting heat energy into mechanical energy

Abstract: In a method for converting heat energy into mechanical energy, carbon dioxide, which is stored in a reservoir (11) is used as working medium in a cyclic process and heat energy is fed to the working medium during the cyclic process. The working medium is then isenthalpically expanded in an engine (15), a part of the heat energy absorbed is drawn off and converted into mechanical energy; one fraction of the working medium leaving the engine is then converted by sublimation into crystalline carbon dioxide and then melted and in turn fed to the reservoir. The other vaporous fraction of the working medium remaining is, on the other hand, compressed adiabatically and introduced as condensate into the reservoir (11). By means of this method it is possible without any great difficulties and without major design expense to utilise the limitless environmental heat available as mechanical energy. In so doing, no environmental damage occurs nor does any pollution have to be accepted.

Two phonon induced single particle widths in thermally excited Fermion matter

Abstract: The broadening of single-fermion levels in a heat reservoir where two quantal harmonic vibrations have been located is examined. The oscillations are assumed to couple to the fermionic system and to directly among themselves. The equations of motion of both the macroscopic and the microscopic coordinates are set and the kinetic collision rates are evaluated in the relaxation time approximation for different macroscopic configurations. Information regarding the evolution of the Fermi sea is thus obtained and analyzed.

Installation for the exploitation of atmospheric and terrestrial heat

Abstract: An installation for the exploitation of atmospheric and terrestrial heat comprises a solid absorber (5) with storage capacity, located in the open, having a heat-withdrawal/heat-exchanger system built on grown soil for withdrawing heat from the solid absorber (5) with storage capacity in one or more planes (20) traversing the natural heat flow and transferring it to a liquid heat transport medium. The withdrawal/exchanger system (6, 22) consists of a layer of material having a thermal conductivity lambda > 200 W/m.K surrounded by concrete and joined to the concrete in a conducting manner. The withdrawal layer is self-contained inside the individual temperature fields created by the heat transport medium using conventional heat transport techniques, but separated from other withdrawal layers. The installation ensures optimal heat exchange between a solid absorber (5) with storage capacity and a conventional heat pump (10) for the supply of hot-water heating or industrial water systems (13, 14).

The thermal modeling of integrated-circuit device packages

Abstract: Heat elimination from power integrated-circuit packages represents an ever present problem due to the highdegree of dissipation of energy emitted from high-voltage devices An important consideration in the removal of large quantities of heat is the choice of material for the heat sink and its geometric configuration The amount of copper used as a heat sink is limited by economic factors An engineering model has been developed to estimate the dimensions of the heat sink based on a simple one-dimensional multilayer steady-state heat transport model The model shows that the transport of energy from the heat sink to the ambient is a weak function of the thickness On the other hand, the areal dimensions play a major role in the efficiency of heat transfer across the surface Beyond a ratio of 4 (length/ width), efficiency of heat transport is not measurably increased A transient analysis was included to see if time dependencies influenced the progress of heat flow

A Carnot Cycle for the Solar Cell

Abstract: The Carnot cycle of an electron-hole gas, exchanging heat in the form of blackbody radiation with two heat reservoirs, can be easily determined and used to study the thermodynamics of photovoltaic conversion. The thermodynamic efficiency (different from the usual practical efficiency) will be maximum, equal to the Carnot factor, when the evolution of the system is reversible. The reversibility conditions are met only for a two-level system, at open circuit, with purely radiative recombination. This case is the equivalent of the ideal gas Carnot engine and yields the Carnot efficiency (although the practical efficiency is zero, since the output power is vanishingly small). All other configurations lead to a loss in thermodynamic efficiency; the practical efficiency will, in all cases, be lower than the thermodynamic one (this discussion does not apply to multispectral cells). The identity of the hot reservoir temperature with the “effective temperature”, as usually defined, can be shown.

Investigation of the properties of helium-4 at low temperatures

Abstract: From the standpoint of the Nernst heat theorem this article mathematically investigates the thermal expansion and outflow of helium 4 from one reservoir through a throttling orifice and into a second reservoir in the form of a cylinder containing a weightless piston and set at a lower pressure than the original reservoir. The thermodynamic behavior of helium 4 during this process at temperatures at or just above absolute zero is assessed.