Showing papers on "Thermal reservoir published in 1988"

Thermal coupling to enhance heat transfer

Abstract: The invention is a thermal coupling to promote heat transfer between a heat source and a heat sink with abutting surfaces using a deposition of a thermally conductive substance having a melting point temperature less than the temperature of the heat source such that the substance when heated will be in a liquid state capable of effectively transferring heat between the heat source and the heat sink. The deposition is situated between and contacts the abutting surfaces of the heat source and the heat sink. The substance is contained using a sealant to completely enclose the substance between the heat source and heat sink surface while an adhesive is used to secure the heat source to the heat sink.

Modeling thermal characteristics of a fixed disk drive

Abstract: The thermal characteristics of an IBM 5-1/4-in. fixed disk drive were experimentally determined to aid in the development of a general disk-drive model. In general, the thermal model was able to predict the transient temperature profiles. At 4000 r/min, the steady-state temperatures of the air and arms were predicted to within 0.4 degrees C, and the base temperature was predicted to within 2.4 degrees C. The air temperature was found to be uniform within experimental uncertainty outside of the disk stack, but was 1.4 degrees C higher between corotating disks. The temperature predictions are extremely sensitive to the external heat transfer coefficients and the heat sources input by the user. It was found that more fundamental information regarding viscous dissipation and air flow within a disk drive must be known to produce a reliable thermal model. >

Kinetic equation for a classical test-particle model in the weak-coupling approximation

Abstract: A kinetic equation for a harmonically bound classical particle, weakly coupled to a thermal reservoir, is presented. The derivation, based on the formalism of master equations developed in Brussels, is outlined and compared to other approaches. Some comments are also made as to the consistency of the so-called Kramers equation in the presence of an external field.

Kinetic theory in the weak-coupling approximation. I: Formal theory and application to classical open systems

Abstract: A general formalism, where irreversible processes are related to singularities of the resolvent of the Liouville operator, is applied to classical open systems. For a system weakly coupled to a thermal reservoir, a kinetic equation is derived. It is shown that the method leads to equations defining a positivity-preserving semigroup with the Maxwell-Boltzmann distribution as a stationary solution and obeying an H-theory. It is pointed out that these properties are not always shared by irreversible equations obtained as asymptotic approximations of the so-called generalized master equation.

New compression heat pump media for medium and high temperature application

Abstract: The economy and operability of compression heat pump systems is to a great extent influenced by the working fluid. However, the choice of the appropriate medium for a given heat pump application is not straight forward, since a great number of physical and non-physical properties of the presumptive working fluids have to be accounted for. A systematic method of looking for the best medium has been developed. With the help of a commercial flowsheet program a simulation routine of the heat pump cycle has been established. This routine was used to screen all substances in the attached data bank in respect to their applicability as working media. In all, 940 substances have been investigated. From these substances 42 show favourable properties as working fluids for the application in three cases, namely with a temperature of the heat source of 2°C and of the heat sink of 70°C respectively, 60°C source temperature and 120°C at the heat sink and of 90°C source temperature and 150°C at the heat sink. A further investigation of these 42 substances with respect to toxicity and stability left four of them as the ultimate proposal for operable compression heat pump fluids. Besides the actual proposal of new media, the investigation produces a much better understanding of the influence of physical properties on the heat pump performance. From the great number of data, a reliable prediction of the applicability of a given substance as a working fluid, based on the critical data, was deduced.

Quantum Langevin equation of parametrically driven linear oscillators

Abstract: The quantum Langevin force of a parametrically driven damped harmonic oscillator is determined from the condition of the preservation of the canonical commutation relations. The arguments are independent of the microscopic modelling of the heat reservoir. For damping with and without retardation the Langevin force is found to be independent of the time-dependent parametric driving force and determined by the damping rate alone.

Extension of the quantal Brownian motion model to bosonic reservoirs

Abstract: We formulate an extension of the Quantal Brownian Motion (QBM) model for collective mode damping designed to include coupling to other normal modes of the system. We derive the equations of motion of the macroscopic coordinates and of the fermionic and bosonic degrees of freedom and investigate their exact solution in the thermodynamic limit of the heat reservoir. We examine the properties of the microscopic transition rates and their dependence on the macroscopic parameters as well as on the coupling strengths. The characteristic times of the damping process are extracted and their trend is analyzed.

The absorption line shape for a molecular system stochastically coupled to a phonon thermal reservoir

Abstract: In this paper we extend earlier results regarding the relaxation properties of a molecular system, stochastically coupled to a phonon thermal reservoir, and interacting with a radiation field. The absorption line shape is derived in the white as well as the colored noise regime. Broadening, shift, and asymmetry are predicted. The expressions for the parameters, which characterize the features of the line, have an explicit dependence on the temperature, which our earlier, microcanonical theory did not include.

Instabilities and Chaos in Optics

Abstract: The onset of deterministic chaos in lasers is studied by referring to low dimensional systems, in order to isolate the characteristics of chaos from the random fluctuations due to the coupling with a thermal reservoir. For this purpose, attention is focused on single mode homogeneous line lasers, whose dynamics is ruled by a low number of coupled variables. In the examined cases, experiments and theoretical model are in close agreement. In particular I describe Shilnikov chaos, how it can be characterized, and the strong resulting coupling between nonlinear dynamics and statistical mechanics.

Heating zone dynamics in in situ combustion

Abstract: The integrodifferential equation of the quasisteady regime of a moving in situ combustion front is obtained and its exact solution is constructed in a particular case; the possibility of the heat generated at the combustion front being projected into the region ahead of the front is analyzed and the heating zone dynamics in the reservoir and the surrounding rock are investigated. In a number of studies of in situ combustion it is assumed that an increase in the water-air factor or, what amounts to the same thing, an increase in convection velocity in the reservoir leads to the total transfer of the heat into the region ahead of the combustion front [1–3]. In [3] the area of the heating zone ahead of the combustion front was calculated in accordance with the Marx-Longenheim model [4]. Below, on the basis of exact solutions of model problems it is shown that in the case of quasisteady Newtonian heat transfer between the surrounding medium, when the latter is assumed to be a thermal reservoir, i.e., maintain a constant temperature, this projection of heat is possible if the convection velocity exceeds the velocity of the combustion front. In the case of unsteady heat transfer in accordance with the Leverrier model there is no total projection of heat into the region in question; in the steady-state regime a limited heating zone, proportional in depth to the square of the difference of the convection and combustion front velocities, is formed ahead of the front.