25 research outputs found
A diagrammatic formulation of the kinetic theory of fluctuations in equilibrium classical fluids. VI. Binary collision approximations for the memory function for self correlation functions
We use computer simulation results for a dense Lennard-Jones fluid for a
range of temperatures to test the accuracy of various binary collision
approximations for the memory function for density fluctuations in liquids. The
approximations tested include the moderate density approximation of the
generalized Boltzmann-Enskog memory function (MGBE) of Mazenko and Yip, the
binary collision approximation (BCA) and the short time approximation (STA) of
Ranganathan and Andersen, and various other approximations derived by us using
diagrammatic methods. The tests are of twotypes. The first is a comparison of
the correlation functions predicted by each approximate memory function with
the simulation results, especially for the self longitudinal current
correlation function (SLCC). The second is a direct comparison of each
approximate memory function with a memory function numerically extracted from
the correlation function data. The MGBE memory function is accurate at short
times but decays to zero too slowly and gives a poor description of the
correlation function at intermediate times. The BCA is exact at zero time, but
it predicts a correlation function that diverges at long times. The STA gives a
reasonable description of the SLCC but does not predict the correct temperature
dependence of the negative dip in the function that is associated with caging
at low temperatures. None of the other binary collision approximations is a
systematic improvement upon the STA. The extracted memory functions have a
rapidly decaying short time part, much like the STA, and a much smaller, more
slowly decaying part of the type predicted by mode coupling theory. Theories
that use mode coupling commonly include a binary collision term in the memory
function but do not discuss in detail the nature of that term. ...Comment: 18 pages, 10 figure
Monte Carlo study of the Widom-Rowlinson fluid using cluster methods
The Widom-Rowlinson model of a fluid mixture is studied using a new cluster
algorithm that is a generalization of the invaded cluster algorithm previously
applied to Potts models. Our estimate of the critical exponents for the
two-component fluid are consistent with the Ising universality class in two and
three dimensions. We also present results for the three-component fluid.Comment: 13 pages RevTex and 2 Postscript figure
Transport properties of dense fluid argon
We calculate using molecular dynamics simulations the transport properties of
realistically modeled fluid argon at pressures up to and
temperatures up to . In this context we provide a critique of some newer
theoretical predictions for the diffusion coefficients of liquids and a
discussion of the Enskog theory relevance under two different adaptations:
modified Enskog theory (MET) and effective diameter Enskog theory. We also
analyze a number of experimental data for the thermal conductivity of
monoatomic and small diatomic dense fluids.Comment: 8 pages, 6 figure
Radius of curvature approach to the Kolmogorov-Sinai entropy of dilute hard particles in equilibrium
We consider the Kolmogorov-Sinai entropy for dilute gases of hard disks
or spheres. This can be expanded in density as , with the diameter of the sphere or disk,
the density, and the dimensionality of the system. We estimate the
constant by solving a linear differential equation for the approximate
distribution of eigenvalues of the inverse radius of curvature tensor. We
compare the resulting values of both to previous estimates and to existing
simulation results, finding very good agreement with the latter. Also, we
compare the distribution of eigenvalues of the inverse radius of curvature
tensor resulting from our calculations to new simulation results. For most of
the spectrum the agreement between our calculations and the simulations again
is very good.Comment: 12 pages, 4 figure
Technical and Economic Feasibility of U. S. District Heating Systems using Waste Heat from Fusion Reactors
In this study district heating systems are shown to be economically attractive for large-scale implementation in the U.S., provided suitable sources of waste heat are available. Fusion reactors appear to be very desirable as sources of waste heat for district heating systems. Since fusion reactors appear to be more environmentally acceptable than fission reactors or coal steam electric plants, they could possibly be located closer to district heat load centers, which should result in substantial cost savings due to lower transmission costs. In this study, CTR distances on the order of 20 miles from urban areas are acceptable in terms of transmission cost. Model district heating systems are designed for nine regions in the U.S. (New York City, Paterson, N.J., Chicago, Philadelphia, Los Angeles, Baton Rouge, New Orleans, Jersey City, and Newark). Estimates are also made as to the implementation and costs to be expected for district heating systems in the U.S. as a whole. The study evaluates the impact of the CRT-district heat option on the U.S. energy system; this was carried out using the BNL BESOM program. It is concluded that two additional markets exist for district heating, those of process heat and air conditioning. (MCW
Technical and Economic Feasibility of U. S. District Heating Systems using Waste Heat from Fusion Reactors
In this study district heating systems are shown to be economically attractive for large-scale implementation in the U.S., provided suitable sources of waste heat are available. Fusion reactors appear to be very desirable as sources of waste heat for district heating systems. Since fusion reactors appear to be more environmentally acceptable than fission reactors or coal steam electric plants, they could possibly be located closer to district heat load centers, which should result in substantial cost savings due to lower transmission costs. In this study, CTR distances on the order of 20 miles from urban areas are acceptable in terms of transmission cost. Model district heating systems are designed for nine regions in the U.S. (New York City, Paterson, N.J., Chicago, Philadelphia, Los Angeles, Baton Rouge, New Orleans, Jersey City, and Newark). Estimates are also made as to the implementation and costs to be expected for district heating systems in the U.S. as a whole. The study evaluates the impact of the CRT-district heat option on the U.S. energy system; this was carried out using the BNL BESOM program. It is concluded that two additional markets exist for district heating, those of process heat and air conditioning. (MCW
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Methodology for modeling geothermal district heating for residential markets
Methodology is presented for geothermal district heat service and for evaluating the economic market potential for such nonelectrical utilization of the geothermal resource. It is based upon accurate determination of the heating demand and its spatial and temporal profile in each potential market, determination of the cost to provide such service, and correlation of markets and resource sites. Two components of the model are discussed in this report. the residential demand submodel and data base, which includes building characteristics and population distribution on a census tract or minor civil division grid for the nation, projects heating demand densities, and temporal profiles along with the building service modifications and costs. The service submodel and data base designs and costs a subtransmission and distribution network, and it evaluates operating losses at design conditions
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Public data sources and modeling of district heating in the United States
A methodology for computerized modelling of hot water district heating service in any urban area in the United States is described. It is distinguished by the depth and breadth of its data bases, the ease with which any urban market can be analyzed and the wide variety of intermediate information which is obtained. Real housing and employment data, canvassed for the entire nation and made available on a very small area basis, are conjoined with local climate profiles, labor costs, land use intensity factors, fuel prices and fuel use profiles to generate profiles of heating demands and markets for district heat. This characterization of residential and commercial space and water heating demands permits a system design and costing of piping systems for distribution of hot water, subject to any penetration constraints imposed. A minimal number of assumptions are needed to generate these products from the data bases, many of which were generated in the public domain for other purposes
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Planning analyses for geothermal district heating
Methodology and data bases are described which can provide a comprehensive planning assessment of the potential for geothermal district heating in any US market. This economic systems model encompasses life-cycle costing over a period of rising competitive fuel prices, it addresses the expansion and financing of a district system over time, and it includes an overall optimization of system design. The elemental area for all analyses is the census tract, for which published data allow estimation of residential and commercial heating demands, building retrofit requirements, and competitive fuel consumption and cost. A system type design, an appropriate hot water district piping system, and costing of heat supply is performed for groups of contiguous tracts in any urban market. Groups are aggregated, in decreasing benefit to cost order, to achieve optimal systems. A specific application for Salt Lake City, Utah, is also described