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 $\simeq 50GPa$ and temperatures up to $3000K$. 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 $N$ hard disks or spheres. This can be expanded in density as $h_{\mathrm{KS}} \propto n N [\ln n a^d+ B + O(n a^d)+O(1/N)]$, with $a$ the diameter of the sphere or disk, $n$ the density, and $d$ the dimensionality of the system. We estimate the constant $B$ 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 $B$ 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

Long-distance transmission of hot water for district heating. [Profile of potential heat source/market distances]

The technical feasibility of hot-water-based district heating has been demonstrated by years of operation of large-scale systems in Europe and parts of Asia. District heating affords the opportunity of substituting low-grade heat resources for prime fossil fuels in the space- and water-heating market, thus conserving scarce fuels. Development of cheap, reliable long-distance hot-water-transmission technology could lead to far-reaching consequences for the U.S. The profile of distances between markets and potential heat sources is investigated. Potential sources include geothermal resources and power plants. Typical market characteristics are analyzed, and the technical and economic aspects of long-distance transmission to these markets is presented. Results show that the limits to feasibility of long-distance hot-water transmission are determined by economic, not technical factors. Inclusion of district-heat service for air conditioning, and heating and drying industrial processes can dramatically affect the economic picture for district heating, especially in warmer climates. Cost-reducing developments in transmission technology could have greater payoff when applied to distribution systems. 11 refs., 5 tables, 8 figs

Application of district heating system to U. S. urban areas

In the last few decades district-heating systems have been widely used in a number of European countries using waste heat from electric generation or refuse incineration, as well as energy from primary sources such as geothermal wells or fossil-fired boilers. The current world status of district-heat utilization is summarized. Cost and implementation projections for district-heating systems in the U. S. are discussed in comparison with existing modes of space conditioning and domestic water heating. A substantial fraction, i.e., up to approximately one-half of the U.S. population could employ district-heating systems using waste heat, with present population-distribution patterns. U.S. energy usage would be reduced by an equivalent of approximately 30 percent of current oil imports. Detailed analyses of a number of urban areas are used to formulate conceptual district energy-supply systems, potential implementation levels, and projected energy costs. Important national ancillary economic and social benefits are described, and potential difficulties relating to the implementation of district-heating systems in the U.S. are discussed. District-heating systems appear very attractive for meeting future U.S. energy needs. The technology is well established. The cost/benefit yield is favorable, and the conservation potential is significant. District heating can be applied in urban and densely populated suburban areas. The remaining demand, in rural and low-population-density communities, appears to be better suited to other forms of system substitution

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

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