Waste heat management in the electric power industry : issues of energy conservation and station operation under environmental constraints

Over the past three years, the Energy Laboratory, in cooperation with the R.M. Parsons Laboratory for Water Resources and Hydrodynamics at M.I.T. has been under contract with DOE/ECT to study various water and waste heat management issues associated with the choice of cooling systems for large steam-electric power plants. The purpose of this report is to summarize the major findings to-date of this study. In addition, an introduction or background section proceeds the summary so that the results can be better integrated into the larger picture of water and waste heat management.Over the past three years, the Energy Laboratory, in cooperation with the R.M. Parsons Laboratory for Water Resources and Hydrodynamics at M.I.T. has been under contract with DOE/ECT to study various water and waste heat management issues associated with the choice of cooling systems for large steam-electric power plants. The purpose of this report is to summarize the major findings to-date of this study. In addition, an introduction or background section proceeds the summary so that the results can be better integrated into the larger picture of water and waste heat management

The mechanics of submerged multiport diffusers for bouyant discharges in shallow water

Prepared by the Ralph M. Parsons Laboratory for Water Resources and Hydrodynamics in association with the Energy LaboratoryA submerged multiport diffuser is an effective device for disposal of water containing heat or other degradable wastes into a natural body of water. A high degree of dilution can be obtained and the environmental impact of concentrated waste can be constrained to a small area. An analytical and experimental investigation is conducted for the purpose of developing predictive methods for buoyant discharges from submerged multiport diffusers. The following physical situation is considered: A multiport diffuser with given length, nozzle spacing and vertical angle of nozzles is located on the bottom of a large body of water of uniform depth. The ambient water is unstratified and may be stagnant or have a uniform current which runs at an arbitrary angle to the axis of the diffuser. The general case of a diffuser in arbitrary depth of water and arbitrary buoyancy is treated. However, emphasis is put on the diffuser in shallow receiving water with low buoyancy, the type used for discharge of condenser cooling water from thermal power plants. A multiport diffuser will produce a general three-dimensional flow field. Yet the predominantly two-dimensional flow which is postulated to exist in the center portion of the three-dimensional diffuser cart be analyzed as a two-dimensional "channel model", that is a diffuser section bounded by walls of finite length and openings at both ends into a large reservoir. Matching of the solutions for the four distinct flow regions which can be discerned in the channel model, namely, a buoyant jet region, a surface impingement region, an internal hydraulic jump region and a stratified counterflow region, yields these results: The near-field zone is stable only for a limited range of jet densimetric Froude numbers and relative depths. The stability is also dependent on the jet discharge angle. It is only in this limited range that previous buoyant jet models assuming an unbounded receiving water are applicable to predict dilutions. Outside of the parameter range which yields stable near-field conditions, the diffuser-induced dilutions are essentially determined by the interplay of two factors: frictional effects in the far-field and the horizontal momentum input of the jet discharge. Three far-field flow configurations are possible, a counter flow system, a stagnant wedge system and a vertically fully mixed flow, which is the extreme case of surface and bottom interaction. A three-dimensional model for the diffuser-induced flow field is developed. Based on equivalency of far-field effects, the predictions of the two-dimensional channel model can be linked to the three-dimensional diffuser characteristics. Diffusers with an unstable near-field produce three-dimensional circulations which lead to recirculation at the diffuser line: effective control of these circulations is possible through horizontal nozzle orientation. The diffuser in an ambient cross-current is studied experimentally. Different extreme regimes of diffuser behaviour can be described. Performance is dependent on the arrangement of the diffuser axis with respect to the crossflow direction. Experiments are performed in two set-ups, investigating both two- dimensional slots and three-dimensional diffusers. Good agreement between theoretical predictions and experimental results is found. The results of this study are presented in form of dilution graphs which can be used for three-dimensional diffuser design or preliminary design if proper schematization of the ambient geometry is possible. Design considerations are discussed and examples are given. For more complicated ambient conditions, hydraulic scale models are necessary. The results of this study indicate that only undistorted scale models simulate the correct areal extent of the temperature field and the interaction with currents, but are always somewhat conservative in dilution prediction. The degree of conservatism can be estimated. Distorted models are less conservative in predicting near-field dilutions, but exaggerate the extent of the near-field mixing zone.Stone and Webster Engineering Corp., Boston, Mass., Long Island Lighting Co., Hicksville, New York, and the National Science Foundation, Engineering Energetics Program. GK-3247

Stability and mixing of submerged turbulent jets at low Reynolds numbers

Originally presented as the first author's thesis (M.S.), Temperature reduction in a submerged vertical jet in the laminar-turbulent transition, M.I.T. Dept. of Civil EngineeringAn experimental study is made of the variation of volume and centerline dilution as a function of Reynolds number in non- buoyant and buoyant round jets discharged vertically from a submerged nozzle. The jet Reynolds numbers covered the laminar- turbulent transition with values ranging from Re = u D/v = 100 to 20,000 where u = jet exit velocity, D = jet diameter, and V = kinematic viscosity. Measurements of jet temperature profiles are obtained by using both fast and slow thermistor probes. Turbulent dilution is found to be independent of Reynolds number for non-buoyant jets above a critical Reynolds number of about 1,500. For buoyant jets (densimetric Froude numbers in the range 25 to 50), the critical Reynolds number is about 1,200. Reasonable agreement is obtained with the results of previous investigators for dilution values at high Reynolds numbers. Dye studies of transition Reynolds numbers are compared with a study by A.F. Pearce (1966) and good agreement is found. The results are useful in determining the minimum length scale ratio for hydro-thermal model studies, especially those of submerged multiport diffusers. It is concluded that modeling of turbulent jets is acceptable provided the model Reynolds number is larger than the critical Reynolds number and provided no other constraint becomes binding. In addition, the model jet's laminar length, if any, must be insignificant when compared to the total length of the path of the jet.New England Electric System and Northeast Utilities Service Company under the M.I.T. Energy Laboratory Electric Power Progra

Stability and mixing of a vertical round buoyant jet in shallow water

Also issued as a M.S. thesis in the Department of Civil Engineering at Massachusetts Institute of TechnologyDischarging heated water through submerged vertical round ports located at the bottom of a receiving water body is a currently used method of waste heat disposal. The prediction of the temperature reduction in the near field of the buoyant jet is a problem of environmental concern. The mechanics of a vertical axisymmetric buoyant jet in shallow water is theoretically and experimentally investigated. Four flow regimes with distinct hydrodynamic properties are discerned in the vicinity of the jet: the buoyant jet region, the surface impingement region, the internal hydraulic jump, and the stratified counterflow region. An analytical framework is formulated for each region. The coupling of the solutions of the four regions yields a prediction of the near field stability as well as the temperature reduction of the buoyant discharge. It is found that the near field of the buoyant jet is stable only for a range of jet densimetric Froude numbers and submergences. A theoretical solution is given for the stability criterion and the dilution of an unstable buoyant jet. A series of experiments were conducted to verify the theory. The experimental results are compared to the theoretical predictions. Good agreement is obtained

A comparison between measured wave properties and simple wave hindcasting models in shallow water

Significant wave heights and wave periods obtained from field measurements in Lake Balaton, Hungary, were compared with two versions of the shallow water wave hindcasting model published by the U.S. Army Corps of Engineers. The version presented in CERC [3, 4] was found to give very good hindcasts of wave height but fall —20% low on wave period. The model presented in CERC [5] was 15-20% above the earlier version at long fetches and approximately equivalent at shorter fetches

Modelling of unidirectional thermal diffusers in shallow water

This study is an experimental and theoretical investigation of the temperature field and velocity field induced by a unidirectional thermal diffuser in shallow water. A multiport thermal diffuser is essentially a pipe laid along the bottom of the water body and discharging heated water in the form of turbulent jets through a series of ports spaced along the pipe. A unidirectional diffuser inputs large momentum in one direction; it can achieve rapid mixing within relatively small areas, and has the advantage of directing the thermal effluent away from the shoreline. The theory considers a unidirectional diffuser discharging into shallow water of constant depth in the presence of a coflowing ambient current. A fully mixed condition is hypothesized downstream of the diffuser. A two dimensional potential flow model is formulated and solved in'the near field, where flow is governed by a dominant balance of pressure and inertia. A control volume analysis gives the total induced flow, which is used as an integral boundary condition in the potential flow solution. The shape of the slip streamline is solved using Kirchoff's method; the velocity and pressure field are then computed by a finite difference method. The correct boundary conditions along the diffuser are deduced. Knowledge of the flow field defines the extent of the near field mixing zone. The near field solution is coupled into an intermediate field theory. In this region turbulent lateral entrainment, inertia and bottom friction are the governing mechanisms of the flow, and the mixed flow behaves like a two dimensional friction jet. An integral model is formulated and solved numerically. The model predictions of induced temperature rises, velocities, plume widths enable comparisons of the overall effectiveness of different heat dissipation schemes. A model for calculating the near field dilution and plume trajectory of a unidirectional diffuser discharging into a perpendicular crossflow is formulated and solved. The phenomenon of heat recirculation from the far field is ascertained in the laboratory and a semi-empirical theory is developed to evaluate the potential temperature buildup due to far field recirculation. A comprehensive set of laboratory experiments have been carried out for a wide range of diffuser and ambient design conditions. The model is validated against the experimental results of this study as well as those of hydraulic scale model studies by other investigators. The analytical and experimental insights gained in this study will aid future numerical modelling efforts and in better design of physical scale models. The principal results are applied to establish general design guidelines for diffusers operating in coastal regions. The ecological implications of the model predictions are discussed.Sponsored by New England Electric System, Westboro, Mass. and Northeast Utilities Service Company, Hartford, Conn. under the MIT Energy Laboratory Electric Power Program

Linked Hydrodynamic and Biogeochemical Models of Water Quality in Shallow Lakes

Scanning notes: Disclaimer inserted for illegible graphs and text.Prepared under the support of the National Science Foundation Water Resources and Environmental Engineering Program.Approaches to lake water quality modeling are critically examined with particular attention to the formulation of water quality transport as the link between hydrodynamics and biogeochemical reaction. A linked water quality model for shallow lakes includes three major components: a biogeochemical reaction component, a lake hydrodynamics component and a water quality transport component. State-of-the-art modeling approaches for each component are reviewed, and a synopsis of phosphorus dynamics in shallow lakes is given. For the water quality transport component, review of the literature shows two significantly different approaches to water transport: a lumped component approach based upon multiple fully-mixed boxes, and a continuum approach employing the finite difference method to approximate the continuous governing equations. The multiple-box model is shown in an analysis of the kindred fully-mixed tanks-in-series conceptual reactor model to create an excessive implicit dispersion due to its formulation. This leads to a model in which the model mass transport is not closely related to the properties of the physical system. being modeled. Rather, dispersive transport in the model is shown to depend heavily upon the model formulation -- the model transport parameters thus cannot be specified from hydrodynamic data but must be found by calibration. In direct contrast, the finite difference model maintains a far closer approximation to the physical system and permits direct specification of water quality transport from the actual lake hydrodynamics. To support these arguments, a computer program incorporating both a multiple-box model and an alternative one-dimensional finite difference model is developed and applied to Lake Balaton in Hungary. The biogeochemical component of both models is a four component phosphorus-phytoplankton interaction model originally proposed by van Straten (1980). Hydrodynamic information is supplied to the one-dimensional finite difference model by linkage to a transient two-dimensional single-layer model of wind-driven circulation. A one-dimensional dispersion coefficient is computed from the two-dimensional velocity field using a method based upon that of Fischer (1966, 1969) and Holley, Harleman and Fischer (1970), but proceeding from the assumption that advection rather than turbulent diffusion dominates lateral mixing. The finite difference model developed for Lake Balaton consists of forty grids and is used to simulate a representative period from early spring to late summer. The results are contrasted with those produced by a four-box model of the lake using long-term average advection and calibrated dispersive exchange flows. The finite difference model is found to lead to a predicted behavior more similar to that observed in field data collected from Lake Balaton. Experimentation with the models is conducted to examine the behavior of the lake and the dominant factors leading to that behavior

Effect of Wind-mixing on the Thermocline Formation in Lakes and Reservoirs

Prepared with the support of the Ford Professorship at MIT and the German Research Society

User's Manual for the MIT Lake Circulation Models (MITLAKE)

Prepared under the support of the National Science Foundation Water Resources and Environmental Engineering Program Division of Civil and Environmental Engineering and Eastern European Program Division of International Programs Grant No. CEE-7906125Introduction: During the course of research into water quality and hydrodynamic interactions in Lake Balaton in Hungary (Shanahan et al., 1981 and Shanahan and Harleman, 1982) two models of wind-driven lake circulation were employed. The models, which were developed from an earlier model by Nelson (1979), are two-dimensional and three-dimensional versions. The 3-D model employs the Galerkin method to solve for the vertical velocity distribution as a function of time and horizontal space. A linear bottom friction relation is used, thus making the model inappropriate to very shallow lakes. The 2-D model was developed in response to this limitation. The 2-D model determines the depth integrated velocity as a function of time and horizontal space. A non-linear bottom friction law is employed, broadening the model applicability to include very shallow lakes. These notes are a brief description of the computer programs developed to perform the 2-D and 3-D model simulations and to plot the model output. The notes are intended as an aid to potential users; however, no effort has been made to be exhaustive in explaining the implementation of the programs

A Mathematical Model for the Prediction of Unsteady Salinity Intrusion in Estuaries

Prepared under the support of the Office of Sea Grant National Oceanic and Atmospheric Administration U. S. Department of Commerce through Coherent Area Project Grant GH-88 2-35150The salinity structure of a tidal estuary fed by upstream fresh water sources is an important factor of water quality. In addition, this structure is intimately related to the circulation of the estuary because of density currents induced by the salt-fresh water relation. Previous investigations in two and three dimensions have been limited to extremely simplified geometrical and steady-state assumptions. One dimensional studies have considered the variable area case, but have been limited to descriptive rather than predictive methods because of the difficulty of handling the downstream boundary condition for the one-dimensional salt balance equation and because of the necessity to specify a longitudinal dispersion coefficient based on field data for the estuary being studied. This study presents a predictive numerical model of unsteady salinity intrusion in estuaries by formulating the problem in finite-difference terms using the one-dimensional, tidal time, variable area equations for the conservation of water mass, conservation of momentum and conservation of salt. Tidal time means a time scale of calculation larger than that defining turbulence, but much smaller than a tidal period in order to correctly represent the tidal advection within a tidal period. The tidal dynamic equations are coupled to the conservation of salt equation through a salinity-density relationship, and the ocean boundary condition for salt is formulated in a manner which depends on the direction of flow at the entrance to the estuary. The longitudinal dispersion coefficient has been shown to be proportional to the magnitude of the local, time-varying longitudinal salinity gradient, and this constant of proportionality has been shown to depend on a dimensionless parameter which expresses the degree of vertical stratification of the estuary. This relationship has been established for a wide range of stratification conditions. The mathematical model has been verified using data from the Waterways Experiment Station salinity flume and field data from the Delaware, the Potomac, and the Hudson. By specifying initial conditions, fresh water hydrographs, and tidal elevations at the ocean, it is possible to predict the time-varying salinity using this model