Abstract
The state of water flow has been modelled numerically by a three‐dimensional method of a complex investigation of heat and mass transfer. This allows examining interaction of some transfer processes in a natural cooling basin (the Drûkšiai lake): variable density of water, heat conduction in water‐air interface, direct and diffuse solar radiation. Combined effect of these natural actions determines the heat amount that the basin is able to dissipate to the surrounding atmospheric media in thermal equilibrium (no change in the mean water temperature). Mathematical model is simplified ignoring transient derivatives in transfer equations, and time as a variable is included in relaxation coefficients for outer iterations. Full time of calculations using this simulation mechanism for this variable is about 6 h. Basing on water stream velocity and mean temperature profiles measured in the cooling pond as well as on their time variations, suggestions are made that the mixing rate in water is caused by natural and forced convection. Comparison of experimental and numerical results showed a qualitative agreement. For a better quantitative approximation, it is necessary to have more boundary conditions variable with time and to solve unsteady set equations for transfer processes.
Highlights
Hydrothermal processes in a cooling pond are determined by heat and mass exchange at water-air interface, together with thermal processes inside the water volume of the pond
The most important conditions for both remote regions and the whole cooling pond are: heat transfer to the atmosphere, the parameters of turbulence, heat balance, that is loss and increase of the heat. The former terms are found from convection, turbulent heat transfer, evaporation and inverse radiation in a long-wave spectrum
Numerical simulation of 41·17·6 cylindrical grid system consumes a lot of computer time, computation was suspended whenever a specific effect of wind became evident [3, 4] or similar to measured data at hotwater discharge [5]
Summary
Hydrothermal processes in a cooling pond are determined by heat and mass exchange at water-air interface, together with thermal processes inside the water volume of the pond. Inverse relations are observed between the two sets of processes, as the surface temperature determines the intensity of cooling, and this influences the temperature field of the pond together with the conditions of different stratification densities of streams and turbulent transfer [1]. The most important conditions for both remote regions and the whole cooling pond are: heat transfer to the atmosphere, the parameters of turbulence, heat balance, that is loss and increase of the heat. The former terms are found from convection, turbulent heat transfer, evaporation and inverse radiation in a long-wave spectrum. An increase of heat occurs whenever a volume of heated water is discharged from a thermal or nuclear power plant as well as by solar and atmospheric radiation [1, 2]
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