Author(s): I. N. Shatalina; G. A. Tregub; R. S. Frid
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Abstract: A new methodological approach to calculations of the temperature stratification in a reservoir is described. It is based on solving heat conductivity equations developed for a reservoir as a whole and for the so-called Ihermics, which form in water near its boundary with air. The approach enables the temperature stratification over a reservoir depth to be established. The results calculated are compared to field observation data, the comparison showing satisfactory agreement in cases when temperatures of surface water exceed those of ambient air. The processes take place in the autumn period of reservoir cooling as well as when hot water is discharged into the surface layer ofa cooling pond. Formation of thermal and ice regimes in a reservoir over an annual thermal cycle depends significantly upon mixing processes in water. Wherever density jumps are available we have the hydrodynamics of the motion of two layers of liquids characterized by different temperatures and densities. The free-convection mixing processes are analysed by J. Turner (Turner, 1977). The problems of free-convection mixing are important for calculating temperatures in a reservoir during water cooling in the autumn period from the maximum summer temperature down to the initial freeze-up and temperatures in cooling ponds where the processes of surface water cooling serve the basis for the power cycle formation. Existing methods of temperature calculations proceed from the methods of thermal balance or equations developed for shallow water under the assumption of the full mixing over the vertical. This leads to erroneous calculations of the date of ice freeze-up, ice cover thickness, cooling capacity of cooling pond et al. Under the conditions of free-convection mixing the mechanism of surface water layer cooling is discontinuous in nature.
Year: 2000