Lake Temperature Dynamics in Hybrid Cooling System

A transient thermal simulation model of a hybrid cooling lake is developed to assess the impact of cooling water withdrawals and cooling tower discharges on the thermal structure of the lake. The model is based on one-dimensional mechanical and thermal energy balances and includes the physical processes of solar heating, wind stirring, vertical advection, and physical processes of solar heating, wind stirring, vertical advection, and hypolimnetic diffusion. Temperature data were collected on two small lakes in northern Indiana, and the simulated temperatures are compared with the measured data for the lake stratification seasons of 1976 and 1978. It is shown that cooling water circulations significantly thicken the epilimnion due to vertical advection of heat. The simulation results are examined in terms of the values of the wind Richardson number, the withdrawal densimetric Froude number, and the dimensionless surface buoyancy flux. The sensitivity of the lake thermal structure to the densimetric Froude number is demonstrated.