Aerial measurements of convection cell elements in heated lakes

Abstract

Power plant-heated lakes are characterized by a temperature gradient in the thermal plume originating at the discharge of the power plant and terminating at the water intake. The maximum water temperature discharged by the power plant into the lake depends on the power generated at the facility and environmental regulations on the temperature of the lake. Besides the observed thermal plume, cloud-like thermal cells (convection cell elements) are also observed on the water surface. The size, shape and temperature of the convection cell elements depends on several parameters such as the lake water temperature, wind speed, surfactants and the depth of the thermocline. The Savannah River National Laboratory (SRNL) and Clemson University are collaborating to determine the applicability of laboratory empirical correlations between surface heat flux and thermal convection intensity. Laboratory experiments at Clemson University have demonstrated a simple relationship between the surface heat flux and the standard deviation of temperature fluctuations. Similar results were observed in the aerial thermal imagery SRNL collected at different locations along the thermal plume and at different elevations. SRNL will present evidence that the results at Clemson University are applicable to cooling lakes.

Direct measurement of heat flux from cooling lake thermal imagery

“…The data collections will be described briefly here. A companion paper [2] describes these data collections in greater detail.…”

“…The hypothesis is that this correction would compensate for the upper end of the spectrum of convective cells that cannot exist in the presence of strong mixing caused by turbulence generated by wind shear. The basis for the correction is the assumption that the spectrum of convective cells will shift toward shorter and shorter wavelengths as the ratio of turbulence generated by wind shear increases relative to the turbulence generated by buoyant convection: (2) where σ COR = corrected value of σ, σ REF = adjusted value of σ derived from equation (1), P ws is the rate of production of turbulence from wind shear and P BF is the rate of production of turbulence from the buoyancy force. Substituting expressions for the two production rates in terms of wind speed and σ leads to the following expression:…”