O’CONNOR, M.P.: Convective heat exchange for animals in and near boundary layers.

Convection is one of the dominant pathways of heat exchange in most terrestrial ectotherms. Hence, ecologists must often estimate convective heat exchanges either to dissect the relative contributions of convection and other pathways or to estimate how energy balances will be affected by different microhabitats and weather conditions. In estimating convective heat exchanges, we commonly use either empirical estimates of convection coefficients (usually from wind tunnel experiments) or rule-of-thumb estimates like Mitchell?s approximations. These estimates are, for obvious reasons, usually derived in conditions of laminar flow with uniform spatial temperature and wind speed profiles, for animals or models suspended in free air streams. In their natural habitats, however, small animals typically operate in turbulent air, near obstructions to air flow (e.g., the ground, tree limbs), and, at least partly, in the boundary layers for those obstructions. Those boundary layers induce spatial gradients in wind speed, air temperature, and turbulence all of which can affect convective heat exchanges. Furthermore, proximity to obstructions and their boundary layers can perturb the air flow around the animal further affecting convection. Although these factors have been shown to be important, they have not been systematically investigated. I used two dimensional computational fluid dynamics models to evaluate the air flows and convective heat exchanges for animals in proximity to air flow obstructions. I used the models to dissect the effects of animal factors like size and height of the torso above the ground and environmental factors including wind speed profiles, air temperature profiles, and turbulence on the convective heat exchanges of the animals.