Air movement and heat loss from sheep. I. Boundary layer insulation of a model sheep, with and whoitut fleece

A model sheep, made from metal cylinders and hemispheres, was heated electrically. Heat loss by forced convection in a wind tunnel was analysed in terms of the dependence of the Nusselt number ($\overline{Nu}$) on Reynolds number (Re). For a bare trunk $\overline{Nu}$ = 0.095 Re$^{0.684,}$ but with fleece covering the trunk to a depth of 3.5 cm $\overline{Nu}$ = 0.0112 Re$^{0.875}$ when the mean radiative temperature of the coat was taken as the surface temperature. Heat transfer by convection from the whole body, including legs, was described by $\overline{Nu}$ = 0.029 Re$^{0.80}$. However, a bulk Nusselt number should not be used to estimate heat loss from a live sheep in a hot environment if the windspeed is below about 4 m s$^{-1}$ because the relation between mean surface temperature, Nusselt number and convective heat flux is not unique.