MIXED CONVECTION ABOVE GREENHOUSE CROP CANOPIES

This paper evaluates the conclusion by Zhang and Lemeur (1992, Effect of aerodynamic resistance on energy balance and Penman-Monteith estimates of evapotranspiration in greenhouse conditions. Agric. For. Meteorol., 58: 209 228) that the use of equivalent Grashof numbers to account for the contribution of forced convection to the heat exchange of greenhouse canopies, leads to underestimates of the aerodynamic resistance for cooler-than-air leaves. It is shown that heat transfer theory for flow regimes typical of greenhouse conditions does not support this conclusion and that the soundness of its empirical proof is undermined by some numerical errors and one unproven hypothesis.