MEASURING AND MODELING HEAT TRANSFER PARAMETERS IN MULCHES
The apparent thermal conductivity (k) of wheat straw, pine straw, tire chips, dry sandy soil, and the thermal resistance of Bermuda grass sods were measured using a guarded hot plate at air velocities between 0 and 5 m/s. For all mulch materials, k ranged between 0.1 and 0.6 W m-1 0C-1, and increased with increasing air velocity, except the more compact materials such as soil and, to a lesser extent, small tire chips. We found a minimum in k around 1m/s for the thicker (>0.1 m) layers of wheat straw and pine straw, which we tentatively attributed to interactions between the straw and the convection (free versus forced convection at the 1m/s velocity). We created a model for predicting apparent thermal conductivity through mulches in thermally unstable environments. Using estimated mulch opacity parameters and fitting convection parameters, we obtained r2 values ranging from 0.72 to 0.99. The model may be used in field situations where the soil under mulch is warmer than the air above the mulch, which is a typical nighttime condition.
Van Donk, S. and Tollner, E.W. (2001). MEASURING AND MODELING HEAT TRANSFER PARAMETERS IN MULCHES. Acta Hortic. 566, 447-453
mulch, thermal conductivity, convection coefficients, radiation heat transfer