Development and validation of model of heat diffusion in maize ear

To calculate the variations of ear temperature, a two-dimensional numerical model of heat transfer within the different parts of the ear was developed and tested. It is based on a heat conduction equation. The ear being considered as a cylinder form with a variable section consisting of three concentric layers: cob, kernels and husk. The heat transfer between two adjoining layers was assumed to be purely conductive and at the external boundary of the ear, free convective heat transfer was assumed. Temperature response curves obtained from cooling and heating experiments were compared with those obtained by the model developed and a simpler model treating the ear as a single cylindrical layer. The average difference between the observed and calculated temperatures was 0.4 and 1 degrees C, respectively for our model and the simple model (ear temperature varied between 5 and 25 degrees C). The delay (lag) of response of ear temperature to air temperature was clearly larger in the deeper layers (center of cob and grains) than just under the husk. The proposed model was used to determine the overall thermal properties of maize ears. Conductivity k*, heat capacity c* and thermal diffusivity a* of each layer within the ear were determined using the model fitting method i.e. their values were obtained fitting a model of heat diffusion in the ear by the least squares method. The values of k* and c* obtained for the kernel layer were respectively significantly higher and lower than those for husk layer. (C) 1999 Elsevier Science B.V. All rights reserved.