Inverse method, Parameter estimation, Conjugate gradient method, Heat pump grain drying
Cereal grains are one of the most important sources of nutrients in both developed and developing countries. Quality preservation of cereal grains is a major issue between harvest and utilization. Heat pump grain dryers can be used to preserve grain quality during storage, since grain spoilage can be averted by drying or chilling the grain. In this paper, the use of inverse methods to estimate grain properties during heat pump drying is investigated. An inverse method was developed to estimate the bulk density and specific heat of cereal grains during heat pump drying during the heat and mass transfer processes associated with drying the grain, using only grain temperature measurements as inputs. The solution for the inverse problem was based on minimizing the sum of the squares of the errors between the estimated and measured temperatures with respect to the unknown parameters. Since inverse problems are very sensitive to inevitable measurements errors, the conjugate gradient method was used to overcome the ill-posedness of the problem. The effects of measurement errors and the sensor location on the inverse solution were discussed. The results showed that the inverse method works better when the sensor is located nearer to the bottom of the grain bed. The close agreement between the exact and the estimated results indicates the potential of the developed method in estimating the thermophysical properties in a variety of cereal grains.