Effect of temperature and particle size on thermophysical properties ofdifferent energy feedstuffs material

Energy feedstuffs,the most important and indispensable components in the pelleted complete feeds,provide energy in the form of soluble carbohydrate,oil and fat.Energy feedstuffs mainly includes cereals,cereal brans,molasses,oil,tuber and tuberous root,among which corn,wheat,barley,sorghum,wheat/rice bran,pelleted cassava residue and beet pulp are widely utilized in diets for livestock and poultry.Knowledge of the thermal properties of different feedstuffs is required for designing and parameter optimization of thermal process such as conditioning and pelleting processing,especially when energy costs,pellet quality and uniformity are the main consideration.The specific heat,thermal conductivity and thermal diffusivity are the most important thermal properties.In this paper,eight energy feed ingredients(4 cereal grains:corn,wheat,barley,sorghum;4 processed by-products:wheat bran,pelleted cassava residue,pelleted beet pulp,rice bran)were obtained from a feed mill in the suburb of Beijing,and ground in a mini-mill equipped with screens having a aperture size of 1.5,2.0 or 2.5 mm to obtain feed meals with 3 particle sizes(except rice bran,which could pass through the 1.5 mm screen completely without being ground).The moisture content of all feed meal samples was conditioned to 12%wet basis in order to eliminate the effect of moisture content difference on thermal properties.The specific heat,thermal conductivity of feed meals at the temperature range of 25-100℃were determined by DSC(differential scanning calorimetry)and KD2 Pro(thermal properties analyzer),respectively.Thermal diffusivity of feed meals was calculated using measured thermal conductivity,specific heat,and bulk density.Based on the experimental data,prediction models of three thermal properties as a function of temperature were established.The effects of particle size on thermal properties of feedstuffs were analyzed.The particle size of 8 feedstuffs grinding through screens with aperture size of 1.5,2.0 and 2.5 mm ranged from^257.61 to 511.79μm,325.6