Research On Thermal Characteristics Of Main Crop Straw In Northwest China

In order to improve basic data of thermal properties for agricultural biomass in northwest China and to provide theoretical and technical support for crop straw resource utilization in China,253 samples of wheat,corn,rice,rape and cotton straw were collected from 97counties(districts)of Shaanxi,Gansu,Ningxia,Qinghai,Xizang and Xinjiang province.Thermal properties of each sample,namely thermal conductivity,thermal diffusivity and specific heat capacity were measured by KD2 Pro thermal physical analyzer.Difference of each thermal property among species and provinces were analyzed.Multivariate linear regression was carried out for determining the effects of particle size,density and moisture content on thermal conductivity and thermal diffusivity of straw.Interpolation method was used to analyze the regional distribution of specific heat capacity of straw in northwest China.The main research conclusions were summarized as follows:Firstly,thermal conductivity of straw decrease with particle size increase,increase with the increase of bulk density,moisture content and temperature.The main factors sequence from large to small which affected thermal conductivity of wheat straw is moisture content,bulk density and particle size.Moisture content,bulk density and their interaction show significant effect on thermal conductivity.Species and regions affect thermal conductivity of cotton straw at the least but affect thermal conductivity of rice straw at the most.Thermal conductivity has very significant difference between cotton straw and other four kinds of straw.Thermal conductivity of wheat straw has significant difference between Shaanxi and Gansu,Qinghai,Xinjiang,Xizang.Thermal conductivity of wheat,corn,rice,rape and cotton straw were respectively 0.110±0.009,0.108±0.009,0.110±0.011,0.113±0.008 and 0.130±0.005 W/m·K.Secondly,thermal diffusivity increase with increase of bulk density,moisture content and temperature.Species and regions affect thermal diffusivity of wheat and rice straw at the least but affect thermal diffusivity of cotton straw at the most.Thermal diffusivity has very significant difference between cotton straw and other four kinds of straw.Thermal diffusivity has significant difference between corn straw and wheat,rape straw.Thermal diffusivity has significant difference between rice and wheat straw.Thermal diffusivity of cotton straw from Shaanxi,Gansu and Xinjiang is affected by regions and species at the most comparing with other provinces.Thermal diffusivity of corn straw has significant difference between Xizang and Shaanxi or Gansu.Thermal diffusivity of wheat,corn,rice,rape and cotton straw were respectively 0.217±0.011,0.208±0.013,0.209±0.011,0.215±0.015,and 0.186±0.015 mm~2/s.Finally,specific heat capacity of rice straw is affected by species and regions at the most.Specific heat capacity has very significant difference between cotton straw and other four kinds of straw.Specific heat capacity of wheat straw has significant difference between Shaanxi and other provinces.Specific heat capacity of rape straw has significant difference between Shaanxi and Xizang.Spatial distribution of specific heat capacity of agricultural biomass straw in northwest China are:specific heat capacity shows gradual increasing from south central to the periphery of Shaanxi,and gradual increasing from central to northwest and southeast of Gansu,and gradual decreasing from south to north in Ningxia.Spatial distribution of specific heat capacity of straw in Xinjiang has largest change among six provinces.Spatial distribution of specific heat capacity of straw has obvious regularity in Shaanxi,Gansu,Ningxia and north Xinjiang.Specific heat capacity of wheat,corn,rice,rape and cotton straw were respectively 0.509±0.047、0.523±0.052、0.528±0.064、0.526±0.047和0.701±0.056MJ/m3·K.