豌豆种子吸附等温线与热力学性质研究  

Sorption Isotherms and Thermodynamic Properties of Pea Seed

作　　者：杨昭[1] 李想[1] 陶志超 YANG Zhao LI Xiang TAO Zhichao(School of Mechanical Engineering, Tianjin University, Tianjin 300072, Chin)

机构地区：[1]天津大学机械工程学院,天津300072

出　　处：《农业机械学报》2017年第10期323-329,共7页Transactions of the Chinese Society for Agricultural Machinery

基　　金：天津市自然科学基金重点项目(16JCZDJC33900)

摘　　要：采用静态称量法测量30、40、50℃时豌豆种子的吸附等温线,对实验数据进行非线性拟合,并通过对净等量吸附热、微分熵、焓熵补偿、扩张压力、净积分焓和净积分熵等热力学性质参数的研究,分析种子吸附特性和进一步揭示吸附机理,为选择和优化种子干燥和贮藏条件提供理论依据。实验结果表明,温度恒定时,平衡含水率随水分活度升高而升高,吸附等温线属于类型Ⅱ且GAB模型拟合效果最佳(R2=0.998 9,误差平方和为4.52×10-5);净等量吸附热和微分熵随着平衡含水率升高而降低的规律符合焓熵补偿理论,该理论反映出吸附过程是非自发反应,属于焓驱动,而当干基含水率达到25%时,净等量吸附热值接近纯水的汽化潜热(43.30 k J/mol);种子吸附过程的扩张压力随水分活度升高而升高,随温度升高而降低,当扩张压力一定时,净积分焓和净积分熵随着平衡含水率升高而降低,净积分熵达到最小值后逐渐升高,此最小值在30、40、50℃温度条件下分别为-137.79、-140.29、-137.74 J/(mol·K),对应的水分活度和平衡含水率分别为0.017、0.045、0.062和2.7%、2.5%、2.4%,这些条件可作为豌豆种子贮藏的最稳定条件。Sorption isotherms of pea seed were determined experimentally by using a static gravimetric at temperature of 30℃, 40℃ and 50℃ and within the water activity （ aw ） range of 0. 11 - 0.92. Four mathematical models were determined by using non-linear regression method. The results showed that equilibrium moisture content （EMC） was decreased as the increase of temperature, and the GAB model fitted well the isotherms data of pea seeds and was considered as the best model for predicting seed moisture. The thermodynamic properties involving in net isosteric heat, differential entropy, enthalpyentropy compensation, spreading pressure, net integral enthalpy and net systematically for further understanding of water sorption mechanism. integral entropy were analyzed The net isosteric heat and differential entropy were obviously decreased with the increase of EMC, which satisfied the compensation theory. The data indicated that moisture sorption of pea seed was non-spontaneous and enthalpy-controlled processes. And the net isosteric heat approached to the latent heat of pure water around 25% （dry basis）. The expansion pressure of seed sorption process was decreased with the increase of temperature at given aw and increased with the increase of a at a given temperature. When expansion pressure was at fixed level, the net integral enthalpy was decreased with the increase of EMC, while the net integral entropy was decreased with the increase of EMC to a minimum value of -137.79J/（mol·K）, -140.29 J/（mol·K） and -137.74 J）（mol·K） at 30℃, 40℃ and 50℃, respectively, and then tended to increasing trends. The aw （0. 017, 0. 045 and 0. 062 ） and EMC （2.7%, 2.5% and 2.4% ）, which resulted in the minimum net integral entropy values at the temperatures of 30℃ , 35℃ and 40℃ , respectively, can be considered as the maximum stability storage conditions of pea seed.

关 键 词：豌豆种子 脱附 吸附 GAB模型 热力学性质 

分 类 号：S375[农业科学—农产品加工]