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豌豆種子吸附等溫線與熱力學性質(zhì)研究
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天津市自然科學基金重點項目(16JCZDJC33900)


Sorption Isotherms and Thermodynamic Properties of Pea Seed
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    摘要:

    采用靜態(tài)稱量法測量30、40、50℃時豌豆種子的吸附等溫線,對實驗數(shù)據(jù)進行非線性擬合,并通過對凈等量吸附熱、微分熵、焓熵補償、擴張壓力、凈積分焓和凈積分熵等熱力學性質(zhì)參數(shù)的研究,分析種子吸附特性和進一步揭示吸附機理,為選擇和優(yōu)化種子干燥和貯藏條件提供理論依據(jù)。實驗結果表明,溫度恒定時,平衡含水率隨水分活度升高而升高,吸附等溫線屬于類型Ⅱ且GAB模型擬合效果最佳(R2=0.9989,誤差平方和為4.52×10-5);凈等量吸附熱和微分熵隨著平衡含水率升高而降低的規(guī)律符合焓熵補償理論,該理論反映出吸附過程是非自發(fā)反應,屬于焓驅動,而當干基含水率達到25%時,凈等量吸附熱值接近純水的汽化潛熱(43.30kJ/mol);種子吸附過程的擴張壓力隨水分活度升高而升高,隨溫度升高而降低,當擴張壓力一定時,凈積分焓和凈積分熵隨著平衡含水率升高而降低,凈積分熵達到最小值后逐漸升高,此最小值在30、40、50℃溫度條件下分別為-137.79、-140.29、-137.74J/(mol·K),對應的水分活度和平衡含水率分別為0.017、0.045、0.062和2.7%、2.5%、2.4%,這些條件可作為豌豆種子貯藏的最穩(wěn)定條件。

    Abstract:

    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, enthalpy-entropy compensation, spreading pressure, net integral enthalpy and net integral entropy were analyzed systematically for further understanding of water sorption mechanism. 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 aw 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), -140.29J/(mol·K) and -137.74J/(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.

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楊昭,李想,陶志超.豌豆種子吸附等溫線與熱力學性質(zhì)研究[J].農(nóng)業(yè)機械學報,2017,48(10):323-329. YANG Zhao, LI Xiang, TAO Zhichao. Sorption Isotherms and Thermodynamic Properties of Pea Seed[J]. Transactions of the Chinese Society for Agricultural Machinery,2017,48(10):323-329.

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  • 收稿日期:2017-01-09
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  • 在線發(fā)布日期: 2017-10-10
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