【作者】 袁智；

【导师】 林其钊； 叶宏；

【作者基本信息】 中国科学技术大学 ， 工程热物理， 2013， 博士

【摘要】 蒸腾作用是植物的一项基本生理活动,蒸腾作用产生的蒸发潜热对植物叶片温度有重要影响。要想模拟植物叶片的热红外辐射特性,必须实现蒸腾作用这一生理过程的模拟。为深入理解植物蒸腾作用,我们首先研究了植物叶片的传热传质过程；实测了长江中下游流域7种典型植被的气孔阻力、叶片温度以及蒸腾耗水；选择蒸腾耗水旺盛的樟树为研究对象,建立了单个樟树叶片的传热传质模型,并利用气孔阻力和叶片温度的实测值验证了模型；将实测气孔阻力拟合成Jarvis模型,结合南京地区典型气象年气象参数计算了夏季樟树叶片温度、蒸腾耗水以及三种方式(对流换热、辐射换热和蒸腾作用潜热)的散热量,并分析了蒸腾作用潜热对叶片温度带来的影响。结果表明：叶片日平均温度受环境空气日平均温度影响,而其蒸腾耗水则由太阳辐照主导；叶片蒸腾作用潜热在叶片散热体系中具有重要作用,蒸腾潜热占叶片总散热量的比例超过30%；蒸腾作用对叶片温度有重要影响,且影响程度与气象条件有关,无风条件下影响程度要高于有风天气。基于对植物叶片传热传质过程的研究,我们提出了一种能模拟植物叶片蒸腾作用且具备植物叶片相似热特性的仿生叶片原理结构,该仿生叶片由表面涂层、保水层、吸脱附层和吸脱附速率控制层组成。复合／混合吸附剂是仿生叶片制备的关键材料。我们分别利用浸渍法和压块法制备了活性碳纤维布-氯化钙复合吸附剂和膨胀石墨-氯化钙混合吸附剂,并测试了复合／混合吸附剂的吸水性能和关键热物性,着重研究了浸渍法制备活性碳纤维布复合吸附剂时活性碳纤维布吸附氯化钙的机理以及复合／混合吸附剂吸水机理。浸渍过程中钙离子会通过离子交换被活性碳纤维布表面含氧官能团吸附,氯化钙会由于范德华力被活性碳纤维布微孔吸附。对于复合吸附剂的制备过程,表面官能团对钙离子的吸附作用可以忽略。微孔对氯化钙的吸附能用Polanyi吸附势理论和D-R方程描述。氯化钙在活性碳纤维布孔道中的填充方式为逐层覆盖。当活性碳纤维布的微孔被氯化钙完全填充满时,复合吸附剂的吸水作用完全由氯化钙决定。当活性碳纤维布的微孔没有被完全填充满时,复合吸附剂的吸水作用是活性碳纤维布与氯化钙共同作用的结果。活性碳纤维布的物理吸附过程受复合吸附剂的有效微孔容积影响,满足D-A方程。分散于孔道中的氯化钙在水合和潮解阶段化学性质发生改变,具体表现在水合和潮解压力降低,且复合吸附剂中氯化钙含量越低,其水合、潮解压力越低。膨胀石墨-氯化钙混合吸附剂的吸水完全由氯化钙发挥作用。活性碳纤维布复合吸附剂吸附速率快,其表面扩散速度系数为0.027-0.041s-1。但活性碳纤维布复合吸附剂的导热系数低,最大值仅有0.063W/(m·K)。膨胀石墨混合吸附剂吸附速率慢,其表面扩散速度系数为2×10-5s-1,但膨胀石墨混合吸附剂具备优异的导热性能,其导热系数能达到5W/(m·K)。基于实测的复合/混合吸附剂吸水性能和热物性,我们建立了仿生叶片的传热传质模型,并通过实验验证了模型,再利用模型完成了仿生叶片的设计计算。结果表明：保水层对仿生叶片温度影响很小,可以去掉保水层；影响仿生叶片上表面温度的关键因素是吸附脱附层的导热系数,应当选取高导热系数的膨胀石墨-氯化钙混合吸附剂来制备仿生叶片,且由于膨胀石墨-氯化钙混合吸附剂吸附速率慢,可以去掉吸脱附速率控制层；当膨胀石墨-氯化钙混合吸附剂中氯化钙含量达到40%时,仿生叶片便能很好地模拟真实叶片的热特征。基于理论分析结果,利用压块法将表面涂层粉末和混合吸附剂压制到一起,制备了氯化钙含量为50%的仿生叶片原理样品,并实测了仿生叶片与真实叶片的辐射温度。结果表明：该仿生叶片能很好地模拟真实叶片的热红外辐射特性,其辐射温度与真实叶片辐射温度差值在2℃以内。更多还原

【Abstract】 Transpiration is one of the basic physiological activities of the plant leaf. It significantly affects leaf temperature. In order to imitate the thermal infrared characteristics of a plant leaf, we must imitate its transpiration.To deeply understand the plant transpiration, the heat and mass transfer processes of the plant leaf were investigated. Stomatal resistance, leaf temperature and transpiration water consumption of7kinds of typical plants in the middle and lower reaches of the Yangtze River Basin were measured. Camphor with large transpiration water consumption was chosen as the investigation object. A general thermophysical model was established for a camphor leaf. The model was verified by the field measured stomatal resistance and temperature of a camphor leaf. Then the leaf temperature, the transpiration water consumption and the heat exchange between the leaf and the environment were calculated throughout the summer using the fitted Jarvis model of the measured stomatal resistance and the weather data of the typical meteorological year in Nanjing. The dynamical simulation revealed that the day-average temperature of the leaf is dominated by the ambient air temperature, diurnal transpiration water consumption is dominated by the solar irradiance; transpiration plays an important role in the cooling of the leaf, it could dissipate more than30%of the total absorbed solar energy; transpiration latent heat has different degree of impact on the leaf temperature under different weather conditions, the impact is more significant in a calm weather than in a windy weather. Based on the above results, a kind of bionic leaf which can imitate the transpiration of the plant leaf and has a similar thermal infrared characteristic to the plant leaf was proposed. It consists of green coating, water holding layer, composite sorbent (CS) layer and adsorption-desorption rate control layer.The CS is the key material of the bionic leaf. Activated carbon fiber cloth (ACFC) and CaCl2CS was prepared by impregnating the ACFC in CaCl2aqueous solution. Expanded graphite (EG) and CaCl2CS was prepared using briquetting method. Then the water vapor sorption performance and thermal conductivity of the CSs were measured. Particular attention was paid to the adsorption mechanism of the ACFC to CaCl2during the impregnating and the water vapor sorption mechanism of the CSs. During the impregnating, Ca2+is absorbed by the surface oxygen functional groups of the ACFC due to the cation exchange, CaCl2is adsorbed by the micropores of the ACFC due to the Van der Waals force. From the quantitative analysis, Ca2+adsorption by the surface functional groups can be ignored for the CS preparation. CaCl2adsorption by the micropores can be described with the Polanyi adsorption potential theory and Dubinin-Radushkevich equation. When all the micropores of the ACFC are fully filled with CaC2, the isotherms of the CS coincide with those of the equivalent CaCl2. When there are still micropores remaining in the ACFC, both the ACFC and dispersed CaCl2contribute to the CS’s water vapor sorption. The physical adsorption quantity of the ACFC of the CS is impacted by the effective micropore volume and can be calculated with the Dubinin-Astakhov equation. During the hydration and deliquescence, the dispersed CaCl2shows a lower hydration and deliquescence pressures than that of bulk CaCl2, and the hydration and deliquescence pressures increase with the CaCl2content of the CS. The sorption quantity of the EG and CaCl2CS equals to that of the equivalent CaCl2. The ACFC and CaCl2CS has a large sorption rate, its mass transfer coefficient is0.027-0.04ls-1. However, its thermal conductivity is low, the maximal thermal conductivity is only0.063W/(m-K). The EG and CaCl2CS has a high thermal conductivity, its thermal conductivity can reach5W/(m·K). However, its mass transfer coefficient is only2×10-5s-1.Based on the measured water vapor sorption property and thermal conductivity of the CS, a thermophysical model was established for the bionic leaf. Then the design calculation of the bionic leaf was completed using the thermophysical model. The dynamical simulation revealed that the influence of the water holding layer on the temperature of the bionic leaf can be ignored, so the water holding layer can be removed; the thermal conductivity of the CS dominates the up surface temperature of the bionic leaf; we should use the EG and CaCl2CS with high thermal conductivity to prepare the bionic leaf; the sorption-desorption rate control layer can be removed due to the low desorption rate of the EG and CaCl2CS; when the CaCl2content of the composite reaches40%, the bionic leaf has the similar temperature to that of the plant leaf throughout the daytime. Based on the above results, we prepared several principle samples of the bionic leaf by compressing the expanded graphite-CaCl2composite and pigment powder together. The radiative temperatures of the bionic and actual leaves were measured. Differeces between them are all less than2℃throughout the whole day.更多还原