苹果冷库气体环境影响因素及通风调控策略研究
发布时间：2019-01-24 11:50
【摘要】：冷藏库内气体组分及其浓度分布是影响果蔬贮藏质量的重要因素,而通风换气是保证库内合理气体环境的关键过程。果蔬贮藏过程中CO2和C2H4浓度过高会影响果蔬食用及商用价值。而实际通风换气过程存在人为操作的随意性,不仅使通风效果不尽理想还会造成不必要的能源消耗。因此,研究苹果冷库CO2和C2H4气体分布情况及通风换气过程影响因素,对探究库内气体环境形成机理及制定通风策略具有重要的学术意义和工程应用价值,也为其他类型果蔬贮藏库的通风换气机制研究提供一定的参考价值。本文用气相色谱法对苹果乙烯释放规律进行了实验研究;并针对实际冷藏间建立了库内气体流动与传热传质的三维数学物理模型,通过数值模拟研究,获得了冷藏库气体组分分布规律及不同冷风机运行模式、排风速度和排风口设置对库内CO2和C2H4分布的影响,主要研究工作如下:(1)采用气相色谱仪对冷藏条件下苹果乙烯释放进规律行研究,得到苹果贮藏初期乙烯释放量较大,且乙烯释放量会随着贮藏浓度的增加而变大,因此苹果在贮藏过程中应及时关注库内乙烯含量,合理进行通风换气。(2)采用编写UDF程序的方法解决了冷库内的两个复杂问题,即货物区苹果的呼吸强度及冷风机送风口CO2和C2H4质量分数随贮藏环境中气体浓度的变化而改变这;并通过实验测量验证了该方法的可靠性。(3)运用CFD软件模拟研究了冷藏环境CO2和C2H4的分布规律。模拟结果表明:苹果贮藏24 h后库内货物区和气体区CO2和C2H4浓度分布比较均匀,但浓度偏高,货物区二氧化碳浓度为2.8%,乙烯浓度超过15 ppm,均已超过苹果冷藏贮存要求。(4)从通风换气过程影响因素出发,对通风换气过程中冷风机的启停、排风速度和排风口设置对库内气体浓度分布的影响进行了研究。研究结果表明:开启冷风机时库内气流扰动增强,通风换气性能变差,因此提出通风时应关闭冷风机;随着排风速度的增加库内气流的传质作用得到增强,贮藏环境得到改善,换气效果更好,并且存在一个最小排风速度,使库内有害气体浓度在规定的时间内降低到贮藏要求,本文所研究冷库,最小排风速度可选8 m/s;双排风扇形式可以改善库内气流组织,与传统单排风扇形式相比可以更加快速高效地降低货物区有害气体浓度。
[Abstract]:The distribution of gas components and their concentration in cold storage is an important factor affecting the storage quality of fruits and vegetables, and ventilation and air exchange is the key process to ensure a reasonable gas environment in the reservoir. The high concentration of CO2 and C2H4 will affect the edible and commercial value of fruits and vegetables. However, the actual ventilation and air exchange process has the randomness of artificial operation, which not only makes the ventilation effect not ideal, but also causes unnecessary energy consumption. Therefore, it is of great academic significance and engineering application value to study the distribution of CO2 and C2H4 gas and the influencing factors of ventilation and ventilation process in apple cold storage, which is of great academic significance and engineering application value in exploring the formation mechanism of gas environment and formulating ventilation strategy in the reservoir. It also provides some reference value for the study of ventilation and air exchange mechanism of other types of fruit and vegetable storage. In this paper, an experimental study on ethylene release from apple by gas chromatography was carried out. A three-dimensional mathematical and physical model of gas flow and heat and mass transfer in a cold storage room is established. Through numerical simulation, the distribution of gas components and the operation modes of different air coolers are obtained. The effects of exhaust air velocity and outlet setting on the distribution of CO2 and C2H4 in the storage were studied as follows: (1) the ethylene release from apple was studied by gas chromatograph under the condition of cold storage. And the amount of ethylene released will increase with the increase of storage concentration. Therefore, during storage, apple should pay attention to the content of ethylene in storage. (2) two complicated problems in the cold storage are solved by the method of writing UDF program. That is to say, the respiration intensity of apple and the mass fraction of CO2 and C2H4 in the air outlet of the air cooler changed with the change of the gas concentration in the storage environment. The reliability of the method is verified by experimental measurement. (3) the distribution of CO2 and C2H4 in refrigerated environment is simulated by CFD software. The simulation results showed that the concentration distribution of CO2 and C2H4 in storage area and gas area of apple was uniform after 24 h storage, but the concentration was on the high side. The concentration of carbon dioxide in cargo area was 2.8, and the concentration of ethylene was more than 15 ppm,. (4) based on the factors affecting the ventilation and ventilation process, the effects of the starting and stopping of the air cooler, the velocity of the exhaust air and the setting of the outlet on the distribution of the gas concentration in the storehouse were studied. The results show that the air disturbance in the storehouse becomes stronger and the ventilation performance becomes worse when the cold air machine is opened, so it is suggested that the air cooler should be closed when ventilating. With the increase of the exhaust velocity, the mass transfer of the air in the reservoir is enhanced, the storage environment is improved, the air exchange effect is better, and there is a minimum exhaust air velocity, which reduces the concentration of harmful gas in the reservoir to the storage requirement within the specified time. In the cold storage studied in this paper, the minimum exhaust velocity can be chosen as 8 m / s; The double exhaust fan can improve the airflow distribution in the reservoir. Compared with the traditional single exhaust fan, it can reduce the concentration of harmful gas in the cargo area more quickly and efficiently.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU834
本文编号：2414450
[Abstract]:The distribution of gas components and their concentration in cold storage is an important factor affecting the storage quality of fruits and vegetables, and ventilation and air exchange is the key process to ensure a reasonable gas environment in the reservoir. The high concentration of CO2 and C2H4 will affect the edible and commercial value of fruits and vegetables. However, the actual ventilation and air exchange process has the randomness of artificial operation, which not only makes the ventilation effect not ideal, but also causes unnecessary energy consumption. Therefore, it is of great academic significance and engineering application value to study the distribution of CO2 and C2H4 gas and the influencing factors of ventilation and ventilation process in apple cold storage, which is of great academic significance and engineering application value in exploring the formation mechanism of gas environment and formulating ventilation strategy in the reservoir. It also provides some reference value for the study of ventilation and air exchange mechanism of other types of fruit and vegetable storage. In this paper, an experimental study on ethylene release from apple by gas chromatography was carried out. A three-dimensional mathematical and physical model of gas flow and heat and mass transfer in a cold storage room is established. Through numerical simulation, the distribution of gas components and the operation modes of different air coolers are obtained. The effects of exhaust air velocity and outlet setting on the distribution of CO2 and C2H4 in the storage were studied as follows: (1) the ethylene release from apple was studied by gas chromatograph under the condition of cold storage. And the amount of ethylene released will increase with the increase of storage concentration. Therefore, during storage, apple should pay attention to the content of ethylene in storage. (2) two complicated problems in the cold storage are solved by the method of writing UDF program. That is to say, the respiration intensity of apple and the mass fraction of CO2 and C2H4 in the air outlet of the air cooler changed with the change of the gas concentration in the storage environment. The reliability of the method is verified by experimental measurement. (3) the distribution of CO2 and C2H4 in refrigerated environment is simulated by CFD software. The simulation results showed that the concentration distribution of CO2 and C2H4 in storage area and gas area of apple was uniform after 24 h storage, but the concentration was on the high side. The concentration of carbon dioxide in cargo area was 2.8, and the concentration of ethylene was more than 15 ppm,. (4) based on the factors affecting the ventilation and ventilation process, the effects of the starting and stopping of the air cooler, the velocity of the exhaust air and the setting of the outlet on the distribution of the gas concentration in the storehouse were studied. The results show that the air disturbance in the storehouse becomes stronger and the ventilation performance becomes worse when the cold air machine is opened, so it is suggested that the air cooler should be closed when ventilating. With the increase of the exhaust velocity, the mass transfer of the air in the reservoir is enhanced, the storage environment is improved, the air exchange effect is better, and there is a minimum exhaust air velocity, which reduces the concentration of harmful gas in the reservoir to the storage requirement within the specified time. In the cold storage studied in this paper, the minimum exhaust velocity can be chosen as 8 m / s; The double exhaust fan can improve the airflow distribution in the reservoir. Compared with the traditional single exhaust fan, it can reduce the concentration of harmful gas in the cargo area more quickly and efficiently.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU834
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