【作者】 李斌；

【导师】 陆华忠； 吕恩利；

【作者基本信息】 华南农业大学 ， 农业机械化工程， 2020， 博士

【摘要】 蓄冷控温箱,因其节能、环保、生产成本低等优点,成为冷链物流的一个新方向。受蓄冷材料、保温材料和控温措施等因素的影响,蓄冷式冷藏箱运输时间相对较短,还存在控温不均匀、保温时间短和信息程度低等问题。本文通过理论分析、数值模拟和试验研究相结合的方法,研究了无源蓄冷箱温度调节特性,建立蓄冷控温箱传热模型,明确蓄冷箱冷量热传导机理,开展了无源蓄冷控温箱的设计与试验,并采用数值模拟,优化了控制参数,为蓄冷控温箱的设计提供参考。主要研究内容如下:(1)无源蓄冷箱温度调节特性研究为了掌握蓄冷控温箱温度调节特性,搭建真空隔热无源蓄冷控温试验平台,以脐橙作为试验填充物料,研究了真空绝热板厚度、聚氨酯保温板厚度和蓄冷剂质量等参数对温度调节的影响,建立了各组参数与评价指标的拟合关系,为后续箱体设计提供理论依据。为了解进口空气流速和蓄冷板厚度对蓄冷板传热系数的影响,开展蓄冷板释冷特性试验,试验结果表明:总传热系数随空气流速及蓄冷板厚度的增大逐渐增大。空气流速增大可有效提高蓄冷板释冷速率,但在释冷中后期释冷速率升高缓慢,综合考虑能耗,在该试验平台条件下,入口空气流速为3.25 m/s时最优;蓄冷板释冷速率随蓄冷板厚度的增大呈先增大后平缓的趋势,当蓄冷板厚度为50mm时蓄冷板释冷速率的增速开始减慢,蓄冷板内部冷量向外传递热阻增大,减缓了释冷速率,蓄冷板厚度为50 mm时最佳。(2)无源蓄冷箱热传导机理研究以无源蓄冷控温箱为研究对象,基于傅里叶定律及热力学理论,计算不同工况下,蓄冷控温箱不同平板内外壁面与空气对流换热系数。分析求解箱体运行能耗与环境、隔热层和蓄冷板等物性参数的关系方程式,建立箱体不同工况下的稳态传热模型。基于热平衡理论及稳态传热模型,建立蓄冷控温箱温度动态调节的瞬态传热模型,建立“蓄冷板-货物-隔热层-外环境”的关系方程式,分析不同参数对蓄冷降温效果的影响,保障冷链运输安全,为无源蓄冷箱设计提供参考。基于蓄冷控温箱传热模型,计算蓄冷控温箱能源成本,采用生命周期成本分析法,对采用不同厚度真空隔热板的蓄冷箱进行经济分析。分析结果表明:随着真空隔热板厚度的增加,保温层材料成本呈上升的趋势,蓄冷控温箱能源成本呈下降趋势,总成本呈先下降后上升的趋势,当真空隔热板厚度为25 mm时总成本最低。(3)无源蓄冷控温箱的设计与试验研制了蓄冷控温运输箱,并对箱体进行相关试验,确定了控制参数。开展蓄冷板温度测试试验,分析不同位置蓄冷板温度分布,确定代表蓄冷区温度的表征点;为提高控温效率降低风机能耗,应用蓄冷板降温能力数学模型,开展自动控温策略优化。开展载货控温时长试验,货物区装载660 kg脐橙,对比不同蓄冷剂用量、外环境温度、开关箱门对控温时长的影响。结果表明:在27℃外环境温度条件下,蓄冷剂用量90 kg、156 kg、180 kg时的控温时间分别为60 h、110 h、132 h;采用156 kg蓄冷剂,外环境平均温度为21.9℃、27.1℃、32.2℃时的控温时长分别为132 h、110 h、101 h。对无源蓄冷箱能耗模型和控温箱内环境空气温度变化瞬态模型进行验证,结果表明试验值和理论值拟合较好,平均误差分别在20%和22%以内。开展箱体空载和载货温度场试验测试,分析了箱体垂直截面和水平截面温度分布,结果表明:空载时,垂直截面和水平截面温度场不均匀系数最大值分别为1.92和1.08,最大温度差值分别为2.8℃和2.7℃;载货时,垂直截面和水平截面温度场不均匀系数最大值分别为1.85和1.86,最大温度差值分别为4.2℃和2.7℃。(4)无源蓄冷环境调控参数优化采用数值模拟,开展无源蓄冷环境调控参数优化研究。对风机位置及空气流速进行分析,进一步优化保鲜区温度和气流分布,提高蓄冷板冷量充足时保鲜区温度场均匀性。试验结果表明:模拟值与试验值吻合较好,证明了模型的可靠性;通风速度对冷却时间影响较大,冷却速率随速度的增加而增加,不均匀系数随入口速度的增加而增大,温度场均匀性逐渐变差;综合考虑风机能耗、蓄冷模块释冷速率和温度场等因素,入口风速为12 m/s时最佳;风机布置在箱内顶部四角时,箱内温度标准差最小(为0.87),不均匀性系数最小(为2.1)。更多还原

【Abstract】 The cold storage temperature control box has become a new direction of cold chain logistics due to its advantages of energy saving,environmental protection,and low production cost.Affected by factors such as cold storage materials,thermal insulation materials and temperature control measures,the transportation time of cold storage refrigerators is relatively short,and there are also some problems such as uneven temperature control,short heat preservation time and low level of information.In this paper,by combining theoretical analysis,numerical simulation and experimental research,the temperature regulation characteristics of the passive cold storage temperature control box are studied,the heat transfer model of the cold storage temperature control box is established,the heat transfer mechanism of the cold storage box is clarified,the design and test of the passive cold storage temperature control box are carried out,and the control parameters are optimized by numerical simulation,which provides a reference for the design of the cold storage temperature control box.The main research contents are as follows:(1)Research on temperature regulation characteristics of passive cold storage tankIn order to master the temperature adjustment characteristics of the cold storage temperature control box,a vacuum insulation passive cold storage temperature control test platform was built,and the navel orange was used as the test filling material to study the effects of parameters such as the thickness of the vacuum insulation board,the thickness of the polyurethane insulation board and the quality of the cold storage agent.Influence,the fitting relationship between each group of parameters and the evaluation index is established,which provides a theoretical basis for the subsequent cabinet design.In order to understand the influence of the inlet air flow rate and the thickness of the cold storage plate on the heat transfer coefficient of the cold storage plate,a cold storage plate discharge characteristic test was carried out.The test results show that the total heat transfer coefficient gradually increases with the increase of the air flow rate and the thickness of the cold storage plate.Increasing air velocity can effectively increase the cooling rate of the cold storage plate,but the cooling rate increases slowly in the middle and late stages of cooling.Considering the energy consumption,under the conditions of the test platform,the inlet air velocity is the best when 3.25 m/s;With the increase of the thickness of the cold storage plate,the cold release rate of the cold storage plate increases first and then gradually increases.When the thickness of the cold storage plate is 50 mm,the increase rate of the cold release rate of the cold storage plate starts to slow down,and the internal cold of the cold storage plate transfers heat outward.The resistance increases,slowing down the cooling rate,and the best when the thickness of the cold storage plate is 50 mm.(2)Research on heat transfer mechanism of passive cold storage boxTaking the passive cold storage temperature control box as the research object,based on Fourier’s law and thermodynamics theory,calculate the convection heat transfer coefficient between the inner and outer walls of the cold storage temperature control box and the air under different working conditions.Analyze and solve the relationship equations between the box’s operating energy consumption and physical parameters such as the environment,insulation layer and cold storage plate,and establish the steady-state heat transfer model of the box under different working conditions.Based on the heat balance theory and steady-state heat transfer model,establish a transient heat transfer model for the dynamic adjustment of the temperature of the cold storage temperature control box,establish the relationship equation of "cold storage board-cargo-insulation layer-external environment",and analyze the effect of different parameters on the cooling storage temperature The impact of the cold chain transportation is guaranteed,and it provides a reference for the design of passive cold storage tanks.Based on the heat transfer model of the cold storage temperature control box,the energy cost of the cold storage temperature control box is calculated,and the life cycle cost analysis method is adopted to conduct an economic analysis of the cold storage box with vacuum insulation panels of different thicknesses.The analysis results show that as the thickness of the vacuum insulation board increases,the material cost of the insulation layer is increasing,the energy cost of the cold storage temperature control box is decreasing,and the total cost is first decreasing and then increasing.The total cost is the lowest when the thickness of the vacuum insulation board is 25 mm.(3)Design and test of passive cold storage temperature control transport boxThe cold storage and temperature control transport box was developed,and related tests were performed on the box body to determine the control parameters.Carry out the cold storage plate temperature test experiment,analyze the temperature distribution of the cold storage plate at different positions,and determine the representative points representing the temperature of the cold storage area;in order to improve the temperature control efficiency and reduce the energy consumption of the fan,the mathematical model of the cooling capacity of the cold storage plate is applied to optimize the automatic temperature control strategy.Carry out a temperature control time test for cargo.The cargo area is loaded with660 kg navel oranges to compare the effects of different cold storage agent dosages,ambient temperature,and opening and closing of the door on the temperature control time.The results show that: under the condition of 27 ℃ outside ambient temperature,the temperature control time of 90 kg,156 kg,and 180 kg of cold storage agent are respectively 60 h,110 h,and 132 h;with 156 kg cold storage agent,the average temperature of the external environment is The temperature control durations at 21.9 ℃,27.1 ℃,and 32.2 ℃ are 132 h,110 h,and 101 h,respectively.The energy consumption model of passive cold storage tank and the transient model of ambient air temperature change in temperature control box are verified.The results show that the experimental value and theoretical value fit well,and the average error is within 20% and 22%respectively.Carry out the box no-load and cargo temperature field test.The temperature distribution of the vertical section and the horizontal section of the box are analyzed.The results show that the maximum value of the temperature field unevenness coefficient of the vertical section and the horizontal section is 1.92 and 1.08 when there is no load.The maximum temperature difference is 2.8 ℃ and 2.7 ℃,respectively;when the cargo is loaded,the maximum uneven coefficients of the temperature field of the vertical and horizontal sections are 1.85 and 1.86,and the maximum temperature difference is 4.2 ℃ and 2.7 ℃,respectively.(4)Optimization of environmental control parameters for passive cold storageUse numerical simulation to carry out research on optimization of passive cold storage environment control parameters.Analyze the position of the fan and the air flow rate to further optimize the temperature and airflow distribution in the fresh-keeping area,and improve the uniformity of the temperature field in the fresh-keeping area when the cold storage plate is sufficient.The test results show that: the simulation value and the test value are in good agreement,which proves the reliability of the model;the ventilation speed has a great influence on the cooling time,the cooling rate increases with the increase of the speed,and the uneven coefficient increases with the increase of the inlet speed.The uniformity of the temperature field gradually deteriorates;taking into account factors such as fan energy consumption,cold storage module release rate and temperature field,the best inlet wind speed is 12 m/s;when the fan is arranged at the top four corners of the box,the temperature standard deviation in the box is the smallest(0.87),the inhomogeneity coefficient is the smallest(2.1).更多还原