【作者】 李锦；

【导师】 谢如鹤；

【作者基本信息】 中南大学 ， 交通运输工程， 2013， 博士

【摘要】 冷藏运输装备作为串联整个冷链的运输工具,担负着保证食品品质、控制运输成本与降低能耗的重任。因此,研究精确控制冷藏运输装备的温度高低及波动范围显得尤为重要。本文围绕运输过程中的温度环境对食品品质的影响、冷藏运输车厢内温度均匀性、典型冷藏车厢的热稳定性、冷藏车厢内的温变特性及影响因素、车厢内温度波动及其控制办法等进行研究,进而对冷藏运输车厢体进行设计优化。具体研究内容如下：(1)温度均匀性及其温度波动冷藏运输过程车厢内温度的均匀性及其波动,都会对冷藏运输的易腐食品品质造成影响。采用airpak流体仿真软件,对影响车内温度均匀性的因素进行了数值模拟。研究表明,车厢聚氨酯隔热材料合理厚度为100-120mm；送风口位于车厢内正前下方位置车厢内温度均匀性最好；冷藏运输温度不同,车内最佳送风速度也不同,送风温度越高,合理的送风速度也高,且均对应有一个最佳风速。基于频域分析法,构建冷藏车厢内温度扰动数学模型与温度响应数学模型,对四种温度扰动的振幅与相角进行了分析。研究发现,在一定条件下,增大车厢体的比热容、厢体材料密度,减小车厢内外表面的对流换热系数,可降低车厢内温度波动；调节制冷频率与融霜频率处于系统衰减域,可达到衰减这两种扰动的作用；制冷与融霜温度扰动的相角相同时,此时温度振幅最小；车辆的气密性越好、车速的变化频率越大、车厢外表面颜色越浅,车厢内温度波动越小。(2)车厢内的热稳定性利用热工理论知识,研究了四种典型冷藏车隔热车厢对温度的衰减与延迟作用,以及对厢内热稳定性的影响。结果表明,车厢的隔热材料不同,对车外综合温度波的延迟时间与衰减倍数不同,厢体热惰性指标、热阻越大,延迟时间与衰减倍数相应越大；车辆行驶的方向、隔热材料不同,车厢体内壁面温度也不同；热稳定性主要由厢体隔热材料的热阻与热惰性指标决定,隔热材料复合厢体的热阻值与热惰性指标值越大,车厢的热稳定就越好。(3)厢内温度变化特性基于动态热平衡理论,构建单温冷藏车、双温冷藏车、以及冷藏车开门过程的车厢内温度变化数学模型。研究结果表明：降温过程中,车厢内的温度均随时间呈指数规律下降,开门过程车厢内的温度随时间呈指数规律上升；当车厢体厚度减小或热导率增大、车厢外表面对太阳辐射的吸收系数增大、车速增大、车厢漏气倍数增大、货物呼吸热增大、制冷量减小等均会导致车厢内降温所需时间延长。对于双温冷藏车,制冷量变小、货物呼吸热增大、车速升高或者车厢导热系数变大,两温区降温所需时间均延长；当两温区之间的电动风扇风速与出风口面积增大时,冷冻车厢内降温时间延长,而冷藏车厢降温时间缩短；当车厢总体积不变,冷冻车厢体积增大,冷冻车厢降温所需时间将会延长,而冷藏车厢降温所需时间基本保持不变。冷藏车开门过程,制冷开启与否、车厢内送风风速大小、车厢体隔热能力对厢内温度变化影响不大；车厢内外的温差越大、车门开启越大、车厢体积越小,车厢内的温度升高也相应的越大；车厢外有无风速以及风速方向不同,开门过程车厢内的升温快慢也不同。(4)厢体优化设计以车厢体传热系数最小与车厢内空间体积最大为目标函数,分析了不同参数条件下车厢内部体积空间与车厢体传热系数变化规律,以及最佳厢体隔热材料厚度。结果表明：不同车速、不同隔热材料厚度、不同隔热材料导热系数条件下对应的车厢体最优体积与传热系数各不相同；同时满足最佳车厢体总传热系数与最大车厢内体积条件的车厢体隔热材料最佳厚度,随着最佳车厢体传热系数的增大而增大。(5)冷藏运输温度条件与易腐食品品质关系每一种易腐食品对整个物流过程的最佳温湿度要求各不相同,通过试验模拟猪肉与荔枝不同温度条件物流全程。研究发现,不同的温湿度运输条件下及其后续的销售条件,荔枝的褐变指数、花色素苷-光密度差值、果皮色值、果肉PH值、失重率等指标的变化情况也不同。猪肉的运输、配送、销售环节的温湿度条件不同,对猪肉的品质影响也不同；肉质好坏、保鲜期的长短主要取决于运输与销售环节对温度的控制。更多还原

【Abstract】 As one of the most important conveyances of connecting each step of the cold chain logistics, refrigerated transportation equipment undertakes an important business of guarantying food quality, controlling transportation costs and reducing energy consumption. Therefore, it is particularly important to study precisely the control of temperature and its fluctuation range of the refrigerated transportation equipment. The dissertation focuses on the aspects of the impact of temperature and environment to the quality of perishable foods during refrigerated transportation process, temperature uniformity inside the refrigerated compartment, the thermal stability of the typical refrigerated compartment, temperature change characteristics of refrigerated compartment, the factors affecting those characteristics, and temperature fluctuations inside refrigerated compartment as well as its control measures. Besides, optimization in the design of refrigerated compartment is covered in the research. Specific contents are as follows:(1) Temperature uniformity and temperature fluctuationsCompartment inside temperature uniformity and its fluctuations will affect the quality of perishable foods during refrigerated transport process. Airpak fluid simulation software was introduced to numerically simulate the factors affecting the temperature uniformity inside the compartment. The results show that the most reasonable thickness of compartment polyurethane insulation materials between100and120mm; the best temperature uniformity could be reached when the outlet is located at the bottom position of the right front compartment; the different refrigerated transport temperature decides different wind speed inside the compartment, the higher of the air supply temperature, the faster of the reasonable wind speed, and it corresponds to a preferred wind speed. Based on the frequency domain analysis, refrigerated compartment temperature disturbance mathematical model and temperature response mathematical model are established to analyze the perturbation amplitude and phase angle of the four kinds of temperatures. It is found that the inside compartment temperature fluctuations could be reduced under certain conditions, which include increasing specific heat capacity of the compartment, insulation materials density of the compartment and reducing convective heat transfer coefficient of the inside and outside surface of compartment; their two perturbations are attenuated when refrigeration frequency and defrost frequency are within attenuation domain range; temperature amplitude reaches its minimum when refrigeration and defrost temperature perturbation are at the same phase angle; the inside compartment temperature fluctuations are reduced when the compartment is equipped with better airtightness, lighter color surface, and the vehicle change its speed with a frequent variation.(2) Thermal stability of inside compartmentBased on thermal theoretical knowledge, the attenuation and delay effect as well as the inside heat stability impact of four typical insulated compartments are investigated. It is founded that different insulating materials decide different outside sol-air temperature time lags and the attenuation coefficients, to be more specific, the bigger of the compartment thermal inertia index or resistance, the longer of the corresponding time lag and the bigger of attenuation coefficient; different traveling directions or insulating materials also decide different inner wall surface temperatures of compartment; thermal stability mainly depends on the thermal resistance and thermal inertia index of compartment insulation material, to put it another way, the higher of the thermal resistance and thermal inertia index value of the insulating material, the better of thermal stability of compartment.(3) Temperature change characteristics of compartmentBased on the dynamic thermal equilibrium theory, the inner compartment temperature changes mathematical model, which covers the temperature changes of single-temperature, multi-temperature refrigerated vehicle and door-opening process, is constructed. It is shown that the inner temperature exponentially decrease during the cooling process and increase during the door-opening process; Longer hours are required when the compartment thickness is reduced or the thermal conductivity increased, the solar radiation absorption coefficient of outside surface of compartment increased, or speed increased, compartment leak multiples increased, goods respiratory heat increased and cooling capacity is decreased. For double-temperature refrigerated compartments, longer cooling hours is consumed in the two zones when cooling capacity is smaller, goods respiratory heat increased, the speed increased or compartments thermal conductivity increased; Longer cooling hours in the freezing compartment is taken, but less cooling hours for the refrigerated compartment, when wind speed of the electric fan and the outlet area increases between the two zones; Longer cooling hours in the freezing compartment is taken, but almost the same cooling hours for the refrigerated compartment, when the total volume of the compartment is unchanged and frozen zone volume increased. Door-opening process of refrigerated trucks, turn on or off the refrigeration system, blowing wind speed in the compartment and the insulation ability of compartment have little effect on temperature changes in the refrigerated compartment; the inside temperature is increased faster if there is a greater temperature difference in and out of the compartment, the door opened broader and the compartment volume decreased. Whether there is wind or no or even wind direction outside the compartment due to the different rates of elevated temperature during the door-opening process.(4) Compartment optimization designThe smallest heat transfer coefficient and the maximum internal space of compartment as the objective function, analysis of the variation of compartment interior space and compartment heat transfer coefficient, and the best thickness of compartment insulation material under different parameters. The results showed that different speeds, different speeds, different thickness of the insulation material, different thermal conductivity of insulation materials, the smallest heat transfer coefficient and the maximum internal space of compartment are not the same; when the optimal compartment heat transfer coefficient and the optimal internal space of compartment conditions at the simultaneously time meet, thickness increases of compartment insulation material along with the optimal compartment heat transfer coefficient increases. (5) The relationship between refrigerated transport and the quality of perishable foodThe best temperature and humidity are different among different perishable foods whole logistics process, simulation pork and lychee logistics process under different temperature conditions. The experiment showed that different temperature and humidity conditions of transport and sale, lychee undergoes different changes in its brown change index, the anthocyanin-optical density difference, peel color values, pulp PH value, weight loss rate and in other indicators; he temperature and humidity conditions affect the quality of pork during the process of transport, distribution and sale; quality of the pork and its shelf life largely depend on the temperature control during the transport and sales process.更多还原