冷藏运输车真空隔热厢体的温度场特性仿真研究

为提高冷藏运输车厢的隔热性能,设计一种聚氨酯嵌套真空隔热板复合结构,对比分析聚氨酯嵌套真空隔热板复合结构、全聚氨酯板的"Z"字型和"工"字型加强筋结构的热力学性能,对嵌套真空隔热板和全聚氨酯板的厢体进行温度场模拟仿真,研究真空隔热板在保温板中的不同嵌套位置对厢体隔热性能的影响。仿真结果表明:聚氨酯嵌套真空隔热板复合结构符合强度要求,可提高车厢的隔热性能,真空隔热板嵌入保温板中间,被聚氨酯形成良性包围的情况下更能充分发挥真空隔热板的隔热性能。     

液氮充注气调对运输厢体内流场均匀性的影响

为了掌握液氮充注气调对厢体内流场的影响,搭建液氮充注气调试验平台,研究不同汽化器的翅片间距、回风道风速和初始温度条件下厢体内的温度场和相对湿度场的均匀性变化。结果表明,翅片间距对厢体内的温度场及相对湿度场的均匀性有一定影响,翅片间距为7 mm时均匀性相对较好,翅片间距为4 mm时均匀性相对较差;回风道风速越大,厢体内温度场的均匀性越好,相对湿度场均匀性越差;初始温度越高,温度场和相对湿度场越均匀。研究结果为气调保鲜装备的进一步开发提供了参考依据。     

保鲜运输用超声波加湿的数值模拟

为掌握保鲜运输用超声波加湿流场的分布特性,本文针对压差原理的保鲜运输厢体结构,以脐橙为试验物料,建立厢体的1/4等比例三维紊流模型,借助有孔模型和组分传输模型,结合SIMPLE算法和壁面函数法,运用Fluent软件进行超声波加湿的数值模拟,分析了厢体内温湿度场的变化。模拟结果表明:采用超声波加湿可以在212 s内将厢体内的相对湿度自70%升高至90%;厢体内温度场和湿度场分布均匀,厢体内温差不超过1℃,相对湿度差小于3.5%;加湿过程对温度场的影响较小;货物表面的相对湿度差不超过3%;货物区水蒸气扩散较快。经试验验证,试验结果与模拟结果相吻合。该研究结果对于保鲜运输加湿装置的结构优化具有一定的参考价值。     

多温区冷藏车厢体内温度场和速度场的数值模拟及优化设计

对多温区冷藏车厢的温度场、速度场进行数值计算,并数值模拟蒸发器出风口风速及厢内不同的堆货形式对流场的影响,从而对出风风速、堆货方式进行分析及优化设计。试验得出从冷冻厢与冷藏厢内都存在中心回流区,为合理利用冷量和空间,应该使用带风道的冷藏车厢,冷藏厢降温初始阶段为保证降温速度可以用较高的风速,而等温度稳定后建议将风速调小到6m／s。     

风速对冷藏车内温度分布的影响

为探究风速对液氮冷藏车内温度分布的影响,实验中液氮冷藏厢内初始温度为288 K在不同的风速条件下经液氮雾化喷淋降温。风机风速vf分别为0、2、5.5、10 m/s。用热电偶测量并记录降温过程中各点的温度,并用Origin软件画出不同风速下冷藏箱体内的温度分布曲线和降温速率曲线,结果表明:单排喷嘴间距1 m工况下随着风机风速的增大,不同高度平面的温度分布越接近,降温速率越慢,此时单嘴喷量较大,风速不是影响冷藏箱体内温度场均匀性最主要的因素。     

易腐食品冷藏运输车内温度场影响因素仿真研究

运用k-ε湍流模型,对不同厚度的车厢隔热材料、不同送风口位置、不同送风温度及不同送风速度条件下冷藏运输车厢内温度场进行数值模拟。结果表明:冷藏运输车车厢聚氨酯隔热材料合理厚度为100～120mm;制冷设备送风口位于车厢内正前下方位置时,车厢内各个不同典型断面温度均匀性最好,并且厢内各处温度更接近于设定值,送风口位于车厢中间位置次之,送风口位于车厢内正前上方最差;冷藏运输温度要求不同,对制冷设备的最佳送风速度要求也不同,冷藏运输车厢内温度要求高,其合理的送风速度也相应要求高,并且每种冷藏运输温度条件下都有与之对应的最佳风速。     

竹纤维真空绝热板芯材的结构和性能研究

以漂白竹浆为原料,探讨了打浆度对竹纤维真空绝热板芯材结构和性能的影响,以期获得隔热性能较好的竹纤维真空绝热板。结果表明,在打浆度为14.9°SR条件下,竹纤维真空绝热板芯材的平均孔径为21.7μm,孔隙率为75.7%,密度为0.287 g/cm~3;由其制备出的竹纤维真空绝热板导热系数为12.6 m W/(m·K),具有较好的隔热性能。通过扫描电子显微镜和透气度测定仪分析表明,随着打浆度的增加,竹纤维真空绝热板芯材纤维表面分丝帚化严重,结构致密,透气性能降低。     

气调贮运摆放位置对荔枝保鲜品质的影响

为研究保鲜气调运输厢体内荔枝不同摆放位置对保鲜品质的影响,采用果蔬气调保鲜运输试验平台对"淮枝"荔枝进行气调贮藏。隔7 d对不同摆放位置的荔枝样品进行测试,测试指标为果皮褐变指数、质量损失率、果皮色差值、可滴定酸以及可溶性固形物含量,并结合厢体内的温度场、湿度场进行分析。试验结果表明:在贮藏期内,厢体内温度呈前低后高、上低下高分布;而相对湿度呈前高后低、上低下高分布。不同纵向摆放位置对无包装荔枝的果皮褐变指数、质量损失率影响较大,质量损失率自上而下逐步减小;处于厢体后部的荔枝的可滴定酸含量较前部和中部的荔枝要高;处于厢体中部的荔枝的可溶性固形物含量要比前、后部的荔枝低。本研究结果为果蔬贮运保鲜提供一定的参考。     

保温材料对保温箱内温度场的影响

通过构建保温箱基本模型,运用有限元法及Fluent进行热流耦合分析,得到保温箱内温度场,并通过实验进行验证。选取3种常见保温材料[挤塑聚苯乙烯(XPS)、发泡聚氨酯(EPU)与真空隔热板(VIP)],通过模拟仿真研究不同材质保温箱内温度场分布规律。结果表明:保温箱使用的保温材料不同,内部温度场有较大的差异性,其中VIP保温箱内温度最接近蓄冷剂相变温度值,且温度场分布最均匀; 3种材料都具有较好的阻热性能,其中VIP的阻热性能最好,在保温箱内相同位置的温度比EPU和XPS要低。     

多温区冷藏车回风导轨对厢内温度场的影响分析

通过冷藏车多温区影响因素分析,建立多温区冷藏车的传热模型,利用计算流体力学方法研究回风导轨对车厢内温度场分布均匀性的影响规律。依靠Fluent软件,采用标准K-ε模型,开展空仓和载货两种状态下的数值模拟试验。结果表明:回风导轨的变化能够改变车厢内温度场分布;其对冷藏区温度场分布影响较大,对常温区温度分布影响较小。空仓状态下,导轨高度与温度不均匀系数近似呈"凸型曲线"分布;载货状态下,导轨高度与温度不均匀系数近似呈正比例线性分布。相比于X方向导轨,冷藏车采用Y方向导轨可以有效提高车厢温度分布均匀性。     

基于CFD技术的高效节能冷柜研发

针对目前冷柜的研究开发主要靠经验和简单的计算,存在产品的开发周期长,费用高的缺点,提出了基于CFD技术的冷柜研发,介绍了CFD技术、封闭式冷冻陈列柜的结构及其热负荷组成。建立三维非稳态模型,编译用户自定义函数即UDF(User-Defined Function)程序,利用有限容积法优化冷柜内温度场/流场。应用结果表明基于CFD技术的冷柜研发不仅具有效率高、能耗低等特点,而且可以掌握柜内温度分布规律、改善了柜内部气流组织状况,提高了温度分布的均匀性,提高食物保鲜效果。     

充氮热灌工艺在PET瓶饮料生产中的应用

PET瓶热灌装工艺具有安全性高,操控性能好,投资少等优点,在饮料生产领域应用广泛,但饮料从热态到常温过程中体积收缩产生负压,给瓶体设计造成一定局限性,必须利用呼吸板块吸收负压,同时瓶体需采用厚加强筋以提高强度。充氮热灌装工艺是在传统热灌装工艺的灌装工序后,旋盖前向瓶体内部注射液氮,通过氮气在热态和常温下的压力变化来消除负压,去除呼吸板块的设计限制;同时,通过液氮气化增加瓶体内压进而提高瓶体抗压强度,打破加强筋过厚的约束,大幅提高了PET瓶体设计的自由度。     

Exposure of meat to methyl bromide during refrigerated-store pest control; residues in beef and lamb and effect on quality

Beef and lamb were exposed to methyl bromide in a refrigerated container during trial fumigations at 1, 3 and 10 times the level considered necessary for rodent control in cold-store insulation material. Traces of residual methyl bromide were detected by GC-MS in fats after periods of up to 3 months in refrigerated storage and some effect on taste and odour after roasting was noted in beef subjected to the highest treatment level.     

Thermal behavior of CMC solutions under simulation of radio frequency pasteurization

Pasteurization and enzyme-inactivation are an economical and convenient way to provide safety and shelf-life stability. However, long heating time and non-uniform temperature distribution are the main issues of traditional thermal processing for enzyme-inactivation. Because of the volumetric heating and high heating rate, radio frequency (RF) treatment is considered as one of the most promising physical enzyme-inactivating methods. A 6 kW, 27.12 MHz RF heating system was applied to explore the effect of cylindrical container dimension and solution concentration on the thermal behavior of high-viscosity liquid food. Carboxymethylcellulose (CMC) solution as a non-Newtonian fluid was selected as a model liquid food in this study. The target temperature for enzyme inactivation was 70 °C. The experimental results showed that the electrode gap, container length, and container diameter affected the heating rate and uniformity of the liquid food. Furthermore, when the concentration of CMC solution increased from 0.5% to 2.0%, the heating rate of the solution firstly increased and then decreased, while the heating uniformity index of the solution increased from 0.008 ± 0.001 to 0.056 ± 0.002. The simulation results showed that the higher electric field strength led to a higher heating rate, temperature, and velocity of natural convection of the solution at the ends of the container. Then, the recirculation zones from the ends to the center of the container were formed, which was diminished with the increasing concentration solution, resulting in the increased maximum temperature difference of solution. The results of this research may provide useful data for subsequent continuous flow studies and information on potential RF enzyme-inactivation in high-viscosity liquid foods.     

冷链可折叠保温箱设计及试验研究

针对目前冷链运输过程中使用保温箱为整体式保温箱,不能折叠拆装,回收利用时空箱储运成本较高的问题,开发可快速折叠的折叠冷链保温箱。基于可折叠保温箱和普通保温箱在296K和308K环境下的储藏试验,进行保温性能分析。结果表明可折叠保温箱保温性能与普通保温箱相近,空箱储运成本比普通保温箱降低60%以上。此折叠保温箱适合应用于冷链运输。     

冷藏集装箱温度场均匀性改善研究进展

综述了货物堆码、送风速度、送回风形式、风机位置等因素对冷藏集装箱温度分布的影响,阐述了箱体内温度场的空间分布特性,进而对影响箱体内温度分布的相关因素进行了对比分析,并对其未来发展方向进行了展望。     

Computational modelling of the impact of polystyrene containers on radio frequency heating uniformity improvement for dried soybeans

Radio frequency (RF) heating has been explored as a new method for postharvest pasteurization and disinfestations, but the non-uniform heating problem needs to be solved. In this study, an experimentally validated simulation model was developed to investigate effects of applying a surrounding polystyrene container on RF heating uniformity improvement in dried soybeans. The computer model was built for soybeans with both low and high moisture contents placed in the rectangular shaped polypropylene and polystyrene containers and heated in a parallel plate RF system. Results showed that the temperature uniformity was greatly improved by placing soybean samples in the polystyrene container other than the polypropylene one. The maximum temperature difference and uniformity index (UI) were reduced. The inner corner radius of 8 cm combined with container thickness of 8 cm could provide the best heating uniformity for soybeans. This newly developed technique can be easily implemented to improve the RF heating uniformity of other low-moisture legumes for industrial applications.Industrial relevanceRadio frequency (RF) heating has been explored as a new method for postharvest pasteurization and disinfestations of low-moisture granular legumes, but the non-uniform heating problem needs to be solved before being applied in industry. A validated simulation model was used to demonstrate the better container material and design for ensuring good temperature distributions in practical RF treatments. The optimal parameters from computer simulation may save time and reduce the cost to facilitate the design and scaling-up of the RF treatment protocols.     

Precooked Reduced-Fat Beef Patties Chemical and Sensory Quality as Affected by Sodium Ascorbate, Lactate and Phosphate

Beef-carrageenan (BC; 10% fat) patties—with sodium ascorbate (0.05%), sodium lactate (3%), sodium tripolyphosphate (0.3%), ascorbate-phos-phate, ascorbate-lactate, or none—and 20%-fat all-beef patties were cooked, aerobically or vacuum packaged, and stored at 4°C or ?20°C. Fat level had a greater effect on texture than did additives. Lactate and phosphate increased cooking yield of BC patties. Phosphate was antioxidative but not antimicrobial. Ascorbate was antioxidative and reduced aerobic plate counts (APCs) of aerobically packaged refrigerated BC. Lactate reduced APCs of both aerobically and vacuum packaged BC patties. Lactate had a prooxidative effect in aerobically-packaged/frozen patties but showed no such effect in vacuum-packaged/frozen patties or refrigerated patties. Ascorbate-phosphate was most effective in minimizing flavor deterioration in refrigerated BC patties.