馒头变温速冻过程的数值模拟与实验研究

发布时间：2018-06-06 14:57

  本文选题：速冻技术 + 三温段食品速冻机　； 参考：《天津商业大学》2014年硕士论文

【摘要】：速冻技术应用十分广泛，其中食品的速冻过程是一个非常复杂的动态过程，涉及的学科包括传热学、食品学、冷冻冷藏学等方面。因此，研究食品的速冻过程及速冻特性，对选取食品最佳速冻工艺条件、改进优化速冻装置结构、降低装置整体制冷系统的能耗以及在复杂条件下对速冻过程进行建模优化具有重要的意义。 本文通过实验和模拟研究了馒头在三温段食品速冻机中的变温速冻过程，分析了速冻特性以及不同速冻工艺对冻结速度和馒头品质的影响。 实验过程中，通过调节节流阀改变进入蒸发器的制冷剂流量，从而改变空气温度，研究各阶段温度对馒头冻结速度的影响；进行一组正交试验，研究预冷段、结晶段、深冷段的风速以及即速冻时间四个因素对冻结速度和馒头品质的影响，同时，通过SPSS软件分析了馒头质构品质与感官品质的相关性。采用Fluent软件，选取k-epsilon中的RNG模型模拟计算了馒头在三温段食品速冻机内速冻时的温度变化，并与实验结果进行对比，得到结论如下： (1)速冻过程中，馒头的表面温度下降最快，中心温度下降最慢；在同一时间内，越接近馒头中心的温度越高；测点的温度梯度在冻结前先逐渐变大，然后逐渐变小，在冻结完成后又逐渐变大，最后逐渐变小；在速冻过程中-3℃左右馒头会出现过冷现象；速冻时间越长，，馒头中心温度越低；速冻时间在4000s以上，馒头中心温度能达到贮藏温度所需的-18℃。 (2)结晶段温度与冻结速度呈高度相关，当结晶段温度越低，冻结速度越快，但是随着温度的降低，冻结速度逐渐趋于平缓；预冷段温度与冻结速度呈高度相关；深冷段温度对冻结速度没有明显影响。 (3)在预冷段、结晶段、深冷段的风速以及速冻时间四个因素中，对馒头品质影响最大的因素是结晶段风速，对冻结速度影响最大的也是结晶段风速，其次是速冻时间。得出的馒头最佳速冻工艺是预冷段、深冷段风速为4m/s，结晶段风速为5m/s，速冻时间为4000s。 (4)馒头比容与硬度、胶着性和咀嚼性呈显著负相关；表面结构与回复力呈显著负相关；馒头的弹性与通过质构仪检测的弹性存在显著性相关，表示质构仪检测的弹性可代替感官评价中的弹性；韧性与硬度呈显著负相关。
[Abstract]:The frozen process of food is a very complicated dynamic process, including heat transfer, food science, refrigeration and so on. Therefore, this paper studies the fast freezing process and characteristics of food, and improves the structure of the fast freezing device by selecting the best technology conditions of food freezing. It is of great significance to reduce the energy consumption of the whole refrigeration system of the unit and to model and optimize the rapid freezing process under complex conditions. In this paper, the variable temperature freezing process of steamed bread in the three-temperature food quick-freezing machine is studied by experiment and simulation. The effects of different freezing processes on the freezing speed and steamed bread quality were analyzed. In the experiment, the air temperature was changed by adjusting the refrigerant flow into the evaporator by adjusting the throttle valve. The effects of temperature at different stages on the freezing speed of steamed bread were studied, and a group of orthogonal experiments were carried out to study the effects of four factors on the freezing speed and the quality of steamed bread, such as the wind speed of the precooling section, the crystallization section, the cryogenic stage and the quick freezing time, at the same time, The correlation between texture quality and sensory quality of steamed bread was analyzed by SPSS software. Using fluent software, the RNG model in k-epsilon was selected to simulate and calculate the temperature change of steamed bread during the rapid freezing of food in the three-temperature section, and the results were compared with the experimental results. The conclusions were as follows: during the rapid freezing, the surface temperature of steamed bread decreased fastest. At the same time, the temperature gradient of the measuring point gradually increased before freezing, then gradually decreased, and then increased gradually after the freezing, and finally became smaller. In the process of quick freezing, the steamed bread will appear undercooling at about -3 鈩

本文编号：1987046