Numerical Simulation And Experiment On Multi-temperature Quick-frozen Process Of Steamed Bread

Quick-frozen technology has a wide range of applications. The quick-freezing processof food is an extremely complex dynamic process, involving heat transfer, food science,refrigeration and other various subjects. Therefore, the study on quick-freezing process andcharacteristics of food has an important significance on choosing the best quick-freezingconditions, improving and optimizing quick freezing plant, reducing the overall energyconsumption of refrigerating system, and optimizing the quick freezing modeling undercomplex conditions.The present paper experimentally studied and simulated the freezing process ofsteamed bread in three-temperature quick freezing plant with planar mesh belt, andanalyzed the quick-frozen characteristics and the impact of different technics on freezingrate and quality of steamed bread.During the experiment, the present paper discussed the effect of temperature onfreezing rate in different stages by adjusting the throttle valve to change refrigerant flow inevaporator and change the temperature; in this paper, an orthogonal experiment was carriedout, which studied the influence of changing the wind speed of precooling stage,crystallization stage, cryogenic stage section and frequency of the conveyor belt (i.e. thefrozen time) on the freezing rate and quality score of steamed bread. Besides, the paperanalyzed the correlation between texture detection index and sensory quality of steamedbread by SPSS software. In the simulation, the paper used Fluent software, selected theRNG k-epsilon model to calculate the temperature of steamed bread in three-temperaturequick freezing plant with planar mesh belt, and compared with experimental results. Theconclusions are as follows:(1) The surface temperature of steamed bread declined fastest, the center temperaturedropped slowest; the closer to the center of steamed bread, the higher the temperature was;before freezing, the temperature gradient of points increased first, then gradually becamesmaller, after freezing, it increased again, and then gradually became smaller; thequick-frozen steamed bread had a supercooling phenomenon; the longer the frozen timewas, the lower the center temperature of steamed bread would be; when frozen time wasover4000s, the center temperature could reach to the required storage temperature whichwas-18℃.(2) The crystallization temperature and freezing rate were highly correlated: the lowerthe crystallization temperature was, the faster the freezing rate would be. However, as thetemperature decreased, freezing rate was gradually leveling off; the precooling temperatureand freezing rate were highly correlated; the cryogenic temperature had no significant effect on freezing rate.(3) In the factors of wind speed in precooling, crystallization, cryogenic stage and thefrozen time, the wind speed in crystallization stage had the greatest impact on steamedbread quality and the freezing rate. The second greatest influence factor is frozen time. Thebest quick-freezing process of steamed bread is that both of the precooling and cryogenicwind speeds are4m/s, and the crystallization wind speed is5m/s, while the frozen time is4000s.(4) Steamed bread specific volume and hardness, gumminess, chewiness weresignificant negatively correlated; surface structure and resilience were negatively correlated;steamed bread hardness and texture analyzer hardness were significantly correlated, whichmeant the springiness of texture analyzer could replace the springiness of sensoryevaluation; toughness and hardness were significantly negatively correlated.