Study On The Temperature Distribution Of Instant Rice During Microwave Reheating

Instant rice is por Tab.and edible safety,which meets the needs of fast-paced life.Microwave heating has the advantages including simple operation,energy saving and high efficiency,which make it well-suited for reheating instant rice.However,The uneven temperature distribution during microwave reheating of instant rice will affect its edible quality.In this study,the dielectric properties,thermal properties and height of instant rice were taken as experimental factors.The dielectric and thermal properties of instant rice after microwave reheating were analyzed with temperature and moisture content,and effect of height on temperature uniformity of rectangular instant rice was studied.The simulation software was empolyed to simulate the process of microwave reheating instant rice,which expounded of uneven temperature distribution of instant rice.The method of microwave intermittent reheating and metalized packaging container were proposed to improve the temperature uniformity of instant rice,which would obtain the optimal parameters of microwave intermittent reheating and metallized packaging container.The results were as follows:(1)The changes of dielectric constant,dielectric loss factor,specific heat capacity and thermal conductivity of instant rice were analyzed with temperature and moisture content.The results showed that the dielectric constant increased with the increase of temperature when it was lower than 30°C,and the dielectric constant decreased with the increase of temperature when it was higher than 30°C.The dielectric loss factor decreased with the increase of temperature.The dielectric constant and dielectric loss factor decreased with decrease of moisture content.The specific heat capacity increased exponentially until it reached a constant value of 2.90 k J/(kg·°C)with the increase of temperature of instant rice,and the increase rate of thermal conductivity increased gradually.(2)The effect of the height of instant rice on its temperature distribution was analyzed.The method of microwave intermittent reheating was proposed,and the effects of microwave action,intermittent ratio and microwave action time on the temperature uniformity of instant rice were investigated.The results showed that instant rice in rectangular container had corner focusing effect,and the cold spot area was concentrated in the inner center of instant rice.The absorption of microwave energy had higher at the edge of instant rice than that at the center,and it gradually decreased along the direction transmission to the center.The degree of attenuation of the microwave increased with the increase of the sample height.The temperature uniformity of instant rice was better when the height of instant rice was 4.5 cm,considering the experimental results andactual requirements.The effect of microwave action on the temperature uniformity of instant rice was greater than that of other factors.The optimal parameters of microwave intermittent reheating were microwave action once,reheating time of 180 s,and intermittent ratio of 1:3.0,which the temperature uniformity of instant rice increased by 30.77%.(3)The metallized packaging container was designed to investigated the effect of the metal widths,metal intervals and angles between metal and bottom on temperature uniformity of instant rice.The results showed that the temperature uniformity of instant rice had better at high level of metal intervals,and middle level of metal widths and angles between metal and bottom.The temperature uniformity of instant rice was improved 38.46% when the metal widths of 0.80 cm,the metal intervals of 1.00 cm,and angles between metal and bottom of 74.00°.The results of this study can provide a theoretical basis for industrial application of microwave reheating in the field of instant foods,and the reasonable design of microwave packaging containers.