| Microwave ovens occupy an indispensable position in home cooking due to its simple operation and fast heating speed.However,the use of microwave ovens also has serious drawbacks,including uneven heating and unstable heating patterns.At present,there are many studies on the improvement of the heating uniformity of the microwave oven,but the stability of the microwave heating pattern is still poor.This article mainly studies the design of microwave ovens from the perspective of microwave cavities.The cavity of a common microwave oven is rectangular,which includes parameter changes in the three directions of length,width,and height.The cylindrical microwave cavity studied by few scholars has only the variables of diameter and height.In theory,it can improve the stability of heating patterns.This article aims to design a microwave oven with stable heating patterns and good heating uniformity during the heating process,to provide theoretical basis and experimental support for the design of microwave ovens.The research contents and conclusions of this article include the following aspects:?1?Heating platform was set up for a cylindrical microwave cavity,and the heating performance of a cylindrical microwave cavity with a diameter of 190mm and a height of 160mm was explored.Utilizing the shielding effect of metal on microwave,the cylindrical stainless steel cavity was placed in a domestic microwave oven to share a microwave source to form a closed cylindrical microwave heating platform.The frequency distribution,actual power and heating patterns of the cylindrical microwave heating cavity were analyzed.When the microwave oven is empty,the frequency distribution of the WEILI microwave heating cavity is concentrated between 2.432 GHz,2.445-2.47 GHz,and 2.48-2.482 GHz,and the frequency distribution of the D190mm H160mm cylindrical microwave heating cavity is concentrated between 2.46-2.47 GHz.The frequency distribution of the microwave heating cavity is affected by the presence or absence of load,the shape of the load,and the shape of the wave cavity.The frequency distribution of the cylindrical microwave cavity is more concentrated and stable than that of the square cavity.The output of the D190mm H160mm cylindrical microwave heating cavity is 5.3%lower than the 25UG26 square microwave cavity.The matching between the cylindrical microwave cavity and the microwave source used is not ideal,and its heating efficiency is lower than that of WEILI microwave oven.The output power can be increased by adjusting the matching between the microwave source and the cylindrical wave cavity,thereby improving the heating efficiency.Cylindrical microwave cavity has better heating patterns repeatability than WEILI square microwave cavity.Temperature difference between cold and hot spot of D190mm H160mm cylindrical microwave cavity is smaller than that of WEILI square microwave cavity,and thus its heating uniformity is better than the square microwave cavity.?2?In order to develop microwaveable salmon products,model food based on Maillard reaction was used to obtain the heating patterns of the salmon after microwave heating.The coaxial probe method was used to measure the dielectric properties of different parts of salmon in the temperature range of 20?110?and the frequency of 300?2 500MHz.The changes of the dielectric properties of the model food with the content of whey protein were analyzed to match the dielectric properties of salmon.When the temperature is constant,the dielectric constant and dielectric loss of salmon in different parts decrease with increasing frequency.When the frequency is constant,the dielectric constant decreases and the dielectric loss factor increases with increasing temperature.At the same temperature and the same frequency,the dielectric constant and dielectric loss factor of the fish in the tail and back are larger than those in the abdomen,which maybe because the fat content of the fish in the abdomen is higher than that in the back and tail.As the whey protein powder content increases,the dielectric constant and dielectric loss factor of the model food decrease.When the composition?mass fraction?of the model food is 10%whey protein powder,1%gellan gum,1%D-ribose,1%L-lysine,0.3%Ca Cl2,and86.7%distilled water,the electrical characteristics of model food are consistent with salmons,which can be used to determine the microwave heating temperature distribution and cold and hot spot location of salmon,and provide a theoretical basis for the development of microwaveable salmon products.?3?This paper analyzes and evaluates the method of microwave oven heating uniformity,optimizes the factors that affect the heating uniformity,such as the size of the microwave cavity of the cylindrical microwave oven,the height position of the food,the material of the tray and so on,so as to provide theoretical basis and experimental support for the design of the microwave oven.When the height of the cylindrical wave cavity is 160mm and the diameter is reduced,the position of the hot spot of microwave heating food is shifted to the position of the wave source.When the height of the wave cavity is reduced to 100mm,the hot spot position is on the left side of the food after microwave heating,and the edge heating is obvious.This may because wave cavity height is too low and the food is too close to the wave source.As the diameter of the cylindrical cavity decreases,the frequency distribution shifts to higher frequencies.The temperature uniformity coefficient of a cylindrical microwave cavity with a height of 160 mm for rotating heated food is significantly smaller than that of stationary heating.Rotary heating can effectively improve the uniformity of heating of the cylindrical microwave cavity.The uniformity of heating of circular food with a cylindrical microwave cavity of 160mm in height is better than that of square food.Among them,the D190mm H160mm cylindrical microwave cavity rotating heating D140mm H20mm food has the smallest temperature uniformity coefficient.The heating patterns change greatly and the hot spot position of the food moves to the left and then to the right with the height of the food in the microwave cavity increased.Heating uniformity first increases and then decreases with increasing temperature.When the height of the food in the microwave cavity is 1-2 cm,heating uniformity of the cylindrical wave cavity is significantly improved.With height of the food increased,the frequency distribution shifts to low frequency.When D190mm H160mm cylindrical microwave cavity heating food,the trays of different materials have great influence on the heating pattern of round food and have little influence on the square food because the edge heating of the square food under this microwave cavity is dominant.The trays made of glass have the least influence on the heating patterns,and ceramic material trays can help food to heat more uniformly,which is related to the dielectric properties of ceramics.In order to obtain a stable and uniform cylindrical microwave cavity,a ceramic material tray can be added,and the height of the food in the cavity can be increased properly and the rotating heating can be coordinated at the same time. |
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