Study On The Flow And Heat Transfer Characteristics Of Blueberry In The Process Of Fluidized Quick-Freezing

With the rapid development of the food freezing and refrigeration industry,people have higher requirements for the quality of quick-frozen food.Fluidized quick freezing technology has the advantages of high heat transfer efficiency,fast freezing speed,low food drying consumption,and high quality of frozen products.It has gradually developed into one of the important industrial quick freezing methods for rapid freezing of monomers.This subject selects the northern characteristic berry-blueberry as the research object to study the flow and heat transfer characteristics of blueberry in the process of fluidized quick freezing.First,theoretically analyze the force and heat transfer of blueberries in the process of fluidized quick freezing,and obtain the analytical solution of the convective heat transfer coefficient during the freezing process of blueberries through numerical calculation.The experimental part measures the nitrogen consumption and uses the heat transfer formula to obtain the convection.The heat transfer coefficient is verified by comparison with it.Secondly,the method of numerical simulation combined with experimental verification was used to study the effect of blueberries on the flow and freezing process of blueberries in the liquid nitrogen fluidized quick-freezer under the three conditions of different freezing temperatures,different inlet wind speeds and different food layer heights.Taking the freezing time of blueberries as the judgment index,the optimal experimental conditions were determined using the range analysis method:the freezing temperature was-50?,the inlet wind speed was 5m/s,and the food layer height was 2 layers.And get the primary and secondary order that affects the freezing time of blueberries.The experimental results are consistent with the simulation results.When the wind speed is set to 4m/s and 6m/s again,the influence on the surface pressure of blueberries is analyzed.The result is that the surface pressure gradient of blueberries is smaller at higher wind speeds,and the pressure gradient of blueberries surface is larger at lower wind speeds.In order to ensure normal fluidization,the inlet wind speed should be reduced in actual operation.Finally,under the condition of freezing temperature of-40? and different blueberry layer heights,air distribution boards with different opening rates were used to analyze the influence on wind speed and pressure difference.The result is:as the opening rate increases,the curve pressure the amplitude of the fluctuation gradually decreases,and the working condition of the fluidized bed will get better and better.By calculating the standard deviation and analyzing the data,when the opening rate is 50.2%,the pulsation amplitude is the smallest and the effect is the best.