The Numerical Simulation And Experimental Study On The Cooking Processing With Oil Heat-transfer

Oil heat transfer cooking method is a common heat treatment method for food materials and has hold a dominant position in Chinese cooking.Short time,intense roasting and accompanied by continuous evaporation were the process features of the oil cooking,which is the most complicated method in oil heat transfer cooking.The temperature and moisture content distribution of granular food materials changed with time and position in the process of oil stir-fried,which led to uneven variation of cooking quality in time and space.Traditional analysis methods can be only used to measure the average quality change for limited granular foods at specific time and space.For showing the dynamic change of quality for granular food during the heat treatment process,the global temperature and moisture content history is required.Therefore,the introduction of numerical simulation technology is imperatively needed in fluid-particle food heat treatment research.Granular foods are mostly wet porous materials,and their internal structure and composition will be changed during heat treatment because of high preheating temperature in Oil heat transfer cooking process.The heat/mass transfer mechanism of granular foods will be affected with the transportation of each components,such as water,air,water vapor,etc.It is worthy and necessary to establish a mathematical model that can simultaneously simulate the global variation of temperature in each components,which can better analyze the transmit characteristics and distribution of food components.In this paper,the pork loin treated by oil stir-frying process was taken as the object of the research.The mathematical model was constructed according to the heat/mass transfer characteristics of pork loin,and some key parameters needed for the model were determined.Then,the effects of different factors on heat/mass transfer of granular food were simulated and analyzed the content and conclusions are as follows:According to the research that basis on the convective mass transfer coefficient of food frying of foreign scholars,the effects of sample shape,specific surface area and heating oil temperature on the convective mass transfer coefficient were investigated by using pork loin which as the raw material.Based on the curve of dimensionless moisture content and heating time,the experiment is based on the principle of dimensionless moisture content analysis of mass transfer model and MATLAB software to obtain the convective mass transfer coefficient of pork loin with different shapes,oil temperature and specific surface area were varies from4.266×10-6 m/s to 3.845×10-5 m/s.With the increase of specific surface area and the increase of oil temperature,the convective mass transfer coefficient increased significantly,and the influence of sample shape change for it was not significant.Furthermore,intrinsic permeability of a liquid of pork loin is determined by the modified DSY porous ceramic permeability determinator based on Darcy's law:the pork loin is taken out when heated to 10?for heat treatment?,20,30,40,50°C,sealed in the sample chamber of the instrument,and then water is used as a fluid medium to apply pressure to the group of the sample.The intrinsic permeability of a liquid of pork loin is calculated according to the flow rate and the pressurization time,and extrapolated to obtain the relation function between intrinsic permeability of a liquid with temperature:k_in,w=3E-21×T⁴-3E-19×T³+1E-17×T²-1E-16×T+7E-16.The basic parameters was provided and a higher accuracy was improved for oil heat transfer mathematical model through the test of convective mass transfer coefficient and intrinsic permeability of pork loin.The mathematical model of heat/mass transfer is a technical means of food cooking science research.Nevertheless,there is a deviation between the measured value and the simulated value of the model established in the early stage,which cannot meet the needs of cooking optimization calculation.In order to improve the reliability of the mathematical model,the mathematical model is improved and verified from the control equations,boundary conditions and model parameters:the describe of evaporation phenomenon is added to the energy control equation,and the internal evaporation temperature of the pork is set as the limiting function of evaporation——?7?H_v I?8??9??7?T?29?=98[degC]?8?;The flow rate carried by the fluid flow is added to the boundary condition of the mass conservation equation;the model parameters are inputted based on the experimental determination and the literature review.After the model is solved,the reliability is verified by the comparison between the simulated and measured values of temperature and moisture content.The measured values of temperature distribution are obtained by the cooking heat transfer and dynamics acquisition system.The measured values of moisture distribution are determined by low field magnetic resonance imaging apparatus?MRI?and MATLAB software processing,the relationship between the gray value?y?and the moisture content?x?of the proton density map obtained by MRI imaging:y=5.6093x-120.7,the coefficient of determination is 0.971.The heat/mass transfer rule of granular foods was simulated and analyzed from the aspects of material properties,cutting treatment and process control by using the improved mathematical model,and the influence of sample shape,specific surface area,intrinsic permeability of a liquid,thermal conductivity,specific heat capacity,mass transfer coefficient and convection heat transfer coefficient on it was obtained.The simulation found that the change of the shape and intrinsic permeability of a liquid of the granular foods has little effect on the temperature and moisture content distribution;while the increase of specific surface area,thermal conductivity,convective heat transfer coefficient and the decrease of convective mass transfer coefficient and specific heat capacity will lead to the heat transfer and mass transfer efficiency of the food increased,and the internal temperature of granular foods increased at the same heat treatment time,the internal moisture content was relatively higher.The construction of the mathematical model can efficiently and cost-effectively obtain the influence of raw material characteristics and operation process on the heat/mass transfer rule of cooking materials,and a technical means for process optimization and scientific guidance of cooking operations was provided.