Simulation By CFD And Engergy Consumption Analysiss For Stir-frying With Oil

In the field of food heat treatment,the study of heat and mass transfer process in wet unsaturated porous media is a subject with great difficulty and wide engineering application value.The surface temperature of particles increases rapidly with the energy obtained by convection heat transfer between particles and heating medium during heating,which leads to the evaporation of water on the surface of the particles and takes away a lot of latent heat.Meanwhile,under the drive of concentration gradient,temperature gradient and pressure gradient,the moisture inside the particles diffuses to the surface and evaporates.The whole process is highly complex,mutually coupled and unstable involving the heat and mass transfer process of heterogeneous materials.The heat and mass transfer process with non steady state characteristics significantly and rapid evaporation of particulate moisture cannot be analyzed globally by traditional analysis methods,such as orthogonal test and response surface model.And the global temperature history of particles as the basis of dynamic calculation and quality analysis is also difficult to obtain,which plays a fundamental role in heat treatment verification and process optimization.Therefore,the numerical simulation technology is very important for the research on heat and mass transfer in the heat treatment process of food,such as stir-frying with oil.Great development and abundant research results have been achieved in the field of numerical simulation for food heat treatment under the unremitting efforts of many researchers,but the numerical simulation of heat treatment for the evaporation of particles has not been solved.The constructed mathematical model of heat and mass transfer neglected either moisture evaporation or water mass transfer control equation or the porous medium properties of particles.Based on the heat and mass transfer simulation of the frying process built by Datta in 2007 and the porous media transmission theory,a heat and mass transfer mathematical model related to surface evaporation of particles and heterogeneous unsaturated porous media was set up,which includes 5 two order partial differential equations,5 initial conditions,5 boundary conditions,26 additional equations and 42 parameters.The solving method for the new model was established by using the finite element software of COMSOL Multiphysics 5.1.The new mathematical model of heat and mass transfer is a theoretical model rather than an empirical model,which is universal and can be applied to the analysis of other food heat treatment processes after reasonable adjustment.It is generally known that Chinese cooking is one of the heat treatment of food.The heat and mass transfer process of the stir-frying with oil,the typical process of Chinese cooking,was analyzed in this paper.Considering the technical characteristics of stir process,the process was simulated with oil bath by opening the pump to produce relative motion between oil and particles.Then,the process parameters were obtained by the determination of temperature and moisture content for particles.At the same time,the distribution of temperature and moisture content of pig tenderloin granules were measured and the effect of water evaporation on the particle temperature distribution was analyzed by using the established model to simulate the process of stir fried pork tenderloin.The LSTD method and correlation coefficient method were used to compare the simulation results with the experimental results.The results of surface simulation were in good agreement with the experimental data,which proved the reliability of the model.Moreover,the influence of particle size,physical parameters,heating medium temperature and mixing intensity on the heat transfer process of pork fillet was analyzed by using the mathematical model and solution method.In order to study the effect of stirring frequency and distance from bottom of the pot to fire on the endothermic power of food system in stir-frying,the heat transfer control equation is constructed for the process.Then,the analysis method was established for determination of endothermic power of food system in stir-frying combined with the experimental heat transfer method.The results show that the endothermic power of food system decreases linearly as the distance from the bottom of the pot to fire increases when the stirring frequency is same;and the endothermic power of food system increases linearly with the increased stirring frequency when the distance from the bottom of the pot to the fire is same.Meanwhile,the endothermic power of food system for two Chinese dishes was measured by using oil instead of cooking materials.The average endothermic powers were 3.17 kW and 2.93 kW,and the peak endothermic powers were 5.32 kW and 5.94 kW,respectively.The error analysis shows that using oil substitution method to study the endothermic power of the food system has significant engineering application value.