Construction of mathematical model for heat and mass transfer of Chinese cooking

Abstract: There has been great development of the food industry and the food preparation equipment industry, and automatic food preparation equipment has come into service. Although research on the principles of the cooking process can explain the advantages and rationality of traditional cooking skills, the more important significance of it is to reveal the principle of cooking quality formation, to find out key control parameters, and to provide a theoretical and practical foundation for automatic cooking. Currently, most Chinese cuisine literature associated with heat transfer is qualitative and vague. In reality, heat transfer plays a crucial role in the quality of the finished product in traditional Chinese cuisine，therefore it is necessary to study the heat transfer of the cooking process in order to reveal the core principle of Chinese cooking. The complicated operation of Chinese cooking were divided into three types: raw material compatibility, cutting controlling and heating controlling, by the author, and it was related to such as the principle of process transport, reaction kinetics, food chemistry, food physical, food microbiology. Thus, process transport - reaction kinetics - food quality change was considered the core principle of Chinese cooking. After a discussion of traditional materials, the related chemical reaction, heat transfer, mass transfer, momentum transfer and reactor for Chinese cuisine, it was considered that heat transfer, mass transfer, relative motion and quality changes of the fluid-particulate system in the open container is characteristic of Chinese cooking. The typical Chinese cooking process is to mix a liquid and particulates with stirring and heating in a vessel open to the atmosphere, where the heat flux direction is from the heating source to the vessel to the liquid to the particles, and includes intraparticle heat conduction from the surface to the center. The heat transfer of Chinese cooking covers all of conduction, convection and radiation. The transient governing equations of the cooking vessel are established depending on the thermal balance, with the boundary conditions of convection and radiation on the outer wall with a combusting gas, and convective heating on the inner wall with liquid, and losing heat via radiation on the exposed outer wall. When the evaporation of particulates don't exist, based on the thermal balance of liquid and particulates, the transient governing equations of intraparticle heat conduction are given with the boundary condition of convection between liquid and particulates. When the evaporation of particulates exists, the governing equations of heat and mass transfer for particulate are given based on the porous media theory, and water, oil, steam and air are considered as the mobile phase. Thus, the complete mathematical model of the Chinese cooking transfer process was put forward. The discussion showed that the mathematical model is well representative, and can be used to describe most Chinese cooking processes directly. The mathematical model has high reliability, because it consists of a theoretical basis and a semi-rational formula with rigour assumptions. This mathematical model can be applied to most cooking processes to explain transport phenomena and analyze controlling parameters and optimize the conditions of the cooking process. The characteristics of the transport process were discussed preliminarily for Chinese cuisine. Via analyzing the thermal resistance from heating source to vessel to liquid to particles in the cuisine, the convection heat transfer of vessel-liquid and liquid-particles, together with thermal conduction, was found to play a dominant role in general heat transfer, and these three have a significant influence on the cooking process. Due to manual stirring, the convection heat transfer in a vessel between liquid-vessel and liquid-particulates is unstable, and shows sophistication, however, the surface heat exchange coefficients of liquid- vessel are close to those of liquid-particulates. Thus, preheating oil is necessary in traditional Chinese cooking to improve the heating rate of the particulates. Research has shown that the heating of food particles has significant unsteady characteristics under the condition of Chinese cuisine.