Energy Flow Method For Modeling And Optimization Of Evaporative Cooling System

To further promote energy conservation and environmental protection,and achieve sustainable development of human society,continuously developing new energy-saving technologies,improving new analysis and optimization methods of clean energy systems,and improving the efficiency of clean energy systems are the main research directions of many scholars.The coupled heat-mass transfer process between water and air is driven by the temperature difference and partial pressure difference between water and air respectively.The process is environmentally friendly,and the latent heat of phase change of water is large.Therefore,the system has high energy utilization efficiency and broad utilization prospects,and the energy utilization system based on water-air evaporative cooling has been widely studied by scholars.In this paper,an evaporative cooling and ventilation system is taken as the research object.Similar to circuit networks,the energy flow model composes of thermal resistances and additive thermo-motive foreces is established by analyzing the heat transfer equation and energy conservation equation of each heat exchange component in the system.The model not only describes the law of heat transport from the system level,but also reflects the topological relationship between the components of the system.It also clarifies the essence relationship between the structure of the component and the operating parameters,and then establishes a simplified algebraic equations of complex nonlinear energy utilization systems.Based on this model,modeling of performance analysis and optimization design are established using the Lagrangian multiplier method,which realizes the optimal matching between system operating and structural parameters.Taking the typical working conditions for instance,the variation of the area distribution,cooling water flow distribution and fresh air distribution are studied for the evaporative cooling and ventilation system,respectively,when the total thermal conductivity(investment cost)or the circulating flow(operation cost)is given.And the optimization results could provide theoretical support for design and optimization processes.Furthermore,for the nonlinear problem caused by the mutual coupled heat and mass transfer during evaporative cooling,the three-flow model of direct evaporative cooling is constructed by theoretical derivation from the basic heat transfer and mass transfer equations.The heat coupled mass transfer process is converted into a three-flow model of single-phase heat transfer process between the cooling water and the air at the dew point temperature and the dry bulb temperature.The thermal resistance of the single-phase heat transfer processes is also derived and established separately.The algebra equations based on the assumption of linear or nonlinear saturation line of the direct evaporative cooling process are established,respectively,which realize the decouple of heat transfer and mass transfer,and provide a theoretical basis for analyzing the interaction between coupled heat mass transfer process.Finally,the energy flow method is combined with the direct evaporative cooling three-stream model to explore its application in specific systems.