Simulation Analysis Of Heat Transfer Characteristics Of Ammonia-Based Compound Solution Chemical Heat Pipes

In recent years,portable electronic devices have been developed towards high performance and lightweight,which has significantly increased the heat flux density per unit area.As the temperature of electronic components increases,the failure rate increases rapidly,so it is urgent to solve the heat dissipation problem of high-performance portable devices.Heat pipes have strong adaptability,good heat transfer capacity,uniform temperature,precise control of heat flow,and are easy to fit electronic devices such as chips,etc.,and are widely used in the thermal design of electronic equipment.Research on heat pipes has also progressed from heat pipe structure design to solid wall and working fluid material research to capillary structure research,all aimed at further improving the heat transfer performance of heat pipes to meet the increasing demand for high heat flux density heat dissipation of electronic devices.However,current research on heat pipes is still limited to physical phase change heat transfer and mass transfer.This article provides a new possibility for future research and development of heat pipes by establishing a comprehensive one-dimensional steady-state chemical heat pipe heat transfer and mass transfer model based on comprehensive consideration of the transmission characteristics of chemical solution working fluid combined with augmented Young-Laplace equation and gas-liquid two-phase thermodynamics and kinetic theory.This article establishes a comprehensive one-dimensional steady-state chemical heat pipe heat transfer and mass transfer model based on comprehensive consideration of the transmission characteristics of chemical solution working fluid combined with augmented Young-Laplace equation and gas-liquid two-phase thermodynamics and kinetic theory.By comparing and analyzing the changes of parameters such as gas-liquid two-phase flow area,mass flow rate,solid wall temperature,thermal resistance,and Me number of working fluid under different heating powers,the heat transfer and mass transfer characteristics of chemical heat pipes with different concentrations of NH₄I solution as working fluid and phase change heat pipes under different heating powers were compared.The results show that under the same working conditions,chemical heat pipes have a longer equilibrium liquid film region than phase change heat pipes;at the same time,the heat transfer performance of chemical heat pipes is better than that of phase change heat pipes of the same size;the higher the concentration of chemical heat pipe working fluid,the smaller the thermal resistance,and the larger the mixed working fluid Me number,the better the heat transfer performance of heat pipes.To further study the heat transfer performance of heat pipes with different combinations of working fluids,this article numerically analyzed phase change heat pipes with ethanol and acetone as working fluids with changed solvent angles and chemical heat pipes with NH₄I-ethanol solution,NH₄I-acetone solution with changed solute angles,and NH₄Cl,NH₄F,and NH₄NO₃ aqueous solutions as working fluids.Comparing their mass flow rates and heat transfer performance,it was found that the change in mass flow rate of heat pipe working fluid is related to the comprehensive unit reaction enthalpy of working fluid,while Me number and heat transfer performance are related to the unit molar reaction enthalpy.The results show that under the same working conditions,the heat transfer performance of different chemical heat pipes is optimal for NH₄I solution,followed by NH₄Cl solution,NH₄F solution,and NH₄NO₃ solution has the worst heat transfer performance.At the same time,the higher the concentration of the solution,the better the heat transfer performance of chemical heat pipes,and Me number still has a positive predictive effect on heat pipe heat transfer performance.