Dynamic Heat Transfer Characteristics And Melting Performance Of Phase Change Material In Inclined Heat Storage Pipe

The dual carbon target has become an important strategy for global response to climate change and promoting green and low-carbon energy transformation.Energy is the foundation and lifeline of a country’s economy.Currently,human society highly relies on traditional fossil fuels.However,the emissions of greenhouse gases such as carbon dioxide face the catastrophic impact of climate change,hindering people’s aspirations for a better life.The energy revolution is imperative,and traditional fossil fuels will gradually be replaced by new energy sources such as solar and wind energy.High quality phase change heat storage technology is a key technology to promote the efficient utilization of solar energy,and solve the imbalance between energy supply and demand sides.Phase change heat storage technology involves interdisciplinary fields such as heat transfer,engineering thermodynamics,chemistry,physics,and materials science.Its melting mechanism and characteristics are very complex.Therefore,mastering the efficient heat transfer characteristics of phase change materials is currently one of the research hotspot for scholars both domestically and internationally.This article adopts a combination of mechanism analysis,theoretical research,numerical simulation,and experimental testing to focus on the dynamic thermal storage characteristics and melting laws of phase change materials under multiple tilt angles.The research mainly adopts a hierarchical/gradual technical strategy,and conducts systematic research from steady-state to non-stationary,point to surface,focusing on the key fundamental issues in this field.The details are as follows:Firstly,this article establishes mathematical heat transfer models for three physical regions of a phase change heat storage system,namely the heat transfer medium(water),heat transfer pipeline,and phase change material(paraffin)regions.The continuity equation,momentum equation,and energy equation of the fluid have been established for the heat transfer medium;Establish energy equations for heat transfer pipelines;Establish continuity equations,momentum equations,and energy equations for phase change materials,and use the enthalpy porosity method to calculate the solid-liquid melting heat transfer model of phase change materials;The results show that the numerical calculation results of this article have been experimentally verified with the self-developed experimental platform,and the overall error of the system is within 20%,meeting the requirements of numerical calculation accuracy and engineering applications.Then,based on the established mathematical model,the influence of multiple parameters on the thermal storage characteristics of the inclined heat storage system was studied,and the different tilt angles(0 °,30 °,60 °,90 °),inlet temperatures of different heat transfer fluids(356 K,361 K,366 K,371 K),initial temperatures of different phase change materials(288 K,293 K,298 K,303 K)As well as the influence of inlet flow rate of different heat transfer fluids(0.085 kg/s,0.17 kg/s,0.255 kg/s,0.340 kg/s)on the dynamic heat transfer process of the whole heat storage system,explore the dynamic heat transfer characteristics and laws of the system.The results show that during the heat storage process,the 30 ° inclination angle has a higher melting rate and average temperature of phase change materials compared to other inclination angles;The total heat stored in phase change materials reaches its maximum at 60 °,while the average heat storage rate reaches its maximum at 30 °.At the same time,phase change materials require the shortest melting time.At the same time,the results also show that the higher the inlet temperature of the heat transfer fluid,the larger the overall melting curve slope of the phase change material,and the higher its average heat storage rate.When the inlet temperature of the thermal conductive fluid increases from 356 K to 371 K,its melting time decreases from 610 minutes to 465 minutes,a decrease of 23.77%;The total heat storage increased from 4689 k J to 5097 k J,an increase of 8.70%;The average heat storage rate increased from 128 J/s to 183 J/s,an increase of 42.97%.Also,in order to explore the melting process of phase change materials in thermal storage systems and the influence of inclination angle,based on the principle of similarity theory,a high-precision inclined pipeline visualization thermal storage system experimental platform is designed and constructed,and a large amount of experimental data and dynamic images of the melting process of phase change materials are obtained through testing.The results show that an increase in tilt angle makes the temperature mixing inside the liquid PCM more uniform,and the speed of solid-liquid interface change increases with the increase of tilt angle;The liquid fraction of the melted phase change material increases with the increase of inclination angle.At inlet temperatures of361 K and 366 K,a 60 ° inclination angle of the thermal storage tank reduces the melting time of PCM by 29.6%and 37.7%,respectively,and increases the energy storage speed by 37.9%and 64.5%,respectively.Finally,based on the knowledge of heat transfer,engineering thermodynamics,fluid mechanics,and multi-phase flow,combined with experimental test data and numerical simulation calculation results,this article establishes a calculation model for four indicators of the heat storage system: supply rate/storage rate/storage/efficiency.The calculation of supply rate/storage rate/storage/efficiency of the heat storage system under different tilt angles is completed.The results show that the inclination angle of the heat transfer tank has the greatest impact on the supply rate/storage rate.When the inclination angle of the heat storage tank is 60 °,the relative performance of the system is optimal,and the system has the maximum efficiency of 0.940.The innovative breakthrough of phase change heat storage technology can provide important support for the efficient supply and stable output of solar energy,and play an important role in building a clean,low-carbon,safe and efficient energy system.The research results of this article can reveal the dynamic heat transfer and melting laws of phase change materials,provide certain technical support for energy conservation and emission reduction in multiple industry fields,and help the country achieve the dual carbon goal as soon as possible.