Experimental Study On The Preparation Of Phase-change Thermal Fluid And Its Heat Transfer Characteristics In The Mode Of Co-extraction Of Coal And Heat

Judging from the current situation of coal resource mining in China,the long-term demand for coal resources,the near-dilution of shallow resources,and the high reserves of deep resources collectively indicate that China’s coal resource mining to deepen is the general trend,and the subsequent raw rock temperature The continuous rise,the continuous increase in heat dissipation of surrounding rocks,and the increasingly serious underground high temperature phenomenon have greatly affected the physical and mental health of workers and the normal production of mining enterprises,but we cannot just treat high rock temperature as a thermal hazard.It is also a geothermal resource that can be utilized.Based on the framework of coal thermal co-production.This thesis focuses on the preparation and research of heat exchange media,and comprehensively adopts theoretical analysis,experimental research,numerical simulation and other methods to carry out the preparation of melamine resin/noctadecane microcapsule phase change fluid.In the experiment,the thermophysical properties of the prepared phase change fluid were measured,and the constant heat flux density circular tube heat transfer experiment system was built and related experiments were carried out.The effect of different working conditions on the phase change fluid transfer under the heat transfer of the buried pipe in the goaf was analyzed.The law of influence of heat.The main conclusions are as follows:(1)The phase change fluid preparation experiment with melamine resin/noctadecane phase change microcapsules as the main functional components was carried out to study the influence of different preparation methods,different types of dispersants,and addition amounts on the stability of phase change fluids.The results show that when the chemical dispersion method is used to compound SDS and SDBS according to the mass fraction of 0.1% and 0.2% and supplemented by a certain physical dispersion method,both the dispersion effect and the stability are good.(2)The DSC curve,TG curve,particle morphology of the phase change microcapsules,as well as the phase change characteristics,viscosity,density and other thermophysical parameters of the prepared phase change fluid were measured.The results show that the phase change characteristics of the prepared phase change fluid are basically the same as those of the phase change microcapsules.The viscosity of the phase change fluid with a mass fraction of 30% phase change microcapsules increases rapidly,and the density changes abnormally within the phase change temperature range.(3)The constant heat flux density circular tube heat transfer experiment system was built and the thermal balance and stability of the experimental system were verified.The influence of mass fraction,Reynolds number,heat flux density and other parameters on the heat transfer characteristics of the phase change fluid was analyzed.The results show that the heat transfer intensity of the phase change fluid is significantly higher than that of the base fluid.As the mass fraction increases,the wall temperature decreases continuously,and the convective heat transfer coefficient continues to increase;the Reynolds number is also a factor that affects the heat transfer effect.One,but as the Reynolds number continues to increase,the increase in heat transfer gradually decreases,and the wall heat flux has no significant effect on heat transfer.(4)The physical model of phase-change fluid heat transfer in downhole working face is established,and fluent numerical simulation software is used to analyze the influence of different working conditions on the heat transfer of phase-change fluid under the heat transfer of buried pipes in the goaf.The results show that as the flow time of the phase change fluid increases,the rate of change of the thermal influence distance presents a fast-slow-stable change trend.The rapid change stage is within 2h of operation,and after 20 h,the influence distance is between 0.7-1m;Changing the inlet temperature of the fluid and increasing the inlet velocity of the phase-change fluid can effectively increase the total heat exchange in the heat extraction process,and the inlet temperature has a greater influence on the heat exchange effect than the inlet velocity.The paper has 59 pictures,8 tables,and 69 references.