Study On Heat Transfer Characteristics Of Cascade Phase Change Floor Heating System

Phase change materials(PCMs)have the characteristics of high phase change latent heat and adjustable thermal conductivity,which can be combined with traditional floor heating systems to provide heat in a day through the way of batching reserve heat.It can realize efficient heat management of floor heating and effectively reduce heating energy consumption.Researchers focus on the current research work on how to influence the temperature variation of one or more test points on the floor surface or indoor space through changing phase change materials,thermal physical parameters and structural characteristics of the floor,and there is less research on how to ensure more uniform floor surface temperature and a longer floor holding time.This paper studies in the following:(1)Aiming at the uneven surface temperature of phase change floor heating floor,a new cascade phase change floor heating system is proposed which base on the temperature field distribution characteristics of the solid-liquid phase change material in the heat storage process.It used the phase change material with lower phase change temperature and the phase change material with higher phase change temperature is used in the near heat source area.After building model and simulating by ANSYS Fluent,many processes about the phase change floor heat storage,exothermic and other are analyzed,and the study finds that the maximum temperature difference between the surface of the cascade phase change floor heating floor is controlled within 3 °C,which is 31.63% and 48.81% lower than that of ordinary phase change floor heating PCM 1 and PCM 2,and the heat preservation time reaches 12.33 h,which is extended by 37.79% and 16.22% compared with ordinary phase change floor heating PCM1 and PCM 2.(2)In order to further clarify the influence of the structural parameters of the geothermal heating phase change regenerative layer and the thermal performance parameters of the phase change material,the influence of parameters such as the arrangement of phase change materials,the latent heat of phase change,and the thermal conductivity on the floor heating system was explored through simulation analysis,and the heat-storage and discharge characteristics of the cascade phase change floor heating under different thermal physical property parameters and conditions are obtained.From this,the normal experiment of three factor and three levels is designed.The following is a summary of the optimal combination.the distance between the bottom of interface of the phase change material PCM 1 and PCM 2 and the centerline of neighbouring water pipe is 20 mm,the phase change latent heat of PCM 1 is 170 k J/kg,and the phase change latent heat of PCM 2 is150 k J/kg and the thermal conductivity of the phase change materials is 2W/(m·K).(3)Based on the conclusions of this study,the chosen two high-load rate,lowcost loading materials and phase-change materials with suitable phase transition temperature and phase change latent heat are synthesized to synthesize a new thermally enhanced composite phase change material,PCM 1 and PCM 2 with the phase change temperature of 37.67 °C and 24.4°C,respectively,and the latent heat of169.7k J/kg and 149.7k J/kg,respectively and the appropriate material ratio is determined through experiments.Various characterization methods were adopted to investigate the thermal conductivity,microstructure and thermal stability of the material.The experimental results show the porosities of illite by activated process was dramatically improved.The heat transfer coefficient of paraffin /illite increase by 6.3 times,the heat transfer coefficient of dodecanol/illite increase by 10.5 times and the composite phase change materials of paraffin/illite and dodecanol/illite had good thermal stability.The simulation experimental room was established and the cascade phase change heat-storage and discharge experiment was carried out.Experimental results show that when the ambient temperature is 0-4 °C,5-12 °C,9-16 °C,the temperature of indoor air can be maintained at 18°C,23°C and 24°C.