Study On Energy Storage Characteristics And Performance Evaluation Methods Of Paraffin Phase Change Materials

Solid-liquid phase energy storage technology is widely used in engineering applications due to its high energy storage density,moderate volume and easy to control.The research of solid-liquid phase energy storage technology in buildings mainly focuses on the paraffin.The surplus renewable energy or waste energy is stored and released on demand within the constant temperature phase transition process.As a result,the energy consumption of buildings is reduced by extending the application of renewable energy or waste energy.However,there are conflicts among the published results because of the influence of boundary conditions and encapsulation structures.Moreover,the actual energy storage process is influenced by the various boundary conditions and encapsulation structures simultaneously.The results considering the single impact factor are not able to predict the energy storage characteristics of paraffin accurately.An experimental setup is established using paraffin as phase change material in this paper.The paraffin energy storage process is studied considering the influence of boundary temperature,boundary airflow velocity and HDPE plate tilt angle.The main conclusions are as follows:1.The effects of boundary temperature,boundary airflow velocity and HOPE plate tilt angle on the phase change energy storage are studied separately.The results show that:(1)increasing the boundary temperature does not change the temperature at which the melting begins but increases the temperature at which the melting completes.When the boundary temperature is 55℃ the heat transfer enhancement rate reaches 47.4%.The higher the boundary temperature,the greater the latent heat storage rate increase ratio.The total stored energy increases with the boundary temperature.(2)The increase in the boundary airflow velocity from 1m/s to 2m/s will not reduce the phase change time.The latent heat storage rate increases by 8.1%from 1m/s to 2m/s.The increase in the boundary airflow velocity from 4m/s to 5m/s increases the phase change time.The heat transfer enhancement rate decreases from 49.2%to 46.7%.(3)When the tilt angle of the HDPE board is 90°,the heat transfer enhancement rate reaches 50.8%.When the tilt angle increases from 300 to 75° the latent heat storage rate increase ratio is 32.3%.2.The variation of paraffin temperature during melting tracked by the infrared camera shows that the existence of boundary airflow velocity leads to uneven paraffin temperature,which is the main reason for the generation of natural convection inside the material.3.The experimental study of the combined effects of boundary temperature,boundary airflow velocity and HDPE plate tilt angle on the energy storage process shows that:(1)The order of importance of factors affecting the melting of phase change materials is:boundary temperature,boundary airflow velocity and tilt angle of HDPE plate.(2)Under the experimental conditions of this paper,the optimal combination of boundary temperature,boundary airflow velocity and HDPE plate tilt angle is 55℃,5m/s,75°,which will result in the maximum latent heat storage rate.