| Water pit for solar seasonal thermal storage,as an important component of sensible heat storage in current heat storage technologies,can effectively solve the problem of mismatched heat collection and use over time.Geomembranes are often used as the main anti-seepage component in the design and construction of water pit thermal energy storage(PTES),and also account for a significant share of the cost.In the overall investment of thermal PTES,geotextile membranes account for 45%,and geotextile membranes for pool bodies account for 54% of the total geotextile membrane investment.Geomembrane,as a type of geosynthetic material,is a flexible material made of polymer organic materials.Geomembranes,with their excellent extensibility,adaptability to deformation,impermeability,and corrosion resistance,are often used as impermeable layers in reservoirs,dams,waterways,and landfills to prevent internal storage fluids from leaking out.Geomembrane,as the anti-seepage unit of PTES,is also an important component.As the main material for anti-seepage,it is often affected by light,temperature,oxygen,and humidity during use,resulting in aging phenomenon.In cross seasonal thermal storage water bodies,with sidewall geomembranes as the main consideration,the combined effects of temperature,oxygen,and water become the main factors affecting the aging of geomembranes.In order to reduce the cost of heat storage,it is necessary to analyze the aging mechanism of the permeability of the geomembrane based on the actual use of cross seasonal heat storage water bodies and the study of the aging performance attenuation law of the geomembrane in the heat storage water body.The anti-seepage geotextile membrane in PTES needs to maintain good anti-seepage effect under thermal environmental conditions for a long time.Based on the actual use of cross season thermal storage water bodies,it is necessary to study the aging performance attenuation law of the geotextile membrane in thermal storage water bodies and analyze the aging mechanism of the permeability performance of the geotextile membrane.The main content and conclusions of this paper include:1.By analyzing the influence of temperature on the lateral and bottom geotextile membranes of PTES,a temperature variation testing platform for the permeability coefficient of geotextile membranes is established.Through the permeability experiment,the vertical permeability coefficient changes of three specifications of geotextile membranes under a temperature environment of 20-90 ℃ are deduced.The trend of gradually decreasing permeability coefficient of geomembranes with increasing temperature is obtained.Based on experimental data,three types of geomembrane permeability coefficients are given in relation to temperature.Based on the changes in the permeability coefficient of the geomembrane after aging,analyze its change mechanism through physical property testing.2.In combination with the long-term use of geomembrane in PTES,considering the aging effects of temperature,oxygen and water,the laboratory artificial immersion thermal aging treatment was carried out for two specifications of geomembrane at 50℃,70℃ and 90℃,and the penetration test was carried out with the geomembrane aged one year after the actual thermal storage water.Two conclusions were drawn: the longer the aging time,the smaller the permeability coefficient;The higher the aging temperature,the faster the decrease rate of permeability coefficient.3.Based on the changes in the permeability coefficient of the geomembrane before and after aging,the change principle was analyzed through physical property testing methods.The melting curve of the geomembrane was analyzed using differential scanning calorimeter(DSC),and the trend of crystallinity change and permeability coefficient change of the geomembrane at different temperatures was consistent.4.Based on the molecular chain fracture mechanism of polyethylene aging,infrared spectroscopy testing was conducted on the geomembrane before and after aging,and the characteristic peaks and strength after infrared spectroscopy were analyzed.The results showed that at 50℃ and 70℃,the majority of geomembranes exhibited molecular chain breakage,and the aging reaction was not significant;At 90 ℃,not only do oxygencontaining groups newly form,but the original molecular chains undergo significant breakage.It shows that the geomembrane has a certain degree of heat aging resistance at a temperature below 70℃,and the molecular structure of geomembrane will be greatly affected by temperature aging at a temperature above 70℃. |
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