Experimental Research On Energy Storage In Standing Column Well System

The essence of the subterranean heat exchangers in single well system is thatproduction (in the low part) and injection (in the top part) are in the same well.Currently， SCW has three forms：standing column well， pumping&recharging well，pumping&recharging well filled with gravel. Standing column well need to drill holesin the base rock， and lets water circulate directly in the borehole to exchange heat withrock of the borehole. For pumping&recharging well， there is clapboards in the wellwhich divide the well into three parts：injection space in the top part；seal section in themiddle part；production space in the low part. In general，pumping&recharging wellfilled with gravel is consistent with pumping&recharging well. And for pumping&recharging well filled with gravel，diameter of the borehole is more than pipe，gravel isfilled in the inter space borehole and pipe. These three wells will be analyzed in thesepaper，to find features and applicable conditions of them. Multiple operating cycleexperimental research on energy storage will be conducted. Meanwhile thermaltransfixion and energy storage is quantitatively analysed.The balance of heating and cooling loads，can effectively maintain the temperatureof aquifer and pumping. Under the same conditions，pumping&recharging well has agood ability to maintain the pumping temperature. For the same well，the greater thespacing of production space and injection space，the more stable pumping temperature.For the case of alternate heating and cooling，when first started heating，pumpingtemperature is more lower than cooling first in the complete experimental period.Furthermore，when the load is consistent in every period，the average (peak) pumpingtemperature varies linearly with the period.In the different period，the temperature variation of temperature measurementpoints in the aquifer is the same，the difference is the magnitude of temperature change.When the system starts cooling(heating)，temperature of the area surrounding theborehole began to change firstly，the area affected by the cooling(heating) diffuse to thedirection away from the borehole. For the three wells，the impact of standing columnwell on the aquifer is smallest，only the temperature of measurement points close to theregion changes slightly；and for pumping&recharging well，thermal transfixion will beoccurred between cliff of the borehole and skeleton of aquifer；and for pumping&recharging well filled with gravel，the impact on the aquifer is the largest.According to the definition of the thermal transfixion，the formula of thermaltransfixion coefficient was derived. And proved by experiments，for the degree of thermal transfixion，standing column well is maximum，pumping&recharging well isminimum，the reason for the above phenomenon is the fast-response thermal transfixionbecause of distinctive of well structure. For the same well，the greater the spacing ofproduction space and injection space，the lesser thermal transfixion，this difference isreflected in the slow-response thermal transfixion. And fast-response thermal of heatingmode is more serious than cooling mode. Furthermore，the more period，the morethermal transfixion. After listing systematically and fitting，it can be considered that theaverage (peak) pumping temperature varies linearly with the load ratio. According to thedefinition of the thermal energy storage，the formula of thermal energy storage ratio wasderived. When only cooling(heating)，thermal energy storage ratio is considered to bezero. Under the same conditions，thermal energy storage ratio of standing column wellis the smallest，it can be considered that thermal energy storage does not appear. Sowhen using this type of system，balance of heating load and cooling load need to beconsidered，aquifer temperature does not change very much because of this imbalanceof load. For two additional wells，when the load is unbalanced，the more period andspacing of production space and injection space，the more thermal energy storage.This project is a part of national natural science foundation "Study on the CouplingMechanisms of Multi-Pattern Flow and Heat Transfer in A Standing Column WellSystem (SCW)(41002085)".