A pressure-composition-temperature test method considering valve motion of Sievert apparatus based on LabVIEW
[Objective]Rapid advancements in computing have led to continuous innovation in volumetric apparatus for measuring absorption/desorption properties of hydrogen storage materials.However,researchers are still dissatisfied with the current test results.The hardware and software of the test device still need to be greatly improved,especially in terms of chamber volume calibration,test accuracy,and test efficiency.Currently,the existing pressure-composition-temperature(PCT)test method of Sieverts apparatus does not consider the influence of valve motion,which will lead to the calculation error of hydrogen storage in the PCT test process,and ultimately has a non-negligible impact on the test accuracy of the apparatus.[Methods]A method for online calibration of valve volume was proposed to address the calculation errors in hydrogen storage caused by changes in chamber volume due to valve action in Sieverts apparatus.This method combines the Leachman equation of state and the principle of mass conservation to construct a mathematical model for determining the variable volume within the chamber.During the calibration process,the counterevidence method was used to analyze the pressure difference between the left and right cavities after closing the valve.In addition,a novel PCT test method that considers valve motion was introduced,which is based on a new hydrogen storage calculation model and uses LabVIEW software to execute valve motion procedures.The final test program development was completed using the QMH framework.[Results]This paper provides a detailed description of the structure of the calibration device,underlying principles of PCT testing,online calibration of valve volume,and practical implementation of PCT testing that considers valve motion.This paper also proposes an online calibration method for the valve volume of the Sieverts apparatus,achieving precise measurement of variable volume in an operational environment.Meanwhile,the conclusions obtained from pressure differential analysis during the valve volume calibration process are utilized to propose a simple,feasible,and cost-effective method for accurately calculating hydrogen storage.This proposed method makes indirect use of known quantities to solve the problem of being unable to directly measure pipeline and sample chamber pressures,significantly reducing the construction cost of the equipment through algorithm modeling.Finally,a PCT test method that considers valve motion is proposed,which avoids calculation errors in hydrogen storage caused by changes in valve volume,greatly enhancing the accuracy and robustness of PCT testing.[Conclusions]The null PCT test verifies that the maximum hydrogen storage calculation error obtained using the method considering valve motion is smaller than that obtained without considering valve motion,and the results are closer to zero,thereby validating the accuracy of the calibration results and PCT testing method.The PCT test of the La0.5Ce0.5Ni4Co alloy demonstrates accurate test results,complete platform information,and smooth curves.Correspondingly,it can be observed that the maximum hydrogen storage calculation error without considering the valve motion is close to the reduction of the maximum hydrogen storage of the alloy under the adjacent temperature PCT test,indicating that the hydrogen storage error caused by valve motion cannot be ignored.Then,the same PCT test of the LaNi4.25Al0.75 alloy with low platform pressure also verifies the above conclusions.Therefore,PCT tests for various hydrogen storage alloys demonstrate the effectiveness of these testing procedures and underscore the importance of considering valve motion.
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