Comparative Analysis of Gas Amount-Estimation Methods in the Non-Isothermal Section of Adsorption Measurements at Liquid-Helium Temperatures

At liquid-helium temperatures， the adsorption capacity of porous materials is typically measured using a volumetric method. Because the adsorption-measurement device consists of a low-temperature section and an ambient-temperature section， a temperature gradient is distributed along the gas pipeline connecting the two sections. This distribution is difficult to determine experimentally； therefore， an approximation is required to estimate the amount of gas in the non-isothermal section and subsequently calculate the adsorption capacity. This study reviews four existing estimation methods for the non-isothermal section and proposes a new temperature distribution based on one-dimensional heat conduction that consider variable thermal conductivity. Using this temperature distribution as a reference， the effects of the four estimation methods on the adsorption capacity are analyzed under different experimental conditions. The results show that the errors introduced by the overall ambient-temperature and linear-distribution methods are smaller than those introduced by the overall low-temperature and segmented-treatment methods when estimating the amount of gas contained in the non-isothermal section. However， these two methods may also result in measurement errors of more than 10% under the experimental conditions of a higher measurement temperature， lower ambient temperature， larger non-isothermal-section volume， smaller adsorbent mass loading， and weaker adsorption capacity per unit mass.