Investigation of Surface Tension of Isobutane (R600a) and Isobutane–Hydrogen Solutions

The paper presents experimental data of the capillary constant and the surface tension of pure isobutane (R600a) and an isobutane–hydrogen mixture in the temperature range (0.731–0.996)Tc1 (Tc1 = 407.81 K) at pressures from the saturation pressure of pure isobutane up to 4 MPa. The concentration of hydrogen in isobutane was determined from the equilibrium pressure in the system using experimental data on the phase equilibrium line of the solution. The temperature dependence of pure isobutane is approximated by a function whose coefficients are determined by the method of regression analysis. For a binary isobutane–hydrogen system, equations that describe the capillary constant and surface tension as functions of the temperature and concentration (pressure) were constructed. The maximum deviation of the equations proposed from the experimental data does not exceed 0.02 mm2 (for the capillary constant) and 0.04 mN·m–1 (for the surface tension). It has been shown that an increase in temperature as well as an increase in the concentration of hydrogen in the solution leads to a decrease in the surface tension of isobutane.