Capillary constant and surface tension of propane (R-290) with helium dissolved in it

•The capillary constant of propane(R-290) + helium solution is measured.•The differential capillary method was used.•The surface tension is calculated.•The equations approximating the obtained data are proposed. The differential capillary method is employed for the measurement of the capillary constant. Based on the knowledge of this parameter, the surface tension of propane (R-290) + helium is calculated. The measurements are performed in a temperature interval from 120 to 350 K at pressures in the range from the saturation pressure of pure propane up to 4 MPa. Equations are proposed for the dependence of the surface tension on temperature, pressure, and concentration. It is shown that in the considered range of values of the parameters small additions of helium into propane may lead both to a decrease and an increase of the surface tension of the solution.