He3flow in dilute−43He mixtures at temperatures between 10 and 150 mK

The mutual friction between ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ II below 150 mK has been studied. Empirical relations for the adiabatic and the nonadiabatic flow properties of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ moving through ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ have been determined using a dilution refrigerator with a single mixing chamber. The validity of the relations is verified by osmotic-pressure measurements and by measuring the properties of a double-mixing-chamber system. It is shown that superleak shunts have a strong effect on the flow characteristics. From the nonadiabatic flow properties an expression is derived for the mutual-friction-force density between ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ II. This has a strong resemblance to the Gorter-Mellink mutual-friction-force density between the normal and the superfluid components in pure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ II. It is speculated that the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ flow in our systems generates a ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ vortex tangle, which leads to the observed mutual friction between ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ and ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ and also to a strong clamping of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ to the walls.