Pressure maxima in the flow of superfluid [sup 4]He in tubes

Calculations based on the standard equations for the flow He II in tubes predict large pressure and moderate temperature maxima when the tube is long and narrow. This effect has not, to our knowledge, been previously observed. Experimental data are presented that confirm the existence of the pressure maxima in capillaries of diameter 0.3 [mu]m. The measured data are in good agreement with predictions. The data validate the model equations for flow in capillaries and porous media using the bulk value of the Gorter-Mellink parameter. This effect may impact interpretations of experimental searches for size effects.