Uniformity of the temperature gradient in the turbulent counterflow of He II

A specially fabricated tubes was used to study the uniformity of the temperature gradient in the turbulent counterflow of He II. The tube has a high-aspect-ratio rectangular cross section and has six thermometers embedded in one wall and evenly spaced along the length. The temperature gradient in one section of the tube was anomalously small and this effect was traced to an imperfection in the tube. Over most of the flow tube the gradient was found to be consistently uniform under a wide variety of conditions. These results are in accord with a superfluid turbulent state that is axially homogeneous. The complexity of the data in the vicinity of the imperfection suggests that such boundary effects contribute to the results of earlier experimental studies of uniformity. The major cause of discrepancy however can probably be traced to entrance length effects