Wall temperature measurement in a herringbone microfin evaporation tube

Experimental data on heat transfer and pressure drop in herringbone microfin tubes reported are very limited and the heat transfer enhancement mechanism has not been clearly explained. In the herringbone microfin tube an increase of heat transfer is probably due to the particular wetting in two directions by the V-shape grooves, resulting in a film layer varying around the circumference of the tube. The herringbone tube tested is made of copper with an outer diameter of 9.52 mm and a wall thickness of 0.3 mm. An experimental facility has been constructed to enable thor-ough local heat transfer and pressure drop measurements at ten subsections along a four-meter tube. The circumfer-ential temperature distribution of the outer wall of the tube is measured by means of thermocouples, which were laser-welded onto the top, bottom, right and left side of the tube. The task of measuring temperatures in temperature gradients as well as very small temperature differences is a very difficult one. Therefore this paper focuses on the applied measurement techniques as well as error analyses and discusses resulting accuracies. First measurement results are shown and the possibility to use local temperature measurements to detect changes in flow patterns is discussed