Experimental investigation on condensation heat transfer coefficient inside multi-port minichannels

Very little experimental information is available in the open literature about condensation inside minichannels. Most of the experimental work has been carried out by using the Wilson plot technique. This method is simple to implement because it does not require the direct measurement of the tube wall temperature. However it becomes inaccurate when a small thermal resistance is present on the test side as compared to the opposite (cooling) side, which is actually the case with a multichannel tube at high values of the internal heat transfer coefficient. In fact, in a multi-port tube internal webs work as fins, and their efficiency is close to unity; thus the internal heat transfer area is higher than the external one. In this paper a new technique to measure the heat transfer coefficient during condensation inside a multi-port extruded minichannel tube is presented. Some R134a preliminary data is also reported.