Natural convection heat transfer from a horizontal offset elliptic tube is experimentally investigated using holographic interferometry. The effect of the ellipse major axis from horizontal to vertical direction on heat transfer is analyzed. Interferometric fringes of the tube in infinite space at different inclination angles 0°—90° are recorded. The local and average Nusselt numbers are determined according to the reconstruction of the temperature field around the tube. The experimental results indicate that the heat transfer increases with the ellipse major axis inclined from horizontal to vertical direction. The local Nusselt numbers above the tube is the minimum and the maximum is located near the major axis when the direction of the major axis are horizontal and vertical. The results obtained in this investigation show good agreement with the existing experimental and numerical studies

which can contribute to the optimal design of heat exchanger and also provide a test method for engineering applications.