Natural convection heat transfer is found in many industrial applications such as nuclear technologies, electronic circuit board cooling, solar panel cooling and many other fields. When natural convection heat transfer coefficients are insufficient, passive heat transfer enhancement devices (called ribs/fins) are often used. In this paper, the effect of periodic patterns of protrusions (ribs) on the free-convection heat transfer of a vertical plate, with a uniform heat flux rate boundary condition, is experimentally investigated. The convective fluid is air. Two-dimensional, high resolution heat transfer measurements are performed by using infrared thermography and the heated thin foil technique. Experiments are performed on two types of ri...