We have investigated the mixing properties of 2D Rayleigh B¿nard convection in infinite Prandtl number flows. The mixing properties were monitored by injecting tracer particles into previously calculated flow fields. A particle correlation function H(r) and the corresponding correlation dimension have been used to characterize the mixing efficiency of the flow as function of its vigor and its's structure. We demonstrate that the chosen method captures the mixing process in a detailed manner. Our study suggests that mixing properties of the flow depend on the spatial scale. At Rayleigh numbers 106<Ra<108 heterogeneities within one circulation cell are destroyed rapidly while two adjacent cells can remain unmixed substantially longer. ¿ American Geophysical Union 1994