Abstract This paper presents an experimental and numerical investigation on the natural convection flow and heat transfer in an enclosure with a single-hole baffle at the median height. The temperature in the fluid is quantified by means of temperature sensitive thermo-chromic liquid crystal (TLC) particles. The fluid flow velocity is measured non-intrusively with a full field particle tracking technique. The three- dimensional numerical model, developed and validated with experimental data, provides a computational tool for further investigation of mass and energy transport through the baffle openings in these types of enclo- sures. The experimentally visualized and numerically simulated flow structures show a pair of streams across the baffle-hole. The two chambers communicate through this pair of streams which carry the fluid ex- change and heat transfer between the two chambers. At the baffle opening, the two streams are aligned in a diagonal direction across of the enclosure. The streams are accelerated and form jet-like flows that drive the whole circulation in the chambers. The jet-like flows leave the baffle opening, approach the vertical cen- terline of the cavity, and finally impinge on the top/ bottom walls. 1 Introduction Industrial applications such as autoclaves for hydro- thermal crystal growth, are characterized by circulating flows with hot fluid in the lower region and cold fluid in the upper region, and have been the focus of various research efforts [1–7]. Hydrothermal synthesis is not only employed in laboratory, but it is also the method of preference in the growth of industrial grade crystals [8–12]. The process includes the dissolving of raw materials and the growth on the high quality seed crystals [9]. This complicated physical and chemical process requires two temperature zones in the growth vessels; one is the high temperature zone in the raw material region and the other is the lower temperature zone in the seed region [10]. The temperature differ- ence favorites a chemical process during which the raw material is first dissolved into the solution only to precipitates out of it later and join the high quality seed crystal lattice in the upper half. The temperature difference also drives the natural convection flow that transports the dissolved material and establishes the temperature profile in the reactor. The flow and temperature fields are critical for the growth quality and uniformity [1, 12]. Industry growth practice has found that a baffle located in-between the growth zone and the dissolving zone significantly im- proves the growth environment [5, 10] by improving the temperature uniformities in both zones. However, experimentally visualized flow structures in such enclosures separated by an internal baffle have not been well reported. The transport mechanism through the baffle opening needs to be better understood, than it presently is, in order to offer valid design guidance for the construction of this type of reactors. H. Li (&) Æ C. Xing Æ M. J. Braun Department of Mechanical Engineering, The University of Akron, Akron, OH 44325, USA e-mail: HL3@uakron.edu Heat Mass Transfer (2007) 43:895–905 DOI 10.1007/s00231-006-0178-7 123 ORIGINAL Natural convection in a bottom-heated top-cooled cubic cavity with a baffle at the median height: experiment and model validation Hongmin Li Æ Changhu Xing Æ Minel J. Braun Received: 21 November 2005 / Accepted: 29 June 2006 / Published online: 26 August 2006 Ó Springer-Verlag 2006