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Abstract: Natural convection in an open ended cavity is simulated using Lattice Boltzmann Method (LBM). The paper is intended to address the physics of flow and heat transfer in open end cavities and close end slots. The flow is induced into the cavity by buoyancy force due to a heated vertical wall. Also, the paper demonstrated that open boundary conditions used at the opening of the cavity is reliable, where the predicted results are similar to conventional CFD method (finite volume method, FVM) predictions. Prandtl number (Pr) is fixed to 0.71 (air) while Rayleigh number (Ra) and aspect ratio (A) of the cavity are changed in the range of 104–106 and of 0.5–10, respectively. It is found that the rate of heat transfer deceases asymptotically as the aspect ratio increases and may reach conduction limit for large aspect ratio. The flow evaluation in the cavity starts with recirculation inside the cavity, as the time proceeds the flow inside the cavity communicates with the ambient. [Copyright &y& Elsevier]

Abstract: The purpose of this paper is to present heat transfer measurements of gas in a tube under rarefied condition. The measurements are made in a circular tube of inner diameter 25mm for approximately constant wall temperature boundary conditions, with nitrogen, oxygen, argon, and helium as the working fluids. The range of Knudsen and Reynolds numbers covered in this study are 0.0022–0.032 and 0.13–14.7, respectively. Whereas the continuum values are correctly reproduced in our setup, the measured values for Nusselt numbers are very small in the slip regime. The measured values are two-five orders of magnitude smaller than the corresponding values in the continuum regime, and suggest that the Nusselt number is a strong function of Reynolds, Knudsen and Brinkmann numbers in the slip flow regime. These are among the first heat transfer measurements in the slip flow regime and the current theoretical and simulation models are inadequate to explain such low values of Nusselt number. [ABSTRACT FROM AUTHOR]