N2 - The reason for undertaking this study was to determine the possible involvement of natural convection in the global heat transfer, that occurs in the heated steel rods bed. This problem is related to the setting of the effective thermal conductivity of the bars bed. This value is one of the boundary conditions for heating modeling of steel rods bundles during heat treatment. The aim of this study was to determine for which geometry of the bed bars, there will be no free convection. To analyze the problem the Rayleigh criterion was used. It was assumed that for the value of the number Ra < 1700 convection in the bed bars does not occur. For analysis, the results of measurements of the temperature distribution in the unidirectionally heated beds of bars were used. It has been shown, that for obtained, during the test, differences of temperature between the surfaces of adjacent rods, convection can occur only when the diameter of the rod exceeds 18 mm. L1 - http://www.czasopisma.pan.pl/Content/94396/PDF/05_paper.pdf L2 - http://www.czasopisma.pan.pl/Content/94396 PY - 2013 IS - No 1 March EP - 83 DO - 10.2478/aoter-2013-0005 KW - Natural convection KW - porous material KW - Bed of bars A1 - Wyczółkowski, Rafał A1 - Musiał, Dorota PB - The Committee of Thermodynamics and Combustion of the Polish Academy of Sciences and The Institute of Fluid-Flow Machinery Polish Academy of Sciences DA - 2013 T1 - Analysis of the occurrence of natural convection in a bed of bars in vertical temperature gradient conditions SP - 71 UR - http://www.czasopisma.pan.pl/dlibra/publication/edition/94396 T2 - Archives of Thermodynamics