Heat transfer through gases contained between two vertical cylinders at different temperatures

Abstract

Heat transfer through gases contained between vertical concentric cylinders was investigated when the radius of the inner cylinder is small compared to the radius of the outer cylinder. Experiments were performed in a modified hot wire type thermal conductivity cell in which end effects could be evaluated in addition to the overall heat transfer between the cylinders. Measurements were made with argon, helium and neon in the pressure range 0[middle dot]1-620 mmHg, for the temperature differences between the cylinders of 10, 50 and 100 degC, and for the length to the outer diameter ratios between 3[middle dot]3 and 6[middle dot]7. The results show that below certain Rayleigh numbers and length to diameter ratios heat is transferred from the hot to cold boundary by conduction only. End effects contribute only in the corner regions. The distance to which these end effects penetrate was determined experimentally, and compared to analytical results obtained from a simple heat balance in the corner region. Relationships, based on the experimental data, were also obtained for the average heat transfer both in the corner regions and over the entire length of the cylinders. It is shown that these results may be used to estimate the error introduced in thermal conductivity and thermal accommodation coefficient measurements by neglecting end effects.