Methodical investigation of free convection from vertical and horizontal plates

This paper attempts of review the literature on free convection from flat surfaces transferring heat in an unlimited space. Data from the references have been presented as final criterial relations both in tabular form and in graphic system, separately for the vertical plates and the horizontal ones. About 45 results of investigations on free convection have been examined and the following mean criterial relations have been calculated:Nu=0.550·(Ra)^0.250 for vertical plates,Nu=0.310·(Ra)^0.290 for horizontal plates. It has been observed for the vertical plates that divergence of these results relatively to the mean values is constant within the whole variability range of the Rayleigh number and amounts to about ± 15%. In the case of horizontal plates the divergencies are more considerable and vary within ± 50% for the laminar, and within ± 25% for the turbulent range. In the next step the attempt was made to determine the causes of these divergencies and errors. The work was performed because of two main reasons: imperfection of measuring methods and a lack of uniformity in the choice of the characteristic linear dimension.