Air Pressure Dependence of Natural-Convection Heat Transfer

Heat transfer is one of the prevalent concepts with many usages in different fields of science, industry and so on. In different applications we need more or less to know about this phenomenon. Control of this phenomenon is too important in some cases and we should be aware how to control it. The importance of heat transfer rate and effect of various parameters on it, is a reason of performing this research. Because of changes of air pressure in different applications, we need to know how heat transfer affected by air pressure. In different places air pressure is higher or lower than atmospheric pressure and we can't use more of experimental equations (e.g. Morgan or Churchill-Chu for a horizontal cylinder) which correlated in standard situation and atmospheric pressure so air pressure changes haven't been calculated. In this paper an experimental study was done in order to investigate the effects of air pressure on natural convection heat transfer from a horizontal cylinder specimen. In this experimental study tests have been done in continuum mechanics range. By using a particular apparatus with ability to change specimen surround Pressure, natural convection calculated by existent equations. Pressure varied from 18 to 220000 Pascal and convection coefficient was calculated in the temperature range from 40 to 100 C. Each test has been done in repeatedly to have high precision. Various diagrams and tables were obtained to show pressure dependence of natural convection. Reduction of convection coefficient was observed by reduction of air pressure and order of these changes is shown in different figures. Vice versa natural convection, radiation is not depend on air pressure so percentages of two types of heat transfer (convection and radiation) are different due to various pressures, and this concept is observed in this literature. Although tests have been done in several input powers but in each pressure, natural convection only had dependency on temperature, and different input powers led to same results. Main aim of this work is to show the rhythm of convection changes in a range of pressure. Also in different temperatures this rhythm can be seen.