Abstract:
The evacuated solar collectors are made by attaching parallel circular tubes with a hemispherical cup at the bottom and generally solar collectors are installed with an acute –angle to horizontal. Thus the present study is focused on the investigation of the sensitivity of the acute angle on heat transfer process in a circular tube in evacuated- solar collector. The heat and fluid flow is assumed to be unsteady, two-dimensional, laminar and incompressible. By giving uniform heat flux 950Wm-2at the upper lateral surface of the tube for a period of 15minutes, the velocity and temperature profiles of the water particles within the tube are studied for several acute angles /8, /6, /4, /3 and 3/8. For discretization of the governing equations, the finite volume method is used and as a numerical tool, the OpenFoam software, and the merged PISO - SIMPLE (PIMPLE) algorithm is used. The results show that, for small acute angles, although the maximum temperature gain is high, the majority of water particles are at low temperature level as well as the velocity profile is at a low level. For large acute angles, the velocity profile is high but maximum temperature gain is low. For moderate level acute angles, the maximum temperature gain is in somewhat high level and a lot of water particles are in high temperature level. Moreover, the velocity profile is in high level. Thus with a moderate level acute angle, the heat transfer process of water through a circular tube with a hemispherical cup at the bottom of the tube improves the performance.
