عنوان مقاله [English]
Thermosyphons are devices used to transfer heat from a hot to a cold source benefiting the effect of gravity. They consist of three main parts, namely, evaporator, condenser and adiabatic section. Working fluid absorbs heat from the heat source and delivers it to the condenser section and releases it into the environment. Thermosyphones are able to transfer heat between the heat sources and sinks. Due to the high latent heat of the working fluid, thermosyphones can transfer huge amounts of energy. Therefore, they are considered one of the best heat transfer devices. They are widely used in various industrial fields, such as in solar systems, microelectronic devices, CPU cooling and air conditioning. Most researchers in this field focus only on heat transfer characteristics, and, due to practical considerations, rarely consider their hydrodynamic specifications. Indeed, the hydrodynamic characteristics of thermosyphones considerably affect their performance. In this paper, the velocity profile in the liquid phase is determined via a particle image velocimetry technique (PIV). For this purpose, a typical thermosyphon has been designed and constructed with transparent up riser and down-comer sections. In this study, a circular thermosyphon is analyzed and water is used as a working fluid in the circular thermosyphon. At the beginning, the velocity field of the liquid phase is detected in the transparent thermosyphon using a high speed camera and an image processing technique. Subsequently, these pictures are used to generate the velocity profiles and are combined with theoretical analyses to evaluate the performance of the thermosyphon. The results are compared with numerical investigations and show good consistency. The results indicate that the particle image velocimetry (PIV) truly determines the hydrodynamic and thermal characteristics of the thermosyphones. Moreover, in this study, the effect of input heat and the inclination angle of the thermosyphon are investigated numerically. It has been shown that the maximum efficiency of thermosyphon is in a horizontal position.