Seleção de um termossifão para aplicação em pré-aquecedores de ar

Abstract

Thermosyphons are effective devices able to transfer large amounts of energy given a small temperature difference using the working fluid latent heat and gravitational forces. This passive heat transfer device is found in many the industrial sector applications, from air preheaters, heat regeneration, solar panels, heat exchangers, to name a few. The thermosyphons are made of a hermetically sealed tube divided in three sections, the evaporator, the adiabatic section, and the condenser. The goal of this Senior Design Project was to select the best settings for a thermosyphon aiming for an air preheater application, experimentally evaluating its thermal performance varying the filling ratio and working slope. Thermosyphons were constructed with copper tubes having a length of 180mm, an outer diameter of 9.45mm and an inner diameter of 7.75mm, where each section of the thermosyphon having a length of 60mm. The working fluid used was distilled water. The evaporator was heated using a thermal resistance of nickelchrome and the condenser was cooled by forced convection using air. The power dissipations provided to the system started at 1 to 11W, using a 2W increment. The selection first step analyzed the filling ratios of 20, 40, and 60%, using a working slope of 45º relative to the horizontal. The best results found were to the filling ratio of 40%, since it showed a smaller operational temperature and smaller thermal resistance. The selection second step analyzed the working slope of 22.5, 45, 67.5, and 90º (vertical position). The working slope selected was 45º, since it showed a smaller thermal resistance.