EVALUATION OF CORRELATIONS FOR THE PREDICTION OF HEAT TRANSFER IN A HEAT PIPE FOR SOLAR COOLING APPLICATIONS

This paper describes the theoretical-experimental study on the heat transfer inside a wickless heat pipe to be used in solar collectors for solar cooling systems. When opportunely developed, solar cooling, that is the production of cold out of solar heat, allows to obtain considerable energy conservation compared to conventional plants. The solar energy activates a thermodynamic cycle for the production of cooled water or for air treatment intended to room conditioning or refrigeration processes. In this regard, for the construction of solar panels, an empty heat pipe has been considered because of the high efficiency of heat transfer inside it. Such pipe is able to transfer a large quantity of heat over relatively large distances with small temperature differences between the heat input and output zones. Further to a series of tests on tubes inclined at 45°, with different filling levels of distilled water (FR = 8.57%÷57.1%), for different levels of input heat into the evaporator section (between 50 and 155 W) and mass flow rate of cooling fluid between 3.0 and 8.5 kg/h, a study has been performed for searching correlations in the open literature that would allow to predict the values of heat transfer coefficients at the evaporator and at the condenser. A positive match was founded between the values predicted by some of the numerous correlations available in literature and the data experimentally recorded. This paper consequently suggests an empirical correlation for the condenser section.