Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
NUMERICAL INVESTIGATION OF THE INTERMITTENT FLOW ONSET IN AN EVACUATED TUBE SOLAR COLLECTOR UNDER MULTIPLE OPERATING CONDITIONS
Submission Author:
Fernando Claudio Spengler , RS , Brazil
Co-Authors:
Fernando Claudio Spengler, Jacqueline Copetti, Nicolas Valmórbida
Presenter: Fernando Claudio Spengler
doi://10.26678/ABCM.COBEM2023.COB2023-1354
Abstract
Heating systems that use evacuated tube solar collectors have proven to be more efficient than other solar heating systems. However, the performance of these systems can be hindered by certain operating conditions that result in fluid recirculation, which negatively impacts the heat transfer cycle inside the solar collectors. This issue can be exacerbated under extreme usage conditions, where water properties can amplify these unfavorable flows and lead to an intermittent flow regime inside the tubes. The heat transfer mechanisms involved in this type of solar collector were studied in this work using computational fluid dynamics. The numerical model is composed of the equations of conservation of mass, energy, and continuity and was validated based on the literature. The case study aimed to determine the transition point between the laminar and turbulent regimes in the internal flow of the evacuated tube, and this was achieved by varying the working temperature of the tube between 300K and 340K at three different inclination angles (30°, 45°, and 60°). The results of the study are presented in the form of velocity vectors, temperature contours, and mass flow rate profiles. The study revealed that the intermittent flow observed in the evacuated tube was due to the gushes that enter it. Additionally, the operating temperature required to promote this gush behavior decreases as the evacuated tube angle increases. Interestingly, the average mass flow rate did not increase uniformly with increasing operating temperature, and the rise in outlet temperature of the evacuated tube decays as the operating temperature rises. Finally, the study identified the start of the turbulent regime in tubes inclined at 30°, 45°, and 60° as occurring between the operating temperatures of 330K and 340K, 310K and 315K, and 305K and 310K, respectively, for a heat transfer rate of 75W. These findings provide important insights into the design and optimization of solar collector systems, particularly about minimizing fluid recirculation and promoting efficient heat transfer.
Keywords
Solar Collector, Evacuated Tube, Computational Fluid Dynamics, Inclination
