PARAMETRIC STUDIES ON ETC TYPE SOLAR WATER HEATER- THREE DIMENSIONAL NUMERICAL MODELING AND ANALYSIS
Thermosyphon effect is solely responsible for the water circulation occurring within a non-pressurized evacuated tube collector (ETC) type solar water heater (SWH). There is a notable paucity of literatures which gives detailed information in regard to three dimensional numerical modeling and simulation of vacuum tube collectors. A number of researchers have attempted various experimental and analytical studies concerned with the performance improvement of ETC type SWH systems. Their dependence on climatic conditions, location, tilt-angles, and thermal properties, such as, absorptivity, flow rates and solar insolation are cited in such literatures. However, in the present study, the role of various design parameters on the overall performance of an ETC type solar water heater is analyzed by using computational methods. The effects of various parameters like tube diameter, tube length, tube spacing and the number of tubes on the performance of an SWH system were numerically examined. The geometry of the model used for computation was based on a non-pressurized solar evacuated tube collector manufactured by M/s. Hykon India (P) Ltd. Meshing was done by using an ICEM-CFD package available in the ANSYS®. A finite volume method was used to discretize the governing equations. In the present analysis, tube diameter was varied from 3.7cm to 5cm, tube length from 115cm to 180cm and the number of tubes from 16 to 20. A mass flow rate (m) of 0.02kg/s and a uniform heat flux (Q) of 800W/m2 were set as the default boundary conditions.
The SWH system has a storage tank, which is of 200 liters tank
capacity. Based on the numerical investigation, it was inferred
that smaller the tube diameter, lower was the outlet water temperature obtained, due to lesser recirculation occurring within the tube enclosures. Moreover, for the foresaid default configuration of the SWH system, tubes with 4.7cm diameter improved the outlet temperature by 0.9°C. However, an increase in tube length beyond 130cm showed only a marginal improvement in the outlet temperature. The tube number and tube spacing played a significant role in improving the performance of the collector. It was found that 20 tubes were considered to be the best design for a 200 liters storage tank capacity. Contours and vector plots depicting the thermosyphon effect occurring within the tube enclosures were also presented.