Numerical Simulation of Evacuated Tube Solar Water Heaters
This paper evaluates the characteristics of water-in-glass evacuated tube solar water heaters including assessment of the circulation rate through single ended tubes. A numerical model of the fluid flow inside a single ended evacuated tube has been developed assuming no interaction between adjacent tubes in the collector array. The numerical model is firstly validated by means of literature data. Then, the performance in terms of circulation mass flow rate in different heat flux condition and at different inclination angle of the collector are evaluated. Moreover, a sensitivity analysis on the effect of the assumptions of different reference parameters and of the choice of the values of the fluid thermophysical properties is carried out and a quantitative analysis of the expected uncertainty is presented. Finally, an extension of previous literature correlations in terms of non-dimensional Reynolds and Rayleigh numbers is proposed. Regarding heating boundary conditions, the circumferential heat distribution was found to be an important parameter influencing the flow structure and circulation rate through the tube.