ESTIMATION OF HEAT LOSSES FOR THE TUBE HEAT RECEIVER OF THE SOLAR TROUGH MODULES
The one-dimensional mathematical model for the quantitative estimation of the heat losses from tube receiver system of the solar trough module was created. Based on this mathematical model the numerical algorithm was developed and numerical experiments were carried out. The studies were conducted for tube heat receiver which placed inside glass envelope as «tube-in-tube». Cases with atmosphere air in annular space and with various vacuum degree were described. Analysis for a unit tube without the glass envelope was carried out separately. A system of nonlinear algebraic equations, which consist basis of the mathematical model, was solved using fixed-point iteration method. Convergence of iterates was provided through initial guess, which were chosen as close to the real values. The thermophysical parameters depend on the temperature and pressure. It was considered in the created mathematical model. The calculation method for the heat flow through a gas layer was offered. The vacuum gas degree was taken into account in the method. As physical model for numerical analysis was chosen solar though module which studied experimentally. Data of the experiments were described in scientific literature. Numerical analyses were carried out for two cases – with heat flow from concentrator and without it. Comparison of numerical and experimental data show good agreement of results. Slight discrepancies were observed for glass temperature and for heat losses in the presence of wind. Analyses show that glass envelope is mandatory design element for heat receiver system of the solar though energy modules. If atmosphere air is used inside glass envelope than heat losses decreased twice, if deeper vacuum – in tree times. Ref. 13, fig. 3.
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