Mathematical modeling of heat transfer processes in elliptical and circular absorbers of the vacuum tube collector

The paper presents numerical findings from a mathematical research of heat transfer processes in evacuated tube solar collectors featuring circular and elliptical absorber profiles. The primary aim is to conduct a comparative performance analysis of these two geometries and to evaluate the potential for heat transfer enhancement when replacing the conventional circular cross-section with an elliptical one.

The research employs a steady-state one-dimensional thermal model grounded in the energy balance equation. The model incorporates radiative exchange between the absorber and the glass envelope, heat conduction through the rarefied gas within the vacuum annulus, internal convection within the heat-transfer fluid channel and convective losses from the outer glass surface to the ambient air. The authors calculate temperature distributions at key system nodes and determine heat flux densities for all balance components — including the collector's useful thermal output. Moreover, the article demonstrates the comparison under identical boundary conditions for two distinct climatic scenarios: cold and warm seasons, representative of the temperate continental climate of the Omsk region.

The results reveal that the elliptical absorber reduces radiative losses up to 17.8 % and residual-gas conduction losses up to 16.7 %, while boosting the useful thermal power as much as 0.8 %. The thermohydraulic efficiency coefficient reaches to 4.8 %, confirming enhanced heat transfer performance with the modified geometry.

The research substantiates a design-based approach for improving the energy efficiency of evacuated tube solar collectors. Therefore, this approach can be recommended for integration into the development of next-generation solar thermal systems.

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