Improved Efficacy of Evacuated-Tube Solar Collectors Using Engine Oil as a Heat Transfer Medium

Abstract:

The high demand for solar power systems has stimulated research efforts to find better heat transfer fluids for evacuated-tube solar collectors. The present analysis aims at evaluating the thermal characteristics of an evacuated-tube solar collector which utilises engine oil as a heat transfer vehicle within a new efficient system beyond conventional flat-plate collectors. An evaluation shows that this system reacts swiftly to solar radiation changes and reaches maximum temperatures of 198 °C which makes water evaporation and superheating possible. Temperature elevation under solar radiation becomes rapid because the evacuated tube contains 20W50 engine oil which possesses a high boiling point of >350 °C and heat transfer properties including 2.5 kJ/kg K heat capacity and 88 kg/m³ density. The through-flow copper pipe is submerged in a single evacuated tube after being bent in a U-shape. Between the inner surface of the tube and the outer surface of the copper pipe, oil serves as a medium for heat transfer. Experiments are conducted for different ranges of solar radiation intensity with consequence different ranges of engine oil temperatures. According to the results, the collector, in comparison to traditional flat-plate collectors, demonstrates a high conversion efficiency and quick response to the influencing parameters. The theoretical computations and experimental findings introduce that the engine oil temperature increases to 198 °C at a solar radiation of 800 w/m². Accordingly, the temperature is high enough to cause it to heat, evaporate, and become superheated when the water passes through the copper tube inside the vacuum oil tub.

• Periodical: Diffusion Foundations and Materials Applications (Volume 39)
• Pages: 119-127
• DOI: https://doi.org/10.4028/p-Wna2vT
• Online since: January 2026
• Authors: Estabraq Khudhair Abbas, Khalil Alwan Hussien, Mudhar A. Al-Obaidi, Farhan Lafta Rashid*, Hazim Abdulla Jasim, Jabbar Ahmed Abdullah
• Keywords: Engine Oil, Evacuated Tube Solar Collector (ETSC), Renewable Energy Systems, Solar Energy, Solar Thermal Energy

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