Evaluation of local heat transfer and friction factors in a U-type compound parabolic collector operating as a thermosyphon

U-type external compound parabolic concentrators (XCPCs) are non-imaging solar collectors for low- to medium-temperature applications (60°C to 300°C). The XCPC collector comprises an aluminium compound parabolic reflector and an evacuated tube receiver with a direct flow U-shaped absorber tube. Although extensive research in the literature has focused on reflector designs and optical components, the heat transfer characteristics and flow patterns within the absorber tube have not been thoroughly investigated. The flow dynamics inside the absorber tube are unique due to various boundary conditions. These include a non-uniform heat flux around the tube, regions of secondary and developing flow, and recirculation flows at the inlet, outlet, and through multiple bends. Therefore, this study aimed to determine the heat transfer coefficients and friction factors in an XCPC absorber tube operating as a thermosyphon. The local Nusselt numbers and local friction factors were obtained numerically. It was found that the heat transfer coefficient and friction factors vary significantly downstream of the tube inlet and alter near the U-bend of the absorber tube. Mixed convection was the primary force along the straight sections of the absorber tube, rather than forced convection as initially assumed in the literature. The study emphasises how the magnitude of heat flux and the geometry of the absorber tube influence the internal hydrodynamic and thermal performance in an XCPC collector.

Grantor dc:publisher

Stellenbosch : Stellenbosch University

Year dc:date.issued

2026

Author dc:creator

• Simon, Sarath Titus

Advisors dc:contributor.advisor

• Meyer, J. P.
• Owen, M. T. F.

Language dc:language.iso

en

Repository record dc:identifier.uri

https://scholar.sun.ac.za/handle/10019.1/135846

OAI identifier oai:identifier

oai:scholar.sun.ac.za:10019.1/135846