Experimental and Numerical Investigation of Various Tube Geometries for Improved Heat Transfer in Solar Central Receivers

Central receiver of Concentrated Solar Power technology constitutes 15% of the total initial cost and plays an important role in achieving high operating temperatures. Central receiver systems are composed of tubes with heat transfer fluid flowing inside that transports heat from radiation on the outer wall of tubes. This work investigates radiation heat transfer to fluid in tubes of various geometries. Experimental and numerical analysis were conducted to observe the boundary layer temperatures, bulk fluid temperatures, and fluid mixing near the tube walls. Four different samples of corrugated tubes adopted from literature were compared to a circular tube and a generic tube designed to provide larger surface area exposed to radiation without corrugation. The circular tube had high temperature in the boundary layer but low bulk fluid temperature due to lack of fluid mixing at wall. A spirally corrugated tube was found to have the highest bulk fluid temperature due to turbulent mixing and low temperature at boundary layer. The generic tube had higher bulk temperature compared to circular tube and two other corrugated tubes.