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Abstract
This work presents an experimental study of the thermal-hydraulic characteristics in a flat-plate solar collector with two different geometries of helical coil inserts. Isothermal pressure drop tests are conducted in a horizontal tube using water as working fluid to obtain the fully developed Fanning friction factor for a range of Reynolds number Re = 80–8,000. Heat transfer tests are performed in the solar collector loop using a mixture of propylene-glycol and water at 30 wt%, covering the ranges Pr = 16–28 and Re = 140–600. A significant decrease in the temperature of the absorber is observed when the appropriate wire coil is selected for the given flow conditions, proving the beneficial effect of this type of insert device for the augmentation of the thermal efficiency in flat-plate solar collectors.
Acknowledgments
The authors are indebted to Mr. F. Hidalgo (Universidad Politécnica de Cartagena) for his technical assistance during the calibration of the heat transfer rig.