Numerical investigation of thermal performance factor in dimpled-solar air heater (SAH)

ABSTRACT

A novel solar air heater design with dimples in a rectangular channel with a 7:1 aspect ratio was examined mathematically by ANSYS FLUENT 14.0. Four different cases of dimples configuration namely A (a spherical dimple), B (hemispherical symmetric protrusion is made in the center), C (secondary protrusion is present at an angle of 26.5^o) and D (secondary protrusion is made tangent to the upstream) were simulated over the Reynolds number range of 10,000 to 30,000. CFD simultaions were performed for the inlet mass flow rate corresponding to the Reynolds number value of 10,000 and constant wall temperature  of 320K. After turbulnec model selection and grid independence study, the numerical results are validated with the experimental data within the error band of ±15%. Secondary protrusion inside the dimple, an improvement in heat transfer and reduced flow recirculation was observed. The maximum thermal performance factor for the B, C, and D cases was found at Reynolds numbers of 10,000, 15,000, and between 20,000 and 30,000, respectively. Over the spectrum of Reynolds numbers, case D exhibits the most promising design overall with an increase of 37.5% in thermal performance factor. These design scenarios demonstrate an encouraging improvement in thermal performance factor.

KEYWORDS:

• Dimple
• thermal performance factor
• heat transfer enhancement
• Friction factor ratio
• solar air heater
• augmentation and protrusion

Acknowledgements

We are truly thankful to the Advanced Computational Research Engineering Lab (ACRE) at the Department of Nuclear Engineering, PIEAS, Nilore, Islamabad.

Disclosure statement

No potential conflict of interest was reported by the author(s).