Research PaperThermal performance of compound heat transfer enhancement method using angled ribs and auxiliary fins

- Compound ribs and in-line auxiliary fins are newly devised to boost HTE effect.
- Detailed Nu of parallelogram ribbed channels with auxiliary fins are measured.
- f and TPF performances are comparatively examined.
- Nu and f correlations for ribbed channels with/without fin are devised.

Detailed Nusselt number (Nu) distributions over two opposite endwalls of two parallelogram channels roughened by 45° ribs without/with in-line auxiliary fins are measured using steady-state infrared thermography method at 5000 ⩽ Re ⩽ 15,000. Pressure drop measurements are individually performed at isothermal conditions to detect the Fanning friction factors (f) for thermal performance factors (TPF) evaluations. Relative heat transfer and f augmentations for this type of passive compound heat transfer enhancement (HTE) method are assessed by comparing with the Nusselt numbers (Nu∞) and f factors (f∞) of smooth plain tube references at the same Reynolds number (Re). With present in-lined auxiliary fins on two opposite ribbed endwalls, the channel averaged HTE ratios fall between 4.43 and 4.21 with the corresponding f/f∞ ratios in the range of 6.5-3.35; giving rise to the TPF values between 2.37 and 2.81. As the comparative HTE ratios, f/f∞ values and TPF values for the similar ribbed channels without auxiliary fins are in the respective ranges of 3.93-3.61, 1.63-1.53 and 2.41-2.35, the present compound HTE method further elevates the Nu/Nu∞ ratios with the associated f amplifications but can still improves the TPF values in general. It is concluded that the present compound HTE method using angled ribs and auxiliary fins is applicable for improving thermal performances of turbulent channel flow.