This work presents the results of an experimental investigation into the effects of variations in the channel aspect ratio and rib angle-of-attack, on the friction factor and local heat transfer in rectangular channels with two opposite ribbed rough walls. Rectangular tubes with three different aspect ratios were tested. Using a thin stainless steel foil, the local heat transfer coefficients were measured both on the ribbed side wall and on the smooth side wall, in the hydrodynamic and thermal entrance region and in the fully developed region. Similarity laws for the friction factor and heat transfer coefficient were used to correlate the experimental results for cases where the rib height-to-equivalent diameter ratio, e/D, was 0.047, 0.078, rib pitch-to-height ratio, p/e, was 10, 20, rib angle-of-attack, (alpha), was 90(DEGREES), 60(DEGREES), 45(DEGREES), 30(DEGREES), for value of the Reynolds number between 10,000 and 60,000 and channel aspect ratio, b/a, between 1 and 4.;The results were compared with previously existing theoretical and experimental results. The results obtained in this study provide an excellent reference for designing advanced turbine blade cooling passages and efficient heat exchangers.
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