Detailed heat transfer and friction factor measurements for square channel enhanced by plate insert with inclined baffles and perforated slots

An applied novel research about the development of heat transfer enhancement element using the plate insert with periodical oblique baffles and perforated slots was conducted for improving the hydrothermal performance of a heat exchanger. The infrared thermography method was adopted to detect the endwall Nusselt number distributions of a square channel enhanced by the newly devised baffle inserts with Fanning friction coefficients and thermal performance factors measured. The present baffle inserts tripped the core fluid toward channel walls and induced near-wall separated and accelerated flows to boost heat convection. The channel averaged Nusselt numbers and Fanning friction coefficients were elevated to 9–5 times of the Dittus-Boelter references and 5–85 times of the Blasius correlation levels at Reynolds numbers between 10,000 and 50,000 with the thermal performance factors in the ranges of 1.6–3.2 and 2–3.4 for forward and backward flows, which went beyond many previous types of baffle inserts. Empirical correlations permitting evaluations of average Nusselt numbers and Fanning friction coefficients with forward and backward flows were devised. Based on the thermal performance measurements, the oblique slots were preferably to be located at downstream locations of the adjacent oblique ribs for acquiring the higher hydrothermal efficiencies.