No abstract

Heat transfer and fluid flow characteristics through a channel with two - dimensional transverse ribs are numerically investigated. The effects of different shaped ribs (rectangular rib, triangular rib, cylindrical rib, concave-concave rib, convex-concave rib, long convex-short concave rib and long concave-short concave rib) are examined. The investigation is performed for the ribs mounted on top and bottom walls with rib pitch to height ratio (P/e) of 6.67, in Reynolds number between 3000 and 7000, under constant wall temperature condition. For the present case, the data predicted by SST k-omega turbulence model show better agreement with the experimental data, than those predicted by RNG k-epsilon turbulence model. The mean heat transfer, flow friction, temperature fields and the local heat transfer coefficients as well as the flow structure behaviors are reported. For the ribs considered, the channel with triangular-ribs yields the highest Nusselt number, the one with concave-concave rib provides the highest friction and the one with cylindrical rib show the best thermal enhancement. At the similar condition, the triangular rib gives higher Nusselt number than that provided by the cylindrical one by around 29.3 percent, while the cylindrical rib offers the highest thermal enhancement factor of 1.4 which is higher than that of the cylindrical one by around 1.33 percent while the cylindrical rib offers the highest thermal enhancement factor of 1.33 which is higher than that of the triangular one by around 9.6 percent. In addition, in spite of their high heat transfer, the concave-concave rib and long concave-concave rib yield low thermal performance factors, due to the prominent effect of high friction factor.

No abstract

No abstract

A numerical investigation is conducted to analyze the flow-field and heat transfer characteristics in a rectangular passage of width-to-height ratio of 6:1 with detached ribs on one wall, where constant wall temperature condition is applied. The effect of detached-rib geometry on heat transfer coefficient, friction factor, and thermal enhancement factor is investigated covering the range of the detached-clearance ratios (c/a) of 0.1, 0.2, 0.3, and 0.4, the Reynolds number based on the channel hydraulic diameter ranges from 8000 to 24,000. The numerical results show that the flow-field, temperature pattern, local Nusselt number distribution, average Nusselt number, and friction factor are strongly dependent on the detached-clearance ratios. The thermal enhancement factor (TEF) under the same pumping power constraint is calculated in order to examine the overall effect of the detached-clearance ratio. For the present range investigated, the maximum TEF of 1.22 is achieved by the use of the ribs with c/a of 0.1 at Reynolds number of 8000.