Numerical investigation of turbulent heat transfer in channels with detached rib‐arrays

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.

Experimental study for the enhancement of heat transfer characteristics and development of thermal correlations of a roughened solar collector

“…Introducing an artificial rib component as a roughness element over the absorber plate surface makes it possible to disturb this laminar sublayer and enhance the thermal performance. 8 Artificial roughness (AR) arranged in periodic repeated ribs is often used to improve the turbulence intensity of flowing fluids in forced convection systems. 9 Adding a roughness element to a heat transfer surface, however, creates high frictional losses, which increases the power consumption of the flow.…”

“…In a smooth surface of the absorber plate of formation of the laminar sublayer takes place which acts as a thermal barrier against the convective heat transfer process. Introducing an artificial rib component as a roughness element over the absorber plate surface makes it possible to disturb this laminar sublayer and enhance the thermal performance 8 . Artificial roughness (AR) arranged in periodic repeated ribs is often used to improve the turbulence intensity of flowing fluids in forced convection systems 9 .…”

Numerical evaluation of the thermal performance of a solar air heater equipped with two different types of baffles

“…A larger average porosity corresponds to a lower inertial constant. Changcharoen and Eiamsa‐ard 58 conducted a numerical investigation 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 was applied. The effect of detached‐rib geometry on heat‐transfer coefficient, friction factor, and TEF was investigated covering the range of the detached‐clearance ratios (c/a) of 0.1, 0.2, 0.3, and 0.4, the Re based on the channel hydraulic diameter ranges from 8000 to 24 000.…”

Thermal visualization on surface with transverse perforated ribs

“…The mechanism of heat transfer enhancement is based on flow separation and reattachment. In general, flow reattachment introduces strong shear flow on the surface behind each rib, resulting in an effective disruption of the thermal boundary layer and thus the improvement of heat transfer [1][2][3][4][5][6][7][8][9][10]. However, in the case of a solid rib, a large hot spot is usually generated just downstream from the rib, leading to heat transfer deterioration around that position [11][12][13] as a result of flow separation in form of flow recirculation.…”