Effects Of Rib Arrangements Research Articles

Heat transfer enhancement of return channel by using rib turbulator for a new impingement cooling scheme

Impingement cooling method is widely applied to leading edge of turbine blade to ease thermal load. However, spent jet always develops into crossflow, which weakens cooling efficiency by deflecting the impingement direction of jet. An innovative impingement cooling structure can suppress the crossflow effect by drawing spent jet into return channel through return holes. This study further improves the heat transfer capability of the structure by introducing ribbed sidewall to the return channel. The effects of rib arrangements are investigated as the Reynolds number increases from 5000 to 15,000. The flow field and the heat transfer performance of the structure are analyzed numerically. The BSL turbulence model is utilized to conduct the simulation. The numerical results indicate that the ribs have a positive effect on improving heat transfer performance. The ribs disturbs the original flow in the return channel and increase the total pressure loss. The average Nusselt number on the sidewall of the return channel in the case with the optimal rib arrangement in this study is increased by 5.4% ∼ 10.4% compared to baseline value as the jet Reynolds number rises.

Numerical analysis on heat transfer, flow structure and exergy loss of combined truncated and circular ribs in a square duct

The heat transfer, friction and exergy loss of a square duct with combined circular and trun-cated rectangular ribs are analyzed using computational fluid dynamics. The study is focused on the effect of rib arrangements on the flow and heat transfer performance. The analysis is carried out with six truncated rib angles varying between 15° and 90° and Re range of 12000 – 43000. The heat transfer is maximum in the middle part of the duct for 30° and 45° rib angles along span wise direction. The position of wake region is highly dependent on separation point over the circular rib as wake moves away radially from the axis of the duct for rib angles of 60°, 75° and 90°. The turbulent flow structures in large scale originates from side wall have marked effect on the heat transfer for the rib angles of 60°, 75° and 90° and with nearly with equal intensity for 15°, 30° and 45° rib angles. The exergy loss associated with friction is higher for 60° rib angle. While the normalized friction factor obtained with Fanning’s equation varied between 1.8 and 4.2 and thermal hydraulic performance varied between 0.2 and 1.3 for the range of reexamined.

Effect of rib arrangements on the flow pattern and heat transfer in internally ribbed rectangular divergent channels

In this article, a numerical investigation is conducted to analyze three-dimensional incompressible Navier-strokes flows through the rectangular divergent square ribbed channels with different Reynolds number value 20,000, 40,000 and 60,000 having five different configurations of square ribs (p/e = 2.5, 3.33, 5, 10, and 20) has been used as roughness element. The commercial finite-volume based CFD code ANSYS FLUENT is used to simulate turbulent airflow through the channels. The RNG k-ε turbulence model is used to solve the transport equations for turbulent flow energy and dissipation rate. Detailed results about average heat transfer and fluid friction in a rectangular divergent square channel are presented and discussed.

Effects of rib arrangements on the performance of a parabolic trough receiver with ribbed absorber tube

Six different arrangements of ribbed tube are employed to improve the performance of parabolic trough receiver (PTR) in this paper. Detailed analyses of flow structure, thermal performance, flow resistance and overall thermo-hydraulic performance are conducted. The results indicate that the symmetrical anticlockwise arrangement of double inclined ribs (SADIR) and symmetrical clockwise arrangement of single inclined ribs (SCSIR) achieve the flow pattern with a pair of counter-rotating vortexes and obtain the best performance with reductions in peak temperature and heat loss reaching up to approximately 177 °C and 80.1%. Nusselt number of the SADIR and SCSIR are about 1.58–3.21 and 1.41–2.98 times that of the PTR with plain tube, respectively. The enhanced PTRs with ribbed tubes achieve great improvements in overall thermo-hydraulic performance at low Reynolds number (Re < 30,000) but suffer poor overall performance at high Reynolds number. For the range of parameters considered, the PEC value and modified thermal efficiency are ranged in 0.62–1.56 and 0.70–0.73, respectively. And the maximum enhancement in modified thermal efficiency is approximately 1.9%.

Effects of Rib Arrangements on Heat Transfer and Flow Behavior in a Rectangular Rib-Roughened Passage: Application to Cooling of Gas Turbine Blade Trailing Edge

Experimentation was conducted to examine the heat transfer and pressure drop characteristics in a rib-roughened rectangular passage with aspect ratio 2:1 for four rib configurations: 90 deg, 75 deg, 60 deg and 45 deg oblique ribs. The ribs were attached to two opposing long side walls instead of short side walls. In this study the oblique ribs were intended to function as secondary flow inducers as well as turbulators to improve the heat transfer of the bottom wall (one of the short side walls). The results revealed that, in order to enhance the heat transfer of the bottom wall, the oblique ribs should be arranged so that the secondary flow along the ribs hits the top wall instead of the bottom wall. Flow visualization test was performed to understand the heat transfer mechanisms. It was confirmed that the heat transfer enhancement at the bottom wall was attributed to the rib-induced secondary flow where the flow along the ribs hit the top wall, turned back and carried cold air from the passage core region towards the bottom wall. The highest average heat transfer was achieved for the 60 deg rib pattern due to the strong rotational momentum of the secondary flow and higher heat transfer enhancement on the rib-roughened walls in comparison to the other three rib patterns.

Effects of Rib Arrangements on Pressure Drop and Heat Transfer in a Rib-Roughened Channel With a Sharp 180 deg Turn

The objective of this study was to investigate, through experiments, the combined effects of a sharp 180 deg turn and rib patterns on the pressure drop performance and distributions of the local heat transfer coefficient in an entire two-pass rib-roughened channel with a 180 deg turn. The rib pitch-to-equivalent diameter ratio P/de was 1.0, the rib-height-to-equivalent diameter ratio e/de was 0.09, and the rib angle relative to the main flow direction was varied from 30 ∼ 90 deg with an interval of 15 deg. Experiments were conducted for Reynolds numbers in the range 4000 ∼ 30,000. It was disclosed that, due to the interactions between the bend-induced secondary flow and the rib-induced secondary flow, the combination of rib patterns in the channel before and after the turn causes considerable differences in the pressure drop and heat transfer performance of the entire channel.