Heat transfer augmentation in a rectangular duct characterized by an impinging jet inlet : design of experiment

Energy is one of the most important engineering challenges of this time. Gas turbine engines a,re responsible for nearly twenty-percent of all electricity produced in the United States today. A small increase in the operating efficiency of these engines could lead to massive reduction in the emission of greenhouse gases into the atmosphere as well as the financial burden on the average homeowner paying the monthly energy bill. In order to improve the efficiency of the engine, the Turbine Inlet Temperature of the hot gas coming from the combustor is continually increased. This requires increasingly advanced active cooling methods to maintain component life in the hot stages of the turbo machine. In this study, a complete experiment is developed for accurate testing of the complex heat transfer and aerodynamic characteristics present in the active cooling design applied to the transition duct of a land-based gas turbine. The transition duct is the component that channels the hot gases from the combustor to the first stage of the turbihe. It is in contact with the hottest mainstream gas flow in the entire machine. The unique cooling design applied to this component is a combination the three main cooling methods. It is characterized by an impinging jet inlet, which splits into two identical channels flowing in exactly opposite directions. The flow travels through these channels, cooling the hot surfaces of the duct through which they are formed. At the flow exit, it is expelled into the hot gas stream flowing from the can-annular combustor to the turbine stage. The channel exit provides a thin film of cool air coverage that protects the metal surface from the harsh temperatures of the hot gas

A Study Of Side Wall Heat Transfer Augmentation In A Narrow Rectangular Duct

This paper is an investigation of the heat transfer augmentation in the fully-developed portion of a narrow rectangular duct (R=2) characterized by dimpled geometries on the bottom wall. Testing is performed at Reynolds numbers of 20000, 30000, and 40000. Thermal efficiency of the channel is the ultimate goal for any cooling channel design. The purpose of the paper is to find the performance of commonly used geometries on the side walls of the channels. Data reported includes the Nusselt Number Augmentation of the side walls of the channel and the thermal performance of the entire duct. A better understanding of the effects produced by these geometries will help in the design and development of more effective cooling-channel design

Heat Transfer In A Rectangular Channel With Dimples Applied To One Wall

This study is an investigation of the heat transfer augmentation through the fully developed portion of a narrow rectangular duct (aspect ratio = 2) characterized by the application of dimples to the bottom wall of the channel. The geometries are studied at channel Reynolds numbers of 20,000,30,000, and 40,000. The purpose is to understand the contribution of dimple geometries in the formation of flow structures that improve the advection of heat away from the channel walls. Experimental data reported include local heat transfer coefficient distributions, channel-averaged Nusselt number augmentation, and overall friction augmentation throughout the length of the duct. The largedimple feature was found to promote significant intensification of convective heat transfer (as high as 80%) at a Reynolds number of 30,000. Furthermore, the double-dimple surface feature was found to promote heat transfer augmentation comparable with the large-dimple feature, accompanied by the pressure loss penalty of the modest small dimple. By contributing to a clearer understanding of the effects produced by these geometries, the development of more effective channel-cooling designs can be achieved. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved

Heat Transfer And Friction Augmentation In High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from fifteen to thirty for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values; 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3,000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically-developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to \u27pull\u27 the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental result shows a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e=37.3) and a high momentum flux ratio: Nu/Nu o = 3.15. This design also yielded the friction with f/f0 = 2.6. © 2010 by ASME

Heat Transfer And Friction Augmentation In High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from 15 to 30 for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values, 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to pull the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental results show a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e = 37.3) and a high momentum flux ratio: Nu/Nuo = 3.15. This design also yielded the friction with f/f0 = 2.6. © 2012 American Society of Mechanical Engineers

Piv Study On The Dimple Mid-Plane Of A Narrow Rectangular Channel With Dimples Applied To One Wall

This paper presents an investigation of the fluid flow in the fully developed portion of a rectangular channel (Aspect Ratio of 2) with dimples applied to one wall at channel Reynolds numbers of 20,000, 30,000, and 40,000. The dimples are applied in a staggered-row, racetrack configuration. Results for three different dimple geometries are presented: a large dimple, small dimple, and double dimple. Heat transfer and aerodynamic results from preceding works are presented in Nusselt number and friction factor augmentation plots as determined experimentally. Using particle image velocimetry, the region near the dimple feature is studied in detail in the location of the entrainment and ejection of vortical packets into and out of the dimple; the downstream wake region behind each dimple is also studied to examine the effects of the local flow phenomenon that result in improved heat transfer in the areas of the channel wall not occupied by a feature. The focus of the paper is to examine the secondary flows in these dimpled channels in order to support the previously presented heat transfer trends. The flow visualization is also intended to improve the understanding of the flow disturbances in a dimpled channel; a better understanding of these effects would lead the development of more effective channel cooling designs. Copyright © 2011 by ASME