The Effect of Axial Flow on Heat Transfer in Decaying, Swirling Flow in a Pipe

2003 ◽  
Author(s):  
Heather L. McClusky ◽  
Donald E. Beasley
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Swirling Flow ◽  
Axial Flow ◽  
Number Range ◽  
Tangential Flow ◽  
Nusselt Numbers ◽  
Swirl Generator ◽  
Inlet Conditions

Local Nusselt numbers were experimentally measured in decaying, swirling flow in a pipe. Using a tangential injection mechanism, the two inlet conditions examined in this study were tangential flow and superimposed tangential and axial flow. Local Nusselt numbers at the pipe inlet were greater for tangential flow than for superimposed tangential and axial flow at the same Reynolds number. Local Nusselt numbers increased as the amount of fluid injected tangentially was increased for the superimposed case. For both inlet conditions employed with the present swirl generator, the local Nusselt number approached the fully-developed value in the far field. At the exit of the pipe, L/D = 62.8, local Nusselt numbers were greater than the fully-developed Nusselt number; therefore, heat transfer enhancement was still present at the exit of the pipe. The effect of axial flow on the local Nusselt numbers is explored in this investigation for air and over a Reynolds number range of 12,000 to 29,000.

Influence of Channel Geometry and Flow Variables on Cyclone Cooling of Turbine Blades

2015 ◽  
Author(s):  
Martin Bruschewski ◽  
Christian Scherhag ◽  
Heinz-Peter Schiffer ◽  
Sven Grundmann
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Swirling Flow ◽  
Turbine Blades ◽  
Transfer Characteristic ◽  
Internal Cooling ◽  
Number Range ◽  
Flow Type ◽  
Magnetic Resonance Velocimetry ◽  
Swirl Generator

The presented study deals with the internal cooling of turbine blades by swirling flow. The sensitivity of this flow type is investigated towards Reynolds number, swirl intensity and the common geometric features of cooling ducts. The flow system consists of a straight and round channel that is attached to a tangential-type swirl generator. The channel outlet features various orifices and 180-degree-bends. The investigated Reynolds number range is Re = 2000…32000 and the geometric swirl numbers are S* = 1,3,5. The experiments were carried out with Magnetic Resonance Velocimetry for which water was used as flow medium. As the main outcome, it was found that the investigated flows are highly sensitive to the conditions at the outlet of the channel. But it was also discovered that for some channel outlets the flow field remains the same. The associated flow type features a favorable topology for heat transfer: The majority of mass is transported in the annular region close to the channel walls. Together with its high robustness, it is regarded as an applicable type for the internal cooling of turbine blades. A Large Eddy Simulation was conducted to analyze the heat transfer characteristic of this flow. For S*=3 and Re=20000, the simulation showed an averaged Nusselt number increase of factor 4.7 compared to fully-developed flow. However, a pressure loss increase of factor 43 must be considered as well. The presented measurements and simulations have led to a further understanding of swirling flows and proved these flows advantageous for the internal cooling of turbine blades.

Experimental Investigation of Heat Transfer in Low Frequency Pulsating Turbulent Flow in Circular Pipe

2010 ◽  
Author(s):  
Chang Wang ◽  
Puzhen Gao ◽  
Chao Xu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Turbulent Flow ◽  
Low Frequency ◽  
Relative Amplitude ◽  
Pulsation Frequency ◽  
Number Range ◽  
Nusselt Numbers ◽  
Reynolds Number Range

Heat transfer characteristic of low frequency pulsating turbulent water flow in a vertical circular pipe which is heated at uniform heat flux, are experimentally studied under different conditions of Reynolds number, pulsation frequency and relative amplitude. The experiments are performed with the Reynolds number range of 3000 to 20000, pulsation frequency range of 0.033 to 0.1 Hz, and the relative amplitude range of 0.1 to 0.8. This pulsating flow situation is used to simulate the phenomenon happened in the ship power system which is induced by ocean conditions. The effects of pulsation on heat transfer characteristics are presented in terms of relative local and mean Nusselt numbers defined as the ratio of the local and mean Nusselt numbers for pulsation flow to that of the ordinary steady turbulent flow with the same time-averaged Reynolds number Reta. The results show that the relative local Nusselt number is strongly affected by Reynolds number, pulsation frequency and relative amplitude. The phenomena that the Nusselt number would increase or decrease with the increase of the Reynolds number are both observed and the variation is more notable in the entrance region than that in the fully developed region. The relative mean Nusselt number decreases initially as the Reta increases, and then recovers gradually, but finally it has the tendency to decrease again. With the increase of pulsation relative amplitude, the relative mean Nusselt number increases at first and then decreases. And for the Reynolds number range of 3176 to 6670, heat transfer enhancement is observed as the pulsation frequency raises, but complete contrary phenomena appears at Reynolds number range of 11904 to 15844. The obtained heat transfer results are analyzed and seem to be qualitatively in accordance with previous investigations.

Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel

2017 ◽  
Author(s):  
Jin Xu ◽  
Jiaxu Yao ◽  
Pengfei Su ◽  
Jiang Lei ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Bottom Surface ◽  
Number Range ◽  
Pin Fin ◽  
Nominal Diameter ◽  
Pin Fins

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.

Spatially Resolved Heat Transfer and Friction Factors in a Rectangular Channel With 45-Deg Angled Crossed-Rib Turbulators

2003 ◽  
Vol 125 (3) ◽  
pp. 575-584 ◽  
Author(s):  
P. M. Ligrani ◽  
G. I. Mahmood
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Test Surface ◽  
Spatially Resolved ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators

Spatially resolved Nusselt numbers, spatially averaged Nusselt numbers, and friction factors are presented for a stationary channel with an aspect ratio of 4 and angled rib turbulators inclined at 45 deg with perpendicular orientations on two opposite surfaces. Results are given at different Reynolds numbers based on channel height from 10,000 to 83,700. The ratio of rib height to hydraulic diameter is .078, the rib pitch-to-height ratio is 10, and the blockage provided by the ribs is 25% of the channel cross-sectional area. Nusselt numbers are given both with and without three-dimensional conduction considered within the acrylic test surface. In both cases, spatially resolved local Nusselt numbers are highest on tops of the rib turbulators, with lower magnitudes on flat surfaces between the ribs, where regions of flow separation and shear layer reattachment have pronounced influences on local surface heat transfer behavior. The augmented local and spatially averaged Nusselt number ratios (rib turbulator Nusselt numbers normalized by values measured in a smooth channel) vary locally on the rib tops as Reynolds number increases. Nusselt number ratios decrease on the flat regions away from the ribs, especially at locations just downstream of the ribs, as Reynolds number increases. When adjusted to account for conduction along and within the test surface, Nusselt number ratios show different quantitative variations (with location along the test surface), compared to variations when no conduction is included. Changes include: (i) decreased local Nusselt number ratios along the central part of each rib top surface as heat transfer from the sides of each rib becomes larger, and (ii) Nusselt number ratio decreases near corners, where each rib joins the flat part of the test surface, especially on the downstream side of each rib. With no conduction along and within the test surface (and variable heat flux assumed into the air stream), globally-averaged Nusselt number ratios vary from 2.92 to 1.64 as Reynolds number increases from 10,000 to 83,700. Corresponding thermal performance parameters also decrease as Reynolds number increases over this range, with values in approximate agreement with data measured by other investigators in a square channel also with 45 deg oriented ribs.

Study of Flow and Convective Heat Transfer in a Simulated Scaled Up Low Emission Annular Combustor

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Sunil Patil ◽  
Teddy Sedalor ◽  
Danesh Tafti ◽  
Srinath Ekkad ◽  
Yong Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat ◽  
Swirling Flow ◽  
Numerical Study ◽  
Swirl Number ◽  
Maximum Heat ◽  
Number Range ◽  
Maximum Heat Transfer ◽  
Annular Combustor

Modern dry low emissions (DLE) combustors are characterized by highly swirling and expanding flows that makes the convective heat load on the gas side difficult to predict and estimate. A coupled experimental–numerical study of swirling flow inside a DLE annular combustor model is used to determine the distribution of heat transfer on the liner walls. Three different Reynolds numbers are investigated in the range of 210,000–840,000 with a characteristic swirl number of 0.98. The maximum heat transfer coefficient enhancement ratio decreased from 6 to 3.6 as the flow Reynolds number increased from 210,000 to 840,000. This is attributed to a reduction in the normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.98 for the Reynolds number range investigated. The location of peak heat transfer did not change with the increase in Reynolds number since the flow structures in the combustors did not change with Reynolds number. Results also showed that the heat transfer distributions in the annulus have slightly different characteristics for the concave and convex walls. A modified swirl number accounting for the step expansion ratio is defined to facilitate comparison between the heat transfer characteristics in the annular combustor with previous work in a can combustor. A higher modified swirl number in the annular combustor resulted in higher heat transfer augmentation and a slower decay with Reynolds number.

Study of a Cooling Feed Pipe With a Covering Plate on a Ribbed Turbine Case

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Fangyuan Liu ◽  
Junkui Mao ◽  
Chao Han ◽  
Yuanjian Liu ◽  
Xingsi Han ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Experimental Tests ◽  
Impinging Jet ◽  
Nusselt Numbers ◽  
Spacing Ratio ◽  
Wall Flow ◽  
Complicated Geometry ◽  
Clearance Control

Considering the complicated geometry in an active clearance control (ACC) system, the design of an improved cooling feed pipe with a covering plate for a high pressure ribbed turbine case was investigated. Numerical calculations were analyzed to obtain the interactions between the impinging jet arrays fed by the pipe. Experimental tests were performed to explore the effect of the Reynolds number (2000–20,000) and the jet-to-surface spacing ratio (6–10) on the streamwise-averaged Nusselt numbers. Additionally, the effect of the crossflow produced by the configuration was investigated. Results showed a confined curved channel was formed by the pipe and ribbed case, which resulted in crossflow. The crossflow evolved into vortices and the streamwise-averaged Nusselt number on the high ribs was subsequently increased. Furthermore, the distribution of the heat transfer on the entire surface became more uniform compared with that of traditional impinging jet arrays. A higher Nusselt number was achieved by decreasing the jet-to-surface spacing and increasing the Reynolds number. This investigation has revealed a cooling configuration for controlling the wall flow and evening the heat transfer on the case surface, especially for the ribs.

Heat Transfer Enhancement in Axial Taylor-Couette Flow

2005 ◽  
Author(s):  
S. Gilchrist ◽  
C. Y. Ching ◽  
D. Ewing
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Couette Flow ◽  
Reynolds Numbers ◽  
Taylor Number ◽  
Number Range ◽  
Taylor Couette ◽  
Number Case ◽  
Taylor Couette Flow

An experimental investigation was performed to determine the effect that surface roughness has on the heat transfer in an axial Taylor-Couette flow. The experiments were performed using an inner rotating cylinder in a stationary water jacket for Taylor numbers of 106 to 5×107 and axial Reynolds numbers of 900 to 2100. Experiments were performed for a smooth inner cylinder, a cylinder with two-dimensional rib roughness and a cylinder with three-dimensional cubic protrusions. The heat transfer results for the smooth cylinder were in good agreement with existing experimental data. The change in the Nusselt number was relatively independent of the axial Reynolds number for the cylinder with rib roughness. This result was similar to the smooth wall case but the heat transfer was enhanced by 5% to 40% over the Taylor number range. The Nusselt number for the cylinder with cubic protrusions exhibited an axial Reynolds number dependence. For a low axial Reynolds number of 980, the Nusselt number increased with the Taylor number in a similar way to the other test cylinders. At higher axial Reynolds numbers, the heat transfer was initially independent of the Taylor number before increasing with Taylor number similar to the lower Reynolds number case. In this higher axial Reynolds number case the heat transfer was enhanced by up to 100% at the lowest Taylor number of 1×106 and by approximately 35% at the highest Taylor number of 5×107.

Passive Control and Enhancement of Low Reynolds Number Slot Jets Through the Use of Tabs and Chevrons

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Andrew Sexton ◽  
Jeff Punch ◽  
Jason Stafford ◽  
Nicholas Jeffers
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Integrated Circuits ◽  
Passive Control ◽  
Low Reynolds Number ◽  
Hydraulic Diameter ◽  
Stagnation Region ◽  
Number Range ◽  
Low Reynolds

Liquid microjets are emerging as candidate primary or secondary heat exchangers for the thermal management of next generation photonic integrated circuits (PICs). However, the thermal and hydrodynamic behavior of confined, low Reynolds number liquid slot jets is not yet comprehensively understood. This investigation experimentally examined jet outlet modifications—in the form of tabs and chevrons—as techniques for passive control and enhancement of single-phase convective heat transfer. The investigation was carried out for slot jets in the laminar flow regime, with a Reynolds number range, based on the slot jet hydraulic diameter, of 100–500. A slot jet with an aspect ratio of 4 and a fixed confinement height to hydraulic diameter ratio (H/Dh) of 1 was considered. The local surface heat transfer and velocity field characteristics were measured using infrared (IR) thermography and particle image velocimetry (PIV) techniques. It was found that increases in area-averaged Nusselt number of up to 29% compared to the baseline case could be achieved without incurring additional hydrodynamic losses. It was also determined that the location and magnitude of Nusselt number and velocity peaks within the slot jet stagnation region could be passively controlled and enhanced through the application of outlet tabs of varying geometries and locations.

Experimental and Numerical Studies of Shell-and-Tube Heat Exchangers With Helical Baffles

2009 ◽  
Author(s):  
Guidong Chen ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Thermal Design ◽  
Number Range ◽  
Tube Heat Exchanger ◽  
Nusselt Numbers ◽  
Shell And Tube ◽  
Cfd Method

In the present paper, flow and heat transfer characteristics of shell-and-tube heat exchanger with continuous helical baffles (CH-STHX) is experimentally studied. Correlations for heat transfer and pressure drop, which are estimated by Nusselt number and friction factor, are fitted by experiment data for thermal design. Computational Fluid Dynamic (CFD) method is also used to compare the heat transfer and flow performance of STHX with continuous helical baffles (CH-STHX), STHX with combined helical baffles (CMH-STHX) and STHX with discontinuous helical baffles (DCH-STHX). The numerical results show that, for the same Reynolds number, the Nusselt numbers Nuo of the CMH-STHX and CH-STHX is about 37.6%, 78.2% higher than that of the DCH-STHX; the friction factor fo of the CH-STHX is about 14.8% and 150.2% higher than that of CMH-STHX and DCH-STHX. If the velocity ratios RCMH, CH and RDCH, CH are bigger than 1.55 and 4.0 in the Nusselt number range from 40 to 70, the CMH-STHX and the DCH-STHX may have higher Nusselt numbers than the CH-STHX for the same mass flow rate in the shell side.

Effect of Laminarization and Retransition on Heat Transfer for Low Reynolds Number Flow Through a Converging to Constant Area Duct

1982 ◽  
Vol 104 (2) ◽  
pp. 363-371 ◽  
Author(s):  
H. Tanaka ◽  
H. Kawamura ◽  
A. Tateno ◽  
S. Hatamiya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Parallel Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Parallel Plates ◽  
Number Range ◽  
Reynolds Number Flow ◽  
Turbulent Air Flow

A fully developed turbulent air flow between two parallel plates with the spacing of 15 mm was accelerated through a linearly converging passage of 200 mm in length, from which it flowed into a parallel-plate channel again. A foil heater was fastened on one wall surface over the entire channel, and local heat-transfer coefficient distribution was measured over the channel Reynolds number range of 5000 to 14,000 and also the slope of the accelerating section between 2/200 mm/mm and 10/200 mm/mm. (The acceleration parameter K ranged between 1.4 × 10−6 and 2 × 10−5.) The Nusselt number at the outlet of the accelerating section was considerably lower than in the initial fully turbulent state, suggesting laminarization of the flow. The measured Nusselt number continued to decrease in the first part of the downstream parallel-plate section to a minimum and then began to increase sharply, suggesting reversion to turbulent flow. Heat transfer along the parallel-converging-parallel plate system was reproduced fairly satisfactorily by applying a k-kL model of turbulence.

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