Experimental Studies and Correlations of Convective Heat Transfer in a Radially Rotating Serpentine Passage

1997 ◽  
Vol 119 (3) ◽  
pp. 460-466 ◽  
Author(s):  
G. J. Hwang ◽  
C. R. Kuo
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flow Direction ◽  
Experimental Studies ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Secondary Flows ◽  
Square Channel ◽  
Effects Of Rotation

The present paper investigates experimentally the effects of rotation on the convective heat transfer of air flow in a radially rotating three-passage serpentine square channel. Due to rotation, the cross-stream and radial secondary flows are induced by the Coriolis force and the centrifugal-buoyancy force, respectively. The channel walls were made of low thermal conductivity material for suppressing wall heat conduction. The wall surfaces were heated individually by four separate stainless-steel film heaters to distinguish the local heat transfer rates. The hydraulic diameter and the mean rotational radius of the flow passages were 4 and 180 mm, respectively. The governing parameters are the through-flow Reynolds number Re, the rotation number Ro, the buoyancy parameter Gr* and the main flow direction. The results show that the local heat transfer rate was enhanced by rotation on the trailing side for outward flow and on the leading side for inward flow. In the first and third passages, the effect of rotation on heat transfer is relatively prominent. The buoyancy effect is favorable to the heat transfer enhancement on four sides of these passages. The data of NuΩ/Nu0 are correlated on the leading and trailing sides of these passages.

Convective Heat Transfer in a Triple-Cavity Structure Near Turbine Blade Trailing Edge

2002 ◽  
Author(s):  
Minking K. Chyu ◽  
Unal Uysal ◽  
Pei-Wen Lee
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Turbine Blade ◽  
Convective Heat ◽  
Internal Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Trailing Edge ◽  
Cavity Structure ◽  
Exit Slot

The present study explores the internal heat transfer in a triple-cavity cooling structure with a ribbed lip for a turbine blade trailing edge. The design consists of two impingement cavities, two sets of crossover holes, a third cavity and an exit slot with eleven ribs attached to it. Local heat transfer in each subregion is determined. Results indicate that the highest heat transfer occurs in the second impingement cavity. The exit slot area between the ribs is identified as a region of low heat transfer in the overall design. A comparison with enhancement induced by arrays of pin fins and fins of other geometries reveals that the triple-cavity design represents a lesser quality cooling scheme in the range of Reynolds numbers tested. Further improvement of the convective heat transfer at the exit slot with either film cooling, or different rib geometries appears to be essential to make the triple-cavity strategy superior to those of the traditional approaches for cooling of blade trailing edge.

Forced Convective Heat Transfer in Cross-Corrugated Solar Air Heaters

1994 ◽  
Vol 116 (4) ◽  
pp. 212-214 ◽  
Author(s):  
Y. Piao ◽  
E. G. Hauptmann ◽  
M. Iqbal
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Fluid Velocity ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Solar Air Heater ◽  
Forced Convective Heat Transfer ◽  
Radiant Heater

Forced convective heat transfer in a cross-corrugated channel solar air heater has been studied experimentally using air as a working fluid. The channel was formed by two transversely positioned corrugated sheets and two flat thermally insulated side walls. One corrugated sheet was heated by a radiant heater, while the other was thermally insulated. The fluid velocity and temperature, and the wall temperature and the local heat flux across the heated corrugated sheet were measured for a variety of operating flow rates. Experimental results for the channel geometry have yielded the correlation Nu=0.0743(Re)0.76. This heat-transfer coefficient is about 2.8 times that of a smooth flat channel. The experiments showed that local heat transfer rate was smaller on the valley of the corrugation than that on the peak. The ratio of the local heat transfer rates on the two locations was related to the Reynolds number.

Convective Heat Transfer of Alumina Nanofluids in a Microchannel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

This work reports an experimental study of convective heat transfer of aqueous alumina nanofluids in a horizontal microchannel under laminar flow condition. The variation of local heat transfer coefficients, in both entrance and developed flow regime, is obtained as a function of axial distance. The heat transfer coefficient of nanofluids is found to be dependent upon not only nanoparticle concentration but also mass flow rate. Different to the behavior in conventional-sized channels, the major heat transfer coefficient enhancement is observed in fully developed region in microchannels. Discussions of the results suggest that the heterogeneous nature of nanoparticle flow should be considered.

Convective Heat Transfer Enhancement Due to Intermittency in an Impinging Jet

1993 ◽  
Vol 115 (1) ◽  
pp. 91-98 ◽  
Author(s):  
D. A. Zumbrunnen ◽  
M. Aziz
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
High Heat Transfer ◽  
Short Period

An experimental investigation has been performed to study the effect of flow intermittency on convective heat transfer to a planar water jet impinging on a constant heat flux surface. Enhanced heat transfer was achieved by periodically restarting an impinging flow and thereby forcing renewal of the hydrodynamic and thermal boundary layers. Although convective heat transfer was less effective during a short period when flow was interrupted, high heat transfer rates, which immediately follow initial wetting, prevailed above a threshold frequency, and a net enhancement occurred. Experiments with intermittent flows yielded enhancements in convective heat transfer coefficients of nearly a factor of two, and theoretical considerations suggest that higher enhancements can be achieved by increasing the frequency of the intermittency. Enhancements need not result in an increased pressure drop within a flow system, since flow interruptions can be induced beyond a nozzle exit. Experimental results are presented for both the steady and intermittent impinging jets at distances up to seven jet widths from the stagnation line. A theoretical model of the transient boundary layer response is used to reveal parameters that govern the measured enhancements. A useful correlation is also provided of local heat transfer results for steadily impinging jets.

scholarly journals An Interferometric Study of Free Convective Heat Transfer in a Double Glazed Window With a Between-Panes Venetian Blind

2021 ◽  
Author(s):  
Bertha Lai
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Flat Plates ◽  
Set Up ◽  
Free Convective Heat Transfer

The free convective heat transfer in a double-glazed window with between-panes Venetian blinds was measured using a Mach-Zehnder interferometer. A vertical cavity with differentially heated/cooled flat plates was set up with an internal blind at slat angles of ø=0⁰, ø=45⁰, and ø=90⁰ from the horizontal and tip-to-plate spacings of s=2mm, s=4mm, and s=8mm. Heat transfer measurements were taken with air as the test fluid and at Rayleigh numbers of Ra~4.5x10(4), RA~6.7X10(4), and Ra~13.1x10(4), based on cavity widths of W=28.7mm, W=32.7mm, and W=40.7mm, respectively. Finite fringe interferograms were used to obtain local and average heat transfer data. Infinite fringe interferograms were taken to visualize the temperature field within the cavity. A preliminary numerical study of the experimental geometry was also conducted. The results show that there was substantial variation in local heat transfer rates caused by the presence of the between-panes blind inside the window cavity. In general, experimental average Nusselt numbers were found to be lower than those of a cavity without blinds.

The Influence of Flexible Strip Height on Convective Heat Transfer Enhancement

2019 ◽  
Author(s):  
Yang Yang ◽  
David S.-K. Ting ◽  
Steve Ray
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortical Flow ◽  
Transfer Enhancement ◽  
Local Flow ◽  
Convective Heat Transfer Enhancement

Abstract A 12.7 mm wide flexible rectangular strip, made from 0.1 mm-thick aluminum sheet, is experimentally explored as a vortical flow generator for promoting heat convection from a flat plate in a wind tunnel. The strip is positioned normal to the freestream with an incoming velocity of 10 m/s, resulting in a Reynolds number, based on the strip width, of 8,500. The influence of the height of the flexible strip on the convective heat transfer enhancement is of interest. Three strip heights, 25.4 mm, 38.1 mm and 50.8 mm, were investigated. The heat transfer results are expressed in terms of Nusselt number, Nu, normalized by the unperturbed reference Nu0. The shortest, 25.4 mm high flexible strip resulted in the highest peak and overall heat transfer enhancement. The distribution of the local heat transfer enhancement is found to correlate well with the turbulent flow motion detailed using a triple-sensor hot-wire anemometer. Pointedly, the heat transfer rate is most elevated when the local flow is moving toward the hot plate, sweeping across a stretch of the surface before moving away from it. These effective convective motions are most effectively generated by the vortices produced by the shortest strip.

Heat Transfer Measurements in Rectangular Channels With Orthogonal Mode Rotation

1991 ◽  
Vol 113 (3) ◽  
pp. 339-345 ◽  
Author(s):  
W. D. Morris ◽  
G. Ghavami-Nasr
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Rotor Blades ◽  
Coolant Temperature ◽  
Internal Cooling ◽  
General Terms

The influence of rotation on local heat transfer in a rectangular-sectioned duct has been experimentally studied for the case where the duct rotates about an axis orthogonal to its own central axis. The coolant used was air with the flow direction in the radially outward direction. This rotating flow geometry is encountered in the internal cooling of gas turbine rotor blades. Local Nusselt number variations along the duct have been determined over the trailing and leading surfaces. In general terms Coriolis-induced secondary flows are shown to enhance local heat transfer over the trailing surface compared to a stationary duct forced convection situation. The converse is true on the leading surface where significant impediment to local heat transfer can occur. Centripetal buoyancy is shown to influence the heat transfer response with heat transfer being improved on both leading and trailing surfaces as the wall-to-coolant temperature difference is increased with other controlling parameters held constant. Correlating equations are proposed and the results compared with those of other workers in the field.

scholarly journals Empirical mapping of the convective heat transfer coefficients with local hot spots on highly conductive surfaces

2017 ◽  
Vol 21 (3) ◽  
pp. 1231-1240
Author(s):  
Murat Tekelioğlu
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Hot Spots ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

An experimental method was proposed to assess the natural and forced convective heat transfer coefficients on highly conductive bodies. Experiments were performed at air velocities of 0m/s, 4.0m/s, and 5.4m/s, and comparisons were made between the current results and available literature. These experiments were extended to arbitrary-shape bodies. External flow conditions were maintained throughout. In the proposed method, in determination of the surface convective heat transfer coefficients, flow condition is immaterial, i.e., either laminar or turbulent. With the present method, it was aimed to acquire the local heat transfer coefficients on any arbitrary conductive shape. This method was intended to be implemented by the heat transfer engineer to identify the local heat transfer rates with local hot spots. Finally, after analyzing the proposed experimental results, appropriate decisions can be made to control the amount of the convective heat transfer off the surface. Limited mass transport was quantified on the cooled plate.

Local Heat Transfer From a Rotating Disk in an Impinging Round Jet

1986 ◽  
Vol 108 (2) ◽  
pp. 357-364 ◽  
Author(s):  
C. O. Popiel ◽  
L. Boguslawski
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Velocity Ratio ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Rotating Disk ◽  
Local Heat ◽  
Tube Diameter ◽  
Air Jet

The results of an experimental investigation of local convective heat transfer from the surface of a rotating disk in an impinging free round air jet, issuing from a long tube, are reported. Using a transient heat transfer method applied to the ring-shaped h-calorimeter (as a single lumped capacitance element) measurements of convective heat transfer rates were made for five impingement radius (fixed) to tube diameter ratios for a range of rotational and jet Reynolds numbers. In the pure impingement-dominated regime, where the rotation of the disk does not show an effect on heat transfer, the velocity ratio is ur/uj ≤ (1 − 2 × 10−4 Re2/3) (1 − 0.18 r/d), where ur = tangential velocity of the disk at the jet impingement radius r, uj = average exit velocity of jet, and d = jet tube diameter. In this regime, the local heat transfer on the rotating disk can be strongly enhanced by jet impingement. For ur/uj ⪞ 5, the effect of the jet impingement on heat transfer can be neglected. The discussion of the heat transfer results has been supported by smoke flow visualization.

Local Convective Heat Transfer From a Constant Heat Flux Flat Plate Cooled by Synthetic Air Jets

2006 ◽  
Vol 128 (10) ◽  
pp. 990-1000 ◽  
Author(s):  
M. B. Gillespie ◽  
W. Z. Black ◽  
C. Rinehart ◽  
A. Glezer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Ambient Air ◽  
Local Heat ◽  
Synthetic Jet ◽  
Operating Conditions ◽  
Small Scale ◽  
Air Jet

The effects of a small-scale, rectangular synthetic air jet on the local convective heat transfer from a flat, heated surface were measured experimentally. The synthetic jet impinges normal to the surface and induces small-scale motions by zero-net mass flux, time-periodic entrainment, and ejection of ambient air at frequencies whose periods are far higher than the characteristic thermal time scale. The velocity field between the jet orifice and the target plate is measured in planar cross sections using particle image velocimetry and is related to the local heat transfer from the plate. The present work suggests that synthetic jets can lead to substantial enhancement of the local heat transfer from heated surfaces by strong mixing that disrupts the surface thermal boundary layer. The dependence of the local heat transfer coefficient on the primary parameters of jet motion is characterized over a range of operating conditions.

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