LOCAL HEAT TRANSFER MEASUREMENT FROM A PAIR OF LONGITUDINAL VORTICES USING A TRANSIENT LIQUID CRYSTAL TECHNIQUE

2007 ◽  
Vol 20 (3) ◽  
pp. 197-212
Author(s):  
J. S. Yang ◽  
C. H. Hong ◽  
M. B. Young
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Longitudinal Vortices ◽  
Transfer Measurement ◽  
Transient Liquid Crystal Technique ◽  
Heat Transfer Measurement

Experimental investigation of local heat transfer measurement having inclined discrete ribs of solar air heater duct using LCT technique

2021 ◽  
pp. 1-15
Author(s):  
Yogendra Rathor ◽  
K.R. Aharwal
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Solar Air Heater ◽  
Distribution Profile ◽  
Air Heater ◽  
Staggered Arrangement ◽  
Transfer Measurement

Abstract The steady-state experiment using liquid crystal thermography has been conducted for the analysis of Nusselt number distribution over the absorber surface of solar air heater duct having a gap with the staggered arrangement in inclined rib geometry to recuperate its thermal performance. The heat transfer experiment is performed with uniform heat flux and thermo-chromic liquid crystal is utilized to show the temperature distribution profile over the ribbed surfaces of the rectangular duct of aspect ratio of 5. The colored pattern image of TLCs was acquired using a 3CCD camera and exported to a TIFF file format using frame grabbing SOFTWARE SAPERALT which was further processed to get HSI values. The flow parameters considered in this present investigation are Re, d/W, and g/e varied from 4000-12500,0.15-0.45 and 1-4 respectively. Experiments has been performed with fixed P/e, r/e, p′/P, a and e/Dh of 10, 2, 0.6, 60° and 0.0303 respectively. The influence of relative gap position and relative gap width on flow pattern has been analyzed. The maximum augmentation in Nu and f over the smooth duct was obtained as 4.01 and 4.28 times respectively at the optimum value of d/W = 0.35 and g/e = 2 under similar flow conditions. The maximum value of THPP obtained at d/W & g/e of 0.35 & 2 respectively and Reynolds number of 12445.

Effects of Embedded Vortices on Film-Cooled Turbulent Boundary Layers

1989 ◽  
Vol 111 (1) ◽  
pp. 71-77 ◽  
Author(s):  
P. M. Ligrani ◽  
A. Ortiz ◽  
S. L. Joseph ◽  
D. L. Evans
Keyword(s):  
Heat Transfer ◽  
Boundary Layers ◽  
Film Cooling ◽  
Free Stream ◽  
Flow Behavior ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Boundary Layers ◽  
Stream Velocity ◽  
Longitudinal Vortices

Heat transfer effects of longitudinal vortices embedded within film-cooled turbulent boundary layers on a flat plate were examined for free-stream velocities of 10 m/s and 15 m/s. A single row of film-cooling holes was employed with blowing ratios ranging from 0.47 to 0.98. Moderate-strength vortices were used with circulating-to-free stream velocity ratios of −0.95 to −1.10 cm. Spatially resolved heat transfer measurements from a constant heat flux surface show that film coolant is greatly disturbed and that local Stanton numbers are altered significantly by embedded longitudinal vortices. Near the downwash side of the vortex, heat transfer is augmented, vortex effects dominate flow behavior, and the protection from film cooling is minimized. Near the upwash side of the vortex, coolant is pushed to the side of the vortex, locally increasing the protection provided by film cooling. In addition, local heat transfer distributions change significantly as the spanwise location of the vortex is changed relative to film-cooling hole locations.

Film Effectiveness Over a Flat Surface With Air and CO2 Injection Through Compound Angle Holes Using a Transient Liquid Crystal Image Method

1997 ◽  
Vol 119 (3) ◽  
pp. 587-593 ◽  
Author(s):  
S. V. Ekkad ◽  
D. Zapata ◽  
J. C. Han
Keyword(s):  
Liquid Crystal ◽  
Flat Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Co2 Injection ◽  
Image Method ◽  
Transfer Coefficients ◽  
Free Stream Turbulence ◽  
Transient Liquid Crystal Technique ◽  
Compound Angle

This paper presents detailed film effectiveness distributions over a flat surface with one row of injection holes inclined streamwise at 35 deg for three blowing ratios (M = 0.5, 1.0, 2.0). Three compound angles of 0, 45, and 90 deg with air (D.R. = 0.98) and CO2 (D. R. = 1.46) as coolants are tested at an elevated free-stream turbulence condition (Tu ≈ 8.5 percent). A transient liquid crystal technique is used to measure local heat transfer coefficients and film effectiveness. Detailed film effectiveness results are presented near and around film injection holes. Compound angle injection provides higher film effectiveness than simple angle injection for both coolants. Higher density injectant produces higher effectiveness for simple injection. However, lower density coolant produces higher effectiveness for a large compound angle of 90 deg. The detailed film effectiveness obtained using the transient liquid crystal technique, particularly in the near-hole region, provided a better understanding of the film cooling process in gas turbine components.

A Technique for Processing Transient Heat Transfer, Liquid Crystal Experiments in the Presence of Lateral Conduction

2004 ◽  
Vol 126 (2) ◽  
pp. 247-258 ◽  
Author(s):  
John P. C. W. Ling ◽  
Peter T. Ireland ◽  
Lynne Turner
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Film Cooling ◽  
Cooling System ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Three Dimensions ◽  
Transient Heat Transfer ◽  
Adiabatic Wall ◽  
Full Intensity

New techniques for processing transient liquid crystal heat transfer experiment have been developed. The methods are able to measure detailed local heat transfer coefficient and adiabatic wall temperature in a three temperature system from a single transient test using the full intensity history recorded. Transient liquid crystal processing methods invariably assume that lateral conduction is negligible and so the heat conduction process can be considered one-dimensional into the substrate. However, in regions with high temperature variation such as immediately downstream of a film-cooling hole, it is found that lateral conduction can become significant. For this reason, a procedure which allows for conduction in three dimensions was developed by the authors. The paper is the first report of a means of correcting data from the transient heat transfer liquid crystal experiments for the effects of significant lateral conduction. The technique was applied to a film cooling system as an example and a detailed uncertainty analysis performed.

Three-Dimensional Transient Heat Conduction Equation Solution for Accurate Quantification of Heat Transfer Coefficient in Transient Liquid Crystal Experiments

2019 ◽  
Author(s):  
Shoaib Ahmed ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Conduction Model

Abstract Liquid crystal thermography and infrared thermography techniques are typically employed to measure detailed surface temperatures, where local heat transfer coefficient (HTC) values are calculated by employing suitable conduction models. One such practice, which is very popular and easy to use, is the transient liquid crystal thermography using one-dimensional semi-infinite conduction model. In these experiments, a test surface with low thermal conductivity and low thermal diffusivity (e.g. acrylic) is used where a step-change in coolant air temperature is induced and surface temperature response is recorded. An error minimization routine is then employed to guess heat transfer coefficients of each pixel, where wall temperature evolution is known through an analytical expression. The assumption that heat flow in the solid is essentially in one-dimension, often leads to errors in HTC determination and this error depends on true HTC, wall temperature evolution and HTC gradient. A representative case of array jet impingement under maximum crossflow condition has been considered here. This heat transfer enhancement concept is widely used in gas turbine leading edge and electronics cooling. Jet impingement is a popular cooling technique which results in high convective heat rates and has steep gradients in heat transfer coefficient distribution. In this paper, we have presented a procedure for solution of three-dimensional transient conduction equation using alternating direction implicit method and an error minimization routine to find accurate heat transfer coefficients at relatively lower computational cost. The HTC results obtained using 1D semi-infinite conduction model and 3D conduction model were compared and it was found that the heat transfer coefficient obtained using the 3D model was consistently higher than the conventional 1D model by 3–16%. Significant deviations, as high as 8–20% in local heat transfer at the stagnation points of the jets were observed between h1D and h3D.

Heat Transfer Enhancement Caused by Sliding Bubbles

2003 ◽  
Vol 125 (3) ◽  
pp. 503-509 ◽  
Author(s):  
Baris B. Bayazit ◽  
D. Keith Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Thin Foil ◽  
Local Heat ◽  
Superheated Liquid ◽  
Enhancement Of Heat Transfer ◽  
Inclined Plates ◽  
Inclined Surface

Measurements that illustrate the enhancement of heat transfer caused by a bubble sliding under an inclined surface are reported. The data were obtained on an electrically heated thin-foil surface that was exposed on its lower side to FC-87 and displayed the output of a liquid crystal coating on the upper (dry) side. A sequence of digital images was obtained from two cameras: one that recorded the response of the liquid crystal and one that recorded images of the bubble as it moved along the heated surface. With this information, the thermal imprint of the bubble was correlated to its motion and position. A bubble generator that produced FC-87 bubbles of repeatable and controllable size was also developed for this study. The results show that both the microlayer under a sliding bubble and the wake behind the bubble contribute substantially to the local heat transfer rate from the surface. The dynamic behavior of the bubbles corresponded well with studies of the motion of adiabatic bubbles under inclined plates, even though the bubbles in the present study grew rapidly because of heat transfer from the wall and the surrounding superheated liquid. Three regimes of bubble motion were observed: spherical, ellipsoidal and bubble-cap. The regimes depend upon bubble size and velocity. A model of the heat transfer within the microlayer was used to infer the microlayer thickness. Preliminary results indicate a microlayer thickness of 40–50 μm for bubbles in FC-87 and a plate inclination of 12 deg.

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