Accurate heat transfer measurements using thermochromic liquid crystal. Part 2: Application to a rotating disc

2009 ◽  
Vol 30 (5) ◽  
pp. 950-959 ◽  
Author(s):  
V.U. Kakade ◽  
G.D. Lock ◽  
M. Wilson ◽  
J.M. Owen ◽  
J.E. Mayhew
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Thermochromic Liquid Crystal ◽  
Rotating Disc

Effect of Radial Location of Nozzles on Heat Transfer in Pre-Swirl Cooling System

2009 ◽  
Author(s):  
V. U. Kakade ◽  
G. D. Lock ◽  
M. Wilson ◽  
J. M. Owen ◽  
J. E. Mayhew
Keyword(s):  
Heat Transfer ◽  
Cooling System ◽  
Convective Heat Transfer Coefficient ◽  
Flow Visualisation ◽  
Thermochromic Liquid Crystal ◽  
Rotating Disc ◽  
Dimensional Solution ◽  
Flow Rates ◽  
Measure Surface Temperature ◽  
High Heat Transfer

This paper investigates heat transfer in a rotating disc system using pre-swirled cooling air from nozzles at high and low radius. The experiments were conducted over a range of rotational speeds, flow rates and pre-swirl ratios. Narrow-band thermochromic liquid crystal (TLC) was specifically calibrated for application to experiments on a disc rotating at ∼ 5000 rpm and subsequently used to measure surface temperature in a transient experiment. The TLC was viewed through the transparent polycarbonate disc using a digital video camera and strobe light synchronised to the disc frequency. The convective heat transfer coefficient, h, was subsequently calculated from the one-dimensional solution of Fourier’s conduction equation for a semi-infinite wall. The analysis accounted for the exponential rise in the air temperature driving the heat transfer, and for experimental uncertainties in the measured values of h. The experimental data was supported by ‘flow visualisation’ determined from CFD. Two heat transfer regimes were revealed for the low-radius pre-swirl system: a viscous regime at relatively low coolant flow rates; and an inertial regime at higher flow rates. Both regimes featured regions of high heat transfer where thin, boundary layers replaced air exiting through receiver holes at high radius on the rotating disc. The heat transfer in the high radius pre-swirl system was shown to be dominated by impingement under the flow conditions tested.

Transient Heat Transfer Measurements Using a Single Wide-Band Liquid Crystal Test

1999 ◽  
Vol 122 (3) ◽  
pp. 546-552 ◽  
Author(s):  
Dragos N. Licu ◽  
Matthew J. Findlay ◽  
Ian S. Gartshore ◽  
Martha Salcudean
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Film Cooling ◽  
Imaging System ◽  
Wide Band ◽  
Thermochromic Liquid Crystal ◽  
Film Cooling Effectiveness ◽  
Flame Ionization ◽  
Square Jets ◽  
True Color

A technique using a thermochromic liquid crystal coating to measure film cooling effectiveness (η) and heat transfer coefficient hf has been developed so that both of these important parameters can be obtained, as a function of time, from a single transient test. The technique combines a real-time, true color (24 bit) imaging system with the use of a wide-band liquid crystal coating and multiple event sampling for the simultaneous determination of η and hf from the single test. To illustrate and validate this technique, the flow from compound-angle square jets in a crossflow is examined. The tests, in which the jet air was suddenly heated to about 40°C, lasted 30 seconds. The measured η is compared with measurements made in the same flow under steady-state conditions in a totally different way, using a mass/heat analogy and a flame ionization detector. Good agreement is obtained. Three different blowing ratios M of 0.5, 1.0, and 1.5 are investigated with a constant jet Reynolds number of about 5000. Detailed quantitative comparisons of the η measured in both ways are made for all blowing ratios, and plots of η and hf are presented. [S0889-504X(00)01403-3]

A Novel Indirect Visualization Method for Studying the Melting Heat Transfer of Nano-Enhanced Phase Change Materials Using Thermochromic Liquid Crystal Thermography

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Nan Hu ◽  
Zi-Rui Li ◽  
Run-Hui Zhang ◽  
Li-Wu Fan
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Phase Change ◽  
Phase Change Materials ◽  
Phase Interface ◽  
Classical Problem ◽  
Dominant Mode ◽  
Thermochromic Liquid Crystal ◽  
Melting Heat ◽  
Melting Heat Transfer

Abstract In order to give more sights into the melting (and solidification) heat transfer processes of nano-enhanced phase change material (NePCM) with invisible phase interfaces, a novel indirect method for tracking the phase interface by thermochromic liquid crystal (TLC) thermography is proposed. As an example case to demonstrate the applicability of the proposed method, the classical problem of melting heat transfer in a differentially heated rectangular cavity was revisited in the presence of NePCM of various loadings. A narrowband TLC was selected and calibrated carefully to build the hue–temperature relationship prior to being applied in the melting experiments. For validation purpose, the case of an unloaded NePCM, with a clear visible phase interface, was tested via combined direct and indirect observations. It was shown that this TLC method can easily and accurately capture the dynamic motions of the phase interface during melting. Based on the shape evolutions of the phase interface, it was concluded that for the NePCM sample with a higher loading (and hence a much greater viscosity), heat conduction becomes the dominant mode of heat transfer during melting as a result of the significantly deteriorated natural convection effect. This gives an intuitive confirmation of the hypothesis made in previous studies that were conducted using volume-average-based indirect methods.

Transient heat transfer measurements using thermochromic liquid crystal. Part 1: An improved technique

2003 ◽  
Vol 24 (1) ◽  
pp. 14-22 ◽  
Author(s):  
Paul J Newton ◽  
Youyou Yan ◽  
Nia E Stevens ◽  
Simon T Evatt ◽  
Gary D Lock ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Transient Heat Transfer ◽  
Thermochromic Liquid Crystal ◽  
Improved Technique

Investigation of Circumferential Variation of Heat Transfer Coefficients During In-Tube Evaporation for R-22 and R-407C Using Liquid Crystal

2002 ◽  
Vol 124 (5) ◽  
pp. 845-853 ◽  
Author(s):  
Seok Ho Yoon ◽  
Min Soo Kim
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Cross Sections ◽  
Outer Wall ◽  
Processing Technique ◽  
Image Processing Technique ◽  
Measured Temperature ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Heat transfer coefficients during evaporation in a horizontal smooth tube for R-22 and R-407C (R-32/125/134a, 23/25/52 wt.%) have been measured using thermochromic liquid crystal. Focus has been put on the circumferential variation of heat transfer coefficients at several cross-sections of the test tube with inner diameter of 11.3 mm for several vapor qualities of refrigerant. The inner wall temperatures were calculated by one dimensional heat conduction equation from the measured outer wall temperatures, which were obtained using an image processing technique with thermochromic liquid crystal (TLC). The relation between measured temperature and color information (Red-Green-Blue values) of thermochromic liquid crystal was calibrated by a neural network method. Results show that circumferential variation of heat transfer coefficients for R-22 is quite large with the highest heat transfer coefficient at the top of the tube. For zeotropic mixture of R-407C, similar trend has been observed with less difference between the heat transfer coefficients at the top and bottom than that of R-22.

Transient Thermal Field Measurements in a High Aspect Ratio Channel Related to Transient Thermochromic Liquid Crystal Experiments

2007 ◽  
Author(s):  
Sean C. Jenkins ◽  
Igor V. Shevchuk ◽  
Jens von Wolfersdorf ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Liquid Crystal ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Field Measurements ◽  
Bulk Temperature ◽  
Fluid Temperature ◽  
Thermochromic Liquid Crystal ◽  
Temperature Distributions

Measurements of transient fluid temperature distributions were made in a high aspect ratio (4:1) internally ribbed two-pass channel relating to the measurement of heat transfer using the transient thermochromic liquid crystal (TLC) technique. The temperature field was measured at several positions leading up to and around the 180° bend in a two-passage channel to account for variations in the bulk temperature used as a reference for the transient TLC technique. Results showed that the normalized distribution of the temperature field was time-invariant, an important result for the validation of heat transfer results using the transient TLC method. The normalized fluid temperature field was shown to be independent of the inlet temperature step and relatively independent of channel Reynolds number. Fluid temperature distributions were shown to be consistent over the length of the inlet channel, however, temperature field measurements made downstream of the bend exhibited a strong asymmetry. Finally, local temperature distributions were used to adjust the reference temperature used in calculating heat transfer coefficient distributions and to show the behavior of heat transfer due to 180° bends.

Heat Transfer Measurements Using Liquid Crystal in a Pre-Swirl Rotating-Disc System

2003 ◽  
Author(s):  
Gary D. Lock ◽  
Youyou Yan ◽  
Paul J. Newton ◽  
Michael Wilson ◽  
J. Michael Owen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Turbine Blades ◽  
Impinging Jets ◽  
Viscous Effects ◽  
Rotating Disc ◽  
Flow Rates

Pre-swirl nozzles are often used in gas turbines to deliver the cooling air to the turbine blades through receiver holes in a rotating disc. The distribution of the local Nusselt number, Nu, on the rotating disc is governed by three non-dimensional fluid-dynamic parameters: pre-swirl ratio, βp, rotational Reynolds number, Reφ, and turbulent flow parameter, λT. A scaled model of a gas turbine rotor-stator cavity, based on the geometry of current engine designs, has been used to create appropriate flow conditions. This paper describes how thermochromic liquid crystal (TLC), in conjunction with a stroboscopic light and digital camera, is used in a transient experiment to obtain contour maps of Nu on the rotating disc. The thermal boundary conditions for the transient technique are such that an exponential-series solution to Fourier’s one-dimensional conduction equation is necessary. A method to assess the uncertainty in the measurements is discussed and these uncertainties are quantified. The experiments reveal that Nu on the rotating disc is axisymmetric except in the region of the receiver holes, where significant two-dimensional variations have been measured. At the higher coolant flow rates studied, there is a peak in heat transfer at the radius of the pre-swirl nozzles. The heat transfer is governed by two flow regimes: one dominated by inertial effects associated with the impinging jets from the pre-swirl nozzles, and another dominated by viscous effects at lower flow rates. The Nusselt number is observed to increase as either Reφ or λT increases.

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