Hysteresis in Liquid Crystal Thermography

2004 ◽  
Vol 126 (3) ◽  
pp. 339-346 ◽  
Author(s):  
M. R. Anderson ◽  
J. W. Baughn
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Narrow Band ◽  
Broad Band ◽  
Peak Temperature ◽  
Temperature Calibration ◽  
Hysteresis Behavior ◽  
Liquid Crystal Thermography ◽  
Heating And Cooling ◽  
Start Temperature

Hysteresis in five different Thermochromic Liquid Crystals (TLCs), both narrow-band and broad-band, has been investigated. All were found to exhibit a similar hysteresis behavior during cooling relative to heating. This hysteresis is characterized by a decrease in reflectivity and a shift in the temperature associated with the peak reflected intensity for each of the R, G, and B components during cooling. This causes a shift in the hue-temperature calibration of the TLC causing temperature biases, when cooled rather than heated, of 20–60% of the useful calibration range. The hysteresis effect increases as the peak temperature during a heating and cooling cycle is increased. Repeatable heating calibrations were obtained when the TLC was cooled below the red start temperature to an apparent low reset temperature. Somewhat repeatable cooling calibrations, different from the heating calibrations, were obtained when the TLC was heated somewhat above the blue stop temperature. A possible explanation of the hysteresis based on the texture of the liquid crystal helices is provided. In addition to hysteresis, a permanent decrease in reflectivity and a shift in the temperature associated with the peak reflected intensity was observed when the TLCs were exposed to extended higher temperatures (60°C–80°C).

Determination of the Temperature Field Using Liquid Crystal Thermography and Analysis of Two-Phase Flow Structures in Research on Boiling Heat Transfer in a Minichannel

2013 ◽  
Vol 20 (2) ◽  
pp. 205-216 ◽  
Author(s):  
Magdalena Piasecka
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Void Fraction ◽  
Two Phase Flow ◽  
Heating Surface ◽  
Flow Structures ◽  
Phase Flow ◽  
Two Phase ◽  
Color Distribution ◽  
Liquid Crystal Thermography

Abstract The paper presents the application of liquid crystal thermography for temperature determination and visualisation of two phase flow images on the studied surface. Properties and applications of thermochromic liquid crystals are discussed. Liquid crystals were applied for two-dimensional detection of the temperature of the heating foil forming one of the surfaces of the minichannel along which the cooling liquid flowed. The heat flux supplied to the heating surface was altered in the investigation and it was accompanied by a change in the color distribution on the surface. The accuracy of temperature measurements on the surface with liquid crystal thermography is estimated. The method of visualisation of two-phase flow structures is described. The analysis of monochrome images of flow structures was employed to calculate the void fraction for some cross-sections. The flow structure photos were processed using Corel graphics software and binarized. The analysis of phase volumes employed Techsystem Globe software. The measurement error of void fraction is estimated.

Liquid crystal thermography of the spine and extremities

1982 ◽  
Vol 56 (3) ◽  
pp. 386-395 ◽  
Author(s):  
Rubem Pochaczevsky ◽  
Charles E. Wexler ◽  
Phillip H. Meyers ◽  
Joseph A. Epstein ◽  
Joseph A. Marc
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
The Body ◽  
Content Type ◽  
Subjective Complaint ◽  
Color Changes ◽  
Liquid Crystal Thermography ◽  
Clinically Significant ◽  
High Degree ◽  
Better Than

✓ Cholesteric liquid crystals are special compounds that display specific color changes in response to variations in temperature. Their responses can be graphically demonstrated by means of color thermography. A new color contact thermographic technique is described utilizing liquid crystals embedded in elastic flexible sheaths. These sheaths, when inflated, conform to the varied contours of the torso and extremities and, therefore, the new thermographic technique is especially well suited to the study of the skin dermatomes and myotomes. Typical heat patterns have been observed in root compression syndromes and particularly at the S-1, L-5, L-4, C-6, C-7, and C-8 levels. A high degree of anatomic accuracy can thus be achieved, comparable to or better than can be achieved by electromyography or myelography. Liquid crystal thermography can serve to screen patients for myelography and can complement myelography in identifying clinically significant abnormalities. The imaging technique correlates well with clinical and surgical findings, and constitutes one of the first attempts by means of a concomitant study of the body dermatomes to objectively document the subjective complaint of pain.

Liquid Crystal Thermography on the Fluid Solid Interface of Rotating Systems

1997 ◽  
Vol 119 (1) ◽  
pp. 20-29 ◽  
Author(s):  
C. Camci ◽  
B. Glezer
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Rotating Disk ◽  
Experimental Methodology ◽  
Liquid Crystal Thermography ◽  
Rotating Systems ◽  
Color Response ◽  
Rotating Surface ◽  
Stationary Conditions ◽  
Steady State Heat Transfer

Liquid crystal thermography is an effective method widely employed in transient and steady-state heat transfer experiments with excellent spatial resolution and good accuracy. Most of the past studies in liquid crystal thermography deal with stationary conditions. The present investigation deals with the influence of rotation on the color response of encapsulated liquid crystals attached to a flat rotating surface. A general methodology developed for the application of thermochromic liquid crystals in rotating systems is described for the first time. The investigation is performed for a rotational speed range from 0 to 7500 rpm using two different coatings displaying red at 30° and 45°C, under stationary conditions. Local liquid crystal color on the surface of a rotating disk is correlated with local temperature as measured by a non-intrusive infrared sensor at various rotational speeds. An immediate observation from the present study is that the color response (hue) of encapsulated liquid crystals is not altered by either the centrifugal acceleration of the rotating environment or the aerodynamic friction force at the rotating disk-air interface. Present investigation also shows that when a stroboscope light is introduced, the color response is not significantly altered due to additional periodic illumination. A complete and general experimental methodology including rotating surfaces with non-axisymmetric temperature distribution is presented. Results from the current liquid crystal technique agree well with the theoretical adiabatic temperature rise of a free rotating disk as predicted by an analytical method.

Liquid Crystal Thermography and Its Application to the Study of Convective Heat Transfer

1975 ◽  
Vol 97 (3) ◽  
pp. 442-450 ◽  
Author(s):  
T. E. Cooper ◽  
R. J. Field ◽  
J. F. Meyer
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Separation Bubble ◽  
Heated Cylinder ◽  
Liquid Crystal Thermography ◽  
Measuring Techniques ◽  
Flow Information ◽  
Temperature Ranges

A thermographic technique is presented that allows visual determination of both qualitative and quantitative heat transfer and fluid flow information to be obtained on heated objects placed in forced convection environments. The technique employs cholesteric liquid crystals as the temperature sensing agent. The liquid crystals indicate temperature by exhibiting brilliant changes in color over discrete, reproducible temperature ranges. The technique has been used to quickly and easily obtain information on the variation of the Nusselt number on a right circular cylinder placed in a crossflow of air. In addition to yielding precise quantitative heat transfer information, the liquid crystal thermographic technique afforded the opportunity to visually observe the effects of flow separation, the separation bubble region, the turbulent boundary layer, and the turbulent wake on the surface temperature of the heated cylinder. The experimental results obtained using the liquid crystal thermographic technique are in close agreement with results obtained by other investigators who have used standard measuring techniques.

Dielectric Relaxation in Filled Nematic Liquid Crystals

1999 ◽  
Vol 559 ◽  
Author(s):  
G.P. Sinha ◽  
M. Kreuzer ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Broad Band ◽  
Low Frequency ◽  
Slow Process ◽  
Hydrophobic Particles ◽  
Total Polarization ◽  
Tumbling Motion ◽  
Frequency Relaxation

ABSTRACTNematic liquid crystals filled with Aerosil particles are new heterogeneous materials important for different optoelectronic applications. These materials are suspensions of small silica particles, about 10-17 nm in diameter, dispersed in nematic liquid crystals. The particles are known to form a network structure dividing liquid crystal into domains with linear size approximately 250 nm. We used both hydrophilic and hydrophobic particles, filling them with the nematic liquid crystal-5CB.Broad band dielectric spectroscopy (1 mHz - 1.5 GHz) was applied for the investigation of these materials. Two bulk-like modes due to the rotation of molecules around the short axis and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and the dispersion of dielectric permittivity due to conductivity were also observed. The modification of the surface of the particles has stronger influence on the slow process and is less important for the molecular modes. The contribution of the slow process for the hydrophilic sample to the total polarization is greater than for the hydrophobic sample. In addition, the corresponding characteristic frequencies are lower for the case of hydrophilic samples. These facts suggest that the low frequency relaxation is an Aerosil particle-liquid crystal interface related phenomena and the origin of this process maybe explained on the basis of surface induced polarization.

New structure induced by elastic anisotropy in cylindrical nematic liquid crystal

2017 ◽  
Vol 13 (2) ◽  
pp. 4705-4717
Author(s):  
Zhang Qian ◽  
Zhou Xuan ◽  
Zhang Zhidong
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystal ◽  
Elastic Anisotropy ◽  
Nematic Liquid Crystals ◽  
Gennes Theory

Basing on Landau–de Gennes theory, this study investigated the chiral configurations of nematic liquid crystals confined to cylindrical capillaries with homeotropic anchoring on the cylinder walls. When the elastic anisotropy (L2/L1) is large enough, a new structure results from the convergence of two opposite escape directions of the heterochiral twist and escape radial (TER) configurations. The new defect presents when L2/L1≥7 and disappears when L2/L1<7. The new structure possesses a heterochiral hyperbolic defect at the center and two homochiral radial defects on both sides. The two radial defects show different chiralities.

scholarly journals Liquid Crystal Devices for Beam Steering Applications

Micromachines ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 247
Author(s):  
Rowan Morris ◽  
Cliff Jones ◽  
Mamatha Nagaraj
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Adaptive Optics ◽  
Beam Steering ◽  
Optical Components ◽  
Advantages And Disadvantages ◽  
Liquid Crystal Devices

Liquid crystals are valuable materials for applications in beam steering devices. In this paper, an overview of the use of liquid crystals in the field of adaptive optics specifically for beam steering and lensing devices is presented. The paper introduces the properties of liquid crystals that have made them useful in this field followed by a more detailed discussion of specific liquid crystal devices that act as switchable optical components of refractive and diffractive types. The relative advantages and disadvantages of the different devices and techniques are summarised.

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