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.

scholarly journals Color Response Modification of Encapsulated Liquid Crystals Used in Rotating Disk Heat Transfer Studies

1995 ◽  
Author(s):  
Cengiz Camci ◽  
Boris Glezer
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Liquid Crystals ◽  
Rotational Speed ◽  
Rotating Disk ◽  
Point Of View ◽  
Centrifugal Acceleration ◽  
Relative Shift ◽  
Color Response ◽  
Stationary Conditions

The liquid crystal thermography can be successfully used in both transient and steady-state heat transfer experiments with excellent spatial resolution and good accuracy. Although most of the past liquid crystal based heat transfer studies are reported in the stationary frame, measurements from the rotating frame of turbomachinery systems exist The main objective of the present investigation is to determine the influence of rotation on the color calibration of encapsulated liquid crystals sprayed on the flat surface of a rotating aluminum disk. The investigation is performed for a rotational speed range from 0 rpm to 7500 rpm using three different liquid crystal coatings displaying red at 30, 35 and 45° C, under stationary conditions. An immediate observation from the present study is that the color response of liquid crystals is strongly modified by the centrifugal acceleration of the rotating environment. It is consistently and repeatedly observed that the hue versus temperature curve is continuously shifted toward lower temperatures by increasing rotational speed. The relative shift of the display temperature of the green can be as high as 7°C at 7500 rpm when compared to the temperature of the green observed under stationary conditions. The present study shows that relative shift of the liquid crystal color has a well-defined functional dependency to rotational speed. The shift is linearly proportional to the centrifugal acceleration. It is interesting to note that the individual shift curves of the green for all three liquid crystal coatings collapse into a single curve when they are normalized with respect to their own stationary green values. When the color attribute is selected as “intensity” instead of “hue”, very similar shifts of the temperature corresponding to the intensity maximum value appearing around green is observed. An interpretation of the observed color shift is made from a thermodynamics energy balance point of view.

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 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.

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).

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.

scholarly journals Optical Response Associated with the Orientation and Structure of Liquid Crystals with Respect to Phosphatidylcholine Concentration

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 678
Author(s):  
Yuqi Han ◽  
Yan Jiang ◽  
Wei Guo ◽  
Bing Li ◽  
Lu Zhang ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Reflectance Spectrum ◽  
Optical Response ◽  
The Self ◽  
Cholesteric Liquid Crystals ◽  
Anchoring Effect ◽  
Self Assembling ◽  
Sensitization Effect ◽  
Structure Of Liquid

Based on the anchoring effect due to the self-assembling behavior of the phospholipid molecules at the interface between the liquid crystal and water phases on the orientation of liquid crystals, the optical response associated with the orientation and structure of liquid crystals with respect to the concentration of 1,2-didodecanoyl-sn-glycero-3-phosphocholine solution has been investigated. The optical response owing to changes in the orientation and structure of the mixed cholesteric liquid crystals with respect to the change in the concentration of phosphatidylcholine has been obtained. Moreover, the feasibility of using as-prepared mixed cholesteric liquid crystals to measure the phosphatidylcholine concentration has been verified. A methodology to measure the reflectance spectrum by using mixed cholesteric liquid crystals to sensitize the phosphatidylcholine concentration has been further realized. The sensitization effect of the mixed cholesteric liquid crystals on the measurement of phosphatidylcholine concentration was also verified.

scholarly journals Optofluidic Platform Based on Liquid Crystals in X-Cut Lithium Niobate: Thresholdless All-Optical Response

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 908
Author(s):  
Fabrizio Ciciulla ◽  
Annamaria Zaltron ◽  
Riccardo Zamboni ◽  
Cinzia Sada ◽  
Francesco Simoni ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Light Intensity ◽  
Lithium Niobate ◽  
Photovoltaic Effect ◽  
Optical Control ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Threshold Behaviour ◽  
All Optical

In this study, we present a new configuration of the recently reported optofluidic platform exploiting liquid crystals reorientation in lithium niobate channels. In order to avoid the threshold behaviour observed in the optical control of the device, we propose microchannels realized in a x-cut crystal closed by a z-cut crystal on the top. In this way, the light-induced photovoltaic field is not uniform inside the liquid crystal layer and therefore the conditions for a thresholdless reorientation are realized. We performed simulations of the photovoltaic effect based on the well assessed model for Lithium Niobate, showing that not uniform orientation and value of the field should be expected inside the microchannel. In agreement with the re-orientational properties of nematic liquid crystals, experimental data confirm the expected thresholdless behaviour. The observed liquid crystal response exhibits two different regimes and the response time shows an unusual dependence on light intensity, both features indicating the presence of additional photo-induced fields appearing above a light intensity of 107 W/m2.

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