The basics and issues of Thermochromic Liquid Crystal Calibrations

Abdullah, Nadia; Talib, Ahmad; Jaafar, Azmi; Salleh, Mohamad Amran Mohd; Chong, Wen Tong

doi:10.1016/j.expthermflusci.2010.03.011

Cited by 93 publications

(54 citation statements)

References 48 publications

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“…The temperature visualization is based on the property of some cholesteric and chiral-nematic liquid crystal materials to refract light of selected wavelength as a function of the temperature. The color change for the TLC ranges from clear at ambient temperature through red as temperature increases and then to yellow, green, blue and violet before turning colorless (isotropic) again at a higher temperature (Abdullah et al 2010;Dabiri 2009). The color of light refracted by TLCs depends both on temperature and on the observation angle.…”

Section: Thermochromic Liquid Crystalmentioning

confidence: 99%

Temperature and chemical composition of droplets by optical measurement techniques: a state-of-the-art review

2013

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Section: Thermochromic Liquid Crystalmentioning

confidence: 99%

Temperature and chemical composition of droplets by optical measurement techniques: a state-of-the-art review

2013

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“…Although digital cameras usually output images in the RGB (red, green, blue) colour space, it is more convenient to transform the images into the HSL (Hue-Saturation-Luminance) colour space representation, because only hue correlates with temperature. An in-situ calibration was performed according to the steady-state method of uniform surface temperature [35]: water supplied by the heating circulator was forced to flow through the channels on both sides of the TLC-polycarbonate wall, and its temperature was progressively increased from 30°C up to 42°C in 0.2°C steps. For each imposed temperature, once steady state conditions were achieved in the module, a photograph of the colorimetric response of the TLCs was acquired, thus resulting into a hue vs temperature (H-T) calibration curve.…”

Section: Experimental Techniquementioning

confidence: 99%

Performance comparison between overlapped and woven spacers for membrane distillation

Gurreri¹,

Tamburini²,

Cipollina³

et al. 2017

dwt

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a b s t r a c tThe sustainable production of freshwater from seawater desalination is receiving increasing attention. Recently, some desalination technologies are taking advantage from the coupling with renewable resources; among them, membrane distillation (MD) is one of the most promising since it can be easily powered by low-grade thermal energy. MD being an emerging technology, efforts are required to optimize geometry and operating conditions of real units in order to reduce the unitary freshwater production cost. In particular, temperature polarization is a well-known detrimental effect for the process driving force; spacers are traditionally used to enhance mixing and make temperature boundary layers thinner, at the cost of higher pressure losses. The present work is devoted to testing and comparing the performance of two different two-layer net spacers: overlapped and woven. Investigations were carried out both by experiments and by computational fluid dynamics (CFD) at different Reynolds numbers, ranging from creeping flow to turbulent flow regimes. Experiments (for intermediate to high Re) made use of thermochromic liquid crystals along with digital image processing. Computational results (for low to intermediate Re) were obtained via steady state (low Re) or direct numerical simulations (intermediate Re) along with the unit cell approach. A good agreement between experiments and CFD results was obtained in the range of superposition. Results showed that woven spacers guarantee a better mixing than overlapped ones, especially in the low to intermediate Re range, thus resulting in Nusselt numbers 2.5-3 times higher. On the other hand, the less disturbed flow field induced by overlapped spacers was found to yield friction coefficients up to 4 times lower, thus allowing lower pumping costs. The choice between the two configurations depends crucially on the relative importance attributed to savings in membrane surface area and in pumping energy for any specific application.

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“…This behavior is exhibited within a range of temperatures called event temperature range. The TLCs with an event temperature range within 5-30 ºC are termed broad band and those within 0.5-4 ºC are termed narrow band [5]. Bandwidth as small as 0.1 ºC has also been reported [10].…”

Section: Introductionmentioning

confidence: 99%

On liquid crystal thermography for determination of the heat transfer coefficient in rectangular ducts

Ghorbani-Tari

Sundén

Tanda

2011

Computational Methods and Experimental Measurements XV

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Liquid crystal thermography (LCT) has been employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement technique. This technique correlates the colour response to temperature for a heated surface which has been treated with thermochromic liquid crystals (TLCs). The LCT has been used extensively in convective heat transfer research in duct flows. In this paper, some experiences by LCT in thermal measurements for rectangular duct flows are provided. A few TLCs examples associated with continuous ribs for two different values of rib pitch-toheight ratio of 4 and 8 at Re=8900 and 28500 are illustrated. Important issues such as heating principles, calibration of TLCs, image acquiring and analysis, problems of treating the surface by TLCs, and expected measurement accuracy are summarized. The main purpose is to assist newcomers in the field and provide some guidelines for proper use of the LCT in heat transfer research.

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The basics and issues of Thermochromic Liquid Crystal Calibrations

Cited by 93 publications

References 48 publications

Temperature and chemical composition of droplets by optical measurement techniques: a state-of-the-art review

Temperature and chemical composition of droplets by optical measurement techniques: a state-of-the-art review

Performance comparison between overlapped and woven spacers for membrane distillation

On liquid crystal thermography for determination of the heat transfer coefficient in rectangular ducts

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