Thermochromic liquid crystals in heat transfer research

Abstract

In recent years Thermochroniic Liquid Crystals (TLC) have been successfully used in non-intrusive heat transfer and fluid mechanics studies. Thin coatings of TLC's at surfaces is utilised to obtain detailed heat transfer data of steady or transient process. Application of TLC tracers allows instantaneous measurement ofthe temperature and velocity fields for two-dimsionaI cross-section of flow. Computerised flow visualisatñi tethniques allow automatic quantification of temperature of the analysed surface or the visualized flow cross-section. Here we describe our experience in applying the method to selected problems studied in our laboratory. They include modeling flow configurations in the differentially heated inclined cavity with vertical temperature gradient simulating up-slope flow as well as thermal convection under freezing surface. The main aim ofthese experimental models is to generate reliable experimental database en velocity and temperature fields for specific flow. The methods are based on computerised tme-colour analysis of digital images for temperature measurements and modified Particle Image Velocimetry and Thermometry (P1VT) used to obtain the flow field velocity.

Aplikasi Thermochromic Liquid Crystal Untuk Mengamati Perpindahan Kalor Pada Permukaan Logam

“…Penggunaan TLC untuk pengamatan berbagai fenomena termal perlu dikembangkan untuk memberikan informasi yang lebih luas mengenai peristiwa termal sekaligus mempelajari karakteristik material liquid crystal [5] . Oleh sebab itu pada penelitian ini, akan diaplikasikan TLC untuk mengamati peristiwa perpindahan kalor pada permukaan logam, dengan penjelasan secara kualitatif dan kuantitatif menggunakan metode pengolahan citra berbasis citra hue [6] , berdasarkan hasil penelitian-penelitian sebelumnya.…”

Liquid crystal thermography and true-colour digital image processing

“…For flow analysis the suspension of thermochromic liquid crystals can be used to make visible the temperature and velocity fields in liquids. By dispersing the liquid crystal material into the liquid they become not only classical tracers used for flow visualization but simultaneously small thermometers monitoring local fluid temperature [2,[6][7][8][9]. A collimated source of white light must be used to illuminate a selected cross-section of the flow (light sheet technique) and colour images are acquired in a perpendicular direction.…”

Three Dimensional Temperature Distribution Analysis of Ultrasound Therapy Equipments Using Thermochromic Liquid Crystal Films

“…Color changes in thermochromic liquid crystal films are repeatable and reversible as long as the films are not physically or chemically damaged. The time response of thermochromic liquid crystal films is approximately 10 ms. Due to the reversibility and the repeatability of color changes, thermochromic liquid crystal films can be calibrated accurately and used in this way as a temperature indicators (Stasiek & Kowalewski, 2002). The use of thermochromatic materials for thermal distribution mapping is based on the fact that the acoustic energy absorption by one medium and the temperature rise, according to the temporal average intensity of the ultrasound, is given by (Martin & Fernandez, 1997):…”