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Title: Simultaneous measurement of velocity and temperature using liquid crystal particles
Author: Ju, Xiangyang
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 1996
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Particle Image Velocimetry (PIV) is a well established, non-intrusive technique, for full field flow measurements. It combines qualitative flow visualization with quantitative measurements, thus providing fluid mechanics with a most powerful tool. The display of colour distribution from Thermochromic Liquid Crystals (TLC) due to changes in temperature have been frequently exploited in the measurement of surface temperature. Thermochromic liquid crystals in encapsulated form can also act as particles for suspension in liquids, and due to their responsiveness to temperature, enable velocity and temperature to be measured simultaneously. Velocity and temperature are two essential parameters for a basic understanding of heat transfer and heat convection phenomena. Traditional techniques for measuring velocity and temperature such as Laser Doppler Anemometry, Hot Wire Anemometry and Thermocouplling are generally point-wise. The technique of combining PIV with thermochromic liquid crystals will provide full field information on velocity and temperature simultaneously and can therefore be more advantageous. For the purpose of simultaneous measurement of velocity and temperature, video based PIV, instead of photographic PIV, is proposed using encapsulated liquid crystals as suspended particles in the liquid. Direct digital colour images are used for temperature measurement instead of colour photographs. This simplifies the procedure of the colour and temperature calibration and also provides fast full field temperature from a single colour image. However, direct usage of digital images for video based PIV leads to limitations caused by low resolution and low frame rate which is inherent to digital image facilities. Low resolution of the video based PIV images, invalidates the assumption that the local velocity distribution in the interrogation region is uniform. The effects of local non- uniformity in the region are investigated. Evidence is provided that the accuracy of video based PIV is largely affected by local non-uniformity. Optimal parameters such as particle image density, the interrogation spot size and the particle image size are selected for video based PIV. An improved cross-correlation method is proposed to deduce the effects of local non-uniformity, which significantly improves the results when compared with the conventional PIV. Several colour spaces are investigated for temperature measurement, especially the hue representations in HSI (Hue, Saturation and Intensity) colour space. The hue representation is selected since this gives a monotonic relationship with temperature and provides the largest temperature measurement range. The effects of saturation, intensity and viewing angle are investigated. Finally, simultaneous velocity and temperature distributions are presented for natural convection flows. Uncertainties in the measurements are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available