Experimental Study On The Temperature Measurement With Liquid Crystal And Its Application To Intermittent Jet Impingement Heat Transfer

With the development of advanced technology, an important revolution is experiencing in the area of experimental technology. The new technology has such kinds of characteristic: presenting whole fields information and non-contact measurement. The liquid crystal temperature measurement is one of the new measuring technologies. It makes use of the property of color-changing with temperature of liquid crystal and provide the quantitative surface information of the temperature field. The main object of this dissertation is to set up a temperature measurement system of thermochromic liquid crystals and to study measures enhancing the precision of liquid crystals temperature measurement. Furthermore, stable circular submerged jet impingement heat transfer is studied by using this system and the results are compared with previous research to confirm the reliance of this system. On the basis of this, intermittent jet impingement heat transfer for nitrogen jetting in air is experimented to investigate its heat transfer enhancement. Firstly, affirmative experiments are made with stable circular submerged jet impingement for Reynolds number of 5400-34200. The average deviation of heat transfer coefficients at the stagnation point from the previous results is about 10.9 percent, which is satisfactory agreement with the public report. The results show that, regardless of the number of relative jet distance Z/D, heat transfer coefficients at stagnation point always increase with the increasement of Reynolds number. When Z/D is equal to 3, a secondary peak of heat transfer coefficient occurs at larger Reynolds number(Re> 16000) and near r/D=2. The secondary peak disappears when Z/D differs from 3. Above this, intermittent circular submerged jet impingement heat transfer for nitrogen jetting in air is studied with the set experimental apparatus. It is found that for the nozzle diameter D3nim, regardless of the intermittent frequency , there is no heat transfer enhancement; for D=I 0mm and larger Reynolds number, heat transfer enhancement occurred only in particular situations. On the whole, it is not an advisable method to enhance heat transfer by means of intermittent jetimpingement for nitrogen jetting in air. But on the other hand, intermittent jetimpingement presents an uniform distribution characteristic of heat transfercoefflcient along radial direction, particularly fOr high frequency, which may beuseful in some speciaI heat transfer sitUations.Furthermore, by theoretical analysis of the intermittent jet impingement, it isinferred tha the heat transfer may be enhanced by aPplying higher density gasesthan air like CO 2 to submerged jet impingement in aiL This is to be confirmed bycontinued research.