Experimental Study Of Complex Enhanced Heat Transfer With Rotary Jet Impingement Using Thermochromatic Liquid Crystal Technique

Rotary jet impingement heat transfer is a complex enhanced heat transfer technique which uses two kinds of ways to improve heat transfer coefficients greatly. Quantitative temperature measurement using thermochromatic liquid crystals (TLCs} is a "field" temperature measurement technique. It utilizes the feature that TLCs change their reflex light colors with variation of temperature and apply an image capturing and processing system to calibrate the characteristic curve of TLCs' colour-temperature, and then use it to measure the distribution of surface temperature. It is an advanced temperature measurement technique, which can not only measure temperature but also provide thermochromatic images. Therefore, it can solve some problem that cannot be solved by traditional "point" temperature measuring methods in heat transfer field.The main object of this dissertation is to set up a temperature measurement system of thermochromatic liquid crystals. Furthermore, a twisted tape is inserted into the tube to produce rotary jetting, and rotary jet impingement heat transfer is studied. And common jet impingement is also studied as the standard for compare. Firstly, a temperature measurement system of thermochromatic liquid crystals is set up, various methods and approaches to improve the precision of thermochromatic liquid crystals temperature measurement are discussed, and affirmative experiments are made with carbon dioxide common jet impingement. The results show that, for Reynolds number of 4400 ~23800, heat transfer coefficients at stagnation point always increase with the increasement of Reynolds number; the average deviation of heat transfer coefficients at stagnation point from published results is about 10.8%, which shows the system is reliable for temperature measurement. Then, a twisted tape is inserted the tube to produce rotary jetting, and rotary jet complex enhanced heat transfer for carbon dioxide jetting in air is studied by the thermochromatic liquid crystals temperature measurement system. It is found that, the heat transfer coefficients in the area after at stagnation point is higher than that of common jetting although the heat transfer coefficients are smaller at stagnation point, and, comparing to common jetting, rotary jetting contributes to the even distributionof heat transfer coefficients near stagnation point. The effect made by rotary jetting decreases with the increasement of Reynolds number.