Study On Impinging Heat Transfer Of A Periodic Jet Based On Infrared Thermal Imaging Technology

As a kind of special flow phenomenon, Impingement has both engineeringapplication background and theory research value. As an effective way ofstrengthening heat transfer, Impingement attaches great importance to academia andengineering. This article studies how impingement influence heat exchange by changeseveral important factors and provides a reference for practical application ofimpingement.Experiment system mainly divided into six modules: periodic impinging jetgenerator, pipeline system, infrared thermal imaging device, data acquisition system,experimental platform, heat exchange plate, software system developed under theenvironment of Labview program, series data collector by Agilent, temperature andNu number displayed currently.Method of experiment study is infrared image technology and temperaturemeasurement method of thermal resistance. Experimental studies have shown thatmore near the stagnation point, better heat exchanging effect at the same average rateof mass flow. Based on infrared thermal image technology, experiments researchshows that although overall stagnation zone heat transfer effect is good, but due tostagnation point by jet, the stagnation point of Nu number is not the biggest, themaximum Nu number was near the shear layer of x=D/2, due to near the shearlayer,the air flow impact under the action of shear force stronger than elsewhere.Waveform is one of the most important factors affecting the effects of cyclical impactjet, in the three typical periodic jet waveform, a jump of rectangular waveform,strengthen heat transfer most, sawtooth wave, sine wave is the worst. Each kind oftypical periodic wave has a frequency threshold value, greater than this value, therelative steady jet heat transfer will be enhanced, Otherwise it will be weaken.Compared to typical wave, the combination wave has little effect on the trend of theexperimental results still follow the influence of the wave, and the combination waveeffect of heat transfer between two typical wave.Under the same conditions, the Nunumber increased with the increase of frequency. Compared with steady jet, there is athreshold frequency, lower than the threshold, will weaken the heat transfer effect,higher than the threshold, strengthen heat transfer effect. Heat exchange effect by height also exists a threshold. It could be a potential nuclear effect jet’s fulldevelopment.In order to verify reliability of experimental results, numerical simulation wasalso conducted to study to observe the effects of periodic impinging jet by differentparameters under typical waveform signal and combination waveform signal. Select aturbulence model in early simulation and find that he Reynolds stress mode best fitsthe result of experimental conditions. the results of simulation and experiment issimilar.