Experimental Study And Numerical Simulation On Impinging Heat Transfer Of Multiple Periodic Jets

Periodic and multiple type jet as the two developing directions is studiedby scholars, and gotten some fruitful achievements, however, which are not uniform.In this paper, the experiment and numerical simulation on impinging jet heat transferis studied with combination of periodic and multiple jets, which draw someconclusions.The whole experimental system is independently designed, includinghardware and software parts. The hardware system consists of gas piping system,flow rate measurement and control system, impinging heat transfer plate and theapparatus framework. The software system is designed with LabVIEW combiningwith the Agilent34970A data acquisition system, which is able to realize the functionof automatic quick acquisition of voltage and resistance.To do experimental study of the double and four nozzles with differentparameters (waveform, frequency, height, Reynolds number and nozzle spacing)bases on this experimental apparatus, which influence the Nu number.Experimental study shows that the rectangle jet can enhances heat transfer, whichis more obvious at high frequency. Sine jet has a slightly intensification at only highfrequency. So the periodic jet can enhance heat transfer comparing with the steady jet,When the periodic signal frequency is higher than a certain threshold, theintensification is more obvious. The nozzle spacing is different under the best heattransfer performance of each kind of periodic signal. The peak Nu number and heattransfer area of the four nozzles are all better than the double nozzles.Reynold stress model is the best suitable for computing periodic and multiplejets. The trend of experimental data and numerical simulation is consistent in thecomparison of numerical simulation and experimental values, but the numericalvalue is slightly larger. The reason why the cause of this difference is that it is easilyto realize the ideal adiabatic conditions in the numerical simulation, however, theheat loss is inevitable in the experimental study. When the H/D is smaller, a secondNu number peak will also come out in the stagnation points with multiple jets. Beseen from the flow diagram of the double nozzle section, the outer impinging jet willbe constantly entraining with the airflow, and developing along the radial direction, which makes the pressure larger between two jets. With the nozzle space increasing,there is enough space to develop the airflow, at the same time, the interactionbetween the jets will weaken. A eddy will be generated at a appropriate nozzle space,then the heat transfer performance is best. We will find in the two styles of ninenozzles with numerical simulation, that the heat transfer of the circular and squarearrangement having their own advantages.While the impinging target surface is out of flaness, so RNGκ? εmodel wasused to compute the heat transfer and rotational flow field of a semi confinedturbulent axisymmetric jet in this paper, It showed that impinging on the stagnationpoint was weakened by the rotating jet under different Reynolds number, and the Nunumber on the stagnation point decreased. The combination of Re=25000androtation number0<R<1.5was found that heat transfer performances on the pedestaltop outer surface, side face and the plate were all enhanced; Moreover, the wholeheat transfer performance was weakened at R=1.5because of the over strong rotatingjet; The combination of Re=5000and rotation number R≤0.5was found that such arotating jet slightly enhanced the average heat transfer on the pedestal top surface,but it enhanced well on the pedestal side face and the plate.