Experimental investigation on heat transfer enhancement of mist/air impingement jet

Abstract

The heat transfer performance of a mist/air jet impingement on a constant-heat flux surface was experimentally investigated. Two objectives were outlined in the current study. The first objective is to assess the effects of mist/air volumetric flow rate ratio, impinging mode and heat flux on the heat transfer characteristics of free mist/air jet impingement. The second objective is to assess the effect of swirl flow induced by the spinning grinding wheel on the mist/air jet impingement, simulating the heat transfer process on a grinding work-piece surface subjected to the mist/air jet impingement. The results show that the addition of dilute water droplets to air flow results in significant heat transfer enhancement. Once the mist/air ratio is increased to a certain value, the increase of heat transfer with the mist/air ratio becomes slow. For a given mist/air ratio, as the increase of heat flux, the contribution of droplet evaporation to the overall heat transfer is weakened relatively, resulting in a decrease of heat transfer enhancement in comparison to the lower heat flux case. The heat transfer coefficient in the stagnation region for the oblique jet is much lower than the normal mist/air jet impingement, while in the region away from the stagnation, the local heat transfer coefficient for the oblique jet is higher than the normal jet. As regards as the mist/air jet impingement in the vicinity of grinding zone is concerned, when the jet impinging direction is consistent with the rotating direction of rotating disk, the swirl flow induced by the rotating disk could entrain more droplets to enter the jet impinging stagnation zone, which is beneficial to convective heat transfer enhancement. Furthermore, as the rotational speed of disk increases, the temperature deceases in impinging jet stagnation zone.