Experimental Investigation on Heat Transfer Characteristics of Low Mass-flux Optimized Rifled Tube

Under sub-critical,near-critical and supercritical pressure,this paper experimentally investigated the heat transfer characteristics of vertical upward low mass-flux optimized rifled tube,which is applied in supercritical W-shape flame boiler.The wall temperature distribution in rifled tube was obtained and the effects of pressure,inner wall heat flux and mass flux on heat transfer characteristics was analyzed.The results illustrate that low mass-flux optimized rifled tube has good heat transfer performance and can efficiently prevent the occurrence of departure from nucleate boiling(DNB).In sub-critical pressure region,with the increase of pressure and inner wall heat flux and the decrease of mass flux,dryout occurs ahead and the wall temperature in post-dryout region increases obviously.Compared with the heat transfer characteristics of rifled tube at sub-critical pressure,that in near-critical pressure region gets worse,the wall temperature significantly rises and the critical quality decreases with increasing pressure.At supercritical pressure,heat transfer enhancement occurs in pseudo-critical enthalpy region in rifled tube;while the pressure approaches critical pressure,the heat transfer is enhanced more;the wall temperature increases with increasing pressure and heat flux and with decreasing mass flux.