Heat transfer and fluid flow performance in internally finned tube with blocked coretube was numerically investigated with the realizable k-ε turbulence model and wall function methodThe working fluid was airThe numerical method was validated by comparing the calculated results with available experimental dataIt was found that there existed an optimal value for the ratio of coretube outside diameter to outertube inside diameter

and this optimal value decreased with the increase of air flow rateThe optimal ratio was about 0.5—0.625 in the range of studied parametersMeanwhile under the condition of identical pressure

the optimal ratio was also about 0.44—0.56The conclusion is useful for the design of this kind of internally finned tubes.