The fluid flow and heat transfer characteristics of internal longitudinal finned tube were investigated experimentally,and were compared with those of circular annulus tube. It was shown that the internally longitudinal finned tube had better heat transfer performance than the circular annulus tube with increase of pressure drop simultaneously.Numerical results based on the realized k-ε turbulence model agreed well with the experimental results.It was found that there existed a critical Reynolds number, that is, when Reynolds number was less than the critical value, the Nusselt number of internally longitudinal finned tube was smaller than that of circular annulus tube in laminar flow.In addition,the Reynolds number for the transition from laminar to turbulent flow was greatly decreased due to the existence of internal fins.
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.
