Experimental studies of heat transfer of air in a double-pipe helical heat exchanger

The overall heat transfer coefficient (OHTC) of air in a double-pipe helical heat exchanger is studied and experimentally investigated. In order to increase the rate of heat transfer in the annulus section, a copper-wire fin is soldered on the outside area of the internal tube. The literature correlations' results are presented against the experimental data by changing mass flow rate and temperature, and consequently changing the Reynolds number. Further, a new method is suggested to obtain the heat transfer coefficients of double-pipe helical heat exchangers for the internal tube and the annulus section by combining two of the previously proposed approaches and making subsequent corrections, e.g. using equivalent diameter instead of hydraulic diameter. Moreover, the influence of the hot and cold mass flow rates on the OHTC, as well as the effect of the installed fin on the heat transfer coefficient of the annulus section are investigated. Finally, obtained results show the strength of the suggested correlation and the enhancement in the OHTC due to the presence of the fin in the annulus.