  The tube-in-tube helically coiled (TTHC) heat exchanger is preferred in the
purifier of IHEP-ADS helium purification system. The position of an internal
tube is usually eccentric in a TTHC heat exchanger in practice, while most TTHC
heat exchangers in the literature studied are concentric. In this paper, TTHC
heat exchangers with different eccentricity ratios are numerically studied for
turbulent flow and heat transfer characteristics under different flow rates.
The fluid considered is helium at the pressure of 20Mpa, with temperature
dependent thermo-physical properties for the inner tube and the annulus. The
inner Nusselt number between the concentric and eccentric TTHC heat exchangers
are compared, so is the annulus Nusselt number. The results show that with the
eccentricity increasing, the annulus Nusselt number increases substantially.
According to the numerical data, new empirical correlations of Nusselt number
as a function of Reynolds number and eccentricity for the inner tube and the
annulus are presented in this paper. The TTHC heat exchanger of the purifier is
designed under the given conditions.
