CFD analyses and correlation of pressure losses on the shell-side of concentric, helically-coiled tubes heat exchangers

This paper presents and discusses the results of Computational Fluid Dynamic (CFD) analyses for calculating the friction pressure losses of isothermal flows of liquid sodium, water, and helium gas, on the shell side of annular heat exchangers (HEXs) of concentric, helically coiled tubes. The analyses covering wide ranges of HEX geometrical parameters and flow Reynolds numbers, varied the number of HEX coils from 4 to 16, and examined the effect of refining the numerical mesh grids on the results. Expressing the friction factor in terms of an effective HEX porosity, a weighted average of the areal and volume porosities, collapses the friction factor results on a single curve for developing a continuous dimensionless correlation. The developed correlation, which agrees with the CFD results for 5.0 < Re < 107 to within ±6%, is given as:f=(58/Re)+(0.315/Re0.02).For low Re flow in helically coiled tubes HEXs, the friction pressure losses increase proportional to the mass flux, G, but inversely proportional to De2. For high Re flow, these losses increase proportional to the mass flux to the 1.98 power, G1.98, and inversely proportional to the equivalent hydraulics diameter to 1.02 power, De1.02. For low Reynolds flows (Re ⩽ 20), the HEX pressure losses are ∼10% lower than in open annuli, but become higher with increased Reynolds number to as much as 97% at Re = 107.