Shell-side falling film flow is extremely important for the heat transfer performance of spiral wound heat exchangers used in liquefied process of natural gas. In this paper, 3-D simulations using hydrocarbon (n-pentane) as the testing fluid are conducted to study the fluid flow characteristic of heat exchanger with curved egg-shaped tube. The effects of different Re numbers (Re) and longitudinal inter-tube spacing (S) on the inter-tube flow modes and the distribution of film thickness (delta) with Re varying from 327 to 2944 are investigated. The axial and circumferential distribution of delta is analyzed qualitatively and quantitatively. The results show that when Re is relatively small (327 and 736), the effect of S on average value of delta (delta(a)) is negligible. When Re is relatively large (1472 and 2944), the increase of S would thicken delta on tube lower perimeter. When Re increased from 327 to 2944, delta(a) firstly increases and then decreases as the increase of Re and the ratio (L-b) of the axial length of basin zone to the axial measurement range increases from 52% to 76%. In addition, delta of basin zone is almost always much lower (59.23% thinner when Re = 2944) than the classic prediction results of equal-perimeter circular tube. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.