Two-phase flow pattern of hydrocarbon working fluids in the shell side of a helically baffled heat exchanger for liquefied natural gas determines the heat transfer performance of the heat exchanger. In this study

the two-phase flow patterns of propane and ethane/propane mixtures in the shell side of a helically baffled heat exchanger were tested using a visualization experimental method. The test results show that with the increase of vapor quality

the experimental observations sequentially included stratified flow

stratified-spray flow

and spray flow; as the mass flux of propane increases from 20 kg/(m2·s) to 40 kg/(m2·s)

the transition vapor quality from stratified flow to stratified-spray flow decreases from 0.7 to 0.3

while the transition vapor quality from stratified-spray flow to spray flow decreases from close to 1 to 0.7; when the proportion of ethane increases from 0% to 50%

the transition vapor quality from stratified flow to stratified-spray flow increases from 0.3~0.45 to 0.43~0.55

while the transition vapor quality from stratified-spray flow to spray flow increases from 0.69~0.85 to 0.83~close to 1. The existing flow pattern map for water-air mixtures was found to be inadequate for predicting the flow patterns of hydrocarbon working fluids. A new set of flow pattern transition criteria was established

with prediction deviations of approximately 6.5%

5.5%

and 4.2% for the experimental stratified flow

stratified-spray flow

and spray flow

respectively.