Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
Two-phase flow of refrigerant R134a in a hairpin was
studied. The hairpin consists of a smooth tube with an inner
diameter of 8mm with a U-bend radius of 11mm. Because of
the forces exerted on the flow in the U-bend the flow needs to
develop again downstream of the U-bend. The effects of this
phenomenon on the pressure drop are studied and linked to a
visual observation of the flow. Pressure drop and videos of the
flow are recorded in the straight sections upstream and
downstream of the U-bend. Afterwards they are compared to
the flow and pressure drop for developed flow. The pressure
drop downstream of the U-bend was found to be consistently
higher than that for developed flow. It exceeded the pressure
drop in case of developed flow by an average of 30% for all
data points. Each video of the flow behaviour was reduced to a
single image by calculating the standard deviation of the time
signal per pixel in time. The standard deviation profiles were
compared in order to quantitatively evaluate the change in the
flow behaviour. For the flow downstream of the U-bend a
disturbance was observed that stretches out over more than 30
diameters downstream of the U-bend.
