An experimental study on dryout pattern of two-phase flow in helically coiled tubes

Experimental results are presented for the effects of coil diameter, system pressure and mass flux on dryout pattern of two-phase flow in helically coiled tubes. Two tubes with coil diameters of 215 and 485 mm are used in the present study. Inlet system pressures range from 0.3 to 0.7 MPa, mass flux from 300 to 500. kg/m(2)s, and heat flux from 36 to 80 kW/m(2). A partial dryout region exists because of the geometrical characteristics of the helically coiled tube. The length of the partial dryout region increases with coil diameter and system pressure. On the other hand, it decreases with increasing mass flux. The critical quality at the tube top side increases with mass flux, but decreases with increasing system pressure. This tendency is more notable when the coil diameter is larger. When the centrifugal force effect becomes stronger, dryout starts at the top and bottom sides of the tube. However, when the gravity effect becomes stronger, dryout is delayed,at the tube bottom side. In some cases when the mass flux is low, dryout occurs earlier at the outer side than at the inner side of the tube because of film inversion.